Surveillance of workers exposed to mercury vapour: Validation of a previously proposed biological threshold limit value for mercury concentration in urine

Abstract

A cross-sectional epidemiological study was carried out among subjects exposed to mercury (Hg) vapour, ie, a group of 131 male workers (mean age: 30.9 yr; average duration of exposure, 4.8 yr) and a group of 54 female workers (mean age, 29.9 yr; average duration of exposure 7 yr). The results were compared with those obtained in well-matched control groups comprising 114 and 48 male and female workers, respectively. The intensity of current Hg vapour exposure was rather moderate as reflected by the levels of mercury in urine (HgU) (mean and 95th percentile: males 52 and 147 micrograms/g creatinine; females 37 and 63 micrograms/g creatinine) and of mercury in blood (mean and 95th percentile: males 1.4 and 3.7 micrograms/dl; females 0.9 and 1.4 microgram/dl). Several symptoms mainly related to the central nervous system (memory disturbances, depressive feelings, fatigue, irritability) were more prevalent in the Hg-exposed subjects. They were, however, not related to exposure parameters. In both male and female Hg-exposed workers no significant disturbances were found in short-term memory (audioverbal), simple reaction time (visual), critical flicker fusion, and colour discrimination ability. Only slight renal tubular effects were detected in Hg-exposed males and females, ie, an increased urinary beta-galactosidase activity and an increased urinary excretion of retinol-binding protein. The prevalence of these preclinical renal effects was more related to the current exposure intensity (HgU) than to the duration of exposure and was detected mainly when HgU exceeds 50 micrograms/g creatinine. Changes in hand tremor spectrum recorded with an accelerometer were found in the Hg-exposed males only. The prevalence of abnormal values for some hand tremor parameters (total velocity and total displacement in the 2-50-Hz band) was mainly increased in male workers exposed for more than 10 yr. Unlike the renal tubular effects, the preclinical signs of tremor were more related to the integrated exposure than to the current exposure. Since the female workers, who have been exposed to Hg vapour levels usually insufficient to increase their HgU levels above 50 micrograms/g creatinine, did not exhibit any change in hand tremor pattern, the results of the present study tend to validate our previously proposed biological threshold limit value of a HgU of 50 micrograms/g creatinine for workers chronically exposed to mercury vapour.

Mercury vapour levels in dental practices and body mercury levels of dentists and controls

“…These authors suggested that other potential nephrotoxic agents used in dental practice, including antibiotics, local anaesthetics or composite resins, might be responsible for the observed increase in protein excretion. The mean concentration of urinary mercury in our study was considerably below the threshold level of 50 µg g -1 creatinine, below which there is no effect on kidney function as suggested by Roels et al 32 It is therefore unclear what might be responsible for this observed incidence of renal symptoms reported by dentists.…”

Subjective symptoms and psychological performance of chlorine-alkali workers.

“…In that way the exposed wor kers were more familiar with the motor tasks, which , to gethe r with the lower motivation of the referents on the performance test s, co uld perhaps explain the significantly poorer per form an ce of the referen ce su bjects in the hand-eye coordi natio n test. The methods used for measuring hand steadiness in our study did not reveal individ ual parameters o f tremor pattern , eg , velocit y or th e effect of loading on the tremor spectra that were distu rbed initially (5,7,10) . On the other hand , fo rearm tremor has been show n to be reversible (12), and the exposed workers had had unstead ines s in their hands only now and then .…”

Health hazard evaluation report: HETA-87-265-1975, Joseph T. Luttmer, D.D.S., Cincinnati, Ohio.

“…Several factors, including mercury body burden, mode of exposure, and physiologic variations in metabolism may influence the urine mercury level. 11,12 VI. RESULTS…”