Last month's worries about contaminated tap water and this week's concerns about bisphenol A (BPA) leaching out of the everyday plastic items we use have prompted understandable hand-wringing online. Are we being poisoned by our environment? Worse still, are we poisoning our babies?
Thinking about those questions raised others: Isn't the human body equipped to deal with at least some of the toxins it's exposed to? If there's evidence of toxic substances in people's urine, mightn't that just show that the body is doing a good job of getting rid of the toxins we ingest?
I put those questions to two toxicologists today, who told me that of course the body is designed to deal with potentially harmful substances that get inside us. And it's a pretty sophisticated system.
Edward Calabrese, professor of toxicology in the environmental sciences division at the University of Massachusetts/Amherst School of Public Health, and JosÃ© E. Manautou,
Everything that goes into your mouth -- including food and water -- goes through your liver before entering the rest of your system, says Manautou. "The liver is like the bouncer at the bar or nightclub," deciding who gets in and who gets kicked out.
Both the good and the bad stuff gets "metabolized" -- or changed into something water-soluble so the body can manage it -- by the liver. This is why it's so important to keep your liver healthy, especially by avoiding smoking and drinking too much alcohol.
Then the liver sends a lot of the metabolized substances to the blood, which carries the good stuff to the parts of the body that need it. The blood gets filtered through the kidneys, and the metabolized toxins are eliminated through your urine.
The liver sticks some of the bad stuff -- typically, the substances with higher molecular weight -- into the bile that it produces. It sends the bile through the biliary system; the, er, end result is that some of the metabolized toxins take this route out, leaving your body via your feces.
Edward Calabrese says metabolism by the liver is one of the body's two main systems for dealing with toxins. The other, which he calls the "transporter efflux system," works to repel pollutants and poisons, keeping them from entering cells.
Calabrese adds that while some toxins are expelled through exhalation, perspiration, and through the growth of hair and fingernails, the bulk of the work is done by the liver and the transporter efflux system.
Not all toxins are created equal, and some pose a greater challenge to your well-designed system. Manautou explains that "A number of environmental contaminants are of great concern because of their limited biodegradation (including metabolism by living organisms). This is one of the reasons why some compounds bioaccumulate in the environment and become toxic. Among these, there is a class of chemicals known as endocrine disruptors that are notorious for their slow metabolism and bioaccumulation. Other chemicals that received a lot of attention recently and have incomplete metabolism are the brominated flame retardants. Some carcinogens are reactive enough that they can produce some of their effects before they can be detoxified."
associate professor of toxicology in the department of pharmaceutical sciences at the
University of Connecticut, helped me understand what happens when bad toxins happen to good people. Here's what I learned:
Got that? There will be a quiz.
Further questions? Check next Tuesday's Health section, where Ranit Mishori will tell you more about BPA and phthalates in plastics -- and whether they really represent a danger to your health.
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