This part looks at the uses of quotas in a variety of conservation and pollution treaties spanning the last century. Some examples are treated very briefly and others in greater detail. Conservation agreements impose limits on harvest and trade in order to save a species, a wider range of living resources, or a non-living resource from overexploitation or from extinction, and sometimes to ensure a sustainable commercial supply. Pollution treaties employ limits on total allowable emissions of particular substances and sometimes mandate reductions in emissions. A number of subjects usually included under the' environmental' umbrella are not considered. The excluded subjects include worker protection and human health, plant diseases and pest control, nuclear regulation, emergency response, outer space, war, navigation and transport, drought, and noise.