Enhanced adsorption and cytotoxicity of hydrothermally aged microplastics for volatile organic compounds in sludge

Microplastics, while widely recognized as an environmental hazard, are particularly prevalent in sludge from wastewater treatment plants. This study addresses the gap in knowledge regarding the impact of hydrothermal treatment on the fate and behavior of microplastics in such settings. We explored the adsorptive interactions of polylactic acid (PLA-MPs) with volatile organic compounds (VOCs) post-hydrothermal aging and assessed the implications on cytotoxicity. Upon hydrothermal treatment, PLA-MPs exhibited a porous, honeycomb-like structure and a significant reduction in crystallinity, suggesting altered physical properties. Hydrothermal aging was shown to increase the hydrophilicity of PLA-MPs, which, coupled with structural changes, facilitated enhanced adsorption of VOCs, notably at elevated temperatures. We hypothesize that the observed increase in VOC adsorption is partly due to the exposure of more amorphous regions, thereby providing additional adsorption sites. The rise in hydrophilicity may also suggest a higher affinity for polar VOCs, potentially via hydrogen bonding with functional groups on the microplastic surface. Our results demonstrated that PLA-MPs aged at 140 °C had a toluene adsorption capacity of 62.17 ± 0.85 mg/g, a significant increase compared to unaged PLA-MPs, which adsorbed 22.25 ± 1.35 mg/g. In cytotoxicity assays, these aged microplastics significantly diminished cell viability at high doses, underscoring the enhanced potential for cytotoxic effects post-aging. Our research underlines the necessity for a deeper understanding of the interactions between aged microplastics and VOCs, paving the way for future studies to mitigate the environmental impact of microplastics from sludge sources.