甲基异噻唑啉酮(MIT)和苯并异噻唑啉酮(BIT)是两种广泛使用的异噻唑啉酮的非氧化杀生物剂。自COVID-19大流行以来,它们的产量和使用量急剧增加,不可避免地导致更多的释放到水环境中。然而,它们在水环境中的光化学行为尚不清楚。因此,这项研究研究了MIT和BIT在模拟阳光下天然水中的光降解特性。结果表明,直接光解是其光降解的主要原因,该光降解是通过其激发的单重态而不是三重态发生的。MIT和BIT光降解的量子产率分别为11-13.6×10-4和2.43-5.79×10-4。pH对MIT的光降解几乎没有影响,而在碱性条件下,由于BIT的去质子化形式(BIT-N-)丰富,BIT的光降解得到了显着促进。Cl-,天然水中的NO3-和溶解的有机物(DOM)抑制了MIT和BIT的光降解,其中DOM的光屏蔽效应是最显著的抑制因子。加入其他异噻唑啉酮,在实际情况下可能与MIT和BIT共存,对MIT和BIT的光降解有一定的抑制作用。在30°N纬度的自然阳光下,估计的半衰期约为1.1天。MIT和BIT的光降解途径相似,主要由N-S键的开环引发,前沿电子密度(FED)计算表明在O处发生氧化和·OH加成反应的可能性,N,S网站。虽然光降解产物与它们的母体化合物相比显示出显著降低的急性毒性,尽管如此,它们还是造成了严重的慢性毒性。这些见解对于评估MIT和BIT在水生环境中的生态影响至关重要。
Methylisothiazolinone (MIT) and Benzisothiazolinone (BIT) are two widely used non-oxidizing biocides of isothiazolinones. Their production and usage volume have sharply increased since the pandemic of COVID-19, inevitably leading to more release into water environment. However, their photochemical behaviors in water environment are still unclear. Therefore, this study investigated
photodegradation properties of MIT and BIT in natural water under simulated sunlight. The results demonstrated that direct photolysis was mainly responsible for their
photodegradation which occurred through their excited singlet states rather than triplet states. The quantum yields of MIT and BIT photodegradation were 11 - 13.6 × 10-4 and 2.43 - 5.79 × 10-4, respectively. pH had almost no effect on the
photodegradation of MIT, while the
photodegradation of BIT was significantly promoted under alkaline condition due to abundance of BIT in its deprotonated form (BIT-N-). Cl-, NO3- and dissolved organic matter (DOM) in natural water inhibited the
photodegradation of both MIT and BIT, with the light screening effect of DOM being the most significantly inhibitory factor. The addition of other isothiazolinones, which possibly coexisted with MIT and BIT in actual condition, slightly inhibited the photodegradation of MIT and BIT. The estimated half-life under natural sunlight at a 30°N latitude was estimated to be approximately 1.1 days. The photodegradation pathways of MIT and BIT are similar, primarily initiated from the ring-opening at the N-S bond, with Frontier electron densities (FED) calculations suggesting the likelihood of oxidation and ·OH addition reactions at the O, N, and S sites. While the
photodegradation products exhibited significantly reduced acute toxicity compared to their parent compounds, they nonetheless posed substantial chronic toxicity. These insights are vital for assessing the ecological impacts of MIT and BIT in aquatic environments.