The major source of methylmercury is diet, particularly large fish like shark and swordfish. The authors of this new research concluded: "methylmercury exposure at levels often encountered by adults in North America may be inducing adverse effects on neurobehavioral performance."
Methylmercury damages or destroys nerve tissue. It affects the visual cortex and the cerebellum, the part of the brain responsible for controlling complex movements and maintaining balance. This new research challenges the assumption that adults are much less sensitive to its toxic effects than children.
Ellen Silbergeld, of John Hopkins University, and her colleagues conducted the first major study on the effects of long-term exposure to small amounts of methylmercury in adults using sensitive neuropsychological tests.
The team, which included researchers from The University of Rio de Janeiro and the University of Maryland, studied a group of 129 men and women living in fishing communities of the Pantanal region of Brazil. They took samples of recent hair growth and analysed them for mercury. Because hair grows constantly, these values reflect the exposure of individuals to methylmercury within the previous three months. About one out of four of the participants were found to have mercury levels that exceeded the 'safe' level set by the World Health Organization (WHO) for women and children. WHO will decide next week whether the current exposure limit should be decreased.
The researchers also used a number of tests to assess mental functions such as learning, attention, memory, accuracy, manual speed and dexterity. Those individua
Contact: Grace Baynes