Preliminary Study On Pollution Status And Assessment Of Mercury In Soils Of The Pearl River Delta And Sediments From The Beijiang River

Mercury is a non-essential element which is harmful to human's health as it could be intook via inhalation, dermal intake and diet, the inorganic could be methylated into methylmercury with high toxicity. After the Minamata Disease happened, mercury pollution has been concerned globally. During the last decades, a great deal of mercury have been discharged into atmosphere by people's activity such as combustion of fuel, metal smelting and industries. As the mercury pollution is more and more serious, mercury is regarded as "a global pollutant". Mercury could be exchanged among atmosphere, soil and water. Soil and sediment are not only the the important source and sink for mercury exchange, but also a main place for mercury methylation. Hence, it is significant to study mercury pollution in soils and sediments.Combustion of fuel and garbage, industries such as cement, ceramic, chlor-alkali and battery are the main artificial mercury pollution source, Economy of the the Pearl River Delta(PRD) is prosperous, and the GDP contributed about 10% to that in China, with an increasing rate of 15% annually. As the economy is developing, the demand of energy increases as well. A quarter of national garbage combustion plants and a half of ceramic plants were located in the PRD,along with many other mercury relative industries, which leading to potential high levels of mercury in the environment. Furthermore, the subtropical climate in the PRD accelerate the transfer and transformation of of mercury among different environmental media. The Beijiang River is the second branch of the Pearl River, and it is the main water source for Shaoguan, Qingyuan, Zhaoqing and Foshan. Along the Beijiang River, there are many industries, mines, and even e-waste dismantling area. Therefore, mercury may be is an significant pollutant in the Beijiang River area.This article is to study on pollution status and assessment of mercury in soil of the PRD and sediment of the Beijiang River,741 soil samples and 19 sediment samples have been collected in this district from April to September of 2009, content of THg and MeHg has been determinated, correlations between mercury, pH and organic matter have also been analyzed.1.The concentration of THg in surface soil from the PRD ranged from 16.72 to 3324.41 ng-g-1, with an average value of 278.01 ng-g-1.The THg levels in surface soil from different cities decreased as the following order:Foshan>Guangzhou>Jiangmen>Dongguan>Zhaoqing> Zhuhai>Huizhou>Zhongshan>Shenzhen;with Guangzhou and Foshan as the high mercury polluted areas.. The vertial distribution shows that, the THg in soils descended from surface layer to sub-layer, with a mercury pool in the 0-40 cm soil. Distribution of THg in different used type is urban>rural area, Park>Living area>Industry area>Vegetable field>Rice filed>Woodland area,The MeHg in top soil from PRD ranged from 0.14 to 1.34 ng-g-1; with an average value of 0.31 ng-g-1, with no obvious distinction and distribution features for soils in different cities. According to single pollution index (SPI) assessment of THg, generally, PRD is at light polluion level, both Guangzhou and Foshan are at medium polluion level, Shenzhen with no pollution, others are at light pollution level. The SPI assessment of MeHg showed that, generally, PRD is at medium pollution level, Guangzhou, Shenzhen, Foshan, Zhaoqing, Zhuhai, Zhongshan are at medium polluion level, and Dongguan, Huizhou, Jiangmen are at light pollution level. The potential ecological risk assessment of THg showed that, generally, PRD is at light ecological risk, Guangzhou and Foshan are at at medium ecological risk level, Shenzhen is at a low ecological risk index, the others are at light ecological risk level.2. The linearity study showed that, pH value was found to have no obvious correlation with THg or MeHg, and organic matter (OM) was significantly correlated with THg and MeHg. Besides, neither pH value nor OM was significantly correlated with mercury methylation rate, indicating mercury methylation is a complex process, and further studies are required.3.The THg levels in sediment from Beijiang River ranged from 73.72 to 3 517.13 ng-g-1,with an average value of 607.62 ng-g-1. Generally, the THg levels decreased as the sampling sites located further from the drain outlet.Shaoguan smelting factory and Dabaoshan mine are the key piont pollution source of THg for the Beijiang River. The MeHg levels in sediment from the Beijiang River ranged from 0.39 to 2.38 ng-g-1,with an average value of 1.30 ng-g-1,with a different spatial distribution from the THg in this area. The SPI assessment of THg and MeHg showed that, the sediments from the Beijiang River are at medium pollution level, but the sampling sites near the drain outlet are suffering from serious pollution. The potential ecological risk assessment of THg showed that, Beijiang River is at a powerful ecological risk index.4.The methylation rate ranged from 0.003% to 1.51% for soils from the PRD, and from 0.024% to 1.45% for sediments from the Beijiang River, respectively. Totally, the methylation rates varied greatly, All these suggest that further studies investigating the affecting factors of mercury methylation are needed.