Determination and prediction of partition coefficient and toxicity for sulfonylurea herbicides and their degradation products

The n-octanol/water partitioning coefficients (logK(ow)) of three sulfonylu rea herbicides metsulfuron methyl, chlorsulfuron and bensulfuron methyl and five of the degradation products were determined by the shake-flask method . The capacity factors (logK') were determined by RP-HPLC with ODS column a nd methanol-water eluent. Correlations between logK(ow) and, logK' and mole cular connectivity index were studied. Acute toxicity to the bacterium Phot obacterium phosphoreum (15-min-logEC(50)) and the green alga Chlorella pyre rloidosa (96-h-logEC(50)) were determined and correlated with logK(ow), and logK'. The quantitative structure-activity-relationship equations showed t hat logK(ow) and logK' are linearly correlated with toxicity, and both logK (ow) and logK' can be used in the prediction. No significant acute toxicity of the tested compounds to the cladocera Daphnia magna was observed in the laboratory tests, and this was explained by ionic forms of the compounds i n neutral aqueous solution.