Toxicologists can use many kinds of animals but most often testing is done with rats and mice. LC values usually refer to the concentration of a chemical in air but in environmental studies it can also mean the concentration of a chemical in water.
Chemicals can have a wide range of effects on our health.
Depending on how the chemical will be used, many kinds of toxicity tests may be required. Since different chemicals cause different toxic effects, comparing the toxicity of one with another is hard. We could measure the amount of a chemical that causes kidney damage, for example, but not all chemicals will damage the kidney. We could say that nerve damage is observed when 10 grams of chemical A is administered, and kidney damage is observed when 10 grams of chemical B is administered. However, this information does not tell us if A or B is more toxic because we do not know which damage is more critical or harmful.