Toxicopathology and Carcinogenesis

Education

Regulation

Among potential harmful environmental factors, tobacco use, unhealthy diet, and not enough physical activity are more likely to affect your personal cancer risk than trace levels of pollutants in food, drinking water, and the air.

However, the degree of risk from those pollutants depends on the concentration, intensity, and exposure. Substantial increases in cancer risk have been shown in settings where workers have been exposed to high levels of ionizing radiation, certain chemicals, metals, and other substances.

Even exposures at low doses, which pose only small risk to individuals, can still cause substantial ill health across the whole population.

Some of these substances include:

Chemicals and radiation
Some chemicals, such as benzene and asbestos, show definite evidence of causing cancer in humans. Others are considered probable human carcinogens (cancer-causing agents) based on animal experiments. These include dichlorodiphenyl-trichloroethane (DDT), formaldehyde, and polychlorinated biphenyls (PCBs).

The only types of radiation proven to cause cancer in humans are ionizing radiation and ultraviolet (UV) radiation.

Evidence that high doses of ionizing radiation causes cancer comes from studies of atomic bomb survivors, patients receiving radiotherapy, and certain occupational groups, such as uranium miners. Ionizing radiation can affect virtually any part of the body, but especially affects bone marrow and the thyroid gland. Diagnostic medical and dental x-rays are set at the lowest dose levels possible to minimize risk without losing image quality and medical usefulness.

Exposure to sunlight (UV radiation) causes almost all cases of basal and squamous cell skin cancer and is a major cause of skin melanoma. Disruption of the earth's ozone layer by pollution may cause rising levels of UV radiation.

In addition, radon exposures in the home can increase risk of lung cancer. Cigarette smoking greatly increases the effect of radon exposure in lung cancer risk. Remedial actions may be needed if radon levels are too high in your home.

Public concern about cancer risks in the environment often focuses on unproven risks, or on situations in which known carcinogen exposures are at such low levels that risks are negligible.

Pesticides
For example, pesticides are widely used in producing foods in agriculture. High doses of some of these chemicals have been shown to cause cancer in animals, but the very low concentrations found in some foods have not been associated with increased cancer risk. In fact, people who eat more fruits and vegetables, which may be contaminated with trace amounts of pesticides, generally have lower cancer risks than people who eat few fruits and vegetables. Workers exposed to high levels of pesticides, in industry workers or in farming, may be at higher risk of certain cancers.

Environmental pollution by pesticides such as DDT, which is now banned but was used in agriculture in the past, degrades slowly and can lead to accumulation in the food chain and persistent residues in body fat. These residues have been suggested as a possible risk factor for breast cancer, although the evidence has not been conclusive.

Continued research into pesticide use is essential for maximum food safety. But pesticides play a valuable role in sustaining the food supply. When controlled properly, the minimal risks they pose are overshadowed by the health benefits of a diverse diet rich in foods from plant sources.

Non-ionizing radiation
Electromagnetic radiation at frequencies below ionizing radiation and UV levels has not been proven to cause cancer. Some studies suggest it is associated with cancer, but most of the now extensive research in this area does not. Low-frequency radiation includes radiowaves, microwaves, and radar, as well as power frequency radiation arising from electric and magnetic fields associated with electric currents (from cellular phones and household appliances, for example).

Toxic wastes
Toxic wastes in dump sites can threaten human health through pollution of the air, water, and soil. Many toxic chemicals found in such sites can be cancer-causing at high doses, but most community exposures appear to involve very low or negligible dose levels. Clean-up of existing dump sites and close control of toxic materials in the future are essential to ensuring healthy living conditions.

Nuclear power plants
Ionizing radiation emissions from nuclear plants are closely controlled and involve negligible levels of exposure for communities near the plants. Reports about cancer case clusters in such communities have raised public concern, but studies show clusters do not occur more often near nuclear plants than they do elsewhere.

Source: American Cancer Society

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