Microplastic and Trace Element Pollution in Farm Soils: A Risk Comparison

Greg Howard
18th September, 2025

Microplastic and Trace Element Pollution in Farm Soils: A Risk Comparison

Representative images of microplastic (MP) categories isolated from agricultural soils in Kirimanjeshwara: a, b films, c, d fragments, and e, f fibres.

Image adapted from: Ashwathi et al. / CC BY (Source)

Key Findings

  • Agricultural soils in coastal Karnataka, India contain microplastics, with higher concentrations found in fields using plastic mulch compared to those without
  • Microplastics were most abundant in surface soils and decreased with depth, with polyethylene being the most common polymer type identified
  • Microplastics present a moderate to high ecological risk, and were found to carry trace elements like iron, zinc, and manganese, potentially impacting soil health
Microplastic pollution is an increasingly recognised global issue, impacting ecosystems worldwide. These small plastic particles, less than 5mm in diameter, originate from the breakdown of larger plastic items and are pervasive in the environment[2]. Concerns stem from their potential ingestion by organisms, bioaccumulation within food chains, and the release of harmful chemicals. Agricultural soils are now recognised as a significant sink for microplastics, yet the extent of contamination and associated ecological risks remain largely unknown. A recent study by researchers at Manipal Academy of Higher Education[1] investigated this issue in coastal agricultural soils from Karnataka, southern India, focusing on the interplay between microplastic presence and trace element concentrations. The study examined soils from two common agricultural practices: fields using plastic mulch (watermelon cultivation) and unmulched fields (rice cultivation). Plastic mulch, a polyethylene film used to suppress weeds and retain moisture, is a known source of microplastic contamination. Researchers collected surface and subsurface soil samples from both types of fields, analysing them for the abundance, size, shape, and polymer composition of microplastics, as well as the concentration of various trace elements. Microplastics were identified using a technique called Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR-FTIR), which essentially identifies the chemical ‘fingerprint’ of different plastic types. The concentration of metals was determined using Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES), a method that measures the light emitted by excited metal atoms. To understand how metals interacted with the microplastics, Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM–EDS) was used to visualize and analyse the elemental composition on the surface of the microplastic particles. The results revealed that surface soils contained significantly higher concentrations of microplastics compared to subsurface soils, as expected. Notably, fields using plastic mulch exhibited substantially higher levels of microplastic accumulation than unmulched fields. Polyethylene (PE) was identified as the dominant polymer type, consistent with the widespread use of polyethylene in agricultural films. The size range of the microplastics was predominantly between 0.1–0.3mm and 0.3–1mm. Film fragments were the most abundant shape, followed by fibres and fragments, with fibres becoming more prevalent in deeper soil layers. Transparent microplastics were the most common colour, alongside blue, white and black particles. To assess the potential risks, the researchers calculated several indices. The Polymer Hazard Index (PHI) indicated a high risk associated with the microplastics present. The Pollution Load Index (PLI) showed low to moderate overall pollution, but was elevated in mulched soils. The Geoaccumulation Index (Igeo) also suggested low to moderate contamination levels. Finally, the Potential Ecological Risk Index (PERI) classified the risk as low to moderate, again with higher values in the mulched fields. Trace element concentrations were highest for iron (Fe), followed by zinc (Zn), manganese (Mn), chromium (Cr), and lead (Pb). This study builds upon previous research highlighting the widespread presence of microplastics in various environmental compartments, including rivers[2]. The Netravathi River study demonstrated the pervasive contamination of a tropical Indian river system, identifying fibres, films and fragments as common microplastic types, with polyethylene and polyethylene terephthalate being the most abundant polymers. The current study extends this knowledge to agricultural soils, revealing a clear link between plastic mulching practices and increased microplastic accumulation. Furthermore, the findings align with research showing that wastewater irrigation contributes significantly to microplastic pollution in agricultural lands[3]. The Konya City study in Türkiye found substantially higher microplastic counts in soils irrigated with treated wastewater, with similar polymer types (PE, film fragments) dominating the samples. Both studies highlight the importance of wastewater management and agricultural practices in controlling microplastic inputs into the environment. Importantly, the Manipal Academy of Higher Education research also investigated the co-occurrence of microplastics and trace elements. The SEM–EDS analysis confirmed the association of metals with the surface of the microplastic particles, suggesting potential implications for metal mobility and bioavailability. This is particularly relevant considering research indicating that microplastics can increase the bioavailability of heavy metals in soils[4], potentially leading to their uptake by plants and entry into the food chain. The study found that the co-occurrence of MPs and metals raises concerns for soil health and food safety. The findings underscore the need for sustainable land management practices, including reducing plastic mulch usage and implementing effective waste management strategies. Regular monitoring of microplastic levels in agricultural soils is also critical to assess long-term risks and inform mitigation efforts.

AgricultureEnvironmentSustainability

References

Main Study

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

Published 14th September, 2025

https://doi.org/10.1007/s10653-025-02746-9

Related Studies

2) The first report on the source-to-sink characterization of microplastic pollution from a riverine environment in tropical India.

https://doi.org/10.1016/j.scitotenv.2020.140377

3) Effects of long-term wastewater irrigation on microplastics pollution in agricultural soil.

https://doi.org/10.1007/s11356-025-36452-x

4) The effects of microplastics on heavy metals bioavailability in soils: a meta-analysis.

https://doi.org/10.1016/j.jhazmat.2023.132369


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