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Polyethylene and polylactic acid microplastics affect the migration of Cr(VI) and Cr(III) in acidic clay soil via distinct mechanisms
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This study found that both conventional polyethylene and biodegradable PLA microplastics in agricultural soil reduce the soil's ability to hold chromium, causing more of the toxic heavy metal to move through the soil profile — with aged microplastics being more disruptive than pristine ones. The two chromium forms (Cr(VI) and Cr(III)) behaved differently, with microplastics primarily inhibiting migration of the more dangerous Cr(VI). These findings matter because they show microplastic contamination in farmland can worsen the spread of heavy metals, compounding risks to groundwater and food crops.
The coexistence of microplastics (MPs) and heavy metals in agricultural soils leads to complex interactions during their adsorption and migration processes. Understanding their fate under realistic soil conditions is crucial for assessing the associated environmental risks. Therefore, virgin and aged polyethylene (PE) and polylactic acid (PLA) MPs were used to investigate their influence on the adsorption and migration of chromium (Cr) in unsaturated steady-state soils via batch and column experiments. Batch experiments revealed that soil adsorbed less Cr(VI) than Cr(III) (0.44 vs. 1.45 mg/g). The addition of MPs inhibited Cr adsorption (specifically, 0.40 and 1.23 mg/g for Cr(VI) and Cr(III), respectively, at 7% MP addition), with adsorption capacity decreasing as MP dosage increased. Column experiments showed Cr(VI) reached adsorption equilibrium faster than Cr(III) (25 vs. 41 pore volumes); its migration was primarily controlled by soil hydraulic conditions, and MPs exerted an inhibitory effect. In contrast, Cr(III) migration was predominantly governed by adsorption, and MP addition promoted its migration. Regarding the MPs themselves, PE exhibits greater migration capacity, which decreased with aging, whereas PLA showed the opposite trend. Interestingly, the presence of Cr(III) reduces the migration of MPs compared to Cr(VI). These findings clarify the effects and mechanisms of MPs on Cr migration under realistic soil conditions, and enhance the understanding of migration dynamics and environmental fate of coexisting pollutants.
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Researchers conducted a five-year experiment examining how microplastics affect the chemical forms and bioavailability of heavy metals across five different soil types. They found that microplastics generally reduced the readily available forms of heavy metals while increasing the mineral- and organic-bound forms, and that the bioconcentration of chromium and lead decreased substantially. The study suggests that soil type and exposure duration both play important roles in how microplastics influence heavy metal behavior in soils.
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Environmental-simulating microplastics (aged under environmental conditions) showed higher cadmium and chromium adsorption capacity than commercial microplastics in agricultural soil solutions, with surface oxidation increasing adsorption—suggesting that aged microplastics are more effective co-transporters of heavy metals in contaminated agricultural soils.
Microplastics alter Cr accumulation and fruit quality in Cr(VI) contaminated soil-cucumber system during the lifecycle: Insight from rhizosphere bacteria and root metabolism
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Researchers studied how three types of microplastics affect chromium accumulation and fruit quality in cucumbers grown in contaminated soil across a full growing cycle. They found that polyethylene microplastics increased chromium uptake in plant tissues, while polyamide and polylactic acid microplastics decreased it, with each type altering root bacteria and plant metabolism differently. The study reveals that the type of microplastic present in agricultural soil can significantly influence how crops absorb heavy metal contaminants.
Influence of polyethylene-microplastic on environmental behaviors of metals in soil
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Researchers investigated how polyethylene microplastics affect the adsorption, desorption, and bioavailability of heavy metals in soil. They found that adding microplastics altered how metals bind to soil particles and increased the mobility of certain metals like cadmium and lead. The study suggests that microplastic contamination in soils may change the environmental behavior of heavy metals, potentially increasing their availability to plants and soil organisms.
Aging properties of polyethylene and polylactic acid microplastics and their adsorption behavior of Cd(II) and Cr(VI) in aquatic environments
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Researchers compared how polyethylene and polylactic acid (PLA) microplastics age in the environment and how that aging affects their ability to absorb heavy metals like cadmium and chromium from water. They found that aging changed the surface chemistry of both plastic types, increasing their capacity to pick up these toxic metals. The findings matter because aged microplastics in the environment may concentrate and transport more pollutants than fresh plastic particles.
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