Archive | August 2012


             Toxicology is the study of the adverse effects of chemicals on living organisms. It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people. Toxicity is measured by LD50 or “lethal dose.” This means that out of a certain number of test subjects (usually rats or other rodents), 50% had died because of their contact with whatever the tested substance was. For example, parathion (which is a type of pesticide) with an LD50 of 3 mg/kg would be highly toxic. That means that half the test animals that are given 3 mg/kg body mass will be expected to die (Basic Chemistry textbook, 34). Toxicology is measured by parts per million (ppm), which equals milligrams per kilogram (mg/kg). For every kilogram of an animal’s weight, you need a corresponding weight of the material being tested.

              Mathieu Orfila is considered to be the modern father of toxicology, having given the subject its first formal treatment in 1813 in his Traité des poisons, also called Toxicologie générale. As technology progressed, testing toxicity has become more concise. However, the study of toxicology comes at a cost: an extremely large number of test subjects. Then again, they are just rats.

How to calculate toxicity:

  1. Take the weight of an animal, such as a rat
  2. Take a substance, like table sugar, and look up its toxicity in LD50
  3. For rats, it will take 29,700 milligrams per kilograms of body weight to kill a rat (all in one dose). If you have a rat that weights 3kg, it will take 29,700mg/kg * 3kg = 89,100 milligrams of table sugar, all in one dose, to kill a rat weighing 3kg

Sources: “Letter to editor…” Calculation of LD50 (Spearman-Karber) “Environment, Health and Safety Committee [EHSC]”