Reprinted from the ACJ - December, 1993
By now I am sure you have astounded your friends and family with your knowledge of hazardous chemicals. The dose-time (how much how often) concept coupled with an explanation of routes of entry makes for some titillating conversation over your favorite beverage. But you probably could use a few more facts for your arsenal.
Consider that there are numerous other factors that affect the toxicity of chemicals and their effect on your body. It is not always a case of what's good for the goose is good for the gander. Unless of course we are talking about a nice orange glaze and some baked yams. So let's take a look at some of the other factors that affect toxicity.
Age plays a role in how nasty a given toxin may be. As we grow, our organ systems change and so does the way in which we process substances, food or chemicals. Anybody who has changed a child's diapers as they grow knows what I am saying. A youngster may be less able to filter out or chemically react to certain substances, thus making them more susceptible to poisoning. On the other hand, certain immune systems are stronger in children and may help them process the toxin more safely than adults.
Nutrition also affects toxicity. Vitamins in your body help aid in the internal processing that turns food to fuel. They also play a role in reacting with or isolating toxins as they pass through. They aid our normal systemic functions in ridding our body of the nasty stuff. The protein and vitamins in milk are believed to aid in the natural removal of lead from our bodies. Thus the explanation of why so few cows die of lead poisoning.
The presence of other chemicals in your body can increase the danger of a given toxin, like bullets increase the danger posed by a gun. This is called a "synergistic effect." Conversely, they can also decrease the toxic effects on your body. This is called "chemical antagonism."
SEX! For those of you joining us at this paragraph, it's not what you think. It is simply the fact that males and females have different types and different concentrations of hormones in their bodies and these differences can affect toxicity synergistically or antagonistically. Now aren't you glad you read the paragraph before this one?
The type of organism being exposed to a given chemical alters the degree of the toxic effect. All of us are Homo Sapiens, though that isn't always obvious if you watch the audience at a football game or boxing match, but generally speaking substances will affect us in similar ways. Other creatures may process toxins differently due to different internal systems. This is extremely important when doing animal testing to determine toxicity.
Scientists try to pick test animals that react to a given chemical exposure similar to humans. Rabbits have skin and eyes that react similarly to ours. Monkeys have nervous systems more likely to give us a human-type response to exposure. Dogs and pigs have livers and kidneys that behave similar to us and the digestive tracts of rats are a good testing ground for ingestible poisons.
Besides that (here's the line you have all been waiting for), rats can't vomit so all the chemicals pass through, yielding a good toxicology test. Realize though that any animal testing cannot be directly translated into human terms and so some ambiguity is always present. But I don't think any of us would line up to be the guinea pig in these tests. So it's a good thing there are actual guinea pigs. Funny how that works.
Adaptation of our bodies to toxins can affect how we react. If we can build up an immunity to a substance, we may be protected from future exposures. There are people in Syria known as the Arsenic Eaters. Over their lifetime they consume small amounts of arsenic trioxide from their environment. This results in them being able to consume what would be a lethal dose of arsenic to you and me without any ill effects. Outside of a job with Barnum & Bailey, I am at a loss as to why this is desirable, but it's true. Closer to home, the same thing can be seen in cigarette smokers. The longer you have been smoking, the more it takes to get that same effect as a single cigarette when you first started.
Individual susceptibility is a major factor affecting toxicity. It's obvious that some of us can handle our liquor better than others even if we are the same size and weight. This is due to individual differences in our metabolism. This is best demonstrated by reviewing our discussion of LD50. Why did only 1/2 of the test animals succumb to the dose given? Because of these individual differences in the way they process the toxin. This would explain why two bench guys working side by side may end up with vastly different blood lead levels. We all process things differently.
It should be obvious that the factors influencing the toxicity of any given substance on any certain individual are so numerous and varied that no concrete, across the board information can be derived. In other words, be cautious when you read the health hazards on the back of a can of anything. Those warnings are a best guess and may affect you more or less than described.
Unless you are ready to test products on yourself, and I don't recommend it, we are going to have to trust the testing and product warnings and use them accordingly. Of course, trying that arsenic eating test on a couple of iron-stomached rats might make for an enjoyable evening of family fun.
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
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