Abstract
At Rosemond Farm, UK, carbofuran was applied broadcast to part of a field, which lies at the top end of a catchment. During several rainfall events, raw runoff samples were collected and analyzed for carbofuran, and a bioassay was performed on the samples using the gammarid amphipod crustacean Gammarus pulex. Carbofuran concentrations peaked initially at 24 mu g/l about 10 h after rainfall began and then declined gradually over 4 d to about 1.9 mu g/l. The entire amount of carbofuran mobilized into the stream was approximately 0.5% of the total applied. Results from the in situ bioassay in the receiving water indicated that G. pulex stopped feeding completely during the rainfall events, which was followed rapidly by the death of all caged animals. Subsequent analysis revealed that the peak concentrations of carbofuran had exceeded the 24-h LC sub(50) value of 21 mu g/l for G. pulex.