John Wiley & Sons, Ltd.

Differential sensitivity of nitrifying bacteria to silver nanoparticles in activated sludge

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Nitrification is known to be one of the most sensitive processes affected when activated sludge (AS) is exposed to antimicrobial silver nanoparticles (AgNPs). However, the impact of AgNPs and their released silver ions (Ag+) on the abundance, activity and diversity of different nitrifying bacteria in wastewater treatment plants (WWTPs) is poorly understood. Herein we investigate the impacts of two sizes of AgNPs (5‐nm and 35‐nm) and Ag+ ions on the nitrifier community in AS, including both ammonia‐oxidizing bacteria (AOB) and nitrite‐oxidizing bacteria (NOB). AOB were more sensitive to AgNPs; a 5‐day and 7‐day exposure of AS to 35‐nm AgNPs (40 ppm) significantly reduced AOB abundance to 24% and 19%, respectively, and was further confirmed by a decrease in AS ammonia oxidation activity measured by 14C‐labeled bicarbonate uptake. In contrast, neither AgNPs (up to 40 ppm) nor Ag+ (1 ppm) affected the abundance of NOB. Both 5‐nm and 35‐nm AgNPs decreased the diversity of AOB, indicated by denaturing gradient gel electrophoresis (DGGE) with ammonia monooxygenase gene (amoA) primers, although some unknown Nitrosomonas species were relatively resistant to AgNPs. The generally greater resistance of NOB than AOB to AgNPs suggests that the accumulation of bacteriostatic nitrite in WWTPs is unlikely to be exacerbated due to accidental or incidental releases of AgNPs. Environ Toxicol Chem © 2014 SETAC

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