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Terbutryn (CASRN 886-50-0)

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0285

Terbutryn; CASRN 886-50-0

Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data, as outlined in the IRIS assessment development process. Sections I (Health Hazard Assessments for Noncarcinogenic Effects) and II (Carcinogenicity Assessment for Lifetime Exposure) present the conclusions that were reached during the assessment development process. Supporting information and explanations of the methods used to derive the values given in IRIS are provided in the guidance documents located on the IRIS website.

STATUS OF DATA FOR Terbutryn

File First On-Line 09/26/1988

Category (section)
Status
Last Revised
Oral RfD Assessment (I.A.) on-line 09/26/1988
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 — Terbutryn
CASRN — 886-50-0
Last Revised — 09/26/1988

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

Hematologic effects
in females

2-Year Rat Feeding
Study

Ciba-Geigy, 1980a

NOEL: 2 ppm
(0.1 mg/kg/day)

LEL: 300 ppm
(15 mg/kg/day)

100
1
1E-3
mg/kg/day

*Conversion Factors -- 1 ppm = 0.05 mg/kg/day (assumed rat food consumption)

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

Ciba-Geigy Corporation. 1980a. MRID No. 00035923. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Two hundred sixty male and 260 female weanling Charles River CD rats were randomly distributed into the following groups: 0, (70 animals/sex), 2 (60 animals/sex), 300 (60 animals/sex) and 3000 ppm (70 animals/sex) (0, 0.1, 15, and 150 mg/kg/day) and administered terbutryn in their diets for 2 years. Based upon a statistical reevaluation of the hematologic data from this study, a NOEL for systemic effects can be set at 2 ppm. The LEL is 300 ppm based upon a statistically significant and dose-related decrease in hemoglobin and erythrocytes in female rats at 18 months. This parameter was not measured for the mid-dose group at term. At the HDT (3000 ppm) there was also a statistically significant decrease in hematocrit in females at both 18 and 24 months.

__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 (oncogenic) - rat: Principal study - see previous description; core grade minimum

2) 6-Month Feeding - dog: NOEL=10 mg/kg/day; LEL=25 mg/kg/day (mucosal thickening of various segments of the small intestine and submucosal lymphoid hyperplasia in the stomach); core grade minimum (Ciba-Geigy Corp., 1980b)

3) 3-Generation Reproduction - rat: NOEL=15 mg/kg/day; LEL=150 mg/kg/day (decreased body weight gain and decreased fertility indices in males and females); core grade minimum (Ciba-Geigy Corp., 1980c)

4) Teratology - rat: Maternal NOEL=50 mg/kg/day; Maternal LEL=500 mg/kg/day (reduced body weight); Developmental NOEL=50 mg/kg/day; Developmental LEL=500 mg/kg/day (weight decrease, reduced ossification - front and rear paws); core grade minimum (Ciba-Geigy Corp., 1985a)

5) Teratology - rabbit: Maternal NOEL=10 mg/kg/day; Maternal LEL=50 mg/kg/day (body weight loss); Developmental NOEL=50 mg/kg/day; Developmental LEL=75 mg/kg/day (reduced ossification of sternebrae); core grade guideline (Ciba- Geigy Corp., 1985b)

Data Gap(s): None

__I.A.5. Confidence in the Oral RfD

Study — High
Database — High
RfD — High

The critical study is of good quality and is given a high confidence rating. Additional studies are supportive; therefore, the database is given a high confidence rating. High confidence in the RfD follows.

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

Source Document — This assessment is not presented in any existing U.S. EPA document.

Other EPA Documentation — Pesticide Registration Standard, July 1986; Pesticide Registration Files

Agency Work Group Review — 07/15/1987, 08/13/1987, 07/20/1988

Verification Date — 07/20/1988

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 Terbutryn conducted in September 2002 identified one or more significant new studies. IRIS users may request the references for those studies from 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)

Substance Name — Terbutryn
CASRN — 886-50-0

Not available at this time.

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_II.  Carcinogenicity Assessment for Lifetime Exposure

Substance Name — Terbutryn
CASRN — 886-50-0

This substance/agent has not undergone a complete evaluation and determination under US EPA's IRIS program for evidence of human carcinogenic potential.

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


_VI.  Bibliography

Substance Name — Terbutryn
CASRN — 886-50-0
Last Revised — 12/01/1989

_VI.A. Oral RfD References

Ciba-Geigy Corporation. 1980a. MRID No. 00035923. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Ciba-Geigy Corporation. 1980b. MRID No. 00029152. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Ciba-Geigy Corporation. 1980c. MRID No. 00035659. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Ciba-Geigy Corporation. 1985a. MRID No. 00152764. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Ciba-Geigy Corporation. 1985b. MRID No. 00152763. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

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_VI.B. Inhalation RfD References

None

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_VI.C. Carcinogenicity Assessment References

None

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_VII.  Revision History

Substance Name — Terbutryn
CASRN — 886-50-0

Date
Section
Description
09/26/1988 I.A. Oral RfD summary on-line
12/01/1989 VI. Bibliography on-line
01/01/1992 IV. Regulatory Action section on-line
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.
12/03/2002 I.A.6. Screening-Level Literature Review Findings message has been added.

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_VIII.  Synonyms

Substance Name — Terbutryn
CASRN — 886-50-0
Last Revised — 09/26/1988

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