Testing the bioaccumulation of manufactured nanomaterials in the freshwater bivalve Corbicula fluminea using a new test method

Abstract

Increasing amounts of manufactured nanomaterials (MNMs) are produced for their industrial use and released to the environment by the usage or disposal of the products. As depending on their annual production rate, substances are subjected to PBT assessment, the availability of reliable methods to evaluate these endpoints for (corresponding) nanoforms/MNMs becomes relevant. The classical method to elucidate the bioaccumulation potential of chemicals has been the flow-through study with fish, which has limitations as regards meeting the requirements of MNMs. Most MNMs tend to sediment in the aquatic environment. Thus, maintenance of stable exposure conditions for bioaccumulation testing with fish is nearly impossible to achieve when using MNMs. Corbicula fluminea, a freshwater filter-feeding bivalve distributed worldwide, has been previously shown to ingest and accumulate MNMs present in the water phase. To investigate the suitability of C. fluminea for bioaccumulation testing we developed a new flow-through system to expose mussels under constant exposure conditions. Two nanoparticles (NPs), the AgNP NM 300K and the TiO₂NP NM 105, were applied. In addition, C. fluminea was exposed to AgNO₃ as a source of dissolved Ag⁺ to compare the bioaccumulation of Ag in dissolved and nanoparticulate forms. For each MNM exposure scenario we were able to determine steady-state bioaccumulation factors. BAF_ss values of 31 and 128 for two NM 300K concentrations (0.624 and 6.177 μg Ag per L) and 6150 and 9022 for TiO₂ (0.099 and 0.589 μg TiO₂ per L) showed the exposure dependence of the BAF_ss estimates. The progression of metal uptake and elimination in the soft tissue provided clear indications that the uptake and thus accumulation is mainly driven by the uptake of NPs and less of dissolved ions.