Gold and silver nanoparticles effects to the earthworm - the importance of tissue over soil concentrations.

To address and to compare the respective impact of gold and silver nanoparticles (Au and Ag NPs) in soil invertebrate, the earthworm was exposed to soil containing 2, 10, and 50 mg/kg of Au and Ag in both nanoparticulate and ionic forms for 10 days. Both metal NPs were 2-15 times less bioavailable than their ionic forms, and displayed similar transfer coefficients from soil to earthworm tissues. Both metal NPs triggered the onset of an oxidative stress as illustrated by increased glutathione S-transferase levels, decreased catalase levels, and increased malondialdehyde concentrations. Protein carbonylation distinguished the nanoparticular from the ionic forms as its increase was observed only after exposure to the highest concentration of both metal NPs. Au and Ag NPs triggered DNA modifications even at the lowest concentration, and both repressed the expression of genes involved in the general defense and stress response at high concentrations as did their ionic counterparts. Despite the fact that both metal NPs were less bioavailable than their ionic forms, at equivalent concentrations accumulated within earthworms tissues they exerted equal or higher toxic potential than their ionic counterparts. At equivalent concentrations accumulated within earthworm tissues Au and Ag NPs exert equal or higher toxic potential than their ionic forms.