PS 86-55
Duration not dose drives bioaccumulation of silver nanoparticles in aquatic mesocosms
An understudied component of global change is the chemical perturbations which can affect organisms, populations, communities, and ecosystems. In examining the effects of chemical perturbations across these levels of biological organization it is essential to focus not only on the concentration, but also the time span over which a contaminant is released. The time span of a pulse-addition from an acute chemical spill will be short and concentrations will be high while a slow but steady press-addition of contaminated groundwater or effluent from a wastewater treatment plant is likely to be continuous or high frequency but at lower concentrations.
We hypothesize that press-additions have the potential to have stronger impacts over the long term due to the chronic exposure, whereas pulse-additions may have stronger short-term impacts. We tested this hypothesis by monitoring bioaccumulation of engineered silver nanoparticles (AgNPs), a contaminant of emerging concern due to their broad toxicity and increasing use as antimicrobials. The AgNPs were added to triplicate wetland mesocosms, which received either a pulse-addition (450 mg Ag, 0.75mg Ag/L), or press-addition (weekly additions of 8.65 mg Ag, 0.01-0.02 mg Ag/L). Silver concentration was measured in the plants, periphyton, and all dominant invertebrates and vertebrates over the course of the 1-year experiment to look at the extent of bioaccumulation under these two different exposure scenarios.
Results/Conclusions
Bioaccumulation of AgNPs varied between treatments and organisms. Across organisms, there was evidence of trophic transfer, and also trophic dilution with the highest trophic levels having lower silver concentrations than grazers and filter feeders. For example, the Eastern mosquitofish (Gambusia holbrooki) had a maximum silver concentration of 3.6 mg Ag/kg, while the Asiatic clam (Corbicula fluminea) had concentrations of 510 mg Ag/kg. In the Pulse treatment, the highest concentrations were measured across all taxa at 30 days, with concentrations either remaining essentially unchanged or declining over time thereafter. In the Press, all taxa increased in concentration from 30 days until the 1-year time point. For most organisms, concentrations at one year were higher in the Press than in the Pulse treatment, and in some cases the concentrations at 1-year in the press were higher than the pulse-treatment had been at 30 days. Thus, our results support our hypothesis, suggesting that it is essential to focus on not just the total dose, but also the duration of the exposure.