Vertical concentration profile of mercury in a 476-cm sediment core from the Bohai Sea: Inferring anthropogenic influence

Mercury is a worldwide contaminant, with a usual concentration range of 10 to 100 μg kg-1 in the marine/oceanic sediments. The Bohai Sea, the largest gulf in China, is nearly enclosed by densely populated and industrialized land and connects to the northwestern Pacific Ocean via the Bohai Strait. The sediment core (profile) may record anthropogenic mercury history. A 476-cm sediment core was collected and sectioned into 1-cm slices, which were analyzed for mercury and conservative tracer scandium. Mercury content ranged from 14.4 to 35.5 μg kg-1 while scandium content ranged from 9.57 to 13.1 μg kg-1. Overall, mercury content increased from the sediment profile base up to top while scandium content decreased, showing that anthropogenic activities around the bay led to mercury enrichment and accumulation in the sediment. In details, mercury content in the sediment ranged from 14.4 to 17.4 μg kg-1 and averaged 16.3 μg kg-1 from 476-cm depth up to 351-cm depth. This average mercury content is considered as its geochemical base level in the bay. From 351-cm depth up to 181-cm depth, mercury content in the sediment ranged from 16.6 to 20.1 μg kg-1 and averaged 18.4 μg kg-1. The fluctuations in mercury content in this period might be related to climate change. Mercury content in the sediment slowly increased from 16.9 μg kg-1 at 181-cm depth to 22.8 μg kg-1 at 38-cm depth, which is supposed to be related to anthropogenic activities. Afterwards, mercury content in the sediment rapidly increased from 22.8 μg kg-1 at 38-cm depth to 35.1 μg kg-1 at 21-cm depth and fluctuated between 33.4 and 35.5 μg kg-1 from 21-cm depth up to 9-cm depth. This rapid and high mercury enrichment and accumulation in the sediment is connected to the intensive anthropogenic activities around the bay. Subsequently, mercury content in the sediment decreased to 26.3 μg kg-1 at 5-cm depth and then increased to 29.0 μg kg-1 at the depth of 0-1 cm. Therefore, the mercury concentration profile in the 476-cm sediment core records the anthropogenic mercury pollution history in the Bohai Sea and can be used to estimate anthropogenic mercury mass and accumulation flux in the sediment.This study was funded by the National Natural Science Foundation of China (42277366).