渤海中部海域沉积物中Hg的校正及其空间分布特征

Normalization and Spatial Distribution of Mercury in the Sediments and Seawater of the Central Bohai Sea

关键词:  渤海  沉积物  水体  汞  二次污染

Key words:  Bohai Sea  Sediment  Water column  Mercury (Hg)  Secondary pollution

摘要:

以2013年5月从渤海采集到的表层沉积物及水样为研究对象，对渤海中部海域汞(Hg)的空间分布规律进行分析。结果显示，沉积物中，Hg的含量为(1.058–9.256)×10-3 mg/kg，平均值为4.781×10-3 mg/kg；水体中，Hg的含量为0.005–0.240 μg/L，平均值为0.090 μg/L。由于沉积物的粒度组成是影响重金属元素沉积中最显著的影响因素之一，故本研究采用归一化法对Hg的“粒度效应”进行校正，并以水体中的Hg作为参照与校正结果进行对比，来分析沉积物中的Hg对周边环境造成的影响。将校正后沉积物与水体中的Hg进行相关性分析，二者相关性显著(R=0.634, P<0.001, n=29)。推测，水体中的Hg主要来自于沉积物中Hg的释放。由此可见，这种“二次污染”会对周边环境造成长期的危害，在治理的过程中需要引起重视。

Abstract:

To study the spatial distribution of mercury (Hg) in the central Bohai Sea, the surface sediment and the seawater were sampled in the survey in May of 2013. The result showed that the concentration of Hg in the sediment was (1.058–9.256)×10-3 mg/kg with an average of 4.781×10-3 mg/kg. In seawater it varied between 0.005 and 0.240 μg/L with a mean value of 0.090 μg/L. According to the national water quality standards (GB3097–1997) the concentration of Hg often failed the first (0.05 μg/L) and the second (0.20 μg/L) water quality standards, which demonstrated noticeable water pollution in the central Bohai Sea. There was no significant correlation between the Hg concentrations in the sediment and in the seawater at investigation stations (R=0.319, P<0.001, n=29). Grain size of solids was one of the most impactful factors that control the sedimentary variability of heavy metals; hence we normalized Hg concentration by the percentage of grains <20 μm. A significant correlation was then observed between the normalized Hg concentrations in the sediment and in the seawater (R=0.634, P<0.001, n=29). This suggested that Hg in the seawater came from the deposit Hg in the sediment. This “secondary pollution” in the sediment may cause long-term harm to the surroundings in the central Bohai Sea. Therefore we suggest policy makers should fully evaluate the environmental risks and bioavailability in the future economic activities in the central Bohai Sea.