ABSTRACT
The expression natural pollutants may sound like a contradiction in terms. Most substances regarded as pollutants are man-made. However, in Chapter 1 the definition given of pollutants included natural chemicals when they occur at abnormally high levels. Very often this happens because of the activities of man-for example, due to mining for minerals, drilling for oil, burning coal, smelting ores to release metals, using internal combustion engines, or operating nuclear power plants. There are also situations where natural pollution occurs outside of any human activity. Cataclysmic events such as the eruption of volcanoes, tsunamis, spontaneous forest fires, or the landing of meteorites can all cause pollution in this sense and have serious and widespread ecological effects. Some examples of this have been seen within historical time on volcanic islands such as those of the Galapagos, Hawaii, and Tristan da Cunha.
