Agriculture Reference
In-Depth Information
4. Petroleum hydrocarbons
4.1 Introduction
Petroleum hydrocarbons (PHCs) are environmental contaminants of great significance.
With production rates of 13.42 million cubic meters of crude oil per day (Energy
Information Administration 2009), their potential as soil and water contaminants is
apparent. Crude oil and refined crude oil products therefore appear in almost every
location on earth at the different stages of crude oil production, handling, transport,
refining and consumption. The widespread use of PHCs for transportation, heating and
industry has led to the release of these fuels into the environment through accidental
spills, long-term leakage, and operational failures. Consequently, many soil and water
areas are contaminated with PHCs.
PHCs are well known to be neurotoxic to humans and animals. They have been found to
affect brain activity and development, and cause many other symptoms including, but not
limited to: nausea, disorientation, mental confusion, speech slurring and memory disorders.
Exposure to higher levels can cause extreme debilitation, loss of righting, coma, seizures and
death. Long-term exposure has been shown to cause changes in neurophysiological or
psychological capacity, and to increase the risk of lung, skin and bladder cancers, as well as
having other carcinogenic effects (Hutcheson et al. 1996); (Boffetta et al. 1997); (Ritchie et al.
2001). Due to its toxicity, several environmental regulations have been enforced worldwide
to protect the environment from PHCs contamination. As a result, attention has also been
devoted to rehabilitating PHCs-contaminated soils. For both the diagnosis of suspected
areas and the possibility of controlling the rehabilitation process, there is a great need to
develop and implement a method that can rapidly detect small amounts of PHCs in soils as
well as identify PHCs type, for better soil management and maintenance as a source of life
and food.
4.1.1 Total PHCs
Various fuel products are the outcome of crude-oil refinement. These products contain
mostly C (83-97%), H (10-14%), N (0.1-2%), O (0.0005-1.5%), S (0.05-6%) and various types of
metals such as V, Fe, Cu and so on (<0.1%). These fuel products are classified by two main
criteria: structure of the hydrocarbon (aliphatic or aromatic), and number of C in the
chemical structure. These two criteria affect several of the products' characteristics, such as
boiling point, solubility, absorption and toxicity. There are some overlapping characteristics
among the various groups of hydrocarbons but in general, aromatic compounds are more
toxic than aliphatic structures and there is a connection between the length of an aliphatic
molecule and its toxicity (Tetra Tech EM Inc. for EPA 2000). Total PHCs (TPH) is a
commonly used measurement index for quantifying environmental contamination
originating from fuel. Choosing an analytical method for assessing TPH in soil samples is a
problematic task due to the complex nature of the fuel ingredients and the fact that those
ingredients change with time. Today, the most commonly used analytical method for
assessing TPH in soil samples is based on the no-longer approved Environmental Protection
Agency (EPA) method 418.1. This method was originally intended for assessment of TPH in
water (EPA 1978), but was later adjusted to assess TPH in soil samples (EPA 1983). Not only
has this previously approved method been withdrawn by the EPA, but it is also problematic
for various other reasons.
