Extraction and decontamination of microplastics from high organic matter soils: A simple, cost-saving and high efficient method

Abstract

This article introduces a simple, cost-saving and high efficient for the extraction and separation of microplastics (MPs) from soil with a high organic matter (SOM) content. In this study, MP with particle sizes of 154-600 μm of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET) were artificially added into the five Mollisols with the high SOM. Three flotation solutions were used to extract these MPs from soils, and four digestion solutions were used to digest the SOM. As well, their destruction effects on MPs were also examined. The results showed that the flotation recovery rates of PE, PP, PS, PVC and PET were 96.1%-99.0% by ZnCl₂ solution, while were 102.0%-107.2% by rapeseed oil, were 100.0%-104.7% by soybean oil. The digestion rate of SOM was 89.3% by H₂SO₄:H₂O₂ (1:40, v:v) at 70 °C for 48 h, and this was higher than by H₂O₂ (30%), NaOH and Fenton's reagent. However, the digestion rate of PE, PP, PS, PVC and PET were 0.0%-0.54% by H₂SO₄:H₂O₂ (1:40, v:v), and this was lower than by H₂O₂ (30%), NaOH and Fenton's reagent. As well, the factors influencing on MP extraction was also discussed. Generally, the best flotation solution was ZnCl₂ (ρ > 1.6 g cm^-3) and the best digestion method was H₂SO₄:H₂O₂ (1:40, v:v) at 70 °C for 48 h. The optimal extraction and digestion method were verified by the known concentrations of MPs (recovery rate of MPs was 95.7-101.7%), and this method was also used to extract MPs from long-term mulching vegetable fields in Mollisols of Northeast China.

Keywords: Digestion; Flotation; Microplastic; Mollisols; Organic matter.