Method for quantitative extraction of copper hydroxide nanoparticles from farmland soil

With the development of nanotechnology, nano-pesticides have been developed and show better application effects than traditional pesticides, which have a good development prospect. Copper hydroxide nanoparticles (Cu(OH)2 NPs) are one of the specific fungicides. However, there is still no reliable method to evaluate their environmental processes, which is essential for the broad application of new pesticides. Since soil is a vital link between pesticides and crops, this study took linear and slightly soluble Cu(OH)2 NPs as the research object and established a method to quantitatively extract Cu(OH)2 NPs from the soil. Five essential parameters in the extraction process were optimized first, and then the extraction effect of this optimal method was further tested under different nanoparticles and soil conditions. The optimal extraction method was determined, including (i) Dispersant: 0.2 % carboxymethyl cellulose (CMC) with a molecular weight of 250,000; (ii) Mixing conditions of soil and dispersant: water bath shaking for 30 min, water bath ultrasonication for 10 min (energy of the ultrasonication = 6 kJ/ml); (iii) Phase separation conditions: settlement for 60 min; (iv) Solid-to-liquid ratio: 1:20; (v) 1 extraction cycle. After optimization, 81.5 % of the supernatant was Cu(OH)2 NPs, and 2.6 % was dissolved copper ions (Cu2+). This method showed good applicability to different concentrations of Cu(OH)2 NPs and different farmland soils. It also showed significant differences in the extraction rates of copper oxide nanoparticles (CuO NPs), Cu2+, and other copper sources. The addition of a small amount of silica was confirmed to improve the extraction rate of Cu(OH)2 NPs. The establishment of this method lays the foundation for the quantitative analysis of nano-pesticides and other non-spherical and slightly soluble nanoparticles.