title: Photodegradation of methylmercury in Jialing River of Chongqing, China.
abstract: Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12×10(-3)±1.5×10(-3) m2/E), followed by summer (9.0×10(-3)±1.2×10(-3) m2/E), autumn (1.4×10(-3)±0.12×10(-3) m2/E), and winter (0.78×10(-3)±0.11×10(-3) m2/E). UV-A radiation (320-400 nm), UV-B radiation (280-320 nm), and photosynthetically active radiation (PAR, 400-700 nm) accounted for 43%-64%, 14%-31%, and 16%-45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl-, NO3-, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%-46%, 6.2%-12%, and 42%-65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m2·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China.
authors.affiliation: Chongqing Key Laboratory of Soil Multiscale Interfacial Process, College of Resource and Environment, Southwest University, Chongqing 400715, China; School of Chemistry and Material, Guizhou Normal University, Guiyang 550001, China.
authors.forename: Rongguo
authors.initials: R
authors.lastname: Sun
authors.affiliation: Chongqing Key Laboratory of Soil Multiscale Interfacial Process, College of Resource and Environment, Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China. Electronic address: dywang@swu.edu.cn.
authors.forename: Dingyong
authors.initials: D
authors.lastname: Wang
authors.affiliation: Chongqing Key Laboratory of Soil Multiscale Interfacial Process, College of Resource and Environment, Southwest University, Chongqing 400715, China.
authors.forename: Wen
authors.initials: W
authors.lastname: Mao
authors.affiliation: Chongqing Key Laboratory of Soil Multiscale Interfacial Process, College of Resource and Environment, Southwest University, Chongqing 400715, China.
authors.forename: Shibo
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Chongqing Key Laboratory of Soil Multiscale Interfacial Process, College of Resource and Environment, Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
mesh_terms: D002681:China; D004784:Environmental Monitoring; D008767:Methylmercury Compounds / Q000032:analysis* / Q000528:radiation effects; D010782:Photolysis; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000528:radiation effects
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical
keywords: Flux; Influencing factors; Jialing River; Methylmercury; Photodegradation