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 sulfonylurea 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 and methanol-water eluent. Correlations between logK(ow) and, logK' and molecular connectivity index were studied. Acute toxicity to the bacterium Photobacterium phosphoreum (15-min-logEC(50)) and the green alga Chlorella pyrerloidosa (96-h-logEC(50)) were determined and correlated with logK(ow), and logK'. The quantitative structure-activity-relationship equations showed that 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 in neutral aqueous solution.