Biogeochemical cycling of mercury in the young Three Gorges Reservoir(TGR), China, is strongly considered. Although methylmercury(MMHg) photodegradation(PD) is an important process involved in mercury cycling in this ...Biogeochemical cycling of mercury in the young Three Gorges Reservoir(TGR), China, is strongly considered. Although methylmercury(MMHg) photodegradation(PD) is an important process involved in mercury cycling in this zone, little is known about this process. In situ incubation experiments were therefore performed to quantify the effect of different wavelength radiations and environmental factors on the PD process of MMHg in the water bodies of TGR. It was found that the effect of solar radiation on MMHg PD was highly dependent on wavelength and water depth. All PD-rate constants resulting from each wavelength range decreased rapidly with water depth. For surface water, UV-A radiation(320?400 nm) was the key driver, accounting for 49%?62% of MMHg PD. For the entire water column, both photosynthetically active radiation(PAR, 400?700 nm) and UV-A were responsible for MMHg PD. MMHg PD fluxes peaked in summer(7.5?18 ng m?2 d?1), followed by spring(3.3?8.0 ng m?2 d?1), autumn(1.0?2.7 ng m?2 d?1), and winter(0.060?0.15 ng m?2 d?1). The annual fluxes of MMHg PD were estimated to be 1.1?2.8 μg m?2 a?1. Filtering the reservoir water and amending it with chemicals(i.e., Cl?, NO3?, and dissolved organic matter(DOM)) showed significant effects on MMHg PD rate constants. Stepwise regression analysis showed that intensity of solar radiation, suspended particulate matter(SPM), DOM, Cl?, and NO3? were involved in the PD process. Path analysis clarified the relationship between MMHg PD rate constants and environmental variables, as well as the comparative strength of direct and indirect relationships among variables. The results are of great importance for understanding MMHg cycling characteristics in TGR and also facilitate the understanding of the underlying process, MMHg PD, in natural waters.展开更多
Photo-reduction of divalent mercury(Hg(II)) in aquatic systems plays a key role in global biogeochemistry cycling of mercury(Hg) in the Earth's surface environment. The mechanisms of this process with various Clco...Photo-reduction of divalent mercury(Hg(II)) in aquatic systems plays a key role in global biogeochemistry cycling of mercury(Hg) in the Earth's surface environment. The mechanisms of this process with various Clconcentrations([Cl-]) under different pH values and irradiation wavelength ranges are still unclear. In this work,photo-reduction and photo-oxidation experiments of Hg with different [Cl-] and pH values under various light conditions were conducted. The results show that photoreduction rate constants of Hg(II) decrease with the increasing of [Cl-] in neutral solution under full light spectrum. Photo-reduction rate constants of Hg(II) with Cl-is highly dependent on Hg(II) species, which is determined by [Cl-] and pH value. Irradiation wavelength ranges have significant effects on reaction processes of photo-reduction of Hg(II) and photo-oxidation of Hg(0) in the presence of Cl-. When cut off ultraviolet(UV) radiation(280–400 nm), the reduction rate constants decrease without Cl-, and increase with higher [Cl-], and the photooxidation rates of Hg(0) decrease with or without Cl-.Except Cl-complexation stabilize the reducible Hg ions in solutions, photo-oxidation is an important reason for Cllowering photo-reduction rate of Hg(II). The results are of great importance for understanding the photo-redox characters of Hg(II) with Cl-.展开更多
Photodegradation（PD） of methylmercury（MMHg） is a key process of mercury（Hg） cycling i water systems, maintaining MMHg at a low level in water systems. However, we posses little knowledge of this important proces...Photodegradation（PD） of methylmercury（MMHg） is a key process of mercury（Hg） cycling i water systems, maintaining MMHg at a low level in water systems. However, we posses little knowledge of this important process in the Jialing River of Chongqing, China. In sit incubation experiments were thus performed to measure temporal patterns and influencin factors of MMHg PD in this river. The results showed that MMHg underwent a ne demethylation process under solar radiation in the water column, which predominantl occurred in surface waters. For surface water, the highest PD rate constants were observed i spring（12 × 10^-3± 1.5 × 10^-3m2/E）, followed by summer（9.0 × 10^-3）± 1.2 × 10^-3 m^2/E）, autum（1.4 × 10^-3± 0.12 × 10^-3m^2/E）, and winter（0.78 × 10^-3± 0.11 × 10^-3m^2/E）. UV-A radiatio（320-400 nm）, UV-B radiation（280-320 nm）, and photosynthetically active radiation（PAR400-700 nm） accounted for 43%-64%, 14%-31%, and 16%-45% of MMHg PD, respectively. PD rat constants varied substantially with the treatments that filtered the river water and amended with chemicals（i.e., Cl^-, NO3^-, dissolved organic matter（DOM）, Fe（III））, which reveals tha 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 wavelengt 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/（m^2·yea in the study site. Our results are very important to understand the cycling characteristics o MMHg in the Jialing River of Chongqing, China.展开更多
To the Editor： Although the triad of palpitations, headaches, and sweating is generally recognized as the classic presentation lbr pheochromocytoma, we reported the case of a patient with pheochromocytoma who first p...To the Editor： Although the triad of palpitations, headaches, and sweating is generally recognized as the classic presentation lbr pheochromocytoma, we reported the case of a patient with pheochromocytoma who first presented with ventricular tachycardia （VT）. This case shows the importance of a broad differential diagnosis when the clinical presentation is unusual.展开更多
基金financially supported by the National Basic Research Program of China(2013CB430004)the National Natural Science Foundation of China(41373113 and 41173116)
文摘Biogeochemical cycling of mercury in the young Three Gorges Reservoir(TGR), China, is strongly considered. Although methylmercury(MMHg) photodegradation(PD) is an important process involved in mercury cycling in this zone, little is known about this process. In situ incubation experiments were therefore performed to quantify the effect of different wavelength radiations and environmental factors on the PD process of MMHg in the water bodies of TGR. It was found that the effect of solar radiation on MMHg PD was highly dependent on wavelength and water depth. All PD-rate constants resulting from each wavelength range decreased rapidly with water depth. For surface water, UV-A radiation(320?400 nm) was the key driver, accounting for 49%?62% of MMHg PD. For the entire water column, both photosynthetically active radiation(PAR, 400?700 nm) and UV-A were responsible for MMHg PD. MMHg PD fluxes peaked in summer(7.5?18 ng m?2 d?1), followed by spring(3.3?8.0 ng m?2 d?1), autumn(1.0?2.7 ng m?2 d?1), and winter(0.060?0.15 ng m?2 d?1). The annual fluxes of MMHg PD were estimated to be 1.1?2.8 μg m?2 a?1. Filtering the reservoir water and amending it with chemicals(i.e., Cl?, NO3?, and dissolved organic matter(DOM)) showed significant effects on MMHg PD rate constants. Stepwise regression analysis showed that intensity of solar radiation, suspended particulate matter(SPM), DOM, Cl?, and NO3? were involved in the PD process. Path analysis clarified the relationship between MMHg PD rate constants and environmental variables, as well as the comparative strength of direct and indirect relationships among variables. The results are of great importance for understanding MMHg cycling characteristics in TGR and also facilitate the understanding of the underlying process, MMHg PD, in natural waters.
基金supported by the National Basic Research Program of China (2013CB430004)the National Natural Science Foundation of China (41173116, 41373113)
文摘Photo-reduction of divalent mercury(Hg(II)) in aquatic systems plays a key role in global biogeochemistry cycling of mercury(Hg) in the Earth's surface environment. The mechanisms of this process with various Clconcentrations([Cl-]) under different pH values and irradiation wavelength ranges are still unclear. In this work,photo-reduction and photo-oxidation experiments of Hg with different [Cl-] and pH values under various light conditions were conducted. The results show that photoreduction rate constants of Hg(II) decrease with the increasing of [Cl-] in neutral solution under full light spectrum. Photo-reduction rate constants of Hg(II) with Cl-is highly dependent on Hg(II) species, which is determined by [Cl-] and pH value. Irradiation wavelength ranges have significant effects on reaction processes of photo-reduction of Hg(II) and photo-oxidation of Hg(0) in the presence of Cl-. When cut off ultraviolet(UV) radiation(280–400 nm), the reduction rate constants decrease without Cl-, and increase with higher [Cl-], and the photooxidation rates of Hg(0) decrease with or without Cl-.Except Cl-complexation stabilize the reducible Hg ions in solutions, photo-oxidation is an important reason for Cllowering photo-reduction rate of Hg(II). The results are of great importance for understanding the photo-redox characters of Hg(II) with Cl-.
基金supported by the National Key Basic Research Program (973) of China (No. 2013CB430004)the National Natural Science Foundation of China (Nos. 41173116, 41373113)
文摘Photodegradation（PD） of methylmercury（MMHg） is a key process of mercury（Hg） cycling i water systems, maintaining MMHg at a low level in water systems. However, we posses little knowledge of this important process in the Jialing River of Chongqing, China. In sit incubation experiments were thus performed to measure temporal patterns and influencin factors of MMHg PD in this river. The results showed that MMHg underwent a ne demethylation process under solar radiation in the water column, which predominantl occurred in surface waters. For surface water, the highest PD rate constants were observed i spring（12 × 10^-3± 1.5 × 10^-3m2/E）, followed by summer（9.0 × 10^-3）± 1.2 × 10^-3 m^2/E）, autum（1.4 × 10^-3± 0.12 × 10^-3m^2/E）, and winter（0.78 × 10^-3± 0.11 × 10^-3m^2/E）. UV-A radiatio（320-400 nm）, UV-B radiation（280-320 nm）, and photosynthetically active radiation（PAR400-700 nm） accounted for 43%-64%, 14%-31%, and 16%-45% of MMHg PD, respectively. PD rat constants varied substantially with the treatments that filtered the river water and amended with chemicals（i.e., Cl^-, NO3^-, dissolved organic matter（DOM）, Fe（III））, which reveals tha 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 wavelengt 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/（m^2·yea in the study site. Our results are very important to understand the cycling characteristics o MMHg in the Jialing River of Chongqing, China.
文摘To the Editor： Although the triad of palpitations, headaches, and sweating is generally recognized as the classic presentation lbr pheochromocytoma, we reported the case of a patient with pheochromocytoma who first presented with ventricular tachycardia （VT）. This case shows the importance of a broad differential diagnosis when the clinical presentation is unusual.
