A Triple Dose Of Studies Highlight PCB Toxins Dangers
by Kirsten Whittaker

Exposure to specific toxins in the environment, also known as PCBs (technically called polychlorinated biphenyls), appears to have an effect on the development of brain cells according to not one or two, but three new studies.

Toxic substances all around us have long been connected with problems in youngsters, but research couldn't explain exactly how PCB toxins impact the brain.

Once PCBs were used in a huge amount of goods, from pesticides, caulking, flame retardants and electronic components. The U.S. banned their use in the 1970s. However, these chemicals stick around in the environment because they do not easily break down.

They're still in the air, seep into our water, are in the ground and contaminate the food we eat, like fish. PCBs are still detectable in all of us, even today.

The latest group of studies has found that these environmental toxins negatively affect the development of brain cells and overexcite brain circuits. This has been linked by earlier work to developmental problems.

"We think we have identified the way in which a broad class of environmental contaminants influences the developing nervous system and may contribute to neuro-developmental impairments such as hyperactivity, seizure disorders, and autism," said researcher Isaac N. Pessah, PhD. The latest of the 3 studies appears in the April 2009 online issue of PLoS-Biology.

One surprising finding from the study was that lower levels of PCB exposures sometimes were more harmful than higher exposures.

The first of the studies discovered that exposures to low levels of PCBs impaired animal subjects' ability to learn to navigate a maze, a universal way to test learning in the lab.

It seems that even low doses of PCBs adversely affected the plasticity of the dendrites, which are key to learning and memory. Problems in this area have been implicated in conditions like autism, schizophrenia and even mental retardation.

The first study was published in the March 2009 issue of Environmental and Health Perspectives.

For the second of the studies, tissue from the animal's hippocampus (part of the brain that manages memory and emotion) was examined in order to measure the excitability of neurons before and during exposures to two different PCBs.

The normal brain needs to strike a balance between excitation and inhibition of the neurons, as too much excitability isn't a good thing. Disorders like autism and attention deficit hyperactivity disorder (ADHD) may in fact involve an imbalance between the two states.

The second study appears in the March 2009 issue of Toxicology and Applied Pharmacology.

The third study looked at a cellular level, looking specifically at how PCBs might affect cell development (as they saw from the first study) and the level of excitement (what they found from that second study).

The researchers exposed receptors in the brain cells that control the release of calcium (key to keeping signalling normal from cell to cell) to PCBs. They found that PCBs bind to the receptors and hinders the release of calcium.

It's this that could be the reason for the results found in the other two studies.

"I think that these studies represent a kind of a turning point for our recognition of how these chemicals, PCBs, can interfere with brain development," says R. Thomas Zoeller, PhD, professor of biology at the University of Massachusetts, Amherst.

So, now that there's a research backed explanation of how PCBs can cause damage, this adds more weight to the research to link toxic exposure and developmental problems.

It may also allow us come up with new ways to evaluate the safety of chemicals that have taken the place of PCBs, and maybe remove the dangerous ones before they become widely used.

What's more, the work shows us that even lower dose exposures to PCB toxins aren't always better and may not be safe at all.

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