Trophic transfer of differently coated zinc oxide nanoparticles using crustaceans (Daphnia magna) and zebrafish (Danio rerio)

During the last couple of years the use of nanoparticles (NP) has dramatically increased. Zinc oxide nanoparticles (ZnO NP) have a wide range of applications e.g. in personal care products, paints and semi conductors. However, only a limited number of studies have so far investigated the ecotoxicity of ZnO NP and to our knowledge the bioaccumulation behavior in regards to difference in functionalization of ZnO NP has not been studied previously. In this study, experiments with trophic transfer using crustaceans (Daphnia magna) as food source for zebrafish (Danio rerio) was carried out to test if changes in functionalization of ZnO NP would affect the bioaccumulation behavior compared to ZnO NP. D. magna was exposed to pristine and functionalized ZnO NP in concentrations considered non-lethal in a 6341 Daphnia immobilization test. Bioconcentration studies with D. magna included a 24h uptake and 24h depuration phase and it was found that steady state with regards to body burden was reached after 24h uptake. The trophic transfer studies were carried out as 14 days of uptake feeding with pre-exposed D. magna and 7 days of depuration feeding with non-exposed D.magna. For the trophic transfer studies,5 days old D. magna were exposed to 1 mg/L ZnO NP (ZnO NP and ZnO-C8H17 NP) for 24h before feeding to D. rerio. This was done at a daily rate corresponding to 8% wet weight of the D. rerio. Food (D. magna) not eaten after 2 hours was removed and the resulting exposure loading was corrected for in the data treatment. The tested ZnO NP was of same primary size (35 nm) but with different functionalizations (ZnO and ZnO-C8H17). Characterization included ICP-MS, DLS, BET and TEM. Results show a fast uptake of ZnO NP in D. rerio reaching steady state after 5 days of exposure yielding a total body burden of 887±184 mg Zn/kg dry weight. A fast depuration (k2=-0.13 d-1) was observed reaching steady state after 3 days of depuration. The calculated BioMagnificationFactor (BMF) was calculated to 0.15 and a biological half-life time of 5.3 days. In contrast, ZnO-C8H17 showed linear uptake in D.rerio during the 14 days of uptake thus not reaching steady state. A total body burden of 2169±414 mg Zn/kg dry weight was observed past 14 days of uptake. However, the depuration rate was faster (k2=-0.32 d-1) compared to ZnO NP. The calculated BMF was 0.42 and a biological half-life time of 2.2 days. The studies demonstrate the feasibility of conducting bioconcentration and trophic transfer studies with NP and the results indicate that functionalizing of NP may affect the uptake and depuration of NP in aquatic organisms.