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Releasing characteristics of toxic chemicals from polystyrene microplastics in the aqueous environment during photoaging process
Summary
This study revealed that as polystyrene microplastics age under UV light, they release a growing number of toxic chemicals including organic compounds and heavy metals into surrounding water. The rate of chemical release increased dramatically with aging time, meaning that weathered microplastics in the environment are more chemically hazardous than fresh ones, with implications for water quality and human exposure.
Microplastics (MPs) are pervasive in the environment and inevitably undergo photoaging due to UV irradiation. This study delved into the dynamic releasing and transformation process of toxic chemicals from polystyrene microplastics (PS MPs) during photoaging, a subject that remains underexplored. It was revealed that photoaging led to substantial alterations in the physicochemical properties of PS MPs, initiating polymer chain scission and facilitating the release of a large number of toxic chemicals, including numerous organic compounds and several inorganic compounds. The kinetic analysis revealed a dynamic release pattern for PS MPs, where under varying UV intensities (2, 5, and 10 mW/cm), the release rate (k) initially increased and then decreased, peaking at a total irradiation energy of approximately 7 kW·h/m. Furthermore, chemicals in leachate were transformed into compounds with smaller molecular weight, higher oxidized and greater unsaturated state over the prolonged photoaging. This transformation was primarily attributed to two reasons. Firstly, the aged PS MPs released chemicals with higher oxidized state compared to the pristine MPs. Secondly, the chemicals previously released underwent further reactions. Besides, among the complex leachate generated by aged PS MPs, the organic chemicals characterized by small molecular weight and high oxidized state exhibited notable acute toxicity, whereas heavy metal ions showed lesser toxicity, and anions were non-toxic. This study shed more light on the photoaging process of PS MPs, releasing characteristics of organic chemicals, and the potential environmental risks associated with plastic wastes.