Distribution and baseline values of trace elements in ...

Distribution and baseline values of trace elements in the sediment of Var River catchment, southeast France Jamal Al Abdullah, Hervé Michèl, Geneviève Barci Funel & Gilbert Féraud

Environmental Monitoring and Assessment An International Journal Devoted to Progress in the Use of Monitoring Data in Assessing Environmental Risks to Man and the Environment ISSN 0167-6369 Environ Monit Assess DOI 10.1007/s10661-014-3996-y

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Author's personal copy Environ Monit Assess DOI 10.1007/s10661-014-3996-y

Distribution and baseline values of trace elements in the sediment of Var River catchment, southeast France Jamal Al Abdullah & Hervé Michèl & Geneviève Barci Funel & Gilbert Féraud

Received: 1 October 2013 / Accepted: 12 August 2014 # Springer International Publishing Switzerland 2014

Abstract This study reports on the determination of trace element (TE)—Li, As, Co, Cs, Cu, Pb, U, and Zn—and major element (ME)—Si, Al, Fe, Mg, Ca, Mn, Na, and K—concentrations in 18 riverbed sediments and a sediment core from the Var River catchment using inductively coupled plasma mass spectrometry (ICPMS). The results were compared with those of a reference sediment core, and the contribution of clay and organic carbon contents in the distribution of TE and ME in the sediment samples was investigated. The mean concentrations of the ME were comparable in both core and riverbed samples and were within the natural averages. In the case of TE, the concentrations were lower in riverbed sediment samples than those found in the sediment core. High mean concentration of As was observed (7.6 μg g−1) in both core and riverbed sediments, relatively higher than the worldwide reported values. The obtained data indicated that the natural high level of arsenic might be originated from the parent rocks, especially metamorphic rocks surrounding granites and from Permian sediments. Statistical approach, viz., Pearson correlation matrix, was applied to better J. Al Abdullah : H. Michèl : G. B. Funel : G. Féraud Laboratoire de Radiochimie Sciences Analytiques et Environnement, Institut de Chimie de Nice, Université Nice Sophia Antipolis, EA1175, 06108 Nice cedex 2, France J. Al Abdullah (*) Department of Protection and Safety, Atomic Energy Commission, DamascusP.O. Box 6091, Syrian Arab Republic e-mail: [email protected]

understand the correlation among TE in both riverbed and sediment core samples. No significant metallic contamination was detected in the low Var valley despite of the localization of several industrial facilities. Therefore, results confirm that the concentrations of the TE obtained in the riverbed sediments could be considered as a baseline guide for future pollution monitoring program. Keywords Trace elements . Major elements . Baseline . Var River . Sediment . Sequential extraction . Arsenic . ICP-MS

Introduction It becomes crucial to follow in details the evolution of the hydrological systems, because of the general rainfall decrease in the Mediterranean region during the last 50 years and the increase of water consumption. Trace element (TE) distribution and evolution through time in European and Mediterranean rivers are not well known (Gaillardet et al. 2003; Cidu and Biddau 2007; Féraud et al. 2009). Major and trace elements (ME and TE) are introduced in the aquatic environment via different ways, i.e., atmospheric deposition, erosion of the geological matrix, or through anthropogenic sources (Azcue et al. 1996; Kumar Sarkar et al. 2004; Pekey et al. 2004; Yang and Rose 2005; Magesh et al. 2011; Vystavna et al. 2012). Trace elements pollution is considered as a serious problem due to their toxicity, ability to accumulate in the biota, and being not biodegradable in the environment (Zhang et al. 2011; Eça et al. 2013; Hsieh et al. 2013).

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The major and trace element contents of soil and sediment are very important in areas with chances to be contaminated from anthropogenic activities (Acosta et al. 2011). In ecosystems, sediment concentrates trace elements from aquatic systems and represents an appropriate medium for contamination monitoring. However, when environmental conditions change (pH, sediment redox potential, etc.), sediments can act as a source of TE and are potential sources of bioavailable elements to benthic flora and fauna leading to dispersion of elements through the food chain (Balls et al. 1997; Dassenakis et al. 1997; Santos Bermejo et al. 2003; StephenPichaimani et al. 2008). Hence, studying the distribution of trace elements in sediments becomes an important issue from the environmental point of view (Chen et al. 2012; Lovrenčić Mikelić et al. 2013). The background level of a given element in sediment is highly dependent on their texture, mineralogical composition, grain size, clay, major elements, organic carbon content, and the weathering conditions (Salminen and Tarvainen 1997; Klassen 1998; Tiwari et al. 2013). When local background is not available, it could be useful to compare TE concentrations with those from different parts of the world, i.e., the average crust or the upper crust continental (Hans Wedepohl 1995; Rudnick and Fountain 1995; Reimann and Garrett 2005; Rudnick 2005). The aquifers of the Var River supply the drinking water for more than half a million inhabitants in the territory of Alpes Maritime, southeast France. Up to date, there are absolutely no data concerning the elemental composition of sediments in this estuary. For these reasons, it is important to study the vertical and spatial distributions of TE and ME in this area. The present study focuses on investigating the concentrations of TE and ME in sediments of the Var River in order to determine the source of pollution and to present preliminary geochemical analysis of sediments of the Var River catchment. The obtained data would serve as a baseline to assess any future anthropogenic contamination by the studied elements. The hydrological system of the Var River The Var River is the largest river of the Côte d’Azur area and starts at 2,600-m altitude in the French Alpes with a catchment of 2,800 km2. It flows southeast for 110 km into the Mediterranean Sea between Nice and SaintLaurent du Var. The main tributaries of Var River are Coulomp, Tineé, Vésubie, Estéron, and Cians Rivers

(Fig. 1), in addition to numerous small streams contributing to the final discharge along the river. As a typical Mediterranean river, with two annual flooding seasons, April/May and October/November, the Var River is affected by contrasted water flow regimes, with a discharge that can be as high as 3,000 m3s−1. Because of the longer dry seasons that were observed in the last few years, various ecosystem parameters of the catchment have been changed, such as mechanical and chemical erosion and fluxes of solid and dissolved matters reaching the Mediterranean. The Var River and its tributaries rise from a relatively protected natural environment, whereas the main aquifers are located in the lower part of the valley, just down the industrial zone. The surface water and groundwater of the catchment are classified as calcium sulphate and calcium bicarbonate types (Féraud et al. 2009). These aquifers are exploited as the most important resource of drinking water in the region (Barci et al. 2009; Alabdullah et al. 2013) for more than 600,000 inhabitants that are increasing for the last 50 years. The low Var River valley is the downstream part from the confluence with Vésubie River to the mouth (into the Mediterranean Sea).

The geology of the catchment basin The main geological formations of the Var River catchment consist of different rocks (see Fig. 1): (a) magmatic (granites) and metamorphic rocks, mainly formed by alumino-silicated minerals; (b) continental sediments of Permian age (red and very fine grain rocks, viz., argillites), mainly clays and fine micas; (c) dolomitic, limestone, sandstones, and marls; (d) marine sediments that consist of marl-limestone alternations; (e) Tertiary sediments; and (f) conglomerates (so-called “poudingues du Var”), with 700-m thickness representing the old Var delta during the Pliocene, which contain pebbles from rock outcropping in the whole basin forming the lower part of the Var Valley. It is important to note that only Tinée and Vésubie Rivers drain the granites and metamorphic rocks of the Mercantour massif in their upper part. However, the Permian argillite is the dominant rock forming Cians, Tinée, and the upper part of Var streams. Estéron River flows on Jurassic, Cretaceous, and Tertiary sedimentary rocks, while Coulomp drains areas where Tertiary sandstones are abundant.

Author's personal copy Environ Monit Assess Fig. 1 Geological map of the Var River catchment and sampling locations (site number in italics, sub-site names): 1, Cap3000-1 and Cap3000-2; 2, Carros-1 and Carros-2; 3, Charl-A-1 and CharlA-2; 4, Upper Var-1 and Upper Var-2; 5, Estéron-1 and Estéron-2; 6, Vésubie-1 and Vésubie-2; 7, Tinée-1 and Tinée-2; 8, Cian-1 and Cian-2; 9, Coulomp-1 and Coulomp-2

Material and methods Study site and sampling procedure Several dams were built across the banks in the low Var River valley in the 1970s with the aim to increase the groundwater’s level. In December 2007, a sediment core (∼900 cm in depth) was collected in the low Var River valley, at dam number 4, which is 6 km upstream (43° 44.537 N, 7° 11.001 E) (Fig. 1). The sediment core location was a typical site to investigate the vertical distribution of the studied elements, with 15 subsamples taken along the sediment core. Riverbed sediment samples were collected from 18 sites along the Var River and its tributaries (Fig. 1) in which 8 of them were chosen on the Var River and 2

locations for each tributary, Tinée, Cians, Vésubie, Coulomp, and Estéron. The collected sediments were directly placed into clean polypropylene bags and transported to the laboratory. Then, the samples were air-dried and mildly ground to pass through a 2-mm sieve in order to ensure homogeneity. Chemical reagents and equipment The chemical reagents used were of analytical grade or super pure quality. Super pure water supplied by ELGA purelab UHQ (18 MΩ·cm) was used throughout the work. Multi-element standard solution (0.01 g L−1) was used for the preparation of inductively coupled plasma-mass spectrometry (ICP-MS) calibration

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solutions. All polypropylene centrifuge tubes and flacons were acid-washed prior to use with 10 % (v/v) nitric acid for 48 h and then rinsed with super pure water. Inductively coupled plasma-mass spectrometry (ICPMS, PerkinElmer, DRC II) was used for the determination of studied element concentrations. Operating conditions of the measurement via ICP-MS are presented in Table 1. Analytical procedures Determination of total element contents An adequate 1.0 g of dried and ground sediment sample was digested using a mixture of 7:3:1 of HNO3/HF/HCl in a microwave oven (Millstone®) by applying the following program: heating up to 250 °C in 10 min, steady heating at 250 °C for 20 min, and flash cooling to 0 °C within 30 min to avoid losses. When necessary, a total of 0.5 g of boric acid was added to neutralize the residual of calcium fluoride. Digestion vessels were then Table 1 ICP-MS operating conditions, measurement parameters, and isotopes measured of the trace elements studied ICP-MS operating conditions Power

1,100–1,300 W

Plasma

Argon

Argon principal flow rate

15 L min−1

Argon auxiliary flow rate

0.8 L min−1

Argon nebulizer flow rate

0.9 L min−1

Sample flow rate

1 mL min−1

rinsed with super pure water and the washings were added to the sample solution. Each solution was, next, transferred to 50-mL volumetric flasks and diluted with 5 % super pure HNO3. The element concentrations in the sediment extracts were determined via ICP-MS. Germanium (Ge) and rhenium (Re) solutions were added as internal standards to correct the intensity shifts. Triplicate measurements were performed for each analysis, with relative standard deviation between measurements that did not exceed 5 %. Negligible contamination was found when blank vessels were processed. It is important to note that sample preparations for ICP-MS analysis was performed in an exclusively clean room. The reference material IAEA-433 (i.e., marine sediment from Algerian coast, supplied by the International Atomic Energy Agency) (Wyse et al. 2004) was used to evaluate the accuracy and precision of the microwave digestion. A good agreement was observed between the experimental and certified values, with trace element recoveries ranging from 92 % for As to 107 % for Zn. Precision of replicate analysis of IAEA-433 expressed as relative standard deviation (RSD) was lower than 5 % for the analyzed elements (n=6). The low recovery of As could be explained by the potential interference with 40Ar35Cl or 40Ca35Cl (Epov et al. 2004). These interferences are enhanced in samples containing high content of chlorine or calcium. In this study, a correction equation was used to eliminate these potential interferences, given as follows:

−3:127  Se77 þ 2:375  Se82




Measurement parameters Sweeps/readings

3

sweeps/replicate

III

Number of replicates

3

Points across peak

1

Resolution

Normal

Scanning mode

Peak hop

Transfer frequency

Replicate

Polarity

+

Sample analysis time

5–6 min

Sample wash delay

60 s

Auto−sampler delay

120 s

Measured isotopes 75

As, 59Co, 133Cs, 63Cu, 7Li, 208Pb, 238U, 66Zn

ICP-MS inductively coupled plasma mass spectrometry

The concentrations of the major elements in the sediment samples were determined via ICP-AES, at CRPG laboratory, in Vandoeuvre lès Nancy (France), after being digested using LiBO2.

Determination of organic carbon and particle size Organic carbon content (Corg) represents the difference between total carbon (TC) and inorganic carbon (Ciorg). Both of TC and Ciorg were determined using carbon analyzer (TOC-VCSH, Shimadzu). Particle size determination was performed on a 1-g dispersed sample by a laser diffractometer using a Malvern Mastersizer 2000®.

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Quality control of trace elements analysis Detection and determination limits According to Eurachem (1998), limit of detection (LoD) was determined for each element of interest. LoDs were calculated as 3σ/a, where a is the slope of the calibration curve and σ is the standard deviation calculated from ten readings of the blank sample. Limits of quantitation (LoQs) were calculated using the same method as 10σ/ a. The results are shown in Table 2; they are in agreement with those found in the literature for elements analyzed by ICP-MS (Alonso Castillo et al. 2011; Potot et al. 2012). ICP-MS measurement precision Repeatability and intermediate precision (reproducibility) are the two most common precision measures (Eurachem 1998). They were determined, herein, for the elements studied and expressed in terms of relative standard deviations (RSD r and RSD R , respectively). Repeatability and reproducibility measurements were performed using a river water reference material SLRS-4, provided by the National Research Council (NRC) of Canada (Yeghicheyan et al. 2001). Table 2 summarizes the ranges of mean, standard deviation, and repeatability and reproducibility relative standard deviation (RSDr, RSDR) of the replicates. The obtained data showed RSDr less than 4 % for all studied elements except for Cs (∼4.8 %), which could be related to the low concentration of cesium in the reference material (i.e., 0.008±0.002 μg L−1). Reproducibility relative standard deviation for the element of interest was two times as high as RSDr. For example, RSDr and RSDR for Cu were 1.5 and 3.6 %, and for As were 2.3 and 4.2 %, respectively. The maximum value for RSDR was reported for the cobalt (i.e., 6.9 %), which may be a consequence of the interference caused by calcium oxide. This effect could be minimized by carrying out the calibration using standard solutions matching the sample matrix, if available.

XLState software (Addinsoft 2013). The variables investigated were the concentrations of trace and major elements, organic carbon, and clay contents.

Results and discussion Organic carbon and clay contents The content of organic carbon in riverbed and core sediments varied considerably within wide ranges as shown in Fig. 2 and Table 3. The maximum values were approximately 4 and 152 times higher than the minimum ones in core and riverbed sediments, respectively. Between riverbed sediment samples, the minimum content of organic carbon (0.01 %) was found in Vésubie-1, associated with the lowest content of clay (1 %). In the sediment core samples, the minimum Corg reached 0.44 % at 740-cm depth, with a high content of clay, i.e., 25 %. For riverbed samples, as shown in Fig. 3, the organic carbon content increased with increasing the low particle size grains (< 2 µm) with a correlation coefficient (r2 =0.8597), while for core samples, a slight variation was noted for both Corg and clay. This is consistent with other studies that cited the correlation between organic carbon contents and clay-rich sediments, where the organic carbon content increases as particle size decreases (Cho et al. 1999). It is noteworthy that the maximum Corg along the sediment core was found at 420-cm depth, where a peak of 137 Cs with activity concentration of 97.1 ± 1.8 Bq kg −1 was detected and attributed to the Chernobyl accident (Alabdullah et al. 2013). The geographical variations of organic carbon contents, especially in riverbed sediments, could be mainly attributed to the geographical variation, biological productivity in the surface water, and sedimentation rate (Lee et al. 1991; Cho et al. 1999; Kumar et al. 2013; Zhang et al. 2013). Major element contents in riverbed and core sediment samples

Statistical analysis Statistical approaches are essential tools to illustrate the correlation among variables studied. Pearson correlation matrix was calculated for the studied samples using

Table 3 summarizes the mean values and ranges of the major element concentrations in the sediment core and riverbed samples as well as the upper crust continental and average crust (Hans Wedepohl 1995; Rudnick and

Author's personal copy Environ Monit Assess Table 2 Detection (LoD) and determination (LoQ) limits of studied trace elements, and means, standard deviations, and relative standard deviations of the repeatability (r) and reproducibility (R) measurement of the elements studied in the reference material SLRS4 Element

Li

Co

Cu

Zn

Cs

As

Pb

U

Meanr (μg g−1)

0.505

0.034

1.815

0.896

0.008

0.706

0.081

0.05

Sr (μg g−1)

0.012

0.001

0.027

0.032

0.0004

0.017

0.003

0.001

RSDr

2.4

3.8

1.5

3.5

4.8

2.3

3.6

1.5

MeanR (μg g−1)

0.519

0.035

1.807

0.821

0.008

0.703

0.081

0.05

SR (μg g−1)

0.014

0.002

0.065

0.036

0.0005

0.03

0.003

0.001

RSDR

2.8

6.9

3.6

4.4

6

4.2

3.6

2.4

LoD (ng g−1)

0.01

0.01

0.01

0.1

0.001

0.02

0.004

0.0005

LoQ (ng g−1)

0.03

0.03

0.03

0.3

0.003

0.07

0.013

0.0017

Fountain 1995). The results of major elements in the sediment core samples are plotted in Fig. 2, and a low variation in major elements along the sediment core was noted. This may confirmed that MEs have similar input sources, mainly from natural origin. Obviously, the results were comparable for both of the core and riverbed samples and laid within the natural averages, with an exception for Ca which was quite high. The mean concentration of Ca reached 25 and 23 % in riverbed sediments and core samples, respectively, whereas Ca

concentration ranged from 3.0 to 6.4 % in the natural crust. The high contribution of carbonate minerals in the sediment evolution in the Var catchment may be responsible for this enrichment. The lowest concentration of Ca, ranging from 2.7 to 5.3 %, was found in sediments of the Vésubie River which could be explained by the fact that the river drains through granites and metamorphic rocks. In the case of Al, which is an important constituent of clay minerals (White 1994), the variability of Al

Fig. 2 The vertical distribution of major elements, organic carbon, and clay contents (%) in the sediment core samples

Author's personal copy Environ Monit Assess Table 3 Means, range values, and standard deviation (SD) of the major and trace elements concentrations (in % and μg g−1, respectively) in riverbed sediments and sediment core samples, and the referenced average values of the Earth’s crust and upper continental crust Element

Upper crust continentalb

This study Riverbed sediment Meana

Average crustc

Sediment core Range

Mean

Range

Li

31.8±16.2

10.0–69.0

48.8±9.8

36.0–66.0

22.0

16.0

As

7.6±3.0

3.6–14.8

7.6±1.4

6.1–10.3

2.0

2.5

Co

5.9±2.1

2.7–9.1

8.9±1.57

6.0–10.3

11.6

26.6

Cs

4. 5±2.8

1.2–12.3

7.4±2.3

4.3–11.8

5.8

2.0

Cu

14.4±5.5

4.9–23.4

23.1±4.2

16.0–27.9

14.3

27.0

Pb

13. 9±2.9

9.5–18.0

17.1±3.2

12.7–23.9

17.0

11.0

U

1.7±0.6

0.8–2.7

2.3±0.4

1.7–3.3

2.5

1.3 72.0

Zn

52.3±17.3

21.7–74.2

75.7±14.2

52.7–99.7

52.0

SiO2

39.2±11.9

22.4–70.0

36.4±2.2

31.0–41.3

30.3

60.6

Al2O3

7.1±2.9

3.2–12.7

10.0±2.0

7.3–12.9

7.7

15.9

Fe2O3

2.7±0.8

1.5–4.1

3.4±0.4

2.7–4.3

3.1

6.7

MgO

1.3±0.4

0.5–1.8

1.7±0.2

1.3–2.1

1.4

4.7

CaO

25.0±9.2

2.7–38.2

23.0±2.8

17.9–28.7

3.0

6.4

Na2O

0.8±0.7

0.35–2.59

0.5±0.2

0.3–0.9

2.6

3.1

K2O

1.8±0.7

1.07–3.29

2.0±0.4

1.5–2.5

2.9

1.8

Corg

0.6±0.5

0.01–1.52

1.1±0.4

0.4–1.9

–

–

Clay

10.1±5.3

1.3–25.9

22.7±7.0

6.2–33.8

–

–

a

Values presented are the mean and SD

b

Hans Wedepohl (1995); numbers are rounded to one decimal place

c

Rudnick (2005); numbers are rounded to one decimal place

concentrations was less in the sediment core samples, i.e., 7.3–12.9 %, with a mean value of 10.0 %, compared to that in the riverbed samples, ∼3.2–12.7 % with a mean value of 7.1 %).

Fig. 3 The organic carbon content and its correlation with the clay percentage in the riverbed sediment samples

Vertical distribution of trace elements The vertical distribution of the TEs studied in the sediment core is illustrated in Fig. 4. In general, the concentrations of the TEs showed similar trends in all layers of the core. A slight increase was observed from the surface layer to the depth of 405 cm, after which a decrease was relative to the depth of 744 cm. This was followed by a minor increase of the TE concentrations at the bottom of the core. For instance, the concentration of Cu was 20.9, 26.8, and 16.9 μg g−1 for the depths of 40, 420, and 744 cm, respectively, with a mean of 27.2 μg g−1 at the bottom 60 cm of the core (i.e., 824– 881 cm). The increase observed at 420-cm depth was consistent with the existence of illuvial horizon and the relatively high content of clay (25 %). The increase of TE concentrations was coherent with the increasing of clay content. This is consistent with the fact that trace elements are mostly associated with fine-grained

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fractions of the soil and sediment (Salminen and Tarvainen 1997; Kumar Sarkar et al. 2004). However, the correlation study showed that, except for Cs, no correlation was found between TEs and clay content in the sediment core samples. This could be due to the low variation of TE concentration along the sediment core and the low anthropogenic contribution. On the other hand, the decrease in the TE concentrations at layers 420–744 cm may be due to the availability of a dilution component such as CaO in the substrate (as seen in Fig. 2). Meaning, the content of CaO was the highest at this depth. The concentration of TEs at the bottom layers (i.e., 824–881 cm) increased slightly due to the enhanced concentration of aluminum and clay content in the sediment samples. As a general conclusion, none of the trace elements displayed a surface enrichment. As shown in Table 3, apart from Li, As, and Cs, the mean concentrations of TEs in the sediment core samples were comparable with the natural levels. The mean concentration of Cs was 7.4 μg g−1, and it was slight higher than the natural value. This might be due to the presence of granite as parent rocks in the studied area. Spatial distribution of trace elements The concentrations of the TEs in the riverbed sediments are presented in Fig. 5. Spatial distribution of the trace elements in the riverbed sediment samples differed widely from one tributary to another. This was reflected by the double or triple increase in the concentration of a particular element among tributaries. For example, As increased from 6.5 to 14.0 μg g−1 for Var and Cian sediments, respectively (sites 4 and 8 in Fig. 1). In other case, Coulomp sediments contained 2.8 μg g−1 of Co while sediments of Cian had 8.9 μg g−1. The texture and physical and chemical properties of the sediment of the studied rivers may be responsible for such distribution. In addition, the maximal concentration means of TEs studied were found in Cian river sediments (site 8), whereas the lowest concentrations were related to both of Coulomp (site 9) and Estéron (site 5). The main reason is that Permian argillites are crossed by the Cian river (discussed later in details), while sandstones are abundant in Coulomp and Estéron streams (Féraud et al. 2009). A closer look at Fig. 5 illustrated that Var riverbed sediments (site 4) contained higher concentrations of TEs comparing to those for Coulomp (site 9). This was compatible to the observations of Féraud et al.

(2009) who stated lower concentrations of TEs in the water samples of the later river than those of the former. In the low Var River valley, the results showed a clear decrease in element concentrations along the stream, from Charl-A-site 3 (at the upper part) to Cap3000-site 1 (at the mouth of the river) (see Figs. 1 and 4). In other words, the concentrations of TEs were lowest in Cap3000 sediments due to the direct and continuous interaction between water and sediment along the watercourse of the river. Values of mean and range of the trace elements concentrations in the riverbed sediments are summarized in Table 3. The obtained results were compared to those of the sediment core samples, as well as to concentration levels reported by Hans Wedepohl (1995) for the upper crust continental and to the average crust data proposed by Rudnick (2005). Generally, the mean concentrations of all studied trace elements were lower in the riverbed than in the sediment core samples. This could be explained by the higher clay and organic carbon contents and lower calcium concentrations in sediment core samples. The former results were, in turn, within the natural levels of the upper crust continental and average crust, with exceptions for Li and As. The means obtained were 31.8 and 7.6 μg g−1 for Li and As, respectively, while the natural ranges of these elements are 16–22 and 2.0– 2.5 μg g−1, in order. The core and riverbed sediment samples had relatively high concentrations of arsenic, which is known to be a toxic element. Thus, a special emphasis was made, in a later section, in order to verify the origin of this element. Statistical study To illustrate the correlation among variables studied, Pearson correlation matrix was calculated using XLState software (Addinsoft 2013) and is presented in Tables 4 and 5. Clay and organic carbon contents are considered to be important factors in evaluating the TE content in the sediments (Klassen 1998); for that, the variables of interest were trace and major element concentrations, and clay and organic carbon contents in both of riverbed and core sediment samples. The statistical study and linear correlation coefficients were used to judge the origin and geochemical paragenesis of element deposits (Harris and Radtke 1976; Jude et al. 2009). Pearson’s correlation matrix has proven to be useful in offering reliable classification

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Fig. 4 The vertical distribution of studied trace elements in the sediment core samples (μg g−1)

of the metals and physicochemical properties of soils and sediments. This approach has been used widely in the classification of sites under investigation in geochemical and water quality analysis (Venugopal et al. 2009; Wu et al. 2009; Bhuiyan et al. 2010; Bam et al. 2011). In other words, when pollution occurred, the concentration of pollutants could not be in correlation with other TE concentrations due to the relative high input of these pollutants. On the other hand, pollutant adsorption onto soil and sediment mostly depends on the concentration of their main components like ME, Corg, and clay (Alonso Castillo et al. 2011; Alabdullah et al. 2013). Regarding the correlation coefficients in the Pearson tables (Tables 4 and 5) and based on the latter concepts, it could be assumed that a good correlation was seen among studied trace elements in both of riverbed and core sediment samples and they mainly originated from the parent rocks. As shown in Tables 4 and 5, correlation between TEs and MEs in core samples was, somewhat, less than the correlation in riverbed sediments. This may be due to the difference in the age of the sediment layers along the core, which in turn is related to the physical and chemical

weathering conditions, sedimentation rate, etc. Trace elements were correlated with the MEs, in particular Al, Fe, Mn, and Mg, for riverbed and core sediments, with the maximal correlation coefficient reaching 0.969 (Fe and Li in riverbed sediments). This is consistent with results found in literature where the mobility and spatial presence of trace elements in surficial environment are controlled by the dominant geological phase in the system like Fe, Mn, and Al (Purohit et al. 2001; Banat and Howari 2003; Alabdullah et al. 2013). On the other hand, low or negative correlations were observed between the studied trace elements, Na and Ca, which could be explained by the presence of these elements (Na and Ca) in carbonated forms (easily soluble in water). Regarding organic carbon content, there was no correlation between TEs and Corg in riverbed sediment samples, whereas a good correlation was found in the case of the core samples. This may be due to the weak sediment development and continuous leaching of riverbed sediments. When clay content was the variable of interest, no correlation was observed between TE and clay content in the core or riverbed samples.

Author's personal copy Environ Monit Assess Fig. 5 The spatial distribution of studied trace elements in riverbed sediment samples (μg g−1); data from each site were presented as an average value with the standard deviation

Comparison study with reference samples To speculate the high level of As in the surface and sediment core samples in this study, it was essential to determine the TEs especially As in an ancient core, socalled “reference core.” The reference core was collected in 1995, near to the mouth of the Var River, with a depth of 96 m. The layers of this core had been dated using 14C technique and found to belong to 2760–10700 BP (before present, i.e., 1950). Herein, four samples of this core, designated as C-1, C-2, C-3, and C-4, were chosen along the core with depths varying accordingly, approximately 18.5, 24.5, 44.3, and 82.7 m. Trace and major elements were determined via ICP-MS by the method described earlier. The obtained data are shown in Table 6. A detailed comparison between ME concentrations in the reference core with riverbed and core samples was performed. It was concluded that all ME results were compatible and a slight variation was noted. For riverbed sediment samples, the mean TE concentrations were always less than those measured in the

reference core samples. While in the case of sediment core, the mean concentrations of Cu, Pb, and Zn were slightly higher than the concentrations found in the reference core. The concentration of arsenic in the reference core ranged from 6.4 to 8.8 μg g −1 (with a mean of 7.6 μg g−1) that was consistent to the concentrations found in core or riverbed sediments (Table 3). This may reflect that the concentration of As could be a consequence of the interaction between the parent rock and water in the studied site. Similar conclusion was drawn by Féraud et al. (2009) and Barats et al. (2010) who cited high concentrations of As (up to 75±2 μg L−1) in the surface water and groundwater of the Var River catchment originating from metamorphic rocks surrounding granites and Permian sediments. The obtained results were compared with those found in the literature in other sites of the globe. Datta and Subramanian (1997) studied the Bengal sediments from Meghna River and reported As concentrations ranging from 1.3 to 5.6 μg g−1, with a mean concentration

0.879

−0.318

0.728

0.918

0.822

Al

Fe

Mg

0.906

0.126

−0.432

0.700

0.650

−0.199

−0.521

Na

K

Mn

Clay

Corg

−0.392

0.066

0.670

0.527

0.118

−0.294

0.803

0.872

0.614

0.066

0.780

0.571

0.566

0.956

0.640

1

Cs

−0.177

0.316

0.804 −0.495

−0.008

0.804

0.661

0.287

0.144

−0.488

−0.139

0.893

0.969

0.786

−0.042

0.694

0.700

0.421

0.909 0.261

0.809

0.753

0.671

1

Li

−0.178

0.400

0.576

0.704

1

Cu

−0.563

−0.083

0.742

0.707

0.512

−0.582

0.701

0.758

0.759

0.433

0.762

0.745

1

Pb

−0.710

−0.266

0.740

0.878

0.682

−0.873

0.843

0.866

0.948

0.737

0.786

1

U

Values in bold are different from 0 with a significance level alpha=0.001

0.482

0.150

−0.498

0.357

Ca

0.899

0.678

0.086

0.928

0.654

0.801

0.731

U

0.765

0.302

0.706

Pb

0.896

Si

0.925

Li

0.904

0.837

1

Co

Zn

0.916

0.554

0.813

Co

Cu

1

As

Cs

As

Variables

−0.515

−0.043

0.929

0.672

0.404

−0.561

0.848

0.945

0.845

0.359

1

Zn

−0.670

−0.638

0.304

0.859

0.948

−0.967

0.334

0.416

0.769

1

Si

−0.730

−0.299

0.799

0.938

0.771

−0.901

0.798

0.875

1

Al

Table 4 Pearson “n” correlation matrix of the major and trace elements in the riverbed sediment samples

−0.600

−0.124

0.851

0.745

0.418

−0.627

0.934

1

Fe

−0.635

−0.032

0.852

0.629

0.298

−0.551

1

Mg

0.739

−0.634

−0.625

0.359

−0.498 0.545

1 0.891

−0.936

Na

−0.917

1

Ca

−0.726

−0.465

0.583

1

K

−0.526

0.109

1

Mn

0.491

1

Clay

1

Corg

Author's personal copy

Environ Monit Assess

0.325

−0.783

0.473

0.635

0.631

0.526

0.441

0.426

0.667

0.466

Li

Pb

U

Zn

Si

Al

Fe

Mg

0.801

−0.005

0.588

0.505

−0.275

0.267

Na

K

Mn

Clay

Corg

0.600

0.521

0.343 0.639

0.028

0.779

0.882

0.240

0.852

−0.805

−0.364

0.271

0.865

0.838

0.379

0.922

0.760

0.830

0.851

1

Cu

−0.646

0.049

0.427

0.935

0.130

0.570

0.300

0.669

0.948

0.706

1

Cs

0.709

0.367

0.494

0.916

−0.180

−0.793

0.197

0.631

0.965

0.299

0.755

0.538

0.786

1

Li

0.726

−0.072

0.685

0.889

0.302

−0.796

0.416

0.825

0.782

0.404

0.785

0.705

1

Pb

0.619

−0.265

0.759

0.678

0.601

−0.763

0.515

0.930

0.566

0.526

0.876

1

U

Values in bold are different from 0 with a significance level alpha=0.001

0.757

0.858

0.285

−0.574

0.475

Ca

0.889

0.812

0.332

0.921

0.837

0.818

0.830

0.953

0.661

0.328

0.611

1

Cu

Co

Co

Cs

1

0.628

As

As

Variables

0.702

0.034

0.805

0.843

0.374

−0.823

0.394

0.911

0.799

0.441

1

Zn

0.093

−0.395

0.084

0.434

0.458

−0.782

0.335

0.493

0.329

1

Si

Table 5 Pearson “n” correlation matrix of the major and trace elements in the sediment core samples

0.703

0.406

0.532

0.949

−0.098

−0.820

0.164

0.654

1

Al

0.590

−0.242

0.875

0.793

0.595

−0.808

0.533

1

Fe

0.325

−0.234

0.361

0.294

0.382

−0.393

1

Mg

−0.756 −0.003

−0.551

0.162 0.501

−0.500 0.065

1 −0.883

Na

−0.303

1

Ca

0.664

0.158

0.626

1

K

0.515

−0.077

1

Mn

0.155

1

Clay

1

Corg

Author's personal copy Environ Monit Assess

Author's personal copy Environ Monit Assess Table 6 Concentrations of the major and trace elements (in % and μg g−1, respectively) in the reference core samples Sample

C-1

C-2

C-3

C-4

Depth (m)

18.50

24.50

44.20

82.70

Li

47.00

34.00

31.00

38.00

As

8.76

8.34

6.38

6.85

Co

9.36

7.55

6.65

6.72

Cs

6.91

4.15

4.53

5.44

Cu

21.22

15.07

15.65

17.01

Pb

16.38

12.21

11.57

15.10

U

2.42

2.07

1.86

3.96

Zn

70.21

82.84

51.45

58.13

SiO2

35.75

34.91

29.58

35.66

Al2O3

9.07

6.92

6.71

8.53

Fe2O3

3.59

2.78

2.61

2.78

MgO

1.80

1.53

1.69

1.56

CaO

23.44

26.59

30.36

25.12

MnO

0.05

0.04

0.04

0.05

Na2O

0.60

0.60

0.55

0.83

K2O

2.00

1.55

1.54

1.94

Corg

0.67

0.63

0.44

1.09

Clay

14.59

16.02

13.97

23.67

3.5 μg g−1. On the other hand, Smedley and Kinniburgh (2002) reported As concentration ranging from 5 to 8 μg g−1 in stream sediments in England and Wales. In addition, the world average concentration of As in river sediments could reach up to 5 μg g−1 (Martin and Whitfield 1983; Mandal and Suzuki 2002). In the studied area as a typical Mediterranean region with humid temperate and arid climates, the drinking water is considered as a scarce commodity. The arsenic pollution could be of great danger to water resources. The enriched sediments studied, herein, may behave as an important source of As for downstream environments and their associated biota. Therefore, more investigations have to be made in the future to monitor the arsenic evolution in order to prevent pollution of the aquifer systems.

Conclusion The concentrations of trace elements Li, As, Co, Cs, Cu, Pb, U, and Zn and major elements Si, Al, Fe, Mg, Ca,

Mn, Na, and K in riverbed sediments and a sediment core from the Var River catchment were determined using inductively coupled plasma mass spectrometry (ICP-MS). The contribution of clay and organic carbon contents in the distribution of TEs and MEs in the sediment samples was investigated. Comparable concentrations of the MEs were found in the core and riverbed samples. The reference core samples were greatly useful in the determination if any pollution was presented in riverbed and sediment core samples. For riverbed samples, the mean TE concentrations were always less than those measured in the reference core. While in the case of sediment core, the mean concentrations of Cu, Pb, and Zn were slightly higher than the concentrations found in the reference core. An important exception for As was noted with concentration ranges of 3.6–14.8 and 6.1–10.3 μg g−1 in riverbed samples and sediment core, respectively. Comparing to the reference sediment core (gave a mean value of 7.6 μg g−1) and the results reported in other area in the world, it could be confirmed that the studied area had a high natural level of As, mainly arising from metamorphic rocks surrounding granites and from Permian sediments. Accordingly, more investigations have to be made in the future to monitor the arsenic evolution in order to prevent pollution of the aquifer systems. With the application of Pearson matrix, linear correlation was observed among trace elements in riverbed and sediment core samples, giving correlation coefficients of 0.928 (for Co and Zn) and 0.953 (for Co and Cu) in riverbed and core samples, respectively. A maximal correlation coefficient between MEs and TEs of 0.969 (for Fe and Li) was recorded in riverbed samples. This study represents preliminary geochemical analysis of the sediments of the Var River catchment, which could serve as a baseline to assess future anthropogenic contamination of the studied elements. For better determination of the TE origins (natural or anthropogenic), further investigation of the geochemical speciation of the TE in the sediments of the studied area might be useful. Acknowledgments The first author would like to thank the Atomic Energy Commission of Syria for the financial support. Authors would like to thank Dr V. Barci and Dr. M. Dubar for technical supports and useful discussion, and the anonym reviewers for the helpful remarks. This study was sponsored by Conseil Général des Alpes Maritimes, Agence de l’Eau RMC, Conseil Régional PACA, Syndicat Mixte d’Etudes de la Basse Vallée du Var, PPF grant, and Véolia-eau.

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