Are aquatic food webs vulnerable to copper and gold engineered nanoparticles?

Abstract

Freshwater ecosystems are exposed to engineered nanoparticles through municipal and industrial wastewater-effluent discharges and agricultural non-point source runoff. These same anthropogenic waste streams which contain high concentrations and diversity of nanoparticles also contain excess nitrogen and phosphorus. The interaction between nanoparticles (NPs) and nutrients remains poorly understood within the context of aquatic food webs. To address this interaction, I examined the impacts of a citrate-coated gold nanoparticle (AuNPs) and a commercial pesticide containing Cu(OH)2 nanoparticles (CuNPs) on aquatic food webs under both ambient and enriched nutrient conditions. In the 2016 CEINT Wetland Mesocosm study, mesocosms were exposed repeatedly with low, environmentally realistic concentrations of nanoparticles and nutrients over the course of a 9-month experiment. My work during this study determined decreased insect emergence in nanoparticle treatments, aquatic to riparian metal export via aquatic insect emergence, and subsequent metal accumulation in riparian spiders. In that same study, I demonstrated that consumers exposed to nanoparticles doubled excretion rates of nitrogen and phosphorus and likely contributed to the increased persistence of algal blooms as observed in our mesocosm experiment. To address these findings, I designed and executed a stream microcosm experiment to validate and mechanistically understand ecological responses observed in our mesocosm study, increased consumer nutrient excretion rates and persistence of algal blooms. The microcosm study demonstrated a high impact of dissolved gold to algal biomass, nutrient uptake, and bacterial community composition of both periphyton and snail gut. Engineered NPs and nutrients have significant and quantifiable effects on aquatic ecosystems, though responses may not be easily measured or are sub-lethal, in many cases and require monitoring over long time periods. Overall, my results suggest that 1) NPs decrease insect emergence and exhibit trophic transfer from aquatic insects to riparian spiders and 2) double consumer mediated nutrient recycling rates resulting in a higher availability of nutrients available for plant uptake and 3) increase the algal biomass and alter microbial communities in periphyton and snail gut microbiome. Thus, the long-term effects of NPs and nutrients in aquatic ecosystems could significantly alter aquatic ecosystem function. Aquatic food webs are indeed vulnerable to engineered nanoparticles.