EPA 749-F-94-009a CHEMICAL SUMMARY FOR METHYL ISOBUTYL KETONE prepared by OFFICE OF POLLUTION PREVENTION AND TOXICS U.S. ENVIRONMENTAL PROTECTION AGENCY September 1994 This summary is based on information retrieved from a systematic search limited to secondary sources (see Appendix A). These sources include online databases, unpublished EPA information, government publications, review documents, and standard reference materials. No attempt has been made to verify information in these databases and secondary sources. I. CHEMICAL IDENTITY AND PHYSICAL/CHEMICAL PROPERTIES The chemical identity and physical/chemical properties of methyl isobutyl ketone are summarized in Table 1. TABLE 1. CHEMICAL IDENTITY AND CHEMICAL/PHYSICAL PROPERTIES OF METHYL ISOBUTYL KETONE _______________________________________________________________________ Characteristic/Property Data Reference _______________________________________________________________________ CAS No. 108-10-1 Common Synonyms MIBK; hexone; 4-methyl- 2-pentanone NIOSH 1990 Molecular Formula C6H120 Chemical Structure O || CH3-C-CH2-CH-CH3 | CH3 Physical State liquid Budavari 1989 Molecular Weight 100.16 Budavari 1989 Melting Point -85/-80øC Verschueren 1983 Boiling Point 117-118øC Budavari 1989 Water Solubility 17,000 mg/L @ 20øC; 19,000 mg/L @ 25øC Verschueren 1983; CHEMFATE 1994 Specific gravity 0.8017 @ 20/4øC Verschueren 1983 Vapor Density (air = 1) 3.45 Verschueren 1983 KOC 19 (estimated) U.S. EPA 1987 Log KOW 1.09; 1.19 (estimated) U.S. EPA 1987; HSDB 1994 Vapor Pressure 19.86 mm Hg @ 25øC CHEMFATE 1994 Reactivity flammable, vapors form explosive mixture with air HSDB 1994 Flash Point 23øC (closed cup) Budavari 1989 Henry's Law Constant 1.38 X 10-4 atm m3/mol @ 25øC (estimated) CHEMFATE 1994 Fish Bioconcentration Factor 2 (estimated) U.S. EPA 1987 Odor Threshold 0.10 ppm (in air) Krasavage et al. 1982 Conversion Factors 1 ppm = 4.10 mg/m3 1 mg/m3 = 0.24 ppm Verschueren 1983 _______________________________________________________________________ II. PRODUCTION, USE, AND TRENDS A. Production There are three methyl isobutyl ketone producers in the United States. Table 2 lists producers, plant locations, and plant capacities. Annual US capacity is approximately 210 million pounds. In 1992, an estimated 160 million pounds of methyl isobutyl ketone were produced in the United States. During that same year, 22 million pounds were imported into the US, and 38 million pounds were exported (Mannsville 1993). B. Use Methyl isobutyl ketone is used in a number of industrial applications. The primary use of methyl isobutyl ketone, accounting for approximately 62 percent of all use, is as a solvent in protective coatings. It is also used as a solvent in specialty adhesives; in ink formulations; in dewaxing mineral oil; and in textile coatings and leather finishing. As a process solvent methyl isobutyl ketone is used in the separation and purification of certain metal ions, such as zirconium from hafnium; in the extraction and purification of antibiotics and other pharmaceuticals; and in the manufacture of insecticides and other pesticides. It is also used in purifying stearic acid; refining tall oil; and extracting rosin from softwood, especially pine (Mannsville 1993; HSDB). Table 3 shows the estimated 1992 US end-use pattern for methyl isobutyl ketone. C. Trends Demand for methyl isobutyl ketone is expected to decrease gradually until alternative, low volatile organic carbon (VOC) coating technologies are readily available (Mannsville 1993). Once such alternatives are available, demand is expected to decrease more rapidly. TABLE 2. United States Producers of Methyl Isobutyl Ketone _______________________________________________________________________ Company Plant Location Plant Capacity (in millions of pounds) _______________________________________________________________________ Eastman Chemical Kingsport, TN 40 Shell Chemical Deer Park, TX 100 Union Carbide Institute, WV 70 _______________________________________________________________________ Source: Mannsville 1993. TABLE 3. Estimated 1992 United States End-Use Pattern of Methyl Isobutyl Ketone _______________________________________________________________________ Use of Methyl Isobutyl Ketone Percentage of (typical Standard Industrial US Methyl Isobutyl Classification (SIC) Code (see Ketone Use end note 1) _______________________________________________________________________ Protective coatings solvent (production, SIC 2851) 62% Solvent for chemical synthesis (production, SIC 2843, 2891, 2893, 2911, 3111) 18% Process solvent (production, SIC 2833, 2879, 3339) 13% Miscellaneous (no applicable SIC Code(s)) 7% _______________________________________________________________________ Source: Mannsville 1993. III. ENVIRONMENTAL FATE A. Environmental Release Of the total methyl isobutyl ketone released to the environment almost all eventually enters the air. It is released into the environment from industrial and domestic uses. The largest man-made sources of methyl isobutyl ketone release are from its primary use as a solvent in paints, lacquers, varnishes, and adhesives. Methyl isobutyl ketone has also been found in vehicle exhaust gases (HSDB 1994). It occurs naturally and has been identified as a volatile flavor component of baked potatoes. It is also found in flavoring agents used in nonalcoholic beverages, ice cream, candy, and baked goods at a concentration of about 6.3 ppm (HSDB 1994). In 1992, releases of methyl isobutyl ketone to environmental media, as reported to the Toxic Chemical Release Inventory by certain types of US industries totaled about 26 million pounds. Of this amount, a total of 25.9 million pounds (98%) was released to the atmosphere, 96 thousand pounds were released to surface water, 129 thousand pounds were released to underground injection, and 195 thousand pounds were released to land (TRI92 1994). Methyl isobutyl ketone has been found in the leachate from various municipal landfills and other waste sites at levels of 25 to 263 ppb (HSDB 1994). Levels of methyl isobutyl ketone in the atmosphere near industrial sources have been measured. A mean atmospheric concentration of 270 ppt (parts per trillion) was measured in Edison, NJ in 1976, and levels ranging from <0.5 ppm to 13 ppm were measured near three municipal waste treatment plants in Cincinnati, OH in 1982 (HSDB 1994). It was qualitatively detected in only one of 204 samples of surface water collected near heavily industrialized areas across the United States (HSDB 1994). B. Transport Methyl isobutyl ketone is not expected to be retarded by adsorption to soils rich in organic material [Koc = 19 (U.S. EPA 1987)]; therefore, it is expected to be mobile in soil and subject to leaching from landfills. The relatively high vapor pressure [14.5 mm Hg @ 20øC (HSDB 1994)] and estimated Henry's Law constant (9.4 x 10-5 atm-m3/mol @ 20øC) indicate that it will volatilize from moist and dry soil (HSDB 1994). When released to water, it does not adsorb significantly to suspended solids, and will volatilize to the atmosphere (HSDB 1994). C. Transformation/Persistence 1. Air - The main degradation pathway for methyl isobutyl ketone in the atmosphere is reaction with photochemically produced hydroxyl radicals. The half-life of methyl isobutyl ketone from the reaction with hydroxyl radicals has been estimated to be about 16-17 hours (HSDB 1994). Based on its UV light absorption spectrum, direct photolysis of methyl isobutyl ketone is expected to occur with a half life of about 15 hours; acetone is a photoxidation product (HSDB 1994). 2. Soil - In wet or dry soil, methyl isobutyl ketone may undergo volatilization to air and photolysis on the soil surface (HSDB 1994). It is also highly mobile and may be leached from the soil by water, and is susceptible to aerobic degradation by mixed populations of microorganisms (HSDB 1994). 3. Water - The most important fate process for methyl isobutyl ketone in water is volatilization (half-time of 15-33 hours). Direct photolysis near the surface is also thought to be an important process (HSDB 1994). Rapid aerobic biodegradation of methyl isobutyl ketone has been reported in marine water (BIODEG 1994). It is not expected to undergo chemical hydrolysis or to be bound to sediment or suspended organic matter (HSDB 1994). 4. Biota - Methyl isobutyl ketone is not expected to bioconcentrate in fish or other aquatic organisms; its estimated bioconcentration factor is 2 (U.S. EPA 1987). IV. HUMAN HEALTH EFFECTS A. Pharmacokinetics 1. Absorption - Studies in humans and animals have demonstrated that methyl isobutyl ketone is primarily absorbed via the lungs; however, it can also be absorbed through the gastro- intestinal system and through the skin (HSDB 1994). 2. Distribution - Methyl isobutyl ketone was found in brain, liver, lung, vitreous fluid, kidney, and blood in two cases where individuals were exposed to lethal levels of paint spray solvent (HSDB 1994). No specific quantitative information on its general distribution was found in the sources searched. 3. Metabolism - Experiments with guinea pigs have shown that methyl isobutyl ketone is metabolized to 4-hydroxy-4-methyl- 2-pentanone and 4-methyl-2-pentanol (HSDB 1994). 4. Excretion - Ketones in general are rapidly excreted in expired air. Small amounts of methyl isobutyl ketone and its metabolites are also excreted in the urine. Humans excreted less than 0.1% of the dose as unmetabolized methyl isobutyl ketone in the urine within the first three hours post exposure (HSDB 1994). The serum half-time for methyl isobutyl ketone in guinea pigs was shown to be 66 minutes with a clearance time of 6 hours. The clearance time for the metabolite, 4-hydroxy-4-methyl-2-pentanone, was 16 hours (ACGIH 1991). B. Acute Toxicity Acute exposure to methyl isobutyl ketone can irritate the eyes and respiratory tract, and cause narcosis at high concentrations in air. 1. Humans - Exposure to 100 ppm (410 mg/m3; 58.6 mg/kg/day) (see end note 2) resulted in headaches, nausea, and respiratory tract irritation among workers occupationally exposed and individuals voluntarily exposed to methyl isobutyl ketone. The majority of the volunteers indicated that the 100 ppm concentration was the highest tolerable level for an 8-hour exposure (U.S. EPA 1987; Krasavage et al. 1982). A concentration of 200 ppm (820 mg/m3) resulted in eye irritation and had a disagreeable odor (U.S. EPA 1987). Higher concentrations can result in serious narcosis (see Section IV.G.1). Eye contact with liquid methyl isobutyl ketone causes painful irritation, which is relieved by flushing the eyes with water (Krasavage et al. 1982). 2. Animals - An oral LD50 value of 2080 mg/kg was reported for rats given 20% methyl isobutyl ketone dissolved in Tergitol 7 surfactant (Krasavage et al. 1982). An oral LD50 value of 5.7 mL/kg (÷4570 mg/kg) was reported for rats given the chemical undiluted. A 24-hour oral LD50 of 1900 mg/kg was determined for mice (Krasavage et al. 1982). An inhalation LC50 value of 23,300 mg/m3 was reported for mice (RTECS 1994). C. Subchronic/Chronic Effects Human studies and animal experiments have indicated that extended or repeated exposure to relatively high concentrations of methyl isobutyl ketone can result in central nervous system, gastrointestinal tract, hepatic, and renal toxicity, 1. Humans - Chronic occupational exposure to an atmospheric concentration of 500 ppm methyl isobutyl ketone for 20-30 minutes/day, and 80 ppm for the remainder of the workday resulted in nausea, headache, burning eyes, and weakness in over half of the workers. Some workers reported somnolence, insomnia and intestinal pain, and 4/19 appeared to have slightly enlarged livers. This study was continued 5 years later after the methyl isobutyl ketone concentrations had been reduced to 100-105 ppm for the 20-30 minutes exposures and 50 ppm for the general exposures. A few workers still experienced gastrointestinal and neurological problems and slight liver enlargement was found in 2 individuals (U.S. EPA 1987). 2. Animals - Male and female Sprague-Dawley rats, given daily doses of 0, 50, 250, or 1000 mg/kg methyl isobutyl ketone in corn oil by gavage for 13 weeks, developed enlarged livers and kidneys at 1000 mg/kg/day. Relative kidney weights were slightly increased in both sexes, and liver weights were marginally increased in males at 250 mg/kg/day. Hypoglycemia and elevated cholesterol were seen in females at 250 mg/kg/day, and in both sexes at 1000 mg/kg/day. No treatment related histopathology was reported (U.S. EPA 1987). Male and female Fischer 344 rats and B6C3F1 mice were exposed by inhalation to 0, 50, 250, or 1000 ppm (0, 205, 1024, or 4097 mg/m3) methyl isobutyl ketone for 6 hours/day, 5 days/week for 14 weeks. Increased absolute liver weight was reported in male mice at 250 ppm, and increased absolute and relative liver weight was seen in male rats and mice at 1000 ppm. An increased incidence of hyaline droplets in the kidney tubules of male rats was seen at 250 and 1000 ppm. No adverse effects were observed with exposed female rats or mice at any dose tested (U.S. EPA 1987). D. Carcinogenicity 1. Humans - No information on the carcinogenicity of methyl isobutyl ketone was found in the secondary sources searched. 2. Animals - No information on the carcinogenicity of methyl isobutyl ketone was found in the secondary sources searched. E. Genotoxicity In mutagenicity assays, requested by and submitted to EPA under Section 4 of the Toxic Substances Control Act (TSCA), methyl isobutyl ketone tested positive in the mouse lymphoma and cell transformation assays. Results were suggestive but equivocal for unscheduled DNA synthesis. Results from submitted Ames tests and the mouse micronucleus test were negative. Methyl isobutyl ketone was negative in E. coli tester strains WP2 and WP2uvrA; and in S. cerevisiae tester strain JD1 with or without S-9 metabolic activation (HSDB 1994). U.S. EPA (1987) has reported methyl isobutyl ketone as negative in the mouse micronucleus assay and for unscheduled DNA synthesis. F. Developmental/Reproductive Toxicity Results from inhalation developmental toxicity studies in mice and rats, requested by and submitted to EPA under Section 4 of TSCA, indicate that methyl isobutyl ketone is a developmental toxicant. Exposure to high concentrations of methyl isobutyl ketone in air during pregnancy can cause maternal and fetal toxicity, resulting in decreased fetal weight and delayed skeletal ossification. 1. Humans - No information on the developmental/reproductive toxicity of methyl isobutyl ketone was found in the secondary sources searched. 2. Animals - Inhalation developmental toxicity studies in mice and rats have been requested by and submitted to EPA under Section 4 of TSCA. In the rat evidence of developmental toxicity (decrease in fetal weight) was seen at concentrations as low as 300 ppm, the lowest dose tested. In addition to fetal weight reductions, increases in the frequencies of ossification variations were seen at 3000 ppm in both rats and mice (Campbell 1988). Maternal toxicity (reduced body weight and reduced body weight gain) was observed at 3000 ppm, the high dose, in both rats and mice. Clinical symptoms of toxicity included adverse neurological effects (see Section IV.G). Relative to these same studies, U.S. EPA (1987) reported that groups of 25 Fischer 344 rats and 25 CD-1 mice were exposed to air concentrations of 0, 300, 1000, or 3000 ppm methyl isobutyl ketone 6 hours/day during days 6-15 of gestation. Results of reproductive parameters showed no treatment related effects on the number of corpora lutea, implantations per litter, percent preimplantational loss, percent live fetuses, or sex ratio in either the rats or mice. A decrease in the number of live births per litter and decreased fetal body weights were reported in the mice, and an increase incidence of poorly ossified or unossified skeletal elements were reported in both rats and mice at 3000 ppm. These results were attributed to maternal and fetal toxicity. There were no significant increases in malformations in either rats or mice at any dose. Campbell (1988) also reports results of a 2-week probe and a 14-week subchronic inhalation study in Fischer-344 rats and B6C3F1 mice. Several reproductive organs (including histopathology of the ovaries and the testes) were examined; no evidence of reproductive organ toxicity was reported. G. Neurotoxicity Neurological effects, observed in humans and animals exposed to high concentrations of methyl isobutyl ketone in air appear to be reversible. 1. Humans - Exposure to high concentrations (>1000 ppm) of methyl isobutyl ketone can produce central nervous system depression and narcosis. Lower doses (80-500 ppm) can cause weakness, headaches, and nausea (Krasavage et al. 1982). 2. Animals - Exposure of mice and rats to 300-3000 ppm, 6 hours/day for 10 days (see Section IV.F) resulted in loss of coordination, negative tail and toe pinch, partial paralysis, and muscular weakness in hind limbs in rats; and irregular gait, partial paralysis, hypoactivity, ataxia and negative toe pinch in mice (U.S. EPA 1987). Very high concentrations of methyl isobutyl ketone (19,000- 20,000 ppm) resulted in rapid anesthesia of mice, which was reversible if the animals were promptly removed to fresh air. Most mice not moved to fresh air died from the narcosis and respiratory failure within 30 minutes at 20,000 ppm. The same effects were reported with rats and guinea pigs at doses of 21,000 and 16,800 ppm, respectively. Lower doses (4000 ppm) resulted in loss of coordination and prostration in rats exposed for 6 hours in one study; whereas, the same dose and exposure time killed all the animals in another study (Krasavage et al. 1982). V. ENVIRONMENTAL EFFECTS The toxicity of methyl isobutyl ketone in aquatic organisms is low; toxicity values are greater than 100 mg/L. It also has low toxicity in terrestrial rodents for oral or inhalation exposure. It appears to have moderate toxicity in birds, based on an oral LD50 value between 50 and 500 mg/kg, as measured in redwinged blackbirds. Methyl isobutyl ketone can contribute to the formation of photochemical smog. A. Toxicity to Aquatic Organisms LC50 values for fish are: 460 mg/L, 24 hours for Carassius auratus (goldfish); 505 mg/L, 96 hours for Pimephales promelas(fathead minnow) (HSDB 1994). 24 Hour LC50 values of 4280 mg/L for Daphnia magna (water flea) and 1230 mg/L for Artemia salina (brine shrimp) were reported (AQUIRE 1994). B. Toxicity to Terrestrial Organisms An LD50 value of 100 mg/kg for oral exposure was reported for Angelaius phoeniceus (redwinged blackbird) (HSDB 1994). The toxicity data reported for rats and rabbits (see sections IV.B.2. and IV.C.2.) suggest that no adverse effects would be expected at normal environmental concentrations. C. Abiotic Effects Smog chamber studies indicate that methyl isobutyl ketone is moderately reactive with nitrogen oxides producing acetone, peroxyacetylnitrate, and methyl nitrate (HSDB 1994). According to the definition provided in the Federal Register (1992), methyl isobutyl ketone is a volatile organic carbon (VOC) substance. As a VOC, methyl isobutyl ketone can contribute to the formation of photochemical smog in the presence of other VOCs. VI. EPA/OTHER FEDERAL AND OTHER GROUP ACTIVITY Methyl isobutyl ketone has been selected for a joint EPA/Industry program of voluntary emission reductions. The Clean Air Act Amendments of 1990 list methyl isobutyl ketone as a hazardous air pollutant. Occupational exposure to methyl isobutyl ketone is regulated by the Occupational Safety and Health Administration (OSHA). The permissible exposure limit (PEL) is 100 parts per million parts of air (ppm) as an 8-hour time-weighted average (TWA) (29 CFR 1910.1000). Federal agencies and other groups that can provide information on methyl isobutyl ketone are listed in Tables 4 and 5. TABLE 4. EPA OFFICES AND CONTACT NUMBERS FOR INFORMATION ON METHYL ISOBUTYL KETONE ________________________________________________________________________ EPA OFFICE LAW PHONE NUMBER ________________________________________________________________________ Pollution Prevention Toxic Substances Control Act & Toxics (Sec. 4/8A/8D/8E) (202) 554-1404 Emergency Planning and Community Right-to-Know Act (EPCRA) Regulations (Sec. 313) (800) 424-9346 Toxics Release Inventory data (202) 260-1531 Air Clean Air Act (919) 541-0888 Solid Waste & Comprehensive Environmental Emergency Response Response, Compensation, and Liability Act (Superfund)/ Resource Conservation and Recovery Act / EPCRA (Sec. 304/311/312) (800) 424-9346 ________________________________________________________________________ TABLE 5. OTHER FEDERAL OFFICE/OTHER GROUP CONTACT NUMBERS FOR INFORMATION ON METHYL ISOBUTYL KETONE _______________________________________________________________________ Other Agency/Department/Other Group Contact Number _______________________________________________________________________ Agency for Toxic Substances & Disease Registry (404) 639-6000 American Conference of Governmental Industrial Hygienists (Recommended TLV-TWA: 50 ppm; TLV-STEL 75 ppm (see end note 3)) (ACGIH 1991) (513) 742-2020 Consumer Product Safety Commission (301) 504-0994 Food & Drug Administration (301) 443-3170 National Institute for Occupational Safety & Health (Recommended TWA: 50 ppm; STEL 75 ppm; IDLH, 3000 ppm (see end note 4)) (NIOSH 1990) (800) 356-4674 Occupational Safety & Health Administration (Permissible-TWA: 100 ppm (see end note 5)) (OSHA 1993) (Check local phone book for phone number under Department of Labor) _______________________________________________________________________ VII. END NOTES 1. Standard Industrial Classification code is the statistical classification standard for all Federal economic statistics. The code provides a convenient way to reference economic data on industries of interest to the researcher. SIC codes presented here are not intended to be an exhaustive listing; rather, the codes listed should provide an indication of where a chemical may be most likely to be found in commerce. 2. Calculated by multiplying the mg/m3 dose by 0.1429 (the occupational 8-hour breathing rate, 10 m3, divided by the assumed adult body weight, 70 kg) to obtain the dose in mg/kg/day assuming 100% absorption (U.S. EPA 1988). 3. TLV-TWA, Threshold Limit Value-Time Weighted Average; TLV-STEL, Threshold Limit Value-Short Term Exposure Limit 4. TWA, occupational, Time Weighted Average; STEL, occupational, Short Term Exposure Limit; IDLH, Immediate Danger to Life and Health. 5. PEL-TWA, Permissible Exposure Limit-Time Weighted Average VIII. CITED REFERENCES ACGIH. 1991. Documentation of the Threshold Limit Values and Biological Exposure Indices, Sixth edition. American Conference of Governmental Industrial Hygienists, Inc., Cincinnati, OH. AQUIRE. 1994. Aquatic Information Retrieval online data base. Chemical Information Systems, Inc., a subsidiary of Fein-Marquart Assoc. Retrieved Aug, 1994. BIODEG. 1994. Syracuse Research Corporation's Environmental Fate Data Bases. Syracuse Research Corporation, Syracuse, NY. Retrieved 9/1/94. Budavari S, O'Neil MJ, Smith A, Heckelman PE (Eds.). 1989. The Merck Index, 11th ed. Merck & Co., Inc., Rahway, N.J., p. 820. Campbell. 1988. Review of the Potential Developmental Toxicity of Methyl Isobutyl Ketone. Memorandum from M. Campbell (Toxic Effects Branch) to E. Dage (Chemical Review and Evaluation Branch), Office of Toxic Substances, Washington D.C. November 1, 1988. CHEMFATE. 1994. Syracuse Research Corporation's Environmental Fate Data Bases. Syracuse Research Corporation, Syracuse, NY. Retrieved 8/15/94. Federal Register. 1992. Part 51 - Requirements for Preparation, Adoption, and Submittal of Implementation Plans. Fed. Reg. 57:3945. HSDB. 1994. Hazardous Substances Data Bank. MEDLARS Online Information Retrieval system, National Library of Medicine. Retrieved 8/3/94. Krasavage, W.J., J.L. O'Donoghue and G.D. Divincenzo. 1982. Ketones. in: Clayton GD, Clayton FE. 1981-1982. Patty's Industrial Hygiene and Toxicology, 3rd ed., Vol. 2C. John Wiley & Sons, New York, pp. 4747-4751. Mannsville, 1993. Chemical Products Synopsis, Methyl Isobutyl Ketone. Mannsville Chemical Products Corporation, 1993. NIOSH (National Institute for Occupational Safety and Health). 1990. NIOSH Pocket Guide to Chemical Hazards. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, NIOSH, U.S. Government Printing Office, Washington, D.C. 20402. OSHA. 1993. Occupational Safety and Health Administration. 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Carcinogen Assessment Group, Office of Health and Environmental Assessment, U.S. EPA, Washington, D.C., pp. 21, 22. OHEA-C-073. U.S. EPA. 1994. Integrated Risk Information System (IRIS) Online. Coversheet for Methyl isobutyl ketone. Office of Health and Environmental Assessment, U.S. EPA, Cincinnati, OH. Retrieved 8/94. Verschueren, K. 1983. Methyl isobutyl ketone. in: Handbook of Environmental Data on Organic Chemicals, Second Edition. Van Nostrand Reinhold Co., New York, pp: 856-858. APPENDIX A. SOURCES SEARCHED FOR FACT SHEET PREPARATION ACGIH. 1991. Documentation of the Threshold Limit Values and Biological Exposure Indices, Sixth edition. American Conference of Governmental Industrial Hygienists, Inc., Cincinnati, OH. AQUIRE. 1994. IPA ERL-Duluth's Aquatic Ecotoxicology Data Systems. U.S. EPA, Duluth, MN. ATSDR. 1989-1994. Agency for Toxic Substances and Disease Registry. Toxicological Profiles. Chamblee, GA: ATSDR. BIODEG. 1994. 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