Nutrient effects on microbial transformation of pesticides in nitrifying surface waters

Multivariate analyses of a large set of physical, chemical, and biological measurements indicated possible effects that specific surface water properties have on biotransformation rates of pesticides. In this study, we investigated the roles of Mg, Mn, and P, which were identified as relevant, discriminating environmental variables in the overall biotransformation process as it occurred under nitrifying conditions. Nematicide aldicarb, herbicides simazine and MCPA were selected as their chemical group representatives. Series of mechanically aerated incubation vessels were set up to test nutrient enrichment effects on microbial development and subsequent pesticide transformation. Accounting for alterations in system conditions, relevant (physico)chemical characteristics were monitored. An increase in total microbial population was observed in surface water samples in the presence of both aldicarb and simazine. No increase was observed when MCPA was added, which was probably cometabolized. Large phosphorus concentrations not only favored bacterial growth, but also increased the residence time of dissolved Mn which under certain conditions promoted biotransformation. Furthermore, PO4 enrichment decreases aldicarb's aerobic metabolites' concentrations. Simazine was persistent over a period of at least 80 days, except for a short period coinciding with the nitrification period in which NH dissipates and NO2 and NO are formed. Selective bacterial growth was observed on simazine's transformation product DES. Relationships of Mg/Mn concentrations to MCPA transformation rates, and of PO4/PT concentrations to aldicarb transformation rates, are presented. These relationships are assessed as environmental indicators for potential biotransformation, but only under conditions warranting development and growth of a degrading population over a prolonged period. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 329–338, 1999