Science of the Total Environment 511 (2015) 407–415

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Environmental risk assessment of the Moroccan Atlantic continental shelf: The role of the industrial and urban area Mohamed Maanan a,⁎, Bendahhou Zourarah b, Mohamed Sahabi b, Mehdi Maanan c, Pascal Le Roy d, Khalid Mehdi b, Fouad Salhi b a

UMR 6554 LETG-Nantes, Université de Nantes, BP 81227, 44312 Nantes, France Marine Geosciences Laboratory (URAC 45), REMER, Faculty of Sciences, El Jadida, Morocco Earth Sciences department, Faculty of Sciences, University Hassan II Ain Chock, Casablanca, Morocco d UMR 6538 Domaines Océaniques, Inst. Univ. Europeen de la Mer, Université de Bretagne occidentale, Plouzané, France b c

H I G H L I G H T S • • • •

Natural and anthropic inputs contribute to heavy metal pollution in shelf sediment. Metal distribution is under dual control sediment facies and marine currents. Generally metals in sediments from the Moroccan shelf were not greatly enriched. Stations close to urban and industrial areas have large concentrations of the metals.

a r t i c l e

i n f o

Article history: Received 14 October 2014 Received in revised form 25 December 2014 Accepted 29 December 2014 Available online xxxx Editor: F.M. Tack Keywords: Atlantic shelf Sediment quality Environmental assessment Heavy metals Anthropogenic input

a b s t r a c t The present research presents the first large-scale analysis of heavy metal assessment in the Moroccan Atlantic shelf. This work provides scientific basis for future studies on environmental research and fills the gap in knowledge on the worldwide continental platforms. Metal distributions identified three different zones, mainly influenced by industrial and urban sewer (northern areas), agriculture runoffs (central zone), and estuarine discharges (southern areas), respectively. In the north part of the shelf, metal enrichments are observed near industrial and urban sewer mouths (Casablanca and Mohammedia cities). In the south and central areas, the probable absence of human impact on sediments is attributed to effective trapping in the estuary (Oum Er Rbia) and coastal zones, as well as dilution with less contaminated sediments and shelf sediments and removal with fine fractions due to estuary discharges. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The deep waters to the north-west of Morocco are now subject to the environmental pressures of a major industrial area. Urban and industrial activities contribute to the input of significant amounts of pollutants (including heavy metals) into the marine environment and directly affect the coastal systems in which they are often deposited (Zourarah et al., 2007; Maanan, 2008). There are certainly other local factors that impact sediment delivery, including the influence of humans (Maanan et al., 2014). The disposal of waste products into rivers and estuaries, especially those in industrial and population centers,

⁎ Corresponding author.

http://dx.doi.org/10.1016/j.scitotenv.2014.12.098 0048-9697/© 2014 Elsevier B.V. All rights reserved.

has led to a significant increase in metal contamination (Zourarah et al., 2009; Kalloul et al., 2012). Until recently, its direct effect on fish stocks and the potential environmental impact on deep-water fisheries have gone largely unremarked (Banaoui et al., 2004; Maanan, 2007; Hennani et al., 2012; Daief et al., 2014). On the Moroccan coast, there have been several studies of the coastal ecosystems (beaches, estuaries and lagoons). However, none has considered the quality of the sediments found on the continental shelf. Previous investigations of Moroccan coastal ecosystems have documented significant anthropogenic enrichment of heavy metals (Cheggour et al., 2005; Maanan, 2008; Mhamdi Alaoui et al., 2010). Therefore, the main objective of this study is to determine the distribution of heavy metals on the continental shelf and to assign the reason for their presence as lithologic, anthropogenic or a cumulative effect of both components.

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We also propose to elucidate the main geomorphological, hydrological, sedimentological, and catchment characteristics affecting these patterns. 2. Materials and methods 2.1. 1—study area The study area is located on the western coast between El Jadida and Casablanca (Fig. 1). This basin is part of the Western Meseta structural domain and is linked to the rifting of the central Atlantic Ocean during Upper Triassic to Lower Liassic times (Sahabi et al., 2004). The Doukkala continental Moroccan margin segment is considered mainly stable during the Cenozoic and is situated between the Rifian chain in the north and the Atlasic chain in the south. Both chains were uplifted during Miocene times in response to the Africa–Europe collision (Piqué and Borntraeger, 2001). Recently, a high-resolution seismic survey along the north-west Moroccan Atlantic continental shelf showed that sedimentary cover is under the dual control of tectonics and climatic variations (Maad et al., 2010; Le Roy et al., 2014). Tectonic deformations occurred mainly during the Upper Miocene and accentuated shelf subsidence through reactivation of inherited N20°/N40° and N140° faults in response to the Europe/Africa collision (Le Roy et al., 2004, 2014; Maad et al., 2010). The available bathymetric data throughout the studied area were provided by the Moroccan Hydrographic and Oceanographic Service of

the Royal Navy and the bathymetric map of the El Jadida continental shelf was manually drawn by Vanney (El Foughali, 1982). It shows a 40-km-wide shelf deepening (0.15–1%) to a water depth of 150 m corresponding to the shelf-break (El Foughali and Griboulard, 1985). The fringing continental slope displays a major structural feature consisting of a wide plateau, named the Mazagan plateau, edged with a huge escarpment. A wide sedimentary wedge extending between water depths of 30 m and 100 m in front of the Oum Er Rbia estuary mouth marks the morphology of the continental shelf. Quaternary deposits are restricted to the low stand sedimentary wedge extending below a water depth of 130 m and to the last high stand system tract corresponding to the Oum Er Rbia prodelta. Terrigenous sediments built up the Oum Er Rbia prodelta during the estimated time interval of 6–2 ka coinciding with the stabilization of high sea level and pluvial stage (Le Roy et al., 2004). These input contributions have decreased since the construction of many hydraulic barrages in its catchment area (Zourarah et al., 2009). The hydrodynamic conditions on the north-western Moroccan continental shelf are mainly dominated by the currents induced by powerful storms and waves in the west and north-west. The general oceanic currents are represented by the Canary Current, which forms a gyre in a clockwise direction in the Ibero–Moroccan bay. Periodically, a branch of this current approaches the coast and affects the continental shelf with a maximum effect on its outer part. Its speed ranges between 25 and 75 cm/s (US Naval Oceanography Office, 1965). It reaches maximum

Fig. 1. Study area — Moroccan Atlantic continental shelf and catchment land-use.

M. Maanan et al. / Science of the Total Environment 511 (2015) 407–415

values when it is combined with the effects of the inner waves and storms. It can then cause a partial recovery of sediment. The strongest hydrodynamic energy is due to the currents of weather origin, such as the swell, and the currents returning to the bottom generated by storms. Storms of the decennial type, such as those described by Gelci et al. (1957), are characterized by swell amplitudes from 6 to 8 m and periods from 14 to 16 s. According to Castaing et al. (1999), these swells are an actuation of the particles of size ranging between 300 and 450 μm involving the inner shelf. Tides along the North Atlantic coast of Morocco are semidiurnal and range between 3.34 (2.45) and 0.35 (1.28) m elevation in spring (neap) conditions offshore of Casablanca, with the highest (lowest) high (low) water reaching 3.79 (0.10) m above the local chart datum (Hydrographic Zero, which lies 1.92 m below local mean sea level) (Charrouf, 1989, quoting results from field surveys in 1970). Another dynamic agent of lower intensity intervening on the Moroccan Atlantic continental shelf is the increase in deep water (upwelling) related to the north-east trade winds. These movements are frequent to the south of El Jadida and more episodic towards the north. The study area is located between two important cities in Morocco (Fig. 1): Casablanca, the largest economic and industrial center with about 4 million inhabitants, and El Jadida, considered Morocco's second industrial center with 2 million inhabitants, which is undergoing a major transformation because of the development of its agricultural, tourist and industrial activities, particularly those related to phosphate production and to the Jorf Lasfar harbor. In these two cities, wastewater is evacuated directly into the marine environment without treatment. In Morocco, 66% of industries are located in these coastal areas. Consequently, 80% of significant industrial waste (more than 2000 point sources) goes directly into the sea. The coast between Casablanca in the north and El Jadida in the south currently includes nearly 4000 large industrial areas (more than 50% of the biggest industrial areas at national level). The largest industrial zones are those of Casablanca, particularly Ain Sebaâ and Sidi Bernoussi-Zenata, El Jadida and Jorf Lasfar. The wastewater of the rural and urban centers of the coast between Casablanca and El Jadida is poured directly into the ocean. These activities, which constitute the backbone of the region's economic boom, together with the growth of population, can affect the exploitation of its maritime resources (fishing, exploitation of algae, oyster farming, etc.), which are subjected to the fatal influence of numerous discharges (industrial, urban, and agricultural). This, of course, may have an impact on the quality of the maritime environment in the long term. 2.2. 2—sampling/experimental Superficial sediments (n = 35) were collected by Van Veen grab (depth penetration varies between 8 and 12 cm) from the inner shelf during three oceanographic cruises: (i) PROTIT I in June 2001 (TIT0199), (ii) PROTIT II in June 2003 (TIT03-99) and (iii) NOMAD from 15th July to 5th August 2007 (NOM07-99). The surveys were carried out aboard the Moroccan vessel Al Manar (PROTIT I and II) and the French R/V Côtes de la Manche (NOMAD). Sediment could not be collected at 12 stations where the substrate is characterized by bedrock. The samples were dried in a drying oven between 35 and 40 °C. Grain size measurements were performed with a laser granulometer (Malvern, Mastersizer at LETG (UMR 6554), University of Nantes). The filters for POC (Particulate Organic Carbon) analysis were acidified with HCl (2 N) to remove carbonates and dried at 60 °C for 24 h before POC analysis was carried out with a LECO CS 125 analyzer (Etcheber et al., 1999; Veyssy et al., 1999). POC content is expressed as a percentage of dry weight of sediment, abbreviated POC%. Precision was better than ±5%. A Bernard calcimeter was used to obtain the calcium carbonate (CaCO3) content in sediment (Lamas et al., 2005). For metal analyses, aliquots of ~0.25 g of dry sediment were digested using 10 mL of a mixture of 5:4:1 HNO3 + HCl + HF. The digested sediment was cooled, filtered, and finally diluted to 25 mL (Loring and

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Rantala, 1992). After complete cooling, the digested solution was evaporated to dryness. Each sample was brought to 5 ml using 150 ml HNO3 and double-deionized water (MilliQ®). Al and Fe concentrations were determined by atomic absorption spectrophotometry (AAS, Varian, SpectrAA 600®). Mercury concentrations were measured by cold vapor atomic absorption spectrometry (CVAAS), detection limits of Hg were 0.005 mg kg− 1 dry wt. Other trace metal concentrations (Cd, Cr, Cu, Mn, Ni, Pb and Zn) were determined using inductively coupled plasma mass spectrometry (ICP-MS, Elan 5000, Perkin-Elmer). Detection limits were several orders of magnitude lower than the elemental concentrations found in the samples (detection limits in pg g−1 are 1 Cd, 14 for Cr, 19 for Cu, 15 for Ni, 0.5 for Pb and 28 for Zn). The determinations were validated using BCSS-1 and PACS-1. Each batch of samples (5 samples per batch) included blanks and certified international marine sediment reference materials (BCSS-1 and PACS-1). PACS-1 and BCSS-1 were digested and analyzed following the same protocol as for the suspended particulate matter, in order to assess the efficiency of the extraction method. For most metals, the recovery from PACS-1 was below 75% (72% Al, 64% Fe, 71% Cu, 73% Zn, 62% Pb, 67% Mn, 71% Ni, 67% Cr, 83% Hg and 85% Cd), which was the result of the incomplete dissolution of certain minerals, such as silicates, by the chosen digestion method. Higher recoveries were achieved from BCSS-1 (85% Fe, 94% Cu, 96% Zn, 97% Pb, 92% Mn, 98% Ni, 97% Cr, 98% Hg and 97% Cd). For each metal, a predicted value and a standard error (95% upper confidence limit for “natural” sediments) were calculated for every sample by regression equations using Al content. These values were used to obtain a regional reference range for all points on the regression line for each metal, which is defined as the predicted value plus twice the standard error of estimate (1 ± 2 s). Because the concentrations and spatial distribution of heavy metals can be related to clay or organic matter content, the Pearson correlation coefficient was calculated for these parameters using the statistical software package Statistica, Release 12 (StatSoft, 2014). 3. Results and discussion 3.1. General character of sediments The sedimentological study shows great variability in sedimentary facies. Biogenic sands and rock formations occupy the sector closest to the coast. More broadly, the inner shelf, up to about 75 m, is covered with fine sands. A mudflat extends over the middle shelf. On the outer shelf, sedimentary cover does not occur everywhere: biogenic muddy sands occupy depressions between rocky entablature. The grain size of the surface sediment on the Moroccan Atlantic continental shelf between El Jadida and Casablanca shows a distribution that follows the normal trends, or those parallel with the coastline, and is closely connected with depth. It changes from coarse sediments (sands), without a fine fraction and with a mean grain size higher than 125 μm, to fine sediments (mud) with a mean grain size ranging from 27 to 39 μm and with a clay and silt content higher than 70% (Fig. 2). Deposits are restricted to the shelf-break with a low stand sedimentary wedge extending below a water depth of −130 m and to the proximal shelf where the last high stand system tract corresponds to the Oum Er Rbia prodelta (Le Roy et al., 2004). The distribution of surficial sediment on the Moroccan continental shelf shows similar characteristics to those of other north-western African shelves that receive significant river inputs (Plewa et al., 2012). The particulate organic matter (POC) content ranges between 0.4 and 4.3%. The highest values are observed in the Casablanca Bay shoreface (content varies between 3.0 and 4.3%). Maximum POC contents are detected in front of the Casablanca–Mohammedia sewer mouths (NOM07-16) and in Casablanca offshore stations (TIT03-09 and TIT03-10) and are probably due to marine dynamics. POC distribution in the surface sediments closely follows the ocean surface

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productivity patterns and anthropogenic inputs. This finding was also revealed at the southern continental shelf of Morocco (Plewa et al., 2012). The CaCO3 contents are mainly controlled by dilution with terrigenous matter. The major sedimentary environments are: (1) the shoreface covered by lithogenic sands, up to 50 m, whose texture is very thin and fairly homogeneous. It is characterized by a median value between 120 and 63 μm, a carbonate ratio of 24 to 30% and a POC ratio varying from 0.4 to 1.0%; (2) the Oum Er Rbia prodelta, located on the inner and middle shelf and covered by mud. It is characterized by high levels of silt (70%), 10 to 30% of carbonates and 1.4 to 2.1% of POC. The particle size of sediment ranges from 40 to 70% silt and 18 to 24% clay; (3) the outer shelf covered by biogenic muddy sands. The bioclastic sands are formed by various macrofaunal debris and are characterized by carbonate content greater than 70%. These sands predominate over the entire outer continental shelf, where they correspond to the maximum regressive Pleistocene shoreline. Holz et al. (2004) showed that the fine-grained fraction representing river-sourced mud is confined to the area off Cape Ghir (in the south of Morocco), where it constitutes up to 90% of the relative sediment composition.

3.2. Heavy metal distribution POC and heavy metal concentrations in marine sediments are shown in Table 1. The aluminum content is 3–5% in the offshore and increases to more than 7% in the Oum Er Bia shoreface (Fig. 1). The distribution pattern of the Fe/Al ratio of the surface sediments shows a slightly zonal gradient along the NW African coast with higher values near shore and lower values in the open ocean with an increase in the ratio again towards the deep waters. Terrigenous elements like Al and Fe reflect the importance of the fluvial influence (Zourarah et al., 2009). The concentration of Mn is not a reliable tracer for productivity in this region (Maanan et al., 2004; Zourarah et al., 2007, 2009), since it is mainly supplied by terrigenous input (coupled with aluminosilicates). Mn is an excellent tracer of continental inputs into aquatic systems produced by the breaking up of rocks and soils of surrounding watersheds (Veron et al., 1992). Mn, with a minimum concentration of 205 mg·kg−1 (station TIT03-15) and a maximum of 799 mg·kg−1 (station NOM07-16), has the highest values in those stations nearest the coast with a decreasing tendency going towards the stations farthest from the coast. In the sediments sampled near the abovementioned

Table 1 POC (%) and heavy metal concentrations compared with Sediment Quality Guidelines (SQG) in marine sediments (Al and Fe are reported in % and other trace elements are reported in mg·kg−1 dry weight). Depth (m) TIT01-01 70.0 TIT01-02 90.0 TIT01-03 120.0 TIT01-05 102.0 TIT01-06 74.0 TIT01-11 99.0 TIT01-12 74.0 TIT01-14 71.0 TIT01-15 92.0 TIT01-16 95.0 TIT01-17 72.0 TIT01-19 70.0 TIT03-01 130.7 TIT03-02 138.7 TIT03-03 120.7 TIT03-04 99.0 TIT03-05 156.7 TIT03-06 137.7 TIT03-09 29.7 TIT03-10 58.0 TIT03-11 84.0 TIT03-14 97.5 TIT03-15 96.5 TIT03-16 65.0 TIT03-17 70.0 TIT03-18 102.0 TIT03-19 99.2 NOM07-22 69.6 NOM07-25 77.0 NOM07-26 96.6 NOM07-27 104.0 NOM07-28 93.5 NOM07-29 74.0 NOM07-16 45.7 NOM07-17 102.0 Min Max Mean Standard deviation Backgrounda TEL SQGb PEL

POC

Al

Fe

Pb

Zn

Cu

Mn

Cr

Ni

Cd

Hg

2.0 1.1 1.0 2.1 1.9 1.6 1.7 1.6 1.5 1.4 1.4 1.3 1.8 2.1 2.4 2.0 1.2 1.9 4.3 3.6 2.0 1.6 2.0 3.0 2.1 2.0 1.6 1.4 1.1 0.9 0.7 0.4 2.1 4.2 0.4 0.4 4.3 1.8 0.9 – – –

4.9 6.4 4.1 6.3 4.3 6.2 5.1 4.2 6.0 6.0 4.5 4.6 7.2 6.6 11.3 6.0 7.7 6.9 7.1 7.9 5.6 4.6 4.0 7.2 4.8 5.1 4.1 4.8 4.9 4.9 5.0 4.2 3.0 10.1 5.9 3.0 11.3 5.8 1.7 8.0 – –

2.8 3.6 3.8 3.5 2.9 3.6 3.3 2.8 3.4 3.6 2.8 2.9 2.0 2.0 2.6 3.1 4.5 4.9 3.9 3.1 3.8 3.0 4.0 3.6 3.7 3.5 2.8 3.1 3.7 2.0 3.8 3.4 2.3 7.7 3.3 2.0 7.7 3.4 1.0 4.7 – –

23.1 28.8 24.5 31.4 15.0 28.9 20.0 23.4 28.6 21.2 15.3 26.0 14.1 13.2 16.2 29.9 12.9 17.9 85.0 77.0 22.7 16.2 18.6 56.0 21.8 16.1 15.1 22.2 15.2 23.3 27.0 21.8 22.5 77.7 11.9 11.9 85.0 26.9 18.1 20 30.24 112

74.1 97.8 66.9 76.3 51.2 79.5 69.7 46.5 75.8 73.5 58.1 55.1 51.0 48.5 46.0 74.0 58.0 57.0 88.0 81.0 51.0 44.0 65.0 75.0 60.0 34.0 45.0 58.0 64.0 55.0 58.0 57.0 53.0 98.9 55.0 34.0 98.9 62.9 14.9 95 124 271

16.5 20.6 11.5 17.3 12.9 17.7 15.7 11.6 17.7 17.9 13.2 13.7 16.5 19.0 21.5 16.8 15.0 15.6 52.7 44.9 14.0 22.0 21.0 32.7 16.0 15.0 14.7 15.8 18.4 12.9 23.8 11.8 12.0 50.9 12.1 11.5 52.7 19.5 10.1 45 18.7 108

376 444 411 448 387 447 404 372 427 448 371 388 299 298 297 425 312 316 725 623 243 311 205 489 308 302 306 305 304 302 304 301 300 799 306 205.0 799.0 380.1 123.1 850 – –

72.6 80.8 53.5 67.3 55.1 69.4 61.9 48.2 46.4 63.3 51.3 55.5 46.5 46.4 46.3 56.7 54.5 52.8 208.6 192.9 89.7 56.9 67.0 180.7 54.5 52.8 57.5 42.7 41.5 40.9 44.9 48.3 51.8 202.8 51.7 40.9 208.6 71.8 46.1 90 52.3 160

34.9 44.5 28.1 36.9 28.7 37.6 33.3 25.5 37.6 36.2 27.5 29.7 21.2 20.1 18.9 32.0 22.8 22.8 56.9 61.9 28.8 23.8 26.5 45.1 33.6 32.9 30.8 26.7 25.5 31.1 23.0 22.1 22.5 58.9 35.1 18.9 61.9 32.1 10.5 68 15.9 42.8

0.59 0.59 0.41 0.48 0.45 0.49 0.50 0.41 0.46 0.50 0.45 0.46 0.51 0.51 0.50 0.56 0.67 0.43 1.95 1.66 0.56 0.67 0.34 1.22 0.55 0.23 0.98 0.56 0.67 0.43 0.28 0.67 0.56 1.77 0.05 0.05 1.95 0.63 0.40 0.3 0.68 1.2

0.08 0.06 0.07 0.06 0.02 0.04 0.04 0.02 0.04 0.04 0.04 0.02 n.d. n.d. n.d. n.d. n.d. n.d. 0.89 0.75 0.09 0.08 0.03 0.55 0.02 0.05 0.08 0.03 0.05 0.05 0.06 0.04 0.05 0.66 n.d. 0.00 0.89 0.11 0.22 0.4 0.13 0.7

n.d.: not detected. a Sedimentary rock from Turekian and Wedepohl (1961). b Sediment Quality Guidelines: probable effect level (PEL) and threshold effect level (TEL) from MacDonald et al.., 1996.

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bank, an increase in concentration values can be noted. The strong correlation of Mn with other trace elements (Pb, Cu, Cr, Ni, Cd and Hg) is noteworthy, indicating a common source for the element and confirming anthropogenic inputs on the continental shelf (Table 1). The trace element analyses display different distributions. Pb, Cu, Cr and Hg, with minimum values found at stations NOM07-17, TIT01-03, NOM07-26 and TIT03-16, and maximums at station TIT03-09, have a distribution influenced by the presence of human activities along the coastline. Gao et al. (2014) and Maanan et al. (2015) showed that the coastal waters near estuaries and big cities had higher potential risks for marine waters. The maximum concentrations, nearest the Casablanca coast, are more than 77 mg·kg−1 for Pb, 45 mg·kg−1 for Cu, 190 mg·kg−1 for Cr and 0.75 mg·kg−1 for Hg. The minimum concentrations of less than background values for Pb, Cu, Cr and Hg are further offshore and situated towards the south at the foot of a 60-m-deep bank. Zinc, with a minimum concentration of 34 mg·kg− 1 (station TIT03-18) and a maximum of 98.9 mg·kg−1 (station NOM07-16), also displays a parallel belt distribution and, furthermore, the coastal stations show higher mean values. Nickel and cadmium have a uniform distribution with minimum values of 18.9 mg·kg−1 (station TIT03-03) and 0.05 mg·kg−1 (station NOM07-17) and maximums of 61.9 mg·kg−1 (station TIT03-10) and 1.95 mg·kg−1 (station TIT03-09), respectively. The sedimentology of surface sediment enables the depositional environments where anthropogenic contaminants may accumulate to be identified (Daief et al., 2014). The distribution results of Pb, Cu, Mn, Cr, Ni, Cd and Hg, compared with background and toxicological reference values for sediments proposed by MacDonald et al. (1996), are summarized in Table 1. It is apparent that the concentrations of all the trace elements differ greatly from the background as defined as continental crust (Turekian and Wedepohl, 1961), and there is significant variation among the values, which indicates that these elements did not originate from natural lithology. It is also evident that the average total concentration of Cd and Pb in the sediment samples exceeds the geochemical background (continental crust). Thus, anthropogenic activities contribute to the enrichment of these metals. Moreover, when compared with effect-based toxicological levels, severe pollution for all the trace metals, except Zn, is observed for sites TIT03-09, TIT03-10, TIT03-16 and NOM07-16. Pearson's correlation coefficient matrix among the selected heavy metals is presented in Table 2. Significant correlations between Cr and Hg (r = 0.97), Pb and Hg (r = 0.96), Pb and Cu (r = 0.94), Pb and Cr (r = 0.94), Cu and Hg (r = 0.93), Cd and Hg (r = 0.92), Cd and Pb (r = 0.90), Cu and Cr (r = 0.89), Cd and Cu (r = 0.89), and Cr and Cd (r = 0.89) could indicate the same or similar source inputs. Pb, Cu, Mn, Cr, Ni, Cd and Hg are positively correlated (Table 2) and their distributions show very clearly the impact of the metal inputs. The greater and wider anomaly of these metals is produced by the supply from the industrial zones. The most contaminated sediment accumulates southward from the Casablanca–Mohammedia industrial areas along the shelf shallower than 50 m, indicating that the waste discharged Table 2 Pearson's correlation matrix of Al, Fe trace elements and POC (n = 36; p-value b 0.05).

Al Fe Pb Zn Cu Mn Cr Ni Cd Hg POC

Al

Fe

Pb

Zn

Cu

Mn

Cr

Ni

Cd

Hg

POC

1.00 0.42 0.39 0.34 0.47 0.43 0.43 0.35 0.34 0.41 0.43

1.00 0.41 0.47 0.43 0.46 0.43 0.42 0.33 0.37 0.28

1.00 0.68 0.94 0.86 0.94 0.85 0.90 0.96 0.78

1.00 0.60 0.77 0.62 0.77 0.55 0.59 0.42

1.00 0.80 0.89 0.74 0.89 0.93 0.80

1.00 0.82 0.88 0.80 0.84 0.71

1.00 0.84 0.89 0.97 0.83

1.00 0.74 0.83 0.65

1.00 0.92 0.80

1.00 0.81

1.00

The matrix showing the relationship between trace elements and Fe–Mn oxides, clays (Al content) and organic matter (POC). Bold text highlights strong correlations (r N 0.7).

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from this wastewater is reoriented by currents that flow mainly in this direction. Heavy metal concentration is influenced by the texture of the sediment and can also be affected by major components such as organic matter, clay minerals, and carbonates (Salomons and Förstner, 1984), although some studies report no correlation between metal concentrations and organic matter or fine sediment contents (Lokas et al., 2010; Maanan et al., 2013). Here, the absence of significant relationships between the heavy metals and POC is noticeable on the Moroccan continental shelf. Also, we noted the absence of a significant correlation of the metals with sediment texture, Al and POC points towards the anthropogenic enrichment of these metals on the continental shelf. The Pearson correlation matrix of the sedimentary parameters of estuary offshore sites reveals differences in the interrelationships between the geochemical parameters in these systems (Fig. 3). According to the analysis results, many metals are significantly correlated (p b 0.05). Al is positively correlated with Fe (r = 0.84) while highly significant positive correlations are recorded between Al, Fe, Pb, Cu, Mn, Ni and Zn (N 0.7). Oliveira et al. (2011) found a significant correlation between Al and metals on the shelf around the Nazaré canyon. Significant correlations indicate that most of the contaminants discharged by the Oum Er Rbia estuary are associated with fine particles (Zourarah et al., 2009). The heavy metal concentrations in the estuary sediment also show the degree of contamination of particles discharged by the Oum Er Rbia estuary onto the El Jadida–Casablanca continental shelf. Moreover, it has been found that activity in the Oum Er Rbia estuary plume is mainly due to the smallest particles, since the coarse ones sink rapidly to the bottom (Zourarah et al., 2009). This produces the observed deposition belt around the estuary and the high activity levels measured in bottom sediments in this area. Zourarah et al. (2009) showed that the Oum Er Rbia estuary sediment contained a wide range of heavy metal concentrations varying from levels similar to those recorded in the estuary bed sediments to maximum values of copper, 19.6 mg·kg−1; chromium, 9.5 mg·kg−1; lead, 28 mg·kg−1; zinc, 138 mg·kg−1 and cadmium, 0.36 mg·kg−1. Natural processes, such as weathering of rocks, have a noticeable effect on heavy metal concentrations in sediments. Montaño-Ley et al. (2007) showed the role of the dilution effect on potential pollutants by ocean waters and the diffusion of pollutants by marine currents. Accumulation of pollutants on the shelf depends on the balance between waste discharge and current dispersal. These currents are weak on average in semi-enclosed seas such as the Casablanca–Mohammedia bay, which favors the accumulation of contaminated solids in nearshore areas around the discharging sources of these seas. On the contrary, very high marine dynamics off the coast of Jorf Lasfar/El Jadida favor the dispersion of pollutants seaward and low accumulation of heavy metals in the south of the study area. 3.3. Quality guideline index 3.3.1. Enrichment factor The EF is an indicator reflecting the degree of environmental contamination. In this paper, EF was calculated using the global average shale data from Turekian and Wedepohl, 1961, which is considered representative of uncontaminated sediment (Reimann and De Caritat, 2005). The average values of shale were used because it is the dominant rock in the region (Snoussi et al., 2002). The EFs used here were calculated as the ratio between the Alnormalized metal values and the Al-normalized metal background values [EF = (Met/Al)sample / (Met/Al)background]. The geochemical normalization was obtained using Al as the reference element for the following reasons: (1) Al is associated with fine solid surfaces; (2) its geochemistry is similar to that of many trace metals; and (3) its natural sediment concentration tends to be uniform. EF values were interpreted as suggested by Birch (2003) where EF b 1 indicates no enrichment; b 3 is minor; 3–5 is moderate; 5–10 is

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100

% Clay

90

% Silts

80

% Sand

70 60 50 40 30 20 10

Sites

TIT01-01 TIT01-02 TIT01-03 TIT01-05 TIT01-06 TIT01-11 TIT01-12 TIT01-14 TIT01-15 TIT01-16 TIT01-17 TIT01-19 TIT03-01 TIT03-02 TIT03-03 TIT03-04 TIT03-05 TIT03-06 TIT03-09 TIT03-10 TIT03-11 TIT03-14 TIT03-15 TIT03-16 TIT03-17 TIT03-18 TIT03-19 NOM07-22 NOM07-25 NOM07-26 NOM07-27 NOM07-28 NOM07-29 NOM07-16 NOM07-17

0

Fig. 2. Sediment distribution on the Moroccan Atlantic continental shelf.

moderately severe; 10–25 is severe; 25–50 is very severe; and N50 is extremely severe. Heavy metals can be divided into two groups, anthropogenic and non-anthropogenic, and it is important to note that this division is based on the enrichment factor. In this study, the elements studied were proven to be deficient to minimally enriched, with EF values ranging 0.4–1.7 for Fe; 0.6–4.8 for Pb; 0.3–1.5 for Zn; 0.3–1.3 for Cu; 0.2–1.0

Mn

for Mn; 0.2–2.6 for Cr; 0.2–1.0 for Ni; 0.2–7.4 for Cd and 0.0–2.5 for Hg (Fig. 4). The enrichment factor of Pb, Cd and Cr in the Casablanca shoreface (TIT03-09, TIT03-10 and TIT03-16) is greater than two, indicating anthropogenic heavy metals in these stations, which can be attributed to the nearby industrial areas of the two big cities: Casablanca and Mohammedia. According to Fig. 4 Hg exceeds also an EF of 2 for TIT03-09.

Fe

500

4

y = 47.2x + 142.6 R² = 0.75

400

y = 0.3x + 1.4 R² = 0.84

3

300 2

200 1

100 0

0

0

1

2

3

Al

4

5

6

7

Zn

0

1

2

3

Al

4

5

6

7

4

5

6

7

4

5

6

7

Ni

100

40

y = 9.6x + 17 R² = 0.70

80

y = 5x + 5.7 R² = 0.78

30

60 20

40 10

20 0

0

0

1

2

3

Al

4

5

6

7

Pb

0

1

2

3

Al

Cu

40

20 y = 2.9x + 11.4 R² = 0.74

30

y = 2.1x + 4.6 R² = 0.80

15

20

10

10

5 0

0 0

1

2

3

Al

4

5

6

7

0

1

2

3

Al

Fig. 3. Regression plots for correlation between Al (%) and trace elements (mg·kg−1) for the Oum Er Bia offshore area.

M. Maanan et al. / Science of the Total Environment 511 (2015) 407–415

EF

413

8

Zn Pb

7

Cu 6

Mn Cr

5 Ni 4

Cd Hg

3 2

1

NOM07-16

NOM07-17

NOM07-29

NOM07-28

NOM07-26

NOM07-27

NOM07-25

TIT03-19

NOM07-22

TIT03-17

TIT03-18

TIT03-16

TIT03-14

TIT03-15

TIT03-11

TIT03-10

TIT03-09

TIT03-06

TIT03-04

TIT03-05

TIT03-03

TIT03-02

TIT03-01

TIT01-17

TIT01-19

TIT01-16

TIT01-15

TIT01-14

TIT01-12

TIT01-11

TIT01-05

TIT01-06

TIT01-03

TIT01-01

TIT01-02

0

Sites

Fig. 4. Enrichment factors (EFs) for heavy metals in surficial sediment.

3.3.2. Contamination factor and pollution load index (PLI) Pollution severity and its variation along the stations were determined using the pollution load index (Tomlinson et al., 1980). This is a quick tool to compare the pollution status of different sites.

Table 3 Contamination factor (CF) and pollution load index (PLI) for marine sediments. Station

CF

PLI

Fe

Pb

Zn

Cu

Mn

Cr

Ni

Cd

Hg

TIT01-01 TIT01-02 TIT01-03 TIT01-05 TIT01-06 TIT01-11 TIT01-12 TIT01-14 TIT01-15 TIT01-16 TIT01-17 TIT01-19 TIT03-01 TIT03-02 TIT03-03 TIT03-04 TIT03-05 TIT03-06 TIT03-09 TIT03-10 TIT03-11 TIT03-14 TIT03-15 TIT03-16 TIT03-17 TIT03-18 TIT03-19 NOM07-22 NOM07-25 NOM07-26 NOM07-27 NOM07-28 NOM07-29 NOM07-16 NOM07-17 Min Max Mean Standard deviation

0.59 0.77 0.81 0.74 0.62 0.76 0.70 0.60 0.73 0.76 0.59 0.62 0.44 0.43 0.55 0.66 0.95 1.04 0.82 0.65 0.80 0.63 0.84 0.76 0.79 0.74 0.59 0.66 0.78 0.43 0.80 0.73 0.50 1.64 0.69 0.43 1.64 0.72 0.21

1.16 1.44 1.23 1.57 0.75 1.45 1.00 1.17 1.43 1.06 0.77 1.30 0.70 0.66 0.81 1.50 0.64 0.90 4.25 3.85 1.13 0.81 0.93 2.80 1.09 0.80 0.76 1.11 0.76 1.17 1.35 1.09 1.12 3.88 0.59 0.59 4.25 1.34 0.90

0.78 1.03 0.70 0.80 0.54 0.84 0.73 0.49 0.80 0.77 0.61 0.58 0.54 0.51 0.48 0.78 0.61 0.60 0.93 0.85 0.54 0.46 0.68 0.79 0.63 0.36 0.47 0.61 0.67 0.58 0.61 0.60 0.56 1.04 0.58 0.36 1.04 0.66 0.16

0.37 0.46 0.26 0.38 0.29 0.39 0.35 0.26 0.39 0.40 0.29 0.30 0.37 0.42 0.48 0.37 0.33 0.35 1.17 1.00 0.31 0.49 0.47 0.73 0.36 0.33 0.33 0.35 0.41 0.29 0.53 0.26 0.27 1.13 0.27 0.26 1.17 0.43 0.22

0.44 0.52 0.48 0.53 0.46 0.53 0.48 0.44 0.50 0.53 0.44 0.46 0.35 0.35 0.35 0.50 0.37 0.37 0.85 0.73 0.29 0.37 0.24 0.58 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.35 0.35 0.94 0.36 0.24 0.94 0.45 0.14

0.81 0.90 0.59 0.75 0.61 0.77 0.69 0.54 0.52 0.70 0.57 0.62 0.52 0.52 0.51 0.63 0.61 0.59 2.32 2.14 1.00 0.63 0.74 2.01 0.61 0.59 0.64 0.47 0.46 0.45 0.50 0.54 0.58 2.25 0.57 0.45 2.32 0.80 0.51

0.51 0.65 0.41 0.54 0.42 0.55 0.49 0.38 0.55 0.53 0.40 0.44 0.31 0.30 0.28 0.47 0.33 0.34 0.84 0.91 0.42 0.35 0.39 0.66 0.49 0.48 0.45 0.39 0.37 0.46 0.34 0.32 0.33 0.87 0.52 0.28 0.91 0.47 0.15

1.97 1.96 1.38 1.60 1.51 1.64 1.67 1.36 1.53 1.68 1.51 1.55 1.71 1.70 1.68 1.83 2.23 1.43 6.50 5.53 1.87 2.23 1.13 4.07 1.83 0.77 3.27 1.87 2.23 1.43 0.93 2.23 1.87 5.90 0.17 0.17 6.50 2.11 1.35

0.20 0.14 0.17 0.15 0.04 0.09 0.10 0.05 0.10 0.09 0.10 0.06 0.00 0.00 0.00 0.00 0.00 0.00 2.23 1.88 0.23 0.21 0.09 1.38 0.06 0.11 0.20 0.09 0.11 0.11 0.14 0.10 0.12 1.65 0.00 0.00 2.23 0.28 0.55

0.62 0.71 0.56 0.64 0.43 0.61 0.55 0.44 0.58 0.58 0.47 0.49 0.00 0.00 0.00 0.00 0.00 0.00 1.65 1.47 0.58 0.55 0.49 1.20 0.51 0.44 0.55 0.49 0.51 0.46 0.52 0.49 0.47 1.72 0.00 0.00 1.72 0.54 0.42

The contamination factor (CF) was used in the present study to determine the contamination status of sediment. It was calculated according to the equation (measured concentration/background concentration) where the background value of the sedimentary rock metal was given by Turekian and Wedepohl (1961). The pollution load index of the place was calculated by obtaining the n-root from the n-CFs for all the metals (PLI = n√(CF1xCF2xCF3x … xCFn)) as developed by Tomlinson et al. (1980). CF values are shown in Table 3 with the PLI for each station. In the present study, contamination factors (CFs) N 4 (indicating very high contamination) are found for Cd at stations TIT03-09, TIT0310, TIT03-16 and NOM07-16 and for Pb at TIT03-09. All the stations have a CF N 1 for Cd except TIT03-18, NOM07-27 and NOM07-17. The contamination factors for Fe, Zn, Cu, Mn, Cr, Ni and Hg are lower than 1 for most stations; a few stations exceeded 1 for one or more metals, e.g., TIT01-02, TIT03-09, TIT03-10 and NOM07-16. The mean CF values are: Fe: 0.7 (low contamination); Pb: 1.3 (moderate contamination); Zn: 0.7 (low contamination); Cu: 0.4 (low contamination); Mn: 0.4 (low contamination); Cr: 0.8 (low contamination); Ni: 0.5 (low contamination); Cd: 2.1 (moderate contamination); and Hg: 0.3 (low contamination). On the basis of these results, sediments are enriched in metals in the following order: Cd N Pb N Cr N Zn N Fe N Ni N Cu N Mn N Hg. The Pollution Load Index values (Table 4) are generally low (b 1) in all the studied stations. The difference in indices is due to their difference in sensitivity towards the sediment pollutants. They confirm that the Casablanca–Mohammedia offshore (TIT03-09, TIT03-10, TIT03-16 and NOM07-16) is facing probable environmental pollution, especially from dangerous heavy metals (Pb and Cd) resulting from the increased level of untreated industrial waste being discharged at the coast. Metal concentrations in sediments from the Moroccan Atlantic continental shelf were compared to other studies performed in other areas of the world (Table 4). Generally, concentrations of Cd, Cu, Hg, Pb, and Zn in sediments of the northern part of the Atlantic continental shelf are similar to levels detected in sediments classified as contaminated from other regions of the world, while metal concentrations in sediments from the deeper part are comparable with uncontaminated sediments. 4. Conclusion The major findings of this research are listed below: • Concentrations of metals in sediment immediately adjacent to the Oum Er Rbia prodelta and high metal concentrations in fluvial sediment suggest that this catchment is a major source of heavy metals in the estuary.

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Table 4 Average metal concentrations found in sediments from other regions of the world. Reference

Ala

Fe

Pbb

Zn

Cu

Mn

Ni

Cr

Cd

Hg

This study Marmara Sea, Turkey Topcuoğlu et al. (2004) Peninsular Malaysia Saraee et al. (2011) Continental shelf, Portugal Oliveira et al. (2011) East China Sea Liu et al. (2011) North Yellow Sea Huang et al. (2014) Florida Bay Caccia et al. (2003) Campeche shelf Gulf of Mexico Macias-Zamora et al. (1999)

5.7 – – 6.7 16 6.47 4.7 –

3.4 11.9 – 2.6 – 2.56 3.3 1.84

26.9 21.6 37.4 20 34.1 24.1 8.4 4.3

62.9 50.9 44.3 84 116 57.3 31 18.5

19.5 16.8 9.3 15.8 37.4 15.9 15 7.5

380 384 – 324 – 353 614 111

32.1 41.3 20.1 17 – 22 162 39.8

71.8 54.5 46.4 58 93.5 48.9 21 23

0.6 0.5 0.25 0.21 0.013 0.09 4.7 0.09

0.1 – 0.1 0.06 0.08 – –

a b

Al and Fe are reported in % sediment. Trace metals are reported in mg·kg−1 sediment.

• Sediments in the Casablanca shoreface are influenced by human activity. The most contaminated sediment accumulates southward from the Mohammedia industrial areas along the shelf shallower, indicating that the waste discharged from this wastewater is reoriented by currents that flow mainly in this direction. A common cause for these higher concentrations might be transport by the north–south flowing currents in the offshore part of the investigated zone. • Sediments on the northern part of the continental shelf exceed the lower guideline values indicating the possibility of some adverse biological effects on benthic animals. Nevertheless, as metal concentrations exceed the lower guideline values in this area, any interference with these materials would require additional environmental investigation. Metal concentrations in sediment of the estuary are at levels that probably pose little risk to benthic animals. • Our recommendations are to identify the primary sources of contamination, especially in the Casablanca shoreface, to consider remedial strategies and to undertake follow-up investigations of sediment on the northern part of the continental shelf to improve the evaluation of possible sediment toxicity. • The results of the three cruises (2001, 2003 and 2007) reflect well the current state of environment quality on the Moroccan continental shelf. According to these findings, local managers and decision makers should take into account the future of the quality of the environment under investigation by incorporating management plans into coastal and offshore management projects. Furthermore, the Atlantic shelf should be preserved to avoid unrecoverable irreversible changes in their unique coastal environment, as metal pollution is already very high, mainly due to negative human impacts.

Acknowledgments The authors gratefully acknowledge Prof. Filip M.G. Tack (Associate Editor, Science of the Total Environment) and four anonymous reviewers for their scientific suggestions and constructive comments. This research was sponsored in part by the ANR French agency “Agence Nationale de la Recherche” for “Investment for the Future” program, in a frame of LabexMer, under grant number ANR-10-LABX-19-01. References Banaoui, A., Chiffoleau, J.-F., Moukrim, A., Burgeot, T., Kaaya, A., Auger, D., Rozuel, E., 2004. Trace metal distribution in the mussel Perna perna along the Moroccan coast. Mar. Pollut. Bull. 48, 385–390. Birch, G.F., 2003. A test of normalization methods for marine sediment, including a new post-extraction normalization (PEN) technique. Hydrobiologia 492, 5–13. Caccia, V.G., Millero, F.J., Palanques, A., 2003. The distribution of trace metals in Florida Bay sediments. Mar. Pollut. Bull. 46, 1420–1433. Castaing, P., Froidefond, J.M., Lazure, P., Weber, O., Prud'homme, R., Jouanneau, J.M., 1999. Relationship between hydrology and seasonal distribution of suspended sediments on the continental shelf of the Bay of Biscay. Deep-Sea Res. II 46, 1979–2001. Charrouf, L., 1989. Les problèmes des ports marocains sur la façade atlantique, leur impact sédimentologique sur le littoral. (Doctorate thesis), Université Paris Sud, Centre d'Orsay (307 pp.).

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