Dissolved trace metal distributions and Cu speciation in the southern Bohai Sea, China

Trace metals play important roles in marine biogeochemical cycling processes. However, due to a lack of clean sampling techniques for trace metals, high quality data on the occurrence of dissolved trace metals in Chinese coastal seawaters are scarce. In this study, we used stringent trace-metal clean sampling and analytical techniques to investigate the spatial distributions of several dissolved trace metals (cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), silver (Ag), and zinc (Zn)) in Bohai Bay and Laizhou Bay, China. The dissolved metal concentrations in the southern Bohai Sea were comparable to those found in other bays or pristine coastal waters around the world. Metal concentrations were also determined at several nearshore sites, including rivers containing sewage discharges, a seaport, and the Yellow River. With the exception of the Yellow River, the metal concentrations at the nearshore sites were all elevated compared with those in the bays. The Cu speciation in the bay waters was also determined. Strong complexing ligands were found, often present as one class with logK = 12.7-13.6, and the sources of the strong ligands could be attributed to either the river/sewage discharges or in situ production. Overall, the dissolved metal concentrations were not as high as expected even though the Bohai Sea is considered to be a heavily polluted inland sea. The low dissolved metal concentrations are in accordance with the relatively low metal concentrations in sediment in the bays, which may be due to the low flows of the rivers that enter the bays, resulting in the deposition of metals in riverbeds before they reach the bays. (C) 2015 Elsevier B.V. All rights reserved.