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Agronomic practices and road proximity drive plastic pollution in agricultural soils: Insights from Bihar, India on weathering, elemental association, and ecological risk
Summary
Researchers surveyed 22 agricultural sites in Bihar, India, measuring microplastic contamination in soil across different farming practices and road distances. Mulched fields near roads had the highest concentrations (up to 1,460 particles/kg), while PE and PP polymers dominated, and microplastics were found to adsorb multiple heavy metals including lead, arsenic, and cadmium.
The widespread use of plastics in agriculture, particularly through mulching and polyhouse practices, has intensified concerns over soil contamination. However, limited research has addressed how spatial factors and agronomic practices, such as proximity to roads and mulching, influence macroplastics (MaP) and microplastics (MP) distribution in agricultural soils, particularly in India. This study assessed plastic contamination across 22 sites in six districts of Bihar, revealing mean MaP concentrations of 7.5 ± 3.6 particles kg soil (d.w.) and MP levels ranging from 150 to 1460 particles kg soil. MP concentrations were highest in mulched fields near roads (803 ± 371 particles kg), followed by distant mulched sites (657 ± 143 particles kg). Elevated levels were observed even in unmulched near-road fields (494 ± 327 particles kg), while the unmulched, distant fields (335 ± 76 particles kg) had the least contamination, indicating a combined influence of agricultural practices and road proximity. Polymer characterization revealed four types of MPs (PP > PE > PET > PS), with PE and PP accounting for over 95 % of the total. Weathering assessment via carbonyl index (CI) showed significantly higher values in MPs than MaPs, and field-extracted mulch films exhibited reduced contact angles relative to pristine films, indicating increased surface oxidation and hydrophilicity. Furthermore, MPs were found to adsorb multiple heavy metals, including Pb, Cu, Cr, Cd, Co, As, and Zn, highlighting risks of co-contaminant transport. Based on the MultiMP framework, all field types were classified as high-risk for MPs related impacts. These findings emphasize the need for sustainable plastic use in agriculture and call for targeted policy measures, including improved disposal practices and adoption of biodegradable alternatives, to mitigate long-term soil degradation and ecological harm.
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