Environmental Health Risk Assessments: How Flawed Are They? A Methyl-Mercury Case Study

Document Type

Journal Article


Faculty of Computing, Health and Science


School of Nursing and Public Health




Oosthuizen, J. (2001). Environmental Health Risk Assessments: How Flawed Are They?: A Methyl-mercury Case Study. Environmental Health, 1(2),11-17. Available here


The objective was to test the reliability of environmental health risk assessment techniques by utilising biological monitoring as a means of verification of risk calculations. The study population consisted of fish consumers living in close proximity to the u'Mgeni River and the Inanda Dam, downstream from a mercury recycling plant. A control group was selected from an area upstream from the mercury plant. Fish in both the study and control areas were sampled in order to obtain the mean mercury levels to which consumers were exposed. Data related to fish consumption rates, as well as the age and body weights of individuals were obtained by interview. Standard risk assessment methodology was used to determine total daily mercury consumption per kilogram body weight per day. These data were compared to the "tolerable daily intake" (TDI) standard of the World Health Organization and the United States Environmental Protection Agency. In order to verify the risk assessment calculations, human hair samples from both the study population and from a control group were analysed as a direct measure of mercury exposure. The results of the risk estimation indicated that the study population is at risk. Human hair samples were obtained from fishermen in both the study area and control area. It was expected that the mercury concentration in hair would exceed 11 g/g (US Environmental Protection Agency 1999), however, all results were found to be below the level of sensitivity of the laboratory test (0.5 g/g). The results of environmental health risk assessments need to be viewed with caution as there are a number of potential sources of error inherent in the risk assessment methods, including the accuracy of data gathered from people, as well as the accuracy of both estimated and measured environmental data. It appears as if a combination of factors may have contributed to the high level of discrepancy in results. It is recommended that studies should include biological monitoring in a small "high risk" purposive sample of exposed individuals to verify risk assessment data.