Enzymatic purification of microplastics in soil

Accurate and effective analysis of microplastics depends on the purification of any biogenic matter present in the environmental sample. Within the soil environment, the presence of biogenic materials (living and non-living) obstruct reliable identification of microplastics. However, while conventional acidic, alkaline, and wet peroxidation methods are often used for microplastics purification, they can result in significant alteration to the polymer integrity. To overcome this issue of polymer damage, we have developed a more efficient protocol using enzymes to eliminate organic materials from soil media without affecting the synthetic polymers. This method describes a simple enzymatic protocol that eliminates the organic matter based on the application of enzymes that target the three natural components of lignocellulosic biomass (cellulose, hemicellulose, and lignin). The enzymatic protocol introduced in this study allows for the use of an oxidizing agent for the pre-treatment of samples and density separation step. Additionally, this method was used to determine the enzymatic digestion efficiencies of soil organic matter and recovery rates of microplastics. Finally, the recovered microplastics were characterized by techniques including stereomicroscopy, FT-IR, and SEM. This method proved to be effective in reducing approximately >90% of organic materials in soil samples. After showing a high digestion efficiency the method was applied to spiked microplastic soil samples where high recovery rates were established and plastic characteristics were conserved. Despite being a time consuming and expensive method when compared to other purification methods. The key benefits of this methodology are:•Minimal sample preparation•Representative purification of microplastic from diverse soil media; and•Most importantly, preservation of polymer integrity aiding requirements needed for particle identification (e.g.,% mass polymer remaining, SEM images revealing no obvious polymer morphology change after enzyme treatment).