Environmental monitoring can be expensive. To reduce costs, biologists, toxicologists, and health specialists rely on wild plants and animals for information about current environmental health. Because wild organisms are constantly in the environment, they continually monitor this environment through their own biological requirements. Different organisms are tolerant of different levels of toxins, and by monitoring which species are present and which have disappeared, a measure of environmental health can be estimated and probed using more sensitive, directed, quantitative techniques. Amphibians frogs, toads, and salamanders have a number of characteristics that make them good bioindicators.
Amphibians have thin skin that is permeable to water and much of the grunge that occurs in water.
Most Midwestern amphibians spend part of their lives as eggs and larvae in water, and part of their lives as adults on land. Thus, the presence of amphibians indicates good quality aquatic and terrestrial habitats. If either of these habitats are missing or severely compromised, amphibians will be absent. As an aside, extrapolating data from amphibians to humans has a long history. The first hint that all was not well with amphibians came at the First World Congress of Herpetology, hosted in Australia in 1989.