Methamidophos (CASRN 10265-92-6)
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Methamidophos;
CASRN 10265-92-6
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 Methamidophos
File First On-Line 09/30/1987
Category (section) |
Status |
Last Revised |
---|---|---|
Oral RfD Assessment (I.A.) | on-line | 03/01/1991 |
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 — Methamidophos
CASRN — 10265-92-6
Last Revised — 03/01/1991
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 |
---|---|---|---|---|
ChE Inhibition One-Year Dog Feeding Mobay Chemical, 1984a |
NOEL: none LEL: 2 ppm diet |
1000
|
1
|
5E-5
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)
Mobay Chemical Corporation. 1984a. MRID No. 00147938, 41234304. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Beagle dogs were divided into groups of 6/sex/dose and fed the following levels of methamidophos: 0, 2, 8, or 32 ppm. The animals were treated for 1 year and appropriate tests were conducted. No treatment-related effects were observed (with the exception of cholinesterase inhibition) in clinical chemistry, hematology, and urinalysis studies; in clinical signs, body weights, organ weights, and food consumption; or in histopathologic and opthalmologic examinations. Inhibition of cholinesterase activities was noted in plasma, RBC, and brain at all levels.
__I.A.3. Uncertainty and Modifying Factors (Oral RfD)
UF — An uncertainty factor of 1000 was used to account for inter- and intraspecies differences, and for the fact that a NOEL was not established for any ChE endpoint.
MF — None
__I.A.4. Additional Studies/Comments (Oral RfD)
Data Considered for Establishing the RfD:
1) 1-Year Feeding - dog: Principal study - see previous description; core grade guideline
2) 2-Generation Reproduction - rat: Reproductive NOEL=none (Compound-related decreases in percentage of sperm-positive females delivering litters at all dose levels (0.15, 0.5 and 1.65 mg/kg/day); Systemic NOEL=10 ppm (0.5 mg/kg/day), Systemic LEL=33 ppm (1.65 mg/kg/day) (reduced body weights during premating period); core grade supplementary (Mobay Chemical, 1984b)
3) 2-Year Feeding (oncogenic) - rat: Systemic NOEL=0.3 mg/kg/day; ChE LEL=0.1 mg/kg/day (erythrocytes, plasma, brain); core grade minimum (Mobay Chemical, 1984c)
4) Teratology - rat: Teratogenic NOEL=3 mg/kg/day (HDT); LEL=none; Maternal and Fetotoxic NOEL=1 mg/kg/day; Maternal and Fetotoxic LEL=3 mg/kg/day (decreased body weights; clinical signs typical of cholinesterase inhibitors); core grade minimum (Mobay Chemical, 1984d)
5) Teratology - rabbit: Teratogenic and Fetotoxic NOEL=2.5 mg/kg/day (HDT); LEL=none; Maternal LEL=0.1 mg/kg/day (LDT; decreased body weight gain) (Mobay Chemical, 1979)
Data Gap(s): Rat Reproduction Study (Repeat to establish a NOEL); Brain Cholinesterase Study with Dogs; Brain Cholinesterase Study with Rats
__I.A.5. Confidence in the Oral RfD
Study — High
Database — Medium
RfD — Medium
The biological effect upon which the RfD is based is debatable in terms of the extent to which this effect is biologically significant. The chosen study is well-conducted and is given a high confidence rating. Other studies of good quality on this chemical are available; however, the rat chronic study also indicates a ChE inhibition at all dose levels tested, and the reproductive study also needs a NOEL. Thus, 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 Files
Agency Work Group Review — 08/05/1986, 05/20/1987
Verification Date — 05/20/1987
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 Methamidophos 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).
_I.B. Reference Concentration for Chronic Inhalation Exposure (RfC)
Substance Name — Methamidophos
CASRN — 10265-92-6
Not available at this time.
_II. Carcinogenicity Assessment for Lifetime Exposure
Substance Name — Methamidophos
CASRN — 10265-92-6
This substance/agent has not undergone a complete evaluation and determination under US EPA's IRIS program for evidence of human carcinogenic potential.
_III.
[reserved]
_IV. [reserved]
_V. [reserved]
_VI. Bibliography
Substance Name — Methamidophos
CASRN — 10265-92-6
Last Revised — 03/01/1991
_VI.A. Oral RfD References
Mobay Chemical Corporation. 1979. MRID No. 00041315. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Mobay Chemical Corporation. 1984a. MRID No. 00147938, 41234304. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Mobay Chemical Corporation. 1984b. MRID No. 00148455, 41234301. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Mobay Chemical Corporation. 1984c. MRID No. 00148452, 41234301. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Mobay Chemical Corporation. 1984d. MRID No. 00148454. 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 — Methamidophos
CASRN — 10265-92-6
Date |
Section |
Description |
---|---|---|
03/01/1988 | I.A.4. | Text deleted |
03/01/1991 | I.A.4. | Citations added |
03/01/1991 | 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. |
_VIII. Synonyms
Substance Name — Methamidophos
CASRN — 10265-92-6
Last Revised — 09/30/1987
- 10265-92-6
- ACEPHATE-MET
- BAY 71628
- BAYER 71628
- CHEVRON 9006
- ENT 27,396
- HAMIDOP
- METAMIDOFOS ESTRELLA
- Methamidophos
- MONITOR
- MTD
- NSC 190987
- ORTHO 9006
- O,S-DIMETHYL ESTER AMIDE of AMIDOTHIOATE
- O,S-DIMETHYL PHOSPHORAMIDOTHIOATE
- PHOSPHORAMIDOTHIOIC ACID, O,S-DIMETHYL ESTER
- PILLARON
- SRA 5172
- TAHMABON
- TAMARON
- THIOPHOSPHORSAEURE-O,S-DIMETHYLESTERAMID