Interactions of carbaryl with estuarine bacterial communities

The addition of carbaryl (100μg/ml) to a model estuarine ecosystem did not affect the number of bacteria in the sediment, but reduced the diversity (as measured by the rarefaction technique) of the microbial community as compared with a control model ecosystem. Two carbaryltolerant strains of bacteria were isolated from the carbaryl-treated system, but none were isolated from the control system. Bacterial growth and filter paper decomposition in mixed cultures was prevented by 100μg/ml carbaryl, but this amount had no effect on the extracellular cellulase of an estuarine isolate. Increasing the amount of organic matter in the medium attenuated the toxicity of carbaryl to pure cultures of an estuarine isolate. The addition of 1, 10, or 100μg/ml carbaryl to field plots had no effect on bacterial numbers, diversity, or filter paper decomposition. The amount of carbaryl in sediments exposed to 100μg/ml fell below the limit of detection by thin-layer chromatography within 12 hours. In sterile and nonsterile model systems, carbaryl rapidly adsorbed to sediment, and hydrolyzed to 1-naphthol in both sediment and water. Although carbaryl may be toxic to bacteria under some conditions, the amounts that might enter and persist in an estuary are insufficient to have a significant impact on the sediment microbial community.