Methyl parathion (CASRN 298-00-0)
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0174
Methyl parathion;
CASRN 298-00-0
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 Methyl parathion
File First On-Line 03/31/1987
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 — Methyl parathion
CASRN — 298-00-0
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
|
---|---|---|---|---|
RBC, ChE inhibition; 2-Year Rat Feeding Monsanto Co., 1984 |
NOEL: 0.5 ppm LEL: 5.0 ppm |
l00
|
1
|
2.5E-4
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)
Monsanto Company. 1984. MRID No. 000139023, 00143965, 00145507. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Sixty rats/sex/group were fed diet containing methyl parathion at concentrations of 0.5, 5 or 50 ppm for 2 years. This study was classified as supplementary because a NOEL for neurologic changes was not adequately defined. Sciatic nerve preparations from 1 of 5 males in the low-dose group and 1 of 5 in the mid-dose group reportedly showed moderate degenerative changes. However, based on effects observed in hematological parameters, a NOEL of 0.5 ppm can be established. Hemoglobin, hematocrit, and RBCs were slightly reduced in mid- and high-dose males, and moderately reduced in high- dose females.
__I.A.3. Uncertainty and Modifying Factors (Oral RfD)
UF — Based on a chronic exposure study, an uncertainty factor of 100 was used to account for inter- and intraspecies differences in the extrapolation of toxicity to humans.
MF — None
__I.A.4. Additional Studies/Comments (Oral RfD)
In a subchronic study with methyl parathion in humans (Rider et al., l97l), RBC cholinesterase depression was reported, with a NOEL of approximately 0.3 mg/kg/day. Using a UF of l00 to adjust for chronic exposure and intraspecies sensitivity, an RfD based on this study would be 0.003 mg/kg/day. Adequate supporting data for human studies are not available. Nevertheless, even anecdotal data directly relating to human exposure should not be dismissed. Therefore, an RfD based on animal studies should not exceed 0.003 mg/kg/day unless additional data for humans can be found to support such a determination.
Data Considered for Establishing the RfD:
1) 2-Year Feeding - rat: Principal study - see previous description; core grade supplementary
2) Teratology - rat: Embryo/fetotoxicity, developmental NOEL=l0 mg/kg/day (i.p., single dose on day 12 of gestation); LEL=l5 mg/kg/day (mortality, growth retardation retardation, delayed ossification); core grade supplementary (Stauffer Chemical Co., 1967a)
3) Teratology - mouse: Teratogenic NOEL=20 mg/kg/day; LEL=60\mg/kg/day (cleft palate); (i.p., single dose on day l0 of gestation) (Stauffer Chemical Co., 1967b)
4) 3-Month Feeding - rat: NOEL=2.5 ppm; LEL=25 ppm [reduced hematocrit and ChE inhibition (brain, plasma and RBC), increased serum alkaline phosphatase urine specific gravity]; core grade guideline (Monsanto, 1980a)
5) 3-Month Feeding - mouse: NOEL=none; LEL=10 ppm (LDT) [decreased testicular weight (no abnormal histopathology), ChE not determined]; core grade minimum (Monsanto, 1980b)
6) 3-Month Feeding - dog: NOEL=0.3 mg/kg/day; LEL=l mg/kg/day (plasma, RBC ChE inhibition); core grade guideline (Monsanto, 1978)
7) Teratology - rabbit: NOEL=3 mg/kg/day (HDT); LEL=none; core grade supplementary (A/S Cheminova, 1984)
8) Teratology - rat: NOEL=0.3 mg/kg/day (gavage); LEL=l mg/kg/day; core grade supplementary (A/S Cheminova, 1977)
9) 3-Generation Reproduction - rat: NOEL=l0 ppm; LEL=30 ppm (stillbirths, weanling mortality, reduced weanling body weight); core grade minimum (Natural Agricultural Chem. Assoc., 1964)
10) 2-Generation Reproduction - rat: Reproductive NOEL=25 ppm (HDT); Maternal NOEL=5 ppm; LEL=25 ppm (reduced body weight); core grade minimum (Monsanto, 1982)
Other Data Reviewed:
1) 2-Year Feeding - rat (Wistar): NOEL=2 ppm; LEL=10 ppm; (ChE inhibition); body weight gain depression at 50 ppm; (incomplete toxicity data); core grade supplementary (A/S Cheminova, 1981)
2) 30-Day Studies - human
a) Rider, J., J. Swader, E. Puletti. l97l. Anticholinesterase toxicity studies with methyl parathion, guthion and phosdrin in human subjects. Fed. Proc. 30(2): 443 [Abstract]. RBC ChE inhibition at 28 and 30 mg/kg/day. Summary data only. No basis for validation (no core grade).
b) Rider, J., J. Swader, E. Puletti. l970. Methyl parathion and guthion anticholinesterase effects in human subjects. Fed. Proc. 29(2): 347 [Abstract]. Summary data only. No basis for validation (no core grade).
Data Gap(s): Chronic Dog Feeding Study; Chronic Rat Feeding Study
__I.A.5. Confidence in the Oral RfD
Study — Medium
Database — Medium
RfD — Medium
The principal study was well conducted with a good number of animals and doses, but confidence is considered medium because it is incomplete in regard to neurological evaluation. Confidence in the database is medium because although it is extensive it fails to confirm the possible neurological problems. Medium confidence in the RfD follows.
__I.A.6. EPA Documentation and Review of the Oral RfD
Pesticide Registration Standard, May 1986 (Draft)
Agency Work Group Review — 05/14/1986, 12/09/1986
Verification Date — 12/09/1986
__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 — Methyl parathion
CASRN — 298-00-0
Not available at this time.
_II. Carcinogenicity Assessment for Lifetime Exposure
Substance Name — Methyl parathion
CASRN — 298-00-0
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 — Methyl parathion
CASRN — 298-00-0
Last Revised — 03/01/1991
_VI.A. Oral RfD References
A/S Cheminova. 1977. MRID No. 00143747. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
A/S Cheminova. 1981. MRID No. 00145574, 40250601. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
A/S Cheminova. 1984. MRID No. 41046101, 41199001. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Monsanto Company. 1978. MRID No. 00072512. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Monsanto Company. 1980a. MRID No. 00074299. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Monsanto Company. 1980b. MRID No. 00072513. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Monsanto Company. 1982. MRID No. 00119087. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Monsanto Company. 1984. MRID No. 00139023, 00143965, 00145507. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Natural Agricultural Chemical Association. 1964. MRID No. 00081923. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Rider, J., J. Swader, E. Puletti. l97l. Anticholinesterase toxicity studies with methyl parathion, guthion and phosdrin in human subjects. Fed. Proc. 30(2): 443 [Abstract].
Rider, J., J. Swader, E. Puletti. l970. Methyl parathion and guthion anticholinesterase effects in human subjects. Fed. Proc. 29(2): 347 [Abstract].
Stauffer Chemical Company. 1967a. MRID No. 00127241. Available from EPA. Write to FOI, EPA, Washington, DC 20460.
Stauffer Chemical Company. 1967b. MRID No. 00127241. 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 — Methyl parathion
CASRN — 298-00-0
Date |
Section |
Description |
---|---|---|
03/01/1991 | I.A.4. | Citations added |
03/01/1991 | III.A. | Health Advisory on-line |
03/01/1991 | VI. | Bibliography on-line |
01/01/1992 | IV. | Regulatory actions 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. |
02/22/2001 | I.A., II. | This chemical is being reassessed under the IRIS Program. |
02/09/2004 | I.A., II. | This chemical is no longer being reassessed under the IRIS Program. See Federal Register February 9, 2004 (Volume 69, Number 26). |
_VIII. Synonyms
Substance Name — Methyl parathion
CASRN — 298-00-0
Last Revised — 03/31/1987
- 298-00-0
- 8056 HC
- Azofos
- Azophos
- BAY 11405
- Bladan-M
- Dalf
- Dimethylfenitrothion
- Dimethyl 4-Nitrophenyl Phosphorothionate
- Dimethyl p-Nitrophenyl Phosphorothionate
- Dimethyl p-Nitrophenyl Thiophosphate
- Dimethyl Parathion
- E 601
- ENT 17,292
- Folidol M
- Folidol M-40
- Gearphos
- Meptox
- Metacid 50
- Metacide
- Metafos
- Metaphos
- Methyl-E 605
- Methyl Parathion
- Methylthiophos
- Metron
- M-Parathion
- NCI-C02971
- Nitrox
- Nitrox 80
- Oleovofotox
- O,O-Dimethyl O-(p-Nitrophenyl) Phosphorothioate
- O,O-Dimethyl O-(p-Nitrophenyl) Thionophosphate
- O,O-Dimethyl O-(p-Nitrophenyl) Thiophosphate
- Partron M
- Penncap M
- Penncap MLS
- Phosphorothioic Acid, O,O-Dimethyl O-(4-Nitrophenyl) Ester
- Phosphorothioic Acid, O,O-Dimethyl O-(p-Nitrophenyl) Ester
- Quinophos
- Sinafid M-48
- Thiophenit
- Vofatox
- Wofatox
- Wofotox