Unravelling the uptake pathway and accumulation of silver from manufactured silver nanoparticles in the freshwater amphipod Hyalella azteca using correlative microscopy

Abstract

Silver nanoparticles (AgNPs) are known to enter the aquatic environment via leachates from landfills or by the effluent or sludge of sewage treatment plants.Even if the AgNPs are sulfidized, Ag from these particles was shown to still be available to several species like the benthic freshwater amphipod Hyalella azteca. However, it is still unknown if the primary uptake of Ag from these particles occurs mainly by Ag ions, or if the main uptake of Ag is by ingestion of AgNPs and if they can be found in the animal tissues or just in the gut content without any tissue transfer.To elucidate the main uptake pathway and localization of AgNPs potentially taken up by H. azteca, we exposed the amphipods to Ag using AgNP containing sewage sludge or dissolved Ag from AgNO3.Further, we seperated the exposed animals into two groups. One had direct contact to the AgNPs enriched sludge, allowing them to feed on it, the second group seperated from the sludge by a strainer allowing only indirect contact by potentially released AgNPs or ions.The animals exposed for 7 days were examined for their total and nano particulate Ag content using (single-particle) inductively coupled plasma mass spectrometry as well as using methods of correlative microscopy. Thus we were able to show, that low amounts of AgNPs were present exclusively in animals with direct contact to the AgNP enriched sludge and only in the region of the gut. No transfer of AgNPs from the gut into the animals tissue was observed by correlative microscopy. However, measurable Ag body burdens in animals from all treatments and groups indicated that ionic uptake is the main uptake pathway for (bio)accumulation of Ag from AgNPs.