Silver nanoparticles (NPs) are an emerging contaminant of concern due to their increased use. The earthworm Eisenia fetida was exposed to a range of concentrations of AgNO3 and two polyvinylpyrolidone coated Ag NPs with different particle size distributions. They were exposed in two different soils: a naturally occurring sandy loam and a standardized artificial soil. The AgNO3 significantly reduced E. fetida growth and reproduction at 7.41 ± 0.01 mg kg−1 Ag in the sandy loam but only reproduction was affected at concentrations of 94.1 ± 3.2 mg kg−1 in the artificial soil. In the artificial soil, significant (α = 0.05) reproductive toxicity was only observed in organisms exposed to the Ag NPs at concentrations approximately eight times higher than those at which the effects from ionic Ag were observed. Eisenia fetida exposed to either AgNO3 or Ag NPs in the sandy loam accumulated significantly (α = 0.05) higher concentrations of Ag than those exposed in the artificial soil and had higher bioaccumulation factors. Earthworms exposed to AgNO3 also accumulated significantly higher concentrations of Ag than those exposed to Ag NPs. No differences in toxicity were observed between the two size distributions. Extended x‐ray absorption fine structure spectroscopy analysis of the soils indicated that the Ag was approximately 10 to 17% Ag(I), suggesting that Ag ions may be responsible for effects on growth and development caused by exposure to Ag NPs. Our results also suggest that soil type is a more important determinant of Ag accumulation from Ag NPs than particle size.

The purpose of this study was to investigate the effect of surface coating on the toxicity of silver nanoparticles (Ag NPs) soil. Earthworms (Eisenia fetida) were exposed to AgNO(3) and Ag NPs with similar size ranges coated with either polyvinylpyrrolidone (hydrophilic) or oleic acid (amphiphilic) during a standard sub-chronic reproduction toxicity test. No significant effects on growth or mortality were observed within any of the test treatments. Significant decreases in reproduction were seen in earthworms exposed to AgNO3, (94.21 mg kg(-1)) as well as earthworms exposed to Ag NPs with either coating (727.6 mg kg(-1) for oleic acid and 773.3 mg kg(-1) for polyvinylpyrrolidone). The concentrations of Ag NPs at which effects were observed are much higher than predicted concentrations of Ag NPs in sewage sludge amended soils; however, the concentrations at which adverse effects of AgNO(3) were observed are similar to the highest concentrations of Ag presently observed in sewage sludge in the United States. Earthworms accumulated Ag in a concentration-dependent manner from all Ag sources, with more Ag accumulating in tissues from AgNO(3) compared to earthorms exposed to equivalent concentrations of Ag NPs. No differences were observed in Ag accumulation or toxicity between earthworms exposed to Ag NPs with polyvinylpyrrolidone or oleic acid coatings.

Because Au nanoparticles (NPs) are resistant to oxidative dissolution and are easily detected, they have been used as stable probes for the behavior of nanomaterials within biological systems. Previous studies provide somewhat limited evidence for bioavailability of Au NPs in food webs, because the spatial distribution within tissues and the speciation of Au was not determined. In this study, we provide multiple lines of evidence, including orthogonal microspectroscopic techniques, as well as evidence from biological responses, that Au NPs are bioavailable from soil to a model detritivore (Eisenia fetida). We also present limited evidence that Au NPs may cause adverse effects on earthworm reproduction. This is perhaps the first study to demonstrate that Au NPs can be taken up by detritivores from soil and distributed among tissues. We found that primary particle size (20 or 55 nm) did not consistently influence accumulated concentrations on a mass concentration basis; however, on a particle number basis the 20 nm particles were more bioavailable. Differences in bioavailability between the treatments may have been explained by aggregation behavior in pore water. The results suggest that nanoparticles present in soil from activities such as biosolids application have the potential to enter terrestrial food webs.