Particle-Specific Toxicity of Copper Nanoparticles to Soybean (Glycine max L.): Effects of Nanoparticle Concentration and Natural Organic Matter.

For the soluble metallic nanoparticles (NPs), which forms (particles [NP ] vs. dissolved ions [NP ]) are the main cause of toxicity of the NP suspension (NP ) remains uncertain. In the present study, soybean was exposed to Cu NPs in a hydroponic system to determine how natural organic matter (NOM; 10 mg/l) and concentration of Cu NP (2-50 mg/l) affect the relative contributions of Cu NP and Cu NP to the overall toxicity. We found that NOM mitigated the phytotoxicity of Cu NP more significantly than that of Cu salt. When no NOM was added, Cu NP rather than Cu NP was the main contributor to the observed toxicity regardless of the concentration of Cu NP . However, NOM tended to reduce the relative contribution of Cu NP to the toxicity of Cu NP . Especially at a low concentration of Cu NP (2 mg/l), the toxicity of Cu NP mainly resulted from Cu NP in the presence of NOM (accounting for ≥70% of the overall toxicity). This might be attributable to the combined effects of increased dissolution of Cu NPs and steric-electrostatic hindrance between Cu NP and the soybean roots caused by NOM. Fulvic acids (FAs) tended to reduce the role of Cu NP in the overall toxicity more effectively than humic acids (HAs), which might partially be due to the higher extent of Cu NP dissolution on FA treatment than in HA treatment. Our results suggest that because of the relatively low metallic NP concentration and the presence of NOM in natural water, NP are likely problematic, which can inform management and mitigation actions. Environ Toxicol Chem 2021;40:2825-2835. © 2021 SETAC.