低密度聚乙烯薄膜微塑料在黄河口海岸带环境中的风化特征

海岸带是受气候变化和人类活动双重影响的陆海交互作用地带,也是环境中微塑料的重要汇集区,目前对这些微塑料在海岸环境中的长期风化特征关注较少。以低密度聚乙烯(Low density polyethylene,LDPE)薄膜为供试微塑料,探究其在黄河口潮上带、潮间带和潮下带等不同海岸环境中的长期风化特征。结果表明,经过长达18个月的野外暴露,不同暴露点位的LDPE薄膜微塑料表面均有微生物的定殖,并伴有显著的风化特征。暴露于潮上带地上部的薄膜微塑料表面裂化现象最为显著。所有野外暴露处理的薄膜微塑料表面均有羰基产生,且羰基指数呈潮上带(0.28~0.81)>潮间带(0.18~0.22)>潮下带(0.16~0.20)的趋势。薄膜微塑料的密度随时间和空间的变化并不显著,仅发现经超声清洗去除表面附着物后,潮上带地上部暴露18个月的薄膜微塑料密度(0.85±0.02 g·cm^-3)与新鲜商品塑料(0.93±0.03 g·cm^-3)相比显著降低。综合LDPE薄膜微塑料的表面微形貌特征、化学官能团(羰基指数)以及密度的动态变化等指标表明,黄河口潮上带地上部暴露的LDPE薄膜微塑料风化特征随时间变化最为显著。未来需加强海岸环境中微塑料在复杂环境因子影响下的潜在环境效应与归趋的研究。

Weathering characteristics of microplastics of low density polyethylene film in the coastal environment of the Yellow River Estuary

【Objective】Microplastic pollution has become a global environmental issue that has caused widespread concern.Coastal zone is a region of land-ocean interaction under the dual impacts of global climate change and human activities.It is also an important sink for microplastics in the environment.However,by far little attention has been paid to long-term weathering characteristics of microplastics in coastal environments.In this study,microplastics of low density polyethylene(LDPE)film,which were commonly found in the coastal environments of the Yellow Sea and the Bohai Sea,were selected as the object for test in exploring long-term weathering characteristics of the microplastics in different coastal environments,including supratidal,intertidal and subtidal zones at the Yellow River Estuary.The aim of this study is to lay down a scientific basis for clarifying fates and effects of microplastics in the coastal environments.【Method】Microplastics of LDPE film were left in the tidal zones for exposure to the coastal environment for 12 and 18 months.At the end of the each exposure period,they were retrieved for analysis of surface morphology,chemical functional groups(carbonyl index)and density with scanning electron microscopy,Fourier transform infrared spectrometry,and pycnometry.Weathering degree of the microplastics was characterized.【Result】Results show that after 18 months of exposure in the field,colonies of microorganisms were observed on the surface of the microplastics in all the zones and so were significant weathering characteristics.The microplastics in the supratidal zone exhibited the highest degree of cracking.Carbonyl groups were also observed on the surface of the microplastics regardless of where they were in,and in terms of carbonyl index of the microplastics,the three zones displayed an order of supratidal zone(0.28-0.81)>intertidal zone(0.18-0.22)>subtidal zone(0.16-0.20).The microplastics did not show much spatio-temporal variation in density.However,having been subjected to ultrasonic cleaning for removal of surface attachments,the microplastics exposed aboveground at the supratidal zone for 18 months were by(0.85±0.02 g·cm^-3)significantly lower than the untreated ones(0.93±0.03 g·cm^-3)in density.【Conclusion】The dynamic changes in morphological characteristics,chemical functional groups(carbonyl index)and density of the microplastics of LDPE film indicate that weathering degree of the microplastics varying with the tidal zone shows a declining order of supratidal zone>intertidal zone>subtidal zone,and the microplastics in the supratidal zone varied sharply with time in weathering characteristics.The microplastics in the coastal environment are subjected to physical,chemical and biological weathering,such as light,friction,chemical oxidation,and biodegradation.Among them,light-triggered photochemical oxidation may contribute the most to the weathering of microplastics.In the future,more attention should be paid to the research on potential environmental effects and fate of microplastics as affected by the complex environmental factors in the coastal environment.