الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The petrochemicals sector plays an important role in the industrial strategies of developed countries. Its pivotal role in industrial modernization has been linked to progress in the manufacturing sector and the ability to promote exports. World sales of petrochemicals continue to increase and surpassing all other sectors of the chemical industry. With relatively low material prices, adequate feedstock supplies and high product prices, the general short¬term outlook is for the industry to continue its strong performance and further penetrate diverse markets in the economy. Although the economic benefits of the chemical and petrochemical industry have been welcomed, the environmental problems have not been applauded. The problems were not just with disposal of solid waste of the petrochemical companies but with releasing fumes and gases into the atmosphere that cause diseases in plant employees and in residents who lived near plants (Reis et al., 2007)1.
The work environment usually contains a large number of chemicals, which may be inhaled and absorbed by the body. (IARC, 1989)2. In addition, the petroleum and chemical industries have introduced substances at the alarming rate of several hundred untested new compounds a year, subjecting workers to unknown hazards. Although chemicals are frequently associated with gases, they are also present in solvent, mists, vapors, dusts, and solids. Depending on their form and structures, chemicals can enter the human body through the lung, gastrointestinal tract, and/or skin. The great number of toxic substances that are present in the work environment may result in respiratory, dermatologic, and other health problems. (WHO, 1985)3. Occupational and environmental surveillance for exposure to chemicals represent, an important global issue as international trade increases the understanding and practice of exposure assessment ,medical surveillance, epidemiology, community and work communication are essential in the control of chemical hazards in the work place and the community (Zober et al., 1998)4. One of the most danger chemicals in work setting is the petroleum derivatives, namely; organic solvents and hydrocarbons. Because solvents are found in a wide range of products and processes, many workers are at risk of exposure. Solvent exposure is common among painters, degreasers, and petrochemical and refinery workers (Rogers, 2000; Waldbott,
1978)5- 6_ Thus benzene, toluene and xylene (collectively known as BTX) are harmful substances in occupational and non-occupation environment and humans are frequently exposed to low levels of these chemicals for prolonged periods (McDermott et al., 2008)7. Benzene, toluene and xylene have been reported to induce oxidative stress, an imbalance of the anti-oxidant system. In this context, alteration of the anti-oxidant system in petrochemical workers was reported (Croute et al., 2002; Georgieva et al., 2002)8,9.
Several studies have implicated oxidative stress as one of the important mechanisms of toxic effects of organic solvents (Costa et al., 2005; Radwan et al., 2010)10,11 Oxidative stress is defined as imbalance between oxidants and antioxidants in favor of the oxidants, potentially leading to damage. When additional oxidative events occur, the pro-oxidant systems outbalance the anti-oxidant, potentially producing oxidative damage to carbohydrates, proteins, nucleic acids, and lipids ultimately leading to cell death in severe oxidative stress. Mild, chronic oxidative stress may alter the anti-oxidant systems by inducing or repressing proteins that participate in these systems, and by depleting cellular stores of anti-oxidant materials such as glutathione (Azzi, et al., 2004)12. The study highlights the need for vigilance environmental monitoring, medical surveillance and safety awareness of workers in petrochemical industry.