| Heavy metals as a major kind of potentially hazardous pollutants, because of its characteristics, such as hidden nature, the long-term, irreversible, can not be permanent removal, its migration, transformation and ultimate in natural water have been active points in environmental research for a long time. Jialing River, as the largest tributary of the Yangtze River, the source of drinking water for Chongqing residents and the protecting area of natural fishes, its water quality will impact on the life of the local people and economic development directly, so studying on the contents, levels and vertical distributions, the existing states and the rules for migration and transfering of toxic heavy metals in the water has a very important value of theoretical and practical aspect for evaluate the polluting states of the heavy metal in this area, protection of the water resource, the health of people in the Three Gorges reservoir area and providing the basis for the policies of environmental protection. One year survey conducted in Jialing River presented in this paper comes to the following major results:1. The relativity correlative of heavy metals levels and basic water quality parametersThe water quality of Jialing River is good, the water quality parameters are accorded to the standards except the hardness. Exceeding hardness of the water has relate with the geological formation. The water of Jialing River is a typical surface water of bicarbonate area. The correlation between dissolved metals of Jialing River is not obvious, but the water quality parameters have a marked impact on the concentration of the metals. The correlation between the water quality parameters like the concentration of suspended solids, TOC, dissolved oxygen, pH and the most of heavy metals is distinct. So the content of organic matter in the river and the environmental conditions play an important role on the distribution and concentration of heavy metals.2. The distribution of heavy metals among phase of Jialing River bodyThe annual average concentration of dissolved metals of Jialing River such as arsenic and mercury are 1.55, 0.64μg/L, respectively. They are not only lower than the "drinking water quality standards" by WHO, but also lower than the national drinking water quality standards (GB5749-2006). The mercury and arsenic content in various kinds of fishes from Jialing River and the upper reaches of the Yangtze River has not exceeded the limits of China's food hygiene standards.3. The temporal and spatial trends of heavy metals in Jialing RiverThe change of every kind of dissolved metal content in Jialing River water is not consistent with the time. The dissolved arsenic has a significant changing trend with the time of dry season and wet season, but the content of mercury changes not so much with the time. Different metals have different contents in different period of river. The order of arsenic content in the water in different period is: flood season>mean flow season>dry season; the order of mercury is: mean flow season>dry season>flood season. The dissolved arsenic content does not change obviously along the flow direction of river, the dissolved mercury content has a clear growing trend from upstream to downstream. It maybe caused by the increasing product and living sewage from the riversides when the river enters the urban area of Chongqing.4. The assessment of heavy metals pollution in Jialing RiverEvaluate the heavy metals pollution in the water of Jialing River by one-pollution index and health risk assessment methods, the polluting degree of mercury and arsenic in water are: light pollution and clean, respective. Its found that the carcinogenic risk level of As mainly concentrated in the 10-5·a-1, by calculating the health risks caused by the carcinogens in drinking water of the Jialing River. The non-carcinogenic risk level of Hg in drinking water of the Jialing River is 10-8·a-1, this shows that the health risk caused by non-carcinogenic chemical substances (Hg) is far less than carcinogens chemical substances (As). We found the potential risks caused by As higher than Hg by eating fish, but both of the risks are not significant by evaluating the potential health risks for the fishes of the Yangtze. Comparing the risk change between before and after sluice of Three Gorges Dam, the results show that there is no significant change. |
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