Scientists revealed the distribution of polycyclic aromatic hydrocarbons and the law of particle-water distribution in the Bohai Sea

Recently, the team of Professor Lin Tian of Shanghai Ocean University analyzed and discussed the distribution and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in the Bohai Sea before and after the rainy season, and the results were published in the environmental science journal Water Research.

Schematic distribution of polycyclic aromatic hydrocarbons. Photo courtesy of Shanghai Ocean

Polycyclic aromatic hydrocarbons are volatile hydrocarbons produced when organic compounds such as coal, oil, wood, and tobacco are incompletely burned, and have a “three-cause” (carcinogenic, teratogenic, mutagenic) effect. Most developed countries and regions have adopted polycyclic aromatic hydrocarbon pollutants as routine environmental quality monitoring projects.

The Bohai Rim Economic Circle is an important base for China’s petrochemical industry in northern China, and its polycyclic aromatic hydrocarbon emissions account for 20% of China’s total emissions. The Bohai Sea is a shallower semi-enclosed marginal sea, and the lower water exchange capacity limits pollutants through mixed dilution with the open ocean. As a result, the Bohai Sea has become one of China’s most polluted marine areas. In a large range, the pollutants remaining in different lower interfaces enter surface water and groundwater through surface runoff, and are enriched in large quantities in the water body, resulting in water environmental pollution. With the continuous improvement of the control level of industrial and agricultural pollution and urban life, non-point sources have become more and more prominent in pollution contribution, and have become the focus of water environment pollution prevention, management and research.

Pollution emissions under the long-standing extensive development model have led to the accumulation of PAHs in the soil and sediments around the Bohai Sea. Through surface runoff, these residual pollutants have become an important secondary source of PAHs in the Bohai Sea. Especially in summer (June to August), the Bohai region accounts for 70% to 80% of the total annual precipitation during this period.

“Studies have found that the particulate polycyclic aromatic hydrocarbons remaining in the surface environment around the Bohai Rim will enter the Bohai Sea in large quantities under heavy rainfall.” Lin Tian said that once a large number of low molecular weight PACs on particulate matter are released into the water body, it will cause the distribution of low molecular weight PAHs in the water body between the dissolved phase and the granular phase in the Bohai Sea to be in an unstable balance, becoming a secondary pollution source of PAHs in the water body, thereby continuously releasing and affecting the water quality and the health of aquatic organisms. This study highlights the potential impact of low molecular weight PAHs release on the pollution of PAHs and the overall source-sink relationship of PAHs in the Bohai Sea during the period after the rainy season.

The reviewers said: “Considering the bioaccumulation of algae and lower organisms on PAHs, the ecological risks associated with PAHs in this specific geographical pattern and meteorological environment of the Bohai Sea deserve further research attention.” (Source: Zhang Shuanghu, China Science News)

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