Department of Environmental Sciences, University of California, Riverside, CA, 92521, United States.
Environmental Toxicology Graduate Program, University of California, Riverside, CA, 92521, United States.
Environ Pollut. 2020 Aug;263(Pt B):114402. doi: 10.1016/j.envpol.2020.114402. Epub 2020 Mar 29.
The toxicity of organic aerosols has been largely ascribed to the generation of reactive oxygen species, which could subsequently induce oxidative stress in biological systems. The reaction of DTT with redox-active species in PM has been generally assumed to be pseudo-first order, with the oxidative potential of PM being represented by the DTT consumption per minute of reaction time per μg of PM. Although catalytic reactive species such as transition metals and quinones are long believed to be the main contributors of DTT responses, the role of non-catalytic DTT reactive species such as organic hydroperoxides (ROOH) and electron-deficient alkenes (e.g., conjugated carbonyls) in DTT consumption has been recently highlighted. Thus, understanding the reaction kinetics and mechanisms of DTT consumption by various PM components is required to interpret the oxidative potential measured by DTT assays more accurately. In this study, we measured the DTT consumptions over time and characterized the reaction products using model compounds and secondary organic aerosols (SOA) with varying initial concentrations. We observed that the DTT consumption rates linearly increased with both initial DTT and sample concentrations. The overall reaction order of DTT with non-catalytic reactive species and SOA in this study is second order. The reactions of DTT with different functional groups have significantly different rate constants. The reaction rate constant of isoprene SOA with DTT is mainly determined by the concentration of ROOH. For toluene SOA, both ROOH and electron-deficient alkenes may dominate its DTT reaction rates. These results provide some insights into the interpretation of DTT-based aerosol oxidative potential and highlight the need to study the toxicity mechanism of ROOH and electron-deficient alkenes in PM for future work.
有机气溶胶的毒性在很大程度上归因于活性氧物质的生成，这些物质随后会在生物系统中引起氧化应激。DTT 与 PM 中氧化还原活性物质的反应通常被假定为伪一级反应，PM 的氧化电势用每微克 PM 每分钟反应时间消耗的 DTT 来表示。尽管人们长期以来一直认为过渡金属和醌等催化活性物质是 DTT 反应的主要贡献者，但有机过氧化物 (ROOH) 和缺电子烯烃（例如，共轭羰基）等非催化 DTT 反应性物质在 DTT 消耗中的作用最近也得到了强调。因此，为了更准确地解释 DTT 测定法测量的氧化电势，需要了解各种 PM 成分与 DTT 消耗的反应动力学和机制。在这项研究中，我们测量了随时间推移的 DTT 消耗情况，并使用模型化合物和具有不同初始浓度的二次有机气溶胶 (SOA) 来表征反应产物。我们观察到 DTT 消耗率随初始 DTT 和样品浓度的线性增加。在本研究中，DTT 与非催化活性物质和 SOA 的总反应级数为二级。DTT 与不同官能团的反应具有明显不同的速率常数。与 DTT 的反应速率常数主要由 ROOH 的浓度决定。对于甲苯 SOA，ROOH 和缺电子烯烃都可能主导其 DTT 反应速率。这些结果为解释基于 DTT 的气溶胶氧化电势提供了一些见解，并强调需要研究 PM 中 ROOH 和缺电子烯烃的毒性机制，为未来的工作提供参考。
