Epidemiological surveillance of employees in a mercury thermometer plant: An occupational health study

A cross-sectional epidemiological survey of 255 individuals (130 current permanent employees, 64 contract workers, 55 ex-employees and 6 scrap dealers) coupled with a retrospective cohort study of the occupational health of 290 employees (all permanent employees who ever worked in the factory over a span of 15 years) was conducted in a mercury thermometer plant at Kodaikanal in India. The cross-sectional study done in March 2001 was based on a clinical protocol developed by the US Dept. of Labor, Mines Safety and Health Administration and was supplemented by the analysis of mercury in urine (HgU) through Inductively Coupled Plasma Emission Spectrometry (ICP) and relevant biochemical investigations. Group averages of HgU in this study was 23.8 μg/L and were well within WHO-recommended limits of group means (50 μg/L). Group analysis was supplemented by appropriate individual analysis. The retrospective cohort study (for the years 1988-2001) included clinical evaluation coupled with analysis of biological monitoring done through Cold Vapor Atomic Absorption Spectrometry (CVAAS). Group averages of mercury in urine measured between 12.9 to 31.9 μg/L over the working life of the factory, and they too were supplemented by appropriate individual analysis. The protocol for epidemiological surveillance and indeed for the occupational health surveillance conducted over the life of the factory (biological monitoring, workplace environmental monitoring, shop floor health and safety practices and clinical evaluations) have been independently validated by the Netherlands-based TNO, the All India Institute of Medical Sciences, and the Indian Association of Occupational Health. None of the employees in this factory were found to be suffering from any ill health that could be attributed to Hg exposure.

Keywords
Biological monitoring, cohort, environmental monitoring, epidemiological surveillance, mercury