Polluted seafood threat to children Prenatal exposure to methylmercury through consumption of seafood during pregnancy has been associated with neurological deficits and high blood pressure in seven-year- olds. Background Methylmercury is an environmental pollutant that attacks the nervous system. It ca... Prenatal exposure to methylmercury through consumption of seafood during pregnancy has been associated with neurological deficits and high blood pressure in seven-year- olds. Background Methylmercury is an environmental pollutant that attacks the nervous system. It can accumulate to high levels in freshwater fish and marine animals. The developing foetus is particularly vulnerable to such attacks, so it is vital to set safe limits on methylmercury exposure, particularly during pregnancy. Current figures are based on cases of more or less severe methylmercury poisoning. The more subtle effects due to lower-level exposure are more difficult to assess. The findings of a major long-term international research project are forcing health authorities to reconsider exposure recommendations. Description, impact and results The project focused first on a group of 1,000 children in the Faeroes (born 1986/87) whose mothers frequently ate whale meat and other seafood during pregnancy. Prenatal exposure to methylmercury was estimated at birth from mercury levels in the cord blood and mothers' hair. Seven years later, the children underwent many tests to assess their neurological development, some of which revealed cognitive deficits correlating with prenatal methylmercury exposure. A team then tested 149 seven-year-olds in a Madeiran fishing community. As maternal dietary habits had essentially remained unchanged since pregnancy, the current mercury level in maternal hair was taken as an indicator of prenatal exposure. Exposures were about twice as high as those in the Faeroes population. Among other indicators of neurophysiological development, the team measured evoked potential latencies (the time it takes sensory signals to reach the brain). The results confirmed those in the Faeroes study: with increasing prenatal exposure, auditory evoked potentials were increasingly delayed. There was no correlation with the mercury concentrations in the children's own hair, indicative of postnatal exposure. The conclusions of these two studies are reinforced by the difference in geographical and cultural settings and by the use of two different methods for estimating prenatal exposure. Blood pressure was also measured in the Faeroese group. Children with high blood pressure, a major risk factor for cardiovascular disease, are more likely to develop hypertension in adulthood. In both rats and humans, methylmercury poisoning can cause blood pressure to rise, and there is evidence of increased cardiovascular mortality among fish-eaters in Finland. Among the Faeroese seven-year-olds, blood pressure rose with increasing prenatal exposure. The effect was seen within a surprisingly low-level exposure range, reaching a plateau near an exposure level corresponding to the new, particularly low German limit. This means that blood pressure is affected in an exposure range typical of communities that do not depend on marine food. WHO and FAO experts met recently in Rome to discuss these findings, which will be re-evaluated in 2002 in the light of ongoing research. Working partnerships "Detection of early neurotoxicity in children with environmental methylmercury exposure" is a project involving European, American, and Japanese teams. Co-funding organisations include the European Commission (under the Fourth Framework Environment Programme), the US National Institute of Environmental Health Sciences, the Danish Medical Research Council, and the Dannin Foundation.
