Mercury, in all its forms, is one of the most toxic metals on Earth. First used in the 1930s and 1940s to kill bacteria in antiseptic products and used inside vaccines to prevent needle puncture contamination, thimerosal was tested in rabbits and later in humans, and though the subjects died days after being given high doses of the compound, mercury was deemed safe.

The methylmercury found in seafood and the ethylmercury ingredient of Thimerosal in vaccines are now known to be potent neurotoxins, especially to the developing brains of preterm babies and children. Mercury can severely disrupt the normal neurodevelopmental processes in the human brain, causing problems in migration and division of neurons, as well as cell degeneration and ultimately cell death. Studies are showing the effects of mercury in populations, including a New Zealand study and Faroe Island study that measured a decline in intelligence and IQ, in line with other studies that have shown mercury’s adverse effects on the brain, including cognitive deficits, ADD, ADHD, and memory loss – though early on in mercury’s history, no neurological or behavioral tests were conducted before the compound hit the shelves.

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