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 between solution and sorbents. Adsorption of pyrethroids to glasswalls was 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. The sorptive capacity of organic coatings was not constant, rather, it decreased with increasing polarity and decreasing aromaticity of organic sorbents, further suggesting hydrophobic bonding is the sorption mechanism. The results implied that the quantity as well as the quality of the organic matter on particle surfaces had to be characterised in order to better predict contaminant transport in aquatic and soil environments. It is therefore inappropriate to predict Koc from Kow or solubility with no consideration of the composition and structure of organic matter.