Although the disease-producing potential of ionizing radiation at low doses is also uncertain, an increase in chromosome damage has been observed in workers in nuclear shipyards. Major physical hazards include traumatic injuries and noise. Trauma arising from unsafe environments accounts for a large proportion of preventable human illness, and noise in the workplace is responsible for the most prevalent occupational impairment: hearing loss or permanent deafness.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. Total frequencies of environmental illness are difficult to measure because of the reasons just described. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust , cotton dust , asbestos fibers , and silica dust . Environmental agents can also cause biological effects without overt clinical illness . The health significance of such subclinical changes is not yet clear.
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