ABSTRACT
Evaluation of the effect of elemental mercury [Hg[0]] vapor exposure on the plasma glutathione peroxidase enzyme [PGLPX] and its impact on the thyroid function as evidenced by changes in the level of free thyroxin [T[4]], free triiodothyronine [T[3]], free T[4] /free T[3] ratio as well as the thyroid stimulating hormone [TSH] level. The level of glutathione peroxidase enzyme was estimated using the PGLPX-enzyme immunoassay [EIA]. Serum concentrations of TSH, free T[4] and free T[3] were determined by radioimmunoassay. Assessment of the urinary mercury level was carried out using the atomic absorption spectrometry. The creatinine-corrected urinary mercury [U-Hg] was considered an index of current exposure. This study was carried out on a group of 20 workers exposed to mercury vapor for an average of 29.15 years during the process of mercury electrolysis in an explosive industry and on 12 matched control workers. The mean U-Hg in the exposed population was high [136.86 +/- 45.68 micro g. gm[-1] creatinine] versus 35.44 +/- 14.87 [micro g. gm[-1] creatinine in the control group. There was a remarkable statistically significant increase in the free T4 level among exposed subjects as compared to controls [mean 1.565 ngm dL-1 versus 0.950 ngm dL[-1]]. The free T[4] /free T[3] ratio was also higher in the exposed subjects, but no significant difference was obtained for the level of T[3] and TSH. As for the PGLPX, a highly significant decrease was obtained in the exposed population compared to the control. A significant association was found between increased U-Hg and decreased TSH as well as PGLPX fall. The drop in the level of TSH was shown to be affected by the duration of exposure as evidenced by the statistically significant negative correlation. Regarding PGLPX, there was a significant negative correlation with the level of urea, bilirubin, as well as the free T4 and the free T[4] /free T[3] ratio. The study could indicate a slight effect of occupational exposure to mercury vapor on the function of the enzyme type I iodothyronine deiodinase, as evidenced by increased free T[4] /free T[3] ratio, and on the PGLPX level, as evidenced by the marked drop in its plasma level. Selenium deficiency might be considered an intermediate step in the pathogenesis of these changes