Effect of Soil Organic Matter, Soil pH, and Moisture Content on Solubility and Dissolution Rate of CuO NPs in Soil

The objectives of this research were to quantify the impact of organic matter content, soil pH and moisture content on the dissolution rate and solubility of copper oxide nanoparticles (CuO NPs) in soil, and to develop an empirical model to predict the dissolution kinetics of CuO NPs in soil. CuO NPs were dosed into standard LUFA soils with various moisture content, pH and organic carbon content. Chemical extractions were applied to measure the CuO NP dissolution kinetics. Doubling the reactive organic carbon content in LUFA 2.1 soil increased the solubility of CuO NP 2.7-fold but did not change the dissolution rate constant. Increasing the soil pH from 5.9 to 6.8 in LUFA 2.2 soil decreased the dissolution rate constant from 0.56 mol1/3·kg1/3·s–1 to 0.17 mol1/3·kg1/3·s–1 without changing the solubility of CuO NP in soil. For six soils, the solubility of CuO NP correlated well with soil organic matter content (R2 = 0.89) independent of soil pH. In contrast, the dissolution rate constant correlated with pH for pH < 6.3 (R2 = 0.89), independent of soil organic matter content. These relationships predicted the solubility and dissolution rate constants of CuO NP in two test soils (pH 5.0 and pH 7.6). Moisture content showed negligible impact on the dissolution kinetics of CuO NPs. Our study suggests that soil pH and organic matter content affect the dissolution behavior of CuO NP in soil in a predictable manner.