Influence of Cation Content on the Biological Activity of Fensulfothion in Plainfield Sand

Abstract A study was conducted to assess the influence of cations on the biological activity of the organophosphorus insecticide, fensulfothion ( O, O ‐diethyl O ‐[ p ‐(methylsulfinyl)phenyl] phosphorothioate)(Dasanit®) in soil. Bioassays were done using first stage crickets, Gryllus spp. as test insects and a Plainfield sand without and amended with various concentrations of reagent chloride salts of NH 4 + , K + , Ca 2+ , Fe 3+ , and Al 3+ . The toxicity of fensulfothion decreased with increasing cation content, with the effect being most pronounced with trivalent > divalent > monovalent cations. Results of the bioactivity study paralleled those of an earlier adsorption study on fensulfothion‐cation montmorillonite suspensions.