Exploring the Influence of Raising Soil pH on the Ecotoxicological Effects of Silver Nanoparticles and Micron Particles on Soil Microbial Communities

Abstract

Silver contamination of soil systems has been shown to have significant negative effects on soil microbial communities and key functional processes. However, few studies to date have addressed the influence that soil physico-chemical characteristics may have on silver toxicity. In this study, the influence of soil pH soil was investigated on the toxicity of both silver nano-(NP) and micron-(MP) particles to microbial communities and community functioning in a pastureland soil. An acidic soil, pH 5.1, was harvested from an agricultural pastureland and divided into two batches, one of which was adjusted with calcium carbonate to a neutral pH of 7. The effect of 50 mg kg−1 of AgNP and AgMP amendment on the acidic soil and the neutral soil microbial communities was then examined in a microcosm-based experiment. Our results found dehydrogenase activity, which was used as a proxy measure for microbial activity, to be far more susceptible to both AgNP and AgMP contamination in the acidic soil than in the neutral soil. Additionally, both AgNPs and AgMPs significantly affected bacterial and fungal community structures in the acidic soil; however, community structures in the pH-neutral soil amended with AgNPs and AgMPs remained similar to those in the unamended control. The results from this study indicate that soil pH was an influential factor affecting AgNP toxicity in our soil system with the acidic soils far more susceptible to silver contamination than the neutral soil.