RESUMO
Toxicity studies tend to use pure pesticides with single organisms. However, natural systems are complex and biological communities diverse. The organophosphate pesticide propetamphos (PPT) has been found exceeding regulatory limits (100 ng L(-1)) in rivers. We address whether solution properties affect the fate of Analar (Analar-PPT) or industrial PPT (PPT-Ind) propetamphos formulations and whether propetamphos and metal toxicant effects are additive, antagonistic or synergistic? The sorption, desorption, biodegradation and microbial toxicology of Analar-PPT and PPT-Ind were investigated in Conwy River and estuary sediment. Results showed elevated salinity enhanced PPT sorption, while higher salinities increased PPT-Ind retention. Higher dissolved organic matter (DOM) and low salinity slowed Analar-PPT biodegradation (1.9×10(-3)h(-1)). Analar-PPT and PPT-Ind biodegradation was further reduced by low salinity, high DOM and dissolved Zn and Pb (6.3×10(-4)h(-1), 1100 ht(½) for Analar-PPT; 7.5×10(-4)h(-1), 924 ht(½) for PPT-Ind). Toxicity effects of PPT, Zn and Pb in equitoxic ratio were higher for PPT-Ind (4.7 µg PPT-Ind g(-1); 581 µg Zn g(-1); 395 µg Pb g(-1)) than for Analar-PPT (34.6 µg PPT g(-1); 312 µg Zn g(-1); 212 µg Pb g(-1)) whilst a toxicant ratio 1:100:10 suggested small quantities of Analar-PPT (EC(10)=0.06 µg g(-1)) affected microbial communities. The combined toxicity effect was more than additive. Thus, industrial formulations and pollutant mixtures should be considered when assessing environmental toxicity.
