Conserved microbial toxicity responses for acute and chronic silver nanoparticle treatments in wetland mesocosms.

Most studies of bacterial exposure to environmental contaminants focus on acute treatments; however, the impacts of single, high-dose exposures on microbial communities may not readily be extended to the more likely scenario of chronic, low-dose contaminant exposures. Here, in a year-long, wetland mesocosm experiment, we compared microbial community responses to pulse (single 450 mg dose of silver) and chronic (weekly 8.7 mg doses of silver for 1 year) silver nanoparticle (Ag-0 NP) treatments, as well as a chronic treatment of "aged" sulfidized silver nanoparticles (Ag2S NPs). While mesocosms exposed to Ag2S NPs never differed significantly from the controls, both Ag-0 NP treatments exhibited reduced microbial diversity and altered community composition; however, the effects differed in timing, duration, and magnitude. Microbial community-level impacts in the acute Ag-0 NP treatment were apparent only within the first weeks and then converged on the control mesocosm composition, while chronic exposure effects were observed several months after exposures began, likely due to interactive effects of nanoparticle toxicity and winter environmental conditions. Notably, there was a high level of overlap in the taxa which exhibited significant declines (>10x) in both treatments, suggesting a conserved toxicity response for both pulse and chronic exposures. Thus, this research suggests that complex, but short-term, acute toxicological studies may provide critical, cost-effective insights into identifying microbial taxa sensitive to long-term chronic exposures to Ag NPs.