南海表层沉积物铅的环境质量状况及其来源的铅同位素示踪

Environmental Quality of Lead and It's Isotope Tracer of the Surface Sediments in the South China Sea

表层沉积物中的铅除主要在河流的入海口的浅海陆架区富集外,在深海的中央海盆区由于粒度效应亦有一定的富集,火山物质的加入不是富集的主要原因。南海表层沉积物铅的背景值计算表明,陆坡区铅背景值(21.18×10-6±12.64×10-6)与陆坡区柱样铅含量实测值接近,深海盆区背景值(27.87×10-6±7.82×10-6)低于深海盆区柱样铅含量实测值。陆架区铅背景值(19.57×10-6±19.95×10-6),低于中国海岸带铅背景值,全区铅背景值(22.87×10-6±14.54×10-6)与全球页岩铅的平均值接近,深海盆区的铅背景值(27.87×10-6±7.82×10-6)远低于现代深海粘土铅含量。南海沉积物铅的分布特征和背景值计算表明,南海沉积物铅含量变化总体处于自然变动范围内,除河流入海口出现异常外,大部分站位的铅含量均在正常范围内。地质累积指数法和富集因子计算结果表明,南海表层沉积物总体无铅污染,只是在近岸的珠江口区和台湾岛西南部浅海区沉积物受到了轻度的污染。南海表层沉积物的铅同位素在陆架区、陆坡区和深海盆变化趋势基本相同,指示南海不同海区沉积物中铅具有相似的主体来源。南海表层沉积物铅同位素继承了扬子块体的铅同位素组成特征,其铅同位素处于在红河和湄公河河流沉积物钾长石铅同位素值范围之内,指示红河、湄公河和珠江等河流将扬子块体的陆源铅输入到了南海沉积物中。

The Pb enrich not only in shallow continental shelf area of main river mouths, but also in central deep sea basin area due to the granularity affect of surface sediment in the South China Sea. Calculating the background values show that the values in continental sloping area （21.18×10^-6±12.64×10^-6） are roughly the same to the measured values of the pole samples in this area; the values in deep sea basin area（27.87×10^-6±7.82×10^-6） are less than the pole sample＇s; the continental shelf area＇s（19.57×10^-6±19.95×10^-6）are less than China coastal zone＇s ; the whole area＇s （22.87×10^-6±14.54×10^-6） are near to the shale average＇s; and the deep sea basin＇s（27.87×10^-6±7.82×10^-6） are much less than modern abyssal clay＇s. The above characteristics indicate that the Pb contents of surface sediments are in natural change range, and most of samples＇ are in normal change range. Geoaccumulation index （Igeo） and enrichment factor（EF） show that the surface sediments of the South China Sea are non-pollution Pb in whole, but low-grade pollution of sediments are in the Pearl River Estuary and shallow sea area of southwestern Taiwan island. It indicates the different sea areas have the similar Pb sources thatthe Pb isotope ratios have the same change trend in continental shelf area, continental sloping area and deep sea basin area. And it indicates continental Pb of the Yangtze Block are transported to the South China Sea by Red River, Mekong River and Pearl River,etc that the Pb isotope composition of surface sediments in the South China Sea inherit the Yangtze Block＇s, and its isotope ratios are in the range of K-feldspar＇s in Red River and Mekong River.