PARTITION OF SYNTHETIC PYRETHROID INSECTICIDES BETWEEN DISSOLVED AND PARTICULATE PHASES

A batch isotherm method is shown to be applicable to the determination of sorption equilibrium for the lipophilic pyrethroid insecticides be tween solution and sorbents. Adsorption of pyrethroids to glasswalls w as significant and cannot be neglected. Sorption of lambdacyhalothrin on organically-coated montmorillonite was linear and much greater than on ''pure'' clay particles, consistent with a partition mechanism. Th e sorptive capacity of organic coatings was not constant, rather, it d ecreased with increasing polarity and decreasing aromaticity of organi c sorbents, further suggesting hydrophobic bonding is the sorption mec hanism. The results implied that the quantity as well as the quality o f the organic matter on particle surfaces had to be characterised in o rder to better predict contaminant transport in aquatic and soil envir onments. It is therefore inappropriate to predict K-oc from K-ow or so lubility with no consideration of the composition and structure of org anic matter.