湘江入湖河段沉积物重金属污染及其Pb同位素地球化学示踪

Heavy Metal Contamination of Inlet Sediments of the Xiangjiang River and Pb Isotopic Geochemical Implication

湘江是我国重金属污染最严重的河流之一。本次工作利用等离子质谱(ICP-MS)和多接收同位素质谱(MC-ICP-MS)等技术,对湘江入湖河段沉积物进行了系统的重金属微量元素和Pb同位素分析。结果表明,湘江河床沉积物明显富集Bi、Sc、V、Mn、Ni、Cu、Zn、Pb、Cd、Sn、Sb等多种重金属微量元素,而湖盆沉积物重金属微量元素的富集程度明显降低。地累积指数(Igeo)评价显示,河床沉积物存在Cd、Sb、Bi、Sn、Pb、Zn、U、Tl、Th、Mn、Cu等重金属污染,其中Cd达严重污染程度,Sb、Bi、Sn、Pb等达到中度至重度污染程度,而Zn、U、Tl、Th、Mn、Cu等达中度或轻度污染程度。湖盆沉积物除存在中度的Cd、Sb污染外,其余多数重金属未达到污染水平。铅同位素示踪分析表明,河床沉积物的铅是来自流域上游花岗岩风化的自然源Pb,和流域上游Pb-Zn矿床的矿石铅与燃煤烟尘带入的铅等人为源Pb组成的多元混合铅。且河床沉积物中人为源Pb占80%的比例。湖盆沉积物中的铅则以人为源Pb为主,受上游岩石风化影响较小,为来自流域Pb-Zn矿床的矿石铅和燃煤烟尘带入的铅组成的二元混合铅。河床沉积物存在的Sc、Cd、Bi、Cu、Zn、Sn、Sb等重金属污染与Pb一样,为自然来源和人为来源重金属组成的多元混合重金属污染。

Xiangjiang River is one of the rivers that have been contaminated most seriously by heavy metals in China.The present study conducted a systematic analysis of concentrations of trace metals and Pb isotopic composition of the sediments using ICP-MS and MC-ICP-MS techniques.The results show that the river sediments are significantly concentrated and enriched with heavy metals Bi,Sc,V,Mn,Ni,Cu,Zn,Pb,Cd,Sn and Sb.This metal enrichment may cause heavy metal contamination to the sediments.Evaluation by using the geo-accumulation index（Igeo）show that the river sediments were potentially contaminated by heavy metals Cd,Sb,Bi,Sn,Pb,Zn,U,Tl,Th,Mn and Cu,among which metal Cd arrives an extremely high degree of contamination,metals Sb,Bi,Sn and Pb strongly to moderately high degree of contamination,and metals Zn,U,Tl,Th,Mn and Cu moderately to slightly high degree of contamination.However,the lake sediments were not significantly contaminated by these metals except moderately high degree of contamination of metals Cd and Sb.Pb isotopic compositions of the sediments suggest that Pb in the river sediments is a mixture of multi-sources of Pb,which Pb contributed from both natural and anthropogenic processes.Pb of natural source may be the Pb contributed from weathering of granites distributed in upper river areas,and the anthropogenic Pb may mostly include Pb from different Pb-Zn ores distributed and exploited in the upper river areas and Pb from coal combustion in the lower river areas.The proportion of such anthropogenic Pb in the river sediments is about 80%.Pb in the lake sediments is mostly composed of anthropogenic Pb from Pb-Zn ores and coal combustion,and is less influenced by Pb from granite weathering taken place in upper river areas.It can be deduced that the heavy metals Sc,Cd,Bi,Cu,Zn,Sn and Sb also are mixtures of natural and anthropogenic processes,like metal Pb.Therefore,the protection of heavy metal contamination for the region should be stressed on various industrial activities of mineral application of Pb-Zn metal ores in the watershed.