杭州西湖与运河沉积物铅同位素组成及其示踪意义

Lead isotopic composition of sediments from West Lake and the Grand Canal in Hangzhou and its significance for lead source tracing

西湖底部表层沉积淤泥与沉积柱中沉积物的铅同位素组成存在明显的差异。沉积柱中206Pb/207Pb=1.1906±0.0029(2σ),208Pb/206Pb=2.0858±0.0074(2σ),而表层沉积淤泥的206Pb/207Pb=1.1705～1.1726,208Pb/206Pb=2.1052～2.1069,存在明显的异常。沉积柱中铅同位素组成演变特征表明,西湖沉积柱的上部受到了现代人为的铅污染,污染物厚度35cm左右,其中顶部10cm污染较为严重。与杭州市有关环境样品的铅同位素背景对比表明,西湖的铅污染主要来源于汽车尾气排放铅。运河(杭州段)0～30cm的沉积柱中除个别样品外,206Pb/207Pb=1.1543～1.1705,208Pb/206Pb=2.1011～2.1540,与西湖沉积柱下部沉积物中的铅同位素组成明显不同,而与西湖表层沉积淤泥的铅同位素组成一致,这表明运河沉积物存在显著的铅污染。对比表明,运河铅污染也主要来自汽车尾气,同时煤铅可能也有一定的贡献。根据西湖沉积柱中铅污染的深度与平均沉积速率估计,杭州地区的铅污染开始于1910年代,但到1970年代铅污染明显加剧。

Lake sediments without disturbance carry important information of modem environmental changes, which have recorded history of the environmental evolution, contamination condition and origin of pollutants. Lead isotope is an important tracer for lead and relative heavy metal pollution. The research on the lead isotopic compositions of the sediments in West Lake and the Grand Canal （Hangzhou section） in Hangzhou City indicates that the surface silts in the West Lake sediment are evidently different from the sedimentary cores in lead isotopic ratios. The deeper sediments in the sedimentary core have the lead isotopic ratios as follows： ^206Pb/^207Pb=1.1906±0.0029（2σ）,^208Pb/^206Pb=2.0858±0.0074（20σ）, but the surface silts show obvious abnormity with ^206Pb/^207Pb=1.1705-1.1726,^208Pb/^206Pb=2.1052-2.1069 Except for one sample, the sediments, from 0 0 30 cm of the Grand Canal （Hangzhou section）, have different lead isotopic ratios （^206Pb/^207Pb=1.1543-1.1705,^208Pb/^206Pb=2.1011-2.1540） from those of the sediment cores in the West Lake section, but agree with those of the surface sediments in West Lake. These characteristics suggest that the surface silt in West Lake and the sediments from 0 - 30 cm in the Grand Canal （Hangzhou section） have been suffered from distinct contamination. Compared with the lead isotopic compositions of the relevant enviromnental samples from Hangzhou City such as automobile exhaust, coal, aerosol and floating dust, these results indicate that the lead contaminations of the West Lake sediments mainly result from the automobile exhaust. The lead isotopic compositions of sediments from the Grand Canal （Hangzhou section） are in accordance with those of surface soils from Hangzhou city, which suggests that the sediments of the Grand Canal originate from the running-out surface soils, and the contamination was mainly resulted from the automobile exhaust and partly from the coal combustion. According to the depth of the lead contamination in West Lake and the average sedimentary rate, it is estimated that lead contamination of West Lake began in 1910s, and the pollution became serious since 1970s.