Elsevier

Applied Geochemistry

Volume 119, August 2020, 104627
Applied Geochemistry

Diffusion of polycyclic aromatic hydrocarbons between water and sediment and their ecological risks in Wuhu city, Yangtze River Delta urban agglomerations, China

https://doi.org/10.1016/j.apgeochem.2020.104627Get rights and content

Highlights

  • Black carbon was found to affect the diffusion of PAHs between sediment and water in Wuhu, China.

  • A higher risk associated with PAHs was found for sediment in industrial areas.

  • PAH risk of water was more serious in education and residential areas.

Abstract

To understand how black carbon (BC) might affect the nature of polycyclic aromatic hydrocarbons (PAHs) diffusion at the water–sediment interface and how their diffusion process and ecological risks vary in different functional areas due to strong heterogeneity of urban system. 24 pairs of samples (water and sediment) were collected across the watery landscape of Wuhu, China in four functional areas. The results suggested that PAHs concentrations ranged between 6.95 and 43.2 ng/L, with a mean value of 19.8 ng/L in water, and were from 32.8 to 3790 ng/g averaging 690 ng/g in sediment. The primary sources of the PAHs might be coal combustion and biomass combustion as was revealed by Positive Matrix Factorization model. BC can absorb PAHs, especially high-molecular-weight (HMW) PAHs with strong lipophilic properties, into sediment and affect their diffusion trend at water-sediment interface in different functional areas. The coexistence of BC and PAHs will affect the associated risks in aquatic environments. The water has a higher risk in the education and residential area, which was polluted by low-molecular-weight (LMW) PAHs. The sediment risk was mainly manifested in industrial areas, which are contaminated by HMW PAHs that was caused by the presence of BC. These results indicate that it is very significant for ecological risk assessment to understand the pollution status of PAHs in different functional areas and their relationship with BC.

Introduction

PAHs are a class of organic contaminants of two or more fused benzene rings within a conjugated system, with carcinogenic, teratogenic, mutagenic and endocrine-disrupting effects, and are commonly found in the environment (Li et al., 2014, 2017; Samanta et al., 2002; Armstrong et al., 2004; Adeleye et al., 2016). Therefore, PAHs have been listed as toxic organic pollutants by the United Nations Environment Programme (UNEP), and 16 compounds of PAHs have also been listed as priority pollutants by the US Environmental Protection Agency (Lauenstein and Kimbroth, 2007).

The United Nations pointed out that more than half of the world's population live in urban areas (United Nations, 2012). China has developed at an unprecedented rate of industrialization and urbanization in the past three decades. Urban environmental pollution has become a very important issue for environmental researchers (Wei and Yang, 2010). Many valuable studies have been conducted to investigate the pollution status, temporal and spatial variation, sources, and ecological risk of PAHs in water, soil, sediment, and air in many large cities in China (Qu et al., 2020; Lu et al., 2020; Duan et al., 2007; Chen et al., 2004). However, most of these surveys were often limited to collecting samples at one or a limited location in a city. It may therefore be difficult to accurately understand PAHs pollution status in these cities between different urban functional areas because they often vary significantly attribute to the different activities carried out in them The problem of water pollution is becoming more and more serious, especially aquatic landscapes of urban areas, where the impact on humans is arguably the greatest given the potential threats to our health. Hence, it is necessary to discuss the pollution situation of different functional areas in detail.

In recent years, the diffusion trend of PAHs has received extensive attention. Specifically, studies have focused on the distribution characteristics, exchange behavior, and diffusion mechanisms of POPs in or between soil and air (Chen et al., 2007), water and air (Chen et al., 2016; Odabasi et al., 2008), and gases and particles (Esen et al., 2019). In addition, many studies have shown that Black carbon (BC), a category of carbon-rich substances produced by the incomplete combustion of biomass and fossil fuel, could strongly absorb PAHs (Wang et al., 2014a; Yin et al., 2009; Oen et al., 2006; Cao et al., 2009). Cornelissen et al. (2005) and Jonker and Koelmans (2002) found that the adsorption capacity of BC for PAHs is several tens to several thousand times stronger than other organic materials. Therefore, BC absorb PAHs may affect the diffusion trend of PAHs in different interface (Zhang et al., 2017; Cui et al., 2016). Taking Chaohu Lake Basin as an example, Liu et al. (2018) pointed out that BC can absorb PAHs into sediments and then affected the diffusion trend, thereby increasing their ecological risk. However, our understanding of the impact of BC on the diffusion tendency of PAHs at the water–sediment interface is insufficient; whilst in urban aquatic landscapes, whether the coexistence of BC and PAHs will likely enhance the ecological risks in each functional area.

Therefore, in this study, the city of Wuhu—a good example with rapid economic development in recent times— in the core area of the Yangtze River Delta, China, was chosen as a case to investigate the increasing deterioration of urban aquatic landscapes. The objectives were to: (1) investigate the effects of BC on the diffusion of PAHs between sediment and water; (2) analyze the behavior of PAH diffusion in different functional areas; and (3) assess the ecological risks associated with the water and sediments of urban-landscape lakes in different functional areas.

Section snippets

Sampling sites and sample collection

The city of Wuhu is located on the middle-lower Yangtze plains, East China (117°28′28″E−118°43′41″E, 30°38′30″N–31°32′25″N), has an area of 6026 km2, and a population of 3.87 million (as of 2016). Fossil fuel consumption and automobile exhaust emissions have been increasing for recent years (Wuhu yearbook, 2018). According to its land-use types, the main urban area of Wuhu was divided into several functional areas, including industrial area, business area, residential area, and education area.

Concentrations and compositions of PAHs in water and sediment

The concentrations of PAHs in water and sediment are listed in Table S2. In general, the concentrations in water ranged between 6.95 and 43.2 ng/L, with a mean value of 19.8 ng/L, similar to those in data Dazhou Island (37.9–233 ng/L; Yang et al., 2019) but much lower than the level of Algoa Bay (nd–24.66 μg/L; Adeniji et al., 2019). As far as the components of PAHs were concerned, the concentrations of MMW and HMW PAHs were much lower than LMW PAHs for water. The fact that LMW PAHs are more

Conclusion

This study confirms that the existence of BC can affect the water–sediment diffusion trend of PAHs and subsequently increase the risks associated with sediment in the industrial area. Water was found to be polluted by LMW PAHs in the education and residential areas. With improvements in the quality of human life, more and more cities are expanding their aquatic landscapes, such as through the construction of artificial lakes. The spatial distribution of sediment pollution in such landscapes is

Declaration of competing interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgements

This study was supported by the National Natural Science Foundation of China (41730646 and 41925032), the Doctoral Scientific Research Foundation of Anhui Normal University (2018xjj42), the Anhui Provincial Natural Science Foundation (1608085QD84), the Strategic Priority Research Program of the Chinese Academy of Sciences, the Pan-Third Pole Environment Study for a Green Silk Road (Pan-TPE; XDA2004050202), and the China Postdoctoral Science Foundation (2018T110146).

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