Vertical migration characteristics of polychlorinated biphenyls (PCBs) in estuarine and coastal zones under complex environmental conditions

As a transitional zone where rivers meet the sea, estuaries are influenced by river transport and ocean tides, resulting in complex variations in parameters such as organic matter content, pH, and sediment salinity. This paper primarily explores the vertical migration patterns of polychlorinated biphenyls (PCBs) under complex conditions, focusing on the soil sediments in the Dagu River estuary area. We designed an indoor soil column leaching experiment to investigate how soil organic matter content, pH, and salinity affect the vertical migration of PCBs in soil. The results indicate that PCBs predominantly migrate within the 0–6 cm depth range in the sediment of various organic-rich soils. In soils with low organic matter, there is higher downward migration of PCBs compared to soils with high organic matter content. Variations in organic matter significantly influence the migration behavior of different PCBs congeners, with highly chlorinated congeners showing a greater tendency for downward migration. Furthermore, both pH and salinity levels influence the migration of PCBs. Alkaline conditions enhance PCBs migration in soil, whereas acidic conditions impede it. Additionally, optimal salinity levels increase the migration depth of PCBs.