Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss

Richard Zeumer,Lara Hermsen,Ralf Kaegi,Sebastian Kühr,Burkhard Knopf,Christian Schlechtriem

doi:10.1016/j.scitotenv.2019.135695

Abstract

Silver nanoparticles (AgNPs) are present in a wide field of applications and consumer products and are likely to be released into the environment, mainly via urban and industrial sewage due to their extensive use. Even though AgNPs are mostly retained within the sludge of wastewater treatment plants (WWTPs), a small amount of mainly sulfidized particles still enters the aquatic environment, where they can be taken up by various aquatic organisms and transferred along the food chain. In this study, uptake and bioavailability of Ag from AgNPs following aqueous and dietary exposure were investigated in the rainbow trout Oncorhynchus mykiss. AgNPs in the effluent of model WWTPs and in tap water were used to perform aqueous exposure studies. No significant Ag uptake into the gills and carcass of the analyzed fish could be found for wastewater-borne AgNPs. However, when added to tap water at a concentration of 12.4 μg L−1, a maximum total Ag tissue concentrations of around 100 μg kg−1 and 50 μg kg−1 in gills and carcass were measured, respectively. For the dietary exposure studies, freshwater zooplankton was exposed to AgNPs, and used for the preparation of food pellets with a total Ag concentration of 121.5 μg kg−1. During the feeding study with rainbow trout significant total Ag concentrations up to 34.3 μg kg−1 could be found in the digestive tract. However, only a limited transfer of Ag through the intestinal walls into the carcass could be detected. AgNPs in plankton and WWTP effluent were characterized by transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy (EDX) and found to be sulfidized. This transformation most presumably has led to their limited bioavailability for fish. The results emphasize the importance of realistic test conditions for the risk assessment of AgNPs by the use of environmental matrices.

Highlights

In the last decades, nanotechnology applications have entered most fields of industry and production, creating new materials and concepts to improve processes in industries like water purification, agriculture, nanomedicine and energy storage (Roco et al, 2011)
Compared to pristine AgNPs supplied to tap water, wastewater borne AgNPs led to a reduced toxicity and bioaccumulation, which might be attributed to sulfidation or detoxification of the AgNPs by organic ligands like proteins or humic acids (Cedervall et al, 2007)
We investigated the uptake and bioavailability of Ag from AgNPs in the rainbow trout Oncorhynchus mykiss that are exposed via the water and their diet

Summary

Introduction

Nanotechnology applications have entered most fields of industry and production, creating new materials and concepts to improve processes in industries like water purification, agriculture, nanomedicine and energy storage (Roco et al, 2011). Even though sulfidized Ag species like Ag2S show a reduced release of ions and are mostly resistant against oxidation and dissolution, they might still be bioavailable for aquatic organisms and potentially accumulate along the food chain (Azimzada et al, 2017; Choi et al, 2009; Kaegi et al, 2011; Kalman et al, 2015; Rozan et al, 2000). Vogt et al (2019) analyzed the concentration of silver–containing nanoparticles in a prealpine lake that receives the discharge of a municipal WWTP They did not find considerable AgNP levels neither in the WWTP effluent, in any of the measured lake water samples, nor in tissues from lake fish. The sedimented Ag could be re-mobilized into the aquatic food chain by benthic organisms and a more detailed analysis of the bioavailability and trophic transfer of Ag in aquatic food webs is needed

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