Effects of Commercial Copper Nanoparticles on Enzymatic Activity and Nutrient Bioavailability in Agricultural Soil

Excessive release of engineered nanoparticles (NPs) into the environment can affect the biological and chemical properties of soils. This study evaluated the effects of two commercial metallic copper nanoparticles (Cu-NPs 25 nm; CuNPs/25, and Cu-NPs 40–60 nm; CuNPs/40–60) on enzymatic activity and nutrient bioavailability in an agricultural soil. An incubation experiment was conducted using Ultisol soil treated with 500 mg kg−1 CuNPs/25 or CuNPs/40–60, simulating a high-exposure scenario, in the presence and absence of 200 mg kg−1 P (K2HPO4). Acid phosphatase, alkaline phosphatase, and β-glucosidase enzymatic activities along with P bioavailability were measured at 0.14, 1, 3, 5, and 8 weeks. The results showed that in most instances, 500 mg kg−1 CuNPs/25 or CuNPs/40–60 significantly decreased the activities of acid phosphatase, alkaline phosphatase, and β-glucosidase. The P bioavailability in soil was lower in the presence of CuNPs/25 than Cu-NPs/40–60. In addition, the Cu2+ concentrations in the water-extractable fraction were higher than in the CaCl2 fraction, and the increase in water-extractable Cu2+ concentrations in the soil solution was correlated with a decrease in enzyme activities. Eight weeks of exposure to NPs did not cause any marked changes in organic matter content or electrical conductivity. However, the Cu2+-(DTPA) bioavailability in soil treated with 500 mg kg−1 CuNPs/25 and CuNPs/40–60 for 8 weeks increased over 90 times, regardless of the presence or absence of P. However, these findings should be interpreted in the context of a high-exposure scenario for CuNPs and should not be directly extrapolated to environmentally realistic exposure levels.