Application of Various Methods to Extract Microplastic from Typical Soils in China

Abstract

Microplastics have been found in many environmental systems, such as oceans, terrestrial soils, sediments, and bodies of freshwater. Microplastic pollution in soils has received extensive international attention; however, there is currently no unified standard extraction method. To identify appropriate extraction and component identification methods for microplastics in typical soils in China, samples were identified and their polymer component properties examined using ATR-FTIR(Thermo Nicolet IS 20). The effects of three treatments of water+oil(T1), a saturated NaCl solution+oil(T2), and a saturated NaCl solution(T3) on the detection of four types of microplastics[polyethylene terephthalate(PET), polypropylene(PP), polystyrene(PS), and polyethylene(PE)]in four typical soils(loess, black soil, red soil, and purple soil) were examined. The results showed that:① The extraction rates of the T3 treatment decreased with microplastic density. For PP, PE, and PS, the extraction rates exceeded 86.67%, and the extraction rates of PET were 0%-13.30%. ② The extraction rates of the four kinds of microplastics were 86.67%-100.00% in loess, black soil, and purple soil using the T1 and T2 solutions; however, the residual oil on the surface of microplastics influenced the identification using FTIR. Furthermore, the cleaning effect of PE and PS was poor after wiping with anhydrous ethanol. ③ In red soil, the extraction rates of PET were 56.60% and 50.00% in T1 and T2, respectively; in the T3 treatment, the extraction rates of PET, PE, and PP were 3.33%, 10.00%, and 56.67%, respectively. These results show that the extraction rates of four types microplastics are highest for loess, black soil, and purple soil using T1 and T2, although these two methods need to be combined with anhydrous ethanol cleaning. T3 dispose making the leak of microplastics PET with the density higher than 1 g·cm-3. Methods to extract microplastics from red soils require further research. Overall, this study can inform the investigation and treatment of microplastic pollution in typical regional soils in China.