Atmospheric cold plasma as a novel approach to remediating microplastics pollution in water

Microplastics (MPs) have become an environmental and health threat to aquatic species and humans because they are small and can easily reach water bodies for municipal and agricultural uses. MPs have been traced in food commodities and products derived from animals and even found in bottles of drinking water. Current treatment techniques for permanently destroying MPs require high energy inputs and thus are generally cost-inefficient. Atmospheric cold plasma (ACP) is a low-cost energy-efficient technology to produce highly reactive species that can induce physicochemical changes in plastic polymers. This study, for the first time, used ACP as a novel method for MPs treatment. Polypropylene (PP) and low-density polyethylene (LDPE) were used to prepare model MPs. The effects of plasma working gas (oxygen, nitrogen, or their mixture) and post-ACP treatment storage (24 h) on MPs were studied. ACP treatments for 30 min successfully degraded both MPs, by 1.4-11.3% in weight. PP MPs had larger weight reduction than LDPE and the ACP of mixture gas was most effective. PP MPs also showed increased carbonyl index after treatments, to up to 6.89, indicating hydrolytic degradation. For LDPE MPs, oxygen ACP caused more oxidation, but storage did not have an enhancing effect. The results of physicochemical analyses indicated that MPs degradation by ACP was possibly mainly through oxidative and hydrolytic reactions, but further characterizations are needed. This study proves that ACP is a promising strategy to remediate MPs pollution, and thus has great potential for addressing the severe challenges of MPs that the food and agriculture sectors are currently facing.