Sulfidation attenuates the adverse impacts of metallic nanoparticles on anammox from the perspective of chronic exposure

The risks of metallic nanoparticles (MNPs) in anammox have attracted increasing attention; however, how sulfidation, an important environmental transformation process, affects their toxicity potential is unclear. The chronic responses of anammox biomass to exposure to pristine and sulfurized MNPs were compared in this study. Exposure to 2.5 mg L(-1)CuNPs and 2.5 mg L(-1)ZnONPs resulted in an almost 99% decrease in nitrogen removal capacity within 55 days; however, 68% of the nitrogen removal capacity could be maintained with the aid of sulfidation. The inhibition on the transcription and enzyme activity of hydrazine dehydrogenase was attenuated by reducing the metal content of the anammox biomass, which induced higher specific anammox activity at the metabolic level and higher abundance of anammox bacteria at the community level over time. Therefore, these results highlight the need to consider environmental transformations of MNPs to accurately evaluate their potential environmental risks.