Spatiotemporal distribution of silver and silver-containing nanoparticles in a prealpine lake in relation to the discharge from a wastewater treatment plant

Abstract

Over two years we assessed silver-containing nanoparticles (SCN) and total silver in the in- and effluent of a wastewater treatment plant (WWTP) discharging purified wastewater into a lake. Additionally, total silver was measured in sludge of the WWTP and in water, sediment, and fish of the receiving lake at several points with varying distance to the discharge point and compared to a reference lake. We used a novel single particle inductively coupled plasma mass spectrometry (SP-ICP-MS, with microsecond time resolution) protocol to detect SCN in environmental samples in addition to total elemental analysis by ICP-MS/OES (optical emission spectrometry), and histological analysis by dark-field microscopy. Total silver was below the limit of quantification in the WWTP influent and effluent, and in lake water and fishes, except for one influent sample. However, comparably high silver concentrations were detected in the sludge, irrespective of the season, indicating accumulation of silver. Furthermore, SP-ICP-MS analysis of influent samples confirmed the presence of SCN. Despite the high removal efficiency of silver and SCN from the wastewater, high silver concentrations were measured in the sediment near the discharge point, suggesting a constant silver input into the lake. Silver and SCN levels were lower than concentrations leading to adverse effects in recently published toxicological studies, thus the investigated lake ecosystem is currently not at risk.