Changes in DNA properties due to treatment with the pesticides malathion and DDVP

Properties of calf thymus DNA were investigated after treatment with the pesticides malathion (0,0-dimethyl-S-(1,2-bis ethoxycarbonyl ethyl)dithiophosphate) and DDVP (0,0-dimethyl-0-(2,2 dichlorovinyl)phosphate) in vitro by means of derivative (differential) pulse polarography (DPP), thermal denaturation curves recorded spectrophotometrically (Tm), viscometric measurements, and chromatography on the hydroxyapatite column. Changes in the properties of DNA were observed by means of DPP after only a few hours incubation with the pesticides, whereas the other methods did not detect any changes even after 48 h. The results obtained by DPP indicate that single-stranded segments and thermolabile regions are formed in DNA due to the action of the pesticides. This behaviour could perhaps be a consequence of guanine alkylation followed by depurination and chain scission at elevated temperatures. Malathion and DDVP differ in the kinetics of reaction with double-helical DNA. DDVP is more reactive and its action is also manifested after 72 h in changes in viscosity, Tm, and chromatographic behaviour on the hydroxyapatite column. The changes induced by malathion were, under identical conditions, not detectable by these methods.