Distribution, Sources, and Possible Adverse Biological Effects of Trace Metals in Surface Sediments of a Tropical Estuary

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Distribution, Sources, and Possible Adverse BiologicalEffects of Trace Metals in Surface Sediments of aTropical EstuaryN’Guessan Louis Berenger Kouassiab, Koffi Marcellin Yaob, Albert Trokoureyc & MetongoBernard Sorob

a Laboratoire de Chimie Physique, Université Félix Houphouët Boigny, Abidjan, Côte d’Ivoireb Centre de Recherches Océanologiques (CRO), Abidjan, Côte d’Ivoirec Laboratoire de Chimie Physique, Université Félix Houphouët Boigny, Abidjan Côte d’IvoirePublished online: 17 Mar 2015.

To cite this article: N’Guessan Louis Berenger Kouassi, Koffi Marcellin Yao, Albert Trokourey & Metongo Bernard Soro (2015)Distribution, Sources, and Possible Adverse Biological Effects of Trace Metals in Surface Sediments of a Tropical Estuary,Environmental Forensics, 16:1, 96-108, DOI: 10.1080/15275922.2014.991433

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Distribution, Sources, and Possible Adverse Biological Effectsof Trace Metals in Surface Sediments of a Tropical Estuary

N’Guessan Louis Berenger Kouassi,1,2 Koffi Marcellin Yao,2 Albert Trokourey,3 and Metongo Bernard Soro2

1Laboratoire de Chimie Physique, Universit�e F�elix Houphou€et Boigny, Abidjan, Cote d’Ivoire2Centre de Recherches Oc�eanologiques (CRO), Abidjan, Cote d’Ivoire3Laboratoire de Chimie Physique, Universit�e F�elix Houphou€et Boigny, Abidjan Cote d’Ivoire

Metal (Cu, Zn, Pb, Cd, Ni, Co, and Fe) contamination in sediments from a tropical estuary (�Ebri�e Lagoon, Ivory Coast) was assessedusing pollution indices, multivariate analyses and sediment quality guidelines (SQGs). The results demonstrate that increased inputof the studied metals occurred over the past 6 years compared to that from 20 years ago, due to rapid population growth, along withthe increase of industrial and agricultural activities in the vicinity of the estuary. �Ebri�e Lagoon was also found to be one of the mostcontaminated tropical coastal estuaries. Very high average total organic carbon (TOC) content was found (1.9–3.70%) withsignificant spatial variation as a result of the influence of anthropogenic activities. This study also found that TOC plays an importantrole in the distribution of Cu, Zn, Co, and Cd in the �Ebri�e Lagoon sediments. Moderate to high sediment contamination was observedfor Cd and Cu, moderate contamination was observed for Zn and Pb, while low contamination was observed for Ni, Co, and Fe.Cluster analysis (CA) and principal component analysis (PCA) investigation revealed that Cu, Zn, Cd, and Co result mainly fromanthropogenic sources while Pb, Ni, and Fe may be of natural origin. The pollution-loading index (PLI) indicated that all of the sitesclose to wastewater discharges were highly polluted. The sediments are likely to be an occasional threat to aquatic organisms due toCu, Zn, Pb, Cd, and Ni contents, based on the SQGs approach.

Keywords: estuary, pollution indices, sediment toxicity, trace metals

Introduction

Heavy metals are regarded as serious pollutants of aquatic eco-

systems due to their environmental persistence, bioaccumula-

tion, and toxicity. A recent study on metal speciation has shown

that concentrations of non-residual and dynamic complexes of

lead (Pb) and cadmium (Cd), which are good indicators of the

bioavailability of these metals, gradually increase with increas-

ing total metal content in sediment (Chakraborty et al., 2012a).

Because toxic metal loading to sediments may increase with

bioavailability, an increase in the total metal concentration in

sediments can be a potential threat to benthic organisms and

aquatic biota. In addition, human population growth, urbaniza-

tion, industrialization and an increase in land used for agricul-

ture in recent decades may lead to an accumulation of metals in

sediments (Jayaprakash et al., 2010). Estuarine and coastal

sediments can act as sources or sinks for metals due to their var-

iable physical and chemical properties, and heterogeneous bind-

ing sites (Pekey, 2006; Marchand et al., 2006). Thus, providing

a better understanding of the distribution, sources and trends of

enrichment levels of metals in sediments over time is important

for metal pollution control in the environment.

Various approaches, including sequential extractions,

kinetic extractions, adsorption/desorption studies, equilib-

rium partitioning models and in vitro digestive fluid extrac-

tions, have been used to understand the quality of sediments

with respect to metals (Yu et al., 2000; Dahlin et al., 2002;

Korfali and Davies, 2004; Zakir and Shikazono, 2008; Anir-

udhan et al., 2012; Chakraborty, 2012; Chakraborty et al.,

2012a, 2012b; Hong et al., 2012). These techniques are use-

ful for studying the fate, bioavailability, and toxicity of

sediments. Also, SQGs are often used, either to protect

aquatic organisms from the toxic effects associated with

sediment-bound contaminants or to predict adverse effects

of contaminants (McCready et al., 2006; Thompson et al.,

1999; Montero et al., 2013). However, all the aforemen-

tioned approaches have been found to be limiting when

determining the source of contamination and the degree of

accumulation of metals in the environment.

In contrast, metal enrichment approaches, including the

PLI, the enrichment factor, and the geo-accumulation index

(Igeo), provide an approximation of the state of accumulation

as well as sources of metals in aquatic systems (Burton and

Johnston, 2010; Christophoridis et al., 2009; Loska et al.,

1997; N’Guessan et al., 2009; Pekey, 2006). In general, envi-

ronmental quality indices are formed using either true back-

ground parameters, or those from a “reference” site and are

used to reliably evaluate the trend of metal contamination in

sediments over time (Tomlinson et al., 1980).

Address correspondence to Koffi Marcellin Yao, Research Scien-tist, Centre de Recherches Oc�eanologiques (CRO), Physical Chemis-try, 29 rue des pecheurs, BP V 18 Abidjan, Cote d’Ivoire.E-mail: [email protected]

96

Environmental Forensics, 16:96–108, 2015

Copyright � Taylor & Francis Group, LLC

ISSN: 1527-5922 print / 1527-5930 online

DOI: 10.1080/15275922.2014.991433

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It is well known that metal distributions in sediments are

governed by factors such as TOC, salinity, Fe and Mn oxides,

carbonates, oxic and anoxic conditions, pH, ionic strength, and

particle grain size (Chen et al., 2012; Hong et al., 2012; Lee

et al., 2013). To our knowledge, none of the trace metal stud-

ies in the �Ebri�e Lagoon (Cote d’Ivoire) have reported organic

matter content in sediments to date. Studies on interactions

between metals and organic carbon are essential for under-

standing the transport, reactivity, and bioaccumulation of these

ubiquitous and hazardous pollutants in the environment.

Therefore, it is essential to establish data and investigate the

influence of organic matter on the distribution of metals in the

environment.

Recent data on metal contamination in surface sediments

of tropical regions show that many riverine and estuarine

sediments are highly contaminated by metals (Tam and

Wong, 2000; Alagarsamy, 2006; Kissao et al., 2011; Yap and

Pang, 2011; Fernandes and Nayak, 2012; Atibu et al., 2013;

Bodin et al., 2013; Nilin et al., 2013; Wan et al., 2013).

Contamination results mainly from human activities such as

mining, fertilizer use in agriculture, and urbanization, which

cause untreated domestic and industrial wastewater discharge

into the environment (Wan et al., 2013). Data on total metal

concentration in tropical polluted wetlands are not readily

available, and sources and trends of pollutants, as well as the

responses of the impacted natural systems to pollution, are

not well documented. Studies on the fate, transport and toxic-

ity of metal elements in tropical aquatic systems are in their

infancy. The major lagoon system in West Africa, the �Ebri�eLagoon in Cote d’Ivoire is facing rapid population growth

surrounding it, along with an increase in nearby industrial

and agricultural development. Despite the fact that the estua-

rine part of the lagoon is surrounded by the city Abidjan,

which hosts almost 70% of all of the industry in the country,

there is a general lack of information available, first, for the

state of metal enrichment, second, for metal distribution and

speciation, and third, for the main factors driving metal distri-

bution in the estuarine sediments.

The objectives of this study were first to determine the dis-

tribution, level of accumulation, and the potential sources of

specific metals (Pb, Cu, Zn, Cd, Ni, Co, and Fe) in the estua-

rine sediments of the major estuary in West Africa (�Ebri�eLagoon, Cote d’Ivoire) using the PLI and Igeo, and multivariate

statistical analyses including principal component analysis and

hierarchical clustering analysis. A second objective was to

screen the possible adverse biological effects of trace metals

in the sediments by comparison with the SQGs. Third, for the

first time in this area, the influence of TOC on the distribution

of selected metals was investigated. Collectively, these objec-

tives are unique because metal dynamics in tropical estuaries,

particularly in Africa, are poorly understood. Most notably,

this work represents the first multi-metal analysis of sediments

from �Ebri�e Lagoon since Kouadio and Trefry (1987), thus

allowing an unprecedented opportunity to examine metal pol-

lution trends in �Ebri�e Lagoon from 1983 to 2012 using PLI.

Materials and Methods

Study Area

The �Ebri�e Lagoon system (3�250N, 4�450W) has a total area of

566 km2 with length of 130 km and a maximum width of

about 7 km and is the largest lagoon bordering the eastern

equatorial Atlantic Ocean in West Africa. The average depth

is 4.8 m. The study area (Figure 1) is surrounded by Abidjan

City (approximately 6 million inhabitants), the largest city of

Cote d’Ivoire. In the Abidjan area, Tertiary and Quaternary

Period sediment basins overlay the Precambrian basement

(Figure 1). Along the southern edge of �Ebri�e Lagoon, marine

sand, river-lagoon clay and sand, as well as clayey sand

derived from the Quaternary continental plateaus, form a

coastal strip that separates the Lagoon from the Atlantic

Ocean. Sediment in the northern region of the �Ebri�e Lagoon

includes argillaceous sands and sandstone weathered from

high continental plateaus that originate from the Quaternary

period. The stratigraphic column coarsens downward, with

clayey, medium-grained, and coarse-grained sand overlaying

Precambrian basement rocks (Kadio et al., 2010). Although no

distinct stratigraphic sequence can be observed in the south,

the sediment cover includes medium to very fine and coarse

sands, muddy sediments, and silt.

Sediment samples were collected from four different

environmentally significant bays in the estuarine part of the�Ebri�e Lagoon (Figure 1). Bietri, Banco, and Cocody Bays

receive direct discharges of urban and industrial wastes while

Abou-Abou Bay receives no direct inputs. There are four main

climatic seasons in the region: a high dry season (December–

March), a high rainy season (April–July), a low dry season

(August–September), and a low rainy season (October–

November). The average annual air temperature is about

26.6�C with average maximum and minimum temperatures of

30�C and 24�C respectively, while the total annual precipita-

tion averages 1847.6 mm. The mean monthly rainfall maxi-

mum is 562 mm in June, while the mean monthly minima are

37 mm in August and 16 mm in January.

Sampling and Sample Conservation

Sampling was conducted from February to May 2012. Sam-

pling stations were chosen at the edge, in the middle and at the

entrance of each bay to ensure that they represented the char-

acteristics of the bays (Figure 1). However, two stations were

sampled in Abou-Abou Bay because its surface area is small.

Thus, Stations 1, 2, and 3 were located in Banco Bay, Stations

4, 5, and 6 in Cocody Bay, Stations 7, 8, and 9 in Bietri Bay;

and Stations 10 and 11 were sampled in Abou-Abou Bay. In

addition, data were collected from literature to study the trend

of metal accumulation during 1983–2012. A Van Veen stain-

less steel grab (with an area of 0.02 m2) was used to collect

surface sediment (0–5 cm). Without emptying the grab, a sam-

ple was taken from the center with a polyethylene spoon (acid

washed) to avoid contamination by the metallic parts of the

dredge. Surface sediments were used in this study because

Trace Metals in Surface Sediments of Tropical Estuary 97

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they are recent, or in direct contact with biota, and they are

susceptible to releasing metals into the water column follow-

ing changes in physical and chemical conditions. Three sam-

plings were conducted at each station. The samples were

transported to the laboratory at 4�C, dried at 60�C in a forced

air oven, and homogenized and stored at 4�C until analysis.

Each sample was sieved through a stainless steel mesh to

remove any particle larger than 63 mm in size.

Sediment Analysis

All chemicals and reagents used in the study were of analytical

grade or better. Glass, plastics, and other laboratory ware were

cleaned by soaking in a 10% HNO3 solution overnight and

then thoroughly rinsed with de-ionized water. All digestions

were performed in Teflon containers. Approximately 0.2 g of

the homogenized sediment were digested and taken to dryness

three times with a mixture of 1 mL of aqua regia (HNO3: HCl;

1:3, v/v) and 3 mL of HF in loosely capped Teflon vessels on

a hot plate, and then left for 15 min at room temperature.

Next, 20 mL of H3BO3 (140 g/L) were added to each vessel to

mask free fluoride ions in the solution and re-dissolve fluoride

precipitates. The final digestates were diluted to 50 mL with

2% ultrapure HNO3. The liquid aliquots were filtered through

0.45 mm pore size membranes (Millex Millipore, Merck,

Darmstadt, Germany) prior to analysis using an air-acetylene

flame atomic absorption spectrometer (AAS, SpectrAA100:

Varian, Tokyo, Japan) air-acetylene flame analyses.

Three replicates of each sample were analyzed, and the

samples presented an error that was within 6%. Duplicate

blanks were prepared and analyzed with each batch of digested

samples. The operational conditions for the AAS were

adjusted in accordance with the manufacturer’s guidelines to

obtain an optimal determination. In addition, the accuracy of

Figure 1. Geological map of Abidjan area and sampling stations.

98 N. L. B. Kouassi et al.

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analysis was checked by replicate measurements of a standard

marine sediment reference material (BCSS-1, National

Research Council, Canada). The measured concentrations fell

within the range of certified values, and the recoveries varied

between 94% and 108% for Ni, Zn, Pb, Cu, and Cd, and

between 85% and 108% for Co and Fe.

The major mineral components of the sediment samples

were determined using a scanning electron microscope (SEM,

D.C.AR MEB FEG Supra 40 VP Zeiss, Oberkochen, Ger-

many) coupled with an energy dispersive spectrometer (EDS,

INCA, Oxford Instruments, Abingdon, Oxfordshire, UK. Dry

Cool, without nitrogen liquid). The sediment sample was

finely crushed using an agate mortar, sieved through a stainless

63-mm steel mesh, and then 0.3 g of sediment were placed on

an aluminum stub using conductive carbon before processing.

TOC concentrations in the sediments were determined

using the standard Walkley-Black method (Walkley and

Black, 1934). This method has been widely used for the deter-

mination of TOC in soil and sediments (Nelson and Sommers,

1996). The detailed procedure is described elsewhere in the lit-

erature (e.g., Schumacher, 2002). Studies have shown that the

recovery of organic C using the Walkley–Black procedure

ranges from 60% to 86% with a mean recovery of 76%, due to

the incomplete oxidation of organic matter. However, recover-

ies in the range of 88%–106% are yielded when a correction

factor of 1.4 is applied to the results (Soon and Abboud, 1991).

Sediment Assessment

The PLI was used to characterize the multi-element contami-

nation level in the sediment samples (Tomlinson et al., 1980):

PLID ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCF1 £CF2 £CF3 £ . . . £CFn

np

(1)

CF1,\ CF2,\ . . .CFn\ are\ contamination\ factors\ of\ the\ sedi-

ment\ sample\ with\ respect\ to\ element\ 1,\ 2. . .and\ n\

respectively;\ n\ is\ the\ number\ of\ metals\ investigated.\

Contamination\ factors\ CFi\ were\ calculated\ using\ Equation

\ 2:

CFi D Cmetal ið ÞCbackground ið Þ (2)

where Cmetal (i) is the concentration of metal (i) in the sedi-

ment sample and Cbackground (i) is the background value of the

metal (i). No heavy metal background values are available for

the study area. Therefore, the average crustal abundances of

metals, with respect to the Upper Continental Crust (UCC)

and the Lower Continental Crust (LCC) from Wedepohl

(1995), were used. A PLI value of one or less indicates that

only baseline levels of elements are present, and a PLI above

one indicates the progressive deterioration of estuarine quality

(Tomlinson et al., 1980).

The geo-accumulation index was used to estimate the level of

metal accumulation:

Igeo D log2 X=1:5bnð Þ (3)

In this equation, X is the total content of the individual ele-

ment X and bn is its geochemical background concentration in

UCC, while 1.5 is the background matrix correction factor due

to lithogenic effects. Seven classes of the geochemical index

have been distinguished (Table 1).

Two sets of SQGs were used to estimate the possible

adverse biological effects of the studied metals in the sedi-

ments of the �Ebri�e Lagoon to organisms. These included ERL

(effects range low) and ERM (effects range medium) as one

pair, and TEL (threshold effects level) and PEL (probable

effects level) as a second pair. These guidelines represent two

separates scales that can be used to assess toxicity, and define

three ranges of contaminant concentrations. Concentrations

below the ERL/TEL are rarely associated with adverse effects,

concentrations between the ERL/TEL and ERM/PEL are occa-

sionally associated with adverse effects, and concentrations

above the ERM/PEL are frequently associated with toxicity

(Ingersoll, 1996; Long et al., 1998).

Statistical Analysis

Analysis of variance (ANOVA) was performed to ascertain

spatial differences. Differences at the p < 0.05 level (95%

confidence interval) were considered statistically significant.

Regression analysis (p < 0.05) was performed to study the

relationships between TOC and metal concentrations in the

sediments. To assess the contributing sources of studied metals

in the sediments, multivariate statistical analyses such as prin-

cipal component analysis/factor analysis (PCA/FA) and hierar-

chical clustering analysis (HCA) were performed on the metal

concentrations and TOC contents using Statistica 7.1 software.

PCA/FA and HCA are usually used to identify associations

between variables with similar sources. FA with Varimax rota-

tion of standardized component loadings was conducted for

extracting and deriving factors, respectively, and principal

components (PCs) with an eigenvalue greater than 1 were

retained. To establish significant associations between varia-

bles, a 0.7 factor loading cut-off was used. HCA was con-

ducted to determine the suitability of the data for PCA/FA by

Table 1. Geo-accumulation index (Igeo) and sediment contaminationlevel

Class Value Contamination level

0 Igeo< 0 Uncontaminated1 0< Igeo< 1 Uncontaminated to moderately contaminated2 1< Igeo< 2 Moderately contaminated3 2< Igeo< 3 Moderately to strongly contaminated4 3< Igeo< 4 Strongly contaminated5 4< Igeo< 5 Strongly to extremely contaminated6 5< Igeo Extremely contaminated


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using the complete linkage procedure (furthest neighbor)

applied to the Euclidean distances.

Results and Discussions

Major Constituents in Sediments Collected from the �Ebri�eEstuary Bays

A preliminary analysis of the sediments was carried out by

determining the relative contents (%) of the major oxides in

selected sediments using SEM/EDS (Table 2 and Figure 2).

Surface sediment mineral phases were primarily dominated by

quartz (34%–a46%), followed by aluminum oxides (17%–

27%), iron oxides (10%–15%) and sulfur oxides (0.88%–14%)

at all sites. A very high content of S was found at Stations 7, 8,

and 10 (12%–14% in S), suggesting an abundance of sulfides.

The quartz phase may serve as a site for the adsorption of

organic matter (Hoch and Schwesig, 2004), while clay surfa-

ces are known to be important sites for metal precipitation due

to their large specific area. Iron and aluminum oxides are well

documented as metal binding phases in the environment, while

sulfide is known to play an important role as a binding phase in

reducing conditions. Thus, we can conclude that the observed

mineral phases are those that would enable the accumulation

of trace metals in sediments. We also found that the mineral

composition of the studied sediments showed some spatial var-

iability, which may account for some of the spatial differences

in metal accumulation.

Distribution of Metals and Total Organic Carbon (TOC) in

Sediments

Table 3 shows trace metal (Fe, Cu, Zn, Pb, Cd, Ni, and Co)

and TOC contents in sediments collected from four bays of the�Ebri�e Lagoon. TOC values ranged from 1.15% to 4.25% with

an average value of 2.67 § 0.67% for all four bays. These val-

ues are relatively high compared with common values for

coastal sediments (0.32%–1.76%). The average level of TOC

contents showed significant spatial variations (ANOVA, p <

0.05) among the stations. In general, the lowest values were

registered at stations in the Abou-Abou Bay, whereas the high-

est average TOC was found in the stations located in Cocody,

Banco, and Bietri Bays as a result of inputs from domestic and

industrial sources, followed by the flocculation of dissolved

organic carbon, which occurs due to the mixing of freshwater

from the Comoe River and marine water from the Atlantic

Ocean.

The ranges of metal concentrations in sediments were:

22.36 § 0.31 –77.72 § 0.04 mg/g for Fe, 21.34 § 4.01–

181.95 § 0.90 mg/g for Cu, 39.79 § 1.01–417.86 § 2.04 mg/

g for Zn, 9.19 § 2.01–141.28 § 0.03 mg/g for Pb, 0.02 §0.01–1.83 § 0.04 mg/g for Cd, 1.35 § 0.91–87.3 § 0.53 mg/g

for Ni and 8.2 § 0.95–18.4 § 1.02 mg/g for Co. The general

levels of trace metal concentrations were relatively high in all

of the studied sediments compared with the average values in

both the Lower and Upper Continental Crusts (Wedepohl,

1995), except for Co and Ni, which showed concentrations

less than the average values of the Lower Continental

Crust (LCC). One-way ANOVA analysis (p < 0.05)

showed that sediments from the Cocody, Banco, and Bietri

Bays had higher concentrations of Cu, Zn, and Cd than the

sediments from Abou-Abou Bay. No significant differences

were found in Ni, Pb, and Co concentrations among sam-

pling stations, but the highest average concentrations of Ni

and Pb were registered in Abou-Abou Bay. The data in

Table 3 indicate that the metal concentrations in sediments

were generally higher during the wet season. This may

result from the combined effect of runoff waters and rapid

sedimentation. However, high sampling frequencies over at

least 2 years are necessary to determine accurate seasonal

variations of trace metals in the �Ebri�e Lagoon. The metal

concentrations in the sediments were higher than concen-

trations reported in tropical coastal sediments from many

other parts of the world (Kissao et al., 2011; Banerjee

et al., 2012; Bastami et al., 2012; Buruaem et al., 2012;

Jiang et al., 2013; Qiao et al., 2013) (Table 4).

It has been reported that large amount of industrial and

domestic liquid effluents, agricultural sewage containing

insecticides and fungicides, and atmospheric emissions from

Table 2.Major oxides relative contents (%) in selected sediments collected from the �Ebri�e Estuary bays in February 2012

Station Statistic Na2O Al2O3 SiO2 SO3 K2O CaO TiO2 FeO CuO MgO P2O5

1 Mean 2.15 26.53 46.49 5.22 0.58 0.53 2.18 13.36 0.21Standard Deviation 0.09 0.69 0.65 0.11 0.07 0.05 0.04 0.08 0.18

7 Mean 3.89 19.82 40.13 12.57 1.50 0.46 0.92 14.96 0.45 1.57Standard Deviation 0.61 0.03 2.81 0.69 0.37 0.07 0.14 1.57 0.07 0.06



6 Mean 12.64 19.33 34.01 3.79 1.12 0.74 1.25 12.33 0.53 1.36 0.66Standard Deviation 1.01 0.52 2.02 0.07 0.30 0.26 0.08 1.42 0.18 0.08 0.11

11 Mean 2.06 22.50 39.03 13.92 1.14 0.79 0.90 15.02 0.47 2.17Standard Deviation 0.08 0.22 0.21 0.29 0.05 0.07 0.08 0.13 0.07 0.04

Station 1 is located in the Banco Bay, Stations 7 and 8 in the Bietri Bay, Stations 4 and 6 in the Cocody Bay, and Station 11 in the Abou-Abou Bay,


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traffic and industries are discharged into the study area

(Kouadio and Trefry, 1987). In addition, under conditions of

fresh water discharges into the �Ebri�e Estuary, metals are also

carried into the estuary environment. Coagulation or precipita-

tion of metal complexes can occur, resulting in an increased

concentration of metals in sediments in enclosed bays (Kar-

bassi and Nadjafpour, 1996; Biati and Karbassi, 2011). How-

ever, these data alone give no information regarding the

sediment metal quality, nor the origin of the metal

accumulation.

The multi-element contamination level in the sediment

samples was estimated by calculating the PLI (Table 3). Find-

ings were that 98% and 93% of the sediments sampled had

PLI values greater than 1, when calculated using the UCC and

LCC, respectively. This indicates a ‘“progressive deterio-

ration” of the sediment quality with respect to metals in the

vicinity of the �Ebri�e Estuary (Tomlinson et al., 1980). The

highest average values of the PLI with respect to both

the UCC and LCC, were found in all the sampling stations of

Cocody Bay, and also in Stations 2 and 8, which were located

in Banco and Bietry Bays, respectively. This clearly shows the

influence of human activities on the metal contamination of

sediments. Untreated industrial and municipal wastewater is

discharged directly into Cocody, Banco, and Bietri Bays, in

contrast to Abou-Abou Bay, which does not receive direct

discharges.

This research also investigated the accumulation of individ-

ual elements in the sediments by the calculation of Igeo with

respect to the UCC and LCC (Wedepohl, 1995), and the results

are shown in Table 5. Different levels of contamination were

found for each metal. The sediments were moderately to

strongly contaminated with Cd, with Igeo values ranging

between 2 and 3. There were moderate levels of Pb contamina-

tion in almost all of the collected sediment samples, as indi-

cated by Igeo values ranging from 1 to 2. For Zn and Cu, the

Igeo values calculated with respect to the UCC indicated that

sediments were moderately to strongly contaminated. Those

calculated with respect to the LCC indicated that almost all

sediments were uncontaminated or moderately contaminated

with Cu and Zn. This observation demonstrates that calculat-

ing the pollution indices of sediments from areas where back-

ground values are lacking based on one single continental

crust value can lead to misinterpretation. The most appropriate

reference value is likely to be the UCC because the local

Figure 2. Scanning electronic images of sediment samples collected from Stations 1, 4, 7, and 10 in Banco, Cocody, Bietri, and Abou-Abou Bays inFebruary 2012.


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geology primarily consists of sediment deposits, but further

study is needed to confirm this assertion. The Igeo values of Ni,

Co and Fe metals varied from 0 to less than 1, indicating that

sediments in the study area are uncontaminated to moderately

contaminated with these elements.

CA and HCA Analysis

To determine the contributing sources of metals in the sedi-

ments, FA/PCA and HCA were performed on specific metals

(Cd, Cu, Ni, Pb, Zn, Co, and Fe) and TOC concentrations. Fe

and Zn data were normalized before PCA analysis to render

all data to the same order of numerical magnitude, and we

used Varimax rotation (Han et al., 2006) to maximize the sum

of the variance of the factor coefficients. Two factors, with

eigenvalues greater than 1 that accounted for 63.37% of the

total variance, were extracted (Table 6). The first factor (F1),

with 43.07% of the total variance, included high loadings for

Cu, Zn, Cd, Co, and TOC, which suggested that Cu, Zn, Cd,

and Co have similar sources or similar affinities to TOC. The

second factor (F2) had high loadings for Pb, Ni, and Fe and

accounted for 24.30% of variance (Table 6). The common

association of Pb and Ni with Fe implies that the source of

these two metals is from natural, geological sources as this is

the primary source of Fe to the lagoon (Chen et al., 2012). Fur-

thermore, the Igeo values showed that sediments were weakly

Table 3.Metals and total organic carbon (TOC) contents in sediments of the �Ebri�e Lagoon bays

Date Bay Station Cu Zn Pb Cd Ni Co Fe TOC

PLI

(UCC)

PLI

(LCC)

02/12/2012 Banco 1 45.95 § 3.01 174.58 § 2.04 116.88 § 1.02 0.57 § 0.09 54.95 § 3.02 9.50 § 1.01 56.75 § 0.02 3.16 3.17 1.65

02/12/2012 2 33.25 § 2.04 124.57 § 2.03 110.42 § 1.02 0.84 § 0.07 57.07 § 2.02 10.40 § 2.01 74.32 § 0.01 2.92 3.07 1.59

02/12/2012 3 37.52 § 2.01 118.29 § 2.05 110.34 § 1.02 0.77 § 0.07 56.91 § 2.02 10.44 § 1.09 77.72 § 0.04 1.83 3.06 1.59

03/12/2012 1 50.15 § 2.06 187.87 § 2.04 82.83 § 0.08 0.55 § 0.09 29.69 § 1.01 8.73 § 2.05 31.37 § 0.06 2.18 2.72 1.41

03/12/2012 2 49.01 § 1.01 224.88 § 1.04 96.30 § 0.09 0.91 § 0.06 50.99 § 1.02 13.60 § 3.02 49.35 § 0.08 2.35 3.67 1.91

03/12/2012 3 34.36 § 0.09 77.94 § 3.01 16.93 § 1.01 0.33 § 0.08 14.94 § 4.01 9.30 § 1.04 45.98 § 9.04 1.15 1.40 0.73

04/12/2012 1 97.30 § 0.09 109.34 § 2.02 59.73 § 0.01 1.10 § 0.05 26.54 § 3.01 10.50 § 1.01 31.72 § 0.03 2.30 2.99 1.55

04/12/2012 2 104.72 § 0.06 134.91 § 2.03 25.47 § 1.05 1.12 § 0.05 36.37 § 3.01 14.10 § 2.01 50.82 § 0.02 2.56 3.02 1.57

04/12/2012 3 85.98 § 3.02 94.14 § 3.02 38.91 § 2.01 1.83 § 0.04 29.63 § 1.01 52.18 § 0.32 2.24 3.73 2.16

05/12/2012 1 107.07 § 2.03 127.42 § 3.02 10.81 § 1.01 0.98 § 0.08 26.21 § 1.01 11.63 § 1.01 35.73 § 0.11 2.43 2.10 1.10

05/12/2012 2 181.95 § 0.90 417.86 § 2.04 74.98 § 1.01 1.81 § 0.04 72.71 § 3.03 17.00 § 1.02 53.65 § 0.32 3.71 6.00 3.12

05/12/2012 3 100.20 § 2.02 96.29 § 3.02 37.63 § 1.06 0.70 § 0.07 37.10 § 2.01 11.00 § 1.01 52.86 § 0.12 2.23 2.69 1.40

02/12/2012 Bi�etri 7 46.31 § 1.01 97.54 § 2.02 65.02 § 2.01 0.86 § 0.09 50.99 § 2.02 14.30 § 2.05 48.65 § 0.52 2.60 2.96 1.54

02/12/2012 8 61.14 § 1.01 318.81 § 1.04 97.27 § 1.04 0.82 § 0.09 17.57 § 3.01 13.00 § 1.08 25.78 § 0.21 3.39 3.30 1.72

02/12/2012 9 56.41 § 3.01 200.30 § 1.03 97.91 § 0.05 0.37 § 0.09 22.61 § 2.01 8.20 § 0.95 27.12 § 0.03 2.49 2.37 1.08

03/12/2012 7 99.27 § 2.03 105.22 § 2.02 25.62 § 1.01 0.93 § 0.07 18.98 § 2.01 9.60 § 1.01 57.43 § 0.02 2.43 2.34 1.22

03/12/2012 8 107.97 § 1.03 244.72 § 0.09 76.78 § 1.01 1.41 § 0.05 73.06 § 3.02 11.80 § 2.01 30.45 § 0.06 4.25 4.56 2.37

03/12/2012 9 96.26 § 2.02 147.20 § 1.03 23.36 § 2.01 0.57 § 0.08 13.08 § 4.01 9.00 § 2.01 36.12 § 0.05 2.76 2.08 1.08

04/12/2012 7 98.48 § 1.02 93.72 § 3.02 54.71 § 0.09 0.64 § 0.09 31.11 § 4.01 12.70 § 22.01 48.98 § 0.03 2.39 2.79 1.45

04/12/2012 8 126.94 § 2.03 172.00 § 1.03 53.29 § 1.01 1.48 § 0.05 63.83 § 1.02 10.50 § 1.01 29.77 § 0.03 3.72 4.02 2.09

04/12/2012 9 118.56 § 1.03 196.31 § 1.03 17.49 § 2.01 1.01 § 0.07 35.40 § 2.01 9.30 § 1.01 34.52 § 0.04 2.99 2.81 1.46

05/12/2012 7 77.54 § 3.02 92.11 § 2.02 45.11 § 0.08 1.03 § 0.07 2.74 § 2.01 13.40 § 2.01 40.39 § 0.03 2.56 1.88 0.98

05/12/2012 8 86.56 § 2.02 224.85 § 1.03 9.19 § 2.01 1.16 § 0.05 1.35 § 0.91 15.40 § 2.02 27.78 § 0.04 2.85 1.58 0.82

05/12/2012 9 106.62 § 1.02 229.78 § 1.03 27.11 § 1.01 1.45 § 0.06 25.74 § 2.01 15.20 § 2.02 39.27 § 0.06 3.19 3.34 1.73

02/12/2012 Cocody 4 63.22 § 2.01 294.10 § 0.07 99.95 § 1.02 0.77 § 0.15 57.72 § 1.02 11.99 § 1.01 76.65 § 0.04 2.82 3.92 2.04

02/12/2012 5 51.14 § 2.01 169.56 § 1.02 50.15 § 2.01 0.67 § 0.10 62.81 § 0.09 10.70 § 1.01 54.74 § 0.12 3.23 2.99 1.55

02/12/2012 6 80.66 § 2.02 239.02 § 1.05 131.97 § 1.03 0.85 § 0.09 46.87 § 0.71 10.50 § 2.01 39.03 § 0.05 3.31 3.97 2.06

03/12/2012 4 127.60 § 1.03 342.63 § 0.09 116.26 § 0.06 1.04 § 0.09 28.67 § 0.61 16.60 § 2.02 64.34 § 0.13 2.76 5.69 3.62

03/12/2012 5 133.78 § 1.03 262.33 § 2.02 92.98 § 0.07 1.73 § 0.05 52.18 § 0.82 18.40 § 1.02 60.46 § 0.03 3.54 5.20 2.70

03/12/2012 6 169.48 § 2.04 352.88 § 1.04 90.95 § 0.06 1.60 § 0.09 46.72 § 1.01 16.40 § 3.02 44.36 § 0.11 4.19 5.39 2.80

04/12/2012 4 125.59 § 2.03 216.24 § 1.02 44.38 § 0.09 1.30 § 0.09 27.67 § 1.01 15.00 § 3.02 44.17 § 0.31 3.22 3.66 1.90

04/12/2012 5 116.27 § 1.03 144.02 § 2.02 24.40 § 1.01 1.21 § 0.09 36.36 § 1.01 14.10 § 2.01 46.43 § 0.21 2.53 3.12 1.62

04/12/2012 6 176.75 § 1.04 194.23 § 2.02 10.89 § 2.01 1.18 § 0.12 57.07 § 0.09 11.81 § 2.01 34.76 § 0.06 3.51 2.40 1.24

05/12/2012 4 89.99 § 1.02 65.45 § 4.01 32.24 § 1.01 1.10 § 0.09 17.56 § 2.01 13.00 § 1.01 36.93 § 0.11 2.85 2.36 1.23

05/12/2012 5 83.25 § 3.02 61.11 § 3.09 47.16 § 1.01 1.23 § 0.09 50.58 § 2.02 14.80 § 2.01 23.36 § 0.21 3.27 3.05 1.59

05/12/2012 6 143.26 § 2.03 285.58 § 1.03 30.80 § 1.01 1.27 § 0.09 32.21 § 2.01 13.76 § 2.01 26.68 § 0.11 3.78 2.62 1.36

03/12/2012 Abou-Abou 10 21.34 § 4.01 39.79 § 1.01 17.12 § 2.01 0.02 § 0.01 30.52 § 4.01 9.00 § 1.01 22.36 § 0.31 1.45 0.81 0.42

03/12/2012 11 55.31 § 2.01 74.16 § 1.01 34.97 § 1.01 0.46 § 0.05 87.30 § 0.53 11.60 § 2.01 58.10 § 0.22 1.99 2.50 1.30

04/12/2012 10 55.23 § 1.01 75.44 § 4.01 83.83 § 0.08 0.94 § 0.01 73.47 § 1.02 12.70 § 2.02 55.69 § 0.12 2.48 3.22 1.67

04/12/2012 11 61.44 § 1.02 73.31 § 2.01 73.30 § 0.09 0.97 § 0.08 65.68 § 2.02 12.29 § 1.01 72.14 § 0.33 2.14 2.50 1.14

05/12/2012 10 53.12 § 2.01 65.70 § 5.01 123.49 § 0.04 0.99 § 0.09 72.47 § 1.02 12.70 § 2.02 47.95 § 0.41 1.83 3.26 2.08

05/12/2012 11 40.83 § 1.01 74.77 § 2.01 141.28 § 0.03 0.96 § 0.01 76.61 § 3.02 10.20 § 2.01 47.13 § 0.41 2.13 3.25 1.69

Upper Continental Crust (UCC) 14.3 52.0 17.0 0.1 18.6 11.6 27.8

Lower Continental Crust (LCC) 37.4 79.0 12.5 0.1 99.0 38.0

*Minimum and Maximum values are in bold, in italic, and underlined. Values (mean § stdv) are in ug/g for all the metals but in mg/g for Fe; TOC values are inpercentage.


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contaminated with Pb and Ni, but were more contaminated

with Cu, Zn, and Cd, which is consistent with a natural

source of Pb and Ni and the segregation of these two

groups of metals in the factor analysis. HCA was per-

formed by using the complete linkage procedure (furthest

neighbor) applied on the Euclidean distances. Two main

clusters were identified (Figure 3). The first cluster included

Cu, Zn, Cd, Co, and TOC, while the second comprised Pb,

Ni, and Fe. The reason for these associations could be the

fundamental geochemistry of each metal, or sources of con-

tamination. It is clear that HCA analysis confirmed the

results obtained with PCA.

Sources of Metal Inputs

As previously mentioned, the supply of Pb, Ni, and Fe in the�Ebri�e Lagoon estuary appears to be largely natural and there-

fore could come from weathering of rocks and soil, atmo-

spheric deposition and inputs from rivers such as the Comoe,

Agneby, and Banco. A cluster analysis performed on the con-

centration of metals derived from anthropogenic sources (Cu,

Zn, Cd, and Co) identified three groups of stations (Figure 4).

The first of these was associated with moderately contami-

nated stations (cluster A), the second the highest contaminated

stations (cluster B), while the third was characterized by the

least contaminated stations (cluster C).

Table 4. Concentrations of metals reported in tropical coastal sediments across the world versus in the �Ebri�e Lagoon sediments

Area

�Ebri�eLagoon

HooghlyEstuaryIndia

ShantouBayChina

LangatRiver,

Malaysia

GorganBay,Iran

Lagoonsof

Lome, Togo

XiawangangRiver(SouthChina)

LargeMarine

Ecosystemsof Brazil

Cu (mg/g) 21.34–181.95 21.89–79.49 2.24–14.84 3.8–31.2 213.9–364.7 0.49–18.77Zn (mg/g) 39.79–417.86 27.28 84.19–248.50 12.26–74.70 13.0–75.0 0.02–1.30 18.98.1–5078.8 25.30–1077.33Cd (mg/g) 0.02–1.83 0.18 0.24–1.75 0.19–1.91 13.8–173.0 0.30–1.41Pb (mg/g) 9.19–141.28 10.15 35.56–64.91 5.57–55.71 4.1–18.3 0.01–0.36 308.2–1050.0 <2.00–16.70Co (mg/g) 8.20–18.40 6.04 8.22–10.87Ni (mg/g) 1.35–87.30 23.55 15.54–31.69 2.33–8.25 <2.00–24.75Fe (mg/g) 22.36–77.72 4.25 12.66–49.52References This study Banerjee

et al., 2012Qiao

et al., 2013Wan et al.,

2013Bastami et al.,

2012Kissao et al.,

2011Jiang

et al., 2013Buruaemet al., 2012

Table 5. Geo-accumulation index (Igeo) of heavy metals in �Ebri�e Lagoon sediments

Igeo (UCC)

Station Cu Zn Pb Cd Ni Co Fe

1 1.81 0.94 1.41 2.42 0.30 0.00 0.002 2.10 1.53 1.59 2.96 0.96 0.00 0.303 1.59 0.31 1.00 2.60 0.31 0.00 0.307 1.91 0.32 0.90 2.53 0.00 0.00 0.088 2.16 1.62 1.21 3.02 0.48 0.00 0.009 2.14 1.31 0.70 2.50 0.00 0.00 0.004 2.24 1.56 1.52 2.81 0.24 0.00 0.265 2.16 1.03 1.07 3.01 0.86 0.00 0.006 2.73 1.78 1.38 3.03 0.71 0.00 0.0010 1.01 0.00 1.55 2.12 1.08 0.00 0.0011 1.29 0.00 1.71 2.41 1.46 0.00 0.35

Igeo (LCC)

1 0.42 0.34 1.85 2.42 0.00 0.00 0.002 0.72 0.93 2.03 2.96 0.00 0.00 0.003 0.20 0.00 1.44 2.60 0.00 0.00 0.007 0.52 0.00 1.34 2.53 0.00 0.00 0.008 0.77 1.02 1.66 3.02 0.00 0.00 0.009 0.75 0.71 1.15 2.50 0.00 0.00 0.004 0.86 0.95 1.97 2.81 0.00 0.00 0.005 0.78 0.43 1.52 3.01 0.00 0.00 0.006 1.35 1.18 1.82 3.03 0.00 0.00 0.0010 0.00 0.00 2.00 2.12 0.00 0.00 0.0011 0.00 0.00 2.15 2.41 0.00 0.00 0.00

UCC, Upper Continental Crust; LCC, Lower Continental Crust. Station 1, 2, and 3 are located in the Banco Bay, Stations 7, 8, and 9 in the Bietri Bay, Stations 4,5, and 6 in the Cocody Bay, and Stations 10 and 11 in the Abou-Abou Bay.


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Cluster A consisted of Stations 1, 5, and 9, which were

located at the entrance of Banco Bay, in the middle of Cocody

Bay, and at the edge of Bietri Bay, respectively. The medium

level of contamination at Stations 1 and 9 in Bietri and Banco

Bays, may have resulted from the combined effect of currents

and oceanic dilution, while Station 5 was not located close to

sources and therefore was not expected to be heavily

contaminated.

Cluster B comprised Stations 2, 4, 6, and 8, which were

located in the middle of Banco Bay, at the entrance and the

edge of Cocody Bay, and in the middle of Bietri Bay, respec-

tively. These stations are subjected to a greater input of metal

than the other stations.

Cluster C was related to Station 3 at the edge of Banco Bay,

7 at the entrance of Bietri Bay, and Stations 10 and 11 in

Abou-Abou Bay. Stations 10 and 11 are farther from direct

effluent discharges, which isolate them from high metal input.

In contrast, the low level of contamination at Station 3 in

Banco Bay may have resulted from the dilution of discharged

effluents by waters from the Banco River.

Overall, the observed patterns of metal distribution high-

light the complexity of contamination sources in the urban

area of the �Ebri�e Lagoon. In Banco Bay, the high levels of pol-lution could be due to the many activities bordering the bay.

These sources include blacksmith activities, vehicle exhausts,

boat and car repair, metal recycling, and dwellings built from

a variety of materials. Secondary, potential anthropogenic

sources could be runoff waters, and diffuse residential water

discharges from neighborhoods close to the bay, including

Banco, Attekoube, Williamsville, Yopougon, and Abobo. It is

likely that anthropogenic sources are mainly of commercial,

residential, and agricultural origin in the Cocody Bay. This

bay receives both solid and liquid wastes from many over-

populated neighborhoods such as Plateau, Adjame, Abobo,

Angre and Cocody. During the rainy seasons, flooding occurs

frequently, which result in the discharge a variety of wastes to

the area near Station 6. Cocody Bay also receives metal inputs

from the Comoe River, which drains large rubber, palm oil,

cocoa, coffee and pineapple plantations. The major sources of

metal pollution in Bietry Bay are the neighborhoods of Kou-

massi, Bietri, Marcory, Treichville, and Vridi, where most of

the industrial activities of Cote d’Ivoire such as oil refining

(SIR), manufacturing (Solibra, Nestle CI, Saprolait), animal

slaughtering, car repair, leather tanning, and painting are

concentrated.

Influence of TOC on Distribution of Metals

Studies of the interactions between metals and organic carbon

are essential for understanding the transport, reactivity, and

bioaccumulation of metals in the environment. From the

regression analysis we found significant relationships between

the TOC contents and Cu (r2 D 0.44; p < 0.01; N D 42), Zn

(r2 D 0.47; p < 0.01; N D 42), Co (r2 D 0.19; p D 0.01; N D42), and Cd (r2 D 0.38; p < 0.01; N D 42) concentrations

(Figure 5). This suggests that TOC plays an important role in

the distribution of these metals in sediments.

Table 6. Sorted rotated factor loadings (Varimax normalized) of metalsand total organic carbon (TOC) in the two principal factors derived fromthe factorial analysis (PCA/FA)

Factor 1 Factor 2

Cu 0.85 -0.29Zn 0.77 0.11Pb 0.02 0.82Cd 0.90 0.04Ni 0.09 0.77Co 0.75 0.09Fe -0.09 0.76TOC 0.85 -0.01Eigenvalue 3.45 1.94% Total variance 43.07 24.30% Cumulative variance 43.07 67.37

*Variables with factor loadings greater than 0.7 are in bold.

Figure 3. Hierarchical dendrograms for studied metals and TOC in sedi-ments collected from four bays of the �Ebri�e Lagoon.

Figure 4. Hierarchical dendrograms for studied stations based on Cu, Zn,Cd, and Co concentrations in sediments collected from four bays of the�Ebri�e Lagoon.


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It has been reported that organic matter may facilitate metal

sorption by providing additional sorption sites after it is

adsorbed on sediment particles, but it may also reduce metal

sorption in sediments through the formations of stable dis-

solved organic matter (DOM)-metal complexes in solution

(Skyllberg et al., 2000). Thus, the first-order fate of metals

that have a high affinity for organic matter will be determined

on the solid-solution partitioning of that organic matter. In

contrast, the poor relationships between total Pb, Ni, Fe and

TOC indicates that the fate of these metals is largely controlled

by factors other than organic carbon cycling, and therefore are

likely to be recalcitrant and not particularly bioavailable.

Figure 5. Relationships obtained by linear regression analysis between TOC and studied metals.


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Application of Sediment Quality Guidelines (SQGs)

Table 7 shows the ERL-ERM and TEL-PEL SQGs along with

the percentage of the sediment samples in each guideline.

With respect to the ERL-ERM SQGs, 95%, 43%, 57%, 36%,

and 48% of the samples may be considered to be an occasional

threat to organisms (between ERL and ERM) for Cu, Zn, Pb,

Cd, and Ni respectively. Almost no sediment samples

exceeded the ERM criterion and could not be described as fre-

quently associated with toxic biological effects for Cu, Zn, Pb

and Cd. Notably, Ni concentrations exceeded ERM in 36% of

the samples. This result suggests that Ni is sometimes at haz-

ardous concentrations. However, high SEQ for Ni seems con-

tradictory since sediments showed low Igeo values (Table 2).

Perhaps the SEQ is unrealistically low for Ni, and most sedi-

ments would therefore have high SEQ regardless of contami-

nation. This effect is because the average Ni concentration in

the continental crust is similar to the ERL and higher than the

TEL. When compared with the TEL-PEL SQGs, the metal lev-

els in most of the sediment samples could be described as

being occasionally associated with toxic effects on aquatic

organisms. However, 24%, 12%, 12%, and 43% of the samples

were found to be associated with frequently adverse biological

effects for Cu, Zn, Pb, and Ni, respectively.

It can be concluded from the SQG data that sediments in

the bays of the �Ebri�e Lagoon may pose an occasional threat

to aquatic organisms due to their metal contents. This threat

level is an estimate of the minimum impact of metal con-

tamination, as it does not consider the possibility of a com-

bined effect of many metals. However, it should be noted

that SQGs may not fully address the local particularities of

each environment, and the total concentration of a contami-

nant alone provides insufficient information regarding the

possible biological effects of that contaminant. SQGs need

to be further evaluated to determine their applicability to

the �Ebri�e Lagoon.

Evolution of PLI over 30 Years

To determine the trend of each PLI over time, the PLIs were

calculated using total metal concentrations from the literature

(Kouadio and Trefry, 1987; Coulibaly et al, 2009, Yao et al.,

2009) and compared to those of this study. Metals that have

been regularly assessed in samples from stations with approxi-

mately the same location as those in the present study were

considered. Total metal concentrations were measured by

atomic absorption spectroscopy (AAS) in all studies. More-

over, the average crustal abundance of metals with respect to

UCC and LCC from Wedepohl (1995) were used for the calcu-

lation of the PLIs. Thus, even if the absolute enrichments cal-

culated in the different studies are in error as a result of not

using an appropriate background value, the time trend found

through a comparison of the studies should be reliable. The

results are shown in Figure 6. It can be clearly seen that the

PLI values of the sediments of Banco, Cocody, and Bietri Bays

increased significantly from 1983 to 2012, with the highest rate

of increase occurring between 2006 and 2012. PLI values were

greater than 2 in 2012, indicating that these three sites were

strongly polluted with respect to metals. This finding suggests

Table 7. Classification of the percentage of the assessed sediment samplesbased on the ERL-ERM and TEL-PEL sediment quality guidelines. Metalconcentrations are expressed in (mg/g)

Sediment quality guidelines Cu Zn Pb Cd Ni

ERL 34.0 150.0 46.7 1.20 20.9ERM 270.0 410.0 218.0 9.60 51.6TEL 18.7 124.0 30.2 0.68 15.9PEL 108.0 271.0 112.0 4.21 42.8Compared with ERL and ERM% of samples <ERL 5.0 55.0 43.0 64.00 17.0% of samples between ERL–ERM 95.0 43.0 57.0 36.00 48.0% of samples >ERM 0.0 2.0 0.0 0.00 36.0Compared with TEL and PEL% of samples <TEL 0.0 40.0 24.0 19.00 10.0% of samples between TEL–PEL 76.0 48.0 64.0 81.00 48.0% of samples >PEL 24.0 12.0 12.0 0.00 43.0

ERL, effects range low; ERM, effects range medium; TEL, threshold effectlevel; PEL, probable effects level.

Figure 6. Evolution of pollution-loading index (PLI) in Banco, Bietri, andCocody Bays over 1983–2012.


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a higher input of metals over the last 6 years when compared

to that from 20 years ago. This is likely to be a consequence of

the recent influx of people from the center, the north, and the

west of the country following the recent war, as well as an

increase in the use of pesticides in agricultural activities in the

vicinity of the estuarine area of the �Ebri�e Lagoon.

Conclusion

The distribution, sources, and possible adverse biological

effects of Cu, Zn, Pb, Cd, Ni, Co, and Fe in the sediments of

four bays of the �Ebri�e Lagoon were assessed using pollution

indices, multivariate analyses, and SQGs. Sediment surface

mineral phases and their TOC contents were also assessed.

Surface sediments were primarily dominated by quartz (34%–

46%), aluminum oxides (17%–27%) and iron oxides (10%–

16%), which may facilitate metal accumulation. High TOC

contents were found with significant spatial variations as a

result of the influence of anthropogenic activities. Sediments

were moderately to strongly contaminated with Cd and Cu,

moderately contaminated with Zn and Pb, and relatively

uncontaminated with Ni, Co, and Fe. Metals Cu, Zn, Cd, and

Co result mainly from anthropogenic sources while Pb, Ni and

Fe are of natural origin. TOC plays an important role in the

distribution of Cu, Zn, Co, and Cd in the sediments. The PLIs

were very high and increased significantly over the period of

1983–2012. The highest rate of increase in the PLI also

occurred between 2006 and 2012, indicating a relatively rapid

increase of both the metal inputs and the deterioration of sedi-

ment quality in the �Ebri�e Estuary. The �Ebri�e Lagoon sediments

are likely to be associated with occasional threats to aquatic

organisms due to Cu, Zn, Pb, Cd, and Ni contents, based on

the SQGs approach. However, chemical speciation studies

need to be investigated in order to understand the fate, bio-

availability, and toxicity of metals in estuarine sediments.

Acknowledgment

We are thankful to the Director CRO for his encouragement

and support. Unconditional help (to determine total metal con-

centrations in the sediments by AAS) from the Director of

INP-HB, Yamoussoukro, is gratefully acknowledged. We

thank Dr. Carl H. Lamborg for making helpful suggestions for

improving the manuscript. We also thank Mary Zawoysky and

Anjali Kumar for improving the edits. A special thank you

goes to the reviewers for their critical contribution.

Funding

This work is a part of the Minist�ere de l’Enseignement

Sup�erieur et de la Recherche Scientifique (Cote d’Ivoire) sup-ported Institutional Project (Plan quinquennal). This article

bears CRO contribution “BGF, chapter 600.”

References

Alagarsamy, R. 2006. Distribution and seasonal variation of trace metalsin surface sediments of the Mandovi Estuary, west coast of India. Estua-rine, Coastal and Shelf Sciences 67:333–339.

Anirudhan, T. S., Bringle, C. D., and Radhakrishnan, P. G. 2012. Heavymetal interactions with phosphatic clay: Kinetic and equilibrium stud-ies. Chemical Engineering Journal 200–202:149–157.

Atibu, E. K., Devarajan, N., Thevenon, F., Mwanamoki, P. M., Tshi-banda, J. B., Mpiana, P. T., et al. 2013. Concentration of metals in sur-face water and sediment of Luilu and Musonoie Rivers, Kolwezi-Katanga, Democratic Republic of Congo. Applied Geochemistry 39:26–32.

Banerjee, K., Senthilkumar, B., Purvaja, R., and Ramesh, R. 2012. Sedi-mentation and trace metal distribution in selected locations of Sundar-bans mangroves and Hooghly estuary, northeast coast of India.Environmental Geochemistry and Health 34:27–42.

Bastami, K. D., Bagheri, H., Haghparast, S., Soltani, F., Hamzehpoor, A.,and Bastami M. D. 2012. Geochemical andgeo-statistical assessment ofselected heavy metals in the surface sediments of the Gorgan Bay Iran.Marine Pollution Bulletin 64, 2877–2884.

Biati, A., and Karbassi, A. R. 2011. Flocculation of metals during mixingof Siyahrud River water with Caspian Sea water. Environmental Moni-toring and Assessment 184:6903–6911.

Bodin, N., N’Gom-Ka, R., Ka, S., Thiaw, O. T., Tito deMorais, L., Le Loc’h,F., et al. 2013. Assessment of trace metal contamination in mangrove eco-systems from Senegal,West Africa.Chemosphere 90(2):150–157.

Burton, G. A., and Johnston, E. L. 2010. Assessing contaminated sedi-ments in the context of multiple stressors. Environmental Toxicologyand Chemistry 29:2625–2643.

Buruaem L. M., Hortellani M. A., Sarkis J. E., Costa-Lotufo L. V., andAbessa D. M. S. 2012. Contamination by metals of port zones sedimentsfrom Large Marine Ecosystems of Brazil. Marine Pollution Bulletin64:479–488.

Chakraborty, P. 2012. Speciation of Co, Ni and Cu in the coastal and estu-arine sediments: Some fundamental characteristics. Journal of Geo-chemical Exploration 115:13–23.

Chakraborty, P., Babu, P. V. R., and Sarma, V. V. 2012a. A study of leadand cadmium speciation in some estuarine and coastal sediments.Chemical Geology 294–295:217–225.

Chakraborty P., Seranya J., Raghunadh Babu P. V., Karri S., Thyadi P.,Yao K. M., et al. 2012b. Intra-annual variation of total arsenic and itsspeciation in surface sediments of a tropical estuary. Chemical Geology322–323:172–180.

Chen, B., Liang, X., Xu, W., Huang, X., and Li, X. 2012. The changes intrace metal contamination over the last decade in surface sediments ofthe Pearl River Estuary, South China. Science of the Total Environment439:141–149.

Christophoridis, C., Dedepsidis, D., and Fytianos, K. 2009. Occurrenceand distribution of selected heavy metals in the surface sediments ofThermaikos Gulf, N. Greece. Assessment using pollution indicators.Journal of Hazardous Materials 168:1082–1091.

Coulibaly, A. S., Monde, S., Wognin, V., and Aka, K. 2009. Analyse deselements trace (ETM) dans les baies estuariennes d’Abidjan en Coted’Ivoire. Afrique Science 5(3):77–96.

Dahlin, C., Williamson, C., Collins, W. K., and Dahlin, D. 2002. Sequen-tial extraction versus comprehensive characterization of heavy metalspecies in Brownfield soils. Environmental Forensics 3:191–201.

Fernandes., L. L., and Nayak., G. N. 2012. Geochemical assessment in acreek environment in Mumbai, West Coast of India. EnvironmentalForensics 13:45–54.

Han, Y. M., Du, P. X., Cao, J. J., and Posmentier, E. S. 2006. Multivariateanalysis of heavy metal contamination in the urban dusts of Xi’an, Cen-tral China. Science of the Total Environment 355(1–3):176–186.

Hoch, M., and Schwesig, D. 2004. Parameters controlling the partition-ing of tributyltin (TBT) in aquatic systems. Applied Geochemistry19:323–334.

Hong, X. -Q., Li, R. -Z., Liu, W. -J., Zhang, X. -S., Ding, H. -S., andJiang, H. 2012. An investigation on reuse of Cr-contaminated sediment:


Dow

nloa

ded

by [

Kof

fi M

arce

llin

Yao

] at

15:

47 1

9 M

arch

201

5

Cr removal and interaction between Cr and organic matter. ChemicalEngineering Journal 189–190:222–228.

Ingersoll, C. G., Haverland, P. S., Brunson, E. L., Canfield, T. J, Dwyer,F. J., Henke, C. et al. 1996. Calculation and evaluation of sedimenteffect concentrations for the amphipod, Hyalella azteca and the midge,Chironomus riparius. Journal of Great Lakes Research 22:602–623.

Jayaprakash, M., Urban, B., Velmurugan, P. M., and Srinivasalu, S. 2010.Accumulation of trace metals due to rapid urbanization in microtidalzone of Pallikaranai Marsh, south of Chennai, India. EnvironmentalMonitoring and Assessment 170:609–629.

Jiang, M., Zeng, G., Zhang, C., Ma, X., Chen, M., et al. 2013. Assessmentof heavy metal contamination in the surrounding soils and surface sedi-ments in Xiawangang River, Qingshuitang District. PLoS ONE 8(8):e71176.

Kadio, E., Coulibaly, Y., Allialy, M. E., Kouamelan, A. N., Pothin, K. B.K. 2010. On the occurrence of gold mineralization in southeastern IvoryCoast. Journal of African Earth Sciences 57:423–430.

Karbassi, A. R., and Nadjafpour, S. 1996. Flocculation of dissolved Pb,Cu, Zn and Mn during estuarine mixing of river water with the CaspianSea. Environmental Pollution 93:257–260.

Kissao, G., Seunghee, H., Rezaie-Boroon, M. H., Porrachia, M., andDeheyn, D. D. 2011. Increased bioavailability of mercury in the lagoonsof Lome, Togo: The possible role of dredging. AMBIO 40:26–42.

Korfali, S. I., and Davies, B. E. 2004. Speciation of metals in sedimentand water in a river underlain by limestone: Role of carbonate speciesfor purification capacity of rivers. Advances in Environmental Research8:599–612.

Kouadio, L., and Trefry, J. H. 1987. Sediment trace metals contaminationin Ivory Coast, West Africa.Water Air & Soil Pollution 32:145–54.

Lee, M.-K., Natter, M., Keevan, J., Guerra, K., Saunders J., Uddin A.,et al. 2013. Assessing effects of climate change on biogeochemicalcycling of trace metals in alluvial and coastal watersheds. British Jour-nal of Environment & Climate Change 3:44–66.

Long, E. R, Field, L. J., and MacDonald, D. D. 1998. Predicting toxicityin marine sediments with numerical sediment quality guidelines. Envi-ronmental Toxicology and Chemistry 17:714–727.

Loska, K., Cebula, J., Pelczar, J., Wiechula, D., and Kwapuli�nski, J. 1997.Use of enrichment, and contamination factors together with geoaccumu-lation indexes to evaluate the content of Cd, Cu, and Ni in the RybnikWater Reservoir in Poland.Water, Air, & Soil Pollution 93:347–365.

Marchand, C., Lallier-Verges, E., Balter, F., Alberic, P., Cossa, D., andBaillif, P. 2006. Heavy metals distribution in mangrove sediments alongthe mobile coastline of French Guiana.Marine Chemistry 98(1-2):1–17.

McCready, S., Birch, G. F., and Long, E. R. 2006. Metallic and organiccontaminants in sediments of Sydney Harbour, Australia and vicinity—A chemical dataset for evaluating sediment quality guidelines. Environ-mental International 32:455–465.

Montero, N., Belzunce-Segarra, M. J., Menchaco, I., Garmendia, J. M.,Franco, J., Nieto, O., et al. 2013. Integrative sediment assessment atAlantic Spanish harbours by means of chemical and ecotoxicologicaltools. Environmental Monitoring and Assessment 185:130–1318.

Nelson, D. W., and Sommers, L. E. 1996. Total carbon, organic carbon,and organic matter, InMethods of soil analysis—Part 2: Agronomy, 2nded. Madison, WI: American Society of Agronomy, Inc., 961–1010.

N’guessan, Y. M., Probst, J. L., Bur, T., and Probst, A. 2009. Trace ele-ments in stream bed sediments from agricultural catchments (GascogneRegion, S-W France): Where do they come from? Science of the TotalEnvironment 407:2939–2952.

Nilin, J., Moreira, L. B., Aguiar, J. E., Marins, R., Moledo de SouzaAbessa, D., Monteiro da Cruz Lotufo, T., and Costa-Lotufo, L. V. 2013.Sediment quality assessment in a tropical estuary: The case of Cear�aRiver, Northeastern Brazil.Marine Environmental Research 91:89–96.

Pekey, H. 2006. The distribution and sources of heavy metals in Izmit Baysurface sediments affected by a polluted stream. Marine Pollution Bul-letin 52:1197–1208.

Qiao, Y., Yang, Y., Gu, J., and Zhao, J. 2013. Distribution and geochemi-cal speciation of heavy metals in sediments from coastal area sufferedrapid urbanization, a case study of Shantou Bay, China. Marine Pollu-tion Bulletin 68:140–146.

Schumacher, B. A. 2002. Methods for the determination of total organiccarbon (TOC) in soils and sediments. Las Vegas, NV: Ecological RiskAssessment Support Center Office of Research and Development. US.Environmental Protection Agency.

Skyllberg, U., Xia, K., Bloom, P. R., Edward, A. N., Bleam, W. F. 2000.Binding of Mercury(II) to reduced sulfur in soil organic matter alongupland–peat soil transects. Journal of Environmental Quality 29(3):855–865.

Soon, Y. K., and Abboud, S. 1991. A comparison of some methods forsoil organic carbon determination. Communications in Soil Science andPlant Analysis 22:943–954.

Tam, N. Y. F., and Wong, Y. S. 2000. Spatial variation of heavy metals insurface sediments of Hong Kong mangrove swamps. EnvironmentalPollution 110:195–205.

Thompson, B., Anderson, B., Hunt, J., Taberski, K., and Phillips, B.1999. Relationships between sediment contamination and toxicityin San Francisco Bay. Marine Environmental Research 48:285–309.

Tomlinson, D. L., Wilson J. G., Harris, C. R., and Jeffry D. W. 1980.Problem in assessment of heavy metals levels in estuaries and theformation of a pollution index. Helgolander Meeresunters 33:566–575.

Walkley, A., and Black, I. A. 1934. An examination of the Degtjareffmethod for determining organic carbon in soils: Effect of variations indigestion conditions and inorganic soil constituents. Soil Science63:251–263.

Wan, Y. L., Ahmad, Z. A., and Tengku, H. T. I. 2013. Spatial geochemi-cal distribution and sources of heavy metals in the sediment of LangatRiver, western peninsular Malaysia. Environmental Forensics 14:133–145.

Wedepohl, K. H. 1995. The composition of the continental crust. Geochi-mica et Cosmochimica Acta 59:1217–1232.

Yao, K. M., M�etongo, B. S., Trokourey, A., and Bokra, Y. 2009a. Assess-ment of sediments contamination by heavy metals in a tropical lagoonurban area (�Ebri�e Lagoon, Cote d’Ivoire). European Journal of Scien-tific Research 34(2):280–289.

Yap, C. K., and Pang, B. H. 2011. Assessment of Cu, Pb, and Zn contami-nation in sediment of north western Peninsular Malaysia by using sedi-ment quality values and different geochemical indices. EnvironmentalMonitoring and Assessment 183:23–39.

Yu, K. -T., Lam, M. H., Yen, Y. -F., and Leung, A. P. K. 2000.Behavior of trace metals in the sediment pore waters of intertidalmudflats of a tropical wetland. Environmental Toxicology andChemistry 19:535–542.

Zakir, H. M., and Shikazono, N. 2008. Metal fractionation in sediments:A comparative assessment of four sequential extraction schemes. Jour-nal of Environmental Science for Sustainable Society 2:1–12.


Dow

nloa

ded

by [

Kof

fi M

arce

llin

Yao

] at

15:

47 1

9 M

arch

201

5

Distribution, Sources, and Possible Adverse Biological Effects of Trace Metals in Surface Sediments of a Tropical Estuary

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