Influence of soil properties on the effect of silver nanomaterials on microbial activity in five soils

We investigated the effects of silver nanomaterials (AgNMs) on five well-characterized soils with distinct physicochemical properties using two standardized test systems. The carbon transformation test (OECD 217) showed minimal sensitivity whereas the ammonia oxidizing bacteria test (ISO 15685) showed extreme sensitivity over 28 days of exposure. AgNM toxicity was compared with the physicochemical properties of the soils, revealing that toxicity declined with increasing clay content and increasing pH. AgNM toxicity did not appear to be affected by the organic carbon content of the soil. Our results showed that AgNM toxicity cannot be attributed to any single soil property but depends on the same parameters that determine the toxicity of conventional chemicals. Recommendations in the test guidelines for soil ecotoxicity studies are therefore applicable to AgNMs as well as conventional chemicals.