Azinphos Methyl - Chemical Fact Sheet 9/86
Name of Chemical: Azinphos-methyl (Guthion)
Reason for Issuance: Issuance of Guidance Document
Date Issued: 9/30/86
Fact Sheet Number: 100
1. DESCRIPTION OF CHEMICAL
-Generic Name: O,O-dimethyl-s-[(4-oxo-1,2,3-benzotriazin-3(4H)-
-Common. Name: Azinphos-methyl
-Trade Names: metiltriazotion, carfene, cotion-methyl, gusathion,
gusation-M, guthion, Bay 9027, Bay 17147, R-1582
- EPA Shaughnessy Number: 058001
- Chemical Abstracts Service (CAS) Number: 86-50-0
- Year of Initial Registration: 1956
- Pesticide Type: Insecticide, Acaricide, Molluscicide
- Chemical Family: Organophosphate
- U.S. and Foreign Producers: Bayer AG (Federal Republic of Germany),
Makhteshim Chemical Co.(Israel), and Mobay
Chemical Corporation (U.S.) and Aceto
2. USE PATTERNS AND FORMULATIONS
Application Sites: fruit and field crops, vegetables, tobacco,
ornamentals and forest trees
Types and methods of application: foliar (by ground or aerial
equipment), ULV foliar application, soil application, transplant water
Application rates: 0.047 to 10.35 lb a.i./A
Types of formulation: Technical, formulation intermediate, dust,
granular, wettable powder, emulsifiable concentrate, flowable
concentrate, soluble concentrate
Usual carriers: Confidential Business Information
All liquid formulations with concentrations of 13.5% or greater are
currently classified as restricted use chemicals
3. SCIENCE FINDINGS
Technical azinphos-methyl is a yellow-brown solid with, a melting
point at around 63 degrees C, that decomposes at elevated temperatures
and is soluble in most organic solvents. The empirical formula is
C10H12N3O3PS2 and the molecular weight is 317.1.
- Acute oral: 4.4 mg/kg (cat), Toxicity Category I, highly toxic
- Acute dermal: 200 mg/kg (cat), Toxicity Category I, highly toxic
- Primary Eye Irritation: Data gap.
- Acute Inhalation.: Data gap.
- Primary Skin Irritation: Data gap.
- Skin sensitization: Data gap.
- Major Routes of Exposure: Handling of the concentrated pesticide and
airblast application produce the largest exposure per pound of
azinphos-methyl handled. Human exposure to azinphos-methyl from
handling, application, and re-entry operations would be minimized by
the use of respirators and protective clothing.
- Oncogenicity: A mouse oncogenicity study showed that no increased
incidence of tumors could be attributed to exposure to azinphos-
methyl. A rat oncogenicity study, that was found to be unacceptable
upon re-evaluation, showed that male rats developed tumors of
the pancreatic islets and of the follicular cells of the thyroid.
Because of the wide range of spontaneous incidence of these tumors in
Osborne-Mendel rats, the Agency concludes that there is no clear link
between the development of tumors to the administration of azinphos-
methyl, the Agency is requiring that a rat oncogenicity study be
conducted and submitted.
- Metabolism: Data gap.
- Teratology: Data gap.
- Reproduction: Data gap.
- Mutagenicity: Data gap.
Physiological and Biochemical Characteristics:
- Mechanism of Pesticidal Action: Cholinesterase inhibition by all
routes of exposure.
- Metabolism and persistence in plants and animals: Radiolabeled
azinphos-methyl residues are absorbed through the roots and
translocated to the shoot of hydroponically treated plants. Available
data indicate that azinphos-methyl is relatively persistent on leaf
surfaces and is gradually degraded to polar metabolites. Although the
submitted studies are not adequate to assess the nature of azinphos-
methyl in animals, metabolites of azinphos-methyl were identified in
chicken excreta and rat urine.
- Available data indicate that azinphos-methyl exhibits both low soil
mobility and low leaching potential in a variety of soil types.
Leaching studies indicate a low potential for leaching of azinphos-
methyl residues to groundwater. In sandy soils azinphos-methyl
dissipates in.the field fairly rapidly and is metabolized by
- The half-life of azinphos-methyl in a non-sterile soil is 21 days
under aerobic conditions and 68 days under anaerobic conditions. It is
more stable in sterile conditions with a half-life of 355 days. Under
aerobic conditions the following azinphos-methyl metabolites were
detected: oxygen, analog residues, mercaptomethyl benzazimide,
benzazimide, hydroxymethyl benzazimide, and bis-methyl benzazimide
sulfide. Benzazimide and hydroxymethyl benzazimide, were identified as
the major degradation products resulting from hydrolysis. Available
photodegradation data are inadequate to assess the photodecomposition
- Re-entry: Treated areas may not be re-entered for at least 24 hours
unless protective clothing is worn.
- Acute avian oral toxicity: Supplemental data indicate an LD50 of 136
mg/kg body weight for mallard ducks, 60-120 mg/kg for bobwhite quail,
74.9 mg/kg for pheasant, and 84.2 mg/kg for chukar. (Moderately toxic
for all species tested).
- Avian dietary toxicity: LC50 = 488 ppm for bobwhite quail (highly
toxic), LC50 = 639 ppm for Japanese quail (moderately toxic), and LC50
= 1940 ppm for mallard duck and 1821 ppm for ring-necked pheasant
- Freshwater fish acute toxicity (LC50): Available data place azinphos-
methyl in the range from very highly toxic to moderately toxic [LD50
values of 0.36-4,270 uq/l], depending on species tested with most
values in the very highly toxic range (less than 100 ug/1).
- Freshwater aquatic invertebrate toxicity: 0.13-56 ug/1, depending on
the species tested (very highly toxic).
- Tolerances have been established for residues of azinphos-methyl in a
variety of raw agricultural commodities in meat, fat and meat by-
products (refer to 40 CFR 180.154 and 40 CFR 180.154a. for listing of
tolerances), and in processed food (21 CFR 193.150) and and feed (21
- The Agency is unable to complete a full tolerance assessment for the
established tolerances due to residue chemistry and toxicology data
- No Mexican tolerances have been established for azinphos-methyl.
Commodity U.S. Canadian Codex
Alfalfa 2.0 0.1 2.0
Alfalfa, hay 5.O - -
Almonds 0.3 - 0.2
Almonds, hulls 10.3 - 10.0
Apples 2.0 2.0 1.0
Apricots 2.0 2.0 2.0
Artichokes 2.0 0.5 0.5
Barley, grain 0.2 0.1 0.2
Barley, straw 2.0 0.1 -
Beans (dry) 0.3 2.0 0.5
Beans (snap) 2.0 2.0 0.5
Birdsfoot Trefoil 2.0 0.1 -
Birdsfoot Trefoil,hay 5.0 0.1 -
Blackberries 2.0 2.0 1.0
Blueberries 5.0 2.0 1.0
Boysenberries 2.0 2.0 1.0
Broccoli 2.0 1.0 1.0
Brussels Sprouts 2.0 1.0 1.0
Cabbage 2.0 1.0 0.5
Cattle, fat 0.1 - -
Cattle, meat byproduct 0.1 - -
Cattle, meat 0.1 - -
Cauliflower 2.0 0.5 0.5
Celery 2.0 0.5 0.5
Cherries 2.0 1.0 1.0
Citrus fruits 2.0 2.0 2.0
Clover 2.0 0.1 -
Clover, hay 5.0 - -
Cottonseed 0.5 - 0.2
Crabapples 2.0 - 1.0
Cranberries 2.0 - -
Cucumbers 2.0 0.5 0.5
Eggplant 0.3 - 0.5
Filberts 0.3 - -
Goats, fat 0.1 - -
Goats, meat byproduct 0.1 - -
Goats, meat 0.1 - -
Gooseberries 5.0 - -
Grapes 5.0 5.0 4.0
Grass, pasture 2.0 0.1 -
Grass, pasture, hay 5.0 - -
Horses, fat 0.1 - -
Horses, meat byproducts 0.1 - -
Kiwi fruit 10.0 0.4 4.0
Loganberries 2.0 2.0 1.0
Melons 2.0 - 2.0
Nectarines 2.0 - 1.0
Nut, Pistachio 0.3 - -
Oats, grain 0.2 0.1 0.2
Oats, straw 2.0 - -
Onions (green) 2.0 1.0 0.5
Parsley (leaves) 5.0 - 0.5
Parsley (roots) 0.2 - 0.5
Peaches 2.0 2.0 4.0
Pears 2.0 2.0 1.0
Peas, black-eyed 0.3 - 0.5
Pecans 0.3 - -
Peppers 0.3 0.2 0.5
Plums 2.0 1.0 1.0
Potatoes 0.3 - 0.2
Quinces 2.0 2.0 1.0
Raspberries 2.0 2.0 1.0
Rye, grain 0.2 0.1 0.2
Rye, straw 2.0 0.1 -
Sheep, fat 0.1 - -
Sheep, meat byproduct 0.1 - -
Sheep, meat 0.1 - -
Soybeans 0.2 0.2 -
Spinach 2.0 2.0 0.5
Strawberries 2.0 1.0 1.0
Sugarcane 0.3 - -
Tomatoes 2.0 1.0 0.5
Walnuts 0.3 0.1 -
Wheat, grain 0.2 0.1 0.2
Wheat, straw 2.0 0.1 -
Milk 0.04 - -
Soybean oil 1.0 - -
Dried citrus 5.0 - -
Sugarcane bagasse 1.5 - -
The data for azinphos-methyl residues in or on pistachios,
sugarcane bagasse and sugarcane are adequate to support the respective
Data are not adequate to support the established tolerance for
residues in or on onions, celery, spinach, broccoli, Brussels sprouts,
cabbage, cauliflower, beans, soybeans, peppers, tomatoes, cucumbers,
melons, citrus fruit, apples, apricots, cherries, nectarines, peaches,
plums, blackberries, blueberries, cranberries, grapes, strawberries,
almonds, almond hulls, filberts, pecans, walnuts, wheat grain, wheat
straw, pasture grass, alfalfa, clover, artichokes, cottonseed, kiwi
fruit, eggplant, crabapples, pears, quinces, boysenberries,
loganberries, raspberries, oat grain, rye grain, barley grain, oat
straw, rye straw, barley straw, birdsfoot trefoil, soybean oil, and
dried citrus pulp.
A Provisional Limiting Dose (PLD) based on a 2 year dog feeding
study has been established using an uncertainty factor of 100. The
Maximum Permissible Intake (MPI) is 0.075 mg/kg for a 60 kg. person. The
Theoretical Maximum Residue Contribution (TMRC) to the human diet from
the existing tolerances is 0.6678 mg for a 1.5 kg diet which is 899% of
the MPI. (This value is greatly inflated when compared to actual dietary
residues expected in practice, and is due solely to the additional lO-
fold uncertainty factor applied for the reduced data base and two-fold
increase in sensitivity of the dog compared to that of the rat). When
the required chronic feeding studies are submitted, the PLD and TMRC
will be re-evaluated.
Reported Pesticide Incidents: The Pesticide Incident Monitoring
System (PIMS) reported on azinphos-methyl from 1966 through 1979. The
1981 report is the latest one available, which cites 71 incidents
associated with human injury. There was one fatality which was a
confirmed suicide. The PIMS report cited one bird kill and 29 incidents
involving fish and other aquatic organisms. For the period 1978-1985,
seven additional fish kills, citing azinphos-methyl, alone, were
obtained at the Agency's Office of Water.
4. Summary of Regulatory Position
A. The Agency is requiring extensive field monitoring data to better
define the extent of exposure and hazard to wildlife.
B. No new tolerances or new food uses will be considered until the
Agency has received data sufficient to assess existing tolerances for
C. The Agency is concerned about the potential for human poisonings
(cholinesterase inhibition) from the use of azinphos-methyl. The Agency
will continue to restrict all liquid formulations of azinphos-methyl
with greater than 13.5% a.i. In addition, registrants must either
classify all products for restricted use (due to acute toxicity) or
submit dermal and inhalation data to support the appropriate toxicity
D. Revised Protective clothing statements are required to be included on
the labels of azinphos-methyl end-use products.
E. The Agency has concluded that data are not adequate to determine the
oncogenic potential of azinphos-methyl and is requiring numerous
toxicology studies mentioned below.
F. The Agency is requiring that endangered species labeling be added to
labels for certain azinphos-methyl uses.
G. A 24 hour re-entry interval, previously established under 40 CFR
170.3 (b)(2) will remain in effect.
H. The Agency is imposing an interim rotational crop restriction of 6
months for root crops and 30 days for all other registered crops until
the required crop rotation data are submitted.
5. SUMMARY OF MAJOR DATA GAPS
- Additional crop residue studies on various commodities and plant and
animal metabolism studies are required to support existing tolerances.
- The following studies are required to assess the toxicological
characteristics of technical azinphos-methyl:
Acute inhalation, Delayed Neurotoxicity, oncogenicity/Chronic testing
in rat, Teratology, Reproduction, Mutagenicity, and General
- The following data are required to fully characterize azinphos-
methyl's environmental fate: Re-entry data (foliar dissipation, soil
dissipation, dermal exposure, inhalation exposure), Special Testing-
Glove Permeability, Photodegradation, Anaerobic Aquatic*, Forestry
Dissipation*, Rotational Crops (Confined), Irrigated Crops Accumulated
Study*, Accumulation in Non-target Organisms
- Additional data are required to assess the impact on wildlife from the
use of azinphos-methyl: acute avian oral toxicity, wild animal
toxicity, avian reproduction, field testing for mammals and birds,
acute toxicity to freshwater invertebrates, acute toxicity to
estuarine and marine organisms, fish early life stage, simulated or
actual field testing for aquatic organisms and honey bee toxicity.
- Product chemistry and acute toxicity data are required.
*Data not needed if label clarifications are made.
Contact person at EPA:
Lawrence J. Schnaubelt
Product Manager (12)
Registration Division (TS-767C)
Office of Pesticide Programs
Environmental Protection Agency
401 M. Street, S.W.
Washington, D.C. 20460
Office location and telephone number:
Room 202, Crystal Mall Building #2
1921 Jefferson Davis Highway
Arlington, Va. 22202
DISCLAIMER: The information presented in this pesticide Fact Sheet is
for informational purposes only and may not be used to fulfill data
requirements for pesticide registration and reregistration.