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The interfacial interaction between typical microplastics and Pb2+ and their combined toxicity to Chlorella pyrenoidosa
Summary
Researchers found that microplastics in freshwater can absorb lead (a toxic heavy metal) onto their surfaces, especially after being weathered by UV light. When combined, the microplastics and lead were more toxic to freshwater algae than either pollutant alone, with PET plastic showing the highest capacity to bind lead. This means microplastics in rivers and lakes may concentrate heavy metals and deliver higher doses of toxins to aquatic life and potentially to people through the water supply.
Microplastics (MPs), a new type of pollutant, have attracted much attention worldwide. MPs are often complexed with other pollutants such as heavy metals, resulting in combined toxicity to organisms in the environment. Studies on the combined toxicity of MPs and heavy metals have usually focused on the marine, while on the freshwater are lacking. In order to understand the combined toxic effects of MPs and heavy metals in the freshwater, five typical MPs (PVC, PE, PP, PS, PET) were selected to investigate the adsorption characteristics of MPs to Pb before and after the MPs aging by ultraviolet (UV) irradiation through static adsorption tests. The results showed that UV aging enhanced adsorption of Pb by MPs. It is noteworthy that MPs-PET had the highest adsorption capacity for Pb, and the interaction between MPs-PET and Pb was the strongest. We specifically selected MPs-PET to study its combined toxicity with Pb to Chlorella pyrenoidosa. In the combined toxicity test, MPs-PET and Pb had significant toxic effects on Chlorella pyrenoidosa in the individual exposure, and the toxicity of individual Pb exposure was greater than that of individual MPs-PET exposure. In the combined exposure, when MPs-PET and Pb without adsorption (MPs-PET/Pb), MPs-PET and Pb had a synergistic effect, which would produce strong physical and chemical stress on Chlorella pyrenoidosa simultaneously, and the toxic effect was the most significant. After the adsorption of MPs-PET and Pb (MPs-PET@Pb), the concentration and activity of Pb decreased due to the adsorption and fixation of MPs-PET, and the chemical stress on Chlorella pyrenoidosa was reduced, but the physical stress of MPs-PET still existed and posed a serious threat to the survival of Chlorella pyrenoidosa. This study has provided a theoretical basis for further assessment of the potential environmental risks of MPs in combination with other pollutants such as heavy metals.
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