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Dicamba (CASRN 1918-00-9)

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0223

Dicamba; CASRN 1918-00-9

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 Dicamba

File First On-Line 09/30/1987

Category (section)
Status
Last Revised
Oral RfD Assessment (I.A.) on-line 07/01/1992
Inhalation RfC Assessment (I.B.) no data
Carcinogenicity Assessment (II.) no data 11/01/1993

_I.  Chronic Health Hazard Assessments for Noncarcinogenic Effects

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

Substance Name — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel
Last Revised — 07/01/1992

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

Maternal and fetal
toxicity

Rabbit Developmental
Study

Velsicol Chemical, 1978

NOEL: 3 mg/kg/day

LEL: 10 mg/kg/day
100
1
3E-2
mg/kg/day

*Conversion Factors: none

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

Velsicol Chemical Corporation. 1978. MRID No. 00028236. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Five groups of female rabbits (31 to 35/group) were dosed with 0.5% methyl cellulose at 1 mg/kg/day containing doses of 0, 1.0, 3.0, or 10.0 mg/kg/day of dicamba (Banvel technical). A positive control group was treated with 3 mg/kg/day of 6-aminonicotinamide on day 9 of gestation only. Dicamba was administered on days 6 through 18 of gestation. Because of an insufficient number of pregnancies in the initial phases of the experiment, additional rabbits were added to each group at a later starting time. Rabbits receiving 10 mg/kg/day (HDT) had a slightly lower net weight gain. Also, there were slightly reduced fetal body weights and increased post implantation loss in the 10 mg/kg/day group. A NOEL was observed for maternal and fetotoxicity at 3 mg/kg/day.

__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) Developmental - rabbit: Principal study - see previous description; core grade minimum

2) 1-Year Feeding - dog: NOEL=2500 ppm (52 mg/kg/day) (HDT); core grade minimum (Sandoz Crop Protection, 1986)

3) 2-Year Feeding (oncogenic) - rat: Systemic NOEL=2500 ppm (125 mg/kg/day); LEL=none; core grade minimum (Velsicol Chemical, 1985)

4) 3-Generation Reproduction - rat: NOEL=500 ppm (25 mg/kg/day) (HDT); LEL=none; core grade minimum (Velsicol Chemical, 1966)

5) Developmental - rat: Maternal NOEL=160 mg/kg/day; Maternal LEL=400 mg/kg/day (ataxia, salivation, decreased motor activity, mortality, decreased body weight); Fetotoxic NOEL=400 mg/kg/day (HDT); Fetotoxic LEL=none; core grade minimum; Teratogenic NOEL=requires clarification because of the occurrence of skeletal malformations at all dosage levels, which are not statistically significant (Velsicol Chemical, 1981a)

Other Data Reviewed:

1) 2-Year Feeding - dog: NOEL=5 ppm (0.125 mg/kg/day); LEL=25 ppm (0.625 mg/kg/day) (decrease in body weight); core grade supplementary (No observations of pharmacologic effects were presented, no gross pathology was done, there was no clinical chemistry data and scant histopathology presented) (Velsicol Chemical, 1962a)

2) 2-Year Feeding (oncogenic) - rat: Systemic NOEL=500 ppm (25 mg/kg/day) (HDT); core grade supplementary (Velsicol Chemical, 1962b)

3) 90-Day Feeding - rat: NOEL=5000 ppm (250 mg/kg/day); LEL=10,000 ppm (500 mg/kg/day) (slight decrease in body weight and food consumption; reduction of cytoplasmic vacuolation of hepatocytes); core grade minimum (Velsicol Chemical, 1981b)

Data Gap(s): None

__I.A.5. Confidence in the Oral RfD

Study — Medium
Database — High
RfD — High

The critical study is of adequate quality and is given a medium confidence rating. Additional studies are supportive and 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 Files

Agency Work Group Review — 05/30/1986, 02/18/1987, 06/22/1988

Verification Date — 06/22/1988

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 Dicamba 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 — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel

Not available at this time.

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_II.  Carcinogenicity Assessment for Lifetime Exposure

Substance Name — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel

Not available at this time.

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


_VI.  Bibliography

Substance Name — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel
Last Revised — 07/01/1992

_VI.A. Oral RfD References

Sandoz Crop Protection Corporation. 1986. MRID No. 40321102. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1962a. MRID No. 00028248, 00028260, 00050492. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1962b. MRID No. 00028248, 00028260. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1966. MRID No. 00028249. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1978. MRID No. 00028236. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1981b. MRID No. 00128093. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1981a. MRID No. 00084024. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Velsicol Chemical Corporation. 1985. MRID No. 00125333. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

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_VI.B. Inhalation RfC References

None

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_VI.C. Carcinogenicity Assessment References

None

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_VII.  Revision History

Substance Name — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel

Date
Section
Description
08/22/1988 I.A. Oral RfD summary replaced; new basis for RfD
01/01/1990 VI. Bibliography on-line
01/01/1992 IV. Regulatory actions updated
07/01/1992 I.A.4. Citation year for 90-day rat study corrected
07/01/1992 VI.A. Reference year corrected
06/01/1993 II. Carcinogenicity assessment under review on 04/01/1993
11/01/1993 II.D.2. Work group review date added
08/01/1995 II., II.D.2. EPA's RfD/RfC and CRAVE workgroups were discontinued in May, 1995. Chemical substance reviews that were not completed by September 1995 were taken out of IRIS review. The IRIS Pilot Program replaced the workgroup functions beginning in September, 1995.
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 — Dicamba
CASRN — 1918-00-9
Primary Synonym — Banvel
Last Revised — 09/30/1987

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