Dose-Response

Toxicology as a science is based of the relationship between the dose of substance absorbed by an organism, and the response it triggers.  Paracelsus said it best when he stated, “the dose makes the poison”. 

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In other words, everything can be toxic in a way, in a certain amounts.  Even something as harmless as water can be harmful, if you drink too much of it.   Likewise very toxic substance may have no effect in very low doses.  But the key thing to take away from this, is the amount of a toxin is what determines the effect.  For example, we breathe in some CO2 in the air with every breath, but if we where to breath 100 percent CO2, we would die.  A more relatable method may be alcohol consumption.   Most are familiar with this dose-effect relationship.  Too much alcohol can make us sick/impaired, and eventually lead to death.  We refer to the lowest dose needed to cause an adverse effect as the threshold dose.  This is when an effect can first be linked to a certain chemical.  This is not the same in every organism however.  A 200lb man who drinks 4 beers may not feel a huge effect from the alcohol.  However, if a 100lb man drinks that same amount, he may feel much more of an effect.  Individuals can however be hyperresponvive, meaning they are just very responsive to a chemical for any of a variety of reasons.  And in contrast, an individual can be hyporesponsive, meaning they are particularly resistant to a toxin for whatever reason.  With all toxins, different people and different organisms react to them differently.  Some organisms can actually consume substances that would strike death to different species.  A dose that kills 50 percent of the individuals it is administered to is a LD50.  Meaning if you have 100 organisms, all given the same does, about 50 will die.  We also use a term called an ED50 or the effective dose (50).  Meaning this is the does were ½ the individuals will experience an effect from a chemical.  An administered or applied dose is the amount of a chemical presented to an absorption barrier.  Which is different than how much your body actually absorbs.  The absorbed dose is the term used to refer to the amount your body would actually absorb.  The delivered dose is similar; it is the amount of the chemical that is readily available to react with any cell or organ within the body.  Much of this information we get from lab animals.  Meaning we test these dose-response relationships in labs on rats, mice, etc.  However humans and mice are not the same organism, so not all data can be drawn in parallel to humans.  Other data we know on human dose response based on the actual past death/response of humans.  But toxicity does not deal with just chemicals necessarily.  For example, radiation can be toxic to humans and other organisms.  And we have LD50’s etc. for radiation just as we do for other chemicals.  Anything that is harmful to us can really be under the umbrella term “toxic” .

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