Environmental diseases can affect any organ system of the body. How the diseases are expressed depends on how the particular environmental agent enters the body, how it is metabolized, and by what route it is excreted. The skin, lungs, liver, kidneys, and nervous system are commonly affected by different agents in different settings. Of particular concern is the capacity of many environmental agents to cause various cancers, birth defects or spontaneous abortions , and mutations in germ cells, the last-named raising possibilities of environmentally caused genetic diseases in later generations. Environmental illnesses can be mild or severe and can range from transient to chronic, depending on the doses of toxin received. Some diseases occur abruptly after a toxic exposure, whereas the time of onset of other diseases varies after exposure. Environmentally induced cancers, for example, commonly involve latency periods of 15 to 30 years or more. Those illnesses that occur directly after a distinct toxic exposure are usually easily identified as being environmentally or occupationally caused. If the exposure is not clear-cut or illness is delayed, however, the cause is difficult to identify, as clinical features alone are usually nonspecific. In addition, many different causes, environmental or otherwise, may produce identical illnesses. In such instances, epidemiological studies of exposed populations can help relate exposures to the illnesses they cause.
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