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Toxicology is the study of the negative effects of chemicals on living things. The main factor in the toxicity of a substance is the dose (how much of the chemical has been given), as almost all substances can be toxic under the right conditions.
Many chemicals that we call poisons are only toxic when made into different chemicals by the body. Many chemicals are made toxic in the liver by enzymes, for example paracetamol, which is a common drug. There is also some variation in liver enzymes (caused by genetic variation) in different people that can cause a substance to be more toxic in one person than it is in another. Some substances are also only toxic when they are with other chemicals, as one liver enzyme can cause activity in another enzyme.
Some measures of toxicity
- LD50 is a test that finds an average dose required to kill half of the animals being tested (normally rats in human toxicity).
- The Fixed Dose Procedure, an alternative to the LD50 which measures oral toxicity in a similar way, but using fewer animals and with less suffering.
- Minimum lethal dose (MLD, also LDmin), the smallest amount of drug that can produce death in an animal species under controlled conditions.
- Draize test