Impact of water chemistry on the particle-specific toxicity of copper nanoparticles to Daphnia magna

Highlights: • Connection between the dynamic fate characterization of CuNPs and their toxicity was drawn. • Toxicity of CuNP suspension varies in dynamic and static exposure treatments, when organic matter (OM) was added. • Toxicity of CuNP suspensions results from the combined effect of the particles and their released ions. • The particle-specific toxicity of CuNPs decreased with increasing pH and contents of divalent cations and OM. Toxicity of metallic nanoparticle suspensions (NP_(total)) is generally assumed to result from the combined effect of the particles present in suspensions (NP_(particle)) and their released ions (NP_(ion)). Evaluation and consideration of how water chemistry affects the particle-specific toxicity of NP_(total) are critical for environmental risk assessment of nanoparticles. In this study, it was found that the toxicity of Cu NP_(particle) to Daphnia magna, in line with the trends in toxicity for Cu NP_(ion), decreased with increasing pH and with increasing concentrations of divalent cations and dissolved organic carbon (DOC). Without the addition of DOC, the toxicity of Cu NP_(total) to D. magna at the LC50 was driven mainly by Cu NP_(ion) (accounting for ≥ 53% of the observed toxicity). However, toxicity of Cu NP_(total) in the presence of DOC at a concentration ranging from 5 to 50 mg C/L largely resulted from the NP_(particle) (57%–85%), which could be attributable to the large reduction of the concentration of Cu NP_(ion) and the enhancement of the stability of Cu NP_(particle) when DOC was added. Our results indicate that water chemistry needs to be explicitly taken into consideration when evaluating the role of NP_(particle) and NP_(ion) in the observed toxicity of NP_(total).