TOXICITY OF ORGANOPHOSPHATE INSECTICIDES AND THEIR METABOLITES TO THEWATER FLEA DAPHNIA-MAGNA, THE MICROTOX TEST AND AN ACETYLCHOLINESTERASE INHIBITION TEST

The toxicity of the organophosphorous insecticides thiometon and disul foton as well as some of their degradation products was determined usi ng Daphnia magna, Photobacterium phosphoreum (Microtox(R)) and an acet ylcholinesterase (AChE) activity assay. For comparison, the toxicity o f the organophosphorous insecticides dichlorvos, fenitrothion, parathi on, etrimfos, propetamphos and quinalphos was measured. Although disul foton and thiometon have a similar molecular structure they showed dif ferent inhibitory effects on D. magna and P. phosphoreum. Some of thei r degradation products (PO analogs) were stronger inhibitors of AChE t han the parent compounds and showed also higher toxicity in the bioass ay with D. magna. D. magna was less sensitive to the degradation produ cts lacking the sulfur containing side-chain and to the low molecular weight sulfur compounds. A toxicological model was used to predict the toxicity of disulfoton and thiometon and their degradation products i n soil leachates in the D. magna and P. phosphoreum bioassays. The pre dictions were based on the toxicity of the single compound and the con centration of each compound in the leachate. The predictions made show ed good correlations with the determined toxicity for both bioassays.