Identifying an accurate and efficient approach to soil organic matter removal for quantifying microplastics in agricultural soils

For efficient microplastic (MP) separation, there is a need to remove the soil organic matter (SOM), which interferes with MP extraction.However, the efficient SOM removal strategy from agricultural soils remain under debate.Therefore, this study investigated the SOM decomposition efficiency and MP recovery yield under varying environmental temperatures (i.e., 0, 20, and 40℃) conditions using five different removal solutions in three types of agricultural soil (i.e., upland, orchard, and greenhouse soils).Considering the thermal sensitivity and characteristics of MP samples, the study aimed to identify pre-treatment conditions that effectively decompose SOM content without significantly compromising MP recovery yield.Soil samples containing 1% (w/w) polystyrene (PS) particles were subjected to distilled water, acid-digestion (HNO 3 ), alkaline-digestion (KOH), and oxidative (H 2 O 2 and Fenton [H 2 O 2 + FeSO 4 ]) treatments, followed by density-separation using NaCl solution (1.21 g•cm -3 ), and the PS recovery rate was quantified after oven-drying.The SOM decomposition accelerated with increasing environmental temperature, and the its highest efficiency, which reduced SOM content by 44, 36, and 29%, were observed in the Fenton reagent-applied upland, orchard, and greenhouse soils, respectively.The MP recovery rates were positively correlated with SOM decomposition efficiency, and the oxidation reaction consistently yielded higher MP recovery yield than other approaches.However, the H 2 O 2 treatment led to variable MP losses, particularly in low-organic soils, suggesting possible MP degradation during excessive oxidation.Hence, treating agricultural soil with the Fenton reagent at 40℃ condition was found to be the most effective strategy for decomposing SOM content while maintaining MP integrity.