TOPICAL APPLICATION OF SYNTHETIC PYRETHROIDS TO CATTLE AS A SOURCE OFPERSISTENT ENVIRONMENTAL CONTAMINATION

Following the application of permethrin or cyhalothrin to cattle for t he control of ectoparasites, the occurrence and persistence of these c hemicals was assessed on the animals and in their environment. The rel ease of permethrin from ear tags containing 1 g of the drug on cattle was followed for 65 days and lead to concentrations of 5 to 35 mu g of permethrin per gram of hair on the shoulders. On the flanks of the an imals, the corresponding values were 10 times lower. Across the 1.5 ac re pasture, high concentrations of permethrin were measured at various locations and long after treatment: 6 mu g/g on bark of a birch after one week, 5 mu g/g on a pole of the fence after two weeks, 1 mu g/g i n grass from a resting site of the animal after six weeks, and 0.5 mu g/g in bark of a pine tree after three month and two weeks after the a nimals had left the pasture. In similar assays, cyhalothrin applied to milk cows as a pour-on preparation was monitored. One week following treatment with 0.2 g/animal, hair cut from the shoulders contained 5 m u g/g of the insecticide, which disappeared with a half-life of 12 day s. Dust collected two weeks after the pour-on treatment from the milk barn where the cows were milked twice daily contained 47 mu g/g of cyh alothrin, which disappeared with a half-life of 44 days. These results show that synthetic pyrethroids used on farm animals can be the sourc e of widespread and persistent contamination.