[Risk assessment and countermeasures of heavy metals pollution in Wanquan segment of Yanghe River]

In order to investigate heavy metals contamination status in Wanquan segment of Yanghe River, Zhangjiakou, 9 water and sediments samples were collected respectively for analyzing Cu, Ni, Cd, Zn, Cr, Pb, Hg and As, with water quality indicators determined at the same time. The potential ecological risk index (PERI) was then employed to evaluate potential ecological risk of heavy metals in sediments. Results indicated that the concentrations of Cu, Ni, Cd, Zn, Cr, Pb, Hg and As in water samples ranged from 1.28-24.13, 1.13-16.84, 0.08-0.11, 1.80-10.65, 1.40-19.12, 0.13-2.05, 0.06-0.99, 0.46-4.22 microg x L(-1), respectively, which are all below the national water quality standard for the demands of industrial use and agricultural irrigation. Principal component analysis (PCA) was conducted to reveal the relationship between water quality indicators and heavy metals pollution in water samples. Concentrations of Cu, Ni, Cd, Zn, Cr, Pb, Hg and As in sediments ranged from 5.90-110.11, 17.34-56.04, 0.07-0.31, 38.71-116.74, 40.39-85.77, 18.65-22.74, nd-0.047, 0.85-9.98 mg x kg(-1), respectively. The descending order of potential ecological risk intensity caused by different heavy metals was: Cd > Cu > Hg > Ni > As > Pb > Cr > Zn, and the average value of each heavy metal was low, while middle-grade risk level of Cd and Hg were also found in several sites. Among all monitoring sites, the descending order of PERI of all target heavy metals was: YH-07 > YH-03 > YH-09 > YH-02 > YH-06 > YH-04 > YH-05 > YH-01, and the average value reached slight grade, while middle-grade risk level was detected in YH-07. Sampling locations in YH-02-YH-03 and YH-07-YH-09 were found with relatively high ecological risk level because of agricultural and anthropogenic activities, respectively. Finally, three risk management regions were figured out and corresponding countermeasures for improving the environmental quality of the watershed were proposed based on the research results.