Effect of silver nanoparticle contaminated biosolids on the soil microbial community

Abstract

This study investigated the effects of AgNPs on soil microbial communities when biosolids, containing AgNPs, were amended into soil. A field-collected sandy loam soil was amended with biosolids containing aged, PVP-coated AgNPs at measured concentrations of 3, 48, 123, 290 and 706 mg Ag kg−1 of soil (dry weight). The control treatment consisted of soil without AgNPs (Con-0) but amended with biosolids. An additional treatment of Ag+ (AgNO3) at 138 mg Ag kg−1 was included as appropriate. The AgNPs were aged in biosolids for 72 h before being spiked into soil. The impact of aged-AgNPs on the in-situ soil microbial community was assessed using a suite of microbial tests that assessed the effects on microbial growth, biomass, activity and diversity. The extractable Ag+ in AgNPs spiked soils increased with increasing AgNP concentrations and ranged from <0.1 to 3.38 mg Ag+ kg−1 soil. The extractable Ag+ in the AgNO3 treatment (i.e., 138 mg Ag kg−1) was 5 times lower than the comparable AgNP treatment (i.e., 123 mg Ag kg−1). A significant impact of AgNPs on the soil microbial community was observed with median inhibitory concentrations (IC50) ranging from 11 to >706 mg Ag kg−1. AgNP treatments showed a 10–64% reduction in microbial activities than the AgNO3 treatment at a similar total Ag concentration. The toxicity of AgNPs were more pronounced overtime, suggesting that Ag+ continued to be released from biosolid-aged AgNPs in the soil environment and likely contributed to the observed toxicity. Emergence of a silver tolerant bacterium (Rhodanobacter sp.) was observed in soils with low to moderately high AgNP concentrations (48 to 290 mg Ag kg−1). Our results suggest that AgNP exposure in soil amended with biosolids may have significant inhibitory effects on the soil microbial community despite their potential sulfidation in biosolid-amended soils.