Pollution Characteristics And Source Analysis Of Heavy Metal In Bivalves From Hangbu River

The quality of the aquatic environment of Hangbu River, has become a major concern in recent years as it was the biggest tributary into Chaohu Lake (taking 65% of the total runoff)-The contents of heavy metals in Anodonta woodiana were determined to study the biogeochemical behavior and response mechanism of heavy metal(Cr, Cu, Zn, Cd, Pb, As and Hg). A special focus was also given to the characteristics of pollution and bioaccumulation effect of Hg and MeHg in anodonta woodianas. Single Pollution Index and Index of Geoaccumulation were used to assess the environmental ecological risks of heavy metals.The research results showed that the nitrogen and phosphorus pollutions in water of certain sections from Hangbu River were severe and the the quality of water was more than the limit of the national III standard of surface water; the contents of total nitrogen and total phosphorus in sediments of certain sections had also exceeded the lowest safety rank of the corresponding risk criteria. The average contents of Cr, Cu, Zn, Cd, Pb, As and Hg were respectively 64.5 mg/kg,21.4 mg/kg,89.1 mg/kg,0.152 mg/kg,30.6 mg/kg,7.16 mg/kg and 0.065 mg/kg. Among the seven heavy metals in sediments, the average contents of Pb, Zn and Cd showed a higher frequency performance of pollution than others congsidering their environmental background values which indicated that the main reason was the influence of increasing human activities in recent years. In addition, the content of Cr in sediments was lower than the natural background value, but it also exceeded the ecological risk threshold of TEC and showed a high level of pollution response.The average contents of Cr, Cu, Zn, Cd, Pb, As and Hg in anodonta woodianas were respectively 80.4 mg/kg,5.2 mg/kg,412.9 mg/kg,0.339 mg/kg,0.43 mg/kg,8.9 mg/kg and 0.134 mg/kg. The anodonta woodianas were prone to accumulating the elements like Zn, Cd and Hg but less accumulating Cu, Pb and As which according to the value of BSAF. The contents of heavy metals in anodonta woodianas were close to or lower than the contents of heavy metals in sediments. The heavy metal contents in their bodies were positively correlative to those in their living environment, taking the sequence as Hg>Cd>Zn>Cr>Cu>As>Pb. Further research results showed that the accumulation of mercury and methyl mercury in anodonta woodianas was obvious and total mercury contents in Anodonta woodiana ranged from 101.34 to 171.15 μg/kg (dry weight), while methyl mercury contents ranged from 54.22 to 89.63 μg/kg(dry weight), and they were all lower than the GB18406.4-2001. The accumulation of mercury in various tissues had obvious selectivity (mantle>guts> gill and muscle).The evaluation results of heavy metal in anodonta woodianas showed that the contents of Cr, Zn and Cd were more than the limited safety standard of shellfish, which were consistent with the trend of heavy metal pollution in sediments. The contents of heavy metals in anodonta woodianas were positively correlative to that in sediments, which indicates that anodonta woodianas can be regarded as bioindicators to monitor and pre-alarm heavy metal pollution in freshwater environment.Relevant analytic results showed that the distribution of total organic carbon(TOC) in sediments showed a significant positive correlation with the contents of Cu, Zn, Cd and Hg, and a negative correlation with the contents of Cr, Pb and As. The result may proved that heavy metal pollution originated from mixed pollution sources. The analysis of pollution sources showed that the heavy metal pollution in Hangbu River was mainly affected by agricultural non-point pollution(52%), shipping pollution(16%) and industrial pollution(14%). Therefore, it should strengthen the control of agricultural non-point source pollution in the process of heavy metal input load, reduce the emission of fuel oil pollution in the process of transportation, and increase the intensity of the relevant pollution related enterprises. With the ecological restoration projects especially for benthic habitat reconstruction of shellfish could improve the overall capacity of the environment and self-purification capability in water environment.