© Kamla-Raj 2009
J Hum Ecol, 27(1): 63-67 (2009)
Metal Pollution Assessment in Sediments of the
Dikrong River, N.E. India
M.Chakravarty1 and A.D.Patgiri2
1. Department of Geology, Cotton College, Guwahati, Assam, India
2. Department of Geological Sciences, Gauhati University,
Guwahati, Assam, India
KEYWORDS Metal, Contamination. Dikrong
ABSTRACT The degree of contamination in the sediments of the Dikrong river, for the metals Al, Fe, Ti, Mn, Zn,
Cu, Cr, Ni and Pb, has been evaluated using Enrichment ratio (ER), Pollution load index (PLI) and Geo-accumulation
index (Igeo). The sediments have been found to be contaminated with Cu and Pb which has been attributed mainly to
dispersion from the mineralized zone of the upper catchment area since no major industrial establishments are
present in the area.
INTRODUCTION
River sediments, derived as a result of weathering, are a major carrier of heavy metals in the
aquatic environment, the physico-chemical processes involved in their association being precipitation, adsorption, chelation, etc. Besides the
natural processes, metals may enter into the
aquatic system due to anthropogenic factors
such as mining operations, disposal of industrial
wastes and applications of biocides for pest. The
concentration in sediments depends not only on
anthropogenic and lithogenic sources but also
upon the textural characteristics, organic matter
contents, mineralogical composition and depositional environment of the sediments (Trefry and
Parsley 1976).
Study on the geochemistry of river sediments
in the present area has not been undertaken by
previous worker so far. However the sediment
chemistry of many Indian rivers has received wide
attention in the recent past. Commendable work
in this line were done, among others, by Borole
et al. (1982); Subramanian et al. (1985, 1987);
Seralathan (1987); Ramesh et al. (1990);
Chakrapani et al. (1990); Singh et al. (1997);
Kotoky et al. (1997) and Singh (1999) in order to
Address for correspondence:
Dr. Madhurjyojit Chakravartty
House No. 20, Sonaru Path, Sankarnagar 781 028,
Beltola – P.O., Guwahati,
Assam, India
Telephone: 091-0361-2222465 (R)
Mobile: 94353 04519
E-mail: madhurjyocbty@rediffmail.com
understand the elemental composition of the
sediments, the influence of anthropogenic activities on riverine chemistry and the transport of
metals from rivers to the coastal areas. River borne
sediments, especially the suspended matter, act
as a major carrier and source of heavy metals in
the aquatic system. Geochemical study of sediments, to evaluate the concentration of heavy
metals, is necessary as it helps to assess the
ecotoxic potential of the river sediments.
STUDYAREA
The Dikrong river, originating near the
Senkeng mountains at an altitude of 2579 m in the
Lesser Himalayan ranges of Arunachal Pradesh,
is a tributary of the Subansiri river lying on the
north bank of the river Brahmaputra. The river
basin comprises the Bomdila Group (Precambrian), the Gondwanas, the Siwaliks and the
Quaternaries. The Gondwanas are thrusted over
the Siwaliks along the Main Boundary Thrust.
The study area is bounded by latitudes
26056’15”N and 27 008’12”N and longitudes
93 045’10”E and 94 057’02”E. Samples were
collected from the river bed along the seventh
order segment of the Dikrong river flowing
through the Kimin Formation (Upper Siwaliks) and
the Quaternaries comprising the Pleistocene and
Recent deposits.
MATERIALS AND METHODS
Samples were collected from five (5) locations,
viz., Doimukh (27 0 08’43”N, 93 045’46”E),
64
M.CHAKRAVARTY AND A.D.PATGIRI
Bandardewa (27006’37”N, 93049’43”E), Baligaon
(27 0 05’27”N, 93 0 55’30”E), Marnaigaon
(27 0 01’41”N, 93 0 55’36”E) and Bihpuria
(27 000’49”N, 93 055’02”E) during both the
monsoon (August) and non-monsoon (January)
periods (Fig.1). Assessment of contamination has
been done on the basis of mean concentration
values of these two periods (Table 1). Collection
of samples from the upper catchment of the basin
could not be done because of the difficult nature
of the terrain. The metal content has been
determined by X-ray Fluorescence Spectrometer
(XRF) – Model: PW 1480.
Many authors prefer to express the metal
contamination with respect to average shale to
represent the degree of quantification of pollution
(Muller 1979; Forstner and Wittmann 1983). Some
authors (Baruah et al. 1998) have considered the
background value of their area of study to be the
geometric mean of concentration at the different
sample sites, which is the antilog of the arithmetic
average of log 10 (log to the base 10) of the
concentration values. According to them, the
geometric mean reduces the importance of a few
high values in a sample group and, therefore, is
numerically less than the arithmetic mean, making
it a useful indicator of background for most
geochemical data. Such background value,
however, varies from place to place. As such, this
methodology of determining background value
has not been considered in the present study.
Instead, the world surface rock average (Martin
and Meybeck 1979) of individual metal has been
taken to be the background following the recent
works of some authors (Rath et al. 2005).
The degree of contamination in the sediments
is determined with the help of three parameters Enrichment Ratio (ER), Pollution Load Index (PLI)
and Geo-accumulation Index (Igeo).
Enrichment Ratio (ER): Enrichment factor
analysis, a method proposed by Simex and Helz
(1981) to assess trace element concentration, is
mathematically expressed as:
Enrichment ratio (ER) =
(Cx/Fe)sample
(Cx/Fe)background
where, Cx stands for concentration of metal
‘x’. The background value is that of the world
surface rock average (Martin and Meybeck 1979)
given in Table 1. According to Forstner and
Wittmann (1983), in case of Fe, particularly the
redox sensitive iron-hydroxide and oxide under
oxidation condition constitute significant sink of
heavy metals in aquatic system. Even a low
percentage of Fe(OH)3, in aquatic system, has a
controlling influence on heavy metal distribution
(Rath 2005). Therefore, Fe is taken as a
normalization element while determining
enrichment ratio (ER).
Pollution Load Index (PLI): Pollution load
index (PLI), for a particular site, has been
evaluated following the method proposed by
Tomilson et al. (1980). This parameter is expressed
as:
PLI = (CF1x CF2 x CF3 x ……….. x CFn)1/n
where, n is the number of metals (nine in the
present study) and CF is the contamination factor.
The contamination factor can be calculated from
the following relation:
CF (Contamination factor) =
Metal concentration in the sediments
Background value of the metal
Fig. 1. Location of core sample collection
Geo-accumulation Index (Igeo): The geoaccumulation index (Igeo), introduced by Muller
(1979) for determining the extent of metal
accumulation in sediments, has been used by
various workers in their studies (Glasby et al. 1988;
METAL POLLUTION ASSESSMENT IN SEDIMENTS OF THE DIKRONG RIVER, N.E. INDIA
65
Table 1: Mean concentration of heavy metals in the Dikrong river sediments and their world surface
rock average
Sample
location
1
2
3
4
5
Std.Dev.
World surface
rock average
Al
4.755
4.434
4.09
4.64
4.085
0.308
6.93
Fe
Ti
1.628
1.978
1.784
1.719
1.668
0.137
3.59
0.231
0.345
0.312
0.252
0.285
0.044
0.38
Mn
Zn
Cu
Cr
484
608
642
441
569
0.103
720
29
33
19
23
28
3.459
129
188
192.5
194.5
182
193.5
5.165
32
43
59.5
53
41.5
56.5
8.067
97
Bhosale and Sahu 1991; Singh 1999; Rath et al.
2005).
Igeo is mathematically expressed as: Igeo =
log2Cn/1.5Bn, where, Cn is the concentration of
element ‘n’ and Bn is the geochemical background
value [world surface rock average given by Martin
and Meybeck (1979)]. The factor 1.5 is incorporated in the relationship to account for possible
variation in background data due to lithogenic
effect.
The geo-accumulation index (I geo) scale
consists of seven grades (0-6) ranging from
unpolluted to highly polluted.
RESULTS AND DISCUSSION
In order to assess the metal content in river
sediments, it is important to establish the natural
levels of these metals. Apart from natural
contribution, heavy metals may be incorporated
into the aquatic system from anthropogenic
sources such as solid and liquid wastes of
industries. Some degree of contamination may
be caused from fall out of industrial emissions
from the atmosphere.
However, in the present study area, no major
industry exists. There are a few minor handicraft
and small scale steel and iron factories registered
under the Directorate of Industries, Assam up to
31st December, 1992.
Metal contamination in the Dikrong river
Ni
13
12
7
9
15
3.193
49
Pb
41.5
38.5
31
37.5
47
5.846
20
sediments has been assessed for Al, Fe, Ti, Mn,
Zn, Cu, Cr, Ni, and Pb.
The ER values, given in Table 2, show
depletion trend for Ni and Zn (<1). The ER of Cr is
about normal, while that in case of Al, Mn and Ti
shows mild enrichment (>1). Cu shows very high
ER values (>10) indicating its high contamination
in sediments. The ER of Pb is also fairly high (>3).
Almost uniformly high values along the entire
reach negate the presence of local enrichment
factors.
Metal concentration values are the mean
values of concentration of individual metals in
the monsoon and non-monsoon periods (Table
1). The background value gives the normal
abundance of an element (Martin and Meybeck
1979). The mean concentration levels of Al, Fe,
Ti, Mn, Zn, Cr and Ni in sediments of all the
locations are lower than the background values.
Concentration of Cu and Pb are uniformly higher
than the background value. Higher concentrations of Cu and Pb are reflected in higher CF values
(>1) (Table 3).
The pollution load index does not show much
fluctuation. Lower values of PLI imply no
appreciable input from anthropogenic sources.
There is, in general, a decrease in PLI values
downstream indicating dilution and dispersion
of metal content with increasing distance from
source areas. However, relatively higher PLI
values at Bandardewa (0.78) and Bihpuria (0.76)
Table 2: Enrichment ratio (ER) values of heavy metals in Dikrong river bed sediments
Sample
location
1
2
3
4
5
Al
1.51
1.16
1.19
1.4
1.27
Mn
1.47
1.51
1.79
1.28
1.7
Ti
Zn
Cu
Cr
1.33
1.62
1.64
1.37
1.59
0.49
0.46
0.3
0.37
0.47
12.95
10.92
12.23
11.88
13.01
0.98
1.11
1.1
0.89
1.25
Ni
0.58
0.24
0.14
0.38
0.66
Pb
4.57
3.49
3.12
3.91
5.06
66
M.CHAKRAVARTY AND A.D.PATGIRI
Table 3: Average concentration (A), contamination factor (B), standard deviation of metal concentration
(SD), background value (BG) and pollution load index (PLI) of the metals in the sediments of Dikrong
river
Sampling A
Location
Al
Fe
B
A
1
4.755 0.69
2
4.435 0.64
3
4.09 0.59
4
4.64 0.67
5
4.085 0.59
SD
0.308
BG
6.93
(surface
rock
average)
Ti
B
A
1.628 0.45
1.978 0.55
1.784 0.50
1.719 0.48
1.668 0.46
0.137
3.59
Mn
B
A
0.23 0.60
0.34 0.89
0.31 0.81
0.25 0.66
0.28 0.74
0.044
0.38
Zn
A B
B
484 0.67
608 0.84
642 0.89
441 0.61
569 0.79
0.103
720
2 9 0.22
3 3 0.25
1 9 0.15
2 3 0.18
2 8 0.22
3.459
129
A
Cu
B
188.0 5.87
192.5 6.02
194.5 6.08
182.0 5.68
193.5 6.05
5.165
32
A
Cr
B
A
Ni
B
Pb
A
PLI
B
43
0.44 1 3 0.26 41.5 2.07
59.5 0.61 1 2 0.24 38.5 1.92
53
0.55 7 0.14 3 1 1.55
41.5 0.43 9 0.18 37.5 1.87
56.5 0.58 15 0.31 4 7 2.35
8.067
3.193
5.846
97
49
20
0.69
0.78
0.66
0.64
0.76
Units: Al,Fe and Ti in % and other metals in ppm
might be due to increased human activity since
these are township area having higher population
and establishments
The calculated Igeo values, based on the world
surface rock abundance, are presented in Table 4
and the variations are shown graphically (Fig. 2).
It is evident from the figure that the Igeo values
for Al, Fe, Ti, Mn, Zn, Cr and Ni fall in class ‘0’ in
all the five sampling locations indicating that
there is no pollution from these metals in the
Dikrong river sediments. The Igeo values of Pb
fall in the range 0-1, while those in case of Cu
have an almost uniform Igeo value of about 2. This
suggests negligible pollution from Pb, whereas
in case of Cu, the Igeo values seem to be influenced
Al
Fe
Ti
Mn
Zn
Cu
Cr
Ni
Pb
3
2
1
0
-1
-2
-3
-4
0
1
2
3
4
Sampling sites
5
Fig. 2. Geo-accumulation indices of heavy
metals in Dikrong river sediments
6
by the lithology of the terrain besides possible
anthropogenic contribution.
The above findings show no contamination
from Al, Fe, Ti, Mn, Zn, Cr and Ni. High Cu content
in the sediment samples, as revealed from the three
parameters, could be mainly due to dispersion or
lithogenic influx from the upper cachment since
contribution from anthropogenic factors appears
negligible in the absence of major industrial
establishments. Geological Survey of India
publications (1974 and 1983) report the presence
of Cu ore minerals, especially chalcopyrite, in the
Subansiri district which falls in the upper
catchment of the Dikrong river basin. High runoff due to heavy rainfall might have served as an
efficient agent for dispersion of Cu from its source
area downstream.
The concentration level of Pb along the entire
reach is also high. In the absence of major
industrial activity, high concentration of Pb can
also be attributed predominantly to influx from
the upper catchment area; the contribution from
domestic waste discharges appears to be
insignificant. Apart from Cu minerals, Ni, Pb and
Zn have also been reported (GSI 1974, 1983) from
the metamorphic belt lying in the Subansiri district
in the upper catchment of the Dikrong river basin.
Further, where stagnant condition prevails at the
bottom of a river, the dissolved oxygen is
completely removed. As a result, free metallic
complexes are formed which influence the
solubility of metal ‘lead’ by forming insoluble
complexes. These complexes tend to strip the
water of its metal content and enrich the bottom
sediments with the metal (Mehrotra et al. 1991).
METAL POLLUTION ASSESSMENT IN SEDIMENTS OF THE DIKRONG RIVER, N.E. INDIA
67
Table 4: Geo-accumulation indices of heavy metals in Dikrong river bed sediments
Sample
location
1
2
3
4
5
Al
Fe
Ti
Mn
Zn
-1.13
-1.22
-1.35
-1.16
-1.36
-1.72
-1.44
-1.59
-1.64
-1.69
-1.32
-0.74
-0.89
-1.18
-1.03
-1.15
-0.84
-0.76
-1.27
-0.91
-2.74
-2.55
-3.35
-3.06
-2.79
ACKNOWLEDGEMENT
The authors are thanksful to the UGC for the
financial assistance provided in the form of Minor
Research Project (MRP) grant (No. F.5-36/200405, MRP/NERO/2527).
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