Microplastics in Plastic-Mulched Sandy Soil: Abundance, Characterization, Heavy Metal Accumulation and Risks in Agricultural Fields

Abstract Microplastics (MPs) significantly impact soil quality and crop health, especially in agricultural systems using plastic mulch and sewage sludge. Detailed studies on their diversity, composition and association with co-contaminants are essential. Therefore, the present study attempted to investigate MP abundance across ten agricultural field soils compared to a control site. Initially, soil physicochemical parameters were analyzed using standard protocols. Subsequently, soil samples underwent H2O2 digestion and density separation for MP enumeration and morphological characterization, complemented by ATR-FTIR polymer analysis. Results indicated higher MP concentrations in mulched fields (1412 ± 529 particles) compared to the control (72 ± 41 particles). MPs predominantly comprised fibers, films, fragments, and pellets. Pearson’s correlation revealed positive associations with soil clay, moisture, and organic matter. ANOVA showed significant variations in MP counts among sites and particle types. FTIR analysis identified eight polymer types, with the microplastic Pollution Load Index ranging from 1.97 to 4.43, suggesting increasing contamination. Moreover, MP counts correlated positively with years of mulching (r2 = 0.46 to 0.94). Heavy metal analysis indicated significant accumulation (Fe > Mg > Ni > Cr > Mn > Zn > Cu > Co > Pb > As > Cd) within MP particles. These findings highlight the dual threat of plastic mulching and sewage sludge on agricultural soil is leading to accumulation of diverse MPs in agricultural soil and their interaction with trace elements can pose considerable risks to soil quality, plant productivity, and environmental health.