ABSTRACT
Pollutants may enter ecosystems as the consequence of human activity in the following ways.
Some of the chemicals so released can also reach unusually high levels locally as a result of natural processes such as weathering of rocks (many metals and inorganic anions) and volcanic activity with associated forest fires (SO
, CO
, and aromatic hydrocarbons). As noted in the Introduction, there are problems of defining what actually constitutes pollution. Some authorities prefer to restrict the terms pollution and pollutants to the consequences of human activity. However, it is sometimes difficult or impossible to determine the relative contribution of human processes and natural ones to residues that are present in the general environment.
