Quantifying the Effect of Copper Oxide Nanoparticles on Duckweed Growth in Simulated Natural Systems.

With increasing demand for agricultural water use, the reuse of wastewater for irrigation purposes is growing in popularity; however, there is concern that the presence of manufactured nanomaterials in some waste streams may threaten crop production, food safety, and agroecosystem functions. Copper oxide nanoparticles (CuO NPs) have previously been shown to impact the growth of Duckweed [L. (Spirodela) Punctata], a model aquatic plant, widely found in agricultural runoff ditches in temperate climates. However, all studies to date involving CuO NP toxicity to Duckweed have focused on systems without the presence of dissolved organic matter. In the current study, decreasing CuO NP size was measured to significantly increase CuO NP toxicity to Duckweed. The dissolution of CuO NPs in ½ Hoagland’s solution increased significantly with decreasing particle size and in the presence of Suwannee River humic acid, fulvic acid, and natural organic matter (SRHA; SRFA; SRNOM). However, CuO NP dissolution in the presence of SRNOM was significantly less than in the presence of SRHA and SRFA, likely due to differences in the operational fractionation and cation content of SRHA, SRFA, and SRNOM. Both Cu and CuO NPs exhibited toxicity to duckweed growth in the presence of SRFA and SRNOM while only the addition of SRHA significantly reduced the toxicity of both forms of copper. These results suggest that the dissolution and toxicity of CuO NPs is DOM dependent and that SRHA and SRFA may be poor proxies for native DOM species in aquatic systems.