ABSTRACT
Some of the chemicals so released can also reach unusually high levels locally as a result of natural processes such as weathering of rocks (metals and inorganic anions) and volcanic activity with associated forest –res (SO2, CO2, and aromatic hydrocarbons). As noted in the introduction, it is dif–cult to de–ne what actually constitutes pollution. Some authorities prefer to restrict the terms pollution and pollutant to the consequences of human activities. However, in some cases it is impossible to determine the relative contributions of human and natural processes that affect the general environment.
