Contents of heavy metals in bottom sediments of the Taiyu River in the Tongguan gold mining area, Xiao Qinling Mountains, and contamination assessments

The authors investigated the total heavy metal content in bottom sediments of the Taiyu River and Taiyu reservoir in the Tongguan gold mining area and studied the contamination level of the river bottom sediments due to gold exploitation. Except for As, the change of heavy metals contents in the river bottom sediments is the same as those in tailings, which indicates that: the heavy metals in the bottom sediments of the river mainly came from the tailings but their contents are higher than those in tailings. The average contents of heavy metals in bottom sediments are 1,048.61-666,030.08 times those in river water at the same site. Take the reference values of average heavy metal contents in river bottom sediments free from the influence of industrial and mining operations in the vicinity, the bottom sediments of the Taiyu River were extremely contaminated with Hg, Pb, Cd, Cu and Zn. The average times of Hg, Pb and Cd in excess of the reference values reach 366.90, 217.42 and 49.97, suggesting that Hg, Pb and Cd are main contamination elements in river bottom sediments. The comprehensive contamination index of heavy metals in river bottom sediments is 278.97, which shows that the river has been extremely contaminated. The fact that the Taiyu River has been extremely contaminated by heavy metals wants suggests that the environmental protection and control of the mining area allow no delay..