Environ Sci Pollut Res DOI 10.1007/s11356-015-5775-x
RESEARCH ARTICLE
Assessing trace metal pollution through high spatial resolution of surface sediments along the Tunis Gulf coast (southwestern Mediterranean) Rym Ennouri 1,2 & Noureddine Zaaboub 2 & Mouna Fertouna-Bellakhal 1,2,3 & Lassad Chouba 2 & Lotfi Aleya 1
Received: 6 May 2015 / Accepted: 6 November 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Tunis Gulf (northern Tunisia, Mediterranean Sea) is of great economic importance due to its abundant fish resources. Rising urbanization and industrial development in the surrounding area have resulted in an increase in untreated effluents and domestic waste discharged into the gulf via its tributary streams. Metal (Cd, Pb, Hg, Cu, Zn, Fe, and Mn) and major element (Mg, Ca, Na, and K) concentrations were measured in the grain fine fraction Mg > Zn > Mn > Pb > Cu > Cd > Hg. Metals tend to be concentrated in proximity to source points, suggesting that the mineral enrichment elements come from sewage of coastal towns and pollution from industrial dumps and located along local rivers, lagoons, and on the gulf shore itself. This study showed that trace metal and major element concentrations in surface sediments along the Tunis Gulf shores were lower than those found in other coastal areas of the Mediterranean Sea. Responsible editor: Philippe Garrigues * Lotfi Aleya [email protected] 1
Université de Bourgogne Franche-Comté, Laboratoire de Chrono-Environnement, UMR CNRS 6249, Besançon, France
2
Institut National des Sciences et Technologies de la Mer (INSTM), Laboratoire Milieu Marin, Centre la Goulette, Tunisie
3
Institut Supérieur de Pêche et d’Aquaculture de Bizerte, Unité de recherche: Exploitation des Milieux Aquatiques, Tunisie et Faculté des Sciences de Bizerte, Errimel, B.P.15, 7080 Bizerte, Tunisie
Keywords Tunis Gulf . Surface sediments . Metal contamination . AQUARISK model
Introduction Coastal Mediterranean ecosystems are generally threatened by pollution from urban and industrial activities. One resulting problem is observed in the ability of marine surface sediments to accumulate toxic metals, becoming an ecological concern. Sediments are the main sink for metals in aquatic ecosystems and thus constitute a threat to human health and the food web (Simpson et al. 2012; Belabed et al. 2013; Ben Salem et al. 2014). Further knowledge of the spatial distribution of metal concentrations in surface sediments from a specific ecosystem has become essential, especially if the system contains abundant fish resources and is located, like Tunis Gulf, in a hydrodynamically complex region (Brahim et al. 2015; Zaaboub et al. 2014b). Tunis Gulf, located adjacent to the metropolitan area of the city of Tunis with its growing population, is an area of heavy industry (chemical manufacturing, metal processing, factories, and electronic and mechanic industries). Industrial and domestic waste is discharged into local rivers where it initially affects animal and plant tissues, but once in the gulf, its metal contents settle to the seafloor. Harbor activities (commercial shipping, fishing, and naval reparation) also constitute potential sources of metals for coastal sediments (Warnken et al. 2001; Forman et al. 2003; Weyrauch et al. 2010; Zaaboub et al. 2014a). These metals, combined with those of continental origin already affecting the tissues of living sea organisms, may also end up in sediment deposits and thus contribute to a permanent reserve of harmful contaminants for aquatic fauna and flora (Hooda 2007; Bhakta et al. 2014). Spatial distributions of metallic elements in sediments are therefore of
Environ Sci Pollut Res
primary significance in locating sources of pollution (Liu et al. 2003; Taylor and Matthai 2001; Zhang et al. 2007; Zhou et al. 2007). Concerning hydrodynamics, Tunis Gulf occupies a paramount position since it is influenced by the hydrological regime of the Mediterranean Sea which, in the western Mediterranean, is driven by a regional current, the Atlantic Water (AW). The current enters the Straits of Sicily splitting into two branches: one flowing into the southeastern Mediterranean and the second, the Atlantic Tunisian Current (ATC), flowing southwards along the Tunisian coast, directly affecting circulation at the mouth of the gulf (Ben Ismail et al. 2012, 2014). Recent studies (Brahim et al. 2015) of Tunis Gulf have pointed out in particular that all sediment distribution is controlled by water movement and that an enhanced fraction of fine sediments is transported by the major Mediterranean currents to be deposited in the gulf’s central zone, while coarse sediments are found along the gulf’s western shore as a result of littoral transport under wave and swell action. A gap remains however in our knowledge of the spatial distribution of metals along the gulf shores, though metals are known to be associated with the sediment fine fraction (Belabed et al. 2013; Zaaboub et al. 2014a). This complex sedimentary context includes both currents and waves, along with an abundant nutrient and metal discharge load generally found in coastal areas (mainly as runoff from urban activities). It thus appeared that an increased knowledge of the metal concentrations arriving in the gulf could be a first step in establishing better management strategies to alleviate the dangers inherent in metal accumulation. High spatial resolution sampling was used in this study to quantify metal accumulation in marine sediment in the western Mediterranean. Risk was assessed using the AQUARISK model to estimate the degree to which contaminant data are likely to exceed critical guideline levels for metals in sediment and critical values determined from species sensitivity distributions (SSD) and probability density distributions (PDD).
Material and methods Study site Tunis Gulf is located in the northwestern Mediterranean (between 36° 43′ N/37° 10′ N and 10° 11′ E/11° 05′ E) and has been heavily affected by the region’s growing population (2.5 million people) and intense industrialization. As in all coastal environments, Tunis Gulf’s industry, urban and harbor activities comprise potential sources of metals, discharging both solid and liquid wastes into the gulf’s tributaries, the
Mejerda, Meliane, and El Abid Rivers. Originating in eastern Algeria, the Mejerda is the principal source of continental water and sediment discharge into the gulf (Fig. 1). With a catchment area of approximately 25,000 km2 and covering most of northern Tunisia, it has an annual total discharge of around 1100 Mm3 year−1, with a total sediment load of 2106 t year−1. Further south, other streams and two main water bodies, Lake Tunis and Ghar El Mehl Lagoon, are connected to the gulf. Due to the presence of neighboring lead and zinc mines, the Mejerda catchment area has for several decades been subjected to multiple sources of trace element contamination. A considerable amount of residue has accumulated in waste dumps, while other streams discharge vehicle compounds of both industrial and urban origin. Previous investigators have noted that the area’s dykes are a potential source of contamination (Ben Hamza 1994; Jdid et al. 1999; Moldenhauer et al. 2008; Mlayah et al. 2009). Sampling Sediment sampling was carried out at 49 stations, each selected so as to provide good area coverage of Tunis Gulf coast (Fig. 1). Sampling depths ranged from 1.7- to 20-m depth. Surface sediments were collected with a Van Veen grab sampler (surface area 0.1 m2) with a depth of 10–20 cm. The samples were placed in polyethylene jars, immediately frozen and stored at −4 °C until analysis. Grain size analysis Grain size was determined for all surface sediment samples using Stokes Law to characterize particle size distribution. Sediment was placed on top of the column for a limited time or until it passed through the sieve at a constant low rate and the different sediment fractions could be separated. Metal analysis Metal analysis was conducted on the
RESEARCH ARTICLE
Assessing trace metal pollution through high spatial resolution of surface sediments along the Tunis Gulf coast (southwestern Mediterranean) Rym Ennouri 1,2 & Noureddine Zaaboub 2 & Mouna Fertouna-Bellakhal 1,2,3 & Lassad Chouba 2 & Lotfi Aleya 1
Received: 6 May 2015 / Accepted: 6 November 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Tunis Gulf (northern Tunisia, Mediterranean Sea) is of great economic importance due to its abundant fish resources. Rising urbanization and industrial development in the surrounding area have resulted in an increase in untreated effluents and domestic waste discharged into the gulf via its tributary streams. Metal (Cd, Pb, Hg, Cu, Zn, Fe, and Mn) and major element (Mg, Ca, Na, and K) concentrations were measured in the grain fine fraction Mg > Zn > Mn > Pb > Cu > Cd > Hg. Metals tend to be concentrated in proximity to source points, suggesting that the mineral enrichment elements come from sewage of coastal towns and pollution from industrial dumps and located along local rivers, lagoons, and on the gulf shore itself. This study showed that trace metal and major element concentrations in surface sediments along the Tunis Gulf shores were lower than those found in other coastal areas of the Mediterranean Sea. Responsible editor: Philippe Garrigues * Lotfi Aleya [email protected] 1
Université de Bourgogne Franche-Comté, Laboratoire de Chrono-Environnement, UMR CNRS 6249, Besançon, France
2
Institut National des Sciences et Technologies de la Mer (INSTM), Laboratoire Milieu Marin, Centre la Goulette, Tunisie
3
Institut Supérieur de Pêche et d’Aquaculture de Bizerte, Unité de recherche: Exploitation des Milieux Aquatiques, Tunisie et Faculté des Sciences de Bizerte, Errimel, B.P.15, 7080 Bizerte, Tunisie
Keywords Tunis Gulf . Surface sediments . Metal contamination . AQUARISK model
Introduction Coastal Mediterranean ecosystems are generally threatened by pollution from urban and industrial activities. One resulting problem is observed in the ability of marine surface sediments to accumulate toxic metals, becoming an ecological concern. Sediments are the main sink for metals in aquatic ecosystems and thus constitute a threat to human health and the food web (Simpson et al. 2012; Belabed et al. 2013; Ben Salem et al. 2014). Further knowledge of the spatial distribution of metal concentrations in surface sediments from a specific ecosystem has become essential, especially if the system contains abundant fish resources and is located, like Tunis Gulf, in a hydrodynamically complex region (Brahim et al. 2015; Zaaboub et al. 2014b). Tunis Gulf, located adjacent to the metropolitan area of the city of Tunis with its growing population, is an area of heavy industry (chemical manufacturing, metal processing, factories, and electronic and mechanic industries). Industrial and domestic waste is discharged into local rivers where it initially affects animal and plant tissues, but once in the gulf, its metal contents settle to the seafloor. Harbor activities (commercial shipping, fishing, and naval reparation) also constitute potential sources of metals for coastal sediments (Warnken et al. 2001; Forman et al. 2003; Weyrauch et al. 2010; Zaaboub et al. 2014a). These metals, combined with those of continental origin already affecting the tissues of living sea organisms, may also end up in sediment deposits and thus contribute to a permanent reserve of harmful contaminants for aquatic fauna and flora (Hooda 2007; Bhakta et al. 2014). Spatial distributions of metallic elements in sediments are therefore of
Environ Sci Pollut Res
primary significance in locating sources of pollution (Liu et al. 2003; Taylor and Matthai 2001; Zhang et al. 2007; Zhou et al. 2007). Concerning hydrodynamics, Tunis Gulf occupies a paramount position since it is influenced by the hydrological regime of the Mediterranean Sea which, in the western Mediterranean, is driven by a regional current, the Atlantic Water (AW). The current enters the Straits of Sicily splitting into two branches: one flowing into the southeastern Mediterranean and the second, the Atlantic Tunisian Current (ATC), flowing southwards along the Tunisian coast, directly affecting circulation at the mouth of the gulf (Ben Ismail et al. 2012, 2014). Recent studies (Brahim et al. 2015) of Tunis Gulf have pointed out in particular that all sediment distribution is controlled by water movement and that an enhanced fraction of fine sediments is transported by the major Mediterranean currents to be deposited in the gulf’s central zone, while coarse sediments are found along the gulf’s western shore as a result of littoral transport under wave and swell action. A gap remains however in our knowledge of the spatial distribution of metals along the gulf shores, though metals are known to be associated with the sediment fine fraction (Belabed et al. 2013; Zaaboub et al. 2014a). This complex sedimentary context includes both currents and waves, along with an abundant nutrient and metal discharge load generally found in coastal areas (mainly as runoff from urban activities). It thus appeared that an increased knowledge of the metal concentrations arriving in the gulf could be a first step in establishing better management strategies to alleviate the dangers inherent in metal accumulation. High spatial resolution sampling was used in this study to quantify metal accumulation in marine sediment in the western Mediterranean. Risk was assessed using the AQUARISK model to estimate the degree to which contaminant data are likely to exceed critical guideline levels for metals in sediment and critical values determined from species sensitivity distributions (SSD) and probability density distributions (PDD).
Material and methods Study site Tunis Gulf is located in the northwestern Mediterranean (between 36° 43′ N/37° 10′ N and 10° 11′ E/11° 05′ E) and has been heavily affected by the region’s growing population (2.5 million people) and intense industrialization. As in all coastal environments, Tunis Gulf’s industry, urban and harbor activities comprise potential sources of metals, discharging both solid and liquid wastes into the gulf’s tributaries, the
Mejerda, Meliane, and El Abid Rivers. Originating in eastern Algeria, the Mejerda is the principal source of continental water and sediment discharge into the gulf (Fig. 1). With a catchment area of approximately 25,000 km2 and covering most of northern Tunisia, it has an annual total discharge of around 1100 Mm3 year−1, with a total sediment load of 2106 t year−1. Further south, other streams and two main water bodies, Lake Tunis and Ghar El Mehl Lagoon, are connected to the gulf. Due to the presence of neighboring lead and zinc mines, the Mejerda catchment area has for several decades been subjected to multiple sources of trace element contamination. A considerable amount of residue has accumulated in waste dumps, while other streams discharge vehicle compounds of both industrial and urban origin. Previous investigators have noted that the area’s dykes are a potential source of contamination (Ben Hamza 1994; Jdid et al. 1999; Moldenhauer et al. 2008; Mlayah et al. 2009). Sampling Sediment sampling was carried out at 49 stations, each selected so as to provide good area coverage of Tunis Gulf coast (Fig. 1). Sampling depths ranged from 1.7- to 20-m depth. Surface sediments were collected with a Van Veen grab sampler (surface area 0.1 m2) with a depth of 10–20 cm. The samples were placed in polyethylene jars, immediately frozen and stored at −4 °C until analysis. Grain size analysis Grain size was determined for all surface sediment samples using Stokes Law to characterize particle size distribution. Sediment was placed on top of the column for a limited time or until it passed through the sieve at a constant low rate and the different sediment fractions could be separated. Metal analysis Metal analysis was conducted on the
