Distribution, fate and risk assessment of PAHs in water and sediments from an aquaculture- and shipping-impacted subtropical lake, China

Highlights

• First comprehensive study on water and sediment PAHs around Lake Guchenghu, China.

• LMW were dominant in the water and HMW in the sediment at both upstream and downstream sites.

• The most contaminated areas were located downstream and upstream of the Wushen Canal.

• Biomass combustion and vehicle emission were the major sources of PAH pollution.

• Exposure to PAHs in sediment poses a potential cancer risk for local residents.

Abstract

The spatial-temporal distribution of polycyclic aromatic hydrocarbons (PAHs), their source, and potential health risks were determined in overlying water and surface sediments from Chinese Lake Guchenghu, adjacent commercial mitten crab ponds and the connected Wushen Canal to assess the contamination profile of the area. The total PAHs concentrations in sediment and water were 86.7–1790 ng g⁻¹ dry weight (dw) and 184–365 ng L⁻¹ in summer and 184–3140 ng g⁻¹ dw and 410–1160 ng L⁻¹ in winter. Two- and 3-ring PAHs were the predominant compounds in water, while PAHs with 4–6 rings dominated in the sediment at both upstream and downstream sites. PAHs concentrations in water and sediment correlated significantly. Diagnostic ratios and positive matrix factorization (PMF) analyses indicated a strong influence of pyrogenic sources, principally biomass combustion and vehicle emission, on the concentrations of PAHs. The distribution, source identification, and mean effects range median quotients (mERMQ) analyses suggested that the most contaminated area was located downstream and upstream of the Wushen Canal, followed by Lake Guchenghu and a commercial crab pond area. From an ecological point of view, PAHs posed a potential risk to drinking water sources as the concentrations exceeded the guideline value of 0.05 μg L⁻¹. The risk posed by sediment PAHs appeared to be low except for the downstream sites, which showed a low to medium ecotoxicological risk. The total incremental lifetime cancer risks ranged between 10⁻⁷ and 10⁻⁵, indicating a potential health risk for the local population when exposed to sediment from the area.

Introduction

The increasing organic pollution of the aquatic environment with polycyclic aromatic hydrocarbons (PAHs) in recent decades is subject of great concern. These compounds, generated from natural and anthropogenic activities, are transported to receiving waters through atmospheric dry and wet deposition (Alves et al., 2016; Franco et al., 2017), surface runoff (Heintzman et al., 2015), industrial wastewater (Kwon and Choi, 2014; Duodu et al., 2017) and sanitary sewage (Tongo et al., 2017), and they may have a negative impact on the water quality. PAHs are characterized by persistence, toxicity, long-range environmental transport ability as well as a propensity to accumulate in plant and animal tissues (Kim et al., 2013). Owing to their mutagenic and carcinogenic nature, sixteen PAHs are considered as priority pollutants by United States Environmental Protection Agency (US-EPA). To date, the growing public and environmental health concerns regarding PAHs in the environment have led many countries to implement various programs and regulations to monitor, control, or restrict their release into the environment.

Due to their low solubility and high hydrophobic-lipophilic characteristics, PAHs in water can be a) dissolved in water; b) adsorbed on suspended solids; c) deposited in the sediment (Liu et al., 2016). Low molecular weight PAHs (LMW), which are usually dominant in water, are considered acutely toxic to aquatic organisms, and the carcinogenicity of PAHs increases with increasing molecular weight (Kim et al., 2013). High molecular weight PAHs (HMW) that predominate in sediments have been linked with liver neoplasm and other abnormalities in bottom-dwelling fish (Tiwari et al., 2017). Moreover, humans can be directly or indirectly exposed to PAHs in aquatic ecosystems via dermal contact of sediment and ingestion of aquatic food. For these reasons, investigation into PAHs pollution of water and sediment pollution and human health risk assessment are required. Industrial complexes such as petrochemical plants, textile factories, and boat building shops, as well as residential areas, are located along the north side of the Wushen Canal in China. The local government plans to increase the waterway transport capacity, and with an annual increase in shipping capacity, the traffic-related pollution of PAHs in the form of oil spills and polluting anthropogenic activities will increase, thus posing a threat to the local aquatic system and human health.

Lake Guchenghu is an ecologically and economically important water body in the middle-lower Yangtze River area of China and serves as a water source for drinking water, domestic use, and commercial mitten crab culture. Mitten crab culture takes place in the reclamation area around the lake, and in 2015 crab production amounted to over 1.55 × 10⁷ kg year⁻¹, equal to a value of $ 2.29 × 10⁸. Thus, mitten crab culture is of great economic and social importance, generating about 15,000 direct and 25,000 indirect jobs, and it is a strategic sector in the present and future economic development of the area.

As the presence of PAHs tends to be closely related to local and regional conditions, studies of PAHs in the Lake Guchenghu area are of paramount interest, both because of the potential economic implications and the already high input of PAHs from the local inhabitants, industry, and canal traffic. Little is, however, known about the organic pollutants in Lake Guchenghu. Dibutyl phthalate, Dioctyl Phthalate, Chrysene, Fluoranthene, and Pyrene were detected in the lake water in 1992 (Gao et al., 1996). In a recent study, Liang (2011) found that a total concentration of 144 ng L⁻¹ of 11 PAHs in Lake Guchenghu, but studies on PAHs distribution and cancer risk assessments are not available. Therefore, identification and quantitative data of the sources as well as of the ecological risks posed by PAHs are critical for the management of these resources. In this study, samples were collected during a field survey in order to (1) elucidate the levels and distribution of 16 US-EPA PAHs in both overlying water and surface sediment; (2) determine the potential sources of PAHs and quantitatively assess the contribution of each source to total load using receptor models; (3) evaluate the potential ecotoxicological and human health risks of PAHs through mean effects range median quotients (mERMQ) analysis and the incremental lifetime cancer risk approach, respectively.