To assess the toxicity of a substance various organisms can be used (Bacteria, Plants, Animals). The choice of test organism depends on several factors, including budget, time, and the organism’s occurrence in a given environment. The simplest and least costly tests are performed with unicellular animals or plants and may last only a few hours or days. In a water environment, for example, Daphnia or algae may be used in testing for potential aquatic pollutants. Short-term tests may look at the death or immobilization of swimming Daphnia, while longer term tests may look at the growth of the organisms (increase in biomass) or numbers of offspring.
Animals higher in the food chain are also important in aquatic (fish, amphibians, and other macro-invertebrates) and terrestrial toxicity (higher plant, rodent, or birds) tests.