Toxicity, bioaccumulation and biotransformation of Cu oxide nanoparticles in Daphnia magna

This study investigated the toxicity, bioaccumulation and biotransformation of copper oxide nanoparticles (nCuO) and CuSO₄ in Daphnia magna. We performed acute and chronic assays, and analyzed the organisms by μ-XRF and μ-XANES. In acute assays 25 nm nCuO (LC₅₀ 0.05 ± 0.011 mg Cu per L) and CuSO₄ (LC₅₀ 0.16 ± 0.015 mg Cu per L) were most toxic, while 40 nm and 80 nm nCuO had similar toxicity (LC₅₀ 2.34 ± 0.479 and 2.26 ± 0.246 mg Cu per L, respectively). In chronic assays, CuSO₄ (EC₅₀ 1.7 × 10^-4 ± 1.0 × 10^-4 mg Cu per L) was most toxic followed by 25 nm nCuO (EC₅₀ 1.8 × 10^-3 ± 8.0 × 10^-4 mg Cu per L), while 40 and 80 nm nCuO were least toxic (EC₅₀ 2.10 ± 0.669 and 1.95 ± 0.568 mg Cu per L, respectively). μ-XRF showed that Cu was accumulated in the intestine and appendages of the daphnids. μ-XANES showed that 25 nm nCuO and CuSO₄ were biotransformed into Cu₃(PO₄)₂ (acute assays), whereas 40 and 80 nm nCuO remained as CuO (chronic assays). The higher toxicity exhibited by CuSO₄ and 25 nm nCuO can be explained from their higher chemical reactivity (probed by catalytic decomposition of H₂O₂ and μ-XANES) compared to 40 and 80 nm nCuO.