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.