Radiation Protection and Environment

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 44  |  Issue : 3  |  Page : 152--160

Assessment of heavy metal enrichment and contamination in the wetlands of Kannur district, Kerala


T Vinodkumar1, V Vineethkumar1, CV Vishnu2, VV Sayooj3, V Prakash1,  
1 Department of Studies and Research in Physics, Payyanur College, Kannur, Kerala, India
2 Department of Physics, Calicut University, Malappuram, Kerala, India
3 Department of Physical Science, PKM College of Education, Madampam, Kannur Kerala, India

Correspondence Address:
V Prakash
Department of Studies and Research in Physics, Payyanur College, Kannur-670327, Kerala
India

Abstract

The present investigation is an attempt to trace the heavy metal enrichment in the soil matrix of the wetlands Kannur district, Kerala. Wetland is an ecosystem which plays significant role in ecological balance. Characteristic vegetation of aquatic plants makes this distinct ecosystem as unique and distinguishable from other land forms and water bodies. The hydric soil prevailing in the wetlands is rich in organic matter content and also enriched with many heavy metals. In view of this, the enrichment of some major heavy metals such as Co, Fe, Mg, Cu, Zn, Cd, Hg, Ni, Pb, and As have been quantified in the soil samples collected from the wetlands of southern part of Kerala using Inductively Coupled Plasma-Mass Spectrometer. The adverse effect of this enrichment on human and environment is of serious concern and hence various pollution index parameters were calculated to assess the extent of contamination. The spatial distribution study confirms the dependence of geological factors on the enrichment of heavy metals. The study on various pollution index parameters reveals the selective enrichment of heavy metals. The continuous monitoring of wetlands is the need of the time as such areas are preserved for the cultivation of aquatic plants. The results of the investigation are presented and discussed in detail in the manuscript.



How to cite this article:
Vinodkumar T, Vineethkumar V, Vishnu C V, Sayooj V V, Prakash V. Assessment of heavy metal enrichment and contamination in the wetlands of Kannur district, Kerala.Radiat Prot Environ 2021;44:152-160


How to cite this URL:
Vinodkumar T, Vineethkumar V, Vishnu C V, Sayooj V V, Prakash V. Assessment of heavy metal enrichment and contamination in the wetlands of Kannur district, Kerala. Radiat Prot Environ [serial online] 2021 [cited 2022 May 20 ];44:152-160
Available from: https://www.rpe.org.in/text.asp?2021/44/3/152/334778


Full Text



 Introduction



In the last few decades, the air, water, and land on the earth have been contaminated by various means including human activities. Hence, risk to the public and environment has been growing day by day as a result of enhanced level of contamination. Environmental pollution is not a new phenomenon on the earth, yet it remains an issue of serious concern to all living organisms for all time. The ecological changes as a result of people intervention to lead a comfort life affect the environment adversely. Pollution is considered as one of the greatest crimes against the environment by people and occurs in the form of air, water, soil pollution. Among the various pollutants, heavy metals enrichment also plays a vital role. Hence, understanding the distribution and enrichment of heavy metals is need of the time as far as the living organisms and natural habitats are concerned. Depending upon the dose and duration, heavy metals can be poisonous to human well-being and causes extreme health issues.[1]

An ecosystem such as wetland plays a major role in the selective enrichment of heavy metals. Generally, wetlands are areas that are inundated or submerged for at least 6 months a year and have unique ecological characteristics. This is a shallow water area where water is constant or stagnant at certain times of the year. In wetlands, water is found on the surface or just below the surface and water can be seawater or freshwater or sewage water. The hydric soil associated to the wetland is rich in organic matter content and enriched with heavy metals. Hence it is important to understand the various physico-chemical parameters and level heavy metals of soil from wetlands. It is also important to study the correlation and draw information on extent of contamination and various factors responsible for the enrichment.

Heavy metals can be classified as essential and nonessential. The essential elements are needed for living organisms for better biochemical and physiological functioning. Whereas nonessential elements have no known function in the body.[2] The elements such as Cu, Ni, Fe, Co, Mo, Se, Mn and Zn are also essential for both plants and animals. Deficiency of these heavy metals manifest as health issue in them. On the contrary, they exhibit toxicity if their uptake exceeds safe limits.[3],[4],[5] Nonessential elements pose a serious threat to living organisms. These elements enter the human body through ingestion, dermal absorption and inhalation. The elements such as Cr, As, Pb and Cd have profound heath impacts even at lower concentrations.[6],[7],[8] Presence of excess concentration of Mn can damage some plants growth severely.[5]

Heavy metals tend to accumulate in living organisms over a long period of time as these are nonbiodegradable in nature. These are considered as a significant environment pollutant due to its persistence, toxicity, and bioaccumulation characteristics. The main sources of heavy metals are fertilizers, soil parent materials (rocks), bio solids, coal combustion residues, irrigation water, auto emissions, and metal-smelting industries. Some heavy metals originate from rocks and some are very useful for plants growth and development. These elements become toxic when present in soils at elevated levels. Major components of heavy metals that have been taken up by plants, particularly those grown on polluted soil, could move up the food chain. It also accumulates in the fatty tissues of animals or humans. Moreover, the plants retain numerous heavy metals in the soil of their root zone with or without the inevitability of these elements.[9] Hence, the estimation of heavy metals concentration in the environment is much important for the prediction of risk to the nature and public. In view of these aspects, an attempt is made to assess the heavy metals concentration and associated pollution indices in soil samples collected from the wetlands of Kannur district, Kerala.

 Materials and Methods



Study area

The study area lies between latitudes 120 0′ N to 120 10′ N and longitude 750 10′ E to 750 18′ E, which covers the areas of wetlands in Payyannur Municipality, Kunjimangalam, Cheruthazham, Ramanthali, and Madayi Panchayaths. The [Figure 1] shows the location map of the study area in which major land areas are divided into nine classes. The nine classes are aquaculture, built up, mangroves, mixed crops, paddy, paddy converted, plantation crops, water body, and waste land. Among these classes, mixed crops cover the major portion of the study area with an area of 79 sq.km followed by converted paddy land of 23.3 sq.km, paddy with 16.1 sq.km, 9.87 sq.km of water body, plantation crops with 7.92 sq. km, waste land covers about 6.55 sq.km, 5.52 sq.km of built up land, mangroves with 1.22 sq.km and aquaculture with 0.22 sq.km. Land use/land cover map of the study area is shown in [Figure 2]. The [Table 1] gives the latitude and longitude of the sampling points.{Figure 1}{Figure 2}{Table 1}

The geographical formations in the study area are of archean and recent age. The Archean formation comprises of gneisses and charnockite group of rocks and recent formations are by alluvium and laterite. The main geological structures found in these regions are acidic rocks, basic rocks, charnockite group of rocks, laterite, migmatic complex, sand and silt, peninsular gneissic complex, and ultrabasic rocks. The geology of the study area is shown in [Figure 3]. The categories of soil type found in the study area are clay, loamy clay, sandy clay, silty clay, and loamy sand. This type of soil is mainly found in the coastal tract because of recent deposits predominantly marine with some fluvial sediment along the coastline which are sandy and sterile with poor water holding capacity. The soil in the coastal plain supports mangrove vegetation and immature due to the high sand content.{Figure 3}

Sample collection, preparation, and elemental analysis

The soil samples were collected from 10 different locations of wetlands of Kannur district, Kerala during the month of January, 2019. Samples were collected around 1 m2 area with a depth of 20 cm. The grass root, pebbles, stones present on the surface of the soil were removed prior to the sample collection and mixed the samples thoroughly for homogeneity. Using quartering process, the thoroughly mixed samples were reduced to 1 kg and is taken as the representative sample. The soil samples were collected in polythene bags and brought to the laboratory for further analysis.[10] 0.2 g of soil sample was weighed and 15 mL of conc. Nitric acid was added to the sample in the beaker and the solution was heated at a temperature not exceeding 120°C. Two to three drops of hydrogen peroxide were added to the solution in the beaker and boiled until it became clear. Nitric acid was added to the solution until there was no residue left in the solution and two to three drops of hydrogen peroxide were added again. Then concentration sulphuric acid was also added to the solution to remove the presence of plastic in it. The prepared solution was filtered using a Whatman-42 filter paper and transferred into a 50 mL standard flask. This digested solution was used for the measurement of heavy metals concentration. The concentration of heavy metalsviz. Co, Fe, Mg, Cu, Zn, Cd, Hg, Ni, Pb, and As were measured using inductively coupled plasma-mass spectrometer.

Pollution indices

The risks associated with the degree of trace elements presence in the environment were evaluated using indices of pollution namely; enrichment factor (EF), contamination factor (CF), geochemical load index (Igeo), pollution load index (PLI), and potential ecological risk index (PERI).[11],[12]

Enrichment factor

EF is a general approach to constitute the existing contamination level in sediment and a good measurement to recognize the heavy metal sources whether anthropogenic or naturally occurring.[13] It is used to determine the level of human effects on heavy metals in soil. The metals EF in soil were determined following the equation given below.[14]

[INLINE:1]

Where; EF: Enrichment factor, Cn: Concentration of metal of interest, CFe: Concentration of reference metal. In this research, iron (Fe) was selected as the reference because of its natural abundance in the earth crust of the study area.

The categories of contamination based on the EF are classified into seven namely; no enrichment (EF < 2); minor enrichment (EF = 2–3); moderate enrichment (EF = 3–5); moderately severe enrichment (EF = 5–10); severe enrichment (EF = 10–25) very severe enrichment (EF = 25–50); and extremely severe enrichment (EF > 50).[15]

Contamination factor

CF is employed to assess the extent of contamination of the heavy metals in the soil. CF was calculated based on model developed by Lacatusu.[15] CF can be measured using the equation given below.[15]

[INLINE:2]

Where; CF: Is contamination factor, Cn is content of metal in the soils, and Co is metal concentration at geochemical background. The department of petroleum resources (DPR), reference (background) value was used as a reference value to the study. This is a value of reference for metals (mg/kg) adapted from the standard table formulated by the DPR of Nigeria for maximum permissible metals concentration in the Nigerian soil.[16]

The classified categories of contamination are: Low contamination (Cf < 1); moderate contamination (1 < Cf < 3); considerable contamination (3 < Cf < 6); and very high contamination (Cf > 6).[2]

Geo-accumulation index (Igeo)

For the comparison of the current heavy metals concentration with the local background or baseline values and to realize the anthropogenic effects, the geo-accumulation index (Igeo) was calculated. The geochemical load index (Igeo), introduced by Muller, as found wide usage for evaluation of soil contamination by heavy metals in soils. It can be computed using the given equation.[17]

[INLINE:3]

Where; Cn is concentration of heavy metal measured in surface horizons of soil dry weight (mg.kg − 1), Bn is geochemical background value of heavy metal, and 1.5 is the standard values attributable to varying lithogenic in the soil. The seven classification of Igeo are: Unpolluted (Igeo ≤ 0); unpolluted to moderately polluted (0< Igeo ≤ 1); slightly polluted (1< Igeo ≤ 2); slightly to heavily polluted (2< Igeo ≤ 3); heavily polluted (3< Igeo ≤ 4); heavily to extremely polluted (4< Igeo ≤ 5); and extremely polluted (Igeo > 5).[14]

Pollution load index

PLI is used to estimate the geometric means of relative concentration factors of trace metals of a potentially polluted site.[18] The PLI reveals the status of an estimated metal concentration in the soil. The PLI was determined by the n-root from the nCFn derived for all the metals.[19]

[INLINE:4]

Where; n: Number of investigated metals, CF: Contamination factor calculated as described in the above equation. The rank of values of PLI <1: Signifies perfection, PLI = 1: Entails only the availability of baseline levels of pollutants, and PLI >1: Portends soil quality deterioration.[12]

Potential ecological risk index

The integrated PERI was calculated using equation given below.[20]

[INLINE:5]

Where Ti is the toxic-response factor for a given substance (Hg = 40, Cd = 30, Cu = 5, Zn = 1, Pb = 5, Co = 5, Ni = 6, and As = 10) and is the CF of a particular element.[20] According to the value of RI, the pollution status is classified into four categories: Low risk (<150), moderate risk (150–300), considerable risk (300–600), and very high risk (≥600).

 Results and Discussion



The concentration of heavy metals in collected soil samples are given in [Table 2]. The statistical parameters of EF, CF, geo-accumulation index measured from the concentration of heavy metals are tabulated in [Table 3], [Table 4], [Table 5] respectively. The PLI and PERI are summarized in [Table 6].{Table 2}{Table 3}{Table 4}{Table 5}{Table 6}

The concentration of Co in soil samples of wetlands of Kannur varies from 40.57 ppm (S9) to 84.34 ppm (S5) with a mean value 51.22 ppm. The mean value of Co exceeds the crustal average value 19 ppm.[21] The EF of Co ranges from 0.65 (S3) to 60.03 (S5) with a mean value of 20.90. Extremely severe enrichment of Co was observed in S5. The sampling stations, S5 and S10 showed considerable contamination by the presence of Co. The geo-accumulation index of Co varies in the range 0.51 (S9) to 1.57 (S5) with a mean value 0.80. The samples collected from S5 to S10 were found to be slightly polluted by Co. The concentration of Fe in the soil samples ranges from 3490 ppm (S5) to 169,940 ppm (S3) with a mean value of 51954.4 ppm. The mean value of Fe was more than the average crustal value 47,200 ppm.[21]

The concentration of Mg in the soil samples varies in the range 1601 ppm (S8) to 8218 ppm (S3) with a mean value 5637.3 ppm. The mean value of Mg was below the average crustal value 15,000 ppm.[21] The EF of Mg varies from 0.13 (S10) to 5.09 (S2) with a mean value 2.50. Moderately severe enrichment of Mg was observed in S2. All the sampling stations were found to be less contaminated by the presence of Mg. The geo-accumulation index of Mg ranges from −3.81 (S8) to −1.45 (S3) with a mean value-2.12. All the samples were found to be unpolluted by Mg. The concentration of Cu in the soil samples varies from 10.4 ppm (S3) to 61.55 ppm (S6) with a mean value 24.56 ppm. The mean value of Cu was less than the crustal average value 45 ppm.[21] The EF of Cu ranges from 0.06 (S3) to 13.03 (S6) with a mean value 4.93. Severe enrichment of Cu was observed in S6. The sampling stations, S6 and S7 showed moderate contamination due to the presence of Cu. The geo-accumulation index of Cu varies in the range-2.70 (S3) to-0.13 (S6) with a mean value-1.75. All the samples were found to be unpolluted by Cu.

The concentration of Zn in the soil samples ranges from 34.65 ppm (S8) to 181 ppm (S3) with a mean value 100.65 ppm. The mean value of Zn was slightly greater than the average crustal value 95 ppm.[21] The EF of Zn varies from 0.20 (S10) to 20.14 (S4) with a mean value 7.56. Severe enrichment of Zn was observed in S4, S5, S6 and S7. The sampling stations, S1, S3, S4, S6 and S7 showed moderate contamination by the presence of Zn. The geo-accumulation index of Zn varies from −2.04 (S8) to 0.34 (S3) with a mean value-0.68. The samples collected from S3 to S4 indicated that the samples are unpolluted to moderately polluted by the presence of Zn. The concentration of Cd in the soil samples varies in the range 0.008 ppm (S2) to 1.35 ppm (S7) with a mean value 0.44 ppm. The mean value of Cd was slightly above the average crustal value 0.3 ppm.[21] The EF of Cd ranges from 0.27 (S2) to 38.98 (S7) with a mean value 5.70. Very severe enrichment of Cd was observed in S7. The sampling stations, S1, S3 and S7 showed considerable contamination due to the presence of Cd. The geo-accumulation index of Cd ranges from −5.81 (S2) to 1.58 (S7) with a mean value-1.94. The samples collected from S1, S3 and S7 were found to be slightly polluted by Cd.

The concentration of Hg in the soil samples varies from 0.027 ppm (S3) to 1.85 ppm (S7) with a mean value 0.49 ppm. The mean value of Hg was slightly greater than the crustal average value 0.4 ppm.[21] The EF of Hg varies from 0.02 (S3) to 44.97 (S5) with a mean value of 12.19. Very severe enrichment of Hg was observed in S5 and S7. The sampling stations, S5 and S7 showed considerable contamination by the presence of Hg. The geo-accumulation index of Hg ranges from-4.47 (S3) to 1.62 (S7) with a mean value-1.28. The samples collected from S5 to S7 were found to be slightly polluted by Hg. The concentration of Ni in the soil samples ranges from 33.42 ppm (S9) to 149 ppm (S4) with a mean value 89.28 ppm. The mean value of Ni was greater than the average crustal value 68 ppm.[21] The EF of Ni ranges from 0.15 (S10) to 28.98 (S5) with a mean value 11.81. Very severe enrichment of Ni was observed in S5. The sampling stations, S2, S4, S5, S6 and S7 showed moderate contamination due to the presence of Ni. The geo-accumulation index of Ni varies from-1.61 (S9) to 0.55 (S4) with a mean value-0.40. The samples collected from S4, S5, S6 and S7 indicated that the samples are unpolluted to moderately polluted by the presence of Ni.

The concentration of Pb in the soil samples varies in the range 0.418 ppm (S10) to 27.72 ppm (S4) with a mean value 21.92 ppm. The mean value of Pb was slightly above the average crustal value 20 ppm.[21] The EF of Pb varies from 0.01 (S10) to 15.38 (S4) with a mean value 8.77. Severe enrichment of Pb was observed in S2, S4, S5, S6, S7, S8 and S9. All the sampling stations except S5, S8 and S10 showed moderate contamination by the presence of Pb. The geo-accumulation index of Pb ranges from −6.17 (S10) to 0.14 (S3) with a mean value-0.91. The sample collected from S3 indicated that the sample is unpolluted to moderately polluted by the presence of Pb. The concentration of As in the soil samples varies from 0.312 ppm (S10) to 90.76 ppm (S5) with a mean value 26.74 ppm. The mean value of As was greater than the crustal average value 13 ppm.[21] The EF of As ranges from 0.01 (S10) to 94.42 (S5) with a mean value 22.24. Extremely severe enrichment of As was observed in S5. The sampling station S5 also showed very high contamination due to the presence of As. The geo-accumulation index of As varies in the range-5.97 (S10) to 2.22 (S5) with a mean value-0.56. The sample collected from S5 indicated that the sample is slightly to heavily polluted by the presence of As.

[Figure 4] shows the spatial distribution of the concentration of heavy metals. The CF observed in the wetlands of Kannur district were compared with the values reported for other regions of the world and summarized in [Table 7]. The comparison study reveals that the CF s obtained from the present investigation were comparable with the reported values of CF s for other parts of the world.{Figure 4}{Table 7}

The PLI of the soil samples varies in the range 0.43 (S8, S10) to 1.40 (S7) with a mean value 0.74. The sampling stations S1 and S7 were found to have PLI value greater than one indicating that there is soil quality deterioration. The PERI of the samples ranges from 64.69 (S9) to 398.84 (S7) with a mean value 144.13. The sampling station S7 was found to be under considerable risk on the basis of PERI.

The present study shows that the study area is significantly contaminated by the presence of heavy metals. The mean concentration of heavy metals quantified exceeds the average crustal value except Mg and Cu. The spatial distribution study confirms the dependence of geological factors on the enrichment of heavy metals. The study on various pollution index parameters reveals the selective enrichment of most of the heavy metals investigated. The significant enrichment of heavy metals in the hydric soils from wetlands of present study may be attributed to the higher level of sedimentation of many organic and inorganic materials. The sedimentation process is expected as the present study areas are near to estuary of Peruvamba river to the Arabian sea. The study also indicates that, anthropogenic activities contribution to the enrichment of heavy metals is insignificant. The study stresses the need for monitoring wetlands while preserving such area for the cultivation of aquatic plants.[27]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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