Mercury hotspots continue to impair human cognition.

Feb 24, 2009

Chang, J-W, M-C Pai, H-L Chen, H-R Guo, H-J Su and C-C Lee. 2008. Cognitive function and blood methylmercury in adults living near a deserted chloralkali factory. Environmental Research 108(3):334-339.

Synopsis by Niladri Basu

Memory and concentration ability were lower in adults living near an abandoned Taiwanese factory where mercury was used many years ago.

This is one of the first studies to document methylmercury's (MeHg) effects on human brain function in Taiwan. Other studies find similar outcomes in people from Japan, the US, New Zealand and Canada.

The findings "raised public concern about local environmental contamination and who specifically has been exposed to MeHg via fish and other seafood from the nearby aquatic environment," report the authors.

Mercury is a metal so it does not degrade and is persistent. Mercury can exist in different chemical forms. Each chemical form of mercury has different properties. These properties affect its toxicity.

Mercury is mainly released from coal-fired plants as a gas by-product. Once this mercury enters waterways it is converted by bacteria into methylmercury. Methylmercury is one of the more harmful chemical forms. It can build up in aquatic food chains and be passed to people mainly through eating contaminated fish and seafood.

Methylmercury has long-lasting health effects, mostly on the brain. Whether a person is exposed during development or as an adult, effects on cognition and mental abilities can occur years after exposures. Changes in brain function can affect a person's quality of life. In turn, this has consequences for society.

Here, the relationship between blood mercury and brain cognition were studied in 240 adults. Total mercury and methylmercury were measured in the blood. Participants filled out health history and lifestyle questionnaires and completed exams that tested for memory, concentration and orientation. Variables such as age, gender and education were also taken into account.

In these people, mercury exposure was associated with impairments in their ability to remember and concentrate.

Those with higher levels of blood mercury also ate more fish and seafood. While the benefits of eating fish are numerous, fish from hotspots of mercury contamination should be avoided as they can affect human brain function.

While the results are compelling, the exposures are quite high. The levels of blood mercury in these affected people (27 ug/L) are higher than the US Environmental Protection Agency’s recommended reference dose (5.8 ug/L) and more than 20 times greater than levels found in the average US citizen (1 ug/L from NHANES 1999-2000 Survey; JAMA. 2005;293:1875-18827).