Degradation of polycyclic aromatic hydrocarbons in sediments of main estuaries in China by bacteria and the methods to enhance the degradation

Abstract:

Estuaries are the transition zones between land and sea, and the health of the ecosystem is essential to the surrounding residents and the sustainable economic development. In recent years, amid the rapid development of the cities nearby, a large number of the permanent polycyclic aromatic hydrocarbons (PAHs) have accumulated in the sediments of estuaries, posing a threat to the health of the aquatic ecosystems. As a result, the degradation and transformation of PAHs have attracted the interest of scholars. According to previous studies, Pseudomonadota, Actinobacteria, and Bacillota dominate the PAHs-degrading bacteria in sediments of main estuaries (Pearl River Estuary, Yangtze River Estuary, Liaohe River Esturay, and Haihe River Estuary) in China, among which Klebsiella, Bacillus, and Pseudomonas have been frequently reported. Bacteria degrade PAHs in estuarine sediments mainly through the anaerobic pathway which is characterized by low efficiency. Low oxygen and high salinity in estuarine sediments are unfavorable for the bacterial degradation of PAHs, and the changeable temperature and pH result in uncertain efficiency of bioremediation. The addition of surfactants, nutrients, and exogenous electron receptors and the co-metabolism can promote the bacterial degradation of PAHs in sediments. At the moment, most studies have been carried out in laboratory, but the environmental conditions of estuarine sediments are complex. Therefore, it is suggested to screen PAHs-degrading strains according to the environmental characteristics of estuarine sediments in the future, and flexibly formulate strategies to enhance the degradation according to the actual situation. This review is expected to serve as a reference for further screening and utilization of indigenous PAHs-degrading bacteria in the sediments of major estuaries in China.