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Published on: July 27, 2022
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Polystyrene microplastics reduce Cr(VI) and decrease its aquatic toxicity under simulated sunlight.
Jun Zhang1, Jiating Wei1, Tian Hu1
1Collaborative Innovation Center of Water Security for Water Source Region of Mid-line of South-to-North Diversion Project of Henan Province, School of Water Resources and Environmental Engineering, Nanyang Normal University, Nanyang 473061, China.
Journal of Hazardous Materials
|December 5, 2022
Summary
Polystyrene microplastics (MPs) reduce toxic chromium(VI) to less harmful chromium(III) under sunlight. This process, influenced by various factors, was observed in reservoir water, reducing environmental toxicity.
Area of Science:
- Environmental Chemistry
- Aquatic Toxicology
- Materials Science
Background:
- Microplastics (MPs) are emerging contaminants in aquatic ecosystems.
- MPs can act as vectors for heavy metals like chromium (Cr).
- The role of MPs in Cr species transformation under sunlight remains unclear.
Purpose of the Study:
- To investigate the photoreduction of Cr(VI) to Cr(III) mediated by polystyrene (PS) MPs under sunlight irradiation.
- To elucidate the underlying mechanisms and influencing factors of this MPs-mediated Cr transformation.
- To assess the impact of MPs-mediated Cr reduction on the toxicity of Cr to aquatic organisms.
Main Methods:
- Experiments were conducted using polystyrene MPs and simulated sunlight irradiation.
- Cr(VI) reduction rates were measured, and reactive oxygen species (ROS) were identified.
- The effects of aged MPs, varying MP characteristics, and environmental factors were evaluated.
- Toxicity tests using Lemna minor were performed in reservoir water.
Main Results:
- Polystyrene MPs demonstrated a capacity to photoreduce Cr(VI) to Cr(III) with a rate constant of 0.0023 h-1.
- The reduction was primarily mediated by superoxide radicals (O2•-) and inhibited by singlet oxygen (1O2), hydroxyl radicals (•OH), and triplet PS states (3PS*).
- Aging of PS MPs, light-screening effects, and environmental factors (humic acid, pH, ions, O2) significantly influenced the reduction efficiency.
- Cr(VI) reduction occurred faster in reservoir water than in double distilled water.
- MPs-mediated Cr reduction decreased the oxidative stress on *Lemna minor*.
Conclusions:
- Polystyrene microplastics can transform Cr(VI) to Cr(III) under sunlight, altering chromium's environmental fate and toxicity.
- The photoreduction process is complex, involving specific ROS and influenced by MP properties and environmental conditions.
- This transformation can mitigate the ecotoxicological effects of Cr(VI) in realistic aquatic environments.
