image: (a) Bathymetry of the Seto Inland Sea. The dots represent the position of river mouths. The black lines represent the Bungo and Kii Channels. (b) Conceptual scheme of the coupled model for CB-153 simulation. Ca, Cw, Cwp, and Cwd are the CB-153 concentrations of the gaseous phase, dissolved, phytoplankton-bound, and detritus-bound, respectively.
Credit: Xinyu Guo, Ehime University
Polychlorinated biphenyls (PCBs) are a traditional and ubiquitous group of persistent organic pollutants (POPs). CB-153 is one of the congeners of PCBs. The atmospheric and riverine inputs are recognized as important sources of CB-153 in the coastal or shelf sea. According to the Long-term monitoring by the Ministry of the Environment of Japan, CB-153 concentrations in rivers and the atmosphere have a significant decreasing trend in recent years, which raises a necessity for a quantitative analysis of the responses of CB-153 concentrations in coastal seas to this decline.
A hydrodynamic-ecosystem-PCB coupled model was developed to investigate the spatial and seasonal variations of CB-153 in the Seto Inland Sea and its responses to the decline of CB-153 input from rivers and the atmosphere. The model simulated dissolved and particulate (phytoplankton- and detritus-bound) CB-153 and their physical and biogeochemical behaviors.
Model results indicated that the dissolved CB-153 concentration peaked in July, which was caused by atmospheric and river input. The particulate CB-153 peaked in April when the phytoplankton uptake was largest due to the spring phytoplankton bloom, and in July when the dissolved CB-153 concentration was highest. High CB-153 concentrations usually appear along the coast of the Seto Inland Sea. Osaka Bay showed the highest annual mean concentration of 10.3 ng m-3 while the other areas had an annual mean of 2.9 ng m-3. The CB-153 budget calculation revealed that the atmospheric input was the largest source (69%), which included the air–sea diffusion process (61%) and wet deposition (8%), while river discharges served as a secondary source (31%).
Three scenario experiments demonstrated that the decline of atmospheric CB-153 concentration dominated the CB-153 decrease in most regions of the Seto Inland Sea, except for Osaka Bay, where the CB-153 decrease depended on the decline of riverine CB-153 concentration. Dissolved and particulate CB-153 concentrations exhibited different responses to the reduction in the atmospheric and riverine concentrations of CB-153. In particular, dissolved CB-153 is more sensitive than particulate CB-153 to the decrease of atmospheric CB-153 concentration, but particulate CB-153 is more sensitive than dissolved CB-153 to the decrease of riverine CB-153 concentration.
Journal
Environmental Research