Abstract：
Octylisothiazolinone (OIT) and Dichlorooctylisothiazolinone (DCOIT), widely used antibacterial agents in coatings, have seen a sharp increase in use in response to the Coronavirus disease 2019 (Covid-19) pandemic, ultimately leading to their increase in the aquatic environment. However, their photodegradation process in surface water is still unclear. The purpose of this study is to investigate the photodegradation kinetics and mechanisms of OIT and DCOIT in natural water environments. Under simulated solar irradiation, they undergo direct photolysis in both natural freshwater and seawater mainly via their excited singlet states, while no self-sensitization photolysis was observed. The direct photolysis rate constants of OIT and DCOIT were 1.19 ± 0.07 and 0.57 ± 0.03 h-1, respectively. In addition, dissolved organic matter (DOM), NO3- and Cl- in natural waters did not contribute significantly to the photodegradation, and the light screening effect of DOM was identified as the main inhibiting factor. The photodegradation half-life of OIT was estimated to be 0.66 to 1.69 days, while the half-life of DCOIT was as high as 20.9 days during winter in surface water at 30°N latitude. Ring opening of the N-S bond and covalent bond breaking between CN are the main pathways for the photodegradation of OIT and DCOIT, which is verified by density-functional theory calculations. Ecological Structure Activity Relationships (ECOSAR) results indicate that OIT and DCOIT have \"Very Toxic\" biological toxicity, and the acute toxicity of their products is significantly reduced. It is noteworthy that the toxicity of the products of DCOIT is generally higher than that of OIT, and the chronic toxicity of most of the products is still above the \"Toxic\" level. Therefore, an in-depth understanding of the photodegradation mechanisms of OIT and DCOIT in aqueous environments is crucial for accurately assessing their ecological risks in natural water environments.
摘要：
辛二异噻唑啉酮（OIT）和二氯辛二异噻唑啉酮（DCOIT），在涂料中广泛使用的抗菌剂，针对2019年冠状病毒病(新冠肺炎)大流行的使用量急剧增加，最终导致它们在水生环境中的增加。然而,它们在地表水中的光降解过程尚不清楚。本研究的目的是研究OIT和DCOIT在自然水环境中的光降解动力学和机理。在模拟太阳辐射下，它们在天然淡水和海水中主要通过其激发的单线态进行直接光解，而没有观察到自敏化光解。OIT和DCOIT的直接光解速率常数分别为1.19±0.07和0.57±0.03h-1。此外,溶解有机物(DOM)，天然水中的NO3-和Cl-对光降解没有显著贡献，DOM的光屏蔽效应被确定为主要抑制因子。OIT的光降解半衰期估计为0.66至1.69天，冬季，在北纬30°的地表水中，DCOIT的半衰期高达20.9天。N-S键的开环和CN之间的共价键断裂是OIT和DCOIT光降解的主要途径，这通过密度泛函理论计算得到了验证。生态结构活动关系（ECOSAR）结果表明，OIT和DCOIT具有“非常有毒”的生物毒性，产品的急性毒性大大降低。值得注意的是，DCOIT产品的毒性通常高于OIT，大多数产品的慢性毒性仍高于“有毒”水平。因此,深入了解水环境中OIT和DCOIT的光降解机制对于准确评估其在自然水环境中的生态风险至关重要。
