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.
Keywords: AgNPs; Aquatic food chain; Bioaccumulation; WWTP effluent.
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