Long-term effects of silver nanoparticles (NM-300K) and soil amendments on soil respiration and mesofauna in a semi-field experiment

The toxicity of silver nanoparticles (AgNPs) has been intensely studied, due to their increased applications in various products. However, most studies were conducted under laboratory conditions and short periods of time. Here we focus on how AgNPs at a concentration of 30 mg kg−1 soil behave under semi-field conditions in a long-term study. The effects of AgNPs (NM-300K) and AgNO3 in three soil treatments with and without additives on microbial biomass, mesofauna and the reproduction of Folsomia candida were studied. We measured silver concentrations by atomic absorption spectrometry. After 200, 400 and 600 days, we recorded soil microbial biomass by substrate-induced respiration, extracted the colonizing mesofauna and used part of the soil for reproduction tests with F. candida. Over the time course of the entire experiment, 71.2% of the added silver was found in the sampling soils, 9.6% in the surrounding soil, and 0.3% in the drainage water. Only in the unamended soil AgNPs and AgNO3 showed inhibitory effects that decreased over time, although more silver was retained in the amended soils. Soil mesofauna abundance was only temporarily reduced by AgNO3 but not by AgNPs. By the end of the experiment no more negative effects on the measured microbial biomass were observed. Biochar and compost as soil amendments demonstrated excellent remediation potential for AgNPs, both for medium- and long-term experiments.