Living By Chemistry SECOND EDITION Unit 4 TOXINS
Living By Chemistry SECOND EDITION Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases
Lesson 74: Lethal Dose Toxicity
Chem. Catalyst Which substance do you think is most toxic to you—alcohol (ethanol, C 2 H 6 O), aspirin (salicylic acid, C 7 H 6 O 3), or arsenic (III) oxide (As 2 O 3)? Explain your thinking.
Key Question How much is too much of a substance?
You will be able to: • calculate the toxic dose for a variety of substances, given the LD 50 • explain the role of dosage in toxicity
Prepare for the Classwork You will work individually or in pairs. Lethal dose (LD 50): the amount of an ingested substance that kills 50% of a test sample of animals. It is expressed in mg/kg, or milligrams of substance per kilogram of body weight.
Discussion Notes Toxicity depends on two quantities: amount of toxic substance and mass of the organism. All substances are toxic in large enough doses, even sugar and water.
Discussion Notes (cont. ) The smaller the lethal dose, or LD 50, the more potentially dangerous a substance is. Many toxic substances can be therapeutic at lower doses.
Wrap Up How much is too much of a substance? • Toxicity is relative to dosage: The toxicity (or therapeutic effect) of a substance depends on the dose in which it is received. • The lethal dose (or therapeutic dose) of a substance is often expressed as a ratio between a certain mass of the substance and 1 kilogram of the body mass of an organism exposed to the substance.
Check-In Methadone is a medication used as a painkiller and as a treatment for those recovering from heroin addiction. The LD 50 for methadone is 95 mg/kg. a. Would you consider methadone to be more or less toxic than acetaminophen (LD 50 = 2404 mg/kg)? than aspirin (LD 50 = 200 mg/kg)? b. Explain how you would calculate the amount of this substance that would be lethal to a 120 lb human.
- Slides: 10