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

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.