Evaluating Ecological Risks and Tracking Potential Factors Influencing
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Liu et al. Environ Sci Eur (2021) 33:42 https://doi.org/10.1186/s12302-021-00487-x RESEARCH Open Access Evaluating ecological risks and tracking potential factors infuencing heavy metals in sediments in an urban river Dongping Liu1, Jian Wang1,2, Huibin Yu1*, Hongjie Gao1* and Weining Xu1 Abstract Background: Heavy metal pollution of aquatic systems is a global issue that has received considerable attention. Canonical correlation analysis (CCA), principal component analysis (PCA), and potential ecological risk index (PERI) have been applied to heavy metal data to trace potential factors, identify regional diferences, and evaluate ecological risks. Sediment cores of 200 cm in depth were taken using a drilling platform at 10 sampling sites along the Xihe River, an urban river located in western Shenyang City, China. Then they were divided into 10 layers (20 cm each layer). The concentrations of the As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were measured for each layer. Eight heavy metals, namely Pb, Zn, As, Cd, Cr, Cu, Ni, and Hg, were measured for each layer in this study. Results: The average concentrations of the As, Cd, Cu, Hg, and Zn were signifcantly higher than their background values in soils in the region, and mainly gathered at 0–120 cm in depth in the upstream, 0–60 cm in the midstream, and 0–20 cm downstream. This indicated that these heavy metals were derived from the upstream areas where a large quantity of efuents from the wastewater treatment plants enter the river. Ni, Pb, and Cr were close or slightly higher than their background values. The decreasing order of the average concentration of Cd was upstream > mid- stream > downstream, so were Cr, Cu, Ni and Zn. The highest concentration of As was midstream, followed by upstream and then downstream, which was diferent to Cd. The potential factors of heavy metal pollution were Cd, Cu, Hg, Zn, and As, especially Cd and Hg with the high ecological risks. The ecological risk levels of all heavy metals were much higher in the upstream than the midstream and downstream. Conclusions: Industrial discharge was the dominant source for eight heavy metals in the surveyed area, and rural domestic sewage has a stronger infuence on the Hg pollution than industrial pollutants. These fndings indicate that efective management strategies for sewage discharge should be developed to protect the environmental quality of urban rivers. Keywords: Heavy metals, Canonical correlation analysis, Principal component analysis, Potential ecological risk index Background considerable attention due to high biotoxicity, wide With recent advances in industrialization and socio- sources, non-biodegradability, and bio-enrichment in economic development, heavy metal pollution of aquatic food webs [1–3]. River sediments have been identifed systems has become a global issue and has received as important carriers and sinks for the heavy metals dis- charged into the aquatic systems [4, 5]. Heavy metals in river sediments mainly stem from rock weathering, soil *Correspondence: [email protected]; [email protected] 1 State Key Laboratory of Environmental Criteria and Risk Assessment, erosion, runof from agriculture, sewage treatment, and Chinese Research Academy of Environmental Science, Beijing 100012, atmospheric precipitation [6, 7]. Te heavy metals loaded People’s Republic of China into the river environment can be transferred to and con- Full list of author information is available at the end of the article centrated in sediments together with organic matter, Fe/ © The Author(s) 2021. 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Environ Sci Eur (2021) 33:42 Page 2 of 13 Mn oxides, and sulfdes by adsorption and accumulation proposed studies on the distribution characteristics and on suspended fne-grained particles, however they can- potential ecological risks of the heavy metals in sedi- not be permanently fxed in sediments [8–10]. Under ments of Xihe River are expected to provide theoretical ecological disturbances such as a decline in redox poten- support and scientifc basis for the efective sewage dis- tial or pH and the degradation of organic matter, the charge management of Xihe River, and then efectively heavy metals in sediments can be released back into the improve the water quality of the urban river. overlying water by various processes of remobilization, which may lead to secondary pollution [11–13]. Materials and methods Te degree of each heavy metal pollution in the sedi- Description of study area ment is diferent, so that it is essential to clarify the inter- Te Xihe River, a tributary of the Hunhe River, is located nal correlation of heavy metals with sediments, and trace in the western part of Shenyang City, China, and extends the potential factors of heavy metal pollution. Statisti- 78.2 km through the Tiexi Industrial District (Fig. 1). It cal method is used widely in studying the relationship experiences a temperate continental monsoon climate. between diferent heavy metal concentrations and sam- Te mean width of the Xihe River is 10.5 m, with a mean ples. Canonical correlation analysis (CCA) and principal annual rainfall of 680.4 mm [27]. Te industry in Tiexi component analysis (PCA) are the most common multi- District is dominated by equipment manufacturing, auto- variate statistical methods used in environmental studies, mobiles and parts, industrial tourism and biopharma- which provide techniques for classifying interrelationship ceutical, and the industrial park has economic–technical of heavy metals and samples [14, 15]. CCA could elabo- development zone, chemical industry park, metallurgical rate on the relationship between observed variables, and industry park and export processing zone. Te average track the latent factors [16]. PCA is widely used to reduce runof volume of Xihe River is about 924,500 m3 day−1 data, extract a small number of latent factors, and dis- dominated by industrial wastewater (67.73%) and domes- criminate the similarity and dissimilarity for analyzing tic (19.79%), and efuents from wastewater treatment relationships among the observed variables [17]. plants are released directly into the river [28, 29]. Tere- A variety of evaluation methods for heavy metals have fore, large quantities of pollutants are discharged into been developed by international organizations and con- the river, which can lead to water quality deterioration ventions, which have been applied to evaluate heavy and ecosystem degradation. In particular, the continu- metal pollution and the potential ecological risks in ous accumulation of heavy metals in the sediments may the sediments. Tese methods are associated with the induce potential ecological risks. enrichment factor, pollution degree, pollution load index, pollution factor, and geo-accumulation index, which may Sampling and analysis be mainly used to evaluate the ecological risks accord- Field observations and sampling campaigns to collect ing to the ratio of a single heavy metal concentration to sediments in the Xihe River were conducted during July the background value [18–23]. However, these methods 15–25, 2019 (Fig. 1). Tree regions were divided along neither provide information on the toxicity of heavy met- a human impact gradient, the centralized wastewater- als nor indicate the comprehensive toxic efects in the discharge region (upstream), the dispersed wastewater- overall heavy metal assemblage. Te potential ecologi- discharge region (midstream), and farmland region cal risk index (PERI), developed by the famous Swedish (downstream). Ten sampling sites were selected cross scholar Håkanson, is a well-known method for the poten- the urban river. Sampling sites #1–#3 were located tial risk of heavy metal pollution in soils and sediments, upstream, where a large amount of efuents from the which could fll this gap and consider both total contents wastewater treatment plants (WWTP) was loaded of heavy metals and the toxic response factors for each into the river. Sampling sites #4–#7 were situated in heavy metal [24–26]. Te PERI had been applied on the midstream, where a small amount of dispersed waste- diagnostic for water pollution control, the evaluation of water (domestic wastewater and livestock breeding) potential ecological risk of heavy metals in the Yellow wastewater were discharged into the river. Sampling River sediments and the assessment of heavy metal pollu- sites #8–#10 were located downstream, where the par- tion in marine sediments, and so on [24, 25]. tial return water from farmlands enters the river. Sedi- Terefore, CCA, PCA and PERI were used to explore ment cores 200 cm in length were collected at each the spatial variations and trace potential factors, to site and divided into 10 horizons (0–20 cm, 20–40 cm, identify regional diferences, and to assess the potential 40–60 cm, 60–80 cm, 80–100 cm, 100–120 cm, 120– ecological risks of heavy metals, namely As, Cd, Cr, Cu, 140 cm, 140–160 cm, 160–180 cm, and 180–200 cm). Hg, Ni, Pb, and Zn, in the sediments of the Xihe River, Each sediment horizon was thoroughly mixed and an urban river located in Shenyang City, China. Te homogenized after carefully removing gravel, shells, Liu et al.