Soils worldwide are increasingly contaminated by both microplastics and toxic metals. When these pollutants meet, their combined effects are far more complicated than simple addition. A new review reveals that microplastics can change the mobility, bioavailability, ecological toxicity, and food-chain transfer of heavy metals, but the direction and magnitude of these changes differ substantially among metals.
Published in New Contaminants, the review compares the interactions of microplastics with five priority contaminants: lead, chromium, cadmium, arsenic, and mercury. It also examines how conventional and biodegradable plastics behave under changing soil conditions, including environmental aging, biofilm formation, pH shifts, dissolved organic matter, and redox processes.
"Microplastics should not be viewed simply as passive particles in contaminated soils," said corresponding author Kunlong Hui. "They can serve as surfaces for metal binding, mobile carriers that redistribute contaminants, and interfaces where chemical and biological transformations occur. Importantly, the same plastic can produce very different outcomes for different metals."
The review found that lead is strongly influenced by surface complexation. Weathering creates oxygen-containing groups on microplastics that can bind lead, particularly under neutral or weakly alkaline conditions. However, strong binding does not always reduce risk. Lead attached to mobile plastic particles may still reach plant roots and enter vascular tissues.
Chromium behaves differently because its environmental risk depends heavily on oxidation state. Microplastics can influence not only chromium adsorption but also transformations between Cr(III) and the generally more mobile and toxic Cr(VI). The authors therefore emphasize that chromium must be evaluated as a coupled adsorption and redox system.
For cadmium, changes in bioavailability and rhizosphere chemistry are especially important. Aging and biofilm development may increase cadmium binding, while plastic-induced changes in dissolved organic carbon, microbial communities, acidity, and sulfur cycling can simultaneously increase or decrease the dissolved cadmium available to plants and soil organisms.
Arsenic is controlled by another set of processes, including anionic speciation, competition with iron minerals, and microbial methylation. Biodegradable plastics may release labile carbon during degradation, potentially increasing arsenic mobility or methylation in some soils. Mercury remains the least understood of the five contaminants, but existing evidence suggests that plastic-derived dissolved organic matter may alter mercury methylation, photoreduction, and re-release.
Biodegradable plastics are not automatically environmentally safer in metal-contaminated soils. As they degrade, they can release organic compounds, change microbial activity, and develop reactive surfaces. These processes may produce effects that differ sharply from those of persistent plastics such as polyethylene or polystyrene.
The review also traces impacts across soil ecosystems. Microplastic and metal mixtures can alter microbial communities, impair soil fauna, increase oxidative stress in plants, and facilitate movement through crops, livestock, dust, and food webs. In multimetal soils, contaminants may compete for the same binding sites, causing one metal to become immobilized while another is displaced into a more mobile form.
Based on these findings, the authors propose a metal and polymer-specific remediation framework. Effective treatment should consider the identity and aging state of the plastic, metal speciation, soil pH, organic matter, redox conditions, microbial processes, and the possibility of particle-assisted transport.
Future research should prioritize long-term field studies, realistic multimetal mixtures, biodegradable plastic aging, cross-trophic transfer, and remediation strategies that simultaneously reduce microplastic carrier effects and heavy metal bioavailability.
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Journal reference: Liang X, Wang L, Sun C, Hui K, Zhang J, et al. 2026. The interplay between microplastics and heavy metals in soil: altered risks and differential responses. New Contaminants 2: e018 doi: 10.48130/newcontam-0026-0015
https://www.maxapress.com/article/doi/10.48130/newcontam-0026-0015
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About the Journal:
New Contaminants (e-ISSN 3069-7603) is an open-access journal focusing on research related to emerging pollutants and their remediation.
