Determination of microplastics in agricultural soil by double-shot pyrolysis-gas chromatography combined with two-step extraction.

A method for the determination of five microplastics in agricultural soil was established by double-shot pyrolysis-gas chromatography combined with two-step extraction. First, polycarbonate (PC), polystyrene (PS), polypropylene (PP), and polyethylene (PE) were extracted from soil samples using a mixed solvent of cyclohexanone and p-xylene, and then PE terephthalate was extracted with m-methylphenol. Subsequently, PC and PE terephthalate were analyzed by thermochemolysis, and PE, PP, and PS were investigated by direct pyrolysis at 600°C. The linearity of the method was satisfactory for five microplastics and the correlation coefficients were higher than 0.97 in the respective concentration range. The limits of detection and the limits of quantification were 0.2-10.0 and 0.5-20.0 μg/g, respectively. The method provided recoveries of 75.1%-141.5%, with acceptable repeatability within 20.0%. It was a supplementary method for the existing characterization of microplastics in agricultural soil.