toxicologybasics - ENVST 110 Toxicology Basics Page 1 of 13...

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ENVST 110 Toxicology Basics Page 1 of 13 Toxicology: What is a toxin, a toxicant? Poison: any agent capable of producing a deleterious response in a biological system. Virtually every known chemical has the potential to produce injury or death if it is present in a sufficient amount. This idea is represented by Paracelsus when he stated “the dose makes the poison.” Toxin: toxic substance produced by biological systems such as plants, animals, fungi, and bacteria. Toxicant: toxic substance produced by or a byproduct of anthropogenic (human) activities. For the sake of the notes and lecture I will simply use the term toxin to refer to either type. Individuals in a population vary in how much they are impacted by a toxin. The graph below shows a hypothetical, but typical, curve for a population exposed to a toxin at a given dose. In any population some will show little effect, most will show some intermediate effect, and a few will show a large effect. So, when we talk about toxins we have to consider the variation in populations. To determine the toxicity of a compound toxicologists define an endpoint, i.e. death, DNA mutation, birth defect of some type, then expose populations of test organisms to different doses of a compound and record the impact. They create a dose response curve that has the percent of a population affected by the particular dose on the y-axis, and the dose on the x-axis. So, if you look at the curve below you see that at a dose of 20 mg, 50% of the population was impacted by the dose. The impact in this curve is death, so that means 20 mg of this compound killed 50% of the animals exposed to it. Remember, any population varies in how it is impacted by a toxin, and that is why only a percent of the population dies while others survive. Not until a high dose (30 mg and above) do we see that all of the population dies, even the resistant ones.
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ENVST 110 Toxicology Basics Page 2 of 13 Dose Response Curve                                                                                                                        LD50: One key constant that you will often see associated with a toxin is the LD50. The LD50 is the lethat dose for 50% of the population. It is simply a value that allows toxicologists to compare among toxins. A toxin with a lower LD50 is more toxic to that species than a toxin with a higher LD50. You will also see ED50, which is the Effective Dose for 50% of the population. This is used when the endpoint, impact on the organism, is something other than death, liver damage, for example. How do toxins get into the body? Ingestion (Gastrointestinal tract)
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This note was uploaded on 10/26/2010 for the course ENVS 110 taught by Professor Green during the Fall '08 term at Santa Barbara City.

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toxicologybasics - ENVST 110 Toxicology Basics Page 1 of 13...

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