Dissolved Heavy Metal Pollution in Bohai Bay

The metal concentration ranges and averages are summarized in Table 2.20 (Meng et al., 2008). The National Seawater Quality Standard of China (GB 3097-1997) was used to assess the levels of heavy metals in coastal waters from Tianjin Bohai Bay. The quality of seawater is plotted by four levels corresponding to the different function zones according to the standard GB 3097-1997. 

Most metals except Zn and Pb in surface waters of Bohai Bay attained the first level, indicating concentrations that are not out of the range of clean seawater. Consequently, Zn and Pb were the main contaminative elements in coastal waters from Tianjin Bohai Bay. 

According to the standard GB 3097-1997, the concentrations of Pb in coastal waters near Tianjin have exceeded the first level since 1994. Moreover, the Pb levels in coastal waters have attained the third level since 2001, despite the continued decrease in annual runoff. As a whole, Pb concentrations 

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