Effects of salinity, DOM and metals on the fate and microbial toxicology of propetamphos formulations in river and estuarine sediment

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 (100ngL^-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^-3h^-1). Analar-PPT and PPT-Ind biodegradation was further reduced by low salinity, high DOM and dissolved Zn and Pb (6.3×10^-4h^-1, 1100ht for Analar-PPT; 7.5×10^-4h^-1, 924ht for PPT-Ind). Toxicity effects of PPT, Zn and Pb in equitoxic ratio were higher for PPT-Ind (4.7μgPPT-Indg^-1; 581μgZng^-1; 395μgPbg^-1) than for Analar-PPT (34.6μgPPTg^-1; 312μgZng^-1; 212μgPbg^-1) whilst a toxicant ratio 1:100:10 suggested small quantities of Analar-PPT (EC₁₀=0.06μgg^-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.