STUDY OF PHYSICO -CHEMICAL PROPERTIES OF SOIL IN SELECTED URBAN WASTE STORAGE SITES OF KERALA

Prameela Thampy Supratha and Venugopalannair Saradamma Anil Kumar Department of Botany, University College, Trivandrum, Kerala695034, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 14 March 2020 Final Accepted: 16 April 2020 Published: May 2020

Soil pollution is the contamination of soil by human and natural activities which may cause harmful effects on living organisms. Soil pollution mainly occurs due to industrial wastes, urban wastes, agricultural practices, radioactive pollutants etc. In the present study, the soil samples from three urban waste storage sites of Kerala-Vilappilsala, Brahmapuram and Njeliyanparambu were analyzed for physico-chemical properties (bulk density, texture, PH, electrical conductivity, available N, available P, available Ca and available Mg) and heavy metals (Cu, Zn, Cd, Hg, Cr and Pb). The soil bulk density was highest in site 3 and 4 (1.10g/cm 3 ) and lowest was in site 2 (1.08g/cm 3 ). Texture of the soil is clayey soil in site 3 and sandy clay loam in site 2 and site 4. pH range was high in site 4 (7.1) and lowest in site 3(4.3). Electrical conductivity was higher in site 4 (2.25 dsm-1) and lower was in site 3 (0.15 dsm-1). Results obtained showed that soils of the various locations are significantly different from one another in terms of physical and chemical properties. Zn was found to be higher than all the other elements. The concentration of the metal was higher than the control site as a result of anthropogenic activities.

…………………………………………………………………………………………………….... Introduction:-
Industrialization together with social and agricultural activities of humans have an effect on environmental pollution and the global ecosystem. This corruption of the ecosystem has a negative effect on human health and other living organisms. Growing industrialization and environmental pollution that stems from technology have started to affect human health (Yadgir et al., 2000). Nearly all human activities generate waste, and the way in which this is handled, stored, collected and disposed can pose risks to the environment and to public health (Zhu et al., 2008). Several fluxes of waste and cover materials from different sources end up at these dumpsites and due to the heterogeneity and complexity of wastes, these dumpsites contain a variety of contaminants which can pollute the soil (Sukop et al., 1979).
Maintaining soil health/quality is indispensable for sustaining the agricultural productivity at higher level. The yields were limited by the physical conditions of the soils rather than their nutrient status in certain situations (Russel, 1975). The sustainability of soil as a medium of plant growth depends on both its chemical and physical fertility (Hillel, 1980). Heavy metal contamination in the biosphere due to human activities has become an important process in the geochemical cycling of these metals. Pollution of heavy metals is a problem of concern due to their nondegradable conditions posing toxic problems to living organisms if they exceeded certain limits (Ruhling and Results and Discussion:-Physical and chemical characteristics of soil: Table 1: and Fig-1 shows the physico-chemical properties of soil samples of study area. Bulk Density: The bulk density was highest at site-3 (1.13g cm -3 ) while it was lowest (1.08g cm -3 ) at site 1 with an average of 1.10 g cm -3 . Tripathi and Misra (2012) reported that the bulk density was highest at site 1 (3.11±0.40g cm-3) while it was lowest (1.47±0.48g cm-3) at site 2 in contaminated soils of municipal waste dump sites at Allahabad, India. In soil sample collected from anthropogenic sites in Abeokuta, Nigeria, Olayinka et al. (2017), reported a bulk density value ranging from 0.78-2.29 gcm-3. High bulk density at dumpsites can reduce the root length and limits the root penetration in dump soil (Rai et al., 2010).

Organic Carbon:
Soil carbon is the last major pool of the carbon cycle. The carbon that is fixed by plant is transferred to the soil via dead plant matter including dead roots, leaves and fruiting bodies (Lal, 2008). Organic carbon contents play a 704 crucial role in sustaining soil fertility, crop production and environmental quality due to their effect on soil physical, chemical and biological properties, such as soil water retention, nutrient cycling, gas flax and plant root growth (Saiju and Kalisz, 1990). In the present study, the organic carbon content in soil samples ranges from 2.63 % (S2) to 5.41% (S1) with an average of 3.46%. Maximum organic carbon content was noted in site 1 and minimum organic carbon was detected at site 2. Deshmukh and Aher (2017) observed the organic carbon in soil sample (0.8-12.2%) in the Municipal Solid Waste (MSW) disposal site near Sangamner city, Maharashtra. The value of percentage organic carbon range between 1.39-5.30% in the active dumpsite of soil samples in south western Nigeria (Badmus et al., 2014). The organic carbon in the soil may be due to biodegradable wastes in municipal solid waste. The decomposition of the soil microbes results in the nutrient rich content of the soil (Obute et al., 2010; Amos-Tautua et al., 2014).

Soil p H :
Soil pH controls various chemical processes in soil. The pH of natural soil lies between 7 and 8.5 and its variation might be possible due to temperature, disposal of municipal waste, biological activity etc. (Oyedele et al., 2008). In the present study, the P H of the dump sites ranged from 4.3 to 7.1. The lowest p H value was recorded at site 2 ie. 4.3 which shows that the soil is highly acidic. This low PH at site S3 (4.3) may be due to the dumping of acid containing waste materials like batteries on the dumping site. The highest pH 7.1 was recorded at site 3. At the control site the soil p H is alkaline.The pH of the contaminated soil by mining activity range from 4.63-8.04 (Baran et al., 2014). Krishna et al (2016) studied the effect of Municipal Solid Waste leachate on the soil quality reported that the pH of the contaminated soil is 7.45. The pH values of soil sample in the municipal solid waste dumpyard in Vellalore, Coimbatore district varied from 8.04-9.20 with a mean value of 8.53 (Uma et al., 2016). A study of contaminated soil physico-chemical properties of municipal waste dump sites at Allahabad, the pH of the soil ranged from 6.42±0.46 to 7.16±0.81 which is tending towards neutral or alkaline pH (Tripathi and Misra, 2012). The study was carried out in five solid waste dump sites in the city of Port Harcourt, Nigeria showed the pH of the soil ranged between moderately acidic 4.8±0.18 and slightly above neutral 7.66 ± 0.44 (Obianefo et al., 2017). The high pH values are due to the presence of soluble sodium along with HCO-3 ions, which precipitates calcium and magnesium carbonates during evaporation (Deshmukh, 2012).

Electrical conductivity (EC):
The EC value depends on the dilution of the soil suspension. The soil electrical conductivity (EC), associated with soil salinity (Santini et al, 2013), is measured as one of main soil characteristics in agricultural production and environmental protection. It is influenced by soil moisture content, salts, and amount and type of clays and other factors (Eigenberg et al, 2002). In the present study, the electrical conductivity at dumpsite 2 was lowest (0.15dSm -1 ) while it was highest at site 3 (2.25dSm -1 ). This shows that the movements of charged particles are more at site 3 which is a good indicator of the growth of plants. Previous studies reported that in Vellalore dumpyard, Coimbatore district of Tamilnadu, the electrical conductivity varied from 1.01 mS/cm -1.0 mS/cm with a mean value of 1.01 mS/cm (Uma et al., 2016). According to Badmus (2014), the soil electrical conductivity value ranged from 5.03-6.08 mS/cm with a mean value of 6.08 mS/cm. Thus, electrical conductivity is a measure of ions present in the soil solution (Ku and Sangita, 2015).

Available Nitrogen:
The rich nutrient content of the soil is due to the activities of soil organisms in the decomposition of the wastes

Available Phosphorous:
Phosphorus is known as the key nutrient to agriculture because lack of available phosphorus in the soils limits the growth of both cultivated and uncultivated plants (Foth and Ellis, 1997). In agricultural fields, phosphorus is added second to nitrogen, in frequency of use as fertilizer nutrient (Trohel and Thompson, 1993). The concentration of available phosphorous ranged from 6.50ppm (site 2) to 64.50ppm (site 1) during the study period. Previous studies showed that the five solid waste dump sites located in Port Harcourt of the Niger delta area of Nigeria showed phosphorous level (0.041±0.01 -4.07±0.02 mg/kg) in dump sites especially in the wet season as compared to the 705 control (Obianefo et al., 2017). Assessment of physico chemical properties in surface soil of municipal open waste dumpsite in Yenagoa, Nigeria showed that the available phosphorous ranging from 35.00±1.01 to 84.20±1.02 mg/kg (Amos-Tautua et al., 2014). It is reported that high phosphate reduces the availability of cation metals to plants (Brady and Weil., 1999).

Available Potassium:
Potassium is the third most required element by the plants, which plays an important role for the biochemical and physiological processes that influence plant growth and development (Wang et al., 2013). Potassium content in soil is due to degradation of solid waste (Eddy et al, 2006). In the present study, the potassium content in soil samples varied from 32 ppm (site 2) to 1570ppm (site 1) during the study period. The highest value obtained with site 1 and the lowest at site 2. Potassium plays essential roles in enzyme activation, protein synthesis, photosynthesis, osmoregulation, stomatal movement, energy transfer, phloem transport, cation-anion balance and stress resistance

Texture:
Texture of the soil is related to physical properties such as plasticity, permeability, ease of tillage, fertility, water holding capacity and soil productivity (Brady, 1996). In the present study the soils of the dump site in site 2 are claysoil while other sites are sandy clay loam in nature. Amos-Tautua (2014) determined the soil quality around municipal open waste dumpsite in Yenagoa, Nigeria, had higher sand and lower clay and silt content. The soils of municipal waste dump sites, Allahabad had very low clay content (0.63±0.42 -6.42±0.92%) and maximum sand content (44.59±1.42 -53.78±1.46%) (Tripathi and Misra, 2012). Soils with separate high sand and low clay content have high pollutant leaching potentials (Nyles and Ray, 1999).

Heavy metals in soils:
The total metal concentrations of selected heavy metals such as Copper, Zinc, Cadmium, Mercury, Chromium and Lead at different study sites are given in Table -

Copper:
The copper content in soil samples varied from 2.5 mg/kg (site 2) to 70.1mg/kg (site 3) but are lower than the permissible limit of WHO (1993) ( Table-3). The copper content in the soils of study sites are in the order S3 >S1>S2. Similar studies were reported by Tripathi and Misra (2012) in contaminated soils of municipal waste dump sites at Allahabad was 70.63±1.62 mg/kg and 90.70±1.84 of copper at site 1 and site 2 respectively. The increase in concentration of heavy metal in soil may be due to the influence of urban wastes dumped in the soil. According to Azeez et al (2011) the concentration of copper ranged from 2.83-72.36 mg/kg in the municipal solid waste deposition was investigated in Abeokuta, Nigeria.

Zinc:
Zinc occurs naturally in soil (about 70mg/kg in crustal rocks) (Davies and Jones., 1988). In the present study, the zinc content in soil samples varied from 3.7 mg/kg (site 2) to 116 mg/kg (site 3) and below the permissible limit of 706 WHO (1993) ( Table-3). Zinc content of soils in the study sites are in the order S3>S1>S2. Earlier studies (Tripathi and Misra, 2012) in the municipal waste dump site, Allahabad, India supports the current findings that the zinc concentration will be 32.46±1.07mg/kg, 54.98±1.29mg/kg and 108.00±3.26mg/kg for site 1, site 2 and site 3 respectively. Amusan et al (2005) carried out work on the soils in municipal waste dump sites in Nigeria. The results showed that the zinc concentration of soils in waste dump sites are 63.2-102.11µg/g. It has been identified that zinc that is soluble in water which is found in soils can pollute ground water (Morgan et al, 2008).

Cadmium:
Cadmium is one of the ecotoxic metals, with highly undesirable effects on soil health, plant metabolism, humans and animal health (Kabata-Pendias, 2000). In the present study, the highest value of cadmium content in site 3 is 0.5 mg/kg while the lowest value is 0.4 mg/kg in site 1 and above the permissible limit recommended by WHO (1993) ( Table-3). At site 2 and control site the cadmium concentrations were not detected. Total concentration of cadmium was <0.1 mg/kg in decomposed municipal solid waste (Tessier et al., 1979). The study conducted in the contaminated soils of municipal waste dump sites reported the cadmium concentration (35.50±0.89mg/kg) were present only in site 1 (Tripathi and Misra, 2012).

Mercury:
At site 2 the concentration of mercury was 0.07 mg/kg and is above the permissible limit by WHO (1993) ( Table-3

Chromium:
Major sources of Cr contamination include releases from electroplating processes and the disposal of Cr containing wastes (Smith et al., 1995).The Chromium content in the soil samples ranged from 3.2 mg/kg (site-2 ) to 21.7 mg/kg (site 3) during the study period and is above the permissible limit recommended by WHO (1993) ( Table-3). Chromium content of soil in the study sites are in the order S3>S1>S2. Previous study reported that the chromium concentration (39.86±3.35mg/kg) were highest at site 1 in contaminated soils of municipal waste dump sites at Allahabad (Tripathi and Misra, 2012). According to Amos-Tautua et al (2014) the mean concentration of chromium in municipal open waste dump site, Yenagoa, Nigeria was 0.05±0.01and 0.06±0.01 mg/kg which is slightly higher when compared with the control (0.005±0.01 mg/kg).The sources of chromium in soil may be due to batteries, discarded plastic materials, empty paint containers and coloured polythene bags.

Lead:
Lead is a naturally occurring, bluish gray metal usually found as a mineral combined with other elements, such as sulphur (ie., PbS, PbSO 4 ), or oxygen (PbCO 3 ), and ranges from 10 to 30 mgkg −1 in the earth's crust (USDHHS,1999). Typical mean Pb concentration for surface soils worldwide averages 32 mg/kg and ranges from 10 to 67 mg kg−1 (Pendias and Pendias, 2001). In the present study, the lead content in soil samples of study area varies from 4.7 mg/kg (site 2) to 19.4 mg/kg (site 3) and is below the permissible limit recommended by WHO (1993) ( Table-3). Lead concentration of soil in study sites are in the order S3>S1>S2. Previous study reported that the highest lead concentration (108.85±3.99 mg/kg) was reported in site 1 followed by site 2 (86.80±1.63 mg/kg) and site 3 (71.47±3.34 mg/kg) in contaminated soils of municipal waste dump sites at Allahabad (Tripathi and Misra, 2012). It was reported that 82.84 mg/kg in the soils of dumping sites in Laloor, Thrissur, Kerala (Divya and Sushama, 2017). Lead is reported as a hazardous element due to its bioaccumulation potential (Raymond and Felix, 2011).

Conclusion:-
Dispersal of industrial and urban wastes causes contamination of the soil. It cause serious environmental concern and turns harmful to human beings and other living organisms. So the knowledge of the sources of contaminants is necessary for the selection of suitable remedial measures. Based on the above study, it has been concluded that the following trend of heavy metal in the selected soil samples is Zn>Cu>Pb>Cr>Cd>Hg in the soil samples. Zn was found to be higher than all the other elements. The concentration of heavy metals was found higher in site 3, compared to other sites. The study warrants cost effective remediation techniques to reduce the level of contaminants in the soil.