MINIMAL IMMUNOLOGICAL EFFECTS ON WORKERS WITH PROLONGED LOW EXPOSURE TO INORGANIC MERCURY

Objectives-This study was carried out to investigate possible immunolo gical changes in workers with prolonged low exposure to inorganic merc ury in a fluorescent light bulb factory. Methods-29 immunological vari ables were examined in 34 workers with prolonged low level exposure to inorganic mercury (exposed workers) and 35 unexposed workers as the c ontrols. The selected indicator of mercury exposure was concentration of mercury in the urine (U-Hg), which declined progressively from 36.0 mu g/l in 1978 to 6.0 mu g/l in the study year 1994. Results-None of the exposed workers had ever shown signs of either acute or chronic in organic mercury toxicity or had shown any form of hypersensitivity. Th e only changes found in the exposed workers, compared with the control s, were a reduction of the cells that express cluster differentiation (CD25,(T activation antigen (Tac antigen))) and concentrations of tumo ur necrosis factor-alpha (TNF-alpha) in serum. However, the decrease o f cells that express CD25 was unrelated to occupational exposure and w as, in all likelihood, a chance finding. Conversely, the decline in se rum TNF-alpha was closely associated with occupational exposure. Howev er, no dose-response relation was found between U-Hg and TNF-alpha con centrations; nor were TNF-alpha concentrations affected by cumulative occupational exposure to inorganic mercury in over 20 years. Conclusio ns-Tentatively, we suggest that reduced serum TNF-alpha concentrations might be indicative of an in vivo functional defect of the monocyte m acrophage system in this particular group of workers even though they were clinically asymptomatic.