Microplastic and trace element contamination in coastal agricultural soils of southern India: a comparative risk assessment of mulched and unmulched fields

Abstract

This study investigates the occurrence and ecological risks of microplastics (MPs) and trace elements in coastal agricultural soils from Karnataka, southern India. Surface and subsurface soils from mulched (watermelon) and unmulched (rice) fields were analyzed for MP abundance, morphology, polymer composition, and trace elements. Microplastics were identified using Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR-FTIR), and metals were quantified via Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES). Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM–EDS) confirmed elemental associations on MP surfaces. Risk was assessed using the Polymer Hazard Index (PHI), Pollution Load Index (PLI), Geoaccumulation Index (I geo ), and Potential Ecological Risk Index (PERI). Results showed higher MP concentrations in surface soils and mulched fields, with polyethylene (PE) as the dominant polymer. Most MPs were 0.1–0.3 mm (49–50%) or 0.3–1 mm (40–47%) in size. Films were the most common type (61%), followed by fibres and fragments, with fibres dominating deeper layers. Transparent MPs were the most abundant, followed by blue, white, and black. The Polymer Hazard Index (PHI) indicated high risk. The Coefficient of Microplastic Impact (CMPI) showed a moderate impact, while the Pollution Load Index (PLI) values for MPs indicated low to moderate pollution, with particularly elevated levels in mulched soils. The Potential Ecological Risk Index (PERI) classified risk levels as low to moderate, with higher values also observed in mulched fields. Among trace elements, the concentration followed the order: Fe > Zn > Mn > Cr > Pb. While PLI and I geo suggested low to moderate contamination, PERI indicated low ecological risk. These findings highlight how plastic mulching increases MP accumulation and alters metal dynamics in soil. The co-occurrence of MPs and metals raises concerns for soil health and food safety. Sustainable land management and regular monitoring are critical to mitigate long-term risks. Graphical abstract

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