Sunday, October 07, 2007

Autistic Children - Canaries In The Coal Mine?

The classic example of animals serving as sentinels is the "canary in the coal mine". Well into the 20th century, coal miners in England and the US brought canaries into coal mines as an "early warning signal" for toxic gases including methane and carbon monoxide. The birds, being more sensitive, would become sick before the miners, who would then have a chance to escape or put on protective respirators.

- Wikipedia

Is the dramatic rise in the diagnoses of autism solely a result of changed diagnostic criteria and enhanced public awareness? Or are environmental factors also involved? Are children suffering increasingly from developmental disorders, including autism, because of degradation of the world environment? Like the canaries in the coal mines do the increasing numbers of autistic children also serve as a warning of serious environmental decay?

The thimerosal/vaccine theories have occupied much public attention over the past several years but have they also distracted from other potential environmental factors? Few would deny the very important role of genetics in autism. The Unified Theory of Autism and the concept of genetic mutation, however, suggest that genetic mutations associated with autism may arise from environmental triggers. Vaccines are not the only human source of mercury which can also be found in thermometers, dental fillings, fluorescent light bulbs, and other consumer products. Environment Canada has a web page called Mercury and the Environment which illustrates how mercury, particularly methylmercury, concentrates in in the environment, and in living organisms.

Some mercury compounds are more easily absorbed by living organisms than elemental mercury itself. When atmospheric mercury falls to earth, it may be altered by bacterial or chemical action into an organic form known as methylmercury. Methylmercury is much more toxic than the original metal molecules that drifted in the air, and has the ability to migrate through cell membranes and "bioaccumulate" in living tissue. Bioaccumulation is the process by which a substance builds up in a living organism from the surrounding air or water, or through the consumption of contaminated food. Bioaccumulation will vary for different species and will depend on emission sources as well as local factors like water chemistry and temperature.

In the following figure, the concept of accumulated methylmercury is illustrated by the red dots, however the dots are not to scale.

The bioaccumulation of methylmercury in natural ecosystems is an environmental concern because it inflicts increasing levels of harm on species higher up the food chain. This occurs through a process known as "biomagnification", whereby persistent substances like methylmercury will increase in concentration from microorganisms, to fish, to fish eating predators like otters and loons, and to humans. Elevated methylmercury levels may lead to the decline of affected wildlife populations and may affect human health when people consume significant quantities of fish or other contaminated foods.

The Environment Canada site states that the amount of mercury in the air arising from human activities has increased by a factor of 2 to 4 since industrialization. In addition to mercury there have been frequent recalls of toy products containing lead. A recent California study suggested a causal connection between some pesticides and autism rates.

With the significant environmental degradation taking place today it seems entirely possible that the increasing prevalence of autism amongst children may be due to more than changes in diagnostic criteria and public awareness. Increasing levels of toxic substances in our environment may be triggering genetic mutations and may be contributing significantly to the increasing diagnoses of autism. Autism research should pursue all possible factors, genetic and environmental. To help our autistic children - and to more thoroughly understand what we are doing to our environment and ourselves.

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