Levels and ecological risk assessment of heavy metals in surface sediments of fishing grounds along Algerian coast
Introduction
Heavy metals are one of the most important pollutants in our environment due to their bioconcentration and their various form of toxicity (Liu et al., 2003; Gonzalez- Macias et al., 2006; Fang and Hong, 1999; Klavins et al., 2000; Tam and Wong, 2000; Yuan et al., 2004; Chakraborty et al., 2014). Because of their numerous anthropogenic uses and their persistence, they represent a risk at long-term scale in many areas of the world.
In the coastal environments, marine sediments have often been regarded as the ultimate reservoir for trace metals issued from anthropic inputs (Sin et al., 2001; Santos et al., 2005), because most of these metals are effectively adsorbed onto the surface of the mineral phases. Sediments play thus an important role in the transport and storage of potentially hazardous metals (Guevara et al., 2005; Masson et al., 2006), but in the same time they constitute the habitat necessary for aquatic organisms to grow, evolve and establish in the ecological system. Furthermore, they may also constitute a secondary source of pollution if the sediment is resuspended (Kalnejais et al., 2010) or through the releasing of non-residual or dynamic metal complexes (Chakraborty et al., 2012). Therefore, sediment contamination is a parameter used for the prediction of potential ecological risks in aquatic systems.
Since the beginning of the industrial revolution and the subsequent increase of industrial development, very large amounts of toxic pollutants have been discharged into coastal environments and estuaries, contaminating marine sediments with metals (Farmer, 1991; Liu et al., 2003; Perkins et al., 1973, Durrieu de Madron and MERMEX group, 2011). Local contaminations are thus usual and can be due to several factors including pipeline construction, wastewater treatment and disposal, runoff, mining, industrial activities, ports, urban development (Balls et al., 1997; Morton and Blackmore, 2001; Nriagu, 1996; Taylor and McLennan, 1995; Zingde et al., 1988). Rivers are also a major source of particulate metals to the continental shelves (Roussiez et al., 2006; Radakovitch et al., 2008).
Like in many developing countries, the Algerian coastal zone has experienced severe deterioration as a result of growing population and industrialization. Great industrially settlements in some areas (Skikda, Arzew, Algiers and Annaba) have been discharging their solid and liquid wastes into the sea directly or after a limited treatment. The maritime traffic and untreated domestic discharges from 16 million inhabitants along the Algerian coast are other factors influencing sea contamination.
Despite of this increasing pressure, only few researches concerning metal concentrations in the surface sediments of the Algerian coast were published (MPRH, 2010; Inal et al., 2014; Bachouche et al., 2017) and none of them discussed the associated ecological risks and biological effects. Belhadj and Aubert (2017) shows that the sediments of the Ghazaouet Bay (western Algeria) are highly polluted by Zn, Cd, Cu and Pb issued from a large industrial complex of zinc electrolysis as well as from leaching of tailings disposal from ore exploitation, but their data was restricted to the bay area. These four works focused on the estimation of the pollutant load in some hot spots, and they do not give a comprehensive view of the entire Algerian coast. However, the needs to better know the ecological risk associated to the surface sediments was recently emphasized by the aquaculture and fisheries development program: “AQUAPECHE 2020” and the wholesomeness of fishing areas and products must be now integrated. In this objective, our work presents and discusses for the first time the ecological risk that could be associated to heavy metals in surface sediments of the Algerian coast. It aims at helping managers from the fishing sector to evaluate the quality of the main fishing areas, and to facilitate decisions regarding the quality control of fishery products.
Section snippets
Study area
The Algerian coast along the southwestern side of the Mediterranean Sea is 1300 km long and receives several rivers, the most important being Seybousse, Lekbir and Soumam on the east, Yesser, Sebaou, Harrach and Mazafran in the centre and Chelif, Tafna on the west (Fig.1). This coast presents a variety of morphological forms with a majority of rocky shores, sometimes with high cliffs, but also sandy beaches and dunes. The distribution of soft-bottom sediments shows an increasing inshore silt
Sediment collection and pre-treatment
Fifty-one surface sediment samples were collected between 18 m and 562 m water depth using a Van Veen grab. They were taken during one oceanographic survey aboard of the Research Vessel “Grine Belkacem” from 20 May to 10 June 2015. The survey covered the entire Algerian coast, and the geographical position and characteristics of each station are reported in Table 1. The large range of water depths is related to our interest onto fishing ground areas, and the fifty-one stations constitute the
Evaluation of the sediment contamination
Numerous methods have been put forward for quantifying the degree of metal enrichment in sediments associated to anthropogenic inputs (Ridgway and Shimmield, 2002). Various authors (Salomons and Forstner, 1984; Muller, 1969; Håkanson, 1980) have thus proposed to evaluate the impact scales (or ranges) of the pollution by converting the analytical results into broad descriptive bands of pollution ranging from low to high intensity. In order to get a global overview of the ecological risk, three
Statistical analysis
Pearson correlation analysis was implemented to determine the relationship between the twelve heavy metals investigated in the surface sediments of Algerian coast. Multivariate analysis (Principal component analysis (PCA) is an effective tool for providing suggestive information regarding trace metal sources and pathways (Hu et al., 2013), and it has been applied on our data set of fifty one stations and twelve metals. Both correlation and PCA were performed using the statistical software
Choice of reference backgrounds
This is not the scope of this paper to discuss the advantages of using general or local geochemical backgrounds in order to evaluate contamination levels, but the fact is that such choice may drastically affect the results in term of ecological risk. If the average crustal or shale values are easy to use, it is also known that they do not represent correctly the carbonate watersheds (Viers et al., 2009), which are particularly developed on the Algerian coast. Table 2 reports these crustal and
Conclusion
This study allowed us to characterize for the first time the extent of heavy metals contamination in the surface sediments of the entire Algerian coast. The stations were choose in relation with the main fishing areas, and they were not related to specific areas of pollution.
Our results revealed that As is the only metal that could be associated to anthropogenic inputs at this scale, the other ones being mainly natural, with few local exceptions. The mean concentrations of Cr, Ni and As in most
Acknowledgements
This work was partly funded by the French program COMECOM-MERMEX, supported by the Envi-Med project. It is dedicated to our friend and colleague Cédric Garnier from PROTEE, codirector of the program. The authors would like to thank CNRDPA, ENSSMAL and CEREGE for their helps, respectively, during the preliminary phase of samples treatment and trace metals analysis, and to express deep gratitude to the scientists and crew of the R/V BELKACEM GRINE for their assistance during the sediment sampling.
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