Wastes are produced by all living things – excreted by an organism or thrown away by society because they are no longer useful and if kept may be detrimental. But the make-up of waste means that once discarded by one body its constituents may become useful to another. In the natural world, a waste produced by an animal, for example, is just one stage in the continual cycle of matter and energy that characterizes the workings of the planet: an animal that urinates is disposing of waste products its body does not need, but the water and nutrients can become resources for other organisms. Similarly, sewage from a town can be used by bacteria that break it down in a river, for example, or an old shirt discarded by one person might be worn by another, often poorer, individual. The term ‘waste’ is therefore a label determined by ecology, economics and/or culture.