Comparative retention of polypropylene and polyvinyl chloride microplastics in sand, clay, and silt loam soils under...

Microplastic pollution in agricultural soils poses growing environmental risks, yet the retention behavior of different polymer types across contrasting soil textures remains poorly understood. This study compared the retention of polypropylene (PP) and polyvinyl chloride (PVC) microplastics (< 50 μm) in sand, clay, and silt loam soils using a single initial microplastic concentration under a standardized 72 h batch contact condition. Retention was quantified by solution depletion, in which the microplastic mass removed from the aqueous phase was normalized to oven-dry soil mass to obtain the retained amount at 72 h (qₑ). A soil-free control confirmed acceptable procedural recovery (~ 95%). The retained amount at 72 h differed significantly among the six microplastic-soil combinations (one-way ANOVA, p = 0.0001), ranging from 157.14 to 585.71 mg/kg. PVC in silt loam showed the highest retention (585.71 mg/kg), whereas PP in silt loam showed the lowest (157.14 mg/kg), indicating that retention was governed by the combination of polymer type and soil texture rather than by any single soil property. Pearson's correlation analysis did not identify a statistically significant association between retention and organic matter, cation exchange capacity, or clay content (all p > 0.5, n = 6). Scanning electron microscopy provided visual evidence of microplastic attachment to soil surfaces. These findings provide a comparative basis for microplastic retention behavior in agricultural soils and highlight the need for future multi-concentration adsorption isotherm studies to establish mechanistic property-retention relationships.