Impacts of polyethylene microplastics on bioavailability and toxicity of metals in soil

In this study, we investigated the bioavailability and toxicity of metals (Cu and Ni) in the soil containing polyethylene microplastics (PE-MPs). The bioavailability of the metals determined by the five-step chemical sequential extraction method increased with the addition of MPs (0.1%, 1%, 10%) in the soil, which was confirmed by the adsorption-desorption characteristics. To further examine the bioavailability and toxicity of metals, earthworms (Eisenia fetida) were exposed to soil containing Cu2+ (100 mg/kg) or Ni2+ (40 mg/kg) with different amounts (0.01%, 0.05%, and 0.1%) of PE-MPs for 21 days. The highest concentrations of Cu2+ and Ni2+ in earthworms reached to 73.3 and 36.3 mg/kg, respectively. Moreover, metal concentrations in earthworms increased with MP contents in the soil, which was consistent with the bioavailability measured by the sequential extraction method. Furthermore, changes in biomarkers including peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activity, malondialdehyde (MDA) contents, and related gene expression levels in earthworms suggested that the pollutants caused toxicity to earthworms. Overall, MPs increased the bioavailability of metals in the soil and the toxic effects to earthworms. These findings provide insights regarding the impacts of MPs on the bioavailability of metals and the combined toxic effects of these two kinds of pollutants on terrestrial animals. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that polyethylene microplastics increased the bioavailability of metals in soil and had toxic effects on earthworms. Metal concentrations in earthworms increased with the amount of microplastics in the soil, leading to changes in biomarkers and gene expression levels, causing toxicity to earthworms.