Aggregation, Sedimentation and Dissolution of Cu(OH)₂-Nanorods-Based Nanopesticide in Soil Solutions

Along with the development of nanotechnology, nanomaterials have been gradually applied to agriculture in recent years, such as Cu(OH)₂-nanorods-based nanopesticide, an antibacterial agrochemical with a high efficacy. Nevertheless, knowledge about physical stability of Cu(OH)₂ nanopesticide in soil solutions is currently scarce, restricting comprehensive understanding of the fate and risk of Cu(OH)₂ nanopesticide in the soil environment. Herein we investigated aggregation, sedimentation and dissolution of Cu(OH)₂ nanopesticide in soil solutions extracted from three different soil samples, wherein commercial Cu(OH)₂ nanopesticide formulation (NPF), as well as its active ingredient (AI) and laboratory-prepared Cu(OH)₂ nanorods (NR) with similar morphology as AI, were used as model Cu(OH)₂ nanopesticides. We found that NPF compared to AI showed less extents of aggregation in ultrapure water due to the presence of dispersing agent in NPF. Yet, moderated aggregation and sedimentation were observed for Cu(OH)₂ nanopesticide irrespective of NPF, AI or NR when soil solutions were used instead of ultrapure water. The sedimentation rate constants of AI and NPF were 0.023 min^-1 and 0.010 min^-1 in the ultrapure water, whereas the rate constants of 0.003-0.021 min^-1 and 0.002-0.007 min^-1 were observed for AI and NPF in soil solutions, respectively. Besides aggregation and sedimentation, dissolution of Cu(OH)₂ nanopesticide in soil solutions was highly dependent on soil type, wherein pH and organic matter played important roles in dissolution. Although the final concentrations of dissolved copper (1.08-1.37 mg/L) were comparable among different soil solutions incubating 48 mg/L of AI, NPF or NR for 96 h, a gradual increase followed by an equilibrium was only observed in the soil solution from acidic soil (pH 5.16) with the low content of organic matter (1.20 g/kg). This work would shed light on the fate of Cu(OH)₂ nanopesticide in the soil environment, which is necessary for risk assessment of the nanomaterials-based agrochemical.