Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental System Science , ETH Zürich , 8092 Zürich , Switzerland.
Eawag Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf , Switzerland.
Environ Sci Technol. 2019 Nov 19;53(22):13191-13200. doi: 10.1021/acs.est.9b04721. Epub 2019 Nov 5.
Photodegradation processes play an important role in releasing elements tied up in biologically refractory forms in the environment, and are increasingly being recognized as important contributors to biogeochemical cycles. While complete photo-oxidation of dissolved organic carbon (to CO) and dissolved organic phosphorous (to PO) has been documented, the analogous photoproduction of sulfate from dissolved organic sulfur (DOS) has not yet been reported. Recent high-resolution mass spectrometry studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter, which was hypothesized to result in the production of sulfate. Here, we provide evidence of ubiquitous production of sulfate, methanesulfonic acid (MSA), and methanesulfinic acid (MSIA) during photodegradation of DOM samples from a wide range of natural terrestrial environments. We show that photochemical production of sulfate is generally more efficient than the production of MSA and MSIA, as well as volatile S-containing compounds such as CS and COS. We also identify possible molecular precursors for sulfate and MSA, and we demonstrate that a wide range of relevant classes of DOS compounds (in terms of S oxidation state and molecular structure) can liberate sulfate upon photosensitized degradation. This work suggests that photochemistry may play a more significant role in the aquatic and atmospheric fate of DOS than currently believed.
光降解过程在释放环境中生物难降解形式结合的元素方面起着重要作用，并且越来越被认为是生物地球化学循环的重要贡献者。虽然已经有文献记录了溶解有机碳（至 CO）和溶解有机磷（至 PO）的完全光氧化，但溶解有机硫（至 DOS）的类似光生产硫酸盐尚未报道。最近的高分辨率质谱研究表明，在溶解有机质的光降解过程中，有机硫选择性地损失，据推测这会导致硫酸盐的产生。在这里，我们提供了在来自广泛的天然陆地环境的 DOM 样品的光降解过程中普遍产生硫酸盐、甲磺酸（MSA）和甲亚磺酸（MSIA）的证据。我们表明，硫酸盐的光化学生产通常比 MSA 和 MSIA 的生产以及 CS 和 COS 等挥发性含 S 化合物的生产更有效。我们还确定了硫酸盐和 MSA 的可能分子前体，并证明了一系列相关的 DOS 化合物（就 S 氧化态和分子结构而言）可以在光敏降解时释放硫酸盐。这项工作表明，光化学可能在 DOS 的水生和大气命运中发挥比目前认为的更重要的作用。
