Effects of exposure route and surface coating on the bioaccumulation of CdTe quantum dots in fish. Considerations for testing nanomaterials following OECD Test guideline No. 305

To identify nanomaterials of potential environmental concern and to support risk assessment for regulatory purposes bioaccumulation testing is required. However, further guidance is needed when applying the fish bioaccumulation OECD test guideline (TG) No. 305 to nanomaterials. Also questions remain surrounding the most appropriate exposure route and if subtle modifications to these materials (e.g. different coatings) will influence bioaccumulation potential. Therefore in this study OECD TG 305 was applied to assess the bioaccumulation potential of CdTe quantum dots (QDs) with additional considerations for testing nanomaterials. CdTe QDs were selected for our studies because of their increasing use, possible release to water and limited information on their bioaccumulation potential in fish. To specifically address the influence of exposure route and surface coating on bioaccumulation, the uptake and depuration kinetics of two differently coated (carboxylate and polyethylene glycol coatings) CdTe QDs were investigated in rainbow trout ( Oncorhynchus mykiss ) following either aqueous or dietary exposure. In the dietary exposure bioaccumulation assays, fish were exposed to CdTe QDs at concentrations of 10 or 100 mg/kg for 28 days, followed by a 28-day depuration period to derive biomagnification factors (BMFs). In the aqueous exposure bioaccumulation tests, fish were exposed to 4 or 40 μg CdTe QDs /L for 28 days, followed by a 14-day depuration period to derive bioconcentration factors (BCFs). Both materials showed a low bioaccumulation potential and while a higher uptake was seen for the PEG coated materials, overall biodistribution, uptake and depuration kinetics were similar. The dietary exposure route allowed good and consistent estimations of BMF following both sequential and simultaneous methods. Aqueous exposures showed CdTe QDs dissolution in aquarium water and a steady state was not reached within 28 days, which challenged derivation of BCF values. This study provides important information on two differently coated CdTe QDs bioaccumulation, on OECD TG 305 applicability to metallic nanomaterials and on the reporting of accurate regulatory acceptable indicators of nanomaterial bioaccumulation potential.