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.
Environmental Research