Bioaccumulation and toxicity of silver nanoparticles and silver nitrate to the soil arthropod Folsomia candida

The growing use of silver nanoparticles (Ag-NP) triggered an increasing interest in their environmental fate and possible ecotoxicological impacts. To investigate the potential risk of Ag-NP to soil organisms, the springtail Folsomia candida was exposed to Ag-NP (reported diameter size 3-8 nm) and AgNO3 in Lufa 2.2 natural soil for 28 days to determine effects on survival and reproduction. Also, the kinetics of uptake and elimination of Ag were studied for F. candida exposed in Lufa 2.2 soil to Ag-NP (at 168 mg Ag/kg dry soil) and AgNO3 (at 30 and 60 mg Ag/kg dry soil). AgNO3 was toxic with an LC50 was 284 mg Ag/kg dry soil for effects on survival and EC10 and EC50 values of 47.6 and 99.5 mg Ag/kg dry soil, respectively for the effect on reproduction. These values did correspond with porewater concentrations of 0.801, 0.042 and 0.082 mg Ag/l, respectively. No effects on survival and reproduction of Ag-NP were observed up to 673 mg Ag/kg dry soil, although porewater concentration was similar to the EC50 for AgNO3. Exposure to both Ag forms caused a fast uptake of Ag, but the Ag elimination rate was significantly higher for Ag-NP than for AgNO3. Bioaccumulation factor was higher for AgNO3 (on average 5.64) than for Ag-NP (1.12). These findings indicate that silver ions are more toxic than Ag-NP and have a higher potential to accumulate in F. candida.