Health risks from increases in methylmercury exposure.

Abstract

Our present knowledge of the human health effects of methylmercury exposure is derived from study of major outbreaks of human poisonings in Japan and Iraq and experimental studies on primates. Methylmercury readily passes through such physiological barriers as the blood-brain barrier, blood-testes barrier, and the placenta. Its major pathological effects are on the nervous and reproductive systems and the developing embryo/fetus. The neurotoxicity of methylmercury is well established in both humans and non-human primates. Lesions in the cerebral and cerebellar gray matter consist of necrosis and lysis of neurons, phagocytosis and gliosis. The changes are most prominent in the deep sulci and may have a vascular component. A late effect is cerebral atrophy. At high dose levels the liver, kidneys, and other organs may also have degenerative changes.Although not yet described in humans, a major effect of exposure of female primates is an adverse effect on pregnancy. Maternal female M. fascicularis blood mercury levels above 1 ppm are associated with a decreased pregnancy rate and increased abortion rate. To date our experimental data lack sufficient numbers to detect infrequent pregnancy effects below 1 ppm. Preliminary studies also reveal that methylmercury may also decrease the number and function (swim speed) of sperm.Both human and primate studies demonstrate deleterious effects of methylmercury on the developing embryo/fetus. Autopsies on human and primate infants reveal retarded brain development and the occurrence of a cerebral palsy-like behavior in the newborns, whereas the mother may be free of signs and symptoms of methylmercury toxicity. The fetal blood level of mercury is higher than the maternal level. Many features of physical and behavioral development of the newborn and infant have been reported from relatively high exposure levels. Behavioral tests of infant primates (object permanence; visual preference) revealed a retardation of cognitive development. Further research is needed to define the level at which methylmercury begins to have significant neurotoxic, reproductive, or fetal developmental effects. The increased level of methylmercury in some fish due to acid precipitation and the demonstration of significant lesions at clinically nontoxic levels suggest that the margin of safety may be narrow.

Improved Chronic Fatigue Symptoms after Removal of Mercury in Patient with Increased Mercury Concentration in Hair Toxic Mineral Assay: A Case

“…It also easily travels through the blood-brain barrier. Consequently, the conjugation is oxygenated and accumulated, which is toxic to humans and is called the chronic exposure of methyl-mercury 14-16). Symptoms resulting from chronic exposure to methyl-mercury gradually develop and may be observed after a long period of time.…”

A Tanscriptomics Study to Elucidate the Toxicological Mechanism of Methylmercury Chloride in a Human Stem Cell Based In Vitro Test

“…A number of adversities have been reported including mental retardation, severe behavioral and sensory deficits including deafness and blindness, neuromuscular weakness and altered neurobehavioral development [4,5]. MeHg exposure may also cause malformations manifested as skeletal variations, reduced ossification, abnormal brain structure, changes in neuronal migration and distribution patterns, and reduction in the number of brain cells [17][18][19][20].…”

Impact of Effects of Acid Precipitation on Toxicity of Metals

“…The toxicities of these compounds are quite different. Pulmonary toxicity is the critical effect after short-term inhalation of high concentration of mercury vapor; after long-term inhalation, neurotoxic effects (e.g., neuroasthenia and tremor) and renal effects may occur (1,(3)(4)(5).…”

“…Observations on humans were made during an outbreak of methylmercury poisoning in Minamata, Japan, in the mid 1950s (14). The prenatal effects of methylmercury have also been documented in several animal species (3,13,15). During a poisoning epidemic in Iraq 1972, detailed dose descriptions of prenatal poisoning cases were made by analysis of hair concentrations of methylmercury in the mothers, as described in the previous section for adult methylmercury poisoning.…”