A long-term survey of environmental, blood and urine mercury levels and clinical findings in workers manufacturing mercury relays

Mercury-induced motor and sensory neurotoxicity: systematic review of workers currently exposed to mercury vapor

The neurotoxicity of elemental mercury (Hg0) is well-recognized, but it is uncertain whether and for how long neurotoxicity persists; among studies that evaluated previously exposed workers, only one examined workers during and also years after exposure ceased. The aim of this review is to document the type, frequency, and dose-relatedness of objective neurological effects in currently exposed mercury workers and thereby provide first approximations of the effects one would have expected in previously exposed workers evaluated during exposure. We systematically reviewed studies of neurotoxicity in currently exposed mercury workers identified by searching MEDLINE (1950-2015), government reports, textbook chapters, and references cited therein; dental cohorts were not included. Outcomes on physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies were extracted and evaluated for consistency and dose-relatedness. Forty-five eligible studies were identified, comprising over 3000 workers chronically exposed to a range of Hg0 concentrations (0.002-1.7 mg/m3). Effects that demonstrated consistency across studies and increased frequency across urine mercury levels (<50; 50-99; 100-199; ≥200 μg/L) included tremor, impaired coordination, and abnormal reflexes on PE, and reduced performance on NB tests of tremor, manual dexterity and motor speed. The data suggest response thresholds of UHg ≈275 μg/L for PE findings and ≈20 μg/L for NB outcomes. These results indicate that PE is of particular value for assessing workers with UHg >200 μg/L, while NB testing is more appropriate for those with lower UHg levels. They also provide benchmarks to which findings in workers with historical exposure can be compared.

Persistence of mercury-induced motor and sensory neurotoxicity: systematic review of workers previously exposed to mercury vapor

Elemental mercury (Hg0) is a well-recognized neurotoxicant, but it is uncertain whether and for how long its neurotoxicity persists. Among studies that evaluated previously-exposed workers, only one examined workers during and also years after exposure had ceased. The objective of this review is to create a series of 'synthetic' longitudinal studies to address the question of persistence of Hg0 neurotoxicity in occupationally exposed workers. We systematically reviewed studies describing objective motor and sensory effects in previously-exposed mercury workers. Data from physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies (EPS) were extracted into structured tables and examined for their consistency and dose-relatedness and then compared with the corresponding results from studies of currently exposed workers. We identified six cohorts that described neurological findings in 1299 workers, examined an average of 4.8-30 years after the cessation of exposure. Historical group mean UHg levels ranged from 23 to >500 μg/L, with UHg levels >6000 μg/L in some individuals. Overall, few findings were significant; most were inconsistent across the previous-exposure studies, and in comparisons between studies of previously and currently exposed workers. The results of this systematic review indicate that Hg0-related neurotoxic effects detectable on PE, NB testing, and EPS are substantially reversed over time. To the extent that such effects do persist, they are reported principally in workers who have had very high-dose exposures. In addition, based on the limited available data, those effects reported to persist have been described as having little or no functional significance.