Photosensitized formation of sulfate and volatile sulfur gases from dissolved organic sulfur: Roles of pH, dissolved oxygen, and salinity

Jian-Long Li; Xing Zhai; Lin Du

doi:10.1016/j.scitotenv.2021.147449

Photosensitized formation of sulfate and volatile sulfur gases from dissolved organic sulfur: Roles of pH, dissolved oxygen, and salinity

Sci Total Environ. 2021 Sep 10:786:147449. doi: 10.1016/j.scitotenv.2021.147449. Epub 2021 Apr 30.

Authors

Jian-Long Li¹, Xing Zhai², Lin Du³

Affiliations

¹ Environment Research Institute, Shandong University, Qingdao 266237, China.
² Marine Ecology Research Center, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China.
³ Environment Research Institute, Shandong University, Qingdao 266237, China. Electronic address: lindu@sdu.edu.cn.

PMID: 33984698
DOI: 10.1016/j.scitotenv.2021.147449

Abstract

The photodegradation of dissolved organic sulfur (DOS) is a potential source of aqueous sulfate and its chemical precursors in surface water. However, the photochemical fate of DOS and factors that control its fate still remain unclear. Herein, we employed a DOS model featuring a photosensitizer (humic acids, HA) to investigate the photochemical degradation pathways of DOS in various natural water sources, from which we observed the substantial photosensitized formation of sulfate, methanesulfonic acid (MSA), carbonyl sulfide (COS), and carbon disulfide (CS₂). However, the photochemical production of sulfate and MSA tends to be more efficient than COS and CS₂. The formation of sulfur-containing photodegradation products was also strongly affected by the identity of the organic sulfur precursor, the oxygen concentration, and the pH, while the salinity did not significantly influence the production ratios. Our results revealed that the photosensitization of DOS contributed significantly to the overall production of sulfate and MSA production, especially in acidic and oxygen-enriched environments, which was attributed to the photochemical production of reactive intermediates, such as excited CDOM (³CDOM*) and reactive oxygen species (ROS). Considering the coexistence of DOS and photosensitizers in aquatic environments, photochemistry may play an essential role in the fate of aquatic DOS.

Keywords: Dissolved organic sulfur; Natural waters; Photodegradation; Potential controls; Sulfate; Volatile sulfur-containing gases.