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.
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