A large number of chemicals are used in everyday products, in agriculture or in industry. At some point, many of these end up in the environment. In order for these substances to be authorized for the market, manufacturers must be able to prove in advance that they are harmless to humans and nature. This is done with toxicity tests in which living creatures are exposed to the effects of the chemicals. Thousands of fish die every year because they are used to test the effect on aquatic vertebrates.