الفهرس 
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Abstract
The petrochemical sector plays an important role in the industrial strategies of developed countries. World sales of petrochemicals continue to increase and surpassing all other sectors of the chemical industry. 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 caused diseases in plant employees and in residents who lived near plants.
Chromium catalysts are used in various reactions such as hydrogenation, oxidation and polymerisation reactions. A range of Cr catalysts is available for use in the polyethylene process to manufacture broad molecular weight products for blow molding, pipe and film applications. The widespread use of Cr in industrial applications has lead to human occupational exposure and to its increased introduction into the environment. The entry routes of Cr into the human body are inhalation, ingestion, and dermal absorption.
The objective of the present study was to investigate the effect of long-term occupational exposure to air-borne dust containing Cr(VI) on Cr levels in blood and urine of workers in petrochemical industry. Moreover, the enzymatic and non-enzymatic antioxidant activities will be measured in the blood of these workers.
The study was carried out on two groups: the first (Worker group) included 30 male workers at the petrochemical industry, who have been exposed to Cr(VI) for longer than 3 years, the second (Control group) included 30 healthy individuals of matched age, sex and socio-economic level.
All cases were subjected to the following investigations:
• Venous blood samples collected from fasting subjects for the measurement of erythrocyte and plasma concentrations of Cr using atomic absorption spectrometry. Moreover, twenty four hours urine were collected in hydrochloric acid cleaned polyethylene bottles for measuring urinary concentrations of Cr using atomic absorption spectrometry.
• Biochemical investigations including complete analysis for liver and kidney functions were carried out for all participants. Moreover, the levels of the non-enzymatic antioxidant (glutathione) and the activities of enzymatic antioxidants [i.e., glutathione peroxidase (GPx), catalase, and superoxide dismutase (SOD)] we also performed. Malondialdehyde (MDA) was also assayed as an index of lipid peroxidation.
One of the main results of our study is the significantly higher level of MDA by 195.68% in the plasma of Cr-exposed workers as compared to healthy controls. There was also a significant correlation between the levels of MDA and Cr in the plasma of Cr-exposed workers
The GPx enzyme activity was also significantly lower by 16.41%, while SOD enzyme activity was significantly higher by 14.3%, only in the hemolysate, but not in plasma, for Cr-exposed workers as compared to healthy controls. Moreover, the activity of Catalase enzyme in the hemolysate of Cr-exposed workers was 13.5% lower than that for healthy controls.
There was also a significant correlation between the activities of Catalase and SOD enzymes in the hemolysate of Cr-exposed workers. This observation shows that occupational exposure to Cr results in disturbances in the antioxidant system in the erythrocytes and plasma, which generate a state of oxidative stress correlated with the Cr levels in the erythrocytes, plasma and urine.
In the present study, Cr levels in the hemolysate, plasma and urine of Cr-exposed workers were significantly higher by 51.58, 117.37 and 316.84%, respectively, as compared to healthy controls. Cr levels in plasma and urine, as determined by atomic absorption, reflect its total concentration, but not the concentration of any of its specific forms. However, the specificity of erythrocytes Cr content as a biomarker for the exposure to Cr(VI) is high, since the chromate ion is transported into erythrocytes via the sulfate anion channel. Thus, the Cr content measured in the erythrocyte fraction is used as a biomarker for systemic uptake of Cr(VI) in workers. It is believed that the urinary Cr measurements for workers may not be remarkable with respect to showing appreciable occupational exposure to Cr(VI). However, the concentration of Cr in whole blood and urine has still been used as a biomarker for evaluating exposure to Cr compounds in occupational settings.
The total and reduced glutathione (GSH) for Cr-exposed workers were significantly lower by 11.39 and 21.16% in the hemolysate and by 7.78 and 9.69% in plasma, as compared to healthy controls. However, the levels of oxidized glutathione (GSSG) were significantly higher by 196.73% only in the hemolysate of Cr-exposed workers in comparison with healthy controls. The intracellular redox status calculated as a ratio of GSH/GSSG in the hemolysate was much lower, and to a lesser extent in plasma, than values for healthy controls (i.e., 21.70 folds for the Cr-exposed workers versus 44.20 folds for healthy controls).
from the above discussion, our study shows that a state of oxidative stress in Cr-exposed workers produced by the exposure to Cr(VI), whether by the enhanced production of ROS or by the depletion of antioxidant capacity, may play a role in the mechanism of its toxicity.
The observations of the present study lend support to the opinion that exposure to Cr in petrochemical industry may result in oxidative stress in the erythrocytes of the workers, since long-term exposure to Cr shifts an oxidant/antioxidant intracellular balance to oxidized environment. The increased plasma lipid peroxidation and decreased plasma and erythrocytes antioxidants (glutathione and enzymes) among Cr-exposed workers suggest that these could be used as biomarkers of oxidative stress, which may help in early detection of high-risk subjects.