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

Abstract

Silver nanoparticles (AgNPs) are efficiently converted during the wastewater-treatment process into sparingly soluble Ag sulfides (Ag 2 S). 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 Ag 2 S. 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 onethird of the previously measured Ag concentration and remained stable at this level until the end of the elimination period. The present study shows that Ag 2 S in sewage sludge is bioavailable to the terrestrial isopod P. scaber. Environ Toxicol Chem 2018;9999:1-8. C 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Nanomaterial Transformations in the Environment: Effects of Changing Exposure Forms on Bioaccumulation and Toxicity

“…[ 33 ] Soil invertebrate, Porcellio scaber exposed to a soil–sludge mixture containing Ag NMs for 14 days revealed uptake of Ag into mostly hindgut tissues indicating exposure to bioavailable metal in this system. [ 97 ] These shorter‐term exposures, <30 days, all showed Ag NM aged in sludge and added to soil to be available to organisms, in some cases equal or more than when AgNO 3 is added in the same manner.…”

“…Studies of NMs applied to soils in sewage sludge have investigated accumulation and effects in plants, earthworms and other soil invertebrates, mostly commonly for Ag [ 33,41,52,70,96,97 ] and to a lesser extent ZnO, CeO 2 , or TiO 2 . [ 41,96,98 ] Measurement of uptake of Ag NM aged for 30 days in sludge by wheat and rape plants only found accumulation in roots at higher concentrations (>50 mg kg −1 ) and did not detect Ag in the shoots.…”

“…Plant studies have shown a general trend of comparable accumulation between pristine and aged (chemical speciation changed forms, e.g., [ 52,53 ] This is in contrast to invertebrates and fish studies which generally show lower accumulation of aged NMs generally compared to their pristine NMs. [ 50,51,97 ] Studies with plants have highlighted how aging can sometimes result in increased availability and accumulation through speciation changes (e.g., CeO2 reduction of Ce(IV)/) as well as revealing how the plant rhizosphere is potentially an important role to play in mediating the bioavailability of aged or aging NMs.…”

Nanomaterial Transformation in the Soil–Plant System: Implications for Food Safety and Application in Agriculture

“…For example, nanoscale CeO 2 can be reduced and release Ce 3+ ions. [20] Further transformation processes, following redox reaction and dissolution, such as precipitation, may occur for metal based ENMs, e.g., sulfidation of Fe, [21] Cu, [22] Zn, [23] and Ag, [24] chlorination of Ag, [25] or phosphorylation of Ce [26] and Zn. [27] Organic ligands may bind to the released metal ions.…”

“…Inorganic ligands such as sulfide, chloride, and phosphate are key drivers involved in the chemical transformation of metal-based ENMs. Sulfide is ubiquitous in the environment and sulfidation is a very common chemical processes for many types of metal based ENMs (e.g., Ag, Cu, ZnO, PbO), based on the Pearson acid-base Natural organic matter (NOM) Aggregation [38,44,46,47] Ionic strength Aggregation [49][50][51] Soil pH Aggregation, dissolution [50,52] Redox potential Reduction, oxidation [42,54] Inorganic ligands Sulfidation, chlorination, phosphorylation [21][22][23][24][25][26][27]56,57] Microorganisms All physical and chemical transformation [29,61] concept. [55] Metal sulfides are usually less soluble than their oxide counterparts.…”