1.0 Introduction
Upon the release of oil into the environment, a broad spectrum of chemical, physical and biological processes occurs during the transformation of the released oil. These processes are collectively known as weathering, which describes the action of altering the composition, performance, exposure and the level of toxicity of the oil [1]. According to the United State Environmental Protection Agency (USEPA), have identified that petroleum contaminated soil can be detrimental to the health of people and animals, affecting the liver, lungs, kidney and nervous system, causing cancer, disorder of immune and reproductive system [2].
There are several methods to determine the total oil content such as total organic carbon (TOC), total carbon (TC), total petroleum hydrocarbon (TPH) etc. Based on environmental sciences division UK [3], TPH is commonly used gross parameter for quantifying environmental contamination originated by petroleum hydrocarbons compounds (PHC) products such as fuels, oils, lubricants, waxes and others. TPH can be classified into four main structural forms: aliphatic, aromatic, resins and asphaltenes compounds. Aromatic hydrocarbons are characterised into two groups based on their molecular structure. These are low molecular weight (LMW) compounds and high molecular weight (HMW) compounds [4]. Traditional wet chemistry methods for determining TPH level is based on extracting the contaminant from the soil sample. The TPH level in the extracted solution is can be determined by several methods such as gravimetric or gas chromatography-mass spectrometry (GC-MS) measurement calibrated by an EPA calibration standard. A series of experimental tests were conducted by Rababah and Matsuzawa [5], Khodadoust et al. [6]; Silva et al. [7], Li et al. [8], at laboratory environment for a range of solvents with various ratios and different time to enhance the extraction process.
According to Li et al. [8], number of experiments were performed at the solvent soil ratio of 2:1, 3:1, 6:1 to assess the extraction efficacy. They found that the solvent extraction with greater than 95% removal at 3:1 solvent soil ratio was suitable in removing oil contaminants. Another experimental test was conducted by Khodadoust et al. [6] for a range of solvents including combinations of solvents to determine hydrocarbons from extremely polluted soil. The experiment revealed that washing procedure of 60 min has successfully eliminated 95% of extractable hydrocarbons compounds. With the exception of type of solvent, the extraction performance is also reliant upon the ratio of soil; solvent. For example, a study was carried by Silva et al. [7] by means of magnetic agitation on the effectiveness of a mix comprising 40% acetone + 50% ethyl acetate + 10% water to get rid of naphthalene from soil samples at various soil: solvent ratios of 1:1, 1:2, 1:3, 1:4 and 1:8 (w/v). It was revealed that a ratio of 1:8 was required to achieve the most efficient removal process. However, Rababah and Matsuzawa [5] discovered that the most efficient solvent was cyclohexane and ethanol mixture at a ratio of 3:1, with excellent removal efficiency of around 93% as well as from the safety aspect.
Due to the lack of information regarding the concentration of petroleum hydrocarbons in the Kuwait oil sand, this study was designed to measure the total petroleum hydrocarbon concentration (TPH), due to its ability to determine a broad family of several hundreds of chemical compounds present in crude oil. The most important reason for selection of TPH over other methods is that the core contaminants to be analysed are petroleum based which would delineate the level of oil pollution while the other methods are less relevant in this case. Another reason for the choice of TPH is that it gives a direct indication of the degree of pollution resulting from oil which is required by regulatory agencies.