title: Sources and extent of pollution.
abstract: Before the sources and extent of pollution can be identified a definition of pollutants has to be agreed. The degree of disruption of natural cycles in the global ecosystem in terms of residence times and assimilation capacities must be assessed as a prerequisite of any system of control. The sources of man-made and naturally occurring chemicals that fall into this definition can be categorized and these are presented for reference. Specific examples of these categories are discussed in detail, e.g. sulphur dioxide, polychlorinated biphenyls and radioactive waste. Their distribution and dilution in the environment are governed by fluid mixing mechanisms. These can be modelled to allow prediction of effects at specific points taking into account disappearance by decay, chemical reaction and deposition. Reappearance through pathways which involve accumulation and remobilization can only be predicted when a complete scientific understanding of the mechanism has been established.
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D000397:Air Pollution / Q000032:analysis*; D004739:England; D006801:Humans; D013458:Sulfur Dioxide / Q000032:analysis; D013548:Sweden; D014874:Water Pollutants, Chemical / Q000032:analysis; D014876:Water Pollution / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D014874:Water Pollutants, Chemical; D013458:Sulfur Dioxide