Assessment of metal concentration in the sediment cores of

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 Edward

2

1Department of Chemistry, Women’s Christian College, Nagercoil 629 001, India 2Suganthi Devadason Marine Research Institute, 44-Beach Road, Tuticorin 628 001, India.

*[E.mail: [email protected]]

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.

INDIAN J. MAR. SCI., VOL. 38, NO. 2, JUNE 2009

236

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.

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

Fig. 1—Location of the stations in the Manakudy Estuary

KUMAR & EDWARD: METAL CONCENTRATION IN THE SEDIMENT CORES OF MANAKUDY

237

Index of Geoaccumulation The Index of Geoaccumulation (Igeo) was

computed using the equation32,33

.

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 Value Soil quality

0 Igeo<0 Practically uncontaminated

1 0< Igeo<1 Uncontaminated to moderately

contaminated

2 1< Igeo<2 Moderately contaminated

3 2< Igeo<3 Moderately to heavily contaminated

4 3< Igeo<4 Heavily contaminated

5 4< Igeo<5 Heavily to extremely contaminated

6 5< Igeo 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

.

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 Deficiency to minimal enrichment

EF=2-5 Moderate enrichment

EF=5-20 Significant enrichment

EF=20-40 Very high enrichment

EF>40 Extremely high enrichment

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

.

i

n

i

oi

fC

CC

1−=

Where 10 −i

C is the mean content of metals from at

least five sampling sites and i

nC 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

......CFn)CF3CF2(CFInPLI ×××=

CF = Contamination factor

n = number of metals

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

.

Cf

i <1 Low contamination factor indicating low

contamination

1≤Cfi <3 Moderate contamination factor

3≤Cfi < 6 Considerable contamination factor

6≤Cfi 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


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%

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 relation-

ship 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

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 64.94 33.79 66.23 35.06 66.21 33.77

5 38.92 37.71 78.18 61.08 62.29 21.82

7.5 29.31 49.17 84.5 70.69 50.83 15.5

10 28.17 67.9 52.27 71.83 32.1 47.732

12.5 34.53 70.25 72.69 65.47 29.76 27.31

15 49.02 75.14 63.57 50.97 24.86 36.43

17.5 20.38 76.99 62.82 79.61 23.01 37.18

20 18.05 83.14 68.76 81.96 16.85 31.24

22.5 26.57 74.56 74.08 73.43 25.44 25.92

25 18.54 67.61 72.28 81.46 32.73 27.72

27.5 20.85 52.73 86.57 79.15 47.27 13.429

30 34.6 52.55 87.09 65.39 47.45 12.91

32.5 46.22 77.89 86.02 53.78 22.11 13.98

35 35.24 91.35 88.76 64.76 8.65 11.24

37.5 53.08 91.72 87.29 46.92 8.28 12.71

40 43.88 89.03 85.04 56.12 10.97 14.96

42.5 34.6 90.85 90.13 65.4 9.15 9.87

45 47.58 94.88 89.3 52.42 5.12 10.7

47.5 50.66 95.86 89.95 49.34 4.14 10.05

50 61.94 96.44 89.58 38.07 3.56 10.42

52.5 56.71 74.55 89.66 43.29 25.45 10.34

55 58.93 40.05 92.24 41.08 59.95 7.76

57.5 57.58 86.52 93.32 42.42 13.48 6.68

60 61.06 57.01 88.84 38.95 42.99 11.16

62.5 48.69 56.08 51.3 43.92

65 48.67 51.33


239

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

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 (%) 16.596 4.458 13.846

OC (%) 1.294 0.875 0.839

S (%) 0.863 0.760 0.570

Fe (µgg-1) 4887.462 4737.792 4561.462

Mn (µgg-1) 358.216 236.238 166.988

Cr (µgg-1) 482.138 377.454 256.908

Cu (µgg-1) 43.677 45.867 37.352

Pb (µgg-1) 176.877 161.254 152.248

Zn (µgg-1) 72.623 71.946 54.584

Co (µgg-1) 4.004 4.400 6.052

Ni (µgg-1) 28.912 24.275 20.148

Cd (µgg-1) 2.819 2.696 3.168

Na (µgg-1) 10476.923 9791.667 10768.000

K (µgg-1) 8106.038 9633.250 9974.000

Ca (µgg-1) 3882.154 2448.458 1673.560

Mg (µgg-1) 5284.064 5126.326 5248.435


240

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


241

Fig. 3(b)—Vertical profiles of metals in the core sediments S1, S2 and S3


242

Fig. 3(c)—Vertical profiles of metals in the core sediments S1, S2 and S3


243

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

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 0.979 1.054 0.980

Mn 0.761 1.793 0.661

Cr 0.965 1.340 0.521

Cu 1.452 1.425 1.316

Pb 0.723 0.784 1.263

Zn 1.006 1.542 1.933

Co 2.858 1.566 1.423

Ni 1.543 1.601 0.732

Cd 2.358 0.486 1.521

Na 1.491 1.403 1.772

K 1.211 1.186 1.361

Ca 2.518 2.189 1.951

Mg 1.534 3.466 2.837


244

Fig. 4(a-c)—Enrichment factor in station 1; Enrichment factor in station 2; Enrichment factor in station 3


245

Fig. 5(a-c)—Index of Geoaccumulation in station 1; Index of Geoaccumulation in station 2; Index of Geoaccumulation in station 3


246

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.

References 1 Martin J M, Jednack J & Pravotic V, The physico-chemical

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