title: The effects of organophosphorus pesticides on estuarine ammonium oxidizers.
abstract: The effects of seven thiophosphorus pesticides and their degradation products on estuarine ammonium oxidizers were examined. Using an axenic, closed-culture, high cell density assay, the pesticides caused little inhibition of ammonium oxidation. However, the degradation product of methyl parathion, p-aminophenol, significantly inhibited ammonium oxidation levels as low as 0.01 mg/L. Estuarine sediments containing indigenous ammonium oxidizers were exposed to the pesticides over a 14-day period and activity of the ammonium oxidizers were inhibited after 14 days. Three pesticides were aged in estuarine sediments under aerobic, anaerobic, and microaerophilic conditions, and axenic cultures of ammonium oxidizers were exposed to the resulting metabolites. Ammonium oxidation was inhibited by 10% in the systems containing pesticides aged under aerobic and anaerobic conditions, whereas under microaerophilic conditions, 20% reduction in activity was observed. The data suggest that the parent compounds of the thiophosphorus pesticides have little effect on ammonium oxidation in estuarine sediments, but that certain metabolites which accumulate from the decomposition of these pesticides, especially in sediments under low O2 levels, may significantly reduce ammonium oxidation.
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D004777:Environment; D007306:Insecticides / Q000494:pharmacology*; D009946:Organothiophosphorus Compounds; D014871:Water Microbiology
chemical_list: D007306:Insecticides; D009946:Organothiophosphorus Compounds; D000641:Ammonia