Effects of Combined Ag and ZnO Nanoparticles on Microbial Communities from Crab Orchard Creek, Illinois, USA

Abstract

The widespread use of Ag and ZnO nanoparticles (NPs) in commercial products has raised concern of their potential adverse impact on humans and the environment. These NPs most commonly enter the environment from the effluents of wastewater treatment plants (WWTPs). To understand the impact of these NPs on microbial communities, this study focused on adding environment-relevant concentrations of Ag (1 μg/L), ZnO (0.1 μg/L), and Ag+ZnO (1 μg/L+0.1 μg/L) to water collected from where the Carbondale Southeast WWTP effluent mixes with Crab Orchard Creek in IL, USA. Nanoparticles-spiked samples were withdrawn immediately and after 72 h for dynamic light scattering analysis. Optical density analysis by ultraviolet–visible spectroscopy, quantitative PCR analysis, and deoxyribonucleic acid sequencing were also conducted after 72 h. The results showed that ZnO NPs, at the studied concentration, were toxic, as a decrease in microbial biomass at Day 3 compared to the Control was reached, with an increase in mass fraction of nanoscale particles over time. However, when ZnO NPs were added in combination with Ag NPs, the adverse impact of ZnO NPs was mitigated, as an increase in microbial biomass was reached compared to the Control at Day 3, with a decrease in mass fraction of nanoscale particles over time. Ag NPs alone, at the studied concentration, did not bring significant impact on the microbial biomass. The relative abundance of the bacterial population affected the most by the addition of NPs was Firmicutes, with an increase in 13.74% compared to the Control when Ag+ZnO NPs were added. This study demonstrated the response of microbial communities to increased environment-relevant concentrations of NPs in a short period of time. The result will provide information that may aid in the preparation of guidance or regulations related to discharge of mixtures of NPs to surface water.