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<br />EN\'IR(JNf\1EN-1AL CANCER Rl~KS
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<br />SEP-11-1997 15:56
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<br />MN DEPT HEALTH MCSS
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<br />Environmental causes probably account for well over
<br />half of all cancer cases. Most environmental risks are
<br />determined b lifes Ie choices smokin , diet, etc.),
<br />wet e rest arise in community and workp ace
<br />settings. The degree of cancer hazard posed by these
<br />voluntary and involuntary risks depends on the concen-
<br />tration or intensity of the carcinogen and the exposure
<br />dose a person received. In situations where high levels
<br />of carcinogens are present and where exposures are
<br />extensive, significant hazards may exist, but where
<br />concentrations are low and exposures limited, hazards
<br />are o~ten negligible. However, when low-dose exposures
<br />an: W1despread, they can represent significant public
<br />health hazards (for example, secondhand tobacco
<br />smoke). Strong regulatory control and constant attention
<br />to safe occupational practices are required to minimize
<br />the ~orkplace potential for exposure to high-dose
<br />carcInogens.
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<br />Risk Assessment
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<br />Risks art assessed to protect people against unsafe
<br />exposures and to set appropriate environmental
<br />standards. The process of risk assessment has two steps.
<br />The first identifies the chemical or physical nature of
<br />a hazard and its cancer-producing potential, both in
<br />clinical and epidemiologic studies and in laboratory tests
<br />using animals or cell systems. Special attention is iiven
<br />to any evidence suggesting that cancer risk increases
<br />with increases in exposure. The second step measures
<br />levels of hazard in the environment (air, water, food,
<br />ete.) and the extent to which people are actually exposed
<br />(how much they eat of a particular food, use a particular
<br />water source, etc.1. Knowledge of how the body absorbs
<br />chemicals or is exposed to radiation is essential for such
<br />dose measurements.
<br />UnfortUnately, evidence of risk for most potential car-
<br />cinogens is usually the result of high-dose experiml:nts
<br />on animals or observations where high-dose exposures
<br />have occurred in humans. To use such information [0 set
<br />human safety standards, sc.ientists must extrapolate from
<br />animals to humans and from high-dose to low-dose
<br />conditions, Because both extrapolations involve much
<br />uncertainty, conservative assumptions arc used so that
<br />risk assessment will err on the side of safety. For cancer
<br />Saffry standards, only increased risks of one case or less
<br />per million persons ~ver a lifetime are usually acceptable.
<br />Safety standards developed in this way for chemical or
<br />radiation exposures are the basis for federal regulatory
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<br />activities at the Food and Drug Administration, the.:
<br />Environmental Protection Agency, and the Occupational
<br />Safety and Health Administration. The application
<br />of laws and procedures by which standards are
<br />implemented and risks are controlled is called risk
<br />management.
<br />
<br />Chemicals
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<br />Various chemicals show definite evidence of human
<br />carcinogenicity (for example, benzene, asbestos, vinyl
<br />chloride, arsenic, aflatoxin) or are probable human
<br />carcinogens based on evidence from animal experiments
<br />(f?r example, chloroform, dichlorodiphenyl-
<br />trIchloroethane [DDT], formaldehyde, polychlorinated
<br />biphenyls [PCBs], polycyclic aromatic hydrocarbons).
<br />Often in the; past, direct evidence of human carcino-
<br />genicity has come from studies of workplace conditions
<br />involving $Ustained, high-dose exposures. Occasionally,
<br />risks are gready increased when particular exposures
<br />occur together (for example, asbestoS exposure and
<br />cigarette smoking),
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<br />Radiation
<br />Only high-frequency radiation, ionizing radiation (IR)
<br />and ultraviolet (UV) radiation. has been proven [0 cause
<br />human cancer. Exposure to sunlight (UV radiation)
<br />causes almost all cases of basal and squamOUS cell
<br />skin cancer and is a major cause of skin melanoma.
<br />Disruption of the earth's ozone layer by atmospheric
<br />chemical pollution (the "'ozone hole") may lead to rising
<br />levels of UV radiation.
<br />Evidence that high-dose IR (x-rays, radon, etc.) causes
<br />cancer comes from studies of atomic bomb survivors,
<br />patienrs receiving radiotherapy, and certain occupational
<br />groups (for e.xamp1e, uranium miners). Virtually any part
<br />of the body can be affected by IR, but especially bone
<br />marrow and the thyroid gland. Diagnostic medical and
<br />dental x-rays are set at the lowest dose levels possible to
<br />minimize risk without losing image quality. Radon
<br />exposures in homes can increase lung cancer risk,
<br />especially in cigarette smokers; remedial actions may be
<br />needed if radon levels are too high.
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<br />Unproven Risks
<br />Public concern abl)ut en\'ironmenral cancer risks often
<br />focuses on risks for which no carcinogenicity has been
<br />Proven or on situations where known \:arcinotTcn
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<br />expostlres are at such low levels that risks arc neg:ligible,
<br />For example:
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