Silver Nanoparticles in Soil: Input, Transformation, and Toxicity

Abstract

The review briefs and analyzes the quantitative data on the input and content of silver nanoparticles (AgNPs) in soil, their possible transformations, and toxicity. The currently available data on the AgNPs content in soil are exclusively based on simulation results and vary in a wide range from 5.33 × 10–6 to 7.4 µg/kg at an annual input rate of 1.2 × 10–3 to 9.68 µg/kg. The main variants of AgNPs transformation in soil (interactions with soil solid phase, soil colloids, and dissolved organic matter and oxidation–reduction) that lead to preferential AgNPs retention in the upper soil layer are outlined. A comparison of the data on the AgNPs content in soil and the conditions of toxicological experiments demonstrates that the toxicity in most experiments has been assessed for an AgNPs concentration of 102–105 µg/kg soil, which is at least tenfold higher as compared with the estimates for actual conditions. Analysis of the existing concepts of the AgNPs translocation from soil to plants suggests no current risk of contamination of agricultural products with AgNPs. Some data demonstrate that the negative effects of AgNPs on microorganisms increase with the time of exposure. Thus, it is necessary to assess the effects of AgNPs in soil in long-term experiments (over 90 days) at the nanoparticle concentration not exceeding 10 µg/kg.