Academic journal article Environmental Health Perspectives

Adverse Effects of Methylmercury: Environmental Health Research Implications

Academic journal article Environmental Health Perspectives

Adverse Effects of Methylmercury: Environmental Health Research Implications

Article excerpt

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 methyl mercury 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.

DATA SOURCES AND EXTRACTION: 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.

SYNTHESIS: 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.

KEY WORDS: empirical research, environmental exposure, epidemiology, methylmercury compounds, prevention and control, public policy, seafood, toxicology. Environ Health Perspect 118:1137-1145 (2010). doi: 10.1289/ehp.0901757 [Online 8 June 2010]

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Although the toxicology and environmental epidemiology of methylmercury have been recently outlined [Clarkson and Magos 2006; Grandjean et al. 2005; United Nations Environmental Programme (UNEP) 2002], the sequence of scientific discoveries and consensus building reveals important caveats and complications that may have a wider relevance to environmental health research.

Metallic mercury and its inorganic salts have been known since antiquity, but organic mercury compounds with a covalent bond between the mercuric ion and the organic radical were first described in the 19th century. The toxic actions became readily apparent in laboratory accidents, and the description of the clinical syndrome noted the "unique character of their symptoms, which do not resemble those produced by any known disease" (Edwards 1865). The clinical picture included sensory disturbance of the lower legs, lower arms, and face; visual field constriction ("tunnel vision"); deafness, ataxia; and dysarthria. This seminal publication became widely known at first but was later forgotten. Major events in the subsequent environmental history of methylmercury are listed in Table 1.

Table 1. Important early warnings about and recognition of
methylmercury (MeHg) toxicity.

Year(s)    Event                                      References

1865       First published record of fatal            Edwards 1865
           occupational MeHg poisoning

1887       First experimental studies on MeHg         Hepp 1887
           toxicity

1930       Report on organic mercury poisoning in     Koelsch 1937
           acetaldehyde production workers

1940-1954  Poisoning cases in workers at MeHg         Franke and
           fungicide production plants                Lundgren 1956;
                                                      Hunter and
                                                      Russell 1954

1952       First report on developmental MeHg         Engleson and
           neurotoxicity in two infants               Herner 1952

1956       Discovery of a seafood-related disease of  SSSGMD 1999
           unknown origin in Minamata, Japan

1959       Studies on MeHg toxicity in cats           Eto et al. … 
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