Decennary variations of dissolved heavy metals in seawater of Bohai Bay, North China.

Characteristics of the spatial and temporal distributions of selected dissolved heavy metals (Cu, Zn, Pb, Hg and Cd) in Bohai Bay, north China was investigated. Water samples from 22 sites were collected and analyzed for the selected metals with atomic absorption spectrometry from the year of 1996 to 2005. Relatively high concentrations of Cu, Zn, Pb and Hg were detected, with maximum concentrations in the 10-year period of 16.30, 422.00, 40.40, 0.23 μg/L respectively. The concentrations of Cd in all samples were quite low, with maximum level of 0.89 μg/L. The spatial distribution of dissolved Cu, Zn and Pb was analogous, where their average concentrations generally descended from the coastline to the central areas of the bay. Differently, for Hg and Cd, relatively high concentrations occurred not only in inshore but also in offshore areas. Measured data of heavy metals were compared with sea water quality standard of China (SWQSC). Cd concentrations in all samples were below SWQSC Grade-I. The percentages of Cu, Zn, Pb, and Hg at Grade-III levels in Bohai Bay were 2.67%, 30.00%, 30.43% and 0.36%, respectively, suggesting the severe contamination of Zn and Pb in this area. Terrestrial inputs via different rivers and sewages may be the important source for the heavy metals contamination.