Distribution and sources of polycyclic aromatic hydrocarbons and phthalic acid esters in water and surface sediment from the Three Gorges Reservoir
Graphical abstract
Introduction
Polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PAEs) are two classes of ubiquitous, persistent toxic substances that are widely detected in air, water and sediment (Deyerling et al., 2014, Li et al., 2016, Liu et al., 2011, Liu et al., 2015, Net et al., 2015, Xu et al., 2013). PAHs mainly originate from the incomplete combustion of carbonaceous materials (Wang et al., 2015) and are known to be toxic and carcinogenic compounds (Grote et al., 2005, Singh et al., 2017). PAEs are widely used as plasticizing agents in cellulosics and elastomers (Zhang et al., 2015), are released mainly by the plastics and cosmetics industries (Zhang et al., 2012) and are reported to be endocrine disruptors (Li et al., 2016, Xu et al., 2010). Due to their easy accumulation, high toxicity, and carcinogenic/endocrine disruption properties, PAHs and PAEs are of considerable concern worldwide. The control of PAHs and PAEs in surface water is also required according to China's environmental quality standards.
The Three Gorges Reservoir (TGR) on the Yangtze River is currently the world's largest hydraulic project, with a total water area of 1084 km2 (Liu et al., 2012, Shen et al., 2014). The water quality in the TGR is essential for both human and ecological health in China (Zhu et al., 2015). The construction of the Three Gorges Project changed the natural flow conditions and the original water distribution of the Yangtze River (Wang et al., 2013). Consequently, the transportation and fate of pollutants changed accordingly. The slower flow rate reduced the diffusion and self-purification abilities of the pollutants (Xu et al., 2007). The water quality in the TGR has begun to deteriorate after impoundment (Xu et al., 2013, Zhao et al., 2011, Zhao et al., 2013a, Zhao et al., 2013b).
The hydrodynamic conditions of the TGR vary greatly with reservoir operation. The reservoir operation of the TGR is divided into two periods: water drawdown period and water impoundment period. During the water drawdown period (usually from January to September), the water is released from the reservoir with a high discharge flow, and the water level drops from 175 to 145 m. During the water impoundment period (usually from September to December), the water level rises to 175 m and is maintained at this level, and the water flow rate is slow. The variation of hydrodynamic conditions between different water periods in a river has significant impact on the distribution, sources and fates of pollutants (Dong et al., 2015, Qi et al., 2014, Yang et al., 2010). Dong et al. (2015) indicated that both free and total dissolved PAH concentrations in water of the Xiaolangdi Reservoir were the highest during sediment regulation, followed by the concentrations during water regulation and before regulation.
PAHs are the predominant toxic organic compounds in the TGR (Floehr et al., 2015, Wang et al., 2013, Zhu et al., 2015). Zhu et al. (2015) investigated the concentrations and sources of PAHs in surface water from the TGR during the water drawdown period (March and April) in 2012. They determined that PAH pollution in the TGR originates from petroleum, coal and biomass combustion. Wang et al. (2013) studied the temporal and spatial variation of PAHs in water from the TGR during the water drawdown period (April to June) in 2008, 2009 and 2011. They observed an obvious decrease of PAH concentration in water after 175-m water impounding in 2011. Floehr et al. (2015) found that PAHs were the key organic pollutants in sediments from the TGR, and pose an ecotoxicological risk. Although some researchers have examined the concentration and source of PAHs in the TGR, there are no reports on the concentrations and sources of PAHs during different water periods in the TGR.
PAEs were also reported to be one of the main organic pollutant classes in the TGR before the 175-m impoundment (Guo et al., 2006, Xu et al., 2007). The concentrations of di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) in 2005 were 0.83–2.21 μg/L and 0.66–3.60 μg/L, respectively (Xu et al., 2007). No relevant reports can be found concerning the PAE concentrations in water and sediments from the TGR after the 175-m impoundment of the TGR. Additionally, the sources of PAEs in water and sediment from the TGR are also not known.
In this study, the concentration, distribution and potential sources of PAHs and PAEs in surface water and sediment from the TGR in 2015 were investigated. Samples during both the water drawdown period (June) and water impoundment period (December) were collected to study the temporal variations and sources of PAHs and PAEs during different water periods. In total, 16 PAHs and 6 PAEs included in the US EPA list of priority pollutants were analyzed in both the water and sediment samples. Our results can also be used as reference levels for future PAH and PAE pollution monitoring programs in water and sediment from the TGR.
Section snippets
Chemicals and reagents
In this study, the 16 target PAHs are naphthalene (Nap), acenaphthene (Ace), acenaphthylene (Acy), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-c,d]pyrene (InP), dibenzo[a,h]anthracene (DahA) and benzo[g,h,i] perylene (BghiP). The 6 target PAEs are dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate
Distribution of PAHs
Table 1 shows the min, max, mean, median and standard deviation (SD) of the sum of all 16 PAH (ΣPAH) concentrations in surface water and sediment from the TGR during the water drawdown period (June) and the water impoundment period (December) in 2015.
In the surface water, the ΣPAH concentrations in the TGR were 8.7–101.7 ng/L (mean value 36.4 ng/L), which were lower than the reported concentrations of 18–159 ng/L (mean value 44.1 ng/L) in 2011 (Wang et al., 2013) and 131–228 ng/L (mean value 155
Conclusions
The concentration, distribution and potential sources of PAHs and PAEs in surface water and sediment from the TGR were investigated. Based on the results presented in this study, the following conclusions can be drawn.
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The ΣPAH concentration in surface water from the TGR was 8.7–101.7 ng/L in water and 202.0–2291.3 ng/g in sediment, respectively. The ΣPAE concentration was 4.0–1169.7 ng/L in water and 177.3–4744.4 ng/g in sediment. The PAH and PAE concentrations meet the restrictions of the national
Acknowledgments
This work was supported by the Public Interest Scientific Research Fund of the Ministry of Water Resource of China (No. 201501042), the National Natural Science Foundation of China (Nos. 51309019, 51379016), the Young Elite Scientist Sponsorship Program by CAST (No. 2015QNRC001), the State-level Public Welfare Scientific Research Institutes Basic Scientific Research Business Project of China (No. CKSF2017062/SH), and the Technology Demonstration Project of the Ministry of Water Resources of
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