International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 782-795. Article ID: IJCIET_10_04_083
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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ASSESSEMENT OF METALLIC
CONTAMINATION OF THE NORTHEN
ATLANTIC COAST OF MAURITANIA
(COASTAL FRINGE “LEVRIER BAY”), USING
PERNA PERNA
M. H. Legraa
Department of Biology, Faculty of Science and Technology, UR / EBIOME,
University of Nouakchott AL Aasriya, Mauritania
H. Er- Raioui
Department of Earth Sciences, Faculty of Science and Technology, Laboratory of
Environmental Geoscience, Abdel Malek Esssaidi University, Morocco
A. Y. Dartige
National Office for Sanitary Inspection of Fisheries and Aquaculture Products (ONISPA),
Mauritania
M. L. C. Zamel
National Office for Sanitary Inspection of Fisheries and Aquaculture Products (ONISPA),
Mauritania
M. M. O. Abidine
Department of Geology, Faculty of Science and Technology,
University of Nouakchott AL Aasriya, Mauritania
Z. Sidoumou
Department of Biology, Faculty of Science and Technology, UR / EBIOME,
University of Nouakchott AL Aasriya, Mauritania
A. Mohamed Saleck
Department of Geology, Faculty of Science and Technology,
University of Nouakchott AL Aasriya, Mauritania
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M. H. Legraa, H. Er-Raioui, A. Y. Dartige, M. L. C. Zamel, M. M. O. Abidine, Z. Sidoumou and
A. Mohamed Saleck
ABSTRACT
This work presents the results of a seasonal survey during 32 months from January
2013 to October 2016 of heavy metals accumulated in the soft parts of the body mussel
Perna perna at four sites in the Lévrier bay (Mauritania). The pattern of the metal
levels at all the sites studied followed Zn>Cu>Cd>Pb>Hg in soft body tissues. So, this
study shows that high values of heavy metals in P. perna were recorded in the cold
season, while during the hot season all metal levels were relatively low. The
concentrations of Hg recorded in P.perna soft tissues were the lowest of all metals,
whatever the site and the season. Mean concentrations of all heavy metals in this study
were in most cases lower than those in other North African areas. Seasonal variations
could be explained by the presence of upwelling currents that predominate in the cold
season, and further by the life cycle of mussels that have their maximum spawning
period in autumn. The maximum values of each metal analysed in P. perna soft tissues
no exceeding the European Union (EU) limit at all sampling sites except for Zn in
COMECA. These results show that P. perna may be used as a bioindicator of heavy
metals and the concentrations found in this work could be used as baseline values.
Keywords: Mussels, Perna perna, Heavy metals, Lévrier bay, Mauritania.
Cite this Article: M. H. Legraa, H. Er-Raioui, A. Y. Dartige, M. L. C. Zamel, M. M.
O. Abidine, Z. Sidoumou and A. Mohamed Saleck, Assessement of Metallic
Contamination of the Northen Atlantic Coast of Mauritania (Coastal Fringe “Levrier
Bay”), using Perna Perna, International Journal of Civil Engineering and Technology,
10(4), 2019, pp. 782-795.
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1. INTRODUCTION
Because the Lévrier Bay Ecosystem is located in the vicinity of the town of Nouadhibou and
surrounded by industrial zones, trace elements reach the bay from several sources such as
industrial discharges, municipal wastewater discharges and aquaculture practices [29, 32]. In
addition, the Lévrier bay is under increasing anthropogenic pressure due to the significant
development of the town of Nouadhibou, the economic capital of Mauritania, and important
economic activities such as the establishment of fishing companies and the construction of
fishmeal factories [22]. Therefore, pollution monitoring is necessary because of the instability
of environmental factors and the incessant increase in anthropogenic pressures [7]. This is
especially acute for contamination by heavy metals, which are often present in industrial and
municipal effluents and which are major pollutants in the industrial world that cause long-term
effects on marine ecosystems [8, 37]. Analysis of heavy metals in the tissues of filtering
organisms such as bivalves provides data on the accumulation of bioavailable fractions of
pollutants as it reflects spatial and temporal variation of concentrations of contaminants. All
these factors pose a potential risk to human health [16]. For the evaluation of biological
pollution effects, monitoring of heavy metals in filter-feeder’s organisms is an effective method
for better understanding their spatial-temporal variability and for highlighting the differences
between them [27]. Therefore, the bivalves are considered as suitable organisms for
biomonitoring in marine environments the extent of anthropogenic pollution [30]. Indeed, the
bivalves are frequently used in monitoring networks (bio-monitoring) of the marine
environment [19]. The availability, tolerance and adaptability of bivalve molluscs have made
them good indicators of the quality of the environment [9]. From a food safety point of view,
these bivalve molluscs are also among the most important marine products for human
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consumption [5, 34]. The bivalve mussel Perna perna's is characterized by relatively narrow
thermal limits, a limited ability to adapt to temperature and low tolerance to the combined
temperature-salinity effect [2]. Many factors can affect the heavy metal bioaccumulation in
molluscs, such as season and physiological state or size of the organisms [25, 29].
The focus is on concentrations of Cd, Cu, Pb, Hg, Zn in the bivalve mussel Perna perna. In
this work, seasonal sampling was conducted in the soft tissues of P.perna at four sites at the
Lévrier bay for 32 months from January 2013 to October 2016. This mollusc is common at
Lévrier bay and also in many Moroccan and European littoral sites. In northern temperate
regions the organism has already been used in environmental monitoring programs as a
bioindicator of metal contamination [3, 22].
This study aims to document the spatial and temporal distribution of trace metals in P.perna
soft tissues at Lévrier bay coastal area and to identify their possible sources of origin. Could
Perna perna be useful as a biomonitor in these restricted environments along the North African
coastline? Then, the rate of pollution in P. perna soft tissues at the Lévrier bay coastal area is
compared to neighboring areas and coasts in other parts of the world. We make
recommendations in terms of environmental governance will be formulated for decisionmakers and managers.
2. MATERIALS AND METHODS
2.1. Study area
The Mauritanian coastline is 720 km long and the surface of the continental shelf is 39000 km2,
including 9000 km2 for the Gulf of Arguin which is composed of the Lévrier bay and the Banc
d'Arguin [13]. The exclusive economic zone of Mauritania (EEZM) covers about 230,000 km2
with a continental shelf of 39.000 km2. It is a transition zone between two current systems: the
cold Canary Current and the warm Guinea Current.
The Mauritanian EEZ is characterized by the existence of a set of hydro-climatic and
morphological phenomena favourable to the development of a rich marine biodiversity. Apart
from the influence of the Canary Current and Guinea Current, it is strongly affected by the
Upwelling phenomenon, which makes it one of the four most productive areas in the world.
Studies on the hydrology of Mauritanian marine waters have identified four major seasons. The
most important is the hot season which corresponds to the summer; it lasts three months and
runs from August to October and the cold season, which corresponds to the northern
hemisphere winter, is the longest and it lasts from January to May. These two seasons are
interspersed by two short seasons but, in this work, we limited the sampling to the cold and hot
seasons [14].
We conducted a seasonal survey of Cd, Pb, Hg, Cu and Zn accumulated in the soft parts of
P. perna for 32 months from January 2013 to October 2016 during both the cold and the hot
season at four stations located in the Lévrier bay coast (Figure 1). The choice of sampling sits
was based ont he abundance of mussels and the proximity to discharge sources. Sampling was
done on a seasonal basis. A total of 97 mussel samples were collected during the four years of
the study period (32 months). Thus, two samples were taken per year. 54 samples were taken
during the cold season and 43 samples were taken during the hot season.
Sampling positions were placed along transects using a Garmin 585 global positioning
system (GPS) with a resolution of about 3.5 m:
• Baie de l'Etoile: BE (21° 02’ 19.2’’ N. 17° 01’ 36.8’’ W): which is themost northen
African bay to be characterized by a significant area of salt marshes spartines.
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A. Mohamed Saleck
•
•
•
Cap Blanc: CB (20° 46' 47.58" N. 17° 03' 30.24" W): Natural Reserve, home to one of
the world's largest threatened colonies of monk seals;
COMECA (CO): This sampling point was located outside Cansado Bay and more
specifically on the southwest side of Cansado Point not far from the oil port and near
the metallurgical company “COMECA” (20° 50’ 24.7’’ N. 17° 02’ 03.6’’ W);
IMROP (IM): This sampling point was located in the southeastern part of Cansado Bay
(20° 51’ 26.2’’ N. 17° 01’ 52.0’’ W). It is the place of all the urban discharges in the
bay, in particular the Cansado effluents containing domestic sewage.
Figure 1 Map of the Lévrier bay indicating sampling sites
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2.2. Sampling and analytical procedure
At the sampling sites CO, BE, CB and IM which are characterized by hard substrates (rocks),
a batch of 50 individuals of Perna perna mussels, were collected by hand during low tide with
disposable latex gloves. So, the mussels were measured with calipers and only individuals
between 3 and 6 cm were retained for analysis. Then, samples were kept in 25-liter coolers
filled with 6-10 liters of seawater taken on site with a 10 liter polyethylene bucket. For 20-28
hours, the mussels thus preserved were purified at room temperature in the ONISPA laboratory
and then frozen at -18 ° C.
Samples for heavy metal analysis should be deep-frozen, except for volatile substances
such as mercury. The organs were not separated: everything was ground and freeze-dried, and
thenanalyzed by atomic absorption spectrophotometer. The analysis of Cd, Pb, Cu and Zn was
done by the graphite furnace method and the Hg analyses were made by DMA-80 Direct
Mercury Analyzer.
The samples were then mineralized in closed Teflon bombs, with nitric acid and hydrogen
peroxide to decompose the sample and solubilize the metals. Exactly 0.2 grams of dry weight
or10 ml of concentrated HNO3 nitric acid (for analysis) was added. The reactors were
hermetically closed and left at room temperature for at least 1 hour. They were then heated by
microwave according to a well-defined program.
Atomic Absorption Spectrophotometry (AAS) measures the absorbance of the light emitted
by an EDL lamp the wave length of which is specific for the element to be assayed. For mercury
analysis, biological tissue samples from Perna perna mussels were thermally decomposed in a
temperature-controlled furnace and in the presence of oxygen. The combustion gases were then
treated in a catalytic tube. The mercury was subsequently amalgamated on a gold support. After
desorption by heating, the mercury was measured by UV spectrometry at 253.7 nm using two
different sensitivity cells placed in series. The signal was measured in each cell. The cell with
a short path was used to measure high concentrations of mercury, when the absorbance in the
long path cell (low concentration) exceeded 0.8 absorbance units. The measurement was
automatically performed with the short-path cell (high concentration).
The detection limits (DL) were calculated as three times the standard deviation of the blank
measurement based on the weight of the average sample size. They were expressed in mg / kg
of wet weight. The reliability of the measurements was tested by the assay. With each series of
analyzes, a certified sample coming from the International Atomic Energy Agency of Monaco
was measured and a blank sample: BCR16-ERM278K (mussel tissue). Recoveries were above
90% for all the heavy metals measured. The accuracy was evaluated by comparing the values
obtained with the certified values of the reference samples
All samples were run in triplicate and all elements were subsequently expressed in mg kg1
dry weight (DW). The measured, certified and detection limits values of trace metals are
summarized in Table 1.
Table 1. Measured, certified and detection limits concentrations of trace metals (mg kg-1 DW) in the
P.perna tissues according to standard reference material BCR16-ERM278K.
P.perna
soft
tissues
Mesured
Certified
Detection
limits
Cd
0.33±0.03
0336±0.025
Pb
2.03±0.20
2.18±0.18
Hg
0.077± 0.008
0.071±0.007
Cu
5.52±1.44
5.98±0.27
Zn
74 ± 7
71 ± 4
AL
7.3+0.5
---
0.008
0.09
0.006
0.35
0.29
---
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A. Mohamed Saleck
2.3. Statistical analysis
In this work, the data were expressed as mean ± deviation. For statistical analysis, a one-way
ANOVA with Duncan's multiple test at a 95% level of significance was used to statistically
assess significant differences in heavy metals concentrations in P. perna between sites
sampling for each season. Differences between trace metals levels from the four sampling sites
were tested by the Levene’s test which was applied to express the homogeneity or inequality
of the variance. A probability value greater than 5% in the Levene test implies the equality of
the variances but does not show the relationship between the averages, whereas a probability
value of less than 5% implies the existence of a difference between averages. Also, principal
component analysis (PCA) was used to study the relationship of heavy metals concentrations
between the different sampling sites. In order to establish correlations that may exist between
the different studied metals (Cd, Pb, Hg, Cu and Zn), the Spearman method was used. Statistical
analyses were performed using SPSS for Windows version 20.0 (2008) and the graphics were
drawn in OriginPro 8.
3. RESULTS AND DISCUSSION
3.1. Heavy metals concentrations in P.perna soft body tissues
3.1.1. Spatial variations of heavy metals in P.perna tissues
The results for the spatial average concentrations of metals in the tissues of Perna perna
recorded at the different sample sites are shown in table 2.
Table 2 Mean Concentrations of heavy metals (mg kg-1 DW) with standard deviation in P. perna
tissues for the studied sites from the Lévrier bay (Mauritania), as well as the number of samples per
season and corresponding replicates. The total number of samples throughout the study period
(N=.97).
Sites
CO
BE
CB
IM
Cold season
Hot season
Sample Replicate Sample Replicate
number number number number
16
5
14
4
12
4
8
3
8
3
8
3
18
4
13
4
Cd
Pb
Hg
Cu
Zn
1.44±0.59
2.55±0.73
1.72±0.14
0.59±0.14
0.70±0.18
0.95±0.21
0.65±0.24
0.68±0.13
0.03±0.01
0.06±0.02
0.06±0.01
0.03±0.01
5.95±1.16
4.48±1.31
5.23±0.82
3.97±1.08
119.04±15.55
90.94±10.87
84.58±11.31
92.75±12.02
The ranking of heavy metals in P.perna soft tissues was: Zn>Cu>Cd>Pb>Hg. The spatial
distribution of Cd (Table 2) shows that the sites Baie de l'Etoile and Cap Blanc presented the
highest contamination (2.55±0.73 and 1.72±0.14 mg kg-1 DW respectively), while the mean
concentrations at COMECA and IMROP varied between 1.44±0.59 and 0.59±0.14 mgkg-1 DW,
respectively. The sites of Baie de l'Etoile and COMECA are respectively the main points of
urban discharges from the new urbanization of Tarhil and wastewater of the COMECA
metallurgy plant, Cap Blanc and IMROP are respectively the main waste disposal points of the
large iron mining industry (SNIM) and the wastewater discharge point of the city of Cansado.
In this study, Cd concentrations are in the same order as those found in P. Perna at the Lévrier
Bay [11, 31]. The highest mean levels of Pb in P. perna (Table 3) were measured at Baie de
l’Etoile and in COMECA (0.95±0.21 and 0.70±0.18 mg kg-1 DW, respectively) whereas where
the lowest values were recorded at Cap Blan and IMROP (0.65±0.24 and 0.68±0.13 mgkg-1
DW, respectively). In the present work, Pb values were lower than those found by work on P.
perna in the Lévrier bay and West African coasts (Table 4). Mercury values were the lowest
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among all the heavy metals recorded at the different sampling sites (Table 2). The highest mean
concentrations of Hg were recorded at Baie de l'Etoile and Cap Blanc (0.06±0.02 mgkg-1 DW,
respectively), while the lowest values (0.03±0.01 mg kg-1 DW) were recorded at COMECA
and IMROP, respectively). Hg levels were similar to those found in P. perna in the Lévrier
Bay and in the subregion (Table 4). The contamination of these sites by Hg may be related to
anthropogenic inputs from different human activities in the Lévrier bay or to liquid discharges
from an electrolysis company located in this region which uses mercury cathodes to obtain
chlorine and sodium hydroxide. The highest mean concentrations of Cu in P. perna (Table 2)
were found at COMECA and Cap Blanc (5.95±1.16 and 5.23±0.82 mg kg-1 DW, respectively),
while the lowest mean levels were found in the Baie de l'Etoile and at IMROP (4.48±1.31 and
3.97±1.08 mg kg-1 DW, respectively). Contamination by Cu in the Lévrier bay may be caused
by anthropogenic sources ; the incineration of garbage or the discharge of wastewater that still
contains copper. The highest mean concentrations of Zn in P. perna (Table 2) were recorded
at COMECA and in IMROP (119.04±15.55 and 92.75±12.02 mg kg-1 DW, respectively), while
le lowest mean values were recorded at Baie de l’Etoile and Cap Blanc (90.94±10.87 and
84.58±11.31 mg kg-1 DW, respectively). The contamination of these sites by Zn may be due to
human and industrial activities, such as the use of anodes for the protection of boat hulls against
corrosion or from certain antifouling paints.
These findings are confirmed by the results of the principal component analysis.
3.1.2. Studies of correlations between metals
The correlation matrix between the analysed elements shows significantly positive coefficients
(table 3).
Table 3 Spearman's correlation of heavy metals levels in Perna perna tissues (only correlation
coefficients r significant at P ˂ 0.05 are indicated)
Element
Cd
Pb
Hg
Cu
Zn
Cd
1.00
0.76
0.80
0.20
-0.18
Pb
Hg
Cu
Zn
1.00
0.46
-0.29
-0.12
1.00
-0.07
-0.69
1.00
0.65
1.00
Cd, Pb et Hg show positive correlations of great significance. The correlation coefficients
vary from 0.764 to 0.800.
Cu et Zn show a significant positive correlation (r=0.646).
Cu and Zn show a relatively significant correlation with a correlation coefficient of 0.646.
Hg et Zn show a negative significant correlation (r=-0.688)
This can sometimes translate the same origin. These correlations require a study of the
existing relations between the studied metals. In this sense, a statistical PCA analysis has been
done. The obtained results are represented in Figure 2.
3.1.3. Principal Component Analysis
The results presented in Figure 2 are derived from a PCA with five variables (Cd, Pb, Hg, Cu
and Zn) and four terms (sampling sites). The first two axes represent respectively 52.68 % and
30.89% of the information ; summing 83.57% of the total variability which leads to the
adoption of a bi-dimensional representation (Figure 2).
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Figure 2 PCA diagram showing the correlation between different heavy metals (Cd, Pb, Hg, Cu and
Zn) and sampling sites (CO: COMECA, BE: Baie de l'Etoile, CB: Cap Blanc, IM: IMROP).
The results presented in Figure 2 are derived from a PCA with 5 variables and 12 modes (2
seasons x 4 sites). The first two components (PC1 and PC2) were extracted and together could
explain 83.57 % of entire variance of the original data. The first two axes are respectively
52.68 % and 30.89 % of the in-formation, a 83.57% total of the total variability. The twodimensional adopted representation of expenses shows the formation of two groups :
The first group includes the sites (Cap Blanc and Baie de l'Etoile) and Hg and Pb, This
suggests an anthropogenic contamination relative to recreational activities at the Baie de
l’Etoile with the use of fuel containing high concentrations of Pb. The site of Baie de l’Etoile
is under the influence of fishing activities (fishing, shellfish farming), tourism, market
gardening, and rampant urbanization in the immediate vicinity, etc. The site of Cap Blanc is
under the influence of industrial waste from SNIM (crushing iron ore, loading port, etc.).
The second group consists of Cu and Zn is relatively linked to COMECA, reflecting an
anthropogenic origin, given the proximity of this site to the effluence of industrial and urban
waste from the metal company 'COMECA' and its proximity to the oil port and passages of all
canoes and fishing and trade vessels to the ports of Nouadhibou. The heterogeneity of the metal
concentrations observed may be explained by the sedentary nature, the mode of nutrition microphage suspension of Perna perna resulting in a substantial accumulation of elements in its
biotope, as well as the continental inputs caused by increased effluents that carry high loads of
metal particles to the sea. According to standards established by the European Community [17].
The maximum values of Cd, Pb, Hg, Cu and Zn found in P. perna soft tissues from the Lévrier
bay (Table 4) were below the maximum acceptable limits for seafood indicating no potential
risk for human consumption according to standards established by the European Community
[17], excepet for Zn at COMECA (23.8 mg kg-1 Wet weight).
3.1.4. Seasonal variations of heavy metals in P.perna tissues
Results of heavy metals seasonal variations in Perna perna are presented in Figure3.
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Figure 3 Mean concentrations (mg kg-1 DW) of heavy metal in P. perna soft bodys tissus for the
studied sites and seasons during the study period.
The average Cd content in P. perna soft tissue collected from Baie de l'Etoile (Figure 3)
reached the highest level during the cold season (3.22±0.74 mgkg-1 DW), while in hot season
this content did not exceed 1.87±0.71 mg kg-1 DW. Similarly, the mean concentration of Cd in
P. perna recorded from COMECA and Cap Blanc was higher in the cold season (1.99±1.01
and 1.93±0.08 mg kg-1 DW, respectively) than in the hot season (0.88±0.17 and 1.51±0.19 mg
kg-1 DW, respectively). Cd concentrations recorded from IMROP were the lowest both in the
cold and hot season (0.73±0.22 mg kg-1 DW and 0.45±0.06 mg kg-1 DW, respectively). These
seasonal variations could be explained by the presence of Upwelling currents in the cold season
and by the life cycle of mussels in which maximum spawning occurs in autumn [38]. In winter,
the cold waters of the coastal Upwelling are mixed with the cold sea surface waters and thus
contributes greatly to the enrichment of the West African coastal ecosystem [36]. The wind
tends to push the water away from the coast which results in the rise of the deep waters all
along Mauritanian coast, creating in this way the coastal upwelling. This phenomenon
contributes to the transport towards the open sea of the contaminants in the coastal effluents
[12]. The highest mean levels of Pb in P. perna (Figure 2) were registered in Baie de l'Etoile
and COMECA during the cold season (0.97±0.16 and 0.90±0.28 mg kg-1, respectively). These
sites represent respectively the main waste disposal points of the new urbanization of Tarhil
and the COMECA metallurgy plant. The mean concentrations of Pb recorded at IMROP and
Cap Blanc in cold season were (0.80±0.10 and 0.64±0.19 mg kg-1, respectively). These sites
are respectively, the wastewater discharge point of the city of Cansado and the main waste
disposal point of the largest iron mining industry (SNIM). The highest mean concentrations of
Pb in the hot season were collected from Baie de l'Etoile and Cap Blanc (0.94±0.26 and
0.66±0.28 mg kg-1, respectively), while, the lowest mean levels of Pb in the hot season were
registred at COMECA and IMROP (0.49±0.09 and 0.56±0.16 mg kg-1, respectively). The mean
concentrations of Pb were lightly higher at Cap Blanc in the hot season than in the cold season
(0.66±0.28 and 0.64±0.19 mg kg-1 DW, respectively). Regarding seasonal variations of Hg
(Figure 2), high mean values were recorded during the cold season at COMECA and Cap Blanc
(0.03±0.01 and 0.07±0.02 mg kg-1 DW, respectively), while, during the hot season, the highest
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mean levels of Hg were collected from the Baie de l'Etoile and Cap Blanc (0.08±0.04 and
0.05±0.01 mg kg-1 DW, respectively). The mean concentrations of Hg were higher in cold
season than in hot season regardless the site, except for the Baie de l'Etoile where the mean
concentration of Hg was higher in the hot season (0.08±0.04 mg kg-1 DW) than in the cold
season (0.04 mg kg-1 DW). Mercury mean levels were the lowest of all heavy metals recorded
at different sampling sites regardless of the site and season. The mean concentrations of Cu in
P. perna (Figure 2) were higher during cold season at COMECA, Baie de l'Etoile and IMROP
(6.62±1.79, 4.69±1.71 and 4.00±1.25 mg kg-1 DW, respectively) than during the hot season
(5.29±0.53, 4.26±0.91 and 3.94±0.92 mg kg-1 DW, respectively). In contrast, the mean
concentrations of Hg at Cap Blanc were higher in the hot season (5.34±1.33 mg kg-1 DW) than
in the cold season (5.12±0.32 mg kg-1 DW). Similar results were found by [15] in P. perna in
Rio de Janeiro (Brazil). For Zn, the mean concentrations (Figure 2) in the cold season were
significantly higher at COMECA, Baie de l'Etoile and IMROP (120.02±23.6, 98.95±10.79 and
98.90±11.26 mg kg-1 DW, respectively) than during the hot season (118.07±7.43, 82.94±10.96
and 86.59±12.78 mg kg-1 DW, respectively), whereas the mean concentrations at Cap Blanc
were lower in the cold season than in the hot season (89.02±11.94 and 80.15±10.68 mg kg-1
DW, respectively). The seasonal values of Pb, Hg, Cu and Zn shows that maximum levels were
recorded during the cold season, while, minimum levels appeared during the hot season (Figure
3). These results agree with many works that have highlighted the influence of the seasons on
the accumulation of metals in mussels, which all show a maximum of bioconcentration in
winter and early spring and a minimum in summer [10, 33]. Thus, the concentrations of most
heavy metals increase significantly in the cold season and decrease in the hot season, consistent
with the work of most authors who found the existence of a winter maximum and a summer
minimum in various species of filtering molluscs: Mytilus edulis, Crassostrea gigas,
Crassostrea virginica, Mytilus californianus, Mytilus galloprovincialis, Cerastoderma edulis
and Donax trunculus [4, 6, 18]. These seasonal fluctuations in metal levels may be the result
of a combination of biological factors such as body weight, maturity and sex cycle, abundance
of food and environmental climatic conditions, and also of other, abiotic factors such as the
biogeochemical cycle and bioavailability of metals [20, 28]. Additional studies must be
undertaken in order to evaluate heavy metal fluctuations between the sexes at the Lévrier bay
in bivalve mussels.
Comparisons of mean heavy metal concentrations measured during the present study to
those published for studies in marine environments of other countries using P. perna as a
bioindicator are presented in Table 4.
Table 4. Comparison of heavy metal concentrations in Perna perna obtained in this study with
literature data from other countries coasts (mg kg-1 dry weight)
Sampling
sites
Cd
Pb
Hg
Cu
COMECA
1.44±0.59
0.70±0.18
0.03±0.01
5.95±1.16
Baie Etoile
Cap Blanc
IMROP
2.55±0.73
1.72±0.14
0.59±0.14
0.33
0.33-0.67
0.59-4.37
22.18±1.46
0.95±0.21
0.65±0.24
0.68±0.13
------0.44±0.05
0.06±0.02
0.06±0.01
0.03±0.01
0.05
--0.01-0.06
0.07±0.02
4.48±1.31
5.23±0.82
3.97±1.08
----2.3-8.97
9.46±1.60
Coastline of
Mauritania
http://www.iaeme.com/IJCIET/index.asp
791
Zn
Reference
119.04±15.5
5
90.94±10.87
84.58±11.31
92.75±12.02
----41-109
90.23±10.35
Present work
[31]
[29]
[11]
[22]
editor@iaeme.com
Assessement of Metallic Contamination of the Northen Atlantic Coast of Mauritania (Coastal
Fringe “Levrier Bay”), using Perna Perna
Sampling
sites
Marocco
Agadir Bay
Cap Ghir
Cd
Pb
Hg
Cu
Zn
Reference
1.5
---
---
---
---
[24]
1.5±0.3
---
---
4.8±0.9
110±26
6
---
0.04-2.6
---
---
[1]
72
---
150
---
[21]
---
---
[3]
---
---
Cap Juby.
Sahara
Jorf Lasfar
Malabata
29
<LD -0.45
Cap Beddouza
0.02 – 3.18
Cap Ghir
Sénégal
Soumbedioun
e
Soumbedioun
e.Hann.
Rufisque
Algeria
0.65 – 10.59
Ghana
1.4-1.9
---
0.33-0.37
Spain
Normes (EU:
Legal limits),
Wet weight
0.33
1.3
1.0
1.5
5
--0.2 – 5.85 0.14 – 0.35
<LD –
0.03 – 2.30
6.60
0.31 – 2.40 0.07 – 2.65
---
---
0.094±0.009
---
---
[32]
3.03±3.83
1.37±1.21
---
9.39±2.65
156±41
[32]
0.51- 0.11
1.68 -0.15 0.159 -0.031 26.74-2.47
358.96-5.4
[2]
15-16
---
[26]
0.05
38
72
[35]
0.5
14
20
17]
4. CONCLUSION
The bivalve molluscs Perna perna studied showed a spatial and temporal variability of the
distribution of trace metals in their soft tissues. The highest concentrations of Cd and Pb were
detected at the Baie de l’Etoile site which is under the effect of fishing activities (fishing,
shellfish farming), tourism, market gardening, and rampant urbanization in the immediate
vicinity, etc. Cu and Zn are also related to the COMECA site that contains an industrial and
urban waste from the metal company 'COMECA' and its proximity to the oil port and passages
of all canoes and fishing and trade vessels to the ports of Nouadhibou. The concentrations of
Hg recorded in P.perna soft tissues are the lowest from all metals, whatever the site and the
season. Accumulation of Pb, Hg, Cu and Zn by sampling period shows that maximum levels
are recorded during the cold season, while during the hot season all metal concentrations were
relatively low. These seasonal variations could be explained by the presence of upwelling
currents which are more pronounced in the cold season and the life cycle of mussels in which
maximum spawning period occurs in autumn. The maximum values of Cd, Pb, Hg, Cu and Zn
found in P.perna soft tissues from the Lévrier bay were below the maximum acceptable limits
for seafood indicating no potential risk for human consumption except for Zn at COMECA.
Comparison of the data obtained in the present work with other studies carried out in the
subregion for the same specie show similar results.
Regular monitoring and appropriate assessment of Cd contamination in the Mauritanian
coastal marine environment is therefore necessary.
http://www.iaeme.com/IJCIET/index.asp
792
editor@iaeme.com
M. H. Legraa, H. Er-Raioui, A. Y. Dartige, M. L. C. Zamel, M. M. O. Abidine, Z. Sidoumou and
A. Mohamed Saleck
ACKNOWLEDGEMENTS
This study results from a collaboration between the University of Nouakchott Al Aasriya
(Mauritania), the Abdel Malek Essaadi University (Morocco), the Mauritanian Institute of
Oceanographic and Fisheries Research (IMROP, Mauritania) and National Office of Sanitary
Inspection of Fisheries and Aquaculture Products (ONISPA, Mauritania). The authors would
like to give a special mention to these institutions for their courtesy, kindness and help. We
also would like to thank Rouane Omar from the Environmental Monitoring Network
Laboratory (LRSE) of Ahmed Ben Bella University 1 for his support.
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