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fenvalerate (Pydrin) Research Document



     Fenvalerate is a synthetic pyrethroid insecticide which is used on 
a wide range of pests on food crops and on such animal parasites as 
cattle ticks. Fenvalerate acts on contact and can cause skin irritation 
in humans(6).



     The acute toxic effects of fenvalerate are dependent on the vehicle 
of administration. When administered in DMSO to rats the oral LD50 is 
451 mg/kg, and in an aqueous suspension the LD50 is > 3200 mg/kg. The 
dermal toxicity is 2500 mg/kg LD50 for rabbits and > 5000 mg/kg for 
rats. In humans, vitamin E is used both to prevent and alleviate the 
discomfort which can occur from fenvalerate contact(6). No incidences of 
human intoxication have been documented, however, forestry workers did 
show skin and upper respiratory tract irritation in a Swedish study. 
This effect is transient(4).

     Since esterases play a major role in the detoxification of 
fenvalerate, some esterase inhibitors serve as enhancers. Profenofos, 
EPN and DEF administered into the stomach cavity of mice at 25 mg/kg 
strongly inhibited the liver microsomal esterase that hydrolyses 
fenvalerate and increased the toxicity by greater than 25-fold(4).


     Rats fed dietary concentrations of 1000 ppm fenvalerate for two 
years had no compound-related changes in the blood or urine. In another 
study with dietary concentrations of 50 to 1500 ppm for 104 weeks, a NEL 
of 150 ppm (6.7-7.3 mg/kg/day) was established.

     Results in mice were similar. In one study the dietary NEL was 
found to be 10 ppm for males and 50 ppm for females and in another study 
the NEL was 30 ppm for both males and females. Significant reduction in 
body weight was the main adverse affect seen in both rats and mice. Dogs 
have an apparent NEL of 500 ppm based on a 90-day feeding study.

     A hen neurological study was negative at 1 g/kg for five days and 
when repeated again at 21 days.


     In a three-generation study with rats fed at levels of 1 - 250 ppm, 
no toxicity to the fetus was seen. Some maternal toxicity was noted in 
the second generation at the 250 ppm level. When mice and rabbits were 
fed levels up to 50 ppm on days 6 through 15 of gestation, there was 
maternal toxicity in both species at 50 ppm.


     The studies cited above (reproductive) for rats, mice and rabbits 
did not produce any teratogenic effects.


     A dominant lethal assay based on total mouse implants and early 
fetal deaths at 100 mg/kg was negative. Other negative tests include a 
mouse, host-mediated bioassay at 50 mg/kg; an Ames in vitro test; and a 
Chinese hamster bone marrow cytogenic study at 20 mg/kg.


     Rats fed at 1000 ppm for two years did not develop compound-related 
effects. The tumors present in the treated males were judged not related 
to compound administration(4). An outside evaluation of the tumors 
confirmed this conclusion. Another rat study with diets from 50 to 1500 
ppm for 104 weeks resulted in no evidence of carcinogenic response.

     Two mouse studies were also run. In one, mice were given diets 
containing 10 to 1250 ppm fenvalerate for two years. The number and type 
of effects were not statistically significant when compared to the 
controls(4). Mice fed diets of 10 to 300 ppm for 87 to 91 weeks did not 
exhibit carcinogenic effects. An additional study concluded that nodular 
changes which occurred were not progressive and were reversible in 

Organ Toxicity:

     The skin and hair of rats and mice contain rather persistent 
cyanide. However, this is not considered to be of toxicological 

Fate in Humans and Animals:

     Cows treated topically with 0.1 g or 0.5 g fenvalerate had 0.03 to 
0.06% of the applied chemical in the milk. When the cows received 
fenvalerate orally (0.454 g and 1/362 g), 0.44 and 0.64% of the dose, 
respectively, appeared in the milk.

     Fenvalerate does not appear to be metabolized by bovine rumen but 
is degraded further down the digestive tract(7). This happens rapidly 
with less than 0.02% of the parent compound found in the urine and 20% 
of the major metabolite present. Higher concentrations of the parent 
compound are present in the feces. In the rat, fenvalerate is rapidly 
metabolized with the acid and aromatic portions of the alcohol moiety 
almost completely eliminated within several days. One study indicated 
mammals eliminated 96% in the feces in 6-14 days.

     Tissue residues reach a plateau within three weeks of dietary 
administration and there appears to be no appreciable bioaccumulation of 
the parent or metabolites by longer exposure. Sheep feeding on pastures 
treated with 50 g and 25 g active ingredient per hectare had fat 
residues of 0.09 mg/kg down to 0.015 mg/kg when slaughtered after > 15 
days of exposure.


     Birds have high oral LD50's with pheasants > 2000 mg/kg, partridges 
> 3000 mg/kg and mallard ducks 9932 mg/kg. Poultry fed 0.03 ppm diets 
for up to 32 days had levels less than 0.001 or 0.008 ppm in the tissue 
and eggs. The LD50 for poultry is > 1600 mg/kg.

     Fish are sensitive to fenvalerate with 96-hour LC50's of 0.64 ppb 
for bluegill, 0.81 ppb for channel catfish and 6.2 ppb for rainbow 
trout. The sheepshead minnow is somewhat more resistant with a 96-hour 
LC50 of 430 ppb. Pink shrimp and fiddler crabs have LC50's of 1.4 ppb 
and 53.0 ppb, respectively.

     Fenvalerate is highly toxic to bees. There is some repellency, 
however, which lasts up to a day after application(6). Since most 
intoxicated bees die in the field rather than going back to contaminate 
the hive, the brood is not exposed except by direct spray.


     Under field conditions, fenvalerate has a half-life of about one 
month in soil. In soil laboratory study, 17% of the applied chemical was 
lost in 90 days. In Kodaira and Azuchi soils under upland conditions, 
the half-life was 15 days and three months, respectively.

     Fenvalerate is stable to hydrolysis for 100 hours under acidic 
conditions at 75 degrees C. It's photodegradation half-life in water is 
500 hours.

     The parent compound is the residue most often found on foliage. In 
a series of trials in Canada where 16 varieties of fruits and vegetables 
were grown under typical outdoor conditions, no degradation products or 
metabolites were found by methods sensitive to 0.05 mg/kg. Sampling was 
from 1 to 112 days after application. Half-life of fenvalerate on plant 
surfaces is two to four weeks.


du Pont                Toll free: 800/441-7515
Walker's Mill
Wilmington, DE 19898   Emergency: 800/441/3637


Common name             fenvalerate
CAS # 61630-58-1        cyano(3-phenoxyphenyl)methyl4-chloro-alpha-
Chemical class/ use     synthetic pyrethroid/insecticide
Solubility in water     0.002 ppm at 20 degrees C (calculated)
Solubility in solvent   hexane >0.7 g/100 g; acetone, chloroform,
                         methanol >45 g/100 g at 20 degrees C
Melting Point           clear viscous liquid at 23 degrees C
Vapor Pressure          1.1 x 10 to the minus 8 mm Hg
Exposure Guidelines
      rat               7.5 mg/kg/day (ppm) toxic effects
      mouse             3.5 mg/kg/day (ppm) toxic effects
      dog               12.5 mg/kg/day (ppm) toxic effects
  ADI                   0.02 mg/kg/day (ppm) (WHO)
                        0.125 mg/kg/day (ppm) (EPA)


1. Hartley, D., and H. Kidd, Editors (1986). The Agrochemicals Handbook.
   The Royal Society of Chemistry, The University, Nottingham, England.

2. Frank, R., H.E. Braun, L A. Miller, and G.W. Allan, (1984).
   Fenvalerate Residues in Milk Following Topical Treatments to Dairy
   Cows, Pesticide Science 15:600-604.

3. Menzie, Calvin M. (1980). Metabolism of Pesticides, Update III. U. S.
   Dept of the Interior, Fish and Wildlife Service, Special Scientific
   Report, Wildlife No. 232.

4. Food and Agriculture Organization of the United Nations, (1981).
   Pesticide Residues in Food - 1981. FAO Plant Production and
   Protection Paper 42.

5. Sumitomo Chemical Company (No date). Pyrid Residual Insecticide.
   Technical Data Information.

6. Shell Chemical Company (1982). Pydrin Insecticide. Technical Manual

7. Wsyolek, P.C., NA. LaFaunce, T. Wachs, and DJ. Link (1981). Studies
   of Possible Bovine Urinary Excretion and Rumen Decomposition of
   Fenvalerate Insecticide and a Metabolite, Bulletin Environ Contam
   Toxicol 26:262-266.

8. Food and Drug Administration (1986). The FDA Surveillance Index.
   Bureau of Foods, Dept of Commerce, National Technical Information
   Service, Springfield, VA.

9. Food and Agriculture Organization of the United Nations, (1984).
   Pesticide Residues in Food - 1981. FAO Plant Production and
   Protection Paper 67.


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