洞庭湖“四水”入湖河床沉积物重金属污染特征

Heavy metal contamination in bed sediments from the four inlets of Xiangjiang,Zijiang,Yuanjiang,and Lishui rivers to Dongting Lake,China

对洞庭湖湘、资、沅、澧“四水”入湖河床沉积物进行了沉积柱芯钻探取样,利用等离子质谱仪(ICP-MS)对沉积物重金属等微量元素进行了地球化学分析。结果表明,“四水”入湖河床沉积物中,重金属Bi、Cd、Cr、Mn、Cu、Zn、Pb和Tl等含量变化大,分布极不均匀,而Ba、Sc、Th、U、Cs、Ga、Ge、Rb、Zr、Hf和Nb等微量元素及稀土元素含量变化小,分布相对均匀。微量元素富集系数(fE,C、fE,D值)和主成分分析结果表明,沉积物中显著富集(fE,C>1.5,fE,D>1.5)的重金属Bi、Cd、Cr、Mn、Ni、Cu、Zn、Pb和Tl等既有自然源的带入,又有人为源的贡献;而Ba、Cs、Sc、Th、U、Ga、Ge、Rb、Nb、Ta、Mo、Sr、Zr、Hf和REE+Y等无明显富集特征的微量元素为自然源。地累积指数评价结果显示,湘、资、沅、澧“四水”入湖沉积物依次存在Cd-Bi-Pb-Zn-Mn-Cu-Tl、Cd-Bi、Cd和Cd-Mn-Cu-Ni-Cr等元素组合的重金属污染。且以湘江入湖沉积物重金属污染的元素种类最多、污染程度最强,澧水次之,沅江沉积物重金属污染的元素种类最少、污染程度最弱。结合洞庭湖沉积物重金属污染空间变化特征的对比分析,本研究得到结论:湘江为洞庭湖沉积物重金属污染带入了Cd、Pb、Zn、Cu、Hg、As、Bi、Cr和Ni等重金属;资江带入了Cd、Pb、Zn、Hg、As和Bi等重金属;沅江带入了Cd和Hg等重金属;澧水带入了Cd、Pb、Cu、Hg、Cr和Ni等重金属。洞庭湖重金属污染治理应密切关注重金属Cd的污染,空间上应特别重视湘江和澧水引起的重金属污染。

This paper reports the results of a study on heavy metal contamination developed in bed sediments from the four inlets of the Xiangjiang, Zijiang, Yuanjiang, and Lishui rivers to Dongting Lake, China. Sediment samples were collected by drilling in the four river channels, and the concentrations of heavy metals and other trace elements in the sediments were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The results show that the concentrations of the heavy metals Bi, Cd, Cr, Mn, Cu, Zn, Pb and Tl vary significantly. This may suggest that these heavy metals are heterogeneously distributed in sediments of the four river inlets. However, the concentrations of trace elements Ba, Sc, Th, U, Cs, Ga, Ge, Rb, Zr, Hf, Nb, and rare earth elements (REE) are significantly less variable, possibly indicating that these trace elements are relatively homogeneously distributed in the sediments. The enrichment factor calculations (fE,C, fE,D value) and the principal component analysis (PCA) on Al-normalized concentrations of heavy metals and others trace elements show that the heavy metals Bi, Cd, Cr, Mn, Ni, Cu, Zn, Pb and Tl are significantly enriched in the sediments, and these metals are believed to be contributed from both natural processes (rock weathering) and anthropogenic activities (mining, metal refining). The trace elements Ba, Cs, Sc, Th, U, Ga, Ge, Rb, Nb, Ta, Mo, Sr, Zr, Hf, Y, and REE are less significantly enriched in the sediment, and these trace elements may be contributed mostly from the natural processes occurring in the watershed. The assessment of heavy metal contamination using the geo-accumulation index (Igeo) suggests that the inlet sediments of the Xiangjiang, Zijiang, Yuanjiang, and Lishui rivers are contaminated by heavy metals as Cd-Bi-Pb-Zn-Mn-Cu-Tl, Cd-Bi, Cd, and Cd-Mn-Cu-Ni-Cr assemblages, respectively. The inlet sediments of the Xiangjiang and Lishui rivers are most seriously contaminated by a suite of heavy metals, while those of the Zijiang and Yuanjiang rivers are slightly contaminated by heavy metal Cd and Bi. In accordance with the spatial variation of heavy metal contamination developed in the Dongting lake sediments, the present study suggests that the Xiangjiang River has contributed to the heavy metal contamination of the Dongting lake with the heavy metals Cd, Pb, Zn, Cu, Hg, As, Bi, Cr and Ni;the Zijiang River by with the heavy metals Cd, Pb, Zn, Hg, As and Bi, the Yuanjiang River by with the heavy metals Cd and Hg, and the Lishui River by with heavy metals Cd, Pb, Cu, Hg, Cr and Ni. Therefore, the strategy for protecting the lake watershed should pay a great attention to the contamination caused by heavy metal Cd in the inlet sediments of the four rivers, and to the heavy metal contamination developed in sediments of the Xiangjiang and Lishui river inlets to the lake.