Effect of Exogenous Addition of Microplastics on the Ability of Plants and Soil to Accumulate Thallium

Thallium (Tl) contamination of soils in lead-zinc mining areas poses potential ecological risks, and the impact of microplastics on Tl accumulation by hyperaccumulator plants remains unclear. This study examined soils collected from the Daliangzi lead-zinc mining area to investigate the characteristics of Tl contamination. These soil samples were used in plant cultivation experiments. The thallium contents in both the soil and plant samples were determined using acid digestion followed by inductively coupled plasma mass spectrometry (ICP-MS). The contamination level, plant enrichment capacity, and ecological risk were then comprehensively evaluated through the Geo-accumulation index (<i>I_geo</i>), Bioconcentration factor (BCF), and potential ecological risk index. The results indicated that the <i>I_geo</i> of Tl in the soil was 2.413, corresponding to a moderately to heavily polluted level, which necessitates focused attention. Polyethylene exhibited markedly opposing effects on <i>Pteris vittata</i> and <i>Solanum nigrum</i>: it significantly promoted Tl accumulation in the former, while distinctly inhibiting it in the latter. Microplastics could modify the pH value of soil, as well as the contents of nitrogen (N) and phosphorus (P). Risk assessment indices indicated that Tl pollution in this region reaches a very high contamination level with moderate potential ecological risk. Polyethylene and polypropylene demonstrated a species-specific promoting effect on Tl adsorption by the two hyperaccumulator plants, with polyethylene significantly enhancing the Tl accumulation capacity of <i>P. vittata</i> and polypropylene distinctly promoting Tl adsorption in <i>S. nigrum</i>.