淡水系统中4种塑料颗粒的老化过程及DOC产物分析

淡水系统中的微塑料污染及其生态效应已经引起国内外学者的广泛关注，但关于不同类型微塑料在自然环境中的老化研究较少.为探究不同类型微塑料的老化过程，分析老化产物，以4种水体中常见的微塑料聚丙乙烯（polystyrene，PS）、低密度聚乙烯（low-density polyethylene，LDPE）、聚丙烯（polypropylene，PP）和聚羟基丁酸（polyhydroxybutyrate，PHB）为研究对象，进行了40 d的自然光老化实验.结果表明：①在老化过程中，4种不同类型塑料老化析出液水质指标pH、ORP、EC和DO均产生不同程度的上升或下降趋势.②经扫描电镜（scanning electron microscope，SEM）观测发现LDPE表面形态变化最大，已经形成裂纹和孔洞.傅立叶红外检测发现，实验中LDPE的羰基指数增加程度最大，增加了31.48%.③微塑料老化会产生溶解态产物，即溶解性有机碳（dissolved organic carbon，DOC），DOC质量浓度随老化时间增加而增加，与本底值相比，老化40 d的PHB、PP和LDPE微塑料析出液中DOC质量浓度增加显著，分别增加了61.29%、69.49%和89.15%.以上结果表明经自然光照射，塑料会在自然水体中出现明显的老化，并释放出有机物，由此带来的生态效应应受到更多的关注和研究.

Aging Process and DOC Analysis of Four Different Types of Plastic Particles in Freshwater Systems

Although the pollution of freshwater systems by microplastics and the resulting ecological effects have attracted widespread attention from scholars at home and abroad, the fragmentation of different types of microplastics in the natural environment has not yet received enough attention. To analyze the fragmentation processes and products of different types of microplastics, a 40 d natural light fragmentation experiment was carried out using four microplastics commonly found in water:polystyrene (PS), low-density polyethylene (LDPE), polypropylene (PP), and polyhydroxybutyrate (PHB). The pH, ORP, EC, and DO of the four types of plastic-aging liquids changed significantly during the aging process. During the weathering process, cracks and pores formed on the surface of LDPE and were later identified through scanning electron microscopy. Fourier transform infrared spectrometry indicated that the carbonyl index of LDPE increased the most in the experiment (an increase of 31.48%), suggesting that PP experienced significant aging. Dissolved organic carbon (DOC), a product of microplastics fragmentation, increased as weathering time progressed, and the concentration of DOC increased significantly after weathering for about 40 d. Compared with the baseline value, the concentration of DOC from PHB, PP, and LDPE in the leaching solution increased significantly, by 61.29%, 69.49%, and 89.15%, respectively. These results suggest that evident aging of microplastics in natural aquatic environments releases significant amounts of dissolved organic matter, and the ecological effects of this should be the subject of future research.