Toxicokinetics of Ag from Ag₂S NP exposure in Tenebrio molitor and Porcellio scaber: Comparing single-species tests to indoor mesocosm experiments

Determining the potential for accumulation of Ag from Ag₂S NPs as an environmentally relevant form of AgNPs in different terrestrial organisms is an essential component of a realistic risk assessment of AgNP emissions to soils. The objectives of this study were first to determine the uptake kinetics of Ag in mealworms (Tenebrio molitor) and woodlice (Porcellio scaber) exposed to Ag₂S NPs in a mesocosm test, and second, to check if the obtained toxicokinetics could be predicted by single-species bioaccumulation tests. In the mesocosms, mealworms and woodlice were exposed together with plants and earthworms in soil columns spiked with 10 μg Ag g⁻¹ dry soil as Ag₂S NPs or AgNO₃. The total Ag concentrations in the biota were measured after 7, 14, and 28 days of exposure. A one-compartment model was used to calculate the Ag uptake and elimination rate constants. Ag from Ag₂S NPs appeared to be taken up by the mealworms with significantly different uptake rate constants in the mesocosm compared to single-species tests (K₁ = 0.056 and 1.66 g dry soil g⁻¹ dry body weight day⁻¹, respectively), and a significant difference was found for the Ag bioaccumulation factor (BAF_k = 0.79 and 0.15 g dry soil g⁻¹ dry body weight, respectively). Woodlice did not accumulate Ag from Ag₂S NPs in both tests, but uptake from AgNO₃ was significantly slower in mesocosm than in single-species tests (K₁ = 0.037 and 0.26 g dry soil g⁻¹ dry body weight day⁻¹, respectively). Our results are of high significance because they show that single-species tests may not be a good predictor for the Ag uptake in mealworms and woodlice in exposure systems having greater levels of biological complexity. Nevertheless, single-species tests could be used as a fast screening approach to assess the potential of a substance to accumulate in biota before more complex tests are conducted.