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Risk of Silver Transfer from Soil to the Food Chain Is Low after Long-Term (20 Years) Field Applications of Sewage Sludge

Author:
Wang, Peng, Menzies, Neal W., Chen, Hongping, Yang, Xinping, McGrath, Steve P., Zhao, Fang-Jie, Kopittke, Peter M.
Source:
Environmental science & technology 2018 v.52 no.8 pp. 4901-4909
ISSN:
1520-5851
Subject:
X-ray absorption spectroscopy, adverse effects, bioavailability, calcium nitrate, diet, field experimentation, food chain, humans, industry, nanoparticles, nanosilver, risk, sewage sludge, silver, soil, terrestrial ecosystems, tissues
Abstract:
The increasingly widespread usage of silver (Ag) nanoparticles has raised concerns regarding their environmental risk. The behavior of Ag and its transfer risk to the food chain were investigated using a long-term field experiment that commenced in 1942 in which Ag-containing sewage sludge was repeatedly applied to the soil (25 applications during 20 years). The speciation of the Ag in both the sludge and the soils retrieved from the long-term experimental archive was examined using synchrotron-based X-ray absorption spectroscopy, and extractable Ag concentrations from soils were determined using 0.01 M Ca(NO₃)₂ and 0.005 M DTPA. The total Ag in the sludge during the time period of 1942–1961 ranged from 155 to 463 mg kg–¹. These values are 1–2 orders of magnitude higher than those in currently produced sludge (ca. 0.5–20 mg kg–¹). Long-term repeated applications of these sludges resulted in an increase of Ag in soils from 1.9 mg kg–¹ in the control to up to 51 mg kg–¹. The majority (>80%) of the Ag in both the sludge and the sludge-treated soils was present as insoluble Ag₂S, thereby markedly reducing the bioavailability of this Ag. Concentrations of Ag in the archived crop samples were generally <0.70 mg kg–¹ in edible tissues, much less than those in diets that may cause an adverse effects in animals and humans (>100 mg kg–¹). These data indicate that the transfer of Ag (derived from both traditional Ag industry and current nano Ag industry) to the terrestrial food chain is limited.
Agid:
6008404