pollution

Harmful effect on the environment of by-products of human activity, principally industrial and agricultural processes – for example, noise, smoke, car emissions, pesticides, radiation, sewage disposal, household waste, and chemical and radioactive effluents in air, seas, and rivers. Air pollution contributes to the greenhouse effect.

Pollution control involves higher production costs for the industries concerned, but failure to implement adequate controls may result in irreversible environmental damage and an increase in the incidence of diseases such as cancer. For example, in agriculture the mismanagement of fertilizers may result in eutrophication, an excessive enrichment of lakes and rivers caused by nitrate pollution; the subsequent rapid growth of algae darkens the water and eventually depletes its oxygen, causing plants and animals to die. Nitrate pollution has also been linked to stomach cancer, although this is unproven. Radioactive pollution results from inadequate nuclear safety.

Transboundary pollution is when the pollution generated in one country affects another, for example as occurs with acid rain. Natural disasters may also cause pollution; volcanic eruptions, for example, cause ash to be ejected into the atmosphere and deposited on land surfaces.

Lichens are sensitive to air pollution and can be used as indicators to map the severity of air pollution. Crusty lichens, such as Leonora species, indicate heavy air pollution; leafy lichens, such as Parmelia saxatalis tolerate moderate pollution; and bushy Usnea lichens only grow where the air is clean.