The situation that arises when the balanced equilibrium of an ecosystem is disrupted by a failure or disruption of an essential link or links in its chain of being. This can happen as a consequence of human-induced pollution of a water source, introduction of alien species, a change in prevailing temperature range or other environmental conditions, or many possible combinations of these variables. Although there may be no adverse effects on human health, there are sometimes indirect health consequences. An example with beneficial effects on human health is draining swamps, which destroys an aquatic ecosystem but, by eliminating mosquito breeding sites, reduces the risk of mosquito-borne diseases such as malaria. An example with adverse health effects is the ecosystem distress in an industrial zone, such as that in which a mining and smelting operation or a petrochemical plant has polluted the environment, killed the vegetation, destroyed wildlife habitat, and exposed human residents to toxic substances such as lead, mercury, and organic compounds such as dioxins and PCBs.
Subjects: Public Health and Epidemiology.