Mercury: major issues in environmental health.

Abstract

In the past, methylmercury compounds were manufactured as fungicides or appeared as unwanted byproducts of the chemical industry, but today the methylation of inorganic mercury in aquatic sediments and soils is the predominant if not the sole source of methylmercury. This form of mercury is bioaccumulated to a high degree in aquatic food chains to attain its highest concentrations in edible tissues in long-lived predatory fish living in both fresh and ocean waters. It is well absorbed from the diet and distributes within a few days to all tissues in the body. It crosses without hindrance the blood-brain and placental barriers to reach its principal target tissue, the brain. It is eliminated chiefly in the feces after conversion to inorganic mercury. The biological half-time of methylmercury in human tissues is about 50 days, but there is wide individual variation. Adult poisoning is characterized by focal damage to discrete anatomical areas of the brain such as the visual cortex and granule layer of the cerebellum. A latent period of weeks or months may ensue before the appearance of signs and symptoms of poisoning. The latter manifest themselves as paresthesia, ataxia, constriction of the visual fields, and hearing loss. The prenatal period is the most sensitive stage of the life cycle to methylmercury. Prenatally poisoned infants exhibit a range of effects from severe cerebral palsy to subtle developmental delays. Methylmercury is believed to inhibit those processes in the brain specially involved in development and growth such as neuronal cell division and migration.

Toxicity of mercury

“…32 The extent of the problem was only realised following the Japanese disaster at Minamata where a factory's effluent was discharged into the local fishing grounds. By a process of biomagnification, the methylmercury accumulated to sufficient amounts in predatory fish 33 to poison over 800 people who relied on the fish for their nutrition. A number were infants in utero.…”

Visual acuity in fish consumers of the Brazilian Amazon: risks and benefits from local diet

“…Methylmercury (MeHg) is a neurotoxic substance known to affect visual functions (1)(2)(3) . Visual impairments were studied in Japan, where people ingested contaminated fish following industrial releases of Hg and MeHg into Minamata Bay.…”

Mercury risk from fluorescent lamps in China: Current status and future perspective

“…Low doses of mercury exert toxicity on various human organs, including the central nervous system, renal system, reproduction system, immune system, cardiovascular system and motor system (Zahir et al, 2005). Mercury particularly impairs the neurological development of fetuses, infants and children, whose nervous system is under development and is sensitive to environmental insults (Clarkson, 1993;Snyder, 1971). Genotoxicity of mercury has also been observed in human beings and animals, as well as in plants (Bonacker et al, 2004;Zahir et al, 2005).…”

“…Mercury, in both inorganic and organic forms, exhibits toxicity to organisms in aquatic and terrestrial ecosystems (Boening, 2000). Mercury toxicity in aquatic ecosystems has received great attention in particular, because inorganic mercury can be methylated in aquatic sediments, and the resulting methylmercury is bioaccumulated to a high degree in aquatic food chains (Clarkson, 1993;Tchounwou et al, 2003). As a result, the highest concentrations of the highly toxic methylmercury are found in tissues of long-lived predatory fish in fresh and ocean waters (Boening, 2000;Clarkson, 1993;Tchounwou et al, 2003).…”

“…Mercury toxicity in aquatic ecosystems has received great attention in particular, because inorganic mercury can be methylated in aquatic sediments, and the resulting methylmercury is bioaccumulated to a high degree in aquatic food chains (Clarkson, 1993;Tchounwou et al, 2003). As a result, the highest concentrations of the highly toxic methylmercury are found in tissues of long-lived predatory fish in fresh and ocean waters (Boening, 2000;Clarkson, 1993;Tchounwou et al, 2003). Because of the great challenges to public health posed by mercury pollution, various voluntary and mandatory programs have been implemented in many developed countries to reduce anthropogenic mercury emissions to protect human health and the environment from the risk posed by mercury.…”