Indian Journal of Marine Sciences
Vol. 38(2), June 2009, pp. 235-248
Assessment of metal concentration in the sediment cores of Manakudy estuary,
south west coast of India
Sugirtha P Kumar1* & J K Patterson Edward2
1
Department of Chemistry, Women’s Christian College, Nagercoil 629 001, India
Suganthi Devadason Marine Research Institute, 44-Beach Road, Tuticorin 628 001, India.
*[E.mail: s_prasannak@yahoo.com]
2
Received 21 November 2007; revised 21 May 2008
Base line data on the metal concentration was obtained from three core sediments (S1, S2 and S3) of Manakudy estuary
on the south west coast of India. The acid leachable trace metals (Cr, Cu, Ni, Co, Pb, Zn and Cd) showed peak values at
sulphidic phase . There is moderate level of pollution related to anthropogenic activities. The trace metals were associated
with Fe and Mn indicating their adsorption onto Fe-Mn oxyhydroxides. The correlation of trace metals with sulphur
indicates that they were precipitated as metal sulphides. Correlation matrix showed elegant association between trace metals
and Fe, Mn, S and mud. The Igeo values revealed that all the core samples fell within uncontaminated to moderately
contaminated category. The concentration factor was low (Cfi <1) indicating low contamination in the core samples. The
anthropogenic factor (AF) values indicate moderate anthropogenic inputs.
[Keywords: Trace metals, Core sediments, Contamination factor, anthropogenic factor, Igeo, Manakudy estuary, Southwest
coast of India].
Introduction
Estuaries are interfacial mixing zones, where river
input to the ocean is modified1,2,3,4. Concentration of
various elements follow closely the texture of
sediments, soil particles of all sizes from clay to sand
play a major role in the deposition of sediments in
estuaries, particularly in semi closed or bar built
estuaries5. Sediment concentrations pose one of the
worst environmental problems to estuarine
ecosystems. Sediments may not only act as sinks but
also as sources of contaminants in aquatic systems6,7.
Contaminants, including trace metals can be
introduced into the aquatic environment and
accumulate in sediments by several pathways
including disposal of liquid effluents, runoff and
leachates carrying chemicals originating from a
variety of urban, industrial and agricultural activities
as well as atmospheric deposition. Heavy metals are
critical in pollution of ecosystem because of their easy
uptake into the food chain and also because of
bioaccumulation processes8. Estuarine sediments may
serve as effective traps of river borne metals9
The concentration of metals found in recent
sediments are significantly higher when compared to
sediments that are deposited during pre-industrial
time10. Most trace metal contaminants are, however,
adsorbed to or occluded within the hydrogenous and
biogenic phases, which coat natural particles11,12,13.
Metals accumulated in this way may be subsequently
released to the overlying water column as a result of
either physical disturbance or diagenesis and the
sediments may persist as a source of pollutants long
after the cessation of direct discharges. Diagenetic
reactions are important near the sediment – water
interface responding to redox changes and affecting
metal concentrations in vertical sediment profiles14.
The assessment of trace metal pollution in sediments,
analysis of the non-residual fractions (acid leachable)
is of prime importance. The sediment act as a useful
indicator of long and medium term metal flux in
industrialized estuaries and rivers, and they help to
improve management strategies as well as to assess
the success of recent pollution controls15,16,17. Acid
leachable trace metals are not part of the silicate
matrix and have been incorporated into the sediment
from aqueous solution by processes such as
adsorption and organic complexation. The study of
core samples provides historical record of various
influences on the aquatic system by indicating both
the natural background levels and the man-induced
accumulation of trace metals over an extended
period of time.
236
INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
The environmental chemistry of river basin and
small estuaries in India has received less attention,
despite some environmental studies in major
rivers18,19. The present study is an attempt to delineate
core sediments of Manakudy estuary and to assess
level of trace metal concentration due to industrial,
agricultural and domestic effluents in three stations
(S1, S2 and S3) of the Manakudy estuary situated on
the southwest coast of India.
Materials and Methods
Study Area
The Manakudy estuary is the confluence of river
Pazhayar and has an area of about 150 ha (Fig. 1). It
is a sand built estuary connected to the sea during the
rainy season. During the period of total occlusion of
the river mouth the estuarine water swells due to
heavy inflow of water from the head of the estuary
and also by the land drainage. During heavy inflow
into the estuary the sand bar opens up under the force
of gravity. Manakudy estuary abounds with fishery
resources and has neighbouring fishing helmets.
There are no major industries near the estuary,
however three small-scale industries viz coconut husk
retting, lime shell dredging and salt works are well
established on the banks of the estuary. Further there
is heavy surface runoff from the paddy fields and
coconut plantations into the estuary.
Fig. 1—Location of the stations in the Manakudy Estuary
Sample collections
Sediment core samples were collected at three
stations (S1, S2 and S3) along the course of the
estuary. The station I (Core1) was selected at the
mouth of the estuary, station II (Core 2) was selected
near the mangroves and the station III (Core 3) was
selected near the head of the estuary. A PVC coring
tube (7.5 cm diameter and 2.5 m length), precleaned
with acid was used for the collection of core samples.
The PVC tube was driven into the sediment until
about 50 cm of the pipe remained above the ground
and the rest was filled with ambient water on the top.
The PVC tube was sealed using a plumber’s dummy
and it was sealed and pulled out from the sediment.
The water on the top was then decanted and the
pipe was just cut off above the top of the cored
sediment and the plastic bags were taped over both
ends of the PVC tube20. From the core samples S1
(Core1) S2 (Core 2) and S3 (Core 3) 26, 24 and 25
sub samples were made respectively by cutting the
coring tube at 2.5 cm interval. The geochemical data
presented in this study have not been corrected for
compaction, as it is likely to be uniform down the
length of the core21.
Textural studies for sand, silt and clay were
performed22 and the Calcium carbonate23 and organic
carbon24 content were determined. Na+ and K+
concentrations were determined with a flame
photometer using suitable chemical standards. Ca2+
and Mg2+ were determined using standard methods25.
For acid leachable metals (Fe, Mn, Cr, Cu, Ni, Co, Pb,
Zn and Cd) 5 g of dry sediment sample was taken in a
100 ml plastic bottle in which 75 ml of 0.5 N HCl was
added and after mechanically shaking for 16 hr it was
filtered with Whatman Grade A filter paper26,27. The
filtered samples were measured in flame ASS (Varian
Spectr AA 200 AAS) equipped with a deuterium
background corrector for analysis of acid leachable
trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb and Zn). A
graphite furnace was used for the determination of Cd
due to its low concentration.. Standard reference
material BCSS-1 was used to ensure the quality
control and accuracy of the analysis. Analysis of
triplicates for every fifth sample suggest that the
precision of analysis lie in the following coefficient of
variation Fe 2.6%, Mn 1.8%, Cr 3.7%, Cu 2.4%, Ni
2.6%, Co 2.2%, Pb 2.5%, Zn 3.7% and Cd 3.9%.
Statistical analyses based on acid leachable elements
were effectively utilized for the interpretation of
geochemical processes20,28,29,30,31,32
KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY
Index of Geoaccumulation
The Index of Geoaccumulation
computed using the equation32,33.
(Igeo)
was
Igeo = log2 Cn / 1.5 Bn
Where Cn is the measured concentration of the
element in the politic sediment fraction and Bn is the
geochemical background value (average shale) in the
earth’s crust34. The constant 1.5 allows for natural
fluctuations in the content of a given substance in the
environment and very small anthropogenic
influences32.
Six classes of the geochemical index35 has been
distinguished
Class
0
Value
Igeo<0
1
0< Igeo<1
2
3
4
5
6
1< Igeo<2
2< Igeo<3
3< Igeo<4
4< Igeo<5
5< Igeo
Soil quality
Practically uncontaminated
Uncontaminated
to
moderately
contaminated
Moderately contaminated
Moderately to heavily contaminated
Heavily contaminated
Heavily to extremely contaminated
Extremely contaminated
Enrichment Factor
The enrichment factor (EF) was based on the
standardization of a tested element against a
reference. A reference element is the one
characterized by low occurrence variability. The most
common reference elements are Sc, Mn, Ti, Al and
Fe36,37,38,39,40. In the present study Fe was used as the
reference metal using the formula41.
237
Anthropogenic factor
The enrichment is normalized relative to the depth
in the sediment core using the following formula
AF = Cs/Cd where Cs and Cd refer to the
concentration of the elements in the surface sediments
and at depth in sediment column42.
If AF is > 1 for a particular metal, it means,
contamination exists; otherwise if AF ≤ 1, there is no
metal enrichment of anthropogenic origin43.
Contamination factor
The assessment of soil contamination was also
carried out using the contamination factor 44.
C if =
C oi − 1
C ni
Where C 0i − 1 is the mean content of metals from at
least five sampling sites and C ni
is the
concentration of elements in Earth’s crust as a
reference value.
Pollution Load Index (PLI)
The pollution level in trace metal was calculated by
the method based on pollution load index 45.
CF = C metal / C background
PLI = n (CFI × CF2 × CF3 × ......CFn)
CF = Contamination factor
n = number of metals
Cn (sample)/Cref (Sample)
EF=
Bn (background)/Bref (background)
Where Cn (sample) is the content of the examined
element in the examined environment. Cref (sample)
is the content of the reference element in the
examined environment. Bn (background) is the
content of the examined elements in the reference
environment and Bref (back ground) is the content of
the reference element in the reference environment.
Five contamination categories are recognized on
the basis of the enrichment factor40.
EF<2
EF=2-5
EF=5-20
EF=20-40
EF>40
Deficiency to minimal enrichment
Moderate enrichment
Significant enrichment
Very high enrichment
Extremely high enrichment
C metal = metal contamination in polluted sediment.
C back ground value = back ground value of that
metal.
Four categories of contamination factor have been
distinguished44.
Cfi <1
1≤Cfi <3
3≤Cfi < 6
6≤Cfi
Low contamination factor indicating low
contamination
Moderate contamination factor
Considerable contamination factor
Very high contamination factor
Results and Discussion
Sediment Texture
Textural studies in the three core samples (S1, S2
and S3) showed that the percentage of sand and mud
INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
238
(silt + clay) differed markedly in relation to depth.
Studies reveal two distinct characters, the upstream
side (S2 and S3) was characterized by (71.98% and
79.81%) sand and the downstream estuarine side (S1)
was dominated by mud (Silt + Clay). The higher mud
content in the downstream estuarine station (S1) is
due to the low fluvial discharge and a better mixing of
saline and fresh water that facilitated flocculation and
faster settling of suspended particles46. The higher
sand content (> 90%) at 35-50 cm depth in S2 and
42.5-60 cm depth in S3 indicating a relatively
higher energy regime that prevents sedimentation of
fine-grained particles20. In addition, S3 shows a good
variation in sand content from 27.5-60 cm indicating
the low flow condition, where finer particles have
settled down in the upstream side and it is similar to
other Southeast Coast rivers20,47. Similar observations
were made in the river Uppanar on the southeast coast
of India20 (Table 1).
Calcium carbonate, organic carbon and Sulphur
Vertical distribution of CaCO3 in all the three core
samples indicates average values of 16.59%, 4.45%
Table 1—Sand and Mud contents in the core samples from
Manakudy estuary
Depth
Sand%
Mud%(Silt+Clay)
(cm)
S1
S2
S3
S1
S2
S3
2.5
5
7.5
10
12.5
15
17.5
20
22.5
25
27.5
30
32.5
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
64.94
38.92
29.31
28.17
34.53
49.02
20.38
18.05
26.57
18.54
20.85
34.6
46.22
35.24
53.08
43.88
34.6
47.58
50.66
61.94
56.71
58.93
57.58
61.06
48.69
48.67
33.79
37.71
49.17
67.9
70.25
75.14
76.99
83.14
74.56
67.61
52.73
52.55
77.89
91.35
91.72
89.03
90.85
94.88
95.86
96.44
74.55
40.05
86.52
57.01
66.23
78.18
84.5
52.27
72.69
63.57
62.82
68.76
74.08
72.28
86.57
87.09
86.02
88.76
87.29
85.04
90.13
89.3
89.95
89.58
89.66
92.24
93.32
88.84
56.08
35.06
61.08
70.69
71.83
65.47
50.97
79.61
81.96
73.43
81.46
79.15
65.39
53.78
64.76
46.92
56.12
65.4
52.42
49.34
38.07
43.29
41.08
42.42
38.95
51.3
51.33
66.21
62.29
50.83
32.1
29.76
24.86
23.01
16.85
25.44
32.73
47.27
47.45
22.11
8.65
8.28
10.97
9.15
5.12
4.14
3.56
25.45
59.95
13.48
42.99
33.77
21.82
15.5
47.732
27.31
36.43
37.18
31.24
25.92
27.72
13.429
12.91
13.98
11.24
12.71
14.96
9.87
10.7
10.05
10.42
10.34
7.76
6.68
11.16
43.92
and 13.84% in S1, S2 and S3 respectively (Fig. 1).
Peak values of CaCO3 at surface level in S1 and S3
are due to the shell fragments present in the
sediments. Further the CaCO3 profiles indicate
enrichment at deeper layers (45-65 cm in S1 and
30-57.5 cm in S3) and it may by enrichment of the
reduced layers due to reprecipitation and increase in
alkalinity generated by sulphate reduction48. Overall,
CaCO3 distribution indicates low values at the
midstream side (S2). The present trend is in
agreement with the similar observations made in the
Uppanar river on the Southeast coast of India20.
Organic carbon (OC) content indicates variation in
all the stations (Fig. 2). Enrichment of OC at different
core intervals indicates incorporation of organic
materials from the river water matter. The enrichment
of OC in subsurface and deeper layers suggests
deposition under calm conditions prevailed during the
slow accumulation of finer sediments49. Further
organic carbon increases with increasing finer fraction
and decreases with the increasing coarser fraction in
the sediments. One of the features of organic carbon
in the sediments is that its concentration increases as
the particle size of the sediments decrease50. The finer
fractions (Silt + Clay) showed an efficacious relationship with organic carbon while the coarser fractions
have no patent kinship. The relatively lower percentage
of organic carbon in the top layers (0-2.5 cm) than the
subsurface in S1 could be attributed to the constant
flushing activity by tides along with the impact of
waves which removes the finer fractions of the
sediments from the fringing area. The tidal influence
and wave action are maximum at S1 since it is near to
the bar mouth area. Also the organic residues from the
decomposed matter appear to be subsided more in the
surface by percolation process50.
Sulphur
The down core profiles of total sulphur (S) in S1,
S2 and S3 indicate a gradual increase of S from fresh
water zone to the estuarine region (Table 2. Fig. 2).
The concentration of S in surface layers in all core
samples indicates that it is transported from bottom
sediment layers to the sediment-water interface51. The
oxidation of Fe-sulphides is responsible for the
decrease in S content at the middle zone of the core
samples S1 and S3.
There is enrichment of sulphur below the suboxic /
anoxic interface indicating that sufficient oxidants
must be present to generate sulphides at these depths
KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY
239
Fig. 2—Vertical profiles of CaCO3, Organic Carbon and S in the core sediments
Table 2—Average values for all geochemical parameters
analysed in core samples (S1, S2 and S3) collected from
Manakudy estuary
Elements
S1
S2
S3
CaCO3 (%)
OC (%)
S (%)
Fe (µgg-1)
Mn (µgg-1)
Cr (µgg-1)
Cu (µgg-1)
Pb (µgg-1)
Zn (µgg-1)
Co (µgg-1)
Ni (µgg-1)
Cd (µgg-1)
Na (µgg-1)
K (µgg-1)
Ca (µgg-1)
Mg (µgg-1)
16.596
1.294
0.863
4887.462
358.216
482.138
43.677
176.877
72.623
4.004
28.912
2.819
10476.923
8106.038
3882.154
5284.064
4.458
0.875
0.760
4737.792
236.238
377.454
45.867
161.254
71.946
4.400
24.275
2.696
9791.667
9633.250
2448.458
5126.326
13.846
0.839
0.570
4561.462
166.988
256.908
37.352
152.248
54.584
6.052
20.148
3.168
10768.000
9974.000
1673.560
5248.435
and they are metal oxides, which interact with sulphur
species to form sulphides52. The complete oxidation
of sulphides with Fe3+has been documented at low pH
in non-marine environment53,20. However, these
results reveal that the flux of liable organic matter to
the sediments is very low, resulting in low values
after sulphate reduction. Overall sulphur results
indicate complete oxidation of H2S all along the
riverine sediments resulting in low values in the study
area20,54. The significant relationship of S with trace
metals shows that these trace metals are precipitated
as metal sulphides and are also responsible for the
fixation of trace metals in core sediments55.
Down core profiles of acid leachable elements Fe
and Mn
The vertical profiles of S1 and S3 show enrichment
in the surface layers due to early diagenetic process.
A decrease in Fe and Mn at the subsurface is
suggestive of the oxic / suboxic interface14. The
Fe–Mn oxyhydroxides dissolved in partly reduced
240
INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
sediment migrate upward in the sediment column and
get precipitated. But in S2, there was increase in
concentration of Fe and Mn at deeper layers which
indicates a reduced layer well above the other core
samples (S1 and S3) Fig. 3a, b & c.
Enrichment of Fe and Mn in HCl extractable
fraction near the interface in all the core samples
indicates that recycling is more intensive under low
oxygen conditions. Further, diagenetic enrichment of
Fe starts at greater depth compared to Mn indicating
higher stability of Fe-Mn oxyhydroxides under
reducing conditions and faster oxidation kinetics of
Fe2+ compared to Mn2+ and is precipitated as
metalliferrous sulphides formed under anoxic
conditions56. The internal recycling of Mn in
sediments either leads to the formation of a Mn peak
near the sediment redox boundary or to surficial
Mn-rich oxic sediments. In addition Mn is enriched in
the surface layers of all the core samples indicating
that Mn2+ has diffused into the suboxic zone and has
precipitated as Mn oxides and subsequently was
reduced again upon downward transport20. The
formation of Mn peak occurs when pore water Mn
concentrations are low in the suboxic zone and the
redox boundary is relatively deep as in S1 and S3 due
to low organic carbon (OC) flux in the sediments57.
Overall Fe and Mn enrichment in S1 than other core
samples indicates recycling of Fe and the
resuspension of bottom sediments is due to tidal
mixing from the coastal zone20,58. In addition,
estuarine mouth acts as an ultimate sink for most
liable Mn entering the estuarine region (S1), where
the depth is also very low20,59.
Cr, Cu, Ni, Co, Pb, Zn and Cd
The trace metal concentrations (Cr, Cu, Ni, Co, Pb,
Zn and Cd) have a similarity among them at different
depths and indicate that the main source of input to
the Manakudy estuary is from the upstream side.
Metal peaks along reduced layers are clearly observed
in S1 and S3 (Fig. 3). The metal peaks also
indicate scavenging of trace metals by Fe and Mn
Fig. 3(a)—Vertical profiles of metals in the core sediments S1, S2 and S3
KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY
Fig. 3(b)—Vertical profiles of metals in the core sediments S1, S2 and S3
241
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INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
Fig. 3(c)—Vertical profiles of metals in the core sediments S1, S2 and S3
KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY
oxyhydroxides and are deposited as metal sulphides
with a common source of origin for S1 and S360.
Cr concentration in the top layers in S2 and S3
indicate that it is present as Cr (VI), which is
relatively mobile and after release to the pore waters,
they migrate downward into the reducing zone and
precipitates again as Cr(OH)261. The hydrolysed form
of Cr (VI) are readily adsorbed by hydrous Fe and Mn
oxides62. Down core profiles of Cu, Ni and Co
indicate moderate removal in the suboxic layers till
the zone of oxygen penetration. Distribution pattern
of Ni and Co are similar to those of Fe and Mn
indicating that they are cycled along with Fe-Mn
oxides in the redox boundaries and are precipitated as
iron sulphides63. In addition the results suggest that
the increase of Ni and Co in S1 and S3 is specially
linked to the anoxic conditions and the addition
of these elements is due to the scavenging of
Fe-Mn oxides20.
Profiles of Pb in the surface layers show higher
concentration in S3 than in S2 and S1 and are
attributed to the local redox conditions, which
allowed Pb to co-precipitate with Mn during Mn
oxide formation in the superficial segment. Additional
Pb has reprecipitated along the redox boundaries
and the downward flux is also bound to biogenic
particles64.
The average values of Zn are high in S1 and S2
compared to S3. Zn can enter the aquatic environment
from a number of sources including sewage effluent
and runoff65. Input of organic wastes into the estuary,
which comes from sewage, contributes to the Zn
increase in sediments66.
Cd indicates that dissolution is taking place in the
upper most layers of S2 with very low values. The
dissolution of Cd is oxygen dependent in the aerobic
degradation of the fresh organic matter to which Cd is
initially bound, followed by the migration of the water
column and downward into the sediment with high
peaks in deeper layers.
The results indicate that acid leachable trace metals
(Cr, Cu, Ni, Co, Pb, Zn and Cd) demonstrate
moderate level of pollution related to anthropogenic
activities20. The coincident peaks more or less at the
same depth displayed by trace metals suggest the
contribution of post-deposited effects, such as
reduction of sulphides and formation of metallic
ferrous sulphides, under anoxic conditions or
reprecipitation of trace metals on Fe/Mn oxides and
oxyhydroxides coatings67,68. The low OC content
243
causes the redox cycling of the metals to occur
relatively deep in the core sediments and the efficient
trapping of the ions within the sediment results in a
build-up of the oxide concentrations at the
suboxic/anoxic boundary69 (Fig. 3 & Table 2).
Elemental Concentration in the Core samples
The enrichment of metals was assessed in relation
to sequence (ES) and anthropogenic factor (AF)
(Table 3).
The elemental sequence42 in the core samples are
placed in the following order
S1=Na > K > Fe > Mg > Ca > Cr > Mn > Pb > Zn
> Cu > Ni > Co > Cd.
S2= Na > K > Fe > Ca > Mg > Cr > Mn > Pb > Zn
> Cu > Ni > Co> Cd.
S3= Na > K > Fe > Ca > Mg >Cr > Mn > Pb > Zn
> Cu > Ni > Co > Cd.
The anthropogenic factor (AF) was assessed43 and
the metals are enriched as follows
S1= Co> Ca > Cd > Ni > Mg> Na > Cu > K > Zn
>Fe > Cr > Mn > Pb
S2= Mg > Ca > Mn > Ni > Co > Zn > Cu >Na > Cr
> K > Fe > Pb > Cd.
S3= Mg >Ca > Zn > Na > Cd > Co > K > Cu > Pb
> Fe > Ni > Mn > Cr.
The calculated AF values indicate that 70% of the
metals in the core samples are moderately enriched,
suggesting anthropogenic input of industries and
sewage load along the river bank70,71. The effluents
from the coir retting pits and domestic sewage from
the fishermen settlements are the chief sources of
Table 3—Average values of anthropogenic factor (AF) in core
samples (S1, S2 and S3) from Manakudy Estuary
Elements
S1
S2
S3
Fe
Mn
Cr
Cu
Pb
Zn
Co
Ni
Cd
Na
K
Ca
Mg
0.979
0.761
0.965
1.452
0.723
1.006
2.858
1.543
2.358
1.491
1.211
2.518
1.534
1.054
1.793
1.340
1.425
0.784
1.542
1.566
1.601
0.486
1.403
1.186
2.189
3.466
0.980
0.661
0.521
1.316
1.263
1.933
1.423
0.732
1.521
1.772
1.361
1.951
2.837
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INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
Fig. 4(a-c)—Enrichment factor in station 1; Enrichment factor in station 2; Enrichment factor in station 3
KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY
245
Fig. 5(a-c)—Index of Geoaccumulation in station 1; Index of Geoaccumulation in station 2; Index of Geoaccumulation in station 3
246
INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009
pollutants to the estuary. Though there are no
industries around the estuary the river Pazhayar drains
pollutants from industries situated in nearby towns
which include dyeing units. The fertilizers in the
agricultural waste water drained from the paddy fields
are the main source of heavy metals.
The enrichment factor (EF) is based on the
standardization of the tested element against iron. It
was found that only Na and K have values between
2 and 5 (EF=2 - 5) showing moderate enrichment. All
other elements have EF <2 showing no enrichment
(Fig. 4(a-c)).
Index of Geoaccumulation (Igeo)
Possible sediment enrichment of metals in
Manakudy was evaluated in terms of the Igeo
values72. The obtained Igeo values revealed that all
the core samples fell within uncontamination to
moderately contaminated category (Fig. 5(a-c)).
Similar observations were made in the soils of Suszee
commune, Poland32 in which there was enrichment in
Cd, Pb, As and Hg and there was elevated Igeo values
for Fe and Mn in the surface of Mandovi estuary, west
coast of India, during the premonsoon period66.
The contamination factor44 was calculated for the
core samples S1, S2 and S3. The contamination factor
was low (Cfi <1) indicating low contamination in the
core samples of Manakudy estuary.
Inter-element relationship
The results of correlation matrix of each core
sample indicate that a significant fraction of the trace
metal are found co-precipitated with or adsorbed on to
Fe and Mn geochemical phases controlling the trace
metals in sediments. These characters are due to their
large surface area, extensive cation exchange capacity
and widespread availability42. The strong correlation
of trace metals with mud (Silt + Clay) indicates that
they are concentrated to the fine-grained particles and
are hosted by clay phases. There was positive
correlation between metals and organic carbon.
The correlation matrix showed that Fe has
significant positive correlation with Cr, Cu and Mg
(P <0.05); Mn has significant positive correlation
with Ni, Cr, Zn, Na, K and Mg (P <0.01); Cu has
significant positive correlation with Zn, Ca, Fe and Cr
(P <0.05) and Zn has significant positive correlation
with Fe, Mn, Cr, Cu, Ni, Na, K and Mg (P <0.01).
The acid leachable trace metals (Cr, Cu, Ni, Co, Pb,
Zn and Cd) demonstrate moderate level of pollution
related to anthropogenic activities (Table 3). The Igeo
reveals that the sediments are uncontaminated. The
contamination factor is also low in the sediments.
The level of metal pollution in Manakudy estuary is
low and it is due to the absence of major factories in
and around the estuary. The only pollution load is
from the coir retting pits and sewage from the
fisherman settlements. Further there is surface runoff
that bring in inorganic fertilizers into the estuary.
Acknowledgement
Authors are also thankful to the authorities of
SDMRI for facilities and first author (SPK) is
thankful to UGC for financial support through FIP
programme.
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