Hope of Israel Ministries (Ecclesia of YEHOVAH):
Our Dying Planet
Mercury's Scary Migration
Exposure to mercury can damage the brain and nervous system, affecting language, attention, and memory, particularly in children. The environmental group Clean Water Action has calculated that the average mercury level in tuna is high enough that eating as little as two ounces of tuna a week would be unsafe for a child weighing 35 pounds.
by Environment News Service
3:00 a.m. 10.Sep.99.PDT
Researchers say they have found the first evidence that mercury can circumvent the blood-brain barrier that usually prevents toxins from entering the brain.
Though the studies involved fish, the findings have implications for humans, particularly children, and for other species as well.
Scientists at Canada's Maurice Lamontagne Institute and the Swedish University of Agricultural Sciences 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 brains of brown and rainbow trout.
The mercury can go directly to the brain, circumventing the blood-brain barrier -- a nearly impermeable membrane that prevents most toxins from reaching the brain. The researchers 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.
"Considering the importance of complex behavior in the life of fish, and the well-known deleterious effects of mercury upon the nervous system, the toxicological significance of this uptake route needs to be assessed," says Claude Rouleau, Ph.D., a research scientist at Environment Canada's National Water Research Institute and the study's primary investigator. Rouleau performed the research at the Swedish University of Agricultural Sciences, Uppsala, and completed it for publication while at the Maurice Lamontagne Institute-Department of Fisheries and Oceans Canada, in Mont-Joli, Quebec.
Mercury pollution in waterways comes from unsafe manufacturing processes, and the combustion of fossil fuels that contain mercury. Natural sources such as the degassing of the earth's crust, forest fires, the evaporation of seawater, and volcanoes also add mercury to the environment. But an estimated two-thirds of environmental mercury is the result of human activities.
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.
Exposure to mercury can damage the brain and nervous system, affecting language, attention, and memory, particularly in children. The environmental group Clean Water Action has calculated that the average mercury level in tuna is high enough that eating as little as two ounces of tuna a week would be unsafe for a child weighing 35 pounds. In May, the Environmental Working Group and Health Care Without Harm issued a report warning pregnant mothers to avoid canned tuna due to mercury contamination risks.
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.
"The accumulation of mercury or other toxic chemicals in the brain via water-exposed nerve terminals may result in an alteration of these functions and jeopardize fish survival," says Rouleau. "We believe that uptake of metals such as mercury and the subsequent transport along sensory nerves is a process common to all fish species, and in this respect, it is possible that other toxins -- such as pesticides -- also could reach fish brains in this way and this is a subject worthy of further study."
Rouleau says that while chemicals in the brains of such fish may not have direct human implications, as most people do not eat fish brains, the survival of these species does affect humans. More importantly, mercury may reach the brains of humans along similar pathways.
Earlier research has shown that manganese, cadmium, and mercury can be taken through the nose and mouth linings of rodents and transported to the brain through the olfactory nerves.
"The fact that mercury is transported along fish nerves can be extrapolated to humans, as nerve transport also occurs in mammals, including humans," said Rouleau. "Thus, mercury and other toxins could possibly accumulate in human brains via nerve transport."
Rouleau's research is published in the 1 October issue of Environmental Science and Technology, a peer reviewed publication of the American Chemical Society.
Copyright 1999 Environment News Service (ENS).
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