Hazard Assessment of Ag Nanoparticles in Soil Invertebrates—Strong Impact on the Longer-Term Exposure of Folsomia candida

Silver nanomaterials (Ag NMs) are widely used, including in consumer products, and they inevitably enter the environment, with the soil compartment acting as a major sink. However, most available toxicity data focus on the reference Ag NM300K and rely on standard tests, even though long(er)-term exposure tests are recognized as particularly important for assessing the risks to soil invertebrates. Hence, the aim of the present study was to investigate the toxicity of commercial Ag NPs (Ag-Sigma, NPs < 150 nm) to the soil ecotoxicology model <i>Folsomia candida</i> (Collembola). Effects were assessed based on the standard OECD reproduction test (28 days) and beyond, with exposure prolonged for a second generation (56 days). Results showed that, based on the standard test (50% reproduction effect concentration-EC50 = 988 mg Ag/kg soil), the commercial Ag NPs were less toxic than the reference Ag NM300K and the ionic form AgNO₃ (from literature). However, the toxicity dramatically increased (ca. 4 times) during the second-generation exposure (EC50(56d) = 234 mg Ag/kg soil), surpassing the toxicity of Ag NM300K. The decrease in adults' size indicates that moulting might be affected. Overall, increased toxicity in prolonged exposure was not expected based on the available and standard test results, which highlights the importance of long(er)-term exposures to fully assess the risks of NMs to soil communities.