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 propert ies have on biotransformation rates of pesticides. In this study, we invest igated the roles of Mg, Mn, and P, which were identified as relevant, discr iminating 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. S eries of mechanically aerated incubation vessels were set up to test nutrie nt enrichment effects on microbial development and subsequent pesticide tra nsformation. Accounting for alterations in system conditions, relevant (phy sico)chemical characteristics were monitored. An increase in total microbia l 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 favore d bacterial growth, but also increased the residence time of dissolved Mn w hich under certain conditions promoted biotransformation. Furthermore, PO4 enrichment decreases aldicarb's aerobic metabolites' concentrations. Simazi ne was persistent over a period of at least 80 days, except for a short per iod coinciding with the nitrification period in which NH4+ dissipates and N O2 and NO3- are formed. Selective bacterial growth was observed on simazine 's transformation product DES. Relationships of Mg/Mn concentrations to MCP A transformation rates, and of PO4/P-T concentrations to aldicarb transform ation rates, are presented. These relationships are assessed as environment al indicators for potential biotransformation, but only under conditions wa rranting development and growth of a degrading population over a prolonged period. (C) 1999 by John Wiley & Sons, Inc.