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Bonita High_HONORS 4211_ld50

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Name: _________________________________________Date: __________________ Unit 7: Human Health and Toxins in the Environment Webquest Toxicology and the LD50 Bioassay “All substances are poisons; t... here is none which is not a poison. The right dose differentiates a poison and a remedy.” ~Paracelsus, 1590 A.D. Background Information: All substances, including the ones that we considered essential for life such as water or sugar, can be toxic if too much is consumed. Therefore, when introducing new chemicals into the human environment, it is essential that scientists determine the dose at which these chemicals can present a significant danger to human health. One method of determining a chemical’s toxicity level is by performing a test known as the LD50 bioassay. This test determines the median lethal dose of the chemical, which is the dose at which 50% of the animals being tested do not survive. Because of ethical issues, LD50 tests are performed on mice or rats. Studies have shown that responses in these animals can be relatively easily extrapolated to humans, and therefore scientists can determine the median lethal dose of a chemical without harming humans. When using an LD50 bioassay to assess a chemical’s toxicity level, it is important to remember that a population includes individuals with different sensitivity levels. While the LD50 gives a good idea of what dose is lethal for the general population, there will always be individuals who will be affected at lower doses and some who may not be affected until higher doses. Your Task: In this activity, you are going to compare the toxicity of sodium cyanide and arsenic to determine which is more dangerous based on their LD50. In addition, we will look at the LD50 for a variety of substances to determine the lethal human dose. Part I: Getting to Know Your Toxins [Show More]

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