Some insecticides have been banned due to their adverse effects on animals or humans.
DDT is an example of a heavily used and misused pesticide. One of the better known impacts of DDT is to reduce the thickness of the egg shells on predatory birds. The shells sometimes become too thin to be viable, causing reductions in bird populations. This occurs with DDT and a number of related compounds due to the process of bioaccumulation, wherein the chemical, due to its stability and fat solubility, accumulates to progressively higher concentrations in the body fat of animals farther up the food chain. The near-worldwide ban on DDT and related chemicals has allowed some of these birds--such as the peregrine falcon--to recover in recent years.