Nonmetric multidimensional scaling and adverse effects on aquatic biota of polycyclic aromatic hydrocarbons in sediments: A case study of a typical aquaculture wetland, China

Highlights

• PAHs in sediments from a typical aquaculture wetland in Chaoshan metropolis in China were investigated.

• Nonmetric multidimensional scaling shows that PAHs may be mainly originated from oil combustion, and coal/biomass combustion.

• Surface sediments had moderately toxic effect to aquatic biota.

Abstract

Aquaculture wetlands, particularly those located within urban areas, are fragile ecosystems which are generally heavily impacted by urban and aquaculture activities. However, there are, to date, no reports on adverse effects related to polycyclic aromatic hydrocarbons (PAHs) in sediments from aquaculture wetlands in metropolitan areas. The characterization, sources, and incidence of adverse effects on aquatic biota of PAHs were studied in the riverine and estuarine sediments of the Rongjiang River in an aquaculture wetland in Chaoshan metropolis. The total PAH concentrations varied from 46.0 to 1665.2 ng/g (dry weight), with a mean of 246.4 ng/g, indicating lower concentrations than those of other comparable rivers and estuaries worldwide. High-molecular-weight PAHs were the major PAH species, with fluorene, benzo(b)fluoranthene, and benzo(a)pyrene as the dominant components. These PAHs are likely to be mainly derived from oil and coal/biomass combustion. Probability risk assessment indicated a moderate PAH ecological risk in the Rongjiang River and its estuary (RJE). Accordingly, a comprehensive management plan should be established to ensure sustainable aquaculture wetlands.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are one of the extremely globally important categories of persistent organic pollutants (POPs) (Jones and de Voogt, 1999; Malaj et al., 2014). These pollutants are mainly formed by incomplete combustion of energy sources, involving fossil fuels and biomass, and are subsequently emitted into the environment (Keyte et al., 2013). The PAH compounds enter aquatic and terrestrial systems through various pathways (e.g., atmospheric deposition, domestic and industrial wastewater) (Khan et al., 2008; Gu et al., 2018a). According to previous studies, they are poisonous for aquatic and terrestrial organisms at concentrations exceeding the threshold levels (Engraff et al., 2011; USEPA, 2017). Some PAHs have been accumulated over decades because of their persistent, carcinogenic, teratogenic, and mutagenic properties (Brette et al., 2014). Although PAHs have been widely monitored in various environments (Ylitalo et al., 2012; Zhang et al., 2012; Mishra et al., 2016; Gu et al., 2018a; Zheng et al., 2016; Kim et al., 2018a), studies on PAHs in riverine sediments in aquaculture wetlands remain scarce.

Aquaculture wetlands are distributed widely in China's riverine, estuarine, and coastal areas and serve as breeding and nursing sites and shelter for migratory and endemic species (Ottinger et al., 2016; Gui et al., 2018). Riverine, estuarine, and coastal ecosystems are typically easily affected by anthropogenic activities (Halpern et al., 2008; Crook et al., 2015; Janse et al., 2015). In China, pond aquaculture takes the prevailing role in freshwater aquaculture in terms of its production and area (Gui et al., 2018). The rapid economic growth in China since 1978 has greatly accelerated the large-scale exploitation of river and estuarine regions, resulting in increased river and estuarine pollution (Han et al., 2016). Pollutants such as persistent compounds, PAHs, nutrients, surfactants, and oils have been released into rivers and estuaries, causing serious adverse ecological effects (Kleindienst et al., 2015; Jardak et al., 2016; Qian et al., 2016; Borges et al., 2019).

Guangdong Province is the leading aquaculture producer in China (Gui et al., 2018; NBSC, 2018). The Rongjiang River and its estuary (RJE), located on a massive aquaculture wetland in Chaoshan metropolis, is the second largest river system in eastern Guangdong Province; the river flows from northwest to southeast through the main urban areas of Jieyang and Shantou and finally discharges into the South China Sea (Li et al., 2015; Wang et al., 2016). This aquaculture wetland mainly consists of pond aquaculture and includes the largest-volume freshwater-aquaculture producer. Undoubtedly, aquaculture has strongly contributed to local economic growth; however, it has also resulted in the rapid deterioration of aquatic ecosystems in recent years. Unprecedented rates of economic development and urbanization on both banks of this river in recent decades have been coupled with increasing environmental pollution (e.g., industrial pollution, agricultural activities, and domestic sewage) (Wu and Zhao, 2005; Fang, 2012; Gu et al., 2018b). The estuarine environment of this river has also been impacted by the world's largest electronic waste site (Guiyu Town) through water channels linking the RJE and the Lianjian River (Fig. 1).

To our knowledge, there is no information on PAH concentrations present in a typical aquaculture wetland. Therefore, the present study aimed to (1) determine PAH contents in the river sediments of aquaculture wetlands in the Chaoshan metropolis, (2) to reveal PAH quantification and composition, and to (3) identify potential PAH sources and to evaluate the potential ecological risks.