Full text of DOI:10.3184/095422903782775181

Chemical Speciation & Bioavailability
ISSN: (Print) 0954-2299 (Online) Journal homepage: http://www.tandfonline.com:80/loi/tcsb20
Chemical fractionation of heavy metals in soils
around oil installations, Assam
P. Kotoky, B. J. Bora, N. K. Baruah, J. Baruah, P. Baruah & G. C. Borah
To cite this article: P. Kotoky, B. J. Bora, N. K. Baruah, J. Baruah, P. Baruah & G. C. Borah (2003)
Chemical fractionation of heavy metals in soils around oil installations, Assam, Chemical
Speciation & Bioavailability, 15:4, 115-126
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Date: 25 December 2015, At: 04:01

Chemical Speciation and Bioavailability (2003), 15(4)
115
Chemical fractionation of heavy metals in soils
around oil installations, Assam
P.Kotoky,* B.J.Bora, N.K.Baruah, J.Baruah, P. Baruah and G.C.Borah
Geoscience Division, Regional Research Laboratory (CSIR) Jorhat - 785 006, Assam, India
ABSTRACT
The chemical fractionation of lead, cobalt, chromium, nickel, zinc, cadmium and copper in soils around Lakwa
oil field, Assam, India was studied using a sequential extraction method. It is evident from the study that the
residual fraction is the most important phase for the seven heavy metals under study. Among non-residual
fractions metals are mostly associated with the Fe–Mn oxides fraction. The association of heavy metals with
organic matter was observed in the following order: copper> cadmium> zinc> lead. The concentration of Pb in
the carbonate fraction for both the seasons is higher compared with other metals, which may pose environmental
problems due to its highly toxic nature. The comparatively low concentration of metals in the exchangeable
fraction indicates low bioavailability. Correlations between physicochemical parameters and metal fractions of
soil do not show consistent behaviour. The local mean values of metals when compared with the accepted values
of normal abundance and geochemical background, indicates two to four fold increases in this area. However,
the values are within the range of normal abundance. As well as from natural soil geochemical behaviour,
anthropogenic influence might have a close bearing on the association of metals with the soil system in the
studied area.
Keywords: Assam, fractionation, Group Gathering Station, heavy metals, oil installation
medium to long term effect on lability and bioavail-
INTRODUCTION
ability of metals (Iyenger et al., 1981; Karczewska et
al., 1998).
Soil, which comprised of detritus, inorganic or organic
particles, is relatively heterogeneous in terms of
its physical, chemical and biological characteristics
(Hakanson 1992). Heavy metals are associated with
various soil components in different ways, and these
associations determine their mobility and availability
(Ahumuda et al., 1999). Water soluble and exchange-
able forms are considered readily mobile and available
to plants, while metals incorporated into crystalline
lattices of clays appear relatively inactive. The other
forms like carbonate bound, occlusion in Fe, Mn and
Al oxides, or complexes with organic matter and Fe–Mn
oxides have been found to be the most important in soil
and might be the components, which influence the
In recent years studies on the speciation or chemical
forms of heavy metals in polluted soils using sequen-
tial techniques have increased, because these provide
knowledge on metal affinity to soil components and the
strength with which they are bound to the matrix
(Narwal et al., 1999). Numerous extraction schemes
have been described in the literature (Chao 1972;
Tessier et al., 1979; Sposito et al., 1982; Welte et al.,
1983; Clevenger 1990; Ure et al., 1993; Howard and
Vandenbrink,1999). The procedure of Tessier et al.
(1979) is one of the most thoroughly researched and
widely used procedures to evaluate the possible chemi-
cal associations of metals in sediments and soils. In this
method, metal distribution is studied through five major
geochemical forms: (i) exchangeable phase; (ii) bound
to carbonate phase; (iii) bound to Fe–Mn oxides; (iv)
bound to organic matter, and (v) residual metal phase.
*To whom correspondence should be addressed:
E-mail: probhatk@ yahoo.com
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Chemical fractionation of heavy metals in soils aroud oil installations, Assam
However, the limitations of chemical extraction
methods have also been addressed (Jonanneau et al.,
1983; Khebonian and Bauer, 1987; Quevauviller et al.,
1997; Rauret et al., 1989; 1999). The limitations include
technical difficulties associated with selective dissolution
and complete recovery of trace metal from chemical
phases in soil and sediments. Therefore, the chemical
forms of heavy metals from the sequential extraction
methods are operationally defined phases only.
Altogether ten sites (five around each GGS) were
selected for sampling around the two GGSs I and III
and ten sampling sites considerably distant (about
2–5km) from the production area which are considered
as unpolluted and were selected for determination of
normal soil background and threshold values. Samples
were collected once in a month by plastic scoop
(Hoffman, 1986) from the topsoil layer (up to 15cm) in
the period 1994–1995 and the average of the replicate
analysis of total metal content at each point was con-
sidered for evaluation in terms of its association and
distribution. The generated data were used for this study.
The soil around Lakwa (27.3° N Lat., 94.7°E Long.),
a major oil producing structure of this region with a
number of Group Gathering Stations (GGSs) compris-
ing more than 200 producing wells is considered to be
contaminated by the unattended industrial develop-
ment. The region is located in a humid tropical climate
with a high rate of rainfall and perennial flood prob-
lems. The advent of unattended industrial development
aggravates the situation and warrants implementation
of continuous multidisciplinary monitoring approaches
with environmental perspectives, as the surface water
is the only major source of water for the inhabitants of
this thickly populated region. The spillage of oil,
untreated formation and drilling water from this field is
a matter of great concern for the entire ecosystem.
Moreover, the damage caused by the oil field water to
the tea planted areas located around the oil field also
poses a serious problem. All these, coupled to a neces-
sity for assessment of chemical forms of certain heavy
metals and to study their long-term environmental
impacts on soil in this area. The importance of studies
related to different chemical forms of metals, its poten-
tial toxicity and bioavailability needs detailed studies
(Forstner, 1983; Tessier and Campbell, 1988; Stamoulis
et al., 1996).
Sample preparation and analysis
All soil samples were air dried and subsequently kept
for 1 hour at 100°C for removal of water. The dried
samples were ground with agate mortar to below 100
mesh size and were utilised for subsequent analysis.
The soil pH was measured at the laboratory with the
help of a Global Digital pH meter following the pro-
cedure of Faniran and Areola (1978). The carbonate
content was determined by the acid neutralization
method (Jackson, 1958). Organic matter content was
determined by the Walkley Black Method (Faniran and
Areola,1978).
Total metals were estimated following the procedure
of Sakata (1983) by Atomic Absorption Spectro-
photometry (AAS) with a Perkin-Elmer Model-2380
instrument using the hollow cathode lamp as light
source. Pb and Cd contents were estimated by electro-
thermal atomisation i.e. graphite furnace (GF), while
Cr, Co, Ni, Cu and Zn were estimated by flame tech-
nique (FAAS). Matrix matching, standard addition and
background corrections were used to overcome inter-
ferences. After every four determinations blanks
and reference standards (SO-1 of Canadian Certified
Reference Material Project) with 95% confidence inter-
val at 2 standard deviation were also run to determine
the precision and instrumental uncertainties.
The local background levels of metals were calcu-
lated as geometric means (the antilog of the arithmetic
average of log10 of the values). The geometric mean
reduces the importance of a few high values, is a use-
ful indicator of background for the most geochemical
data (Govett, 1983). The threshold or upper limit of
normal background fluctuation (Hawkes and Webb,
1965; Karauskopf, 1967) is determined from the back-
ground population to know the anomaly by utilizing
mean + 2 standard deviations (Govett, 1983).
The aim of the present study was to investigate the
different chemical forms of heavy metals in soil around
oil installations i.e., GGSs and to assess the association
and bioavailability of certain metals, viz., Cu, Cr, Cd,
Co, Ni, Zn and Pb in soil. In order to assess the impacts
of soil components on metal associations, relationships
between metal accumulation patterns and soil charac-
teristics have also been investigated.
MATERIALS AND METHODS
Study area and sampling
Sampling sites were selected after detailed survey
around GGS-I and GGS-III (Figure 1). During the mon-
soon the water flows through this low-lying area and
causes extensive damage to water bodies and agricul-
tural/grazing land. The overflowing water acts as a
carrier of the contaminated brines and other waste
products from these oil installations. The metals under
consideration were selected on the basis of site specific
geochemical studies and their expected relationship
with the oil field development activities.
High purity Certified/Analar or its equivalent grade
reagents (obtained from Aldrich, Sigma or E-merck
only) were used throughout the work. HNO3 and HCl
used in this study were purified through a sub-boiling
distillation unit (all quartz). Stock standard solutions of
metals were prepared by dissolving ultrapure metals/
compounds (99.99% pure) obtained fromAldrich only.
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P. Kotoky, B.J. Bora, N.K. Baruah, J. Baruah, P. Baruah and G.C. Borah
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Figure 1 Location map of the area with sampling points.
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118
Chemical fractionation of heavy metals in soils aroud oil installations, Assam
The t-test was applied to determine significant
vary from 4.8 to 5.3 and 4.8 to 5.20 and hence do not
show any distinct change. Soil pH values below 5.0 to
5.5 warn that soluble level of certain metals, particu-
larly Al3+ and Mn2+, may be high enough to be biologi-
cally toxic (McBride, 1994). Conversely pH values
above 7 are often associated with very low solubility of
micronutrient metal cations such as Zn2+. In the case of
GGS-III pH values of NM period (4.4 to 8.4) is dis-
tinctly higher than M period (4.2 to 5.8). The higher
value of pH during NM in S-3 of GGS-III is likely to
be related to the higher carbonate content (8.5%) of the
sample. However, the overall pH of the soil near two
oil installation sites (GGS-I and GGS-III) is within the
normal soil pH of the region.
Soil organic matter (SOM) expressed in terms of per-
centage of organic carbon refers to the sum of all
organic carbon containing substances in soils. Organic
matter content (Table 1a and b) of GGS-I was higher
during M period than the NM period. The high value
(7.5%) at S-4 during NM is exceptional and could be
related to anthropogenic influences through accidental
leakage and release of oil contaminated wastewater
from the GGSs. In the case of GGS-III the organic
matter content during NM and M periods does not show
any appreciable change. Presence of crude oil in soil is
harmful since it immobilizes soil N and P, and reduces
the population and biomass of soil microfloura. It may
also restrict seed germination, possibly, by limiting the
inhibition of water and diffusion of gases into the seed.
In oil saturated soil, the root hairs get plasmolysed and
the root systems of plants get damaged / killed leading
to eventual death (Rao, 1992). This might be one of the
main causes for stunted growth and decreased yield of
crops, particularly paddy crops around these installations.
The carbonate content (Table 1a and b) of the soil is
comparatively low. It varies from 1.3 to 2.2% during
NM and 1.7 to 2.8% in M period near GGS-I. In case
of GGS-III it varies from 1.6 to 8.5% in NM and 1.7 to
3.8% in M periods. The low value of carbonate content
is related to the acidic nature of soil with the exception
at S-4 of GGS-III during NM period. This might be
related to the site-specific geochemical behaviour of the
soil profile.
correlation coefficients between various pairs of soil
components under study at 5% level of significance
(ꢀ = 0.05). The results thus obtained are utilised to under-
stand the interrelationship between them at the existing
physicochemical conditions of the soil system under
study.
Trace metal fractionation
The procedure of Tessier et al. (1979; 1985) was
selected for this study. In this method heavy metals are
separated into five operationally defined fractions:
exchangeable (F1), bound to carbonate (F2), bound to
Mn oxide (F3a), bound to Fe-Mn oxide (F3b), bound to
organic matter (F4) and residual fraction (F5).
One gram of soil sample was weighed and extrac-
tions have been made through steps (f) by centrifuga-
tion at 10,000rpm placing the sample in polypropylene
centrifuge tube.
(a) F1: Exchangeable metals: The sediment samples
was extracted for 1 hour with 8 mL of 1M MgCl2 at
pH7.0 at room temperature;
(b) F2: Metals bound to carbonate: The residue from (a)
was leached with 1M sodium acetate (NaOHc)
adjusted to pH 5.0 with acetic acid (HoAc) for 5
hours;
(c) F3a: Metal bound to Mn-oxide: The residue from (b)
was leached for 30 minutes at room temperature
with 0.1M NH2OH.HCl in 0.01M HNO3;
(d) F3b: Metals bound to Fe-Mn oxide: The residue
from (c) was extracted at 960C for 6 hour with
0.04M NH2OH.HCl in 25% (v/v) HoAc;
(e) F4: Metals bound to organic matter: The residue from
(d) was extracted at 850C for 5 hour with 30% H2O2
adjusted to pH 2.0 with HNO3 and then at room tem-
perature with 3.2M NH4OAc in 20% (v/v) HNO3;
(f) F5: Residual metals: The residue from (e) was
digested with a mixture of concentrated hydroflouric,
nitric and perchloric acids.
Step(c), suggested by Chao (1972), was included to
distinguish between manganese and iron oxyhydroxides.
The ‘selective’ extraction was conducted in centrifuge
tubes (polypropylene. 50 mL) to minimize losses of
solid material. Effective separation was achieved
between each successive extraction by centrifuging at
10,000 rpm for 30 minutes. The supernatant was
removed with a pipette and analysed for metals under
study.
Total concentration of heavy metals
The total concentrations of heavy metals are reported
in Table 1a and 1b. The nature of concentrations and
distributions of certain heavy metals under study is
observed not to be similar for both the GGSs under
existing physicochemical conditions. The nature of dis-
tribution of Cu, Ni, Co and Cd has shown similar
behaviour whilst Cr, Zn and Pb signify a different
situation for both the stations. The lower concentration
of Co, Ni, Cu and Cd during the monsoon period can
be attributed as the dilution and dispersion of metal
contents by the flowing water during that period. The
RESULTS AND DISCUSSION
Soil properties
The values of pH (Table1a and b) of soil around GGS-
I during non monsoon (NM) and monsoon (M) periods
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P. Kotoky, B.J. Bora, N.K. Baruah, J. Baruah, P. Baruah and G.C. Borah
119
Table 1a Geochemical parameters of soil around GGS-I
Sample
points
pH
Carbonate Organic
Pb
Co
NM
Cr
NM
Ni
NM
Zn
NM
Cd
NM
Cu
NM
content
content
NM
M
NM
M
NM M
NM
M
M
M
M
M
M
M
S-1
S-2
S-3
S-4
S-5
5.3 4.9 2.2 2.8 2.5 3.9 26.2 44.0 50.4 24.7 74.0 129.7 130.3 72.0 41.4 89.1 0.09 0.09 42.3 29.3
4.9 4.9 1.9 2.2 2.7 4.1 13.5 46.0 61.3 16.7 96.9 94.1 148.5 52.4 24.3 87.8 0.12 0.05 69.2 31.9
4.8 4.9 1.4 1.8 2.3 5.7 12.0 38.0 60.6 16.0 105.6 100.6 151.6 45.2 23.6 107.0 0.13 0.07 74.3 34.5
5.2 5.2 1.9 1.9 7.5 4.54 17.2 46.0 47.6 18.8 102.0 162.5 128.7 53.9 17.2 74.9 0.18 0.17 82.9 26.9
4.9 4.8 1.3 2.2 3.9 4.8 18.4 42.7 40.6 37.1 91.4 145.5 121.8 85.1 18.4 95.3 0.27 0.10 64.3 33.9
NM, Non -monsoon; M, Monsoon; all concentrations are ꢁg/g except organic matter and carbonate content which are %.
Table 1b Geochemical parameters of soil around GGS-III
Sample
points
Carbonate Organic
content matter
pH
Pb
Co
Cr
Ni
Zn
Cd
Cu
NM
M
NM M NM M NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM M
S-1
S-2
S-3
S-4
S-5
5.6 5.2 1.4 2.1 4.6 4.7 64.8 42.7 29.2 25.1 112.8 145.5 135.1 58.5 173.9 105.1 0.37 0.86 55.5 32.6
6.3 5.6 2.2 2.2 4.7 4.7 43.3 47.3 33.4 30.6 98.5 132.6 125.1 53.8 169.5 98.5 0.33 0.24 59.8 31.1
8.4 5.8 8.5 3.8 4.9 5.6 71.7 42.0 36.8 30.9 94.0 129.8 97.7 56.5 185.7 86.9 0.49 0.28 70.6 25.5
4.9 4.4 1.7 1.8 5.2 4.6 56.7 56.0 43.8 37.4 188.7 142.7 104.1 69.7 115.9 112.7 0.48 0.26 40.2 26.6
4.4 4.2 1.6 1.7 6.2 5.6 52.7 37.3 29.0 28.9 116.7 147.1 138.2 65.1 163.2 94.7 0.54 0.16 46.5 30.7
NM, Non -monsoon; M, Monsoon; all concentrations are ꢁg /g except organic matter and carbonate content which are %.
higher concentration of Co, Ni, Cu and Cd during non-
monsoon period might have a close relationship with
their association with the suspended sediments. With
the drop in competency of flowing water the suspended
sediments were deposited with the soil profile and
thereby causes an increase in total metal concentrations
of elements during that period. The total concentration
of Zn, Pb and Cr in the non-monsoon period was
observed to be lower in GGS I than the concentration
in monsoon period. The higher concentration of metals
during monsoon period clearly indicates their incorpo-
ration from the nearby areas. The total concentration of
Cr also exhibits similar behaviour in case of GGS III.
However, Zn and Pb have shown a completely different
behaviour in case of GGS III. The possibility of incor-
poration of Cr contents by the flowing water from the
overflowing chromite bearing rock types of the catch-
ment areas and from the corrosion-erosion of the
chromite bearing fixtures/fittings related to oil
exploration-exploitation activities also cannot be ruled
out. The enhancement of Zn concentration in soils
around GGS I has got definite linkage with the appli-
cation of fertilizers in the low lying areas and paddy
fields existed around it.
under study concentrations of Cd, Cu, Ni, Zn and Cr
are lower than the local background. Pb and Co, how-
ever, exhibited higher values than the local background.
All the values are within the range of background fluc-
tuation and below the calculated threshold values. The
high local background values can be interpreted as the
presence of less weathered immature soil profiles with
abundant soil mineral components coupled with anthro-
pogenic incorporation from the associated development
activities nearby.
Chemical fractionation of metals under study
The geochemical behaviour of trace metals and their
chemical forms can be ascertained with the help of frac-
tionation. The metals present in exchangeable (F1) and
carbonate (F2) fractions are considered to be weakly
bound and may equilibrate with the aqueous phase thus
becoming readily bioavailable. On the other hand, the
metals in the residual fraction (F5) are not easily
released under normal conditions. The Fe–Mn oxide
(F3b) and organic fractions (F4) provide a sink or reser-
voir for heavy metals. The hydrous Mn-oxide fraction
exhibits more isomorphic substitution than amorphous
Fe-oxide and shows greater conditional equilibrium
constants for the heavy metals than Fe-oxide. The dis-
tribution of heavy metals in different chemical fractions
as evident from the present study is shown in Figures
2a and 2b.
Table 2 summarises the background values of seven
heavy metals. Comparisons of values with the inter-
nationally accepted shale standard (Wedepohl, 1972)
and normal abundance values (Hawkes and Webb,
1972) indicate two to four fold increase over the mean
values. However, all the values are within the range of
normal abundance. On comparison with the two locations
The fractionation of lead shows that a major portion
is associated with the residual fraction (F5), followed
by Fe–Mn oxide (F3b), organic matter (F4), carbonate
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Chemical fractionation of heavy metals in soils aroud oil installations, Assam
Figure 2a Chemical partitioning of heavy metals (%) in soil around G.G.S.-I.
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P. Kotoky, B.J. Bora, N.K. Baruah, J. Baruah, P. Baruah and G.C. Borah
121
Figure 2b Chemical partitioning of heavy metals (%) in soil around G.G.S.-III.
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Chemical fractionation of heavy metals in soils aroud oil installations, Assam
Table 2 Local background and threshold value of heavy metals in soil along with their normal abundance (values are ꢁg/g dw)
Metal
Normal abundancea
Average shale
valuesb
Background values(present study)
Threshold values
(present study)
Mean
Range
Mean
Range
Pb
Co
Cr
Ni
Zn
Cd
Cu
10
8
100
40
50
0.5
20
2–200
1–40
5–1000
5–500
10–300
01–0.7
2–100
20
19
90
68
95
0.3
45
18.62
19.17
120.22
103.21
107.76
0.31
6.8–72.0
81.28
57.54
250.61
281.83
316.22
0.75
13.6–50. 2
51.8–229.6
70–256
38.4–310.6
0.12–0.64
21.8–85.7
48.42
90.38
After aHawkes and Webb (1965); aKarauskopf (1967); bWedepohl (1972)
(F2), Mn oxide (F3a) and exchangeable (F1) fractions.
Pb shows different behaviour in relation to pH,
carbonate and organic matter contents for the two
GGSs. In the case of GGS-I in NM period, Pb shows
positive relationship with all parameters, except organic
matter content, where it exhibits a negative significant
(r = -0.86) correlation. The significant positive (r = 0.81)
correlation with pH during the M period suggests an
increasing tendency of sorption with increasing pH.
Association of Pb with Fe–Mn oxides (up to 25%) frac-
tion is also supported by their positive correlation. In
case of GGS-III, Pb shows non-significant negative
correlation with respect to pH and carbonate content
for both the periods. However, in case of organic matter
content Pb shows significant negative correlation (r =
-0.76) in M period. The higher concentration of lead in
the Fe-Mn oxide is due to the formation of stable com-
plex (Lopez-Sanchez et al., 1996; Jones and Turkie,
1997). The lower concentration of Pb in the exchange-
able fraction suggests low bioavailability but slightly
higher concentration in the carbonate fraction indicates
a problem to the ecosystem as carbonates may dissolve
readily with a change in soil characteristics.
The association of cobalt with different fractions was
observed in the order: residual > Fe–Mn oxide > Mn
oxide > organic > carbonates > exchangeable (Figures
2a and 2b). The higher concentration of Co in the
Fe–Mn oxides fractions (up to 42.5%) indicates that
Fe–Mn oxides act as a natural sink for cobalt. The
correlation matrix for both the GGSs shows a non-
significant negative correlation with the physicochemi-
cal parameters.Chromium was mostly concentrated in
the residual fraction. The partitioning of chromium
with different fractions was in the order: residual > Fe
oxide > organic > Mn- oxide > carbonate > exchange-
able. The significant difference in residual Cr content
in GGS-I (80.8%) and GGS-III (42.3%) clearly indi-
cates the role played by soil mineral components in its
distribution under the existing physico-chemical con-
ditions. The formation of dichromate at the existing soil
pH is minimised and reduces the affinity of sorption by
hydrous metal oxides (Fe–Mn). However, at a low pH
and concentration, where solubility of Cr (III) is higher,
strong specific adsorption on Fe-Mn oxides occurs.
Probably because of this reason, we observed a different
situation in GGS-I (12.2%) and GGS-III (39.5%) in
case of Cr association with Fe-Mn oxides fraction. The
relatively higher proportion of organic matter content
in the topsoil layer around GGS-III might have clearly
indicated its association with the soil system by form-
ing stable organic complexes at the existing physico-
chemical conditions. In moderate to highly organic
soils, Cr and Cu are present in less mobile and less
available forms to soil organisms and plants, the soluble
and exchangeable metals (labile fraction) usually being
considered as most hazardous (Gupta et al., 1996; Maiz
et al., 2000). The higher association with the residual
fraction indicates its low bioavailability.
Nickel was mostly concentrated in the residual frac-
tion although it has shown its affinity towards Fe-Mn
oxide fractions. The percentage of nickel in the residual
fraction ranges from 50.3 to 53.7%. The correlation
coefficient (Table 3a and 3b) shows an overall negative
effect except carbonate (CO32–) content in the NM
period of GGS-I. The organic matter associated with
the soil fraction also retains a small amount of nickel.
The lower concentrations in the exchangeable and
carbonate fractions and alternately higher concentration
in the residual fraction indicate reduced rate of inter-
actions with the biotic community of the soil.
The sequential extraction showed that residual frac-
tion dominated the Zn distribution in the soil, which
ranges from 46.9 to 52.0% for both the GGSs. Similar
results for distribution of Zn were also reported by other
authors (Gupta and Chen, 1975; Ma and Rao, 1997;
Izquirdo et al., 1997; Ramos et al., 1999; Li et al., 2000;
Li et al., 2001). As evident from the study the non-
residual Zn is likely to be retained in order as: Fe–Mn
oxides>organic fraction>carbonate>exchangeable. The
organic matter fraction [F4] also contains a consider-
able amount of zinc (16–18%) and apparently forms
organic complexes. The enrichment of total zinc up to
5% is reported to be bound in the humic acid fraction
of the soil (Bodek et al., 1988). The high content of zinc
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P. Kotoky, B.J. Bora, N.K. Baruah, J. Baruah, P. Baruah and G.C. Borah
123
Table 3a Correlation coefficients of soil properties and heavy metals around GGS-I
Non-monsoon
Co
2–
pH
CO3
#O.M.
Pb
Cr
Ni
Zn
Cd
Cu
pH
CO3
S.O.M.
Pb
Co
Cr
Ni
–0.03
–0.24
–0.83
0.48
0.47
–0.86
–0.28
0.29
–0.06
0.01
0.69
0.07
–0.15
0.36
0.50
–0.22
0.54
–0.30
0.16
0.96
0.49
–0.79
–0.29
0.69
–0.91
0.08
–0.60
–0.04
–0.91
–0.14
–0.04
0.34
0.14
0.92
–0.91
–0.35
0.61
–0.71
0.23
–0. 59
0.07
2–
0.11
Zn
Cd
–0.67
0.90
–0.71
Cu
Monsoon period
pH
CO3
S.O.M.
Pb
Co
0.85
0.33
0.04
0.81
0.52
0.01
–0.28
0.24
–0.51
–0.54
–0.66
–0.51
0.32
–0.93
0.35
–0.33
–0.32
0.69
–0.71
0.07
0.57
0.65
–0.57
0.70
0.19
–0.37
–0.73
0.44
–0.13
–0.75
0.23
–0.46
–0.40
0.58
–0.81
0.15
2–
Cr
0.90
–0.82
0.95
Ni
Zn
Cd
–0.87
0.34
–0.72
0.99
–0.89
0.33
Cu
Table 3b Correlation coefficients of soil properties and heavy metals around GGS-III
Non-monsoon
2–
pH
CO3
#O.M.
Pb
Co
Cr
Ni
Zn
Cd
Cu
pH
CO3
S.O.M.
Pb
Co
Cr
Ni
Zn
Cd
0.92
–0.51
–0.16
–0.57
–0.49
0.22
0.17
0.23
–0.12
–0.47
–0.55
–0.43
0.20
0.18
0.70
–0.62
–0.70
0.23
0.56
–0.85
0.60
0.50
–0.23
–0.06
–0.68
–0.98
0.23
–0.14
0.26
0.83
0.17
0.20
0.29
0.34
–0.72
0.92
0.78
2–
–0.50
–0.44
–0.21
–0.82
0.99
–0.89
–0.89
–0.28
Cu
Monsoon period
pH
CO3
S.O.M.
Pb
Co
0.78
–0.006
0.42
–0.12
–0.20
–0.76
–0.32
–0.05
–0.20
0.78
–0.83
–0.80
–0.12
–0.11
–0.17
–0.91
–0.56
–0.05
0.36
0.58
0.67
–0.51
–0.70
–0.84
0.73
0.36
0.54
0.23
–0.09
–0.57
–0.27
–0.37
–0.74
0.48
2–
–0.02
–0.42
–0.10
–0.60
0.31
Cr
Ni
Zn
0.56
–0.23
0.32
–0.27
0.18
Cd
0.49
Cu
in the organic matter fraction is due to its scavenging
effect. The present finding can be corroborated with the
studies of Tessier et al. (1980); Jordao and Hickless
(1989); Nriagu and Coker (1980); Gadh et al. (1993)
and Baruah et al. (1996). Fe–Mn oxides seem to play
a major role in zinc accumulation in the profile, as pre-
cipitation and co-precipitation products. The association
of zinc with Fe–Mn oxides in soil has been widely
recognised (Kuo et al., 1983; Comber et al., 1995;
Jones and Turkie, 1997). The sorption of zinc in soil
and sediments strongly imparts its mobility in the
environment. For this reason, severe zinc contamination
tends to be confined to the region of the source (Li et
al., 2000). Hydrous Fe and Mn oxides, clay minerals,
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124
Chemical fractionation of heavy metals in soils aroud oil installations, Assam
carbonate minerals, and, to a lesser extent, organic
matter have been noted as sorbents that control the
behaviour of zinc in soil.Aminor amount is also associ-
ated with exchangeable [F1] and carbonate fractions
[F2]. Calcium carbonate forms complexes with zinc as
a double salt (CaCo3.ZnCo3) in the soil (Li et al., 2000).
The association of Zn with carbonate appeared to be
less pronounced due to the low content of carbonate
in the soil. Lower concentration in the exchangeable
fraction indicates low bioavailability.
large amounts of copper salts to organic soils over time
without causing toxicity to crops (Mcbride, 1994). The
higher amount of Cu in the residual fraction [F5] is
suggestive of non-availability to biotic community. The
lower concentrations in exchangeable (1.3–2.1%) and
carbonate fractions (1.1–1.8%) are also indicative of a
low bioavailability.
CONCLUSIONS
Association of Cd is observed as maximum in resid-
ual fraction. The association of Cd with the different
fractions was observed in the following order: residual
> Fe–Mn oxides > organic > carbonate > exchangeable.
The correlation coefficients (Table 3a and 3b) exhibited
wide variation for both the group-gathering stations
(GGSs I and III) during NM and M periods. The higher
association of Cd with the organic matter fraction (15.3
to 18.5%) is also manifested by the positive correlation
coefficients.
The chemical fractionation of metals under study
revealed the geochemical nature of seven metals and
their probable association with different chemical
forms in soils around the group gathering stations of
Lakwa oil field, Assam. The study also focused on the
influence of soil physicochemical characteristics on the
retention and partitioning of seven heavy metals. The
heavy metals are mainly associated with the residual
and Fe–Mn oxides fractions. The Fe–Mn oxides and
organic matter fractions readily form complexes and
may provide a sink for heavy metals. The acidic nature
of the soils restricts the association with the carbonate
and exchangeable fractions. It is evident from the study
that the soil characteristics played a significant role in
defining the chemical forms of the metals within the
system. The present study indicates that the metals
under study do not pose environmental risks under the
existing physicochemical environment.
Association of copper with different fractions is
observed as residual > Fe-Mn oxides > organic >
exchangeable > carbonate. Copper is strongly sorbed
by hydrous Fe-Mn oxides, clay minerals and organic
matter. Because of the high affinity of copper for soil
colloids, copper is rated a low-mobility element in near
neutral soils. Sorption is probably the most important
controlling mechanism determining the association and
mobility of copper under the existing physicochemical
conditions. Several investigators have demonstrated
that the sorption of copper on hydrous Fe–Mn oxides
is due to co-precipitation of copper in the Fe–Mn oxide
lattice. However, the organic matter fraction [F4] con-
tains a significant amount (21.3–26.5%) of copper.
Copper is preferentially retained on organic matter by
complexation rather than by ion exchange (Balasoiu,
2001; Wu et al., 1999). A significant positive relation-
ship between copper and organic matter (Table 3a) is
observed in case of GGS-I, however, in case of GGS-
III (Table 3b) it shows opposite relationship. This might
be related to the local geochemical behaviour of soil.
The strong positive effect can be related with the fact
that, copper easily form complexes with organic matter
due to the high stability constant of organic-Cu com-
pounds. Organic material exhibits a high degree of
selectivity for divalent ions and the probable order of
binding strength for metals onto organic matter is cop-
per>lead>zinc. Thus, the organically bound form is an
important phase for copper in the soil. The carrier effect
is more pronounced in the case of copper organic com-
plexes compared to free copper (Cu2+) ions available
within the system (Mcbride, 1994). Organically com-
plexed copper (Cu2+) is bound more tightly than any
other divalent transition metal; lability of these com-
plexes is rather low, limiting bioavailability. Probably
this is the reason why farmers have been able to apply
However, the present study warrants implementation
of a continuous monitoring system in the area, as surface
water is one of the major sources of water for this thickly
populated area apart from regular use by thousands of
cattle and other domestic animals.
ACKNOWLEDGEMENTS
The authors are grateful to the Director, Regional
Research Laboratory (CSIR), Jorhat, Assam, India for
his kind permission to publish the article. The financial
help (No.19/19/93-RE,1994) given by the Ministry of
Environment and Forests, Govt. of India to carry out
the work is gratefully acknowledged.
REFERENCES
Ahumuda, I., Mendoza, J. and Ascar, L. 1999. Sequential
extraction of heavy metals in soils irrigated with
wastewater. Commun. Soil Sci Plant Anat., 30,
1507–1519.
Balasoiu, C.F., Zagury, G.J. and Deschenes, L. 2001.
Partitioning and speciation of chromium, copper, and
arsenic in CCA-contaminated soils : influence of soil
composition. Sci. Total Environ., 280, 239–255.
Baruah, N.K., Kotoky, P., Bhattacharyya, K.G. and Borah,
G.C. 1996. Metal Speciation in Jhanji River sediments.
Sci. Total Environ., 193, 1–12.
www.scilet.com

P. Kotoky, B.J. Bora, N.K. Baruah, J. Baruah, P. Baruah and G.C. Borah
125
Bodek, I., Lyman, W.J., Reehl, W.F. and Rosenblatt, D.H.
1988. Environmental Inorganic chemistry, Pergamon
press, 7.0–7.15.
Jonanneau, J.M., Latouche, C. and Pautrizel, F. 1983.
Critical analysis of sequential extraction through the
study of several attack constituent residues, Envir.
Technol. Lett., 4, 509–514.
Jordao, C.P. and Hickless, G. 1989. Chemical associations
of Zn, Cd, Pb and Cu in soils and sediments determined
by the sequential extraction technique, Environ. Tech.
Lett., 10, 743–752.
Karczewska, A., Szerszen, L. and Kabala, C. 1998. Forms
of selected heavy metals and their transformation in soils
polluted by emissions from copper smelters, Avd. Geo.
Ecology., 31, 705–712.
Khebonian, C. and Bauer, C. 1987. Accuracy of selective
extraction procedures for metal speciation in model
aquatic sediments, Anal. Chem., 59, 1417–1423.
Chao, T.T. 1972. Selective dissolution of manganese
oxides from soils and sediments with acidified hydroxyl-
amine hydrochloride. Proc. Soil Sci. Soc. Am., 36,
764–768.
Clevenger, T.E. 1990. Use of sequential extraction to
evaluate the heavy metals in mining washes. Water, Air,
Soil Pollut., 50, 241–255.
Comber, S.D.W., Gunn, A.M. and Whalley, C. 1995.
Comparison of the partitioning of trace metals in the
Humber and Mersey estuary. Mar. Pollut. Bull., 30,
851–860.
Faniran, A. and Areola, O. 1978. Essential of soil study,
Krauskopf, K. 1967. Introduction to geochemistry, Mc Graw
Heinemann, London, pp. 255–256.
Hill, N.Y., 721pp.
Forstner, U. 1983. Assessment of metal pollution in rivers
and estuaries. In: I. Thornton (ed.) Applied Environmental
Geochemistry, Academic Press, London, pp.395–423.
Kuo, S., Heilman, P.E. and Baker, A.S. 1983. Distribution
and form of copper, Zinc, Cadmium, Iron and Manganese
in soils near a Copper smelter, Soil Sci., 135, 101–109.
Li, X.D., Wai, O.W.H., Li, Y.S., Coles, B.J., Ramsey, M.H.
and Thornton, I. 2000. Heavy metal distribution in sedi-
ment profiles of the Pearl River estuary, South China.
Appl. Geochem., 15, 567–581.
Gadh, R., Tandon, S.N., Mathur, R.P. and Singh, O.V. 1993.
Speciation of metals in Yamuna river sediments, Sci.
Total Environ., 136, 229–242.
Govett, G.J.S. 1983. Handbook of exploration geochemistry,
3, Elsevier, Amsterdam, New York, pp. 29–47.
Li, X.D., Zhenguo, S., Wai, O.W.H. and Li, Y.S. 2001.
Chemical partitioning of heavy metal contaminants in
sediments of the Pearl River estuary, Chem. Speciat.
Bioavail., 12, 17–25.
Lopez-Sanchez, J.F., Rubio, R., Samitier, C. and Rauret, G.
1996. Trace metal partitioning in marine sediments and
sludges deposited off the coast of Barcelona (Spain), Wat.
Res., 30, 153–159.
Ma, L.Q. and Rao, G.N. 1997. Chemical fractionation of
cadmium, copper nickel and zinc in contaminated soils,
J. Envir. Qual., 26, 259–264.
Maiz, I,. Arambarri, I., Garcia, R. and Millan, E. 2000.
Evaluation of heavy metal availability in polluted soils
by two sequential extraction procedures using factor
analysis, Environ Pollut., 110, 3–9.
Gupta, S.K. and Chen, K.Y. 1975. Partitioning of trace
metals in selective chemical fractions of nearshore sedi-
ments. Environ. Lett., 10, 129–158.
Gupta, S.K., Vollmer, M.K. and Krebs, R . 1996. The impor-
tance of mobile, mobilisable and pseudo total heavy metal
fractions in soil for three-level risk assessment and risk
management. Sci. Total Environ., 178, 11–20.
Hoffman, S.J. 1986. Soil Sampling, Review in Economic
Geology, Economic Geology Pub.Com., University of
Texas, USA, 3, pp.39–77.
Hakanson, L. 1992. Sediment variability. In: Burton G. A.
Jr. (ed.) Sediment Toxicity Assessment, Lewis Publishers,
Boca Raton, Fl, pp.19–36.
Hawkes, H. E. and Webb, J.S. 1972. Geochemistry in
mineral exploration, Harper and Row, 409pp.
Mcbride, M.B. 1994. Environmental Chemistry of Soils,
Howard, J.L. and Vandenbrink, W.J. 1999. Sequential
extraction analysis of heavy metals in sediments of
variable composition using nitrilotriacetic acid to counter-
act resorption. Environ. Pollut., 106, 285–292.
Oxford University Press, New York, 397pp.
Narwal, R.P., Singh, B.R., and Selbu, B. 1999. Association
of cadmium, zinc, copper and nickel with components in
naturally heavy metal rich soils studied by parallel and
sequential extraction. Commun. Soil Sci. Plant Anal., 30,
1209–1230.
Iyenger, S.S., Martens, D.C. and Miller, W.P. 1981.
Distribution and plant availability of soil zinc fractions.
Soil Sci Soc. Am. J., 45, 735–739.
Nriagu, J.O., and Coker, R.D. 1980. Trace metals in humic
and fulvic acids from lake Ontario sediments. Envir. Sci.
Technol., 4, 443–446.
Quevauviller, P., Rauret, G., Lopez-Sanchez, J.F., Rubio, R.,
Ure, A. and Muntau, H. 1997. Certification of trace metal
extractable contents in a sediment reference material
(CRM 601) following a three-step sequential extraction
procedure. Sci. Total Environ., 205, 223–234.
Izquierdo, C., Usero, J. and Garcia, I. 1997. Speciation of
heavy metals in sediments from salt marshes on the
southern Atlantic coasts of Spain. Marine Pollut. Bull.,
34, 123–128.
Jackson, M.L. 1958. Soil Chemical Analysis. Prentice Hall,
Englewood Cliffs, N. J., 498pp.
Jones, B. and Turkie, A. 1997. Distribution and speciation
of heavy metals in surfacial sediments from the Tees
Estuary, northwest England. Mar. Pollut. Bull., 34,
768–779.
Ramos, L., Gonzalez, M.J. and Hernandez, L.M. 1999.
Sequential extraction of copper, lead, cadmium and zinc
in sediments from Ebro River (Spain): Relationship with
www.scilet.com

126
Chemical fractionation of heavy metals in soils aroud oil installations, Assam
levels detected in earthworms. Bull. Envir. Contam.
Toxicol., 62, 301–308.
Tessier, A., Campbell, P.G.C. and Benon, M. 1979.
Sequential extraction procedure for the speciation of
particulate trace metals. Anal. Chem., 51, 844–851.
Tessier, A., Campbell, P.G.C. and Benon M. 1980. Trace
metal speciation in the Yamaska and St. Francois rivers
(Quebec). Can. J. Earth Sci., 17, 90–105.
Rao, D.N. 1992. Petroleum Production Operation – an
ecological perspective. In: Wahi S. P. (ed.) Environmental
Management in Petroleum Industry, Wiley Eastern Ltd.,
New Delhi, pp. 375–381.
Tessier, A., Rapin, F. and Casignan, R. 1985. Trace metals
in oxic lake sediment: Possible adsorption onto iron
oxyhydroxides. Geoch. Cosmoch. Acta., 49, 183–194.
Tessier, A. and Campbell P. 1988. Partitioning of trace
metals in sediments. In: J.R. Kramer and H. E. Allen,
(eds) Metal speciation: Theory, Analysis and application,
Lewis Publishers, Chelsea, MI, USA, pp 183–199.
Rauret, G.R., Rubio, R. and Lopez-Sanchez, J.F.1989.
Optimization of Tessier procedure for metal solid speci-
ation in river sediments. Int. J. Envir. Anal. Chem., 36,
69–83.
Rauret, G.R., Lopez-Sanchez, J.F., Sahuquillo, A., Rubio,
R., Davidson, C., Ure, A. and Quevauviller, P. 1999.
Improvement of the BCR three step sequential extraction
procedure prior to the certification of new sediment and
soil reference materials. J. Envir. Monitor, 1, 57–61.
Ure, A., Quevauviller, P., Muntau, H. and Griepink B. 1983.
Speciation of heavy metals in soil and sediments. An
account of the improvement and harmonization of extrac-
tion techniques undertaken under the auspices of the BCR
of the CEC. Int. J. Envir. Analyt. Chem., 51, 135–151.
Sakata, M . 1983. Simple and rapid methods for the deter-
mination of 10 heavy metals in sediments, Central
Research Institute of Electric Power Industry Report, E
2, 83001.
Wedepohl, K.H. 1972. Handbook of geochemistry, Springer
Verlag, Berlin, Heidelberg, New York, pp.227–247.
Sposito, G., Lund, J. and Chang, A.C. 1982. Trace metal
chemistry in arid-zone field soils amended with sewage
sludge: I. Fractionation of Ni, Cu, Zn, Cd and Pb in solid
phases. Soil Sci. Soc. Am. J., 46, 260–164.
Welte, B.N. and Montiel, A. 1983. Study of the different
methods of speciation of heavy metals in the sediments:
II. Applications. Environ. Technol. Lett., 4, 223–238.
Wu, J., Laird, D.A. and Thompson, M.L. 1999. Sorption and
desorption of copper on soil clay components, J. Envir.
Qual., 28, 334–338.
Stamoulis, S., Gibbs, R.J. and Menon, M.G. 1996.
Geochemical phases of metal in Hudson River estuary
sediments. Envir. Int., 22, 185–194.
www.scilet.com