Distribution pattern of trace metal pollutants in the sediments of an urban wetland in the southwest coast of India

Distribution pattern of trace metal pollutants

in the sediments of an urban wetland in the

southwest coast of India

Centre for Water Resources Development and Management,Kozhikode,Kerala,India

Abstract: A study was carried out to invstigate the concentrations and spatial distribution of trace metals in the sediments of Kottuli Wetland,whuich is in the south west coast of India Eight stations were strategically positioned along the length of wetland and sampled for trace metals (Cu, Mn, Cd, Ni, Pb, Zn &Cr) content. From the analysis, it was observed that the mean concentration of all the analysed trace metals exceeded the average world wide shale concentrations and average Japanese river sediment values. Pollution load index value (PLI) of the studied area ranged from 0.10 to 58.78 which indicated that the wetland sediments were polluted. From the study, PLI of the downstream area of the wetland had the highest values of Cu, Mn, Cd, Zn & Cr. According to the index of Geoaccumulation, Igeo, all the sampling stations may face a severe trace metal pollution contamination problem in the future.

Keywords: Kottuli weland; enrichment factors; trace metal contamination; pollution load index; index of geoaccumulation; principal component analysis.

1. Introduction

Trace metals are among the most common environmental pollutants and their occurrence in waters and sediments indicate the presence of natural or anthropogenic sources. Trace metals may be recycled via chemical and biological processes, within the sedimentary compartment and back to the water column [10],[34] . The accumulation of metal contaminants in sediments can pose serious environmental problems to the surrounding areas. Trace metal contamination in sediment could affect the water quality and the bio-assimilation and bio-accumulation of metals in aquatic organisms, resulting in potential long-term implications on human health and ecosystem. Elements like Pb, Cd, As etc. exhibit extreme toxicity even at trace levels [22]. The behavior of metals in natural waters is a function of the substrate sediment composition, the suspended sediment composition and the water chemistry [26], [28], [13]. During their transport, the trace metals undergo numerous changes in their speciation due to dissolution, precipitation, sorption and complexation phenomena [3], [2], [1] which affect their behavior and bioavailability. The negative effect of heavy metals depends on the percentage weight of their concentration as well as on a series of physical and chemical soil specific characteristics, such as: texture, organic matter content, pH, redox potential, etc. A large proportion of trace metals in sediment fraction are in a crystalline solid state (usually in low concentration) and are environmentally immobile. On the other hand, fine particles, such as clay and colloidal materials, are generally surface-active and contain organic matter and Fe/Mn oxide surface coatings, and they can play an important role in controlling deposition of trace metals to sediments from an estuary to a coastal area. Human activities have greatly altered the geochemical cycle of trace metals, resulting in widespread environmental contamination [24]. The concentration in sediments depends not only on anthropogenic and lithogenic sources but also upon the textural characteristics, organic matter contents, mineralogical composition and depositional environment of the sediments [35]. The list of sites contaminated with trace metals grows every year, presenting a serious problem for human health and a fearful danger to the environment [19]. Kottuli wetland is a wetland of national importance lies in the heart of Calicut, a south coastal city of India. The wetland receives significant amount of wastes containing toxic metals from municipal wastewater through the adjoining Canoly canal, household garbage and vehicle discharges. A study has been done to determine the extent of trace metal content in sediments of the wetland.

1.1 Description of the study area

species include aquatic, errestrial and migratory birds. The Kottuli wetland is an ideal habitat for estuarine fish, prawns, crustaceans and molluscs, wetland flora and fauna including avia, fauna and the endangered Asian otter (Lutrus lutrus). The wetland system has been subjected to degradation and loss of biodiversity owing to reclamation, pollution and human intervention. This wetland has been identified by the Ministry of Environment and Forests, Government of India, under National Wetland Conservation Programme. The Ministry, in 2004, had approved a programme for the conservation of the wetland under Management Action Plan for Kottuli Wetland.

Table 1: Details of sampling locations of Kottuli wetland

Sl No. Name of Station Latitude-N Longitude-E

1 Elathur 110 54’11.6” 750 12’.21.8

2 Korappuzha 110 19’25.9” 750 50’.24.3”

3 Eranjikkal 110 16’ 36.1” 750 22’54.3”

4 Eranjippalam 110 15.590’ 750 47.546’

5 Kalipoyka 110 16’ 29.6” 750 47’12.9”

6 Kottuli 110 15’ 82.2” 750 46’44.5”

7 Kottuli 110 15’ 10.4” 750 46’32.5”

8 Kallayi 110 14’18.1” 750 47’43.6”

Fig.1. Location of Kottuli wetland showing sampling sites

2. Materials and Methods

2.1 Sediment sampling

material were oven dried at 450C for 48 hours and ground using mortar and pestle. Then the samples were sieved by a sieve (aperture 125μm). The lower particle size fraction was homogenized by grinding in again in mortar and stored in plastic bottles until chemical analyses were carried out and marked well. Precautions were taken to avoid contamination during drying, grinding, sieving and storage.

2.2 Analysis of sediment samples

The pH of the sediments was measured in 1:10 sediment to water ratio. Electrical conductivity was measured in saturation extract of sediments using an EC meter and organic carbon was measured using titrimetric method. For the determination of trace metals (Cu, Mn, Ni, Cr, Pb &Zn) the acid extraction was carried out and trace metal concentration [14]was determined by AAS (Varian Spectra AA10). All the reagents and chemicals used were of analytical grade.

2.3 Determination of enrichment factor

To evaluate the magnitude of contamination in the environment, the enrichment factors (EFc) were computed relative to the abundance of species in source material to that found in the Earth’s crust and also it is a convenient measure of geochemical trends and is used for making comparison between areas [29]. The following equation was used to calculate the EFc values,

EFc= X/Fe (sediment) = X/Fe (Earth’s crust)

Where X is the metal studied and X/Fe is the ratio of the concentration of element X to iron. Iron was chosen as the element of normalization because natural sources (1.5 %) vastly dominate its input [33]. The crustal abundance data of [6] were used for all EF values.

2.4 Determination of contamination factor

The level of contamination of sediment by a metal is often expressed in terms of a contamination factor calculated as follows,

Contamination Factor (CF) = Metal content in the sediment Background level of metal

Where CF < 1 refers to low contamination, 1 ≥ CF ≥ 3 means moderate contamination, 3 ≥ CF ≥ 6 indicates considerable contamination, and CF > 6 indicates very high contamination.

2.5 Index of Geoaccumulation (Igeo)

The geoaccumulation index Igeo values were calculated for different metals as introduced by Muller (1969) is as follows:

Igeo = log2 (Cn/1.5*Bn)

Where Cn is the measured concentration of element n in the sediment sample and Bn is the geochemical background for the element n which is either directly measured in pre-civilization sediments of the area or taken from the literature (average shale value described by [37]. The factor 1.5 is introduced to include possible variation of the background values that are due to lithogenic variations. Muller (1981) proposed seven grades or classes of the geo accumulation index. Different geo accumulation index classes along with the associated sediment quality are givenin table 2,

Table 2: Igeo classes with respect to sediment quality [21]

Igeo Igeo class Sediment Quality

0-0 0 Unpolluted

0-1 1 Unpolluted to moderately polluted

1-2 2 Moderately polluted

2-3 3 Moderately polluted to highly polluted

3-4 4 Highly polluted

4-5 5 Highly polluted to very highly polluted

The Igeo class 0 indicates the absence of contamination while the Igeo class 6 represents the upper limit of the contamination. The highest class 6 (very strong contamination) reflects 100-fold enrichment of the metals relative to their background values.

2.6 Pollution Load Index

The extent of pollution by trace metals has been assessed by employing the method based on Pollution Load Index (PLI) developed by Thomilson etal [ 36] and the relation is shown below

PLI = n√Product of n number of CF values, Where CF = contamination factor and n= number of metals

PLI provides a simple, comparative means for assessing a site or estuarine quality: a value of zero indicates perfection, a value of one indicates only baseline levels of pollutants present and values above one would indicate progressive deterioration of the site and estuarine quality [36].

3. Result and Discussion

Table 3: Trace metal concentration (µg/kg) in sediment of Kottuli wetland.

Trace metal concentration, mg/kg Sampling

sites Cu Mn Ni Cd Pb Zn Cr

1 0.80 6.67 1.93 0.08 2.31 420.30 0.53

2 25.36 6.43 0.02 0.00 6.35 342.50 0.00

3 32.10 19.42 0.05 0.00 3.55 318.25 0.00

4 0.82 21.24 0.24 0.00 6.83 322.50 0.01

5 102.30 14.60 0.09 0.00 2.31 444.30 0.23

6 56.90 19.21 0.05 0.04 4.85 218.65 0.03

7 152.30 25.48 0.12 0.04 5.44 554.23 0.54

8 243.60 29.47 0.53 0.05 23.62 456.30 0.71

Range 0.80-243.60 6.43-29.47 0.02-1.93 ND-0.08 2.31-23.62 218.65-554.23 ND-0.71

Mean 492.39 127.80 2.78 0.20 43.46 2848.88 1.71

ND: Not detected

Trace metal concentration and the mean concentration of different sediment samples collected from Kottuli wetland is presented in table 3. The mean concentration of Cu, Mn, Pb, Zn exceeded the average concentration of these metals in shale as proposed by Turekian and Wedepohl (1961) and in Japan’s river sediments as postulated by Gamo[12] . The highest concentration of Cu, Mn, Pb &Cr were found in the sample at location 8 (Kallayi estuary). At sampling position1 (Korappuzha estuary), the content of Ni &Cd was maximum. The concentration of Zn was found to be high at sampling site 7. Shreshtha [28] had reported that domestic construction and car related sources and untreated waste water are the main sources of Zn in urban water bodies. High level of Cu indicate a higher input of organic matter deposition in those sites, which might have come from urban and industrial waste water sediment deposition [8]. Increased Cd concentration might be related to industrial activity, atmospheric emission and deposition of organic and fine grain sediments [15]. Other possible sources of Cd include leachates from defused Ni-Cd batteries and Cd plated items [32]. Pb is considered as a good indicator of pollution by urban run-off water. The use of gasoline is mainly responsible for the lead pollution especially in urban area [26]

.

Table 4: Concentration of trace metals of sediment samples of Kottuli wetland and the toxicological reference values for sediments (mg/g).

Trace metal

Geochemical back ground

US DOE

Canadian EQG

US EPA

Ontario

MOE Japan’s

Present study (average) Shale

standard

Continental

crust TEC PEC HNEC ISQG PEL TRV LEL SEL EQS

Cu 45 55 28 77.7 54.8 35.7 197 16 16 110 125 76773

Ni 68 76 39.6 39.6 37.9 - - - - - - 381

Cd 0.3 0.2 0.59 11.7 41.1 0.6 3.5 0.6 0.6 10 1 37

Pb 20 12.5 34.2 396 68.7 35 91.3 31 31 250 0.01 6909

Zn 95 70 159 1532 541 123 315 110 120 820 - 38462

Cr 90 100 56 159 312 37.3 90 26 26 110 - 259

TEC: Threshold effect concentrations, PEC: Probable effect concentrations, HNEC: High no effect concentrations, TRV: Toxicity reference values, Ontario MOE: Ontario Ministry of Environment, LEL: Lowest effect levels, Japan EQS: Japan’s Environmental Quality Standard, Canadian EQG: Canadian Environmental Quality

Guidelines, USEPA: U.S. Environmental Protection Agency.

The available data for a comparative analysis with background and toxicological reference values for sediments, along with average values obtained for trace metals of Kottuli wetland sediments are summarized in Table.3. It is evident that the average total concentration of all the trace metals in the sediment samples exceeded the geochemical background (shale standard and continental crust). It is apparent from the table that the concentration of all the trace elements were very much varied from the average shale values, and there was significant variation among the values which indicate that these elements were not originated from lithogenic sources and anthropogenic sources has high contribution to the enrichment of these metals. However, when comparing with effect based toxological levels, severe pollution was observed for Kottuli sediments. The mean total concentrations of all the analysed trace metals were higher than those of the Ministry of Environment (MOE), Japan’s Environmental Quality Standard (Japan EQS), Canadian Environmental Quality Guidelines (Canadian EQG), U.S.Environmental Protection Agency’s (USEPA) toxicity reference values (TRV), Ontario Ministry of Environment’s (Ontario MOE) lowest effect levels (LEL) and U.S. Department of Energy’s (US DOE) threshold effect concentrations (TEC). The concentrations of the trace metals presented in the sediments of Kottuli wetland was found to be higher than the probable effect concentrations (PEC) and high no effect concentrations (HNEC) defined by the U.S DOE and severe effect level (SEL) defined by the Ontario MOE for all the studied trace metals. The results indicate that the levels of trace metals found in the sediments of the wetland might create an adverse effect on the aquatic ecosystem associated with the wetland, especially since it receives urban wastewaters.

3.2 Correlation coefficient.

Table 5:Correlation coefficient matrix of different physico-chemical characteristics and trace metal concentrations of sediment samples

pH E.C OC, % Cu Mn Ni Cd Pb Zn Cr

pH 1

E.C -0.59 1

OC -0.94 0.72 1

Fe -0.64 0.97 0.77

Cu -0.88 0.72 0.94 1

Mn -0.67 0.64 0.59 0.72 1

Ni 0.08 -0.3 -0.4 -0.18 -0.37 1

Cd 0.08 -0.1 0.05 0.26 0.04 0.76 1

Pb -0.53 0.92 0.65 0.75 0.62 -0 0.21 1

Zn -0.36 0.22 0.51 0.59 0.24 0.22 0.28 0.22 1

Cr -0.33 0.33 0.51 0.7 0.35 0.53 0.74 0.79 0.8 1

Most of the physico-chemical properties of the sediments showed highly significant positive correlation with each other. Except Ni & Cd, all trace metal studied showed good to excellent positive correlation with percentage of organic carbon of the sediments. This implies that the presence of organic matter has an influence on accumulation of trace metals in sediments of the Kottuli wetland region. It is evident from Table 5 that majority of trace metals show good to excellent correlation except with Zn & Cd, indicating a common source for these metals. Zinc is positively correlated with all the analysed metals which can be well corroborated with the results obtained by Alomary and Belhadj [4].

3.3 Assessment of anthropogenic pollution in sediments of Kottuli wetland

3.3.1 Contamination Factor (CF)

Table 6: Contamination factor for the trace metals of Kottuli wetland

Sampling

stations Cu Mn Ni Cd Pb Zn Cr

1 0.084 0.17 0.24 0.45 36.36 0.05 0.01 2 2.636 0 0.07 1.23 29.63 0 0

3 3.337 0 0.13 0.69 27.53 0 0 4 0.086 0.02 0.01 1.32 27.9 0 0 5 10.63 0.01 0.02 0.45 38.43 0.02 0 6 5.915 0 0.14 0.94 18.91 0 0

7 15.83 0.01 0.12 1.05 47.94 0.05 0.01 8 25.32 0.05 0.16 4.57 39.47 0.07 0.01

The contamination factors of the various trace metals in the sediment of Kottuli are presented in Table 6. The concentration of copper is reported to be high in the downstream stations and lead was found to be high at all the stations. It was found that sampling stations 2, 4, 7 were moderately contaminated by Cd and station 8 faces considerable contamination. Ni, Zn & Cr were present at much lesser concentrations. From the contamination factor calculations, it was found that a regular monitoring for the concentrations of Cu, Cd &Pb is essential since their contamination factor at all the sampling sites except site1 exceeded the desirable limit for CF values and can cause potential pollution risk in the future.

3.3.2 Enrichment factors (EF)

sediment samples of the wetland. All the sampling sites have EFc values >5 for Pb &Zn and except site 4 for Cu. According to Khan etal [15] EFc values <5 are considered significant. Areas with EFc values <1 should be viewed with caution as they imply preferential release of these metals, making them bioavailable. If the value of EFc >1.5, the trace metal is delivered from others sources [9] suggesting environmental contamination by that particular trace element. It is presumed that high EFc values indicate an anthropogenic source of trace metals, mainly from activities such as industrialization, urbanization, deposition of industrial values and others. Since, the bioavailability and toxicity of any trace metals in sediments depend on the chemical form and concentration of the metal [16], it can be inferred that trace metals in sediment samples with high EFc values, along with higher labile fractions in sediments are potential sources for mobility and bioavailability in the aquatic ecosystems.

0 5 0 0 10 0 0 15 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0

1 2 3 4 5 6 7 8

S a mp l i ng s t a t i o ns

C u N i C d P b Zn C r

.

Fig.2. EFc values of different sampling sites of Kottuli wetland

3.3.3 Index of Geoaccumulation (Igeo)

The values for Zn in the sediments exhibited class>5 and hence are very highly contaminated with Zn. From fig.3 it can be interpreted that all the sampling stations may face a severe trace metal contamination problem.

Fig. 3: Igeo values of different sampling sites at Kottuli wetland

3.3.4 Pollution Load Index (PLI): A reflex of urbanization

0

20

40

60

80

1

2

3

4

5

6

7

8

Sampli ng stations

PL

I v

a

lu

e

s

Fig. 4: PLI values of different sampling sites at Kottuli wetland

4 Statistical analysis

In the present study, both Pearson Correlation (PC) and Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were carried out using SYSTAT software package. In order to study the general characteristics of the sediments of the Kottuli wetland, the concentrations of trace metals content of the surface sediments were used as the input data in the PC, HCA and PCA. The sediments that showed a close correlation were identified and grouped to undergo a further spatial pattern analysis.

4.1 Principal Component Analysis

In multivariate statistical analysis, PCA can be used to identify the sources of contamination. Principal Component (PC) analysis have been employed to find out the possible linear combination of the original variables of trace metals, which could account for the largest part (80%) of the total variance. Reduction in number of variables during future monitoring of the system without significant loss of information can be done by this technique [27].

Table.7: Principal Component (PC) analysis of correlation matrix of trace metal of Kottuli wetland.

PC score coefficients

PC Latent roots Variance (%) Cu Mn Ni Cd Pb Zn Cr

PC1 3.334 47.265 0.824 0.854 -0.253 0.102 0.901 0.145 0.436

PC2 2.144 30.629 -0.026 -0.235 0.898 0.926 0.153 0.081 0.545

PC3 0.855 12.22 0.502 0.138 0.2 0.033 0.065 0.978 0.711

studies it was shown that Cd and Ni were associated mostly with the same soil minerals (Pierce et al., 1982; Chen et al., 1999). The 3rd PC (12.22%) is contributed by Zn, Cr, Cu and Ni and in contrast by Cr and Pb, out of these Zn from the traffic emission, especially from the vehicle tyres[18]. The remaining PCs have less importance on the entire variance accounted for. Zinc had a very different distribution from other metals. This was consistent with the result of PCA that only Zn had high loadings in F3.

Fig. 5: Loading plots of PCA analysis of trace metal concentration for Kottuli wetland

From the loading plots, it appears that the distribution characteristics of metals in Kottuli wetland mainly focus on component 1. The high positive loadings of component 1 for the metals show that all the metals are mostly originated from the identical source (Fig. 5). The loading plot shows that metals of Group 2 tend to cluster closely along the axis of component 1, which indicates they might be discharged from the same sources or had similar depositional activities.

4.2 Cluster analysis

Cluster Tree

0.0 0.1 0.2 0.3 0.4 0.5

Distances

CD

CR

PB

CU

MN

ZN

Fig. 6: Dentogram using Average Linkage between groups

5. Conclusion

This study revealed that the enhanced concentration of trace metals in most populated urban areas like Kottuli wetland is due to strong anthropogenic influences. The distribution pattern of trace metals in the sediments according to EFc and Igeo index were severely polluted with Cu, Mn, Zn &Pb. However the PLI values confirmed that the sediment quality is deteriorated and this may have severe impact on the ecosystem that depends on it. To prevent severe heavy toxic metal pollution of the Kottuli wetland area, especially at and in the vicinity of communities exposed to anthropogenic-derived metal inputs, it becomes imperative to implement timely monitoring and remediation strategies to alleviate the loadings and cumulative concentrations of trace metals in the studied area

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