Distributions of Heavy Metals and Their Variations over the Past Three Decades in the Bohai Sea of China

In this paper, status of metal contamination in Bohai Sea was assessed by a comprehensive review of metal concentrations recorded in sediments. The average concentrations in the samples collected in recent years (summarized 3171 samples) were 0.31, 87.0, 25.7, 25.8, 0.11, 16.9, 52.2 and 27.7μg/g for Cd, Zn, Cu, Pb, Hg, As, Cr and Ni, respectively. In the samples collected in the 1980s, the concentrations were 22.6μg/g for Cu, 21.3μg/g for Pb, 69.13μg/g for Zn, 0.26μg/g for Cd and 57.5μg/g for Cr (summarized 218 samples). The concentrations of Cu, Pb, Zn and Cd in the samples collected in recent years were higher than in the samples collected in the 1980s (p＜0.05). The inputs of heavy metals from the land through rivers inputs, coastal urbanization and coastal industrial activities in recent years were higher than 1980s.

The distribution patterns of heavy metals were significantly different between samples collected in recent 10 years and those in 1980s. In the 1980s, higher concentrations of Zn, Cd and Pb were measured in the samples collected from Bohai Bay. However, in recent years, higher concentrations of Zn, Cd and Pb were measured in the samples collected from the Liaodong Bay. This indicated that the sources of heavy metals in the Bohai-Rim region were changed significantly during the past decades. This is due to the changes of coastal activities and the inputs from the rivers discharges. The water and sediments discharges from the rivers flow into the Bohai Bay, such as the Haihe River and Luanhe River, have dramatically decreased since the 1980’s due to the water diversion in the upper stream and almost reached the point of drying out in the estuaries. While in the Liaodong Bay, the Liaohe River and its tributaries are still steadily brought water and sediment discharges into the coast and offshore area and increased the inputs of heavy metals from the upper stream mining industries and urbanization in the drainage areas.