巢湖市环城河沉积物重金属形态及垂直分布特征

Chemical Speciation and Vertical Distribution Characteristics of Heavy Metals in Sediment Cores of an Urban River from a Typical Cityin Chaohu Lake Watershed

采用改良的连续提取法（BCR）对巢湖市环城河沉积物重金属总量及其赋存形态进行了测定和分析．结果表明，巢湖市环城河采样点表层（O～10cm）沉积物中重金属的质量分数分别为29．5 ～224．3mg·kg^-１（Pb），21．3～78．1nag·kg^-１（Ni），67．5～1126．3mg·kg^-１（Cr），50．7～217．4mg·kg^-１（Cu）；新城区西环城河沉积物重金属的质量分数明显高于老城区东环城河；其中以Cr的质量分数在不同采样点差异最为显著．不同采样点沉积物中重金属总量随深度变化特征差异明显，西环城河沉积物不同深度重金属的质量分数较低，且随深度变化较小；受污染较严重的东环城河沉积物不同深度重金属的质量分数普遍较高，且垂直变化波动较大；所调查的4个沉积物柱状样能较好表征周边环境现状和污染历程．4个采样点不同深度沉积物重金属的可交换及碳酸盐结合态的质量分数占总量的百分比均不超过5％，Pb主要以铁锰氧化物结合态存在；Ni主要以残渣态存在；Cr主要以有机物及硫化物结合态和残渣态存在；Cu则主要以铁锰氧化物结合态和残渣态存在；不同采样点柱状沉积物各重金属形态垂向分布也存在显著差异．次生相与原生相分布比值（Rsp）法分析结果显示，巢湖市东环城河2个采样点柱状沉积物Rsp值明显高于西环城河，其重金属潜在污染生态风险较高，其中Pb和Cr属于中度或重度污染水平．

The total concentrations and different forms of heavy metals were investigated and analyzed to evaluate pollution characteristics and potential release risk of heavy metals in sediment cores in an urban river of Chaohu City of Anhui province in China by using a modified BCR sequential extraction procedure. The result shows that the total concentrations of heavy metals range from 29. 5 to 224. 3 mg· kg^-1 for Pb, from 21.3 to 78.1 mg· kg^-1 for Ni, 67.5～ 1 126.3 mg· kg^-1 for Cr, 50.7～217.4 mg· kg^-1 for Cu, respectively. Sediments from the East Ring River （ERR） located in the old town show significantly higher total concentrations of Pb, Ni, Cr, Cu than those from the West Ring River （WRR） in the new town. Especially, the differences in total Cr concentration between sampling sites are more significant, as compared to the other heavy metals. There are significant differences in vertical distributions of total concentrations of heavy metals in sediments cores from four sampling sites. In general, the two sediment cores from the WRR have significantly lower heavy metals and smaller variations with depths than those from the ERR. Due to historical heavy pollution, the ERR shows high concentrations of heavy metals not only in subsurface but also in deeper layers of the sediment cores and the heavy metals fluctuates dramatically with depths. The vertical distribution characteristics of heavy metals can well indicate the surrounding environment situation and heavy metal pollution dynamics. The ratios of exchangeable and carbonate-bound fractions in the total heavy metals are not more than 5 %. Pb and Ni exist mainly in reducible and residual fractions, respectively. Cr exists mainly in oxidizable and residual fractions, and Cu exists mainly in reducible and residual fractions. Potential ecological risk assessment based on the ratio of secondary phase to primary phase （RSP） for the four sediment cores shows that sediment cores from the ERR have the significantly highest Rsp than those from WRR. Especially, the sediments from the ERR are moderately or heavily polluted with Pb and Cr based on the RSP analysis and have a potential and high ecological risk