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Reference Dose for Chronic Oral Exposure (RfD) Reference Concentration for Chronic Inhalation Exposure (RfC) Carcinogenicity Assessment for Lifetime Exposure Bibliography Revision History Synonyms

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Ethylene glycol monobutyl ether (EGBE) (2-Butoxyethanol); CASRN 111-76-2 (12/30/1999)

Health assessment information on a chemical substance is included in IRIS only after a comprehensive review of chronic toxicity data by U.S. EPA health scientists from several Program Offices and the Office of Research and Development. The summaries presented in Sections I and II represent a consensus reached in the review process. Background information and explanations of the methods used to derive the values given in IRIS are provided in the Background Documents.

STATUS OF DATA FOR Ethylene glycol monobutyl ether (EGBE)

File First On-Line 12/30/1999

Category (section)	Status	Last Revised
Oral RfD Assessment (I.A.)	on-line	12/30/1999
Inhalation RfC Assessment (I.B.)	on-line	12/30/1999
Carcinogenicity Assessment (II.)	on-line	12/30/1999

_I.  Chronic Health Hazard Assessments for Noncarcinogenic Effects

_I.A. Reference Dose for Chronic Oral Exposure (RfD)

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2
Last Revised — 12/30/1999

The oral Reference Dose (RfD) is based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. It is expressed in units of mg/kg-day. In general, the RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Please refer to the Background Document for an elaboration of these concepts. RfDs can also be derived for the noncarcinogenic health effects of substances that are also carcinogens. Therefore, it is essential to refer to other sources of information concerning the carcinogenicity of this substance. If the U.S. EPA has evaluated this substance for potential human carcinogenicity, a summary of that evaluation will be contained in Section II of this file.

__I.A.1. Oral RfD Summary

Critical Effect	Experimental Doses*	UF	MF	RfD
Changes in mean corpuscular volume (MCV) Subchronic (rat and mice) drinking water study NTP, 1993	HED: 5.1 mg/kg/day (PBPK and BMD05)	10	1	0.5 mg/kg/day

*Conversion Factors and Assumptions - A benchmark dose (BMD) assessment was performed using EPA Benchmark Dose Software (BMDS) version 1.1b. A copy of the latest BMDS program can be obtained from the Internet at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=20167. C_max (peak blood concentrations) for butoxyacetic acid (BAA) in arterial blood of female rats following oral exposure was estimated using the PBPK model of Corley et al. (1994) as modified by Corley et al. (1997). The BMD₀₅ was determined to be 64 µM, using the 95% lower confidence limit of the dose-response curve expressed in terms of the C_max for BAA in blood. The PBPK model of Corley was used to "back-calculate" human equivalent dose of 5.1 mg/kg/day, assuming that rats and humans receive their entire dose of EGBE from drinking water over a 12-hr period each day. A detailed textual description of this assessment is provided in U.S. EPA (1999).

__I.A.2. Principal and Supporting Studies (Oral RfD)

NTP. (1993) Technical report on toxicity studies of ethylene glycol ethers 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol administered in drinking water to F344/N rats and B6C3F1 mice. U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP No. 26. NIH Publ. No. 93-3349.

NTP (1993) performed a 13-week toxicity study in Fischer 344 rats and B6C3F1 mice using EGBE (2-butoxyethanol). Groups of 10/sex/species received EGBE in drinking water at doses of 0, 750, 1500, 3000, 4500, and 6000 ppm. The daily consumption of EGBE was calculated to be 0, 69, 129, 281, 367, or 452 mg/kg/day in male rats (based on water consumption of 22.3, 20.9, 19.6, 20.5, 17.7, and 16.4 g/day); 0, 82, 151, 304, 363, or 470 mg/kg/day in female rats (based on water consumption of 18.8, 17.1, 15.5, 15.2, 11.8, and 10.7 g/day); 0, 118, 223, 553, 676, or 694 mg/kg/day in male mice (based on water consumption of 5.1, 5.2, 4.9, 6.0, 4.8, and 3.7 g/day); and 0, 185, 370, 676, 861, or 1306 mg/kg/day in female mice (based on water consumption of 6.2, 6.6, 6.5, 5.6, 4.8, and 5.6 g/day). Complete histological exams were performed on all control animals and all animals in the highest dose group. Vaginal cytology and sperm indices were evaluated in rats and mice from the control and three highest dose groups. Hematologic changes in both sexes persisting until or developing by 13 weeks included dose-related indications of mild to moderate anemia. Male rats evaluated at 13 weeks showed significantly reduced red blood cell (RBC) counts at >= 281 mg/kg/day, reduced hemoglobin (Hgb) concentration, reduced platelets, and increased bone marrow cellularity at >= 367 mg/kg/day. Significant hematologic effects in female rats at week 13 included reduced RBC counts and Hgb concentration at >= 82 mg/kg/day, and increased reticulocytes, decreased platelets, and increased bone marrow cellularity at approximately 304 mg/kg/day. There were no histopathological changes in the testes and epididymis at any dose. Liver lesions, including cytoplasmic alterations, hepatocellular degeneration, and pigmentation, were observed in the males above 129 mg/kg/day and in the females above 151 mg/kg/day. As with the hematologic effects, these effects appeared to be more severe in females than in males. Cytoplasmic alterations of liver hepatocytes, consisting of hepatocytes staining more eosinophilic and lacking the basophilic granularity of the cytoplasm in hepatocytes of control animals, were observed in the low-dose groups (69 mg/kg/day for males [54.9 mg/kg/day using water consumption rates and body weights measured during the last week of exposure], and 82 mg/kg/day for females [58.6 mg/kg/day using water consumption rates and body weights measured during the last week of exposure]). The lack of cytoplasmic granularity or "ground-glass" appearance of the hepatocytes suggests that this response was not due to enzyme induction (Greaves, 1990). The hematological (decreased RBC count and Hgb) and hepatic changes were dose-related and were associated with more severe blood and liver effects at higher doses; 69-82 mg/kg/day was considered a lowest-observed-adverse-effect level (LOAEL). A no-observed-adverse-effect level (NOAEL) was not identified. Fewer effects were observed in male and female mice exposed to EGBE. Mean final body weight and body weight gain were essentially the same as control values at the two lower dose levels, but were slightly reduced at the three highest dose levels.

Based on a comparison of NOAELs and LOAELs for hematological and liver effects, rats are more sensitive to EGBE than are mice. However, it is less clear whether male or female rats are the more sensitive to oral exposure. Hematologic and hepatocellular changes were noted in both sexes of rats. In female rats, both hematologic and hepatocellular changes were noted at the low-dose level (58.6 mg/kg/day). Only hepatocellular cytoplasmic changes were observed in low-dose male rats (54.9 mg/kg/day). However, these changes are likely to be adaptive responses to the subclinical level of hemolysis produced at this dose. Although a lower LOAEL was reported in male rats, this value gives no indication of the relative slope of the dose-response curve for males and females. Because this is an important factor for BMD analyses, a comparison of the mean corpuscular volume (MCV) and RBC count results for both male and female rats was performed, which demonstrated that female rats are more sensitive to the effects of EGBE than are males. For this reason, dose-response information on the hematological effects in female rats was selected as the basis for the oral RfD BMD analyses.

As discussed in Section I.A.4 below, until more is known about the molecular interaction between 2-butoxyacetic acid (BAA) and specific cellular molecules, changes in MCV (as an indicator of erythrocyte swelling and increased numbers of reticulocytes) and RBC count (as an indicator of cell lysis) serve as the earliest measurable response for both oral and inhalation exposures to EGBE. Model analyses of the data from this study (NTP, 1993) estimated steeper dose-response curves for MCV. For this reason, dose-response information on MCV is used to derive an RfD for EGBE.

Two important pieces of information were used to select C_max for BAA in the blood as the more appropriate dose metric. First, there is convincing evidence (for details see Section I.A.4 and U.S. EPA, 1999) to indicate that an oxidative metabolite, BAA, is the causative agent for EGBE-induced hemolysis (Carpenter et al., 1956; Ghanayem et al., 1987a, 1990). With this in mind, dose metrics for BAA in blood appear to be more appropriate than those for EGBE in blood, since they are more closely linked mechanistically to the toxic response. Second, EGBE-induced hemolysis appears to be highly dependent upon the dose rate. Ghanayem et al. (1987b) found that gavage doses to F344 male rats of 125 mg/kg EGBE resulted in hemolytic effects including reduced RBC count, Hgb, and Hct, and kidney pathology (Hgb casts and intracytoplasmid Hgb). However, hemolytic effects were not reported at a similar acute drinking water dose of 140 mg/kg (Medinsky et al., 1990). Although a slight drop in RBC count and Hgb (9% and 7%, respectively) was noted in F344 male rats after 1 week of drinking water exposure to 129 mg/kg/day EGBE, dose-related kidney pathology was not observed in these rats, even after 13 weeks of drinking water exposure to up to 452 mg/kg/day EGBE (NTP, 1993). Finally, Corley et al. (1994) have also suggested that C_max may be a better dose metric than AUC (area under the blood concentration x time curve).

C_max (peak blood concentrations) for BAA in arterial blood of female rats following oral exposure was estimated using the PBPK model of Corley et al. (1994) as modified by Corley et al. (1997). This model incorporates allometrically scalable physiological and biochemical parameters (e.g., blood flows, tissue volumes, and metabolic capacity) in place of the standard values for a 70-kg human. These parameters normalize standard values to the actual body weights of the subjects in several human kinetic studies. The physiology of humans under exercise conditions was maintained in the model. The rat was included to expand the database for model validation and to assist in interspecies comparisons of target tissue doses (BAA in blood).

Using C_max for BAA in blood as the dose metric, the BMD₀₅ was determined to be 64 µM. The PBPK model was used to "back-calculate" a human equivalent dose of 5.1 mg/kg/day, assuming that rats and humans receive their entire dose of EGBE from drinking water over a 12-hour period each day. For a more detailed discussion of these and other issues pertaining to the derivation of EGBE RfD, reference concentration (RfC), or cancer assessment, refer to U.S. EPA (1999).

__I.A.3. Uncertainty and Modifying Factors (Oral RfD)

UF = 10 (to account for intrahuman sensitivity).

A value of 10 was selected to account for variation in sensitivity within the human population (UF_H). Potentially susceptible subpopulations include individuals with enhanced metabolism or decreased excretion of BAA, and individuals whose red blood cell walls are less resistant to the lysis caused by BAA. An uncertainty factor of 10 was retained in order to account for the uncertainty associated with the variability of the human response to the effects of EGBE. Human in vitro studies suggest that the elderly and patients with fragile RBCs would not be more sensitive to the hemolytic effects of EGBE than normal adults, and laboratory animal (rats, calves, and mice) studies suggest that older animals are more sensitive than neonates and females are more sensitive than males (see further details in I.A.4). However, actual human responses to EGBE have not been observed in a broad enough range of exposure conditions (e.g., repeat/long-term exposures) and potentially sensitive subjects (e.g., individuals predisposed to hemolytic anemia, infants) to warrant reduction of the UF_H below the default value of 10. Even though developmental studies do not reveal increased susceptibility in infants, none of the developmental studies examined fetal or infant blood for signs of effects from prenatal exposure to EGBE.

The UF for interspecies variation (UF_A) accounts for pharmacodynamic and pharmacokinetic differences between animals and humans. There is in vivo (Carpenter et al., 1956) and in vitro (Ghanayem and Sullivan, 1993; Udden and Patton, 1994; Udden, 1995) information indicating that, pharmacodynamically, humans are less sensitive than rats to the hematological effects of EGBE. For this reason, a fractional component of the UF_A was considered. However, the in vivo relative insensitivity of humans cannot be quantified at this time. Thus, a value of 1 was used to account for pharmacodynamic differences between rats and humans. Because pharmacokinetic differences were adequately accounted for by a PBPK model, an overall UF_A of 1 (1 for pharmacodynamics x 1 for pharmacokinetics) was used.

A value of 1 was selected for extrapolating the results from a subchronic study to chronic exposures (UF_S). Although no chronic oral studies are currently available for EGBE, there does not appear to be a significant increase in the severity of hemolytic effects beyond 1-3 weeks of oral (NTP, 1993) or inhalation (NTP, 1998) EGBE exposures.

A value of 1 was used for the database UF_D for all methods of analyses. Although no chronic oral studies or adequate human data are available for EGBE, oral and inhalation dose-response data indicate that there would be little if any increase in severity of hemolytic effects beyond subchronic exposure durations (NTP, 1993; NTP, 1998). There are chronic and subchronic studies available in two species (rats and mice) and adequate reproductive and developmental studies, as well as limited studies in humans following short-term inhalation exposure.

MF = 1.

__I.A.4. Additional Studies/Comments (Oral RfD)

In laboratory animals, EGBE is absorbed following inhalation, oral (gavage), or percutaneous administration, and distributed rapidly to all tissues via the bloodstream. The uptake and metabolism of EGBE is essentially linear following a 6-hour inhalation exposure of up to 438 ppm, a concentration that caused mortality (Dill et al., 1998; Sabourin et al., 1992a). BAA is the primary metabolite in rats (Medinsky et al., 1990; Dill et al., 1998) and humans (Corley et al., 1997) following drinking water and inhalation exposures to EGBE. EGBE is eliminated primarily as BAA in urine, with lesser amounts of the glucuronide and sulfate conjugates of the parent alcohol (Bartnik et al., 1987; Ghanayem et al., 1987c). No significant differences in the urinary levels of BAA were found following administration of equivalent doses of EGBE either dermally or in the drinking water (Medinsky et al., 1990; Sabourin et al., 1992b; Shyr et al., 1993). Corley et al. (1997) report that elimination kinetics of EGBE and BAA appear to be independent of the route of exposure. Elimination of EGBE and BAA following repeated inhalation exposure appears to be dependent on species, sex, age, time of exposure, and exposure concentration (NTP, 1998; Dill et. al., 1998).

Hematological effects appear to be the most sensitive of the adverse effects caused by EGBE in laboratory animals. Less clear, however, is the decision as to which of the hematological endpoints (changes in RBC count, reticulocyte count [RTC], MCV, hematocrit [Hct], and Hb) observed in EGBE-exposed animals is the most appropriate basis for an RfC/RfD. The suggested mechanism of action of EGBE is based on the fact that BAA, an oxidative metabolite of EGBE, appears to be the causative agent in hemolysis (Carpenter et al., 1956; Ghanayem et al., 1987a, 1990). The first event in this mechanism of action is the interaction between BAA and cellular molecule(s) in erythrocytes. The second event is erythrocyte swelling. The third event is cell lysis mediated by increase in osmotic fragility, and a loss of deformability of the erythrocyte (Ghanayem, 1989; Udden, 1994; Udden and Patton, 1994), which results in decreased values for RBC count, Hb, and Hct. The last event is compensatory erythropoiesis; that is, in response to the loss of erythrocytes, the bone marrow increases production of young RBCs (reticulocytes).

Although changes in RTC sometimes represent the largest measurable differences between exposed animals and unexposed controls, this parameter is highly variable (CV = 30%-60%) and does not always exhibit a clear dose-dependent trend (NTP, 1993; 1998). The use of RTC as the critical endpoint is analogous to the use of cell proliferation versus quantification of cell death (histopathological). Whereas cell death has a direct relationship to chemical exposure, cell proliferation has multiple feedback control processes that can be both very sensitive and variable. Therefore, changes in RTC are not considered a suitable endpoint for deriving the RfC or RfD. Thus, until more is known about the molecular interaction between BAA and specific cellular molecules, changes in MCV (as an indicator of the second and last event of the mechanism described above) and RBC count (as an indicator of the third event) serve as the earliest measurable responses for both oral and inhalation exposures to EGBE. For this reason, dose-response information on MCV and RBC count are considered for derivation of an RfC and an RfD for EGBE.

While the toxicokinetic mechanism proposed above may suggest that MCV should theoretically be the earlier indicator of hemolytic effects from EGBE exposure, recent studies suggest that the relationship between the rate of MCV increase and RBC count decrease may not be consistent across exposure protocols. In gavage studies of Ghanayem et al. (1987b) and NTP (1998) inhalation studies Hct, a measure of erythrocyte volume relative to blood volume, tended to decrease along with RBC count and Hgb at all exposure levels for which a hematologic effect was observed. However, Hct did not change as RBC count and Hgb decreased following drinking water exposures (NTP, 1993). Thus, the loss of erythrocytes (reduced RBC count) was apparently offset by a concurrent increase in the size of the individual cells (increased MCV) in the drinking water studies. This was not the case in the gavage and inhalation studies. Until the reason for this difference is known, EPA has chosen to make use of the empirically more sensitive endpoint (the endpoint that results in the steepest dose-response curve) in the following RfD/RfC derivations.

A case of an intentional suicide attempt with an industrial-strength window cleaner was reported by Gualtieri et al. (1995). An 18-year-old male weighing 70 kg consumed between 360 and 480 mL of a concentrated glass cleaner containing 22% EGBE (dose 1131-1509 mg/kg). The patient was admitted to the hospital within 3 hours after ingestion with no abnormalities other than epigastric discomfort. Approximately 10 hours after admission, the patient was noticeably more lethargic, weak, and hyperventilating, consistent with the onset of metabolic acidosis. BAA and EGBE levels were measured. The patient was transferred to a tertiary care hospital, where hemodialysis was initiated (approximately 24 hours after ingestion) and ethanol therapy started 30 minutes later. Treatment also consisted of intravenous doses of 100 mg thiamine and 50 mg folic acid every 12 hours, and 50 mg pyridoxine every 6 hours. Following 4 hours of dialysis, the patient was alert and remained hemodynamically stable. Ten days following discharge, the patient was readmitted following a second ingestion of 480 mL of the same cleaner (EGBE dose 1509 mg/kg). Treatment, including ethanol therapy and hemodialysis, was initiated within a few hours of ingestion to control the metabolic acidosis. Because treatment was initiated soon after ingestion, ethanol therapy did have an impact on the disposition of EGBE (higher concentrations were detected than following the first ingestion) and BAA (lower levels were detected). As with the first episode, clinical manifestations of high-dose oral ingestion of nearly 1.1-1.5 g/kg body weight consisted of metabolic acidosis. No evidence of hemolysis or renal abnormalities was detected.

As discussed in Sections I.A.2 and I.A.3 above, adult females have been identified as a sensitive subgroup for the purposes of deriving the RfD. Section I.A.2 describes laboratory animal studies that indicate that female rats are more sensitive than male rats to the hemolytic effects of EGBE. The following discussion describes why adults are believed to be more sensitive than neonates, infants, and children. The only human toxicity information available on the toxicity of EGBE to children is from the case study by Dean and Krenzelok (1991), who observed 24 children, age 7 months to 9 years, subsequent to oral ingestion of at least 5 mL of glass window cleaner containing EGBE in the 0.5% to 9.9% range (potentially 25 to 1500 mg EGBE exposures). The two children who had taken greater than 15 mL amounts of the cleaner did well after gastric emptying or lavage and observation in the hospital. The remainder were watched at home after receiving diluting oral fluids. No symptoms of EGBE poisoning or hemolysis were observed. Although the effects reported in adult poisonings have been more severe than those reported in these children, the adults tended to consume larger volumes and different concentrations of EGBE, making a comparison of toxic effects observed to age sensitivity of the human extremely difficult.

There are numerous risk factors for anemia that might predispose an individual to or compound the adverse effects of EGBE-induced hemolysis (Berliner et al., 1999). It is generally recognized, however, that children have fewer risk factors for anemia than are present for adults because of (1) a higher rate of RBC turnover, (2) lower incidence of neoplastic disease in childhood as either a direct or indirect cause of anemia (<7000 of the 1,000,000 new cases of cancer each year in the United States occur in individuals < 15 years of age), (3) the fact that iron deficiency is almost always secondary to nutritional factors in children, (4) the relative rarity of alcoholism and its related liver disease, (5) a much lower incidence of anemia associated with thyroid disease, and (6) a rarity of cardiovascular disease other than congenital heart diseases so that valve replacement, malignant hypertension, and the use of certain drugs are not usually a factor (Berliner et al., 1999; Hord and Lukens, 1999).

The primary cause for anemia in children is usually associated with an abnormality of the hematopoietic system (Berliner et al., 1999; Hord and Lukens, 1999). Studies of the osmotic fragility and deformability of RBCs exposed to EGBE's toxic metabolite BAA (Udden, 1994) suggest that certain patients with abnormal hematopoietic systems (sickle-cell anemia and hereditary spherocytosis patients) are not more sensitive to the hemolytic effects of EGBE than normal adults. Other studies suggest that the RBCs of children may be pharmacodynamically less sensitive to hemolysis than those of adults. RBCs of neonates and children (up to 6 months) differ from normal adult red blood cells in that they are larger and have higher levels of Hemoglobin F versus adult Hemoglobin A (Lewis, 1970). Frei et al. (1963) showed that the larger calf erythrocytes containing Hemoglobin F were osmotically more resistant than smaller adult erythrocytes containing Hemoglobin A. Frei et al. (1963) suggested that as fetal erythrocytes are replaced by postnatal erythrocytes, the total population of RBCs becomes more susceptible to lysis.

The effect of age on EGBE-induced hematotoxicity was studied in male F344 rats by Ghanayem and co-workers (1987c, 1990). These studies also demonstrated the time course for the onset and resolution of hematological and histopathological changes accompanying hemolysis. Adult (9-13 week) male F344 rats were significantly more sensitive to the hemolytic effects of EGBE than were young (4-5 week) male rats following administration of a single gavage dose of EGBE at 32, 63, 125, 250, or 500 mg/kg. Concurrent metabolism studies also found increased blood retention of EGBE metabolite BAA (as measured by increased Cmax, AUC, and T½). It was also found that young rats eliminated a significantly greater proportion of the administered EGBE dose as exhaled carbon dioxide (CO₂) or as urinary metabolites as well as excreting a greater proportion of the EGBE conjugates (glucuronide and sulfate) in the urine. These researchers suggested that the pharmacokinetic basis of the age-dependent toxicity of EGBE may be due to a reduced ability by older rats to metabolize the toxic metabolite BAA to CO₂ and a diminished ability to excrete BAA in the urine.

NTP (1998) also found that young mice (6-7 weeks) eliminated BAA 10 times faster than aged mice (19 months) following a 1-day exposure to 125 ppm EGBE. This difference was not as apparent after 3 weeks of exposure, suggesting that factors other than age may be involved (Dill et. al., 1998).

Because of the known reproductive toxicity (i.e., toxicity to male testes and sperm) of two other glycol ethers, ethylene glycol methyl ether (EGME; 2-methoxyethanol) and ethylene glycol ethyl ether (EGEE; 2-ethoxyethanol), the reproductive toxicity of EGBE has been studied in a variety of well-conducted oral (Nagano et al., 1979, 1984; Grant et al., 1985; Foster et al., 1987; Heindel et al., 1990; Exon, 1991; NTP, 1993) and inhalation (Dodd et al., 1983; Doe, 1984; Nachreiner, 1994; NTP, 1998) studies using rats, mice, and rabbits. In addition, several developmental studies have addressed EGBE's toxicity from conception to sexual maturity, including toxicity to the embryo and fetus, following oral (Wier et al., 1987; Sleet et al., 1989), inhalation (Nelson et al., 1984; Tyl et al., 1984) and dermal (Hardin et al., 1984) exposures to rats, mice, and rabbits. In many instances, LOAELs and NOAELs were reported for both parental and developmental effects, therefore the developmental studies can also be used to assess systemic toxicity as well as developmental toxicity.

EGBE did not cause adverse effects in any reproductive organ, including testes, in any study. In a two-generation reproductive toxicity study, fertility was reduced in mice only at very high, maternally toxic doses (> 1000 mg/kg). Maternal toxicity related to the hematologic effects of EGBE and relatively minor developmental effects have been reported in developmental studies. No teratogenic toxicities were noted in any of the studies. It can be concluded from these studies that EGBE is not significantly toxic to the reproductive organs (male or female) of parents, nor to the developing fetuses of laboratory animals.

For more detail on Susceptible Populations, exit to the toxicological review, Section 4.7 (PDF)

__I.A.5. Confidence in the Oral RfD

Study — Medium
Database — Medium-to-high
RfD — Medium-to-high

The overall confidence in this RfD assessment is medium-to-high. The RfD value was calculated for EGBE using the combined PBPK/BMD method. A higher confidence is placed in the RfD values derived from internal dose measures because pharmacokinetic differences between rats and humans were accounted for using a validated PBPK model (Corley et al., 1994). Medium confidence is placed in the NTP (1993) study because it was not a chronic study; however, the study employed both male and female rats and mice, provided a wide range of exposure levels (0-6000 ppm EGBE in drinking water), and observed animals twice daily. Medium-to-high confidence is placed in the database because data are available for a variety of animal species, including humans. Although the database lacks long-term human studies, the available short-term human controlled studies and case reports, and laboratory animal and in vitro studies, provide ample evidence to suggest that long-term human exposures would be no more adverse than long-term rat exposures. Confidence in the database is not "high" because the potential for liver effects in humans from long-term exposure has not been investigated.

For more detail on Characterization of Hazard and Dose Response, exit to the toxicological review, Section 6 (PDF).

__I.A.6. EPA Documentation and Review of the Oral RfD

Source Document — U.S. EPA, 1999.

This assessment was peer reviewed by external scientists. Their comments have been evaluated carefully and incorporated in finalization of this IRIS summary. A record of these comments is included as an appendix to the Toxicological Review of Ethylene Glycol Monobutyl Ether in support of summary information on the Integrated Risk Information System (IRIS) (U.S. EPA, 1999). To review this appendix, exit to the toxicological review, Appendix A, Summary of and Response to External Peer Review Comments (PDF).

Agency Consensus Date — 11/16/1999

Screening-Level Literature Review Findings — A screening-level review conducted by an EPA contractor of the more recent toxicology literature pertinent to the RfD for Ethylene glycol monobutyl ether (EGBE) conducted in September 2002 did not identify any critical new studies. IRIS users who know of important new studies may provide that information to the IRIS Hotline at hotline.iris@epa.gov or (202)566-1676.

__I.A.7. EPA Contacts (Oral RfD)

Please contact the IRIS Hotline for all questions concerning this assessment or IRIS, in general, at (202)566-1676 (phone), (202)566-1749 (FAX), or hotline.iris@epa.gov (Internet address).

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_I.B. Reference Concentration for Chronic Inhalation Exposure (RfC)

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2
Last Revised — 12/30/1999

The inhalation RfC is analogous to the oral RfD and is likewise based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. The inhalation RfC considers toxic effects for both the respiratory system (portal-of-entry) and for effects peripheral to the respiratory system (extrarespiratory effects). It is generally expressed in units of mg/m3. In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily inhalation exposure of the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Inhalation RfCs were derived according to the Interim Methods for Development of Inhalation Reference Concentrations (EPA/600/8-88/066F August 1989) and subsequently, according to Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry (EPA/600/8-90/066F October 1994). RfCs can also be derived for the noncarcinogenic health effects of substances that are carcinogens. Therefore, it is essential to refer to other sources of information concerning the carcinogenicity of this substance. If the U.S. EPA has evaluated this substance for potential human carcinogenicity, a summary of that evaluation will be contained in Section II of this file.

__I.B.1. Inhalation RfC Summary

Critical Effect	Experimental Doses*	UF	MF	RfC
Changes in red blood cell (RBC) count Subchronic rat inhalation study NTP, 1998	HEC: 380 mg/m3 (PBPK and BMC05)	30	1	13 mg/m3

*Conversion Factors and Assumptions - A benchmark dose (BMD) assessment was performed using EPA Benchmark Dose Software (BMDS) version 1.1b. A copy of the latest BMDS program can be obtained from the Internet at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=20167. C_max (peak blood concentrations) for BAA in arterial blood of female rats following inhalation exposure was estimated using the PBPK model of Lee et al. (1998). The BMD₀₅ was calculated to be 225 µM, using the 95% lower confidence limit of the dose-response curve expressed in terms of the C_max for BAA in blood. The PBPK model of Corley et al. (1994; 1997) was used to "back-calculate" human equivalent concentration of 78 ppm (380 mg/m³) assuming continuous exposure (24 hours/day). A detailed textual description of this assessment is provided in U.S. EPA (1999).

__I.B.2. Principal and Supporting Studies (Inhalation RfC)

National Toxicology Program (NTP). (1998) NTP technical report on the toxicology and carcinogenesis studies of 2-butoxyethanol (CAS No. 111-76-2) in F344/N rats and B6C3F1 mice (inhalation studies). U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP TR 484 NIH Draft Publication No. 98-3974.

In the subchronic portion of this study, both F344 rats and B6C3F1 mice (10/sex) were exposed via inhalation to concentrations of 0, 31, 62.5, 125, 250, and 500 ppm of EGBE 6 hours/day, 5 days/week for 14 weeks (NTP, 1998). Both sexes of rats exhibited clinical signs consistent with hemolytic effects of EGBE at the three highest doses. Hematologic evaluation showed a mild to moderate regenerative anemia at all concentrations in females and at the highest three concentrations in males. Exposure-related trends were noted for reticulocytes (RTC), RBC count, MCV, hemoglobin, and hematocrit. Liver-to-body weight ratios were significantly increased in males at the two highest concentrations and in females at the highest concentration. Histopathological effects consisted of excessive splenic congestion in the form of extramedullary hematopoiesis, hemosiderin accumulation in Kupffer cells, liver necrosis, centrilobular hepatocellular degeneration, renal tubular degeneration, intracytoplasmic hemoglobin and hemosiderin deposition, and bone marrow hyperplasia at concentrations in excess of 62.5 ppm for male rats and 31 ppm for females. Also, five female rats were sacrificed moribund from the highest concentrations and one from the 250 ppm group. The LOAEL for hematological alterations was 31 ppm for female rats and 62.5 ppm for male rats. The 31 ppm exposure level was considered a NOAEL for male rats. The mice exposed via the inhalation route exhibited clinical signs consistent with the hemolytic effects of EGBE at the two highest concentrations for both sexes. Hematologic evaluation indicated a moderate regenerative anemia with an increase in platelets at the three higher concentrations in both sexes. Histopathological effects consisted of excessive extramedullary splenic hematopoiesis and hemosiderosis, hemosiderin accumulation in Kupffer cells, renal tubular degeneration and hemosiderin deposition, and testicular degeneration. Forestomach necrosis, ulceration, inflammation, and epithelial hyperplasia were observed at concentrations greater than 31 ppm for females and 62.5 ppm for males. Also, four females and four males either died or were sacrificed moribund at the highest concentration. The NOAEL for male and female mice was 31 ppm and the LOAEL in mice was 62.5 ppm, based on histopathological changes in the forestomach.

NTP also completed a two-species, 2-year inhalation study on EGBE (NTP, 1998). In the chronic study, exposure concentrations of EGBE were 0, 31, 62.5, and 125 ppm for groups of 50 F344/N rats, and 0, 62.5, 125, and 250 ppm for groups of 50 B6C3F1 mice. The highest exposure was selected to produce a 10% to 15% depression in hematologic indices. Survival was significantly decreased in male mice at 125 and 250 ppm (54.0% and 53.1%, respectively), but no effect on survival was observed in rats.

Mean body weights of all groups of male and female rats exposed to 31 and 62.5 ppm were similar to controls. From week 17 to the end of the study, the mean body weights of 125 ppm female rats were generally less than those of controls. Mean body weights of the exposed male and female mice were generally less than for controls, with females experiencing greater and earlier reductions. Nonneoplastic effects in rats included hyaline degeneration of the olfactory epithelium in males (13/48, 21/49, 23/49, 40/50) and females (13/50, 18/48, 28/50, 40/49), and Kupffer cell pigmentation in the livers of males (23/50, 30/50, 34/50, 42/50) and females (15/50, 19/50, 36/50, 47/50). The severity of the nasal lesion was not affected by exposure and was deemed to be, in general, an adaptive rather than adverse response to exposure (NTP, 1998). The Kupffer cell pigmentation results from hemosiderin accumulation and is a recognized secondary effect of the hemolytic activity of EGBE (NTP, 1998).

Nonneoplastic effects in mice included forestomach ulcers and epithelium hyperplasia, hematopoietic cell proliferation and hemosderin pigmentation in the spleen, Kupffer cell pigmentation in the liver, hyaline degeneration of the olfactory epithelium (females only) and bone marrow hyperplasia (males only). As in the rats, the nasal lesion is deemed an adaptive rather than an adverse response to exposure, and the Kupffer cell pigmentation is considered a secondary effect of the hemolytic activity of EGBE. Bone marrow hyperplasia, and hematopoietic cell proliferation and hemosiderin pigmentation in the spleen, are also attributed to the primary hemolytic effect, which is followed by regenerative hyperplasia of the hematopoietic tissue. The forestomach lesions do not appear to be related to the hemolytic effect of EGBE. Incidences of ulcers were significantly increased in males exposed to 125 ppm and in all exposed female groups. Ulcers consisted of a defect in the forestomach wall that penetrated the full thickness of the forestomach epithelium, and frequently contained accumulations of inflammatory cells and debris. Incidences of epithelial hyperplasia, usually focal, were significantly increased in all exposed groups of males and females. The hyperplasia was often associated with ulceration, particularly in the females, and consisted of thickness of the stratified squamous epithelium and sometimes the keratinized layer of the forestomach.

Using the same exposure groups described above, additional groups of rats (27/sex/exposure group) and mice (30/sex/exposure group) in the 2-year study were examined at 3, 6, and 12 months (8-10/duration) for hematologic effects. Rats in the 31 ppm exposure group were not examined at 12 months, and only hematology was examined at 3 months. As in the 14-week study, inhalation of EGBE by both species resulted in the development of exposure-related hemolytic effects, inducing a responsive anemia. In rats, the anemia was persistent and did not progress or ameliorate in severity from 3 months to the final blood collection at 12 months. Statistically significant (p < 0.05) decreases in automated and manual hematocrit values, hemoglobin, and erythrocyte counts occurred at 3, 6, and 12 months in the 62.5 ppm females and the 125 ppm males and females. Statistically significant decreases in these same endpoints were also observed in 31 ppm females exposed for 3 and 6 months, and in 62.5 ppm males exposed for 12 months. At 3 months, MCV was increased following 31 ppm and higher exposures in both males and females. In vitro studies by Ghanayem et al. (1989) have shown that the hemolysis caused by EGBE metabolite BAA is preceded by erythrocyte swelling. If the observed increase in MCV is in reponse to cell swelling, it could be a preliminary indicator of the hemolytic effect. Other researchers, however, have attributed the increased MCV at all exposures and the increased mean cell hemoglobin at higher exposure levels to the erythropoietic response subsequent to hemolysis and the corresponding increase in the number of larger reticulocytes in circulation (NTP, 1998). Reticulocyte count was increased significantly in female rats at 62.5 ppm (6 and 12 months) and in male rats at 125 ppm (3 and 6 months). Since a statistically significant increase in reticulocyte count was not observed at any duration in males or females exposed to 31 ppm, nor in males exposed to 62.5 ppm, it appears that reticulocyte count alone cannot account for the increase in MCV at these levels of exposure. The observed increases in MCV may be a combined result of erythrocyte swelling prior to and an increased number of reticulocytes subsequent to hemolysis, with the former being more influential at lower exposure levels and the latter having more relative impact at higher exposure levels.

Similar effects indicating anemia were also observed in mice, with females being the more sensitive of the species. However, the anemia response was observed at higher doses and changed somewhat with duration of exposure. Statistically significant (p < 0.05) decreases in automated and manual hematocrit values, hemoglobin, and erythrocyte counts occurred at 3, 6, and 12 months in the 125 ppm females and the 250 ppm males and females. Statistically significant decreases in these endpoints were also observed in 62.5 ppm females exposed for 6 months and in 125 ppm males exposed for 6 and 12 months (decreases in hematocrit were observed only at 3 and 6 months). No changes were observed in the MCV of mice, except for an increase in females at the highest duration (12 months) and exposure (250 ppm) levels. Reticulocyte count was increased significantly in 125 ppm females at 3 and 6 months, and in 125 ppm males at 6 months.

Based on a comparison of NOAELs and LOAELs for hematological and liver effects, rats are more sensitive than mice to EGBE. Based on a comparison of effect levels, female rats (NTP, 1998) appear to be more sensitive to the hematological effects of EGBE than the other animals. For this reason, concentration-response information on the hematological effects in female rats was selected as the basis for the inhalation RfC BMD analyses.

As discussed in Section I.B.4 below, until more is known about the molecular interaction between BAA and specific cellular molecules, changes in MCV (as an indicator of erythrocyte swelling and increased number of reticulocytes) and RBC count (as an indicator of cell lysis) serve as the earliest measurable response for both oral and inhalation exposures to EGBE. Model analyses of the data from this study (NTP, 1998) predicted steeper dose-response curves for RBC count. For this reason, dose-response information on RBC count is used to derive an RfC for EGBE.

Two important pieces of information were used to select C_max for BAA in the blood as the more appropriate dose metric. First, there is convincing evidence (for details see I.B.4 and U.S. EPA, 1999) to indicate that an oxidative metabolite, BAA, is the causative agent for EGBE-induced hemolysis (Carpenter et al., 1956; Ghanayem et al., 1987a, 1990). With this in mind, dose metrics for BAA in blood appear to be more appropriate than those for EGBE in blood, since they are more closely linked mechanistically to the toxic response. Second, EGBE-induced hemolysis appears to be highly dependent upon the dose rate. Ghanayem et al. (1987b) found that gavage doses to F344 male rats of 125 mg/kg EGBE resulted in hemolytic effects including reduced RBC count, Hgb, and Hct, and kidney pathology (Hgb casts and intracytoplasmid Hgb). However, hemolytic effects were not reported at a similar acute drinking water dose of 140 mg/kg (Medinsky et al., 1990). While a slight drop in RBC count and Hgb (9% and 7%, respectively) was noted in F344 male rats after 1 week of drinking water exposure to 129 mg/kg/day EGBE, dose related kidney pathology was not observed in these rats, even after 13 weeks of drinking water exposure to up to 452 mg/kg/day EGBE (NTP, 1993). Finally, Corley et al. (1994) have also suggested that C_max may be a better dose metric than AUC.

C_max (peak blood concentrations) for BAA in arterial blood of female rats following inhalation exposure was determined using the PBPK model of Lee et al. (1998). Using C_max for BAA in blood as the dose metric, the BMC₀₅ was determined to be 225 µM. The PBPK model of Corley et al. (1994; 1997) was used to "back-calculate" human equivalent concentration of 78 ppm (380 mg/m³) assuming continuous exposure (24 hours/day). For a more detailed discussion of these and other issues pertaining to the derivation of EGBE RfD, RfC, or cancer assessment, refer to U.S. EPA (1999).

__I.B.3. Uncertainty and Modifying Factors (Inhalation RfC)

UF = 30 (a UF of 10 including 10 for intrahuman sensitivity and 3 for extrapolation from an adverse effect level).

A value of 10 was selected to account for variation in sensitivity within the human population (UF_H). Potentially susceptible subpopulations include individuals with enhanced metabolism or decreased excretion of BAA and individuals whose red blood cell walls are less resistant to the lysis caused by BAA. An uncertainty factor of 10 was retained in order to account for the uncertainty associated with the variability of the human response to the effects of EGBE. Human in vitro studies suggest that the elderly and patients with fragile RBCs would not be more sensitive to the hemolytic effects of EGBE than normal adults, and laboratory animal (rats, calves, and mice) studies suggest that older animals are more sensitive than neonates and females are more sensitive than males (see further details in I.B.4). However, actual human responses to EGBE have not been observed in a broad enough range of exposure conditions (e.g., repeat/long-term exposures) and potentially sensitive subjects (e.g., individuals predisposed to hemolytic anemia, infants) to warrant the reduction of the UF_H below the default value of 10. While developmental studies do not reveal increased susceptibility in infants, none of the developmental studies examined fetal or infant blood for signs of effects from prenatal exposure to EGBE.

The UF for interspecies variation (UF_A) accounts for pharmacodynamic and pharmacokinetic differences between animals and humans. There is in vivo (Carpenter et al., 1956) and in vitro (Ghanayem and Sullivan, 1993; Udden and Patton, 1994; Udden, 1995) information indicating that, pharmacodynamically, humans are less sensitive than rats to the hematological effects of EGBE. For this reason, a fractional component of the UF_A was considered. However, the in vivo relative insensitivity of humans cannot be quantified at this time. Thus, a value of 1 was used to account for pharmacodynamic differences between rats and humans. Because pharmacokinetic differences are adequately accounted for by a PBPK model, an overall UF_A of 1 (1 for pharmacodynamics x 1 for pharmacokinetics) was used.

A value of 3 was selected for extrapolating an adverse effect level to a NOAEL (UFL). A UF_L value of less than 10 is justifiable because there is information that indicates that the estimated BMC₀₅ value is near the threshold level for the hematological effects of concern. The effect (decreased RBC count) that formed the basis for this value was within 5% of the control value. In addition, the female rat BMC₀₅ (130 mg/m³) derived from the NTP (1998) subchronic/chronic inhalation study was very close to the 121 mg/m³ (25 ppm) NOAEL identified for male and female rats in the Dodd et al. (1983) subchronic inhalation study. In the case of the RfD (Section I.A.3), a UF_L value of 1 was used for the BMD analyses because the RfD BMD was based on a minimal and precursive lesion (cell swelling as measured by increased MCV). A threefold UF_L is retained for the RfC because the RfC BMC is based on a more serious hematologic endpoint (red blood cell lysis as measured by a decrease in RBC count).

A value of 1 was used for the database UF_D for all methods of analyses. Subchronic and chronic inhalation studies suggest that there is little, if any, increase in severity of hemolytic effects beyond subchronic exposure durations (NTP, 1993; 1998). There are chronic and subchronic studies available in two species (rats and mice) and adequate reproductive and developmental studies, as well as limited studies in humans following short-term inhalation exposure.

MF = 1.

__I.B.4. Additional Studies/Comments (Inhalation RfC)

In laboratory animals, EGBE is absorbed following inhalation, oral (gavage), or percutaneous administration and distributed rapidly to all tissues via the bloodstream. The uptake and metabolism of EGBE are essentially linear following a 6-hour inhalation exposure of up to 438 ppm, a concentration that caused mortality (Dill et al., 1998; Sabourin et al., 1992a). BAA is the primary metabolite in rats (Medinsky et al., 1990; Dill et al., 1998) and humans (Corley et al., 1997) following drinking water and inhalation exposures to EGBE. EGBE is eliminated primarily as BAA in urine, with lesser amounts of the glucuronide and sulfate conjugates of the parent alcohol (Bartnik et al., 1987; Ghanayem et al., 1987c). No significant differences in the urinary levels of BAA were found following administration of equivalent doses of EGBE either dermally or in the drinking water (Medinsky et al., 1990; Sabourin et al., 1992b; Shyr et al., 1993). Corley et al. (1997) report that elimination kinetics of EGBE and BAA appear to be independent of the route of exposure. Elimination of EGBE and BAA following repeated inhalation exposure appears to be dependent on species, sex, age, time of exposure, and exposure concentration (NTP, 1998; Dill et. al., 1998).

Hematological effects appear to be the most sensitive of the adverse effects caused by EGBE in laboratory animals. Less clear, however, is the decision as to which of the hematological endpoints (changes in RBC count, reticulocyte count [RTC], MCV, Hct, and Hb) observed in EGBE-exposed animals is the most appropriate basis for an RfC/RfD. The suggested mechanism of action of EGBE is based on the fact that BAA, an oxidative metabolite of EGBE, appears to be the causative agent in hemolysis (Carpenter et al., 1956; Ghanayem et al., 1987a, 1990). The first event in this mechanism of action is the interaction between BAA and cellular molecule(s) in erythrocytes. The second event is erythrocyte swelling. The third event is cell lysis mediated by increase in osmotic fragility, and a loss of deformability of the erythrocyte (Ghanayem, 1989; Udden, 1994; Udden and Patton, 1994), which results in decreased values for RBC count, Hb, and Hct. The last event is compensatory erythropoiesis; that is, in response to the loss of erythrocytes, the bone marrow increases production of young RBCs (reticulocytes).

Although changes in RTC sometimes represent the largest measurable differences between exposed animals and unexposed controls, this parameter is highly variable (CV = 30%-60%) and does not always exhibit a clear dose-dependent trend (NTP, 1993; 1998). The use of RTC as the critical endpoint is analogous to the use of cell proliferation versus quantification of cell death (histopathological). Whereas cell death has a direct relationship to chemical exposure, cell proliferation has multiple feedback control processes that can be both very sensitive and variable. Therefore, changes in RTC are not considered a suitable endpoint for deriving the RfC or RfD. Thus, until more is known about the molecular interaction between BAA and specific cellular molecules, changes in MCV (as an indicator of the second and last events of the mechanism described above) and RBC count (as an indicator of the third event) serve as the earliest measurable responses for both oral and inhalation exposures to EGBE. For this reason, dose-response information on MCV and RBC count is considered for derivation of an RfC and an RfD for EGBE.

While the toxicokinetic mechanism proposed above may suggest that MCV should theoretically be the earlier indicator of hemolytic effects from EGBE exposure, recent studies suggest that the relationship between the rate of MCV increase and RBC count decrease may not be consistent across exposure protocols. In gavage studies of Ghanayem et al. (1987b) and NTP (1998) inhalation studies Hct, a measure of erythrocyte volume relative to blood volume, tended to decrease along with RBC count and Hgb at all exposure levels for which a hematologic effect was observed. However, Hct did not change as RBC count and Hgb decreased following drinking water exposures (NTP, 1993). Thus, the loss of erythrocytes (reduced RBC count) was apparently offset by a concurrent increase in the size of the individual cells (increased MCV) in the drinking water studies. This was not the case in the gavage and inhalation studies. Until the reason for this difference is known, EPA has chosen to make use of the empirically more sensitive endpoint (the endpoint that results in the steepest dose-response curve) in the following RfD/RfC derivations.

Three controlled studies using inhalation exposure were conducted by Carpenter et al. (1956). In the first study, a group of two men and six rats was exposed simultaneously to an EGBE concentration of 113 ppm in a 1250 cubic ft. room for two 4-hour periods. Effects observed in humans included nasal and ocular irritation, a metallic taste in the mouth, and belching. Erythrocyte osmotic fragility did not change for the men; however, it rose appreciably for the rats. In a second study, a group of two men, one woman, and three rats was exposed to 195 ppm EGBE for two 4-hour periods, separated by a 30-minute recess, in a 6.5 cubic ft. room. There was no change in the blood pressure, erythrocyte fragility, or pulse rate of the human subjects. Irritation of the nose and throat followed by ocular irritation and disturbed taste were noted; one subject reported a headache. In the rats, an increase in erythrocyte fragility values was noted during exposure. In the third study, a group of two men and two women was exposed for an 8-hour period to an EGBE concentration of 100 ppm. No change in blood pressure, erythrocyte fragility, or pulse rate was observed. Irritation of the nose and throat followed by ocular irritation and a disturbing metallic taste were mentioned. Two subjects reported headaches.

A cross-section of 31 male workers (22 to 45 years old; employed for 1 to 6 years) exposed to low levels of EGBE in a beverage packing production plant was evaluated by Haufroid et al. (1997). The effect of external EGBE and internal BAA exposure on erythrocyte lineage (RBC numeration, Hb, Hct, MCV, MCH, mean corpuscular hemoglobin concentration [MCHC], haptoglobin [Hp], reticulocyte numeration [Ret] and osmotic resistance [OR]), as well as hepatic (SGOT, SGPT) and renal creatinine and urinary retinol binding protein parameters was investigated. The average airborne concentration of EGBE was 2.91 mg/m³ (0.6 ppm) (SD ± 1.30 mg/m³ or 0.27 ppm). Single determinations of BAA in post-shift urine samples were used to assess exposure to low levels of EGBE. No difference between exposed and control workers was observed for RBC count, Hb, MCV, MCH, Hp, Ret, and OR (a measure of osmotic fragility). The only statistically significant change observed in exposed workers when compared with a matched control group (n=21) was a 3.3% decrease in Hct (p = 0.03) and a 2.1% increase in MCHC (p = 0.02). The implications of these small erythroid effects are unclear. Both values are within their corresponding normal clinical ranges and, given that no statistically significant changes were observed in other erythroid parameters, do not appear to be related to the more severe adverse effects observed in laboratory animals. No significant differences were observed in hepatic and renal biomarkers.

As discussed in Sections I.B.2 and I.B.3 above, adult females have been identified as a sensitive subgroup for the purposes of deriving the RfC. Section I.B.2 describes why females were identified as being more sensitive than males. The following discussion describes why adults are believed to be more sensitive than children. The only human toxicity information available on the toxicity of EGBE to children is from the case study by Dean and Krenzelok (1991), who observed 24 children, age 7 months to 9 years, subsequent to oral ingestion of at least 5 mL of glass window cleaner containing EGBE in the 0.5% to 9.9% range (potentially 25 to 1500 mg EGBE exposures). The two children who had taken greater than 15 mL amounts of the cleaner did well after gastric emptying or lavage and observation in the hospital. The remainder were watched at home after receiving diluting oral fluids. No symptoms of EGBE poisoning or hemolysis were observed. Although the effects reported in adult poisonings have been more severe than those reported in these children, the adults tended to consume larger volumes and different concentrations of EGBE, making a comparison of toxic effects observed to age sensitivity of the human extremely difficult.

There are numerous risk factors for anemia that might predispose an individual to or compound the adverse effects of EGBE induced hemolysis (Berliner et al., 1999). It is generally recognized, however, that children have fewer risk factors for anemia than are present for adults because of (1) a higher rate of RBC turnover, (2) lower incidence of neoplastic disease in childhood as either a direct or indirect cause of anemia (<7000 of the 1,000,000 new cases of cancer each year in the United States occur in individuals < 15 years of age), (3) the fact that iron deficiency is almost always secondary to nutritional factors in children, (4) the relative rarity of alcoholism and its related liver disease, (5) a much lower incidence of anemia associated with thyroid disease, and (6) a rarity of cardiovascular disease other than congenital heart diseases, so that valve replacement, malignant hypertension, and the use of certain drugs are not usually a factor (Berliner et al., 1999; Hord and Lukens, 1999).

The primary cause for anemia in children is usually associated with an abnormality of the hematopoietic system (Berliner et al., 1999; Hord and Lukens, 1999). Studies of the osmotic fragility and deformability of RBCs exposed to EGBE's toxic metabolite BAA (Udden, 1994) suggest that certain patients with abnormal hematopoietic systems (sickle-cell anemia and hereditary spherocytosis patients) are not more sensitive to the hemolytic effects of EGBE than normal adults. Other studies suggest that the RBCs of children may be pharmacodynamically less sensitive to hemolysis than those of adults. RBCs of neonates and children (up to 6 months) differ from normal adult red blood cells in that they are larger and have higher levels of Hemoglobin F versus adult Hemoglobin A (Lewis, 1970). Frei et al. (1963) showed that the larger calf erythrocytes containing Hemoglobin F were osmotically more resistant than smaller, adult erythrocytes containing Hemoglobin A. Frei et al. (1963) suggested that as fetal erythrocytes are replaced by postnatal erythrocytes, the total population of RBCs becomes more susceptible to lysis.

The effect of age on EGBE-induced hematotoxicity was studied in male F344 rats by Ghanayem and co-workers (1987c, 1990). These studies also demonstrated the time course for the onset and resolution of hematological and histopathological changes accompanying hemolysis. Adult (9-13 week) male F344 rats were significantly more sensitive to the hemolytic effects of EGBE than were young (4-5 week) male rats following administration of a single gavage dose of EGBE at 32, 63, 125, 250, or 500 mg/kg. Concurrent metabolism studies also found increased blood retention of EGBE metabolite BAA (as measured by increased C_max, AUC, and T_½), and that young rats eliminated a significantly greater proportion of the administered EGBE dose as exhaled carbon dioxide (CO₂) or as urinary metabolites, as well as excreting a greater proportion of the EGBE conjugates (glucuronide and sulfate) in the urine. These researchers suggested that the pharmacokinetic basis of the age-dependent toxicity of EGBE may be due to a reduced ability by older rats to metabolize the toxic metabolite BAA to CO₂ and a diminished ability to excrete BAA in the urine.

NTP (1998) also found that young mice (6-7 weeks) eliminated BAA 10 times faster than aged mice (19 months) following a 1-day exposure to 125 ppm EGBE. This difference was not as apparent after 3 weeks of exposure, suggesting that factors other than age may be involved (Dill et al., 1998).

Because of the known reproductive toxicity (i.e., to male testes and sperm) of two other glycol ethers, ethylene glycol methyl ether (EGME; 2-methoxyethanol) and ethylene glycol ethyl ether (EGEE; 2-ethoxyethanol), the reproductive toxicity of EGBE has been studied in a variety of well-conducted oral (Nagano et al., 1979, 1984; Grant et al., 1985; Foster et al., 1987; Heindel et al., 1990; Exon, 1991; NTP, 1993) and inhalation (Dodd et al., 1983; Doe, 1984; Nachreiner, 1994; NTP, 1998) studies using rats, mice, and rabbits. In addition, several developmental studies have addressed EGBE's toxicity from conception to sexual maturity, including toxicity to the embryo and fetus, following oral (Wier et al., 1987; Sleet et al., 1989), inhalation (Nelson et al., 1984; Tyl et al., 1984), and dermal (Hardin et al., 1984) exposures to rats, mice, and rabbits. In many instances, LOAELs and NOAELs were reported for both parental and developmental effects; therefore the developmental studies can also be used to assess systemic toxicity as well as developmental toxicity.

EGBE did not cause adverse effects in any reproductive organ, including testes, in any study. In a two-generation reproductive toxicity study, fertility was reduced in mice only at very high, maternally toxic doses (> 1000 mg/kg). Maternal toxicity related to the hematologic effects of EGBE and relatively minor developmental effects have been reported in developmental studies. No teratogenic toxicities were noted in any of the studies. It can be concluded from these studies that EGBE is not significantly toxic to the reproductive organs (male or female) of parents, nor to the developing fetuses of laboratory animals.

For more detail on Susceptible Populations, exit to the toxicological review, Section 4.7 (PDF)

__I.B.5. Confidence in the Inhalation RfC

Study — High
Database — Medium-to-high
RfC — Medium-to-high

The overall confidence in the RfC assessment is medium to high. A higher confidence is placed in the RfC values derived from internal dose measures because pharmacokinetic differences between rats and humans were accounted for using two PBPK models (Lee et al., 1998; Corley et al., 1994; 1997). High confidence is placed in the NTP (1998) study because it was a chronic study, it employed both male and female rats and mice, it had a wide range of exposure levels, and it observed animals twice daily. Medium-to-high confidence is placed on the database because data are available for a variety of animal species including humans. Although the database lacks long-term human studies, the available short-term human controlled studies and case reports, and laboratory animal and in vitro studies, provide ample evidence to suggest that with respect to the hemolytic effects of EGBE, long-term human exposures would be no more adverse than long-term rat exposures. Confidence in the database is not "high" because the potential for liver effects in humans from long-term exposure has not been investigated.

For more detail on Characterization of Hazard and Dose Response, exit to the toxicological review, Section 6 (PDF)

__I.B.6. EPA Documentation and Review of the Inhalation RfC

Source Document — U.S. EPA, 1999.

This assessment was peer reviewed by external scientists. Their comments have been evaluated carefully and incorporated in finalization of this IRIS Summary. A record of these comments is included as an appendix to the Toxicological Review of Ethylene Glycol Monobutyl Ether in support of summary information on the Integrated Risk Information System (IRIS) (U.S. EPA, 1999). To review this appendix, exit to the toxicological review, Appendix A, Summary of and Response to External Peer Review Comments (PDF).

Agency Consensus Date — 11/16/1999

Screening-Level Literature Review Findings — A screening-level review conducted by an EPA contractor of the more recent toxicology literature pertinent to the RfC for Ethylene glycol monobutyl ether (EGBE) conducted in September 2002 did not identify any critical new studies. IRIS users who know of important new studies may provide that information to the IRIS Hotline at hotline.iris@epa.gov or (202)566-1676.

__I.B.7. EPA Contacts (Inhalation RfC)

Please contact the IRIS Hotline for all questions concerning this assessment or IRIS, in general, at (202)566-1676 (phone), (202)566-1749 (FAX) or hotline.iris@epa.gov (Internet address).

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_II.  Carcinogenicity Assessment for Lifetime Exposure

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2
Last Revised — 12/30/1999

Section II provides information on three aspects of the carcinogenic assessment for the substance in question, the weight-of-evidence judgment of the likelihood that the substance is a human carcinogen, and quantitative estimates of risk from oral exposure and from inhalation exposure. The quantitative risk estimates are presented in three ways. The slope factor is the result of application of a low-dose extrapolation procedure and is presented as the risk per (mg/kg)/day. The unit risk is the quantitative estimate in terms of either risk per µg/L drinking water or risk per µg/m³ air breathed. The third form in which risk is presented is a concentration of the chemical in drinking water or air associated with cancer risks of 1 in 10,000, 1 in 100,000, or 1 in 1,000,000. The rationale and methods used to develop the carcinogenicity information in IRIS are described in the Risk Assessment Guidelines of 1986 (EPA/600/8-87/045) and in the IRIS Background Document. IRIS summaries developed since the publication of EPA's more recent Proposed Guidelines for Carcinogen Risk Assessment also utilize those Guidelines where indicated (Federal Register 61(79):17960-18011, April 23, 1996). Users are referred to Section I of this IRIS file for information on long-term toxic effects other than carcinogenicity.

_II.A. Evidence for Human Carcinogenicity

__II.A.1. Weight-of-Evidence Characterization

No reliable human epidemiological studies are available that address the potential carcinogenicity of EGBE. A draft report of the results of a 2-year inhalation bioassay performed using rats and mice has recently become available (NTP, 1998). NTP (1998) reported no evidence of carcinogenic activity in male F344/N rats, and equivocal evidence of carcinogenic activity in female F344/N rats on the basis of increased combined incidences of benign and malignant pheochromocytoma (mainly benign) of the adrenal medulla. They also reported some evidence of carcinogenic activity in male B6C3F1 mice on the basis of increased incidences of hemangiosarcoma of the liver, and some evidence of carcinogenic activity in female B6C3F1 mice based on increased incidences of forestomach squamous cell papilloma or carcinoma (mainly papilloma). As is discussed in more detail below, because of the uncertain relevance of these tumor increases to humans, the fact that EGBE is generally negative in genotoxic tests, and the lack of human data to support the findings in rodents, the human carcinogenic potential of EGBE, in accordance with the recently proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1996), cannot be determined at this time, but suggestive evidence exists from rodent studies. Under existing EPA guidelines (U.S. EPA, 1986), EGBE is judged to be a possible human carcinogen, Group C.

For more detail on Characterization of Hazard and Dose Response, exit to the toxicological review, Section 6 (PDF)

For more detail on Susceptible Populations, exit to the toxicological review, Section 4.7 (PDF)

__II.A.2. Human Carcinogenicity Data

There are currently no human epidemiological or occupational studies addressing the potential carcinogenicity of EGBE.

__II.A.3. Animal Carcinogenicity Data

Two-year inhalation bioassays were conducted in mice and rats exposed to EGBE (NTP, 1998). In the chronic portion of this study, exposure concentrations of EGBE were 0, 31, 62.5, and 125 ppm for groups of 50 F344/N rats, and 0, 62.5, 125, and 250 ppm for groups of 50 B6C3F1 mice. The highest exposure was selected to produce a 10% to 15% depression in hematologic indices. Survival was significantly decreased in male mice at 125 and 250 ppm (54.0% and 53.1%, respectively), but no effect on survival was observed at other exposure levels in mice or in rats at any exposure level. Significant increases in several tumor types were observed. NTP (1998) reported no evidence of carcinogenic activity in male F344/N rats, and equivocal evidence of carcinogenic activity in female F344/N rats on the basis of increased combined incidences of benign and malignant pheochromocytoma (mainly benign) of the adrenal medulla. They also reported some evidence of carcinogenic activity in male B6C3F1 mice on the basis of increased incidences of hemangiosarcoma of the liver, and some evidence of carcinogenic activity in female B6C3F1 mice based on increased incidences of forestomach squamous cell papilloma or carcinoma (mainly papilloma).

With respect to the pheochromocytomas reported in female rats, the NTP (1998) tables indicate a marginally significant trend (p=0.044), and high-dose findings (16%) are only slightly different from the upper range of historical controls (13%). Further, pheochromocytomas can be difficult to distinguish from nonneoplastic adrenal medullary hyperplasia and, according to the NTP report, most of these tumors were "small and not substantially larger than the more severe grades of adrenal medullary hyperplasia." Thus, these tumors must be interpreted with caution.

The hemangiosarcomas in livers of male mice appear to be exposure related. However, the fact that the incidence of hemangiosarcomas was not increased in other organs (bone, bone marrow), and an increased incidence of liver hemangiosarcomas was not noted in either rats or female mice, raises the question of whether this effect is related to accumulation of hemosiderin from hemolytic effects in the liver and related oxidative stress in male mice. Mice are known to be more susceptible to oxidative stress than are rats because of their lower antioxidant capability (Bachowski et al., 1997). On page 118 of their draft report, NTP (1998) states that a review of past NTP studies found no association between hemosiderin deposition in the liver and liver neoplasms in 79 male mice and 103 female mice from 2-year NTP studies in which liver was a site of chemical-related neoplasms. NTP (1998) goes on to state that: "At least for mice, it does not appear that an accumulation of hemosiderin and possible oxidative stress alone were the cause of liver neoplasm in male mice." However, recent work suggests that iron accumulation from the hemolytic effects of EGBE occurs in the livers of mice and can lead to oxidative stress (Xue et al., 1999). Humans have been shown to be much less sensitive to the hemolytic effects of EGBE. Thus, if the slight increase in the incidence of hemangiosarcomas in male mice observed in the NTP study is related to the hemolytic effects of EGBE, they are unlikely to be relevant to human risk. Ongoing research on the effects of hemosiderin accumulation in male mice could help to resolve this issue.

The increased incidence of forestomach squamous cell papillomas or carcinomas was another effect observed in mice, but not rats. Increased incidences of forestomach neoplasms in the male and female mice occurred in groups in which ulceration and hyperplasia were also noted. NTP (1998) notes (page 115) that: "A direct association of neoplasia with ulceration and hyperplasia was not shown in this study although it is hypothesized that 2-butoxyethanol exposure-induced irritation caused the inflammatory and hyperplastic effects in the forestomach, and that the neoplasia was associated with a continuation of the injury/degeneration process." The mechanism for forestomach accumulation of EGBE or a metabolite following inhalation exposure is not known. However, Ghanayem et al. (1987) found that the levels of EGBE in the forestomach of rats 48 hours after gavage exposure were three times the levels in the glandular stomach, suggesting a different reactivity and/or absorption in the two parts of the stomach.

__II.A.4. Supporting Data for Carcinogenicity

In addition to the 2-year bioassay data, data from short-term tests and subchronic studies were evaluated along with EGBE's chemical and physical properties to gain some insight into EGBE's potential carcinogenicity. From what is known of the metabolic pathways of EGBE in animals, metabolic production of a species capable of significant reactivity with DNA is not anticipated. Available data on EGBE derived from conventional genotoxicity tests do not support a mutagenic or clastogenic (chromosomal breaking) potential of the compound. Further details on these genotoxicity tests can be found in U.S. EPA (1999). Not all carcinogens, however, are DNA reactive (Ashby and Tennant, 1991). A paucity of information was available on other potential modes of action for EGBE. Some information was available on gap-junctional intercellular communication (GJIC), which is widely believed to play a role in tissue and organ development and in the maintenance of a normal cellular phenotype with tissues. Thus, interference of GJIC may be a contributing factor in tumor development. Elias et al. (1996) reported that EGBE inhibited intercellular communication in Chinese hamster V79 fibroblast cells. They reported negative results for cell transformation in Syrian Chinese hamster embryos. This cell transformation assay is capable of detecting genotoxic or nongenotoxic carcinogens; however, the gene mutation data presented by Elias et al. (1996) is in graphic form and cannot be critically evaluated given that only mean values are displayed with no standard deviations. Furthermore, survival data are not reported.

On the basis of chemical structure, EGBE does not resemble any known chemical carcinogens and is not expected to have any electrophilic or DNA reactive activity. As discussed above, genotoxicity data on EGBE are predominantly negative. Thus, considering the weight-of-evidence on EGBE, it is not expected to be a mutagen or clastogen.

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_II.B. Quantitative Estimate of Carcinogenic Risk from Oral Exposure

As discussed above, there are currently no human epidemiological occupational studies addressing the potential carcinogenicity of EGBE. A 2-year inhalation bioassay using mice and rats has recently been completed (NTP, 1998) and reports significant increases in certain types of tumors in exposed mice compared to controls, but not in rats. Because of the uncertain relevance of these tumor increases to humans, the fact that EGBE is generally negative in genotoxic tests, and the lack of human data to support the findings in rodents, the human carcinogenic potential of EGBE, in accordance with the recently proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1996), cannot be determined, though suggestive evidence exists in rodent studies. Thus, inhalation or oral quantitative assessments are not being performed at this time.

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_II.C. Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

As discussed above, there are currently no human epidemiological occupational studies addressing the potential carcinogenicity of EGBE. A 2-year inhalation bioassay using mice and rats has recently been completed (NTP, 1998) and reports significant increases in certain types of tumors in exposed mice compared to controls, but not in rats. The relevancy of these tumors to humans is not clear at this time. Consequently, a quantitative assessment was not performed.

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_II.D. EPA Documentation, Review, and Contacts (Carcinogenicity Assessment)

__II.D.1. EPA Documentation

Source Document — U.S. EPA, 1999.

This assessment was peer reviewed by external scientists. Their comments have been evaluated carefully and incorporated in finalization of this IRIS Summary. A record of these comments is included as an appendix to the Toxicological Review of Ethylene Glycol Monobutyl Ether in support of summary information on the Integrated Risk Information System (IRIS) (U.S. EPA, 1999). To review this appendix, exit to the toxicological review, Appendix A, Summary of and Response to External Peer Review Comments (PDF).

__II.D.2. EPA Review (Carcinogenicity Assessment)

Agency Consensus Date — 11/16/1999

Screening-Level Literature Review Findings — A screening-level review conducted by an EPA contractor of the more recent toxicology literature pertinent to the cancer assessment for Ethylene glycol monobutyl ether (EGBE) conducted in September 2002 did not identify any critical new studies. IRIS users who know of important new studies may provide that information to the IRIS Hotline at hotline.iris@epa.gov or (202)566-1676.

__II.D.3. EPA Contacts (Carcinogenicity Assessment)

Please contact the IRIS Hotline for all questions concerning this assessment or IRIS, in general, at (202)566-1676 (phone), (202)566-1749 (FAX) or hotline.iris@epa.gov (Internet address).

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_III.  [reserved]
_IV.  [reserved]
_V.  [reserved]

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_VI.  Bibliography

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2
Last Revised — 12/30/1999

_VI.A. Oral RfD References

Bartnik, FG; Reddy, AK; Klecak, G; et al. (1987) Percutaneous absorption, metabolism, and hemolytic activity of n-butoxyethanol. Fundam Appl Toxicol 8:59-70.

Berliner, N; Duffy, TP; Abelson, HT. (1999) Approach to adult and child with anemia. In: Hoffman, R., ed. Hematology: basic principles and practice. 2nd ed. New York: Churchill Livingstone; pp. 468-483.

Carpenter, CP; Pozzani, UC; Wiel, CS; et al. (1956) The toxicity of butyl cellosolve solvent. AMA Arch Ind Health 14:114-131.

Corley, RA; Bormett, GA; Ghanayem, BI. (1994) Physiologically-based pharmacokinetics of 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in rats and humans. Toxicol Appl Pharmacol 129:61-79.

Corley, RA; Markham, DA; Banks, C; et al. (1997) Physiologically-based pharmacokinetics and the dermal absorption of 2-butoxyethanol vapors by humans. Toxicol Appl Pharmacol 39:120-130.

Dean, BS; Krenzelok, EP. (1991) Critical evaluation of pediatric ethylene glycol monobutyl ether poisonings. Vet Hum Toxicol 33:362.

Dill, JA; Lee, KM; Bates, DJ; et al. (1998) Toxicokinetics of inhaled 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in F344 rats and B6C3F1 mice. Toxicol Appl Pharmacol 153:227-242.

Dodd, DE; Snelling, WM; Maronpot, RR; et al. (1983) Ethylene glycol monobutyl ether: acute, 9-day, and 90-day vapor inhalation studies in Fischer 344 rats. Toxicol Appl Pharmacol 68:405-414.

Doe, JE. (1984) Further studies on the toxicology of the glycol ethers with emphasis on rapid screening and hazard assessment. Environ Health Perspect 57:199-206.

Exon, JH; Mather, GG; Bussiere, JL; et al. (1991) Effects of subchronic exposure of rats to 2-methyoxyethanol or 2-butoxyethanol: thymic atrophy and immunotoxicity. Fundam Appl Toxicol 20:508-510.

Foster, PMD; Lloyd, SC, Blackburn, DM. (1987) Comparison of the in vivo and in vitro testicular effects produced by methoxy-, ethoxy-, and n-butoxy acetic acids in the rat. Toxicology 43:17-30.

Frei, YF; Perk, K; Dannon, D. (1963) Correlation between osmotic resistance and fetal hemoglobin in bovine erythrocytes. Exp Cell Res 30:561.

Ghanayem, BI. (1989) Metabolic and cellular basis of 2-butoxyethanol-induced hemolytic anemia in rats and assessment of human risk in vitro. Biochem Pharmacol 38:1679-1684.

Ghanayem, BI; Sullivan, CA. (1993) Assessment of the hemolytic activity of 2-butoxyethanol and its major metabolite, butoxyacetic acid, in various mammals including humans. Hum Exp Toxicol 12(4):305-311.

Ghanayem, BI; Burka, LT; Matthews, HB. (1987a) Metabolic basis of ethylene glycol monobutyl ether (2-butoxyethanol) toxicity: role of alcohol and aldehyde dehydrogenases. J Pharmacol Exp Ther 242:222-231.

Ghanayem, BI; Blair, PC; Thompson, MB; et al. (1987b) Effect of age on the toxicity and metabolism of ethylene glycol monobutyl ether (2-butoxyethanol) in rats. Toxicol Appl Pharmacol 91:222-234.

Ghanayem, BI; Burka, LT; Sanders, JM; et al. (1987c) Metabolism and disposition of ethylene glycol monobutyl ether (2-butoxyethanol) in rats. J Pharmacol Exp Ther 15:478-484.

Ghanayem, BI; Sanders, JM; Clark, AM; et al. (1990) Effects of dose, age, inhibition of metabolism and elimination on the toxicokinetics of 2-butoxyethanol and its metabolites. J Pharmacol Exp Ther 253:136-143.

Grant, D; Sulsh, S; Jones, HB; et al. (1985) Acute toxicity and recovery in the hemopoietic system of rats after treatment with ethylene glycol monomethyl and monobutyl ethers. Toxicol Appl Pharmacol 77:187-200.

Greaves, P. (1990) Hepatocellular hypertrophy and hyperplasia. In: Histopathology of preclinical toxicity studies: interpretation and relevance in drug safety evaluation. New York: Elsevier, pp. 403-406.

Gualtieri, JF; Harris, CR; Corley, RA; et al. (1995) Multiple 2-butoxyethanol intoxications in the same patient: clinical findings, pharmacokinetics, and therapy. Rochester, NY: North American Congress of Clinical Toxicology.

Hardin, BD; Goad, PhT; Burg, JR. (1984) Developmental toxicity of four glycol ethers applied cutaneously to rats. Environ Health Perspect 57:69-74.

Heindel, JJ; Gulati, DK; Russell, VS; et al. (1990) Assessment of ethylene glycol monobutyl and monophenyl ether reproductive toxicity using a continuous breeding protocol in Swiss CD-1 mice. Fundam Appl Toxicol 15:683-696.

Hord, JD; Lukens, JN. (1999) Anemias unique to infants and young children. In: Lee, R. G., ed. Wintrobe's clinical hematology, volume 2. 10th ed. Baltimore, MD: Williams & Wilkins; pp. 1518-1537.

Krasavage, WJ. (1986) Subchronic oral toxicity of ethylene glycol monobutyl ether in male rats. Fundam Appl Toxicol 6:349-355.

Lewis, AE. (1970) Principles of hematology. New York: Appleton-Century-Crofts.

Medinsky, MA; Singh, G; Bechtold, WE; et al. (1990) Disposition of three glycol ethers administered in drinking water to male F344/N rats. Toxicol Appl Pharmacol 102:443-455.

Nachreiner, DJ. (1994) Ethylene glycol butyl ether: acute vapor inhalation toxicity study in guinea pigs. Bushy Run Research Center, Union Carbide Corporation. Sponsored by Chemical Manufacturers Association, Washington, DC, 94N1392.

Nagano, K; Nakayama, E; Koyano, M; et al. (1979) Testicular atrophy of mice induced by ethylene glycol mono alkyl ethers. Jpn J Ind Health 21:29-35.

Nagano, K; Nakayama, E; Oobayashi, H; et al. (1984) Mouse testicular atrophy induced by ethylene glycol alkyl ethers in Japan. Environ Health Perspect 57:75-84.

National Toxicology Program (NTP). (1993) Technical report on toxicity studies of ethylene glycol ethers 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol administered in drinking water to F344/N rats and B6C3F1 mice. U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP No. 26. NIH Publ. No. 93-3349.

National Toxicology Program (NTP). (1998) NTP technical report on the toxicology and carcinogenesis studies of 2-butoxyethanol (CAS No. 111-76-2) in F344/N rats and B6C3F1 mice (inhalation studies). U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP TR 484 NIH Draft Publication No. 98-3974.

Nelson, BK; Setzer, JV; Brightwell, WS; et al. (1984) Comparative inhalation teratogenicity of four glycol ether solvents and an amino derivative in rats. Environ Health Perspect 57:261-271.

Sabourin, PJ; Medinsky, MA; Birnbaum, LS; et al. (1992a) Effect of exposure concentration on the disposition of inhaled butoxyethanol by F344 rats. Toxicol Appl Pharmacol 114:232-238.

Sabourin, PJ; Medinsky, MA; Thurmond, F; et al. (1992b) Effect of dose on the disposition of methoxyethanol, ethoxyethanol, and butoxyethanol administered dermally to male F344/N rats. Fundam Appl Toxicol 19:124-132; and Erratum, Fundam Appl Toxicol 20:508-510 (1993).

Shyr, LJ; Sabourin, PJ; Medinsky, MA; et al. (1993) Physiologically based modeling of 2-butoxyethanol disposition in rats following different routes of exposure. Environ Res 63:202-218.

Sleet, RB; Price, CJ; Marr, MC; et al. (1989) Teratologic evaluation of ethylene glycol monobutyl ether administered to Fischer 344 rats on either gestational days 9-11 or days 11-13. Final Report. Research Triangle Institute/National Toxicology Program. NTP-CTER-86-103.

Tyl, RW; Millicovsky, G; Dodd, DE; et al. (1984) Teratologic evaluation of ethylene glycol monobutyl ether in Fischer 344 rats and New Zealand white rabbits following inhalation exposure. Environ Health Perspect 57:47-68.

Udden, MM. (1994) Hemolysis and decreased deformability of erythrocytes exposed to butoxyacetic acid, a metabolite of 2-butoxyethanol: II. Resistance in red blood cells from humans with potential susceptibility. J Appl Toxicol 14:97-102.

Udden, MM. (1995) Effects of butoxyacetic acid on rat and human erythrocytes. Abstract, 37th annual meeting, American Society of Hematology, Dec. 1-5, Seattle, WA.

Udden, MM; Patton, CS. (1994) Hemolysis and decreased deformability of erythrocytes exposed to butoxyacetic acid, a metabolite of 2-butoxyethanol: I. Sensitivity in rats and resistance in normal humans. J Appl Toxicol 14:91-96.

U.S. EPA. (1999) Toxicological review of ethylene glycol monobutyl ether (111-76-2) in support of summary information on the Integrated Risk Information System (IRIS). Available online at http://www.epa.gov/ncea/iris.

Wier, PJ; Lewis, SC; Traul, KA. (1987) A comparison of developmental toxicity evident at term to postnatal growth and survival using ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethanol. Teratog Carcinog Mutag 7:55-64.

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_VI.B. Inhalation RfC References

Bartnik, FG; Reddy, AK; Klecak, G; et al. (1987) Percutaneous absorption, metabolism, and hemolytic activity of n-butoxyethanol. Fundam Appl Toxicol 8:59-70.

Berliner, N; Duffy, TP; Abelson, HT. (1999) Approach to adult and child with anemia. In: Hoffman, R., ed. Hematology: basic principles and practice. 2nd ed. New York: Churchill Livingstone; pp. 468-483.

Carpenter, CP; Pozzani, UC; Wiel, CS; et al. (1956) The toxicity of butyl cellosolve solvent. AMA Arch Ind Health 14:114-131.

Corley, RA; Bormett, GA; Ghanayem, BI. (1994) Physiologically-based pharmacokinetics of 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in rats and humans. Toxicol Appl Pharmacol 129:61-79.

Corley, RA; Markham, DA; Banks, C; et al. (1997) Physiologically-based pharmacokinetics and the dermal absorption of 2-butoxyethanol vapors by humans. Toxicol Appl Pharmacol 39:120-130.

Dean, BS; Krenzelok, EP. (1991) Critical evaluation of pediatric ethylene glycol monobutyl ether poisonings. Vet Hum Toxicol 33:362.

Dill, JA; Lee, KM; Bates, DJ; et al. (1998) Toxicokinetics of inhaled 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in F344 rats and B6C3F1 mice. Toxicol Appl Pharmacol 153: 227-242.

Dodd, DE; Snelling, WM; Maronpot, RR; et al. (1983) Ethylene glycol monobutyl ether: acute, 9-day, and 90-day vapor inhalation studies in Fischer 344 rats. Toxicol Appl Pharmacol 68:405-414.

Doe, JE. (1984) Further studies on the toxicology of the glycol ethers with emphasis on rapid screening and hazard assessment. Environ Health Perspect 57:199-206.

Exon, JH; Mather, GG; Bussiere, JL; et al. (1991) Effects of subchronic exposure of rats to 2-methyoxyethanol or 2-butoxyethanol: thymic atrophy and immunotoxicity. Fundam Appl Toxicol 20:508-510.

Foster, PMD; Lloyd, SC; Blackburn, DM. (1987) Comparison of the in vivo and in vitro testicular effects produced by methoxy-, ethoxy-, and n-butoxy acetic acids in the rat. Toxicology 43:17-30.

Frei, YF; Perk, K; Dannon, D. (1963) Correlation between osmotic resistance and fetal hemoglobin in bovine erythrocytes. Exp Cell Res 30:561.

Ghanayem, BI. (1989) Metabolic and cellular basis of 2-butoxyethanol-induced hemolytic anemia in rats and assessment of human risk in vitro. Biochem Pharmacol 38:1679-1684.

Ghanayem, BI; Sullivan, CA. (1993) Assessment of the hemolytic activity of 2-butoxyethanol and its major metabolite, butoxyacetic acid, in various mammals including humans. Hum Exper Toxicol 12(4):305-311.

Ghanayem, BI; Burka, LT; Matthews, HB. (1987a) Metabolic basis of ethylene glycol monobutyl ether (2-butoxyethanol) toxicity: role of alcohol and aldehyde dehydrogenases. J Pharmacol Exper Ther 242:222-231.

Ghanayem, BI; Blair, PC; Thompson, MB; et al. (1987b) Effect of age on the toxicity and metabolism of ethylene glycol monobutyl ether (2-butoxyethanol) in rats. Toxicol Appl Pharmacol 91:222-234.

Ghanayem, BI; Burka, LT; Sanders, JM; et al. (1987c) Metabolism and disposition of ethylene glycol monobutyl ether (2-butoxyethanol) in rats. J Pharmacol Exp Ther 15:478-484.

Ghanayem, BI; Sanders, JM; Clark, A; et al. (1990) Effects of dose, age, inhibition of metabolism and elimination on the toxicokinetics of 2-butoxyethanol and its metabolites. J Pharmacol Exp Ther 253:136-143.

Grant, D; Sulsh, S; Jones, HB; et al. (1985) Acute toxicity and recovery in the hemopoietic system of rats after treatment with ethylene glycol monomethyl and monobutyl ethers. Toxicol Appl Pharmacol 77:187-200.

Hardin, BD; Goad, PhT; Burg, JR. (1984) Developmental toxicity of four glycol ethers applied cutaneously to rats. Environ Health Perspect 57:69-74.

Haufroid, V; Thirion, F; Mertens, P; et al. (1997) Biological monitoring of workers exposed to low levels of 2-butoxyethanol. Int Arch Occup Environ Health 70:232-236.

Heindel, JJ; Gulati, DK; Russell, VS; et al. (1990) Assessment of ethylene glycol monobutyl and monophenyl ether reproductive toxicity using a continuous breeding protocol in Swiss CD-1 mice. Fundam Appl Toxicol 15:683-696.

Hord, JD; Lukens, JN. (1999) Anemias unique to infants and young children. In: Lee, RG, ed. Wintrobe's clinical hematology, volume 2. 10th ed. Baltimore, MD: Williams & Wilkins; pp. 1518-1537.

Krasavage, WJ. (1986) Subchronic oral toxicity of ethylene glycol monobutyl ether in male rats. Fundam Appl Toxicol 6:349-355.

Lee, KM; Dill, JA; Chou, BJ; et al. (1998) Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol. Toxicol Appl Pharmacol 153:211-226.

Lewis, AE. (1970) Principles of hematology. New York: Appleton-Century-Crofts.

Medinsky, MA; Singh, G; Bechtold, WE; et al. (1990) Disposition of three glycol ethers administered in drinking water to male F344/N rats. Toxicol Appl Pharmacol 102:443-455.

Nachreiner, DJ. (1994) Ethylene glycol butyl ether: acute vapor inhalation toxicity study in guinea pigs. Bushy Run Research Center, Union Carbide Corporation. Sponsored by Chemical Manufacturers Association, Washington, DC, 94N1392.

Nagano, K; Nakayama, E; Koyano, M; et al. (1979) Testicular atrophy of mice induced by ethylene glycol mono alkyl ethers. Jpn J Ind Health 21:29-35.

Nagano, K; Nakayama, E; Oobayashi, H; et al. (1984) Mouse testicular atrophy induced by ethylene glycol alkyl ethers in Japan. Environ Health Perspect 57:75-84.

National Toxicology Program (NTP). (1993). Technical report on toxicity studies of ethylene glycol ethers 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol administered in drinking water to F344/N rats and B6C3F1 mice. U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP No. 26. NIH Publ. No. 93-3349.

National Toxicology Program (NTP). (1998) NTP technical report on the toxicology and carcinogenesis studies of 2-butoxyethanol (CAS No. 111-76-2) in F344/N rats and B6C3F1 mice (inhalation studies). U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP TR 484 NIH Draft Publication No. 98-3974.

Nelson, BK; Setzer, JV; Brightwell, WS; et al. (1984) Comparative inhalation teratogenicity of four glycol ether solvents and an amino derivative in rats. Environ Health Perspect 57:261-271.

Sabourin, PJ; Medinsky, MA; Birnbaum, LS; et al. (1992a) Effect of exposure concentration on the disposition of inhaled butoxyethanol by F344 rats. Toxicol Appl Pharmacol 114:232-238.

Sabourin, PJ; Medinsky, MA; Thurmond, F; et al. (1992b) Effect of dose on the disposition of methoxyethanol, ethoxyethanol, and butoxyethanol administered dermally to male F344/N rats. Fundam Appl Toxicol 19:124-132; and Erratum, Fundam Appl Toxicol 20:508-510 (1993).

Shyr, LJ; Sabourin, PJ; Medinsky, MA; et al. (1993) Physiologically based modeling of 2-butoxyethanol disposition in rats following different routes of exposure. Environ Res 63:202-218.

Sleet, RB; Price, CJ; Marr, MC; et al. (1989) Teratologic evaluation of ethylene glycol monobutyl ether administered to Fischer 344 rats on either gestational days 9-11 or days 11-13. Final Report. Research Triangle Institute/National Toxicology Program. NTP-CTER-86-103.

Tyl, RW; Millicovsky, G; Dodd, DE; et al. (1984) Teratologic evaluation of ethylene glycol monobutyl ether in Fischer 344 rats and New Zealand white rabbits following inhalation exposure. Environ Health Perspect 57:47-68.

Udden, MM. (1994) Hemolysis and decreased deformability of erythrocytes exposed to butoxyacetic acid, a metabolite of 2-butoxyethanol: II. Resistance in red blood cells from humans with potential susceptibility. J Appl Toxicol 14:97-102.

Udden, MM; Patton, CS. (1994) Hemolysis and decreased deformability of erythrocytes exposed to butoxyacetic acid, a metabolite of 2-butoxyethanol: I. Sensitivity in rats and resistance in normal humans. J Appl Toxicol 14:91-96.

Udden, MM. (1995) Effects of butoxyacetic acid on rat and human erythrocytes. Abstract, 37th annual meeting, American Society of Hematology, Dec. 1-5, Seattle, WA.

U.S. EPA. (1994) Methods for derivation of inhalation reference concentrations and application of inhalation dosimetry. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA/600/8-90/066F October 1994.

U.S. EPA. (1999) Toxicological review of ethylene glycol monobutyl ether (111-76-2) in support of summary information on the Integrated Risk Information System (IRIS). Available online at http://www.epa.gov/ncea/iris.

Wier, PJ; Lewis, SC; Traul, KA. (1987) A comparison of developmental toxicity evident at term to postnatal growth and survival using ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethanol. Teratog Carcinog Mutag 7:55-64.

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_VI.C. Carcinogenicity Assessment References

Ashby, J; Tennant, RW. (1991) Definitive relationships among chemical structure, carcinogenicity and mutagenicity for 301 chemicals tested by the U.S. NTP. Mutat Res 257(3):229-306.

Bachowski, S; Kolaga, KL; Xu, Y; et al. (1997) Role of oxidative stress in the mechanism of dieldrin's hepatotoxicity. Ann Clin Lab Sci 27(3):196-209.

Elias, Z; Daniere, MC; Marande, AM; et al. (1996) Genotoxic and/or epigenetic effects of some glycol ethers: results of different short-term tests. Occup Hyg 2:187-212.

Ghanayem, BI; Burka, LT; Sanders, JM; et al. (1987a) Metabolism and disposition of ethylene glycol monobutyl ether (2-butoxyethanol) in rats. J Pharmacol Exper Ther 15:478-484.

National Toxicology Program (NTP). (1998) NTP technical report on the toxicology and carcinogenesis studies of 2-butoxyethanol (CAS No. 111-76-2) in F344/N rats and B6C3F1 mice (inhalation studies). U.S. DHHS, PHS, NIH, Research Triangle Park, NC. NTP TR 484 NIH Draft Publication No. 98-3974.

U.S. EPA. (1986) Guidelines for carcinogen risk assessment. Federal Register 51(185):33992-34003.

U.S. EPA. (1996) (new proposed) Guidelines for carcinogen risk assessment, 1996. (Currently, these guidelines are available only as a draft.)

U.S. EPA. (1999) Toxicological review of ethylene glycol monobutyl ether (111-76-2) in support of summary information on the Integrated Risk Information System (IRIS). Available online at http://www.epa.gov/ncea/iris.

Xue, H; Kamendulis, LM; Klaunig, JE. (1999) A potential mechanism for 2-butoxyethanol (2-BE) induced mouse liver neoplasia. Abstract, Annual Meeting, Society of Toxicology, March 14-18, New Orleans, LA.

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_VII.  Revision History

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2

Date	Section	Description
04/01/1997	III., IV., V.	Drinking Water Health Advisories, EPA Regulatory Actions, and Supplementary Data were removed from IRIS on or before April 1997. IRIS users were directed to the appropriate EPA Program Offices for this information.
12/30/1999	I...VI	RfD, RfC, and carcinogenicity assessment first on line
12/03/2002	I.A.6., , I.B.6., II.D.2.	Screening-Level Literature Review Findings message has been added.
02/09/2004	I., II.	This chemical is being reassessed under the IRIS Program.

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_VIII.  Synonyms

Ethylene glycol monobutyl ether (EGBE)
CASRN — 111-76-2
Last Revised — 12/30/1999

• 2-Butoxyethanol

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