Influence of polyethylene-microplastic on environmental behaviors of metals in soil

Microplastics (MPs) in terrestrial ecosystems have attracted increasing attention all over the world. The adsorption-desorption behavior and bioavailability of metals in soil would affect its toxicity to organisms. However, the influences of MPs on adsorption-desorption behavior between metals and soil as well as bioavailability of metals in soils are scarcely investigated. Herein, different percentage (0, 0.1%, 1%, 10%) of polyethylene-microplastic (PE-MP) were thoroughly mixed into the soil to investigate the impacts of PE-MP on adsorption-desorption and bioavailability of metals (Zn2+, Pb2+) in the soil. A series of characterization were carried out to determine the change of PE-MP before and after adsorption to investigate the mechanisms. When MP100 (average size: 129 mu m) content in soil increased to 10%, the adsorption capacities of soil with Pb2+ and Zn2+ were 3.73 and 4.56 mg/g, respectively, which were significantly (p < 0.05) lower than that of pure soil. When MP300 (average size: 293 mu m) content in soil increased to 10%, the extraction fraction of Zn2+ and Pb2+ from soil by diethylenetriaminepentaacetic acid reached 12.35% and 23.96%, respectively, which were significantly (p < 0.05) higher than that of pure soil, indicating high concentration (10%) of MPs in soil would decrease the adsorption capability of soil to metals and increase the mobility of metals in terrestrial environment. However, when MPs content in soil was 0.1%, the extraction fraction of Zn2+ and Pb2+ showed no significant difference with that of pure soil, indicating that actual MPs in soil is unlikely to bring significant influence on metal bioavailability.

Automated summary

The study found that when the concentration of PE-MPs in soil increased to 10%, the adsorption capacities of soil for Pb2+ and Zn2+ were significantly lower compared to pure soil. In addition, when the concentration of PE-MPs in soil increased to 10%, the extraction fraction of Zn2+ and Pb2+ by diethylenetriaminepentaacetic acid was significantly higher, indicating that a high concentration of MPs in soil can decrease the adsorption capability of soil for metals and increase metal mobility in terrestrial environment. However, when the content of MPs in soil was 0.1%, there was no significant difference in the extraction fraction of Zn2+ and Pb2+ compared to pure soil, suggesting that actual MPs in soil are unlikely to significantly influence metal bioavailability.