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fonofos (Dyfonate) Chemical Fact Sheet 2/84


Fact Sheet Number:
Date issued:  February, 1985 (Previous issuance:  March, 1984)
Reason for Issuance:  Registration Standard

                  1.  DESCRIPTION OF CHEMICAL

Generic Name:  O-ethyl S-phenyl ethylphosphonodithioate
Common name:  Fonofos
Trade name:  Dyfonate
EPA Shaughnessy code:   041701
Chemical abstracts service (CAS) number:  944-22-9
Year of initial registration:   1967
Pesticide type:   Insecticide
Chemical family:  organophosphate
U.S. and foreign producers:  Stauffer Chemical Co.


   Fonofos in a soil applied insecticide used primarily on corn (95%).  
It is used also on various vegetable crops, ornamentals, home lawns and 
home vegetable gardens and commercial turf.   Fonofos is applied mainly 
with ground equipment.  Aerial application are made to hybrid seed corn.  
Application rates vary from 1-4 lb./acre.  The usual carrier is water.

                       3.  SCIENCE FINDINGS

Fonofos is a yellow liquid with a mercaptan-like odor.  The boiling 
point is 212 degrees F (100 degrees C) and the melting point is -32 
degrees C at 0.3mm.  Fonofos is almost insoluble in water and miscible 
in common organic solvents.

Toxicology characteristics:

Technical fonofos is highly toxic based on acute oral, dermal, eye and 
inhalation effects.

Results of toxicological studies on fonofos are as follows:

- Oral LD50, ranges from 3.16-18.5 mg/kg
- Dermal LD50, ranges from 121-359 mg/kg
- Primary Eye Irritation, negative to 0.01 ml; 0/6 dead
- Inhalation LD50, 0.9 mg/L (male and female combined)
- 3 generation reproduction rat, reproductive and fetotoxic NOEL= 31.6
  ppm (highest dose tested)
- 2 year dog feeding study - NOEL, ChE and non-cholinergic = 8 ppm; 
  LEL, ChE and non-cholinergic = 60 ppm

   Available data are insufficient to fully assess the toxicological 
properties of fonofos.  Data gaps must be filled in areas of neuro-
toxicity, subchronic and chronic toxicity, oncogenicity and mutagenicity 
before a total risk assessment can be made.

Physiological and Biochemical Behavioral Characteristics:

   Fonofos is not absorbed by foliage and is not translocated in the 
plant body.  It is a cholinesterase inhibitor and accumulates in 

Environmental Characteristics

   Fonofos is immobile in sandy loom and silt loam soils.  It is mobile 
in quartz sand.  It decomposes in aerobic soils by microbes i 4-8 weeks.  
Fonofos is non-volitile from soil but volatile from water.  It degrades 
in aerobic soils with a half like of 3-16 weeks.  Fonofos is moderately 

Ecological Characteristics:

   Fonofos is moderately to highly toxic to birds and highly toxic to 
freshwater fish and salt water organisms.

   Simulated avian field studies indicate granular treatment of fonofos 
may result in some mortality, as well as brain AChE inhibition, but that 
effects are not likely to diminish wildlife resource.

   See under Data Gaps for additional data requirements.

Tolerance assessments

   Tolerances are established for residues of the insecticide O-ethyl S-
phenyl ethylphosphonodithioate, including its oxygen analog O-ethyl S-
phenyl ethylphosphonothioate, in or on raw agricultural commodities as 
follows (40 CFR 180.221):

- 0.5 part per million in or on asparagus.
- 0.1 part per million (negligible residue) in or on bean forage, bean
  vine hay, fresh corn including sweet corn (kernels plus cob with husk
  removed), corn grain (including popcorn), corn forage or fodder
  (including sweet corn field corn, and popcorn), fruiting vegetables,
  leafy vegetables, mint (peppermint, spearmint, peppermint hay, and
  spearmint hay), pea forage, pea vine hay, peanuts, peanut forage,
  peanut hay, peanut hulls, root crop vegetables, seed and pod vege-
  tables, sorghum (grain, fodder, and forage), soybean forage, soybean
  hay, strawberries, sugar beet tops, and sugarcane.


   The Agency has determined that certain formulations of fonofos 
warrant classification as restricted use pesticides. These include all 
emulsifiable concentrates 44% or greater and the 20% granular formula-
tion.  All products of these types which are released for shipment after 
September 1, 1985 must be labeled for restricted use. All products of 
these types which are in channels of trade after September 1, 1986 must 
be labeled for restricted use.

   A 24 hour interim reentry interval has been established for all uses 
of fonofos including the home lawn and home vegetable garden use.

Gloves and shoes must be worn when applying fonofos.

                     5.  SUMMARY OF MAJOR DATA GAPS *

- Delayed neurotoxicity - hen
- 90 day rodent feeding study
- 90 day neurotoxicity study-hen/mammal
- Chronic toxicity study-rodent
- Oncogenicity study
- Teratogencity study - 1 species
- Gene mutation study
- Chromosomal aberration study
- Reentry Data
- Acute LD50 - freshwater invertebrates
- Fish early life cycle stage and aquatic invertebrate
  lifecycle studies
- Residue data in:
  - root and tuber vegetables
  - leaves of root and tuber vegetables
  - fruiting vegetables (except cucurbits)
  - cereal grains
  - forage, fodder and straw of cereal grains
  - miscellaneous crops ( asparagus, peanuts,
    sugarcane and tobacco)
- Poultry feeding study and ruminant feeding study
- Photodegradation in water, soil and air
- Hydrolysis study
- Metabolism study in anaerobic soil
- Mobility studies (leaching and adsorption/desorption,
  volatility lab, and volatility field)
- Soil dissipation study
- Accumulation studies - rotational crops and fish

*All major data gaps are to be filled by March 31, 1987.


Contact Person

William H. Miller, PM 16
Registration Division (TS-767)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street SW
Washington, DC 20460
(703) 557-2600

DISCLAIMER:  The information presented in this Chemical Information Fact 
Sheet is for informational purposes only and may not be used to fulfill 
data requirements for pesticide reregistration and reregistration.