" all things are poisonous, for there is nothing without poisonous qualities. It is only the dose which makes a thing poisonous" ** dose response relationship (or exposure response relationship) Dose-response: assumptions, response is due to the toxicant, response is related to the amount of exposure (does/concentration) Species have different sensitivities to toxicants, but it is not practical to test every species: extrapolate from one species to another, similar to human toxicology; mice/rats are surrogate species to humans. Environment and climate change canada biological test methods. Components of toxicity tests: receptor, toxicant, xenobiotic-foreign to body, anthropogenic- human made, route of exposure. Ingestion: toxicant ingested into gastro-intestinal system, gut: dermal: toxicant interacts with surface of organism, skin. Non-nutrient: noec (no observed effect concentration) -highest concentration with no observable effects, not different from the control. Loec (lowest observed effect concentration) -lowest concentration that is significantly different than the control.