Occupational exposure of dental staff to elemental mercury vapor released from dental amalgam is an issue of concern because of the possible immunological and neurological adverse outcomes. Recently, studies have reported that inorganic mercury induces immunosuppression by decreasing the production of thymus gland hormone (thymulin). This study aimed at investigating mercury body burden in dental staff and the relation of this burden to the potential impact of mercury on thymus gland hormone level (thymulin). Besides, the work aimed at verifying mercury effect on nitric oxide synthetase as a possible mechanism of its immunotoxicity. The study population consisted of a group of dental staff (n = 39) [21 dentists and 18 nurses] and a matched control group (n = 42). Each individual was subjected to detailed occupational and medical history taking and to estimation of urinary mercury (U-Hg) and blood mercury (B-Hg) as indicators of mercury body burden and exposure, respectively. Measurement of total thymulin hormone blood level, and plasma level of nitrite and nitrate (indicators of nitric oxide) was also done. The study showed a significantly increased U-Hg and B-Hg levels in the dental staff compared to their controls. This elevation of mercury body burden was associated with significant reduction in thymulin hormone blood level and nitric oxide parameters. These results were more evident in the group of nurses compared to the dentists. In conclusion, our results show that dentists and dental nurses have significant exposure to mercury vapor and point to the negative impact of mercury on thymus gland functions and confirm the implication that the nitric oxide pathway is a possible mechanism for this impact. Moreover, the study raises attention to the importance of hygiene measures in reduction of exposure to mercury vapor released from dental amalgam.

The current work aimed at investigating the cognitive functions impairment among workers of sewer networks due to exposure to hydrogen sulfide (H(2)S) and the relation of this impairment, if any, to the level of H(2)S exposure biomarker 'urinary thiosulfate.' Besides, the validity of using Mini Mental State Examination (MMSE) as screening test for cognitive impairment among the exposed workers was tested. The work was conducted among 33 sewage network maintenance male workers and a matched unexposed control group (n = 30). The participants were subjected to clinical neurological history, estimation of urinary thiosulfate, and assessment of cognitive dysfunction by using neurophysiological (simple reaction time, P300 test) and neuropsychological tests (Wechsler Memory Scale) and frontal executive functions tests. Clinical neurological history revealed significantly higher neurological symptoms (headache, memory defects, lack of concentration) among exposed workers compared to their controls (p < 0.05). Exposed workers had significantly prolonged simple reaction time and delayed P300 latency and showed poor performance of most of neuropsychological tests. Marked elevation of urinary thiosulfate was observed among the exposed workers (p < 0.001) but this elevation was not correlated with the duration of exposure or any of the other measured parameters. Exposed workers had significantly lower mean value of MMSE scoring than that of the controls (p < 0.001). In conclusion, exposure to H( 2)S among sewer network workers is associated with cognitive impairment, which can be screened by applying MMSE as a simple rapid test for H( 2)S occupationally exposed workers.

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