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Environmental Pollution 154 (2008) 12e20 www.elsevier.com/locate/envpol
Seasonal variation in dissolved gaseous mercury and total mercury concentrations in Juam Reservoir, Korea Jong-Sung Park, Sehee Oh, Mi-Yeon Shin, Moon-Kyung Kim, Seung-Muk Yi, Kyung-Duk Zoh* Institute of Health & Environment, School of Public Health, Seoul National University, 28 YeonGeon-Dong, Jongro-Gu, Seoul 110-799, South Korea Received 27 November 2007; accepted 6 December 2007
The first seasonal measurements of DGM and THg concentrations in a Korean reservoir. Abstract Dissolved gaseous mercury (DGM) and total mercury (TM) concentrations were measured in Juam Reservoir, Korea. DGM concentrations were higher in spring (64 13 pg L1) and summer (109 15 pg L1), and lower in fall (20 2 pg L1) and winter (23 6 pg L1). In contrast, TM concentrations were higher in fall (3.2 0.1 ng L1) and winter (3.3 0.1 ng L1) than in spring (2.3 0.1 ng L1) and summer (2.2 0.4 ng L1). DGM concentrations were correlated with water temperature ( p < 0.0001), ORP ( p < 0.0001), UV intensity (UV-A: p ¼ 0.008; UV-B: p ¼ 0.003), and DOC concentration ( p ¼ 0.0107). DGM concentrations varied diurnally with UV intensity. The average summer DGM (109 15 pg L1) and TM (2.2 0.4 ng L1) concentrations in Juam Reservoir were higher than the averages for North American lakes (DGM ¼ 38 16 pg L1; TM ¼ 1.0 1.2 ng L1), but lower than levels reported for Baihua Reservoir in China. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Dissolved gaseous mercury; Total mercury; UV intensity; DOC (dissolved oxygen concentration); Algae; pH
1. Introduction In nature, mercury, especially methyl mercury (MeHg), is a neurotoxin that affects human and ecological health via bioaccumulation through the food chain in aquatic systems (Meili, 1991). The effects of MeHg on the human nervous system lead to body tremors, speech disorders, motor disturbance, and learning disabilities (National Research Council, 2000). Thus, mercury has been designated a priority pollutant and is controlled by the U.S. Environmental Protection Agency (US EPA, 2005). In natural waters, mercury occurs as several chemical species, including dissolved gaseous mercury (DGM, Hg0), dissolved reactive mercury (DRM, Hg2þ), and organic mercury, mainly in the form of MeHg (CH3Hgþ; Morel et al.,
* Corresponding author. Tel.: þ82 19 9150 8891; fax: þ82 2 745 9104. E-mail address:
[email protected] (K.-D. Zoh). 0269-7491/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2007.12.002
1998). DRM, which is mainly deposited from air to water by dry and wet deposition (Fitzgerald et al., 1991; Keeler, 1994; Keeler et al., 1994), has two fates: adsorption to sediments where it may be transformed to MeHg, which is the most toxic environmental Hg species; or reduction to DGM (Slemr et al., 1985; Tokos et al., 1998). DGM is volatile and is thus readily emitted to the atmosphere, or it may be oxidized to DRM and potentially methylated to become bioavailable in the food chain. Mercury has the specific property of continuously cycling between air and water phases (Mason et al., 1994; Schroeder and Munthe, 1998). The cycle and fate of mercury in the environment (Fig. 1) illustrates the importance of DGM formation because the volatilization of DGM to the atmosphere is the only process that removes mercury from aquatic systems. This process limits MeHg production and accumulation in fish (Xiao et al., 1991; Lindberg et al., 1995). Recent studies have shown that DGM is produced in surface waters by the reduction of Hg2þ. Many physical and
J.-S. Park et al. / Environmental Pollution 154 (2008) 12e20
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TGM SUN
Visible Light UV Radiation
Hg0(g)
Hg2+(g) (RGM)
Air
Deposition Hg2+(aq) (DRM)
Deposition
Reduction Oxidation
Evasion Hg0(aq)
DGM
Water
Biota
CH3Hg+
CH3Hg-L Sediments
Hg2+(aq)
Sedimentation
CH3Hg+
TGM: Total Gaseous Mercury DRM: Dissolved Reactive Mercury
RGM: Reactive Gaseous Mercury DGM: Dissolved Gaseous Mercury
Fig. 1. Schematic diagram of mercury cycling in the environment.
chemical environmental parameters can accelerate the reduction of Hg2þ to DGM, including light intensity, water temperature, pH, and the concentration of dissolved organic matter (Yamamoto, 1996; Amyot et al., 1997a; Waite et al., 2002; O’Driscoll et al., 2003; Ravichandran, 2004). Of these parameters, light intensity is a major factor in producing DGM (Amyot et al., 1994; Zhang and Lindberg, 2001; Zhang et al., 2006). However, the importance of other environmental factors which contribute to the formation of DGM in natural waters is still debated; therefore, it is important to examine the relationships between DGM concentration and a variety of environmental factors in natural systems. Although most of the world’s mercury emissions occur in Asia (Pacyna and Pacyna, 2002; Jaffe et al., 2005), there have only been a few studies of mercury concentrations in Asian lakes. Most studies of mercury in Asia have examined levels of total mercury in the air (Kim et al., 2002; Jaffe et al., 2005). Recently, Feng et al. (2004) measured DGM concentrations in Baihua Reservoir in western China. Although this reservoir is located west of the industrialized region of China, the DGM concentrations were quite high, ranging from 93 to 242 pg L1. Due to the prevailing wind direction from the west, high DGM concentrations are also expected to occur in eastern China, Korea, and Japan. Our purpose was to quantify the concentrations of DGM and TM in an unpolluted aquatic system in Korea. DGM concentrations were measured in Juam Reservoir in the southern part of Korea from August 2005 to May 2006. Seasonal patterns in DGM and TM concentrations in the reservoir were investigated, and the relationships between DGM and various environmental parameters were examined. Finally, DGM concentrations in Juam Reservoir were compared to levels in lakes in other countries.
2. Materials and methods 2.1. Site description Juam Reservoir, located in the southern part of Korea (35 000 N, 127 140 E), is fed by Dongbuk Stream and Bosung River (Fig. 2 and Table 1). We chose this site because the reservoir has a long retention time (0.36e2 years, Table 1) and is known to be clean and uncontaminated by pollutants. Therefore, it is relatively easy to determine the variation in and characteristics of DGM concentrations. Possible sources of airborne mercury inputs to this lake may be the Kwangyang iron mill, located 40 km to the southeast from the lake, and the Chonam industrial complex, located 50 km south-southeast of the lake. These sources may contaminate the lake via dry and wet mercury deposition in summer, when southeasterly winds are common. We sampled at five points around the reservoir: two input locations, i.e., Bosung River and Dongbuk Stream; and upstream (site 3), midstream (site 2), and downstream (500 m above the dam, site 1) in the reservoir (Fig. 2). Approximately 70% of the water flowing into the reservoir is supplied by the Bosung River.
2.2. Preparation of experimental apparatus All experimental apparatus was acid-washed prior to sampling and analysis for low concentrations of DGM (pg L1). First, deionized water was bubbled with zero-air gas (99.9999% purity) until the Tekran 2537A gaseous mercury analyzer (Tekran Inc., Canada) detected no DGM (approximately 30 min). The bubbled water was then poured into a 1-L Teflon-coated sample bottles and analyzed for DGM using the Tekran 2537A as a sample blank (i.e., control). The sample blanks were analyzed for DGM three times daily with the refreshed deionized waters, and the average concentration of DGM in the blanks (
