Adverse effects of methylmercury: environmental health research implications.
BACKGROUND
The scientific discoveries of health risks resulting from methylmercury exposure began in 1865 describing ataxia, dysarthria, constriction of visual fields, impaired hearing, and sensory disturbance as symptoms of fatal methylmercury poisoning.


OBJECTIVE
Our aim was to examine how knowledge and consensus on methylmercury toxicity have developed in order to identify problems of wider concern in research.


METHODS
We tracked key publications that reflected new insights into human methylmercury toxicity. From this evidence, we identified possible caveats of potential significance for environmental health research in general.


RESULTS
At first, methylmercury research was impaired by inappropriate attention to narrow case definitions and uncertain chemical speciation. It also ignored the link between ecotoxicity and human toxicity. As a result, serious delays affected the recognition of methylmercury as a cause of serious human poisonings in Minamata, Japan. Developmental neurotoxicity was first reported in 1952, but despite accumulating evidence, the vulnerability of the developing nervous system was not taken into account in risk assessment internationally until approximately 50 years later. Imprecision in exposure assessment and other forms of uncertainty tended to cause an underestimation of methylmercury toxicity and repeatedly led to calls for more research rather than prevention.


CONCLUSIONS
Coupled with legal and political rigidity that demanded convincing documentation before considering prevention and compensation, types of uncertainty that are common in environmental research delayed the scientific consensus and were used as an excuse for deferring corrective action. Symptoms of methylmercury toxicity, such as tunnel vision, forgetfulness, and lack of coordination, also seemed to affect environmental health research and its interpretation.
Department of Environmental Medicine, University of Southern Denmark, Odense, Denmark. pgrand@hsph.harvard.edu
Philippe
P
Grandjean
Hiroshi
H
Satoh
Katsuyuki
K
Murata
Komyo
K
Eto
D000818:Animals; D002648:Child; D002657:Child Development / Q000187:drug effects; D002675:Child, Preschool; D004781:Environmental Exposure / Q000266:history*; D004782:Environmental Health; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D018811:Maternal Exposure; D008628:Mercury / Q000737:chemistry; D008767:Methylmercury Compounds / Q000633:toxicity*
D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D008628:Mercury