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Bioavailability of Metals in Estuarine Sediments and Their Possible Impacts on the Environment


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Mangroves and mudflats, important sub environments within the estuaries, are rich in nutrients and are potential sources for flora and fauna and thus provide shelter to thousands of animal and plant species. The sediments in these sub-environments composed of different geochemical phases that act as potential binding sites for metals. The metals are present in various forms and metal bioavailability includes metal species that are bio-accessible. A modified sequential extraction procedure, screening quick reference table, sediment quality guidelines as standard approaches are available to quantify different forms of metals. Our investigation revealed that Mn values are above Apparent effects Threshold (AET), indicating Mn is bioavailable and toxic to biota in mudflats of many estuaries in India. Among the trace metals Co and Zn show higher bioavailability. Distribution pattern of bioavailable metals can also be used to understand anthropogenic input to the estuaries and their mobilization.
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Mangroves and mudats, important sub environments within the estuaries, are rich in nutrients and are potential sources for ora and fauna and thus
provide shelter to thousands of animal and plant species. The sediments in these sub-environments composed of different geochemical phases that act as
potential binding sites for metals. The metals are present in various forms and metal bioavailability includes metal species that are bio-accessible. A modied
sequential extraction procedure, screening quick reference table, sediment quality guidelines as standard approaches are available to quantify different
forms of metals. Our investigation revealed that Mn values are above Apparent effects Threshold (AET), indicating Mn is bioavailable and toxic to biota in
mudats of many estuaries in India. Among the trace metals Co and Zn show higher bioavailability. Distribution pattern of bioavailable metals can also be
used to understand anthropogenic input to the estuaries and their mobilization.
estuaries which are formed wherever the tidal range is between 2 to
4 m. ese estuaries have meandering characteristics. Macrotidal
estuaries which are formed wherever there are strong tidal currents
(tidal range is more than 4 m). ese are trumpet in shape.
e estuaries are complex systems which receive inputs from
dierent sources like land derived material through river, banks,
marine, atmosphere etc. e river waters that mix with sea water
in estuaries varies with the rate of freshwater discharge from the
drainage basin and with the geological and geochemical characters
of each drainage basin. Estuaries are the favourable environments
of deposition of sediments derived from both the catchment area
(terrestrial) and the marine sources. So, the sedimentation in estuaries
is within three distinguishable regimes viz. estuarine uvial, estuarine
brackish and estuarine marine. Fine sedimentary deposits or mud are
a characteristic feature of estuaries. e most signicant sorting is the
coarse (gravel and sand), which are found in the more energetic areas
and ne (silt and clay) sediments, which accumulate in low energy
conditions or quite waters. It is also necessary to mention here that
the sediments are composed of dierent geochemical phases such
as clay, silt, sand, organic material, oxides of iron and manganese,
carbonate and sulphide complexes that act as potential binding sites
for metals entering an estuarine system. In the sediments, metals can
e coastal zone is characterized by variety of landforms like
estuaries, lagoons, beaches, islands. Estuaries are one of the important
sub environments of the coastal zone. Estuaries are rich in nutrients
and are potential sources for ora and fauna and thus provide shelter
to thousands of animal and plant species. Estuaries are coastal bodies
of water, occupying an existing river valley and their characters are
typied by the discharge of rivers and therefore they are regarded
as complementary extensions of rivers. Estuarine regimes are
governed by several factors such as river inow, tides, waves, wind
and meteorological forces making the system more complicated and
dynamic thus temperature, salinity and turbidity uctuate on daily,
fortnightly and seasonal basis and reach more extremes in estuarine
waters than they do at sea or in rivers.
Pritchard [1] dened an estuary as ‘’An estuary is a semi enclosed
coastal body of water, which has a free connection with the open sea,
and within which sea water is measurably diluted with fresh water
derived from land drainage’’. Estuaries are classied based on tides,
as Microtidal estuaries which are formed wherever the tidal range is
less than 2 m and are dominated by freshwater discharge, which leads
to ‘’salt wedge’’ type estuary. ese are highly stratied. Mesotidal
Volume 2, Issue 1 - 2015
© G. N. Nayak 2015
Bioavailability of Metals in Estuarine Sediments
and eir Possible Impacts on the Environment
Research Article
G. N. Nayak*
Department of Marine Sciences, Goa University, Goa - 403 206, India
*Corresponding author: Dr. G. N. Nayak, Department of Marine Sciences, Goa University, Goa - 403 206, India, E-mail:
Article Information: Submission: 10/02/2015; Accepted: 14/03/2015; Published: 19/03/2015
Citation: Nayak GN. Bioavailability of Metals in Estuarine Sediments and Their Possible Impacts on the Environment . J Environ Soc Sci. 2015;2(1): 105.
e fractions can be digested in Teon beakers using the
combination of HF, HClO4 and HNO3. e digested samples can be
analyzed for various metals on Varian 240FS model Atomic
In recent years, there has been increasing concerns about
pollutants entering the aquatic environment. A need to discover
simple and reliable pathways to monitor levels of particular metals
or other pollutants in the aquatic environment has resulted in a
proliferation of studies. Jonathan et al. [4] studied recent sediments
o Gulf of Mannar along the southeast coast of India and their studies
revealed the enrichment of Cr, Pb, Cd, Cu, Ni, and Zn and indicated
that the area has been contaminated by riverine sources and industries
nearby. Alagarsamy [5] had studied the seasonal distribution of trace
metals such as Fe, Mn, Co, Cu, Zn and Pb in the Mandovi Estuary,
west coast of India. His results revealed that the surface sediments of
Mandovi Estuary are moderately or strongly contaminated to some
extent by Fe and Mn. Cu and Zn showed the inuence of organic
wastes from municipal sewage entering into the estuary, in the river
mouth region. Janaki - Raman et al. [6] have reported that the trace
metals in sediments of Muthpet mangroves, South - East Coast
of India are diagenetically modied and anthropogenic processes
control Pb and to some extent Ni, Zn and Fe. Nayak et al. [7] have
studied the abundance and distribution of total suspended matter
(TSM) from Mandovi and Zuari estuaries in three dierent seasons
over the last seventeen years. ey have reported that in Zuari estuary,
TSM concentration increased in both surface and bottom waters from
year 1991 to 2004. Recently, Department of Marine Sciences of Goa
University under the research project “Reading pollution history,
paleoclimate and sea level changes from the study of mudats, central
west coast of India’ has carried out a detailed study on mudats along
central west coast of India [8-11].
Mud deposition is characteristic of protected low energy
environments such as estuaries and lagoons. is occurs in the
intertidal zone where regular and increased depth of ooding prevents
salt tolerant plants growing. Intertidal mudats are a prominent
geomorphological component of estuaries and the development of
an estuarine mudat is both complex and dicult to predict because
of the multiple relationship between the physical, chemical and
biological properties of the sediment. Further, due to their potential
role as contaminant storage areas, mudats tend to release heavy
metals into the estuarine waters by various chemical, physical and
biological processes which may facilitate mixing and remobilization
Speciation of metals is the identication of metals that are bound
to dierent components of the sediment [12] and the phases have
been dened [2,13]; as exchangeable ions, adsorbed ions / carbonates,
Fe and Mn oxides, sulphides / organics and metals bound to
lithogenic minerals and residual. Bioavailable metal fractions include
Exchangeable fraction which consist of metals bound to colloidal or
particulate material. Generally, clay and organic matter controls ionic
exchange thus responsible for availability of metal in exchangeable
metal form. Further it is understood that pH plays an important role
in governing concentrations of soluble metals. Mn solubility is low at
high pH and with high organic matter content, while in acid soils with
be present in various forms and generally exhibit dierent physical
and chemical behaviour in terms of chemical interactions, mobility,
biological availability and potential toxicity. erefore, the fate
of various metals, in the natural environment is of great concern.
Metals may be partitioned into six fractions: dissolved, exchangeable,
carbonate, iron-manganese oxide, organic, and crystalline. e
metal bioavailability includes metal species that are bio-accessible
and are absorbed or adsorbed by an organism with the potential for
distribution, metabolism, elimination, and bioaccumulation.
e sediment samples may be surface and/or subsurface can be
collected from sub-environments like mudats, mangroves etc. within
estuaries using a hand driven PVC coring tube. Representative of
each sub-sample can be powdered by using an agate mortar and pestle
for geochemical analysis. A modied sequential extraction procedure
[2] can be adopted to quantify the metals in dierent operationally
dened geochemical phases. e steps involved in separating the
phases are detailed below.
Fraction 1: It is a soluble / exchangeable fraction in which the
contaminants are weakly adsorbed to the clays and organics in the
sediment via electrostatic attraction. From a biological availability
point of view, metals in this fraction are readily available [2].
Magnesium chloride is an eective reagent for desorbing adsorbed
trace metals.
Fraction 2: In this fraction the contaminants are bound to
carbonates. e metals are very susceptible to changes in temperature
and pH of the solution and therefore the next most readily available
[2]. Buered acetic acid and sodium acetate was applied to leach the
metals in this fraction.
Fraction 3: In this fraction the contaminants are bound to Fe and
Mn oxy- hydroxides. ey exist in sediment as cement, nodules and
concretions and tend to be thermodynamically unstable in anoxic
conditions. ey are most susceptible to changes in Eh (increased
availability at low Eh). ese contaminants are most biologically
available under reducing conditions [2].
Fraction 4: e contaminants here are bound to various forms
of organic matter with strong bonds. Metals in this fraction may be
associated with organic matters, such as organic coatings on inorganic
particles including biotic detritus. Under oxidising conditions, these
contaminants are released upon degrading the organic matter.
Contamination in the Organic matter fraction is the least biologically
available [2] among the rst four phases. Stability of the metals in this
fraction is high when compared with above three fractions and thus
incorporation in geochemical cycle is dicult. Hydrogen peroxide in
acid medium used to oxidise organic matter whereas, Ammonium
acetate is used to prevent adsorption of extracted metals on the
oxidized sediment.
Fraction 5: Residual fraction includes metals incorporated into
the crystal structure of the primary and secondary minerals. ese
contaminants are not biologically available and can only be released
with the use of a very strong acid such as HF [2,3]. Metals in this
fraction are inert and may not take part in the biochemical or chemical
reactions under normal environmental conditions.
Citation: Nayak GN. Bioavailability of Metals in Estuarine Sediments and Their Possible Impacts on the Environment . J Environ Soc Sci. 2015;2(1): 105.
low organic matter its solubility and availability is high. e solubility
of Mn is high at pH above 6 in anaerobic condition. Metals associated
with carbonate minerals constitute the carbonate fraction, which can
be newly precipitated in soil. e element in carbonate fraction would
be released more into the environment if the conditions became more
acidic. e co-precipitation with carbonate minerals is of importance
for a number of metals in addition to Mn which includes Zn and
Pb. e iron-manganese oxide fraction consists of metals adsorbed
to iron-manganese oxide particles or coatings. Fe-Mn oxide fraction
includes the metal oxides/hydroxides soluble under slightly acidic
pH, as well as the metals associated with reducible amorphous Fe-
Mn Oxy-hydroxides. Metals from this fraction are released into the
environment with a decrease in pH and if sediments change from oxic
to anoxic condition. e organic fraction consists of metals bound to
various forms of organic matter. Most metal hydroxide minerals have
very low solubility under pH conditions in natural water. Adsorption,
which occurs when dissolved metals are attached to surfaces of
particulate matter (notably iron, manganese, and aluminium oxide
minerals, clay, and organic matter), is also strongly dependent on
pH and, of course, the availability of particulate surfaces and total
dissolved metal content. erefore, organic matter/Sulphide fraction
represents the amount of metals bound to the organic matter and
sulphides that would be released into the environment if conditions
became oxidative. However, the intensity of complexation is found to
vary progressively with the metal concentration, with high-intensity
sites being lled rst, followed by sites of lower intensity. Residual
fraction named as inert phase, corresponds to that part of the metal,
which cannot be mobilized.
Dessai and Nayak [14] had studied speciation of metals in Zuari
estuary and reported that Mn and Co are higher in concentration in
exchangeable fraction. Li et al. [15] had studied the metal distribution
in the coastal wetland of the Pear River Estuary, China, and they
have reported higher content of Cd and Zn in the exchangeable
fraction indicating their ecological risk. Farkas et al. [16] had studied
chemical speciation by using sequential extraction procedure and
also evaluated geoaccumulation Index of the sediments to assess the
heavy metal pollution in surface sediments of the River Po.
Further, Buchman [17] introduced Screening Quick Reference
Table (SQUIRT) for metals in marine sediments, which can be used
as a standard to declare the given estuarine sediments have reached
the threshold with respect to pollution of metals. Screening Quick
Reference Table (SQUIRT) developed by (NOAA) is presented in
Table 1. Based on SQUIRT, the guideline values are categorized into
ve classes which are also presented in the Table 2.
TEL: reshold eect level; ERL: Eect range low; PEL: Probable
eects level;
ERM: Eect range median; AET: Apparent eects threshold
(Except for Fe, all values are in ug/g)
When the speciation data is compared with SQUIRT (Table 1),
Mn shows values above AET indicating Mn is bioavailable and toxic
to biota in mudats of many estuaries in India. Among the trace
metals Co and Zn show higher bioavailability.
e metals in acid soluble fractions are considered to be the
weakest bonded metals in sediments which may equilibrate with the
aqueous phase, and thus become more easily bioavailable [18]. us,
metal speciation is of critical importance to their potential toxicity
and mobility [19]. A criterion called ‘‘Risk Assessment Code (RAC)’’
has been used to assess the potential mobility and hazard of metal
based on the percentage of exchangeable and bound to carbonate
metal in the sediment [20,21]. e metals in dierent fractions are
bound with dierent strengths in the sediments. If a sediment sample
can release in these fractions less than 1% of the total metal, it will
be considered safe for the environment. On the contrary, sediment
releasing in the same fractions more than 50% of the total metal has
to be considered highly dangerous and can easily enter into the food
chain. e classes based on RAC is given in Table 3.
Our studies have shown class III to V RAC for Mn, Co and Pb
Fe - - - - 22% (Neanthes)
Mn - - - - 260 (Neanthes)
Cu 18.7 34 108 207 390 (Microtox & oyster larvey)
Zn 124 150 271 410 410 (Infaunal community)
Cr 52.3 81 160 370 62 (Neanthes)
Co - - - - 10 (Neanthes)
Table 1: Screening quick reference table for metals in marine sediments [17].
Sediment guidelines
Threshold Effect Level (TEL) Maximum concentration at which no toxic effects are observed
Effects Range Low (ERL) 10th percentile values in effects or toxicity may begin to be observed in sensitive species
Probable Effects Level (PEL) Lower limit of concentration at which toxic effects are observed
Effects Range Median (ERM) 50th percentile value in effects
Apparent effects Threshold (AET) Concentration above which adverse biological impacts are observed
Table 2: Sediment guidelines and terms used in SQUIRT.
Citation: Nayak GN. Bioavailability of Metals in Estuarine Sediments and Their Possible Impacts on the Environment . J Environ Soc Sci. 2015;2(1): 105.
in some of the estuaries along west coast of India. e bioavailability
of Mn is higher with organic fraction as a major phase in some
areas. Mn association with carbonate fraction shows its ability to
replace calcium in carbonate minerals as a result of their similar
ionic radii and charges. Mn is also higher near surface compared
to subsurface. is could be due to Mn remobilization from the
reducing deeper sediment sections and accumulation in oxidized
surface sections. Distribution pattern of bioavailable metals can also
be used to understand anthropogenic input to the estuaries and their
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... Calcium carbonate in tropical estuaries is mostly originated from the continental shelf and calcareous shell material from organisms. Whereas metal complexing with organic matter may vary from weakly to strongly bound, association with carbonates is generally a weak binding event that is susceptible to changes in temperature and pH (Costa et al. 2015;Nayak 2015). Therefore, mobility and bioavailability of metals in the estuarine environment strongly depends on metal binding to carbon substrates present in sediments. ...
... In addition to natural Mn source, anomalous values are probably linked to harbor activities involving manganese ore shipment rather than the binding capacity of SMB sediments, as observed by the negative correlation with fine-grained fraction. Higher Mn contents in sediments from ARE result from the association with clay-sized particles and the abundant organic matter in this estuary relative to SMB, as observed in other studies in organic-rich estuarine sediments (Nayak 2015;Williams and Block 2015). The anomalous values for Cr in SMB and ARE indicated lithogenic sources that were deposited in sites more upstream and diluted downstream of each estuary; these values were also similar to observed results in other tropical estuaries in Brazil (Amorim et al. 2007). ...
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The present work aims to observe the spatial distribution of metals associated with carbon forms (fraction < 2 mm) in surface sediments of two macrotidal estuaries, São Marcos Bay and Anil River Estuary, which are located within the transition region between the Amazonian and the semi-arid northeast regions. Grain size, metal content (Al, Fe, Mn, Cu, Pb, Cr, Zn, and Ni), organic matter, and calcium carbonate content were determined. Grain size analyses showed the predominance of the sand-sized fraction < 2 mm due to the local hydrodynamic conditions. Anil River Estuary sediments exhibited high organic matter content due to both the mangrove outwelling and domestic sewage discharge. They also presented high calcium carbonate content as a result of abundant remnants of gastropod shells. Organic matter acted as the primary geochemical carrier for most metals in both estuaries, while calcium carbonate acted as the secondary carrier. Enrichment factors indicated Mn sediment contamination in São Marcos Bay and Fe, Pb, and Zn contamination in the Anil River Estuary. These results also suggest that São Marcos Bay is influenced by harbor activities, mostly ore shipment, whereas Anil River Estuary sediments are enriched in these metals as a result of domestic and hospital effluents reaching the urbanized drainage basin.
... Trace metals gather in sediments in different forms are probable to be mobilized and become toxic in the environment in the path of utilization (Wen et al. 2016). Trace metals within the exchangeable or carbonate-bond portions emitted from sediments, approximately 1% is regarded safe to the ecosystem, and more than 50% of the total quantity may constitute an immense risk and perhaps through the food chain (Nayak 2015). ...
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This study reports the concentrations of trace metals in core sediments profile from the coastal and four rivers estuary in the Kuching Division of Sarawak, Malaysia, and the controlling mechanisms influencing their availability in sediments of the studied area. The bonding of trace metals with non-mobile fractions was confirmed with the sequential extraction. Inductively coupled plasma–optical emission spectroscopy (ICP–OES) was used to measure the concentrations of the trace metals. Granulometric analyses were performed using normalized sieve apertures to determine the textural characteristics of the sediments. Enrichment factor was used to evaluate the level of metal enrichment. Heavy metals concentrations in sediment samples varied in the range: Pb (8.9–188.9 mg/kg d.w.), Zn (19.4–431.8 mg/kg d.w.), Cd (0.014–0.061 mg/kg d.w.), Ni (6.6–33.4 mg/kg d.w.), Mn (2.4–16.8 mg/kg d.w.), Cu (9.4–133.3 mg/kg d.w.), Ba (1.3–9.9 mg/kg d.w.), As (0.4–7.9 mg/kg d.w.), Co (0.9–5.1 mg/kg d.w.), Cr (1.4–7.8 mg/kg d.w.), Mg (68.8–499.3 mg/kg d.w.), Ca (11.3–64.9 mg/kg d.w.), Al (24.7–141.7 mg/kg d.w.), Na (8.8–29.4 mg/kg d.w.), and Fe (12,011–35,124.6 mg/kg d.w.). The estimated results of the enrichment factor suggested enrichments of Pb, Zn, and Cu in all the core sediment samples and depths at all sites. The other trace metals showed no enrichments in almost all the sampled stations. Continuous accumulation of Pb, Zn, and Cu metals over a period can be detrimental to living organisms and the ecology. The results obtained from the statistical analyses suggested that the deposition of trace metals in the studied sites is due to anthropogenic inputs from the adjacent land-based sources.
... HMs accumulate in sediments in various forms; some of them are likely to be mobilized and become environmentally toxic in the course of utilization (Wen et al. 2016). Within the exchangeable or carbonates-bond fractions of heavy metals released from sediments, only \ 1% is considered safe to the environment, and over 50% of the total amount may pose a high risk and possibly enter the food chain (Nayak 2015). ...
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Concentrations of seven heavy metals (HMs): Zn, Cu, Pb, Cd, Ni, Cr, and Fe in core samples of bottom sediments from four retention tanks (RTs) located along the Strzyza Stream in northern Poland (Gdansk) were measured to obtain a general view of sediment quality. The recognition of contamination and potential environmental impacts is the main aim of this paper. A total of 96 sediment samples were collected from eight sampling sites at depths of 0-2 cm, 8-10 cm, 16-18 cm, 24-26 cm. Concentrations of Cu, Zn, Pb, Fe, Ni, and Cr were measured with AAS while Cd concentration was measured with ICP-MS. Granulometric analyses with normalized sieve apertures were carried out. Geochemical indices: enrichment factor, anthropogenic factor, and modified degree of contamination (mCd) were used to assess the contamination level. Concentrations of HMs in sediments changed in the range: Cu (3.24-119 mg/kg d.w.), Zn (12.5-584 mg/kg d.w.), Pb (4.91-309 mg/ kg d.w.), Cd (0.003-0.716 mg/kg d.w.), Ni (1.57-25.8 mg/kg d.w.), Cr (2.45-74.5 mg/kg d.w.), and Fe (3993-63817 mg/kg d.w.). The sequential extraction verified the bonding of HMs with non-mobile fractions. Geochemical indices showed widespread pollution by Cu, Pb, Cd, and Zn. Cluster and factor analysis distinguished three related subgroups of HMs: Pb, Ni-Cr, and Fe-Cd-Cu-Zn, suggesting possible common source of each subgroup. Strongly contaminated sediments were distinguished in sediment cores in two middle stream RTs characterized by intense urbanization in their direct catchments.
... Fe (792.99 mg kg -1 ) and Cr (22.51 mg kg -1 ) levels found in Mugil curema can be related to its carnivorous feeding habit and the local geological conditions rich in ophiolites (Rodríguez-Meza et al. 2008). Moreover, Fe is considered to be an essential element for the transportation and functioning of blood (Voigt et al. 2015 (Nayak 2015). High average Zn levels in fishes (93.05 mg kg -1 ) are due to the biophilic property of the element (Moiseenko and Kudryavtseva 2000) and high physiological demand. ...
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Trace element (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd, As, Hg) concentrations were assessed in marine organisms (n = 52) sampled from the Magdalena Bay lagoon complex in Baja California Sur, Mexico, a pristine marine environment. The overall trend of metal concentrations (dry weight) in the organisms was found to be Fe > Zn > Cd > Cu > Mn > Pb > As > Hg > Ni > Cr > Co. Bivalve mollusks (53.83 mg kg⁻¹) contained twofold higher levels of metals than the finfishes (20.77 mg kg⁻¹). Calculated BioConcentration Factor (BCF) values showed that dissolved Mn is readily bioavailable to the organisms, whereas Biota Sediment Accumulation Factor (BSAF) indicated high values for Zn, Cu and Cd. Cd and As levels were observed to be increasing with the trophic levels. Toxic elements, namely Pb, Cd and As in the studied fish species were found to be higher than the values recommended for human seafood consumption. The study provides a comprehensive baseline report on trace element bioaccumulation in several marine organisms that will aid in developing effective conservation strategies of the highly biodiverse lagoon complex.
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A detailed study of sediment components and selected metals has been carried out in two mudflat cores collected from the creeks of Kalinadi Estuary, India, in order to assess the variations in distribution of sediment components, metals, and the controlling processes, including early diagenetic movements, if any. Grain size analyses reveal the possibilities of three episodes of deposition in a highly varying depositional environment with overall fining up of the cores. Organic carbon (OC) is comparatively high in muddy Core KM, which was collected from a more sheltered creek with a narrow mouth in the estuarine interior, than sandy Core KH, which was collected from a creek with a wide mouth nearer to the sea. Geochemical data show an upper zone of marked enrichment of all trace metals, including Fe and Mn, in both the cores. The variations in sediment components as well as associated metals between the two cores reveal variations in controlling factors including the morphology setup. The distribution of trace metals in Core KH are controlled by the proportions of finer fraction of sediments, degradation of organic carbon, and redox-sensitive Fe and Mn oxides, while the distribution of trace metals in Core KM are probably controlled by the finer sediments as well as by redox-sensitive Fe and Mn oxides.
Spatial and depth-wise distribution of sediment components, organic carbon and selected metals (Fe, Mn, Al, Ni, Cr, Co, Zn and Pb) is studied across upper and middle tidal flats from lower and middle estuarine regions of Kundalika Estuary, central west coast of India. Silt and clay form the major components in lower and middle estuary, respectively. Sand, silt, clay and organic carbon showed band-type distribution along the estuary. The sediment deposition over the years took place in varying hydrodynamic conditions in lower and middle estuarine regions. Upper flats of the lower estuary represent mud while middle flats of the lower estuary facilitated the deposition of sandy mud. Correlation results indicated the importance of clay and organic carbon in removal and trapping of metals at lower and middle estuary, respectively. Factor analysis indicated that the distribution of metals is largely controlled by Fe–Mn oxyhydroxides and organic carbon. The middle flats of the lower estuary showed an anthropogenic source for Ni, Cr and Co while middle flats of the middle estuary showed a mainly lithogenic source.
We have analysed the contents and speciation of Zn, Cd, Pb, Cu, Ni and Co in sediments taken in the Pisuerga river, that flows through the town of Valladolid and is polluted by industrial and municipal effluents. All heavy metals were determined by voltammetric methods, and their mean total contents were (in μgg−1): Zn, 245.49; Cd, 1.05; Pb, 18.77; Cu, 66.53; Ni, 46.51; and Co, 11.41. We also determined the % H2O, % loss at 800°C, % CaCO3, % organic matter and % organic N for each sediment. All the data were examinated by principal components analysis in order to explain the behaviour of each metal and sampling point.The speciation was carried out by Tessier's method to find five metal categories: (a) adsorptive and exchangeable, (b) bound to carbonates, (c) bound to reducible phases, (d) bound to organic matter and sulphides and (e) residual metals. Cd and Pb, and to a lesser degree Zn, appeared in fractions (a), (b) and (c), whereas Cu, Ni and Co were mainly found in fractions (c) and (d). The residual metal fractions, taken as a guide for pollution, were found to be similar to the ones obtained in rivers belonging to our same European zone.
Present study provides results of trace metal distribution in mangrove sediment cores collected from macro-tidal Khonda and Dudh creeks of Northern Maharashtra coast, India. Most of the metals showed significant higher addition in Dudh creek (core DC) as compared to Khonda creek (core KC). However, Khonda creek sediments did show anthropogenic enrichment of Mn, Zn and Ni, while Dudh creek sediments showed anthropogenic enrichment of almost all the studied metals. Large difference in metal concentration between the two creeks was attributed to their proximity to industries. The higher Mn, Zn and Ni content in Khonda creek was mainly attributed to addition from domestic and agricultural wastes. While high deterioration of Dudh creek sediments was the outcome of addition from industrial effluents.
Conference Paper
The sediments in 228 sampling stations in the Northern Adriatic Sea covering an area as large as 1000 square kilometers, were collected by dredging. Heavy metal content (Cadmium, Cobalt, Copper, Lead, Zinc, Nickel, Chromium, and Berillium), were analyzed for geochemical speciation the inorganic matrix being determined by XRD and XRF Analysis. A method is presented for forecasting the envirotoxicity of sediment metal pollution. For each metal the mean risk assessment value (RAC) was calculated. The metal behavior is very different. For Cadmium and Zinc RAC exceeds 50% in area 2, 3 and 4 indicating those as very high risk areas. Zinc, again, and Berillium reach high RAC's in area 5. Chromium, Cobalt, Copper, and Nickel show RAC values less than 30% in all the areas considered indicating a medium environmental hazard. Due to the very low metal concentration, in some areas it has been impossible to calculate the RAC's. For Berillium, Cadmium, and Zinc the influence of Tagliamento and Livenza rivers seems to change the reactivity of the sediments so that they cannot complex the metal in a very effective way. In fact the two rivers carry large quantity of carbonates which bond metals weakly. The results for Cd are in good agreement with the data of Feiyong et al. but disagree with those of Welté et al. For other elements the findings are difficult to compare because of the different environment considered. In any case the proposed method seems to be useful for sediment classification in terms of enviroreactivity. This classification can be utilized, therefore, for preventive setting of new standards for metal-containing wastes discharged in marine and estuarine environments. In such a case the new standards will be able to avoid disruption of the ecosystem equilibrium.
The concentration and distribution of selected trace metals in surface sediments of the Mandovi estuary were studied to determine the extent of anthropogenic inputs from mining activities and to estimate the effects of the monsoon on geochemical processes in this tropical estuarine system. Analysis of bulk sediments from the Mandovi estuary shows that the concentrations of iron, manganese, cobalt, copper, zinc and lead vary from 2.2 to 49.7%; <Detection Limit (DL)–1.61%; 2.5–45.3 μg g−1; 11.5–77.5 μg g−1; 19.9–83.5 μg g−1; and 4.5–46.5 μg g−1, respectively. An important observation is that, in general, lowest metal concentrations are found during the monsoon, compared to the pre- and post-monsoon. Comparison of the metal levels in the sediments from different areas of the estuary indicates that there is a detectable anthropogenic input to the Mandovi estuary. The enrichment of Fe and Mn reflects the intensity of anthropogenic inputs related to iron ore processing in the upstream region of the estuary, however, the highest enrichment levels were not found near the mouth region. Igeo values calculated for Fe (2.5) and Mn (3.4) showed higher values in the pre-monsoon period in the upstream region of the estuary than in the post-monsoon and monsoon seasons. Cu and Zn enrichment in the river mouth region, associated with high organic carbon contents, is indicative of the influence of organic wastes from municipal sewage entering the estuary. The intermetallic relationship revealed the identical behaviour of metals during its transport in the estuarine environment.
The Gulf of Mannar along the Tuticorin coast is a coral base of the southeast coast of India. To obtain a preliminary view of its environmental conditions, geochemical distribution of major elements (Si, Al, Fe, Ca, Mg, Na, K, P), trace elements (Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd) and acid leachable elements (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd) were analyzed in surface sediment samples from two seasons. Geochemical fractionation confirmed the lithogenic origin of metals, which were mainly associated with the detrital phase. The sediments in the gulf are sandy with abundant calcareous debris, which controls the distribution of total and acid leachable elements. Enrichment factors relative to crust vary by a magnitude of two to three and the presence of trace metals indicates the input of Cr, Pb, Cd, Cu and Zn in both forms through industrial activities. Factor analysis supports the above observation with higher loadings on acid leachable elements and its association with CaCO 3. The increase in concentration of trace metals (Cr, Pb, Cd, Cu, Co, Ni, Zn) along the Gulf of Mannar indicates that the area has been contaminated by the input from riverine sources and the industries nearby. The present study indicates that other sources should be evaluated in the long-term monitoring program.