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Transcript of V. Rajeswari-Ph.D. (Physics) Thesisshodhganga.inflibnet.ac.in/bitstream/10603/45182/5/c5.pdf111 Fe,...
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Chapter 5
HEAVY METAL ANALYSIS
5.1. INTRODUCTION
Heavy metals are the chemical elements found in all kinds
of soils and sediments mostly with density greater than 5 g dm-1, the
very low general level of their content in soils and plants as well as the
biological role of most of them are microelements (Lacatusu, 1998).
Many of these metals find their way into the living systems through
air, water and food and tend to accumulate in the body, some of them
even in minor ·concentrations threaten to affect the metal dependent
enzyme catalyzed reactions in the body. At least 11 metals are known
to be essential for living organisms and these are Fe, Cu, Zn, Co, Mn,
Cr, Mo, V, Se, Ni and Sn. Essential metals always function in
combination with organic molecules and most commonly with proteins
either tightly bound in metallo-proteins or more loosely bound in
metal protein complexes (Brouwer et al., 1986). There is little evidence
that marine organisms ever suffer from metal deficiencies and
presumably the optimum concentrations are those that occur naturally.
Some heavy metals are essential to maintain human
metabolism, however, many may be poisonous at higher concentrations
(greater than the permissible limit), as they tends to bio-accumulate in
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human bodies making them dangerous and thereby poses great
health and environmental risks. The toxicity of heavy metals causes
morphological abnormalities, neuro-physiological disturbances, genetic
alteration of cell (mutation), terato-genesis and carcinogenesis.
In addition, heavy metals effect on enzymatic and hormonal activities
reduces growth and increases mortality (Idris, 2008).
Coastal and estuarine regions are the important sinks for
many persistent pollutants and they accumulate in organisms and
bottom sediments (Szefer et al., 1995). Sediments are essential
components of terrestrial and marine ecosystem. The marine sediments
are considered as sensitive indicators of both organic and inorganic
contamination in both spatial and temporal trends for monitoring the
marine environment (Larsen and Jensen, 1989). Sediments are important
carriers of heavy metals in the hydrological cycle because metals are
partitioned with the surrounding waters and they reflect the quality of
an aquatic system. Sediment-associated metals have the potential to be
ecotoxic due to their mobility and bioavailability, and this in turn affects
both ecosystems and human life through a process of bioaccumulation
and bio-magnification respectively (Buccolieri et al., 2006; Ip et al., 2007).
The analysis of heavy metals in marine sediments is
widely used to assess long-term anthropogenic inputs into the marine
environment (Fukushima et al., 1992; Ravichandran et al., 1995;
Li et al., 2010). The studies of metals like, Cr, Cd, Ni, Cu, Zn, Pb and
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Fe, which have an affinity for biota, and have nutrient-like distribution
in the oceans, are important. Metals such as Ni, Cd, Cr and Zn, etc.
are used in contamination studies in marine systems due to their
relationship with anthropogenic activities (Burton et al., 2004;
Munuz et al., 2004).
Metals enter the marine environment by two means:
natural processes (including erosion of ore-bearing rocks, wind-blown
dust, volcanic activity and forest fires); and processes derived from
human activities by means of atmospheric deposition, rivers, and
direct discharges or dumping (Clark, 2001). For some metals, natural
and anthropogenic inputs are of the same order (for example Hg and
Cd), whereas for others (for example Pb) inputs due to human
activities (Clark, 2001; Chatterjee et al., 2007). Once the metals are
released to the environment, they are transferred to the sediments
through adsorption onto suspended matter and subsequent
sedimentation (Hart, 1982).
Heavy metal contamination in terrestrial and aquatic
environments has significantly increased since the onset of the
industrial revolution (Forstner and Wittmann, 1981). The consequence
of heavy metal contamination is more serious in comparison to
organic or microbial contamination because heavy metals are cycled
between aqueous and particulate phases over a long period (Salomons
and Forstner, 1984).
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Heavy metals in the environment have many sources
(1) geologic weathering, (2) industrial processing of ores and metals,
(3) use of metals and metal compounds, (4) leaching of metals from
garbage and soil waste dumps, and (5) animal and human excrete
(Forstner and Wittmann, 1981).
Enrichment Factors are commonly used in the literature as
a means of identifying and quantifying human interference with global
element cycles. The geo-accumulation index (Igeo) was originally
defined by Muller (1979); Igeo is a quantitative measure of
contamination of aquatic sediments (Ridgway and Shimmield, 2002).
The spatial distribution of heavy metals in marine sediment
is of major importance in clarifying the pollution history of aquatic
systems (Rubio et al., 2001; Liu et al., 2003) and the study of the
seasonal variation of trace metals is important to assess the influence
of hydrographic changes because it plays a principal role in modifying
metals in sediments. It is therefore the goal of this study to provide
the spatial distribution and seasonal variation of trace metals in the
marine sediments from Visakhapatnam coast, Bay of Bengal, India.
5.2. REVIEW OF LITERATURE
Metals have exerted a profound influence on the course of
biological evolution, their modern day industrial usage, mainly during
the course of last fifty years has led to their bioaccumulation in the
environments (Moore and James, 1992).
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Valsecchi et al. (1995) reported that heavy metals appeared
to cause an alteration in the soil Carbon cycle, and modify energy
metabolism of soil Olicroflora leading to a decrease in the net
mineralization of soil organic matter. However other research has
shown that heavy metals at low concentrations, or inputs of heavy
metals with organic matter, stimulate bacterial growth and population
size (Dusek, 1995).
With the rapid industrialization and economic development
in coastal region heavy metals are continuing to be introduced to
estuarine and coastal environment around the world (Feng et al., 2004;
Romano et al., 2004; Santos et al., 2005).
Geochemical characteristics of the sediments can be used
to infer the weathering trends and the sources of pollution (e.g.,
Forstner and Salomons, 1980; Fedo et al., 1996; Nesbitt et al., 1996;
Nath et al., 2000). Therefore, chemical availability of metals on
sediments has been used to deduce the sources and pathways by
which major and trace elements have entered the marine environment
(Loring and Rantala, 1992).
Sediments are the main repository and source of heavy metals
in the marine environment and play an important role in the transport
and storage of potentially hazardous metals (Guevara et al., 2005;
Mason et al., 2006; Yu et al., 2009).
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Sediments are preferable monitoring ‘‘tools’’ since contaminant
concentrations are orders of magnitude higher and they show less
variation in time and space, allowing more consistent assessment of
spatial and temporal contamination (Tuncer et al., 2001; Beiras et al., 2003;
Caccia et al., 2003). Sediment analyses play an important role in
assessments of pollution status of marine environment.
Pollution of the natural environment by heavy metals is a
worldwide problem, because these metals are indestructible and most
of them have toxic effects on living organisms, when they exceed a
certain concentration (Nuremberg, 1984; Forstner, 1990; Harte et al., 1991;
Schuurmann and Market, 1998; MacFarlane and Burchett, 2000).
Arsenic, Cr, Cu, Mn, Ni and Fe are used as markers or
tracers of metal industries (Jervis et al., 1993; Nkono et al., 1999;
Kumar et al., 2001; Lin et al., 2002; Gallego et al., 2002; Loska et al., 2004).
Cadmium, Co, Pb, Sn, and Zn are known as the markers of
paint industries (Aksu et al., 1998; Yasar et al., 2001; Lin et al., 2002)
many of which are present in the study area.
Various studies have demonstrated sediments from coastal
areas greatly contaminated by heavy metals; therefore, the evaluation
of metal distribution in surface sediments is useful to assess pollution
in the marine environment (Jayaprakash et al., 2008; Pekey, 2006;
Buccolieri et al., 2006; Bellucci et al., 2002).
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Trace metals can be recirculated in the aquatic
environments via natural or anthropogenic processes and then back
to the water bodies, resulting in deterioration of the water quality and
long-term implication of human health and ecosystem (Fatoki and
Mathabatha, 2001; Ip et al., 2007).
The analysis of heavy metals in the sediments permits
detection of pollutants that may be either absent or in low
concentrations in the water column (Davies et al., 1991) and their
distribution in coastal sediment provides a record of the spatial and
temporal history of pollution in a particular region or ecosystem.
All heavy metals exert toxic effects at some concentration,
including mining, smelting, electroplating, and other industrial
processes that have metal residues in their wastes and by non-point
source surface runoff (Bakan and Ozkoc, 2007).
The accumulated potentially toxic metals are taken up by the
bottom-dwelling animals and their concentrations are seen increasing in
their tissues (Sulochanan et al., 2007; Rao et al., 2006, 2007, 2009;
Krishna Kumar et al., 2010) causing a threat to the ecosystem and
pose a risk to human health.
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The increasing heavy metals contamination of coastal
sediments is a cause of growing concern, since these elements are
highly persistent and may exert toxic effects at all levels of biological
organization from cells to population and community structure
(Chapman et al., 1988; Thompson et al., 2007; Koigoora et al., 2013).
Trace metal concentrations in sediments can be influenced
by variations in organic carbon content, grain size, carbonate and
sulfide content, Fe-Mn oxyhydroxide content (Adriano, 2001;
Roychoudhry, 2007), reduction/oxidation reactions, adsorption/
desorption, and physical transport or sorting, as well as anthropogenic
metal inputs (Luoma et al., 1997).
Studies on the Indian shelf region are limited when compared
to other regions of the world. Considerable work has been carried out
on the sediments of the west coast of India by Gogate et al. (1976)
Paropkari et al. (1978) and Bhosle et al. (1978), whereas, the inner
shelf of the Bay of Bengal of the east coast has received very much less
attention. Overall, the geochemical characters of surface sediments of the
Bay of Bengal, indicate that the metal distribution is mainly controlled
by their sediment texture and studies along the Visakhapatnam coast
(Satyanarayana et al., 1985; Raman, 1995), Puri to Port Novo
(Mohapatra et al., 1992), central east coast of India (Rao and Sarma, 1993)
and the Madras coast (Pragatheeswaran et al., 1986) were limited to
the northern part of the east coast of India.
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Jonathan and Rammohan (2003) reported that the
analyzed data confirms that metal pollution is a significant factor in
the coastal region off the Tuticorin coast, justifying the need for
suitable treatment plants as well as continued monitoring.
Jonathan et al. (2004) concluded that the heavy metals in
the sediments of Gulf of Munnar were indicative of the direct effect of
industrial discharge.
Alagarsamy (2006) studied the spatial and temporal
distribution of trace metals in surface sediments of the Mandovi
estuary and observed that the lowest metal concentrations during the
monsoon, compared to the pre- and post-monsoon.
Roychoudhry (2007) reported that minor variations in the
total trace metal content and depth profiles were observed seasonally,
despite drastic changes in the microbial activity, major ion chemistry
and in the vegetation pattern.
Sundararajan and Natesan (2010) reported that the heavy
metals in the Palk Bay sediments shown a relatively very low degree of
seasonal variation in the concentrations.
Various studies have demonstrated marine sediments from
industrialized coastal areas are greatly contaminated by heavy metals;
therefore, the evaluation of metal distribution in surface sediments is
useful to assess pollution in the marine environment (Salomons and
Forstner, 1984; Bellucci et al., 2002; Buccolieri et al., 2006).
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Based on examination of the Namibian shelf sediments,
major and trace element geochemistry reflects the complex
intermixture of several sedimentary components of minor metal
enrichments (Calvert and Price, 1983).
Detailed study on the surface sediments and mineralogical
composition of Sulu Sea and South China sea revealed that the
sediments are carbonate rich and the compositional variability of the
sediments is controlled to some extent by variations in sediment
supply from adjacent land mass (Calvert and Pederson, 1993).
Taliadouri and Varnavas (1995) observed an increase in trace
metal concentration in surface sediments from Thermaikos Gulf, mainly
attributable to sewage outfall, the industrial zone and the river input.
Valdes et al. (2005) concluded that the higher
concentrations of heavy metals in the Mejillones Bay surface
sediments might be associated with the flux of organic matter and the
water column’s persistent strong hypoxic environmental conditions.
Choi et al. (2006) suggested that the limited water flow and
reduced flushing have been proposed elsewhere as promoting heavy
metal pollution of sediments in constricted parts of estuaries.
Preda and Cox (2002) reported that all trace metals in
sediments of Coastal Pumicestone region, Australia were controlled by
the presence of Fe and Mn oxides, and the grain size of the sediment.
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5.3. SAMPLE PREPARATION AND EXPERIMENTAL PROCEDURE
The sediment samples collected along Visakhapatnam
coast; Lawson’s Bay in the north and Appikonda Beach in the south,
Bay of Bengal, India during three seasons viz., post-monsoon
(December 2009), pre-monsoon (May 2010) and monsoon (September
2011) were dried at 40°C, homogenized and powdered using an agate
mortar. About 0.5 g of the sediment sample was accurately weighed
into pre-cleaned glass vessel and digested at room temperature with
HNO3/HClO4 (4:1) mixture for 24 hours. Following, the suspensions
were evaporated at 120ºC until dryness. Then, 10% HNO3 was added
to residues. The final suspensions were filtered through Whatmann
Grade ‘A’ filter paper. The solution was transferred into a polyethylene
volumetric flask and diluted with Milli-Q water to 100 ml. One
milliliter of the solution was then diluted to 10 ml by adding HNO3
(Walting, 1981). Metal concentrations (Fe, Cd, Cr, Cu, Ni, Pb and Zn)
were measured using Inductively Coupled Plasma Optical Emission
Spectroscopy (ICP-OES, Perkin-Elmer, Optima 2100 DV, U.S. EPA
Method 6020, 1996) at Centre of Advanced study in Marine Biology,
Annamalai University (Plate 5.1). Suitable internal chemical standards
(Merck, Germany) were used to calibrate the instrument. Precision
and accuracy of the metal analysis were checked against the marine
sediment Standard Reference material from NIST. All glass wares and
plastic containers were washed with 10% nitric acid solution and
rinsed thoroughly with Milli-Q water.
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Plate 5.1. Photograph of ICP-OES
5.4. METHODS FOR ESTIMATING POLLUTION IMPACT
Number of calculation methods have been used for
quantifying the degree of metal enrichment in sediments by many
authors (Salomons and Forstner, 1984; Muller, 1969; Hokanson, 1980).
They have proposed pollution impact scales or ranges to convert the
calculated numerical results into broad descriptive bands of pollution
ranging from low to high intensity.
5.4.1. Enrichment factor (EF)
In the present study, enrichment factor was used to assess
the level of contamination and the possible anthropogenic impact in
sediments. To identify anomalous metal concentration, geochemical
normalization of the heavy metals data to a conservative element,
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such as Al, Fe, and Si was employed. Several authors have successfully
used iron to normalize heavy metals contaminants (Schiff and
Weisberg, 1999; Baptista Neto et al., 2000; Mucha et al., 2003). In this
study iron has used as a conservative tracer to differentiate natural
from anthropogenic components. According to Ergin et al. (1991) the
metal enrichment factor (EF) is defined as follows
Sample
Upper crustal average
Me
FeEF
Me
Fe
where, (Me/Fe)sample is the metal to Fe ratio in the samples,
(Me/Fe)Upper crustal average is the metal to Fe in the continental crust
(Wedepohl, 1995).
5.4.2. Index of geo-accumulation
To understand the current environmental status and the
extent of metal contamination with respect to natural environment,
other approaches should also be applied. A common criterion to
evaluate the intensity of heavy metal pollution in sediments is the geo-
accumulation index (Igeo), which was originally defined by Muller (1969)
to determine metals contamination in sediments, by comparing
current concentrations with pre-industrial levels and can be
calculated by the following equation
2log1.5
CnIgeo
Bn
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where, Cn is the measured concentration of the examined metal; Bn is
the background value of the metal n (Wedepohl, 1995) and the factor
1.5 is used to minimize the effect of possible variations in the
background values, which may be attributed to lithogenic variations
in the sediments for a given metal in the environment, as well as very
small anthropogenic influences (Ruiz, 2001).
5.5. RESULTS AND DISCUSSION
5.5.1. Spatial and seasonal distribution of trace metals
The spatial distribution and seasonal variations of major (Fe)
and some trace metals (Cd, Cr, Cu, Ni, Pb and Zn) in surface
sediments from Visakhapatnam coast collected in three different
seasons viz., post-monsoon, pre-monsoon and monsoon seasons are
shown in Figs. 5.1 to 5.7(a-c).
Iron (Fe)
Iron is the most abundant and consistent transition metal,
is also probably the most well-known metal in biological systems.
Recent evidences indicate that iron is an essential nutrient limiting
phytoplankton production in ocean (Coale et al., 1996) as well as in
some coastal upwelling environments (Hutchins and Bruland, 1998;
Firme et. al., 2001). The spatial distribution maps of Iron in post-
monsoon, pre-monsoon and monsoon seasons are shown in Fig. 5.1a-c.
The concentrations of Iron in the surface sediments of Visakhapatnam
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coast during post-monsoon varied between 1,782 and 11,392 µg/g,
while it varies in the range of 1,516 to 8,504 µg/g during pre-monsoon
and it varies in the range 670 to 8,748 µg/g during monsoon.
The maximum concentration was measured at V1, near Lawson’s bay
during post-monsoon and minimum was measured at V14, near
harbour during monsoon. The average concentration of Fe was higher
during Pre-monsoon compared to other two seasons. Concentrations
of Fe decreased seaward during post-monsoon and it increased seaward
during pre-monsoon and monsoon seasons. High concentrations of Iron
were observed in the northern region during post and pre-monsoon
seasons and it was observed in the southern region during monsoon.
Cadmium (Cd)
Cadmium is a very bio-tonic element, it has no biological
function and it is a highly toxic non-essential metal. The spatial
distribution maps of cadmium in post-monsoon, pre-monsoon and
monsoon seasons are shown in Fig. 5.2a-c. The concentrations of
cadmium in the shelf sediments of Visakhapatnam during post-
monsoon varied between 0.04 and 0.76 µg/g, while it varies in the
range of 0.04 to 0.36 µg/g during pre-monsoon and it varies in the
range 0.24 to 1.00 µg/g during monsoon. The maximum concentration
was observed at V19, near Gangavaram port during monsoon and
minimum was observed at V27, near AK beach during post-monsoon
and at V20 and V22, near Gangavaram port during pre-monsoon. The
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average concentration of Cadmium was higher during monsoon
compared to other two seasons. Concentrations of Cd decreased
seaward during post-monsoon and it increased seaward during pre-
monsoon and monsoon seasons. High concentrations of Cadmium
were observed in the northern region during post and pre-monsoon
seasons and it was observed in the southern region during monsoon.
The anthropogenic sources of cadmium in the study area includes the
primary uses of cadmium in electroplating other metals or alloys for
protection from corrosion, in photographic industry and in the
manufacture of storage batteries, pigments, glass ceramics and plastic
stabilizers. It was found that cadmium content is high in rock
phosphate, which is the raw material, for the manufacture of
phosphate fertilizers (Forstner and Wittmann, 1979).
Chromium (Cr)
Chromium is one of the least toxic of the trace elements on the
basis of it’s over supply and essentiality (Forstner and Wittmann, 1979).
Generally mammalian body can tolerate 100-200 times its total body
content of chromium without harmful effects. The spatial distribution
maps of chromium in post-monsoon, pre-monsoon and monsoon
seasons are shown in Fig. 5.3a-c. The concentrations of chromium in
the shelf sediments of Visakhapatnam during post-monsoon varied
between 27.26 and 58.50 µg/g, while it varies in the range of 10.16 to
30.66 µg/g during Pre-monsoon and it varies in the range 14.33 to
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62.27 µg/g during monsoon. The maximum concentration was
observed at V19, near Gangavaram port during monsoon and
minimum was observed at V19, near Gangavaram port during pre-
monsoon. The average concentration of Cr was higher during monsoon
compared to other two seasons. Concentrations of Cr decreased
seaward during post-monsoon and it increased seaward during
monsoon season. High concentrations of chromium were observed in
the northern region during post and pre-monsoon seasons and it was
observed in the southern region during monsoon. The anthropogenic
sources of chromium in Visakhapatnam coastal sediments are metal
plating, organic and petro-chemicals, fertilizers, petroleum refining
and industrial dyes. Of these sources, electroplating industry is the
major contributor of chromium.
Copper (Cu)
Copper is an essential micronutrient, which is widely
distributed in nature in free state as well as in combined state. It is
highly toxic to most aquatic plants. Inhibition of growth generally
occurs at 0.1 mg/l, regardless of test conditions and species. The
spatial distribution maps of copper in post-monsoon, pre-monsoon
and monsoon seasons are shown in Fig. 5.4a-c. The concentrations of
copper in the shelf sediments of Visakhapatnam during post-monsoon
varied between 8.40 and 47.32 µg/g, while it varies in the range
of 2.88 to 37.66 µg/g during Pre-monsoon and it varies in the range
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6.74 to 45.15 µg/g during monsoon. The maximum concentration was
observed at V1, near Lawson’s bay during post-monsoon and minimum
was observed at V19, near Gangavaram port during pre-monsoon.
The average concentration of Cu was higher during post-monsoon
compared to other two seasons. Concentrations of Cu decreased
seaward during post-monsoon and it increased seaward during
monsoon season. High concentrations of copper were observed in the
northern region during post and pre-monsoon seasons and it was
observed in the southern region during monsoon. One of the major
sources of copper in the study area is the contribution from the
anti-fouling paint for the hulls of ships (Clark, 2001). Copper is
characterized by strongly scattered anthropogenic influence. This
particularly relates to the uncontrolled waste dumps and liquid waste
from industries.
Nickel (Ni)
Nickel is essential at trace levels for human health (Moore
and Ramamoorthy, 1984). Acute toxicity arises from competitive
interaction with five essential elements calcium, cobalt, iron, copper
and zinc. Nickel can replace essential metals in the metallo-enzymes
resulting in the disruption of metabolic pathways (McGroth and
Smith, 1990). The spatial distribution maps of Nickel in post-monsoon,
pre-monsoon and monsoon seasons are shown in Fig. 5.5a-c. The
concentrations of Nickel in the shelf sediments of Visakhapatnam
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during post-monsoon varied between 17.76 and 34.04 µg/g, while it
varies in the range of 2.37 to 23.66 µg/g during Pre-monsoon and it
varies in the range 8.19 to 34.40 µg/g during monsoon. The maximum
concentration was observed at V3, near Lawson’s bay during monsoon
and minimum concentration was observed at V20, near Gangavaram
port during pre-monsoon. The average concentration of Ni was higher
during post-monsoon compared to other two seasons. Concentrations
of Ni decreased seaward during post and pre-monsoon seasons and it
increased seaward during monsoon season. High concentrations of
Nickel were observed in the northern region during post-monsoon and
monsoon seasons and it was observed in the southern region during
pre-monsoon. The connection between Ni and the nutrient cycle is
also reflected by high Ni contents found in marine organic matter
(Collier and Edmond, 1984). A third factor affecting Ni concentrations
in sediments is its tendency to bind to metals, especially sulfides to Fe
(pyrite). The anthropogenic sources of Nickel in the study area are the
use of Ni in steel and other alloys, electroplating, and batteries.
Lead (Pb)
Lead is ubiquitous in the environment, present usually in
small amounts from natural geological sources in all rock, soil, dust,
water and air. Lead is a non-essential metal and it is a highly toxic
metal. The spatial distribution maps of lead in post-monsoon,
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pre-monsoon and monsoon seasons are shown in Fig. 5.6a-c. The
concentrations of lead in the shelf sediments of Visakhapatnam
during post-monsoon varied between 16.20 and 36.08 µg/g, while it
varies in the range of 4.98 to 20.15 µg/g during Pre-monsoon and it
varies in the range 8.38 to 32.45 µg/g monsoon. The maximum
concentration was observed at V1, near Lawson’s bay during post-
monsoon and minimum concentration was observed at V22, near
Gangavaram port during pre-monsoon. The average concentration of
Pb was higher during post-monsoon compared to other two seasons.
Concentrations of Pb decreased seaward during post and pre-
monsoon seasons and it increased seaward during monsoon season.
High concentrations of lead were observed in the northern region during
post and pre-monsoon seasons and it was observed in the southern
region during monsoon. The relatively high acid-leachable Pb in the
surface sediments is mainly due to lead-based paint industries and
input of effluents from the thermal power plant very close to the coast
add additional stress to the high concentration of Pb (Jonathan and
Ram-Mohan, 2003; Velde et al., 2003). Increase in Pb concentrations
may be due to the direct input of nitrate compounds from external
sources, mainly from the aquaculture effluents, agricultural runoff
and domestic sewage (Purvaja and Ramesh, 2000; Subramanian, 2004).
129
Zinc (Zn)
Zinc is one of the most essential trace elements in the
human body. It is a constituent of all cells, and several enzymes
depend upon it as a co-factor. Concern has arisen because of the
intimate connection of zinc with cadmium in the geosphere and
biosphere. The spatial distribution maps of zinc in post-monsoon,
pre-monsoon and monsoon seasons are shown in Fig. 5.7a-c. The
concentrations of zinc in the shelf sediments of Visakhapatnam
during post-monsoon varied between 31.00 and 154.00 µg/g, while it
varies in the range of 8.56 to 49.94 µg/g during Pre-monsoon and it
varies in the range 9.40 to 77.60 µg/g monsoon. The maximum
concentration was observed at V5, near Lawson’s bay during post-
monsoon and minimum concentration was observed at V22, near
Gangavaram port during pre-monsoon. The average concentration of
Zn was higher during post-monsoon compared to other two seasons.
Concentrations of Zn decreased seaward during post and pre-
monsoon seasons and it increased seaward during monsoon season.
In all the three seasons, high concentrations observed in the northern
region of the study area. The anthropogenic sources of zinc in
Visakhapatnam coastal sediments are the input of organic wastes into
the sea, which comes from municipal sewage, contributes to the Zn
increase in sediments (Alagarsamy, 2006).
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Fig. 5.1. Spatial distribution of Fe in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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Fig. 5.2. Spatial distribution of Cd in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
132
Fig. 5.3. Spatial distribution of Cr in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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Fig. 5.4. Spatial distribution of Cu in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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Fig. 5.5. Spatial distribution of Ni in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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Fig. 5.6. Spatial distribution of Pb in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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Fig. 5.7. Spatial distribution of Zn in Visakhapatnam coast, Bay of Bengal, India
during (a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons
respectively
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5.5.2. Seasonal variations
The concentrations of trace metals indicate enrichment in
the samples which are very close to the shoreline and they vary in the
following order Fe > Zn > Cu > Cr > Pb > Ni > Cd (Pitchaimani et al., 2008).
Similar distribution patterns of Cd, Cr, Cu, Fe, Pb and Zn (except Ni)
indicate that the area is affected by coal fueled iron and steel
industries (Muthuraj and Jayaprakash, 2008). An important observation
is that, in general, lowest metal concentrations were found during the
pre-monsoon and monsoon seasons, compared to the post-monsoon
season.
Generally, post-monsoon is associated with increase of
metals, which become enriched in the accumulative phases of the
sedimentary material. Terrestrial transport appears to occur mostly
during monsoon, which is associated with higher river discharge and
bed-load movements. The concentrations of trace metals were decreased
seaward during post-monsoon, while it increased seaward during pre-
monsoon and post-monsoon seasons. Fe had high concentration
during pre-monsoon due to the spillage and transportation of iron
ores (Alagarsamy, 2006) in the harbour to the ships and also the low
flow conditions of the coastal waters in the study area which is
attributed to the change in current direction. Based on their average
concentration of trace metals, Cd and Cr were had high concentrations
during monsoon due to heavy rainfall, leading to high fluvial inputs
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which are carrying metals from industrial and agricultural wastes
might have been responsible for the increased concentration of Cd and
Cr in monsoon period (Padma and Periakali, 1998; Periakali and
Padma, 1998; Kamala-kannan et al., 2008). Cu, Ni, Pb and Zn had
high concentrations during post-monsoon due to the deposition of
these metals into the sediments from untreated effluents being
discharged into the coast via monsoonal runoff from Meghadrigedda
(Sarma et al., 1996) could be higher as the increased monsoonal water
flow. The point sources of metal pollution were mainly from thermal
power plant, Visakhapatnam steel plant, petrochemical industries,
fertilizer industries, paper mills, tanneries, polymers, lead and zinc
mining, zinc smelter, fertilizers, shipyard, metal alloy, shipping
industries, and oil refineries. Transportation to and from the
Visakhapatnam port and industrial activities also play a major role in
increasing the metal level in this region (Alagarsamy and Zhang, 2010).
In general, Cd, Cr and Ni levels were high in pre-monsoon, while Pb
and Cu were high in post-monsoon (Satyanarayana et al., 1995).
5.6. ENRICHMENT FACTOR
In order to determine, whether the trace metals were
originated from natural weathering processes or from anthropogenic
activities, enrichment factors were calculated for trace metals
concentrations in Visakhapatnam marine sediments measured for
three different seasons (post-monsoon, pre-monsoon and monsoon)
and were shown in Fig. 5.8a-c.
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Fig. 5.8. Spatial distribution of enrichment factors in three different seasons
(a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons respectively
140
The normalization technique enabled to assess the magnitude
of enrichment relative to naturally occurring concentrations rather
than relying on a limited number of measurements from the selected
areas (Alagarsamy et al., 2010). EF values less than 1.5 suggest that
the heavy metals may be entirely from natural weathering processes
and greater than 1.5 suggest an anthropogenic source. The EF values are
interpreted as the levels of metal pollution suggested by Chen et al. (2007).
Chen et al. (2007), suggested that EF < 1 indicates no
enrichment, EF = 1-3 indicates minor enrichment, EF = 3-5 indicates
moderate enrichment, EF = 5-10 indicates moderately severe enrichment,
EF = 10-25 indicates severe enrichment, EF = 25-50 indicates very
severe enrichment, and EF > 50 indicates extremely severe enrichment.
As indicated by their respective enrichment factor (EF)
values, the enrichment of heavy metals in surface sediments from the
Visakhapatnam shelf were decreased during post-monsoon in the
order of Cd > Pb > Ni > Cu > Zn > Cr, while it decreased during pre-
monsoon in the order of Cd > Cu > Pb > Ni > Cr > Zn and it decreased
during monsoon in the order of Cd > Pb > Ni > Cr > Cu > Zn.
Enrichment of cadmium, chromium, nickel, lead in surface sediments
from Visakhapatnam was higher during monsoon than pre-monsoon
and post-monsoon seasons, while Enrichment of copper and zinc was
higher during post-monsoon than pre-monsoon and monsoon seasons.
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The high proportions of Pb, Cd and Zn imply that the
sediments are contaminated by the offshore drilling activities,
atmospheric deposition of finer particles, domestic effluent discharges
and the extensive use of paints (Yasar et al., 2001; Lin et al., 2002).
Enrichment of Cd, Pb and Ni could be due to the operation of
numerous oil refineries in the study area and also the shallow nature
of the offshore region facilitating the deposition of trace metals and
also due to the north-south long shore currents which are obstructed
and terminated in this region. The wave action process might help in
transportation, deposition and enrichment of trace metals from the
heavily industrialized region in the northern part of southeast coast of
India. Moreover, the higher values are also due to the dynamic
movement of finer sediments, local industrial activities and movement
of fishing/commercial vessels in this region.
5.7. INDEX OF GEO-ACCUMULATION (Igeo)
To find out the contamination level of heavy metals in
marine sediments, Index of geo-accumulation was calculated and is
shown in Fig. 5.9a-c.
On the basis of average Igeo values, the contamination by
heavy metals in surface sediments from Visakhapatnam shelf was in
the order of Cd > Pb > Ni > Zn > Cu > Cr during post-monsoon, while
it was in the order of Cd > Pb > Cu > Cr > Ni > Zn during pre-monsoon
and it was in the order of Cd > Pb > Ni > Cr > Cu > Zn during monsoon.
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Muller scale (Muller, 1981) of sediment quality description is shown in
Table 5.1, the calculated results of Igeo values (Fig. 5.9a-c) indicate
that Cd can be considered as a strong pollutant in this study area in
all the three seasons. Cd showed unpolluted to strongly polluted and
other metals showed unpolluted to moderately polluted situation in
this region. The high Igeo values identified for cadmium in the study
area indicate that the surface sediments are extremely contaminated,
probably as a result of anthropogenic activities and provide a useful
means of distinguishing between the natural and anthropogenic
sources of metal entering in to the coastal zone.
Table 5.1. Description of the sediment quality (Muller, 1981)
Igeo value Class Quality of sediment
< 0 0 Unpolluted
0-1 1 From unpolluted to moderately polluted
1-2 2 Moderately polluted
2-3 3 From moderately polluted to strongly polluted
3-4 4 Strongly polluted
4-5 5 From strongly to extremely polluted
> 5 6 Extremely polluted
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Fig. 5.9. Spatial distribution of geo-accumulation index in three different seasons
(a) post-monsoon, (b) pre-monsoon and (c) monsoon seasons respectively
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5.8. CONCLUSION
An important observation is that, in general, lowest metal
concentrations were found during the pre-monsoon and monsoon
seasons, compared to the post-monsoon season. The concentrations
of trace metals were decreased seaward during post-monsoon, while it
increased seaward during pre-monsoon and post-monsoon seasons.
Cu, Ni, Pb and Zn had high concentrations during post-monsoon due
to the deposition of these metals into the sediments from untreated
effluents being discharged into the coast via monsoonal runoff from
Meghadrigedda could be higher as the increased monsoonal water
flow. The high EF and Igeo values identified for cadmium in the study
area indicate that the surface sediments are extremely contaminated,
probably as a result of anthropogenic activities and provide a useful
means of distinguishing between the natural and anthropogenic
sources of metal entering in to the coastal zone.