Silver nanoparticles in sewage sludge: Bioavailability of sulfidized silver to the terrestrial isopod Porcellio scaber

Silver nanoparticles (AgNPs) are efficiently converted during the wastewater‐treatment process into sparingly soluble Ag sulfides (Ag2S). In several countries, sewage sludge is used as a fertilizer in agriculture. The bioavailability of sulfidized Ag to the terrestrial isopod Porcellio scaber was investigated. Sewage sludge containing transformed AgNPs was obtained from a laboratory‐scale sewage‐treatment plant operated according to Organisation for Economic Co‐operation and Development (OECD) guideline 303a. The results of transmission electron microscopy with energy dispersive X‐ray of sludge samples suggest that AgNPs were completely transformed to Ag2S. Adult isopods were exposed to OECD 207 soil substrate amended with the AgNP spiked sludge for 14 d (uptake phase) followed by an elimination phase in unspiked soil of equal duration. Most of the Ag measured in P. scaber at the end of the uptake phase was found in the hindgut (71%), indicating that only a minor part of the estimated Ag content was actually assimilated by the isopods with 16.3 and 12.7% found in the carcass and hepatopancreas, respectively. As a result of this, the Ag content of the animals dropped following transition to unspiked sludge within 2 d to one‐third of the previously measured Ag concentration and remained stable at this level until the end of the elimination period. The present study shows that Ag2S in sewage sludge is bioavailable to the terrestrial isopod P. scaber.