]Pollution is an unwanted change in the physical, chemical, or biological characteristic of the environment, caused by human activities.
These ones lead to a several environmental disasters, like acid rains, global warming and ozone depletion. These problems involve, above all, the atmosphere, soil, rivers and seas.
Pollutans can be biodegradable and non-biodegradable. The former, example sewage, may be dissolved through natural processes. The latter, example heavy metals, do not break down by microorganisms methabolism and, therefore, they accumulate in the environment.