Mercury Pollution in Guizhou , China – A Status Report

Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry , Chinese Academy of Sciences, 46 Guanshui Road , Guiyang 550002, PR China
The Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China
* Corresponding author. Tel: +86 851 6891356; Fax: +86 851 5891609; E-mail: fengxinbin@vip.skleg.cn

Guizhou is located in Southwestern China with an area of 170,000 km 2, accounting for about 1.8% of the total area of China . It is known as the “mercury capital” of China because more than 60 % of total national mercury resources were discovered in this province. Guizhou is located in the Global Circum-Pacific Mercury Belt, and at least 13 large and super large-scale mercury mines have already been discovered in the province. The background mercury concentrations in soil from this area are very elevated. Meanwhile, Guizhou is one of the largest coal producing provinces and is also one of the areas where acid deposition occurs frequently due to coal combustion emissions. Mercury concentrations in coal from Guizhou are significantly elevated compared to the average mercury concentration in Chinese coal due to low-temperature thermal fluid activities in the Mesozoic and Cenozoic Eras in this area. Mining of mercury and other metals, coal combustion, and other human activities significantly polluted the environment with mercury. Tremendous national and international attention has been given to mercury pollution in the province.

1. Mercury emission fluxes from soil in mercury mineralized areas in Guizhou

We have contacted intensive in situ Hg emission fluxes measurement at Wanshan mercury mine, Wuchuan mercury mine, Lanmuchang mercury mine and Guiyang area using dynamic flux chamber method coupled with automated mercury vapor analyzer (Tekran 2537A). Our results demonstrated that soils in mercury mineralized areas are strong atmospheric emission source. The maximal mean Hg flux was 2283.3±2434.2 ng m -2 h -1 with a range from -622.9 ng m -2 h -1 to 10543.7 ng m -2 h -1 (n ＝292). The significant Hg emission fluxes produced serious atmospheric Hg pollution. The maximum Hg concentration in air reached 468.0 ng m -3 in the sampling site F3 from Lanmuchang in warm season. The mean Hg concentration in air of this area was 111.2±91.8 ng m -3 (n=903) with the range of 468.0 ～12.7 ng m -3 during the sampling period. At the same time, the correlations between mercury emission fluxes and environmental parameters (such as solar radiation, temperature, humidity, mercury concentration) were significant. This indicated that environmental factors have a strong impact to mercury emission fluxes from soil. The most important parameters controlling Hg emission flux from soil are soil mercury concentration and solar radiation.

2. Mercury contamination to local environment in Hg mines in Guizhou

We found that the tailings and calcine from past Hg mining activities are the important sources of Hg contamination to the local environment, such as surface water systems, soil compartment, food and vegetables. Concentrations of total mercury and methylmercury (MeHg) were measured in soil and vegetation samples collected from a small but long historic Hg-mining area. Simultaneously, Hg distributions were determined on stream-waters during two sampling periods. Total Hg concentrations in soil and vegetation samples were highly elevated ranging from 0.41 - 610 mgKg -1 and from 0.02 - 55 mgKg -1, respectively. MeHg concentrations varied from 0.41 - 8.8 µgKg -1 in soil samples and from 0.65 - 5.5 µgKg -1 in vegetations. The concentrations of total Hg in stream waters varied from 55.0 - 7,020 ngL -1 in the flood-flow regime and from 24.8 - 679 ngL -1 in the base-flow regime, respectively. Average dissolved Hg concentration was 15.7 ngL -1 in wet season and 21.0 ngL -1 in dry season. However, particulate Hg was typically > 70% of total Hg in the flood-flow regime. Higher concentrations of particulate Hg primarily originated from summer floods were the major pathway of Hg transportation, which were evidenced by the positive correlation between particulate Hg and total suspended solids (TSS). The contaminated soils and distribution patterns of Hg in the stream-waters suggest derivation from historic Hg-mining sites and may serve as an important additional source of Hg to the local environment in the study area.

3. Mercury emission from artisanal zinc smelting in Hezhang, Guizhou

Zinc smelting is one of important anthropogenic atmospheric mercury emission sources, but research on mercury emission from this source category is limited. Using a mass balance method, we estimated the average mercury emission factors from artisanal zinc smelting using indigenous method in Hezhang , Guizhou , China to be 155 and 79 g Hg t -1 of Zn produced from sulfide ore and oxide ore, respectively. These emission factors are much higher than the literature value used to estimate mercury emission from zinc smelting in developing countries, which is 25 g Hg t -1 of Zn produced. Annual mercury emission rates from artisanal zinc smelting in this area were calculated from 1989 to 2001. Up to 2003, a few metric tons mercury was annually emitted to the ambient air from zinc smelting in such a small area (<150 km 2), posing a threat to the local environment. It highlighted that artisainal zinc smelting in Hezahng was an important global atmospheric mercury emission source. The local surface waters were seriously contaminated with mercury due to zinc smelting. Apart from the deposition of mercury species that emitted from zinc smelting, smelting residues are also the sources of mercury contamination to surface water systems.

4. Mercury emission from coal combustion in Guizhou

Forty-eight coal samples from the major coal mines in Guizhou were collected by means of subterranean channel sampling. The average mercury content in coal from this Chinese province is 0.53 mg kg -1, which is substantially higher than coal produced in any other provinces of China . A strong link is proposed to exist between atmospheric mercury emissions and the combustion of coal. During the last two decades, the amount of mercury emitted from coal combustion in Guizhou has increased invariably to 8.3 tons in 1998. Being concentrated to the pyrite fraction in the coal, the implementation of physical coal cleaning is likely to be an effective way to reduce the mercury content. Total and fractionated mercury in air and precipitation was measured in the provincial capital. During a measurement campaign in October 1999, the reactive gaseous mercury (RGM) concentration averaged at 450 pg m -3, which is much higher than that in pristine area (less than 20 pg m -3). The average total mercury in rainwater of 1996 was estimated to be 33 ng l -1, and the total annual wet deposition of mercury in the area was 39 g km -2 in 1996.