Researchers say they have found the first evidence that mercury can circumvent the blood-brain barrier that usually prevents such toxins from entering the brain. Their studies were with brown and rainbow trout - two of the most popular species for anglers and fish consumers - but may have implications for humans and other species as well, they say. The study was carried out by researchers at Canada's Maurice Lamontagne Institute and the Swedish University of Agricultural Sciences and is published in the October 1 issue of Environmental Science and Technology, a peer-reviewed publication of the American Chemical Society, the world's largest scientific society.
The researchers found that mercury dissolved in lake and river water can enter the nerves that connect water-exposed sensory receptors (for odor, taste, vibration and touch) to the fishes' brains. It can go directly to the brain, they say, circumventing the blood-brain barrier, a nearly impermeable membrane that prevents most toxins from reaching the brain. They also say this is the first study concerning mercury levels in fish brains (as opposed to levels accumulated in other body areas) and the first time it has been established that mercury can enter fish brains through sensory receptors and their connected nerves.
Mercury's toxic effects on fish and human brains are well established. Fish depend on their nervous systems to find food, communicate, migrate, orient themselves and recognize predators. Dissolved mercury usually is taken in by fish through their gills and dispersed by blood as it circulates through the body. In most cases, little mercury accumulates in the brain, which is protected by the blood-brain barrier. However, mercury that does accumulate, having passed through the bloodstream or through nerves, is concentrated in specific sites connected to primary sensory nerves critical to the function of the nervous system.