Terbacil (CASRN 5902-51-2)
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0105
Terbacil;
CASRN 5902-51-2
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 Terbacil
File First On-Line 01/31/1987
Category (section) |
Status |
Last Revised |
---|---|---|
Oral RfD Assessment (I.A.) | on-line | 09/01/1989 |
Inhalation RfC Assessment (I.B.) | no data | |
Carcinogenicity Assessment (II.) | no data |
_I. Chronic Health Hazard Assessments for Noncarcinogenic Effects
_I.A. Reference Dose for Chronic Oral Exposure (RfD)
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
Last Revised — 09/01/1989
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 |
---|---|---|---|---|
Increase in thyroid/ 2-Year Dog Feeding duPont, 1967a |
NOEL: 50 ppm LEL: 250 ppm |
100 |
1 |
1.3E-2 mg/kg/day |
*Conversion Factors: 1 ppm = 0.025 mg/kg/day (assumed dog food consumption)
__I.A.2. Principal and Supporting Studies (Oral RfD)
E.I. duPont de Nemours & Company, Inc. 1967a. MRID No. 00060851. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
In the 2-year feeding study young purebred male and female beagle dogs
(4/sex/dose group) 4 to 6 months old were fed diets containing terbacil (80%
wettable powder) at levels of 0, 50, 250, or 2500 ppm (0, 1.25, 6.25, and 62.5
mg/kg/day). The highest dose tested was periodically increased from the 26th
to the 46th week of the study to a final concentration of 10,000 ppm (500
mg/kg/day). All the animals had periodic physical examinations, individual
food consumption and individual body weight measurements weekly. After 12
months of compound administration one male and one female from the control and
each of the test groups were sacrificed and necropsied. Periodic
hematological and 24 hour urine studies were obtained. Periodic blood
glucose, total protein, total albumin, BUN, BSP, alkaline phosphatase,
prothrombin time, SGOT and SGPT, plus cholesterol determinations were done.
No adverse effects of the test compound were observed with respect to
biochemical parameters, food consumption, body weight, or gross or microscopic
changes. The NOEL was 50 ppm (1.25 mg/kg/day) based on increased thyroid/body
weight ratio, slight increase in liver weights and elevated alkaline
phosphatase in dogs administered 250 ppm (6.25 mg/kg/day) and above.
__I.A.3. Uncertainty and Modifying Factors (Oral RfD)
UF — An uncertainty factor of 100 was used to account for the inter- and
intraspecies differences.
MF — None
__I.A.4. Additional Studies/Comments (Oral RfD)
Data Considered for Establishing the RfD
1) 2-Year Feeding - dog: Principal study - see discussion above; core grade
minimum
2) 2-Year Feeding (oncogenic) - rat: Systemic NOEL=250 ppm (12.5 mg/kg/day),
Systemic LEL=2500/10,000 ppm (125/500 mg/kg/day) (HDT; impaired weight gain,
slight increase in liver weight); core grade supplementary (duPont, 1967b)
3) 3-Generation Reproduction - rat: Systemic NOEL=none; Systemic LEL=50 ppm
(2.5 mg/kg/day (LDT; slight decrease in body weight gain); Reproductive
NOEL=250 ppm (12.5 mg/kg/day) (HDT); Reproductive LEL=none; core grade minimum
(duPont, 1967c)
4) Teratology - rat: Maternal NOEL=250 ppm (12.5 mg/kg/day); Maternal
LEL=1250 ppm (62.5 mg/kg/day) (reduction in body weight); Embryotoxic NOEL=250
ppm (12.5 mg/kg/day); Embryotoxic LEL=1250 ppm (62.5 mg/kg/day); Teratogenic
NOEL=5000 ppm (250 mg/kg/day) (HDT); Teratogenic LEL=none; core grade minimum
(duPont, 1980)
5) Teratology - rabbit: Maternal
NOEL=200 mg/kg/day; Maternal LEL=600 mg/kg/day (HDT; body weight loss);
Embyrotoxic NOEL=200 mg/kg/day; Embyrotoxic LEL=600 mg/kg/day (HDT;
significantly reduced mean live fetal weights); Teratogenic NOEL=600 mg/kg/day
(HDT); Teratogenic LEL=none; core grade minimum (duPont, 1984)
Other Data Reviewed
1) 2-Year Feeding (oncogenic) - mouse: Systemic NOEL=50 ppm (7.5 mg/kg/day);
Systemic LEL=1250 ppm (187.5 mg/kg/day) (hypertrophy of centrilobular
hepatocytes in males; decreased pituitary weights in males and high-dose
females); decreased survival (significant in males at 5000/7500 ppm (750/1125
mg/kg/day); core grade supplementary (pending re-analysis of liver slides)
(duPont, 1981)
2) 90-Day Feeding - rat: NOEL=100 ppm (5 mg/kg/day); LEL=500
ppm (25 mg/kg/day) (increased liver weight, vacuolization and hypertrophy of
hepatocytes); core grade minimum (duPont, 1964)
Data Gap(s): Chronic Rat Feeding Oncogenicity Study; Mouse Oncogenicity Study
__I.A.5. Confidence in the Oral RfD
Study — Medium
Database — Medium
RfD — Medium
The critical study is of adequate quality and is given a medium confidence rating. Since and adequate chronic rodent feeding study is lacking, the database is given a medium confidence rating. Medium confidence in the RfD follows.
__I.A.6. EPA Documentation and Review of the Oral RfD
Pesticide Registration Standard, March 1989
Pesticide Registration Files
Agency Work Group Review — 06/10/1986
Verification Date — 06/10/1986
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 terbacil conducted in August 2003 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).
_I.B. Reference Concentration for Chronic Inhalation Exposure (RfC)
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
Not available at this time.
_II. Carcinogenicity Assessment for Lifetime Exposure
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
This substance/agent has not undergone a complete evaluation and determination
under US EPA's IRIS program for evidence of human carcinogenic potential.
_VI. Bibliography
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
Last Revised — 09/01/1989
_VI.A. Oral RfD References
E.I. duPont de Nemours & Company, Inc. 1964. MRID No.
00068035. Available from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1967a. MRID No. 00060851. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1967b. MRID No. 00060850. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1967c. MRID No. 00060852. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1980. MRID No. 00050467. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1981. MRID No. 00126770. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
E.I. duPont de Nemours & Company, Inc. 1984. MRID No. 00150945. Available
from EPA. Write to FOI, EPA, Washington DC. 20460.
_VI.B. Inhalation RfC References
None
_VI.C. Carcinogenicity Assessment References
None
_VII. Revision History
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
Date |
Section |
Description |
---|---|---|
03/31/1987 | IV. | Regulatory Action section on-line |
09/01/1989 | I.A. | Oral RfD summary sheet revised |
09/01/1989 | I.A.5. | Confidence levels changed |
09/01/1989 | VI. | Bibliography on-line |
01/01/1992 | IV. | Regulatory action updated |
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. |
10/28/2003 | I.A.6 | Screening-Level Literature Review Findings message has been added. |
_VIII. Synonyms
Substance Name — Terbacil
CASRN — 5902-51-2
Primary Synonym — Sinbar
Last Revised — 01/31/1987
- 5902-51-2
- 5-CHLORO-3-(1,1-DIMETHYLETHYL)-6-METHYL-2,4(1H,3H)-PYRIMIDINEDIONE
- 5-CHLORO-3-tert-BUTYL-6-METHYLURACIL
- DU PONT 732
- 2,4(1H,3H)-PYRIMIDINEDIONE, 5-CHLORO-3-(1,1-DIMETHYLETHYL)-6-METHYL-
- SINBAR
- Terbacil
- 3-tert-BUTYL-5-CHLORO-6-METHYLURACIL
- TURBACIL
- URACIL, 3-tert-BUTYL-5-CHLORO-6-METHYL-