Key Laboratory of Yangtze River Water Environment of the Ministry of Education, College of Environmental Science and Engineering , Tongji University , Shanghai 200092 , China.
Department of Earth and Environmental Science, Meadowlands Environmental Research Institute , Rutgers University Newark , Lyndhurst 07071 , New Jersey United States.
Environ Sci Technol. 2019 Sep 17;53(18):10741-10752. doi: 10.1021/acs.est.9b03428. Epub 2019 Aug 23.
Photochemical weathering leads to degradation of microplastics and releases chemical additives, polymeric fragments, and/or byproducts. This study evaluated the release kinetics of organotin compounds (OTCs) from three different sized (10-300 μm) polyvinyl chloride (PVC) microplastics under UV- and visible light irradiation. Four OTCs, dimethyltin (DMT), monomethyltin (MMT), dibutyltin (DBT), and monobutyltin (MBT), were found to release from PVC particles after 24 h leaching in darkness ranging from 2 to 20 μg·g-PVC. Under UV/visible light irradiation, only DMT and DBT were detectable, whereas MMT and MBT were not detected due to rapid photodegradation. The total tin concentrations (including organic and inorganic tins) in the aqueous phase monotonically increased under light exposure. By contrast, they reached plateaus after 24 h in darkness, confirming the photodegradation of OTCs. A release kinetics model was established and correctly interpreted the microplastics size effect on the OTC release process. Finally, the impacts of salinity and dissolved organic matter (DOM) were investigated. The release and photodegradation of OTCs were both inhibited at high salinity conditions, probably due to the enhanced readsorption of OTCs on PVC microplastics and the formation of halogen radicals that were less reactive toward neutral OTCs. The presence of DOM, however, increased OTCs release probably because the excited state triplet DOM (DOM*) formed and reacted with OTCs from PVC microplastics.
光化学风化导致微塑料降解，并释放化学添加剂、聚合碎片和/或副产物。本研究评估了三种不同尺寸（10-300 μm）聚氯乙烯（PVC）微塑料在紫外光和可见光照射下释放有机锡化合物（OTCs）的释放动力学。在黑暗中浸泡 24 小时后，发现四种 OTCs（二甲基锡（DMT）、甲基锡（MMT）、二丁基锡（DBT）和丁基锡（MBT））从 PVC 颗粒中释放出来，释放量范围为 2 至 20 μg·g-PVC。在紫外/可见光照射下，只有 DMT 和 DBT 可检测到，而 MMT 和 MBT 由于快速光降解而未检测到。在光照下，水相中的总锡浓度（包括有机和无机锡）呈单调增加。相比之下，在黑暗中 24 小时后达到平台，证实了 OTCs 的光降解。建立了释放动力学模型，并正确解释了微塑料尺寸对 OTC 释放过程的影响。最后，研究了盐度和溶解有机物（DOM）的影响。在高盐条件下，OTCs 的释放和光降解均受到抑制，这可能是由于 OTCs 在 PVC 微塑料上的增强再吸附以及对中性 OTCs 反应性较低的卤代自由基的形成所致。然而，DOM 的存在增加了 OTCs 的释放，这可能是因为形成了激发态三重态 DOM（DOM*）并与 PVC 微塑料中的 OTCs 反应。
