Introduction:
The presence of land contamination is an inevitable legacy of the past. Since the Industrial revolution of the late 18th century, an increasing range of new compounds have been manufactured and added to the list of contaminants, and the affected area of land has increased dramatically. England has a substantial legacy of chemical contaminants in soil. Sometimes the contaminants may be present naturally, and often they result from human industrial and domestic pollution. In most cases, levels of contaminants are sufficiently low that there is no appreciable risk. However, sometimes there can be significant risks to people or the environment. It is only when such risks exist that land is considered to be "contaminated land". In the United Kingdom, the main emphasis have been to bring contaminated land back into productive use as cheaply as possible(Thomas et al,1998).
The potential risk for the environment arises due to soil heavy metals. Several studies have reported a high degree of metal pollution in soils affected by the oxidation of pyritic materials. After the accumulation of metallic elements in the soil, several physico-chemical factors condition the transfer of each heavy metal from the solid to the liquid soil phase, causing differences in the availability and, finally, the toxicity of elements such as Cadmium(Cd), Copper(Cu), Lead(Pb), Nickel(Ni) or Zinc(Zn). Heavy metals can induce toxicity in wildlife if the soil level reaches critical values(Nathanail et al, 2004).
The sorption behavior of Cd, Cu, Ni, and Zn in soils varies from soil to soil and is influenced by soil
properties, such as pH, organic matter, cation exchange capacity (CEC), and clay contents (McBride, 1989). Soil organic matter has been of particular interest in studies of heavy metal sorption by soils, because of its significant impact on CEC, and more importantly, the tendency of transition metal cations to form stable complexes with organic ligands (Elliott et al., 1986). Cadmium is a pollutant and potential toxin that has no known function in any biological organism (Wagner,
1993). Increased adsorption of Cd by soil components with increasing amounts of organic matter has been reported (Christensenn, 1984; Eriksson, 1988). High organic matter content or addition of organic matter decreases solution concentrations of Cd and Ni, but increases the extractability of Zn (McGrath et al.,1988; Arnesen and Singh, 1999). Amendment with organic matter and resulting degradation may change the soil pH and thereby indirectly affect the bioavailability
of metals.
Cd causes chronic accumulation in the kidneys which causes dysfunction of it, which is a major health hazard to humans. Cu limits the lifetime sludge loading of the soil(Hester, et al 1997). Pb pose a potential risk to health it can remain in the soil for a long time and contaminates the pasture especially near major lead using industries. Ni and Zinc has a deleterious effect on soil microbial activity, seed germination and plant growth(Alloway et al, 1995; Robson,A.D,1994).
Our study focuses on the determination of the Bio available trace elements, total metal contents dispersed in the soil, to assess the degree of contamination and a proper remediation of a Tolworth Court Farm fields(Hester et al, 2001).
Materials and Methods:
The whole site is prone to water logging during periods of high precipitation and surface cracking during long dry spells, as is dictated by the type of soil. There are ditches in the hedge bottoms which run north south toward the stream and river and occasionally carry water Field 1 is low lying and damp for most of the year and can become flooded during prolonged rainfall(Natural Environment and Bio Diversity,2009).
Tolworth Court Farm Fields - It comprises of 7 fields, of neutral, semi-natural and unimproved, lowland grassland of which one meadow is wet grassland. It is rectangular in shape and extends over an area of 50 Hectare. The site lies to the south west of Kingston Road by forming one side a broad shallow valley along the course of the Hogsmill River. The roadside boundaries of Tolworth Court Farm Fields consist of large grassed bunds. The Hogsmill River and Bonesgate Stream run along the southern edge of the site. An ancient trackway provides a boundary along the southwest. The site forms one side of a shallow valley, where the south facing slope gently rises to a height of 25m. The rest of the site, with the exception of the peripheral bunds, is relatively flat(Natural Environment and Bio Diversity,2009).
Sampling Strategy and Sampling preparation:
The site was divided into five sections. In each section the random sampling was done. Random sampling is done by throwing a shovel by which 20 different spot was selected. In each spot 10cm deep sample was taken. This is done by the help of auger by digging the depth of 10 cm. The collected samples were then oven dried over a night. The samples are finely crushed, sieved in 2 mm sieve and collected. From which a smaller amount of sample is taken, finely grained and collected in a polythene cover.
Soil Analysis:
Oxidizable organic carbon, pH, calcium carbonate equivalent (CCE) and cation exchange capacity (CEC) of the soils were determined using standard procedures(Rowell, 1994).Total mineral nutrient contents of the soils were estimated by digestion in concentrated HCl (15.5M), which included standard quality control procedures. The total elemental contents in the digest solutions were then analysed by inductively coupled plasma Atomic emission spectrometry (ICP-AES) (Hooda et al,2004). Total concentrations of a range of mineral elements considered relevant to the present study.
Data Quality Assurance:
In order to assure the quality of the data, certain things have to be taken under considerations.
A replicated test are used to confirm the reproducibility of a procedure. The reagent blanks are the samples prepared parallel with the sample to calibrate the values. This reagent is used as a base value measurement to find out the sample values. The Certified reference material (CRM) is the given set of readings or valuables which shows the allowable limit of metals to present in. The CRM we use over here is NCS DC73319 - NCS DC87105.The Calibrations of instruments pH meter, Flame Photometer, ICP - AES are calibrated correctly by removing the errors either by error correction or by adjusting the meters to the correct values (Thomas et al,1998).
The Environmental Agency and DEFRA published Soil Guideline Values. The lists gives out the concentrations for 10 substances in soil as per the government´s view there would be no risk to human health in generic land use situations which will be used as our base line and the guidance for this whole project shown in Table 1.
Conclusion:
From the above tables and Interpretations we can come to a conclusive idea. The metal contents present in the soil are very low. The errors could have caused the concentrations obtained for zinc, lead and cadmium during the analysis of the Certified Reference Material. So we can use this given land for the purpose of residential buildings. But care should be taken since the soil properties tend to retain metals. This can be managed in such a way by preventing further contamination of the land in the future.
Reference:
