通过屋顶暴露方法模拟聚碳酸酯微塑料在长江水样的长期老化行为

Long-term aging behavior of polycarbonate microplastic in the Yangtze River via a rooftop exposure protocol

由于较低的自然老化速率,微塑料在实际水体长期户外暴露过程中老化行为的数据仍较缺乏.通过聚碳酸酯(Polycarbonate,PC)微塑料在长江表层水样的18个月户外暴露试验以揭示自然老化过程对微塑料表面特征及对金属离子(Cr^(6+)和Co^(2+))吸附行为的重要影响.结果显示,户外暴露改变了PC微塑料的理化性质,包括表面开裂、粒径降低、亲水性和熔点增加以及表面氧化(产生羰基和羟基).同时,户外老化过程明显影响微塑料对金属离子的吸附行为.原始和低老化程度PC对金属离子的吸附主要通过物理作用控制,而高老化程度微塑料由于产生含氧功能团对金属离子的吸附主要由化学过程如络合和共价键等作用控制.并且,不同老化程度PC微塑料对Cr^(6+)和Co^(2+)的吸附性能不同.对于Cr^(6+),PC的吸附性能随其老化程度增加呈先升高后降低的趋势,然而对于Co^(2+),平衡吸附性能随老化程度增加呈增加的趋势.户外老化过程产生含氧官能团、破碎和开裂以及生物膜可能是影响吸附性能的主要因素.本研究证实了长期户外老化过程中微塑料表面特征和吸附性能的变化,为评价实际水环境微塑料污染提供关键的数据支撑.

Owing to low aging rate,information about environmental behavior of microplastics(MPs)during long-term natural exposure processes is still not fully understood.In this study,18 months of outdoor exposure of polycarbonate(PC)MPs in water samples of Yangtze River was conducted to investigate changes of physicochemical properties of PC and their adsorptions of Cr^(6+)and Co^(2+)in water.Results showed that the physicochemical properties were significantly changed during outdoor exposure,including surface cracking,fragmentation,increased hydrophilicity and melting point,and surface oxidation(e.g.carbonyl and hydroxyl groups).Outdoor exposure also altered their adsorptions of metal ions,where the adsorption of metals on pristine and low aged PC was mainly controlled by physical interaction,while the chemical effects,e.g.complexation and covalent interactions were responsible for adsorptions on highly aged MPs due to oxygen functional groups.In addition,aged PC MPs with different degrees exhibited various adsorptions of Cr^(6+)and Co^(2+).For Cr^(6+),adsorption capacities firstly increased,but then decreased as exposure time prolonged.However,for Co^(2+),adsorption capacities were linearly correlated with exposure period.Oxygen functional groups,cracking,fragmentation and biofilm on the aged PC MPs mainly resulted in different adsorption behaviors toward metal ions.The findings revealed important information about environmental behavior of PC MPs during long-term outdoor weathering,which improved the understanding of pollution with PC MPs in the real aquatic environment.