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(particle) ) versus dissolved ions (NP(ion) )) are the main cause of toxicity of the NP suspension (NP(total) ) remains uncertain. In this 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(total) (2-50 mg/L) affect the relative contributions of Cu NP(particle) and Cu NP(ion) to the overall toxicity. We found that NOM mitigated the phytotoxicity of Cu NP(particle) more significantly than that of Cu-salt. When no NOM was added, Cu NP(particle) rather than Cu NP(ion) were the main contributor to the observed toxicity regardless of the concentration of Cu NP(total) . However, NOM tended to reduce the relative contribution of Cu NP(particle) to the toxicity of Cu NP(total) . Especially at a low concentration of Cu NP(total) (2 mg/L), the toxicity of Cu NP(total) mainly resulted from Cu NP(ion) in the presence of NOM (accounting for ≥ 70% of the overall toxicity). This might be due to the combined effects of increased dissolution of Cu NPs and steric-electrostatic hindrance between Cu NP(particle) and the soybean roots caused by NOM. Fulvic acids (FAs) tended to reduce the role of Cu NP(particle) in the overall toxicity more effectively than humic acids (HAs), which might partially be due to the higher extent of Cu NP dissolution upon FA treatment than in case of HA treatment. Our results suggest that due to the relatively low metallic NP concentration and the presence of NOM in natural water NP(ion) are likely problematic, which can inform management and mitigation actions. This article is protected by copyright. All rights reserved.