More mercury is used for ASGM—an estimated 1,400 metric tons in 2011—than for any other use of the metal.5 The ASGM industry emits an estimated annual average of 1,000 metric tons of inorganic mercury, about one-third of which is thought to go into the air while the rest winds up in piles of mining waste (“tailings”), soils, and waterways.7 Some of the inorganic mercury that reaches aquatic ecosystems also gets converted by microbes into organic methylmercury, which accumulates in fish.
Both the inorganic and organic forms can cause neurological problems. However, methylmercury, which passes more easily into the brain, is generally considered the more toxic species, particularly among children, who can experience IQ losses, delayed speech, and other neurodevelopmental deficits from exposure. Early-life exposures are the most harmful, says Roberta F. White, chair of environmental health and associate dean for research at the Boston University School of Public Health, because they can damage the whole brain. Exposures later in life, on the other hand, produce more localized damage to the cerebellum, visual cortex, and motor strip. In adults, these exposures can lead to visuospatial problems and effects on executive functioning, memory, and mood.8
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