Aggregation is the most fundamental process affecting the fate, transport, and risks of nanoplastics in aquatic environments. Weathering of nanoplastics alters their physiochemical properties and, consequently, aggregation behavior. Herein, we show that two weathering pathways, namely, UV irradiation (the primary aging pathway in surface water) and sulfide-induced transformation (a common process in anoxic environments), affect the aggregation and colloidal stability of polystyrene (PS) nanoplastics differentially. Compared to sulfide-induced aging, UV-induced aging introduced more oxygen-containing functional groups on the nanoplastic surface, although significant amounts of O-functional groups were formed during sulfide-induced aging, owing to hydroxyl radicals formed through the spontaneous oxidation of sulfides. Accordingly, UV-aged PS nanoplastics (PS-UV) exhibited higher stability than sulfide-aged PS nanoplastics (PS-S) in a monovalent cation-dominated solution because of enhanced electrostatic repulsion and weakened van der Waals attraction. However, the stability of PS-UV was lower than that of PS-S in a divalent salt solution considering the bridging effects of divalent ions. These results underline the importance of comprehending the effects of diverse environmental weathering processes on nanoplastics' behaviors, particularly those that readily occur in anoxic environments but are insufficiently investigated.

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风化途径对纳米塑料的胶体稳定性产生不同的影响


聚集是影响纳米塑料在水生环境中的命运、运输和风险的最基本过程。纳米塑料的风化会改变它们的理化性质，从而改变聚集行为。在此，我们表明两种风化途径，即紫外线照射（地表水中的主要老化途径）和硫化物诱导的转化（缺氧环境中的常见过程），对聚苯乙烯 （PS） 纳米塑料的聚集和胶体稳定性的影响不同。与硫化物诱导的老化相比，紫外线诱导的老化在纳米塑料表面引入了更多的含氧官能团，尽管由于硫化物自发氧化形成羟基自由基，硫化物诱导的老化过程中会形成大量的 O 官能团。因此，紫外线老化的 PS 纳米塑料 （PS-UV） 在一价阳离子主导的溶液中表现出比硫化老化的 PS 纳米塑料 （PS-S） 更高的稳定性，因为静电排斥力增强，范德华吸引力减弱。然而，考虑到二价离子的桥接作用，PS-UV 在二价盐溶液中的稳定性低于 PS-S。这些结果强调了理解不同环境风化过程对纳米塑料行为影响的重要性，尤其是那些容易在缺氧环境中发生但研究不足的行为。