Clinical and epidemiological aspects of methylmercury poisoning

Abstract

Summary An opportunity to study the effects of methylmercury poisoning in humans was provided by the large outbreak in Iraq in 1971-2. In adults, poisoning resulted from the ingestion of home-made bread prepared from methylmercury-treated seed grain and there was a highly significant correlation between the amount of bread ingested and blood mercury levels. Poisoning in infants resulted either from prior exposure in utero or from suckling or both. Blood mercury levels were higher in infants and children than in adults. There was no increased incidence of congenital defects. Symptoms and signs of poisoning and histopathological changes were mainly confined to the CNS. Symptoms developed, on average, 1-2 months after exposure. In children there was mental retardation with delayed onset of speech and impaired motor, sensory and autonomic function. Severely affected children were blind and deaf. In adults, the clinical picture could be classified as 1, mild (mainly of sensory symptoms) 2, moderate (sensory symptoms accompanied by cerebellar signs) and 3, severe (gross ataxia with marked visual and hearing loss which, in some cases, progressed to akinetic mutism followed by coma). Grades 1 and 2 carried a better prognosis thant grade 3. Interference with transmission at the myoneural junction was found in 14% of patients studied. There was no evidence of peripheral nerve involvement per se and sensory symptoms may be of central origin. The clinical differences between the Iraqi and Japanese outbreaks may be a result, in part at least, of the severe, prolonged and continuous exposure which occurred in the latter outbreak. Improvement was observed among the mild and moderate group. Treatment with chelating agents, thiol resin, haemodialysis and exchange transfusion lowered blood mercury concentrations but produced no convincing clinical benefit. To be effective, treatment may need to be instituted soon after exposure.

Characteristics of hand tremor and postural sway in patients with fetal-type Minamata disease

“…Similar neuromotor dysfunctions including ataxic gait and clumsiness of hands were observed in patients with methylmercury poisoning at the time of medical examinations (Bakir et al, 1980;Igata, 1993;Harada, 1995). The crucial matter for this study is that such symptoms/signs in the above patients remained irreversibly after the outbreak of Minamata disease, even though these patients underwent medical care and rehabilitation services (Harada, 1978).…”

“…In 1962, one 6-year-old girl residing in Minamata was pathologically diagnosed as fetal-type Minamata disease due to intrauterine methylmercury exposure (Eto et al, 1992). Bakir et al (1980) also reported similar patients with delayed onset of speech and impaired motor, sensory, and autonomic functions in Iraq. For the exposure levels in 23 cases with certified Minamata disease born during [1950][1951][1952][1953][1954][1955][1956][1957][1958][1959][1960][1961][1962][1963][1964][1965], the median methylmercury concentration in dry umbilical cord tissue was reported to be 1.63 μg/g and considerably higher than those (0.054 to 0.131 μg/g) in Japanese children of six prefectures (Akagi et al, 1998;Sakamoto et al, 2010).…”

Environmental factors associated with a spectrum of neurodevelopmental deficits

“…Mental retardation and seizures were observed with greater frequency among the more highly exposed children [Marsh et al, 1987]. The most severely affected children were blind and one was reported to have a hearing impairment [Bakir et al, 1980]. Age at first independent walking and an index of neurologic signs were correlated with maternal hair mercury levels.…”

Manifestações neurológicas em ribeirinhos de áreas expostas ao mercúrio na Amazônia brasileira

“…A exposição humana ao mercúrio pela ingestão de alimentos contaminados é, sem dúvida, a mais importante forma de exposição não ocupacional. Além da Amazônia, esse tipo de exposição tem sido relatado em diferentes acidentes ambientais, com negativos impactos sobre a saúde das populações envolvidas 8,9,10,11 . O diagnóstico da intoxicação por mercúrio se baseia em achados epidemiológicos, clínicos e nas concentrações elevadas de mercúrio no sangue ou em amostras de cabelo 12 .…”