Human impacts on polycyclic aromatic hydrocarbon distribution in Chinese intertidal zones

Intertidal zone is a transitional boundary between terrestrial and marine environments, while gathers intense human activities. Our study elucidates that profiles of polycyclic aromatic hydrocarbons (PAHs) in intertidal zones can be used to index regional development status.

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The intertidal zone is the area with the most abundant resources and the most intense material and energy exchange in the surface earth system. Compared with the vast ocean and land, intertidal zone seems to be insignificant, but it is a high productivity area that makes the intertidal zone full of vitality. Thus, the ecosystem health and safety of the region has a profound impact on the sustainable development of nature and human society.

However, since the industrial revolution, with the rapid growth of population and a large number of aggregations to the intertidal zone, the pollutants from human activity are increasing and have a strong impact on ecosystems. PAHs have been identified as priority pollutants by the USEPA long time ago and the semivolatile and persistent properties of PAHs enhance their dissemination and iniquitousness in the environment. It is known that PAHs are unintentionally generated by incomplete combustion of carbonaceous materials and release of petroleum products, and many factors arising from either traditional energy consumption or economy development influence the generation and emission of PAHs. On the other hand, the concentration and composition profiles of individual PAHs also can be used for identifying and assessing the origin of PAHs. Given that the hydrological and ecological significance of intertidal zone, to elucidate the source apportionment of PAHs and what are the key anthropogenic factors influencing PAH distributions in intertidal sediment will provide insights to protect the ecological system of intertidal zone.

First of all, it is critical to know basic pollution status of PAHs in the intertidal zones. With support by the Basic Special Program of Ministry of Science and Technology, China, we made a thorough sampling campaign to collect a total of 315 surface sediments from 14 intertidal zones over 4500 km of coastline that crosses all 11 Chinese coastal provinces and municipalities during 2014-2015. A lot of hard works were done for measurement of sediment PAHs in laboratory, involving freeze drying, homogenization, sieving, extraction, purification, and instrumental determination. Meanwhile, a series of sediment parameters, such as total organic carbon (TOC) content as well as fractions of clay, silt and sand, were analyzed.

Afterwards, data mining of anthropogenic factors took our great efforts, which is much more complicated than expected initially. What criteria should be taken account of is essential for selection of anthropogenic parameters. After making a thorough literature survey from either peer-reviewed publications or governmental statistical yearbooks, we figured out 34 related anthropogenic parameters, including population size, economic development, energy consumption, industrial emission, and maritime transportation, as well as climatic parameters, including temperature and rainfall. Further refining the key factors from a number of anthropogenic factors is another tough work. We employed dimension reduction analysis to avoid redundancy among highly correlated variables and refine the main dimensions of variations for further modeling.

The chemical analysis results unveiled that the pollution status of PAHs in Chinese intertidal zones are moderate in comparison to some heavy polluted areas. Individual PAHs were found to be positively correlated with TOC in sediment and as a result, spatial distribution of TOC-normalized PAHs in intertidal zones clearly exhibits discrepancy in development status in coastal regions of China. Anthropogenic factors, in particular population size and economic development, urbanization, and energy consumption structure, were demonstrated to directly influence PAH patterns in intertidal sediment. Meanwhile, human activities can indirectly influence PAH concentrations by affecting TOC content. Overall, our findings provide profound insights into the roles of sediment properties, human activities and climate factors in spatiotemporal distributions of PAHs in intertidal sediments on a continent scale, advancing our understanding of the driving mechanisms for PAH distribution patterns. The most importance is that the PAH patterns in intertidal zones can be used to index regional development status, which will be of great significance in protection of the delicate coastal ecosystem in China and elsewhere.

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Lingxin Chen

Professor, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences

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