Exposure to chemical carcinogens and ionizing radiation causes cancer. Initiator carcinogens have their effect by damaging DNA. A single increment of DNA damage is referred to as a lesion. When several such lesions have occurred in a gene controlling cell division, thereby rendering the product of that gene ineffective in its role of controlling division, a cancer cell line is initiated. Increased exposure to initiator carcinogens increases the probability of enough damage to DNA taking place to decontrol cell division. The abnormal cell line will grow more rapidly, leading to earlier onset of a cancer, when chemical compounds that promote cancer cell growth are present in the affected tissue. Thus, increased exposure to a promoter carcinogen increases the probability of a clinically diagnosable cancer developing during one's lifetime.
Inhabitants of industrialized nations are exposed to benzene and polycyclic aromatic hydrocarbons (PAHs), which contaminate the air, due to the exhaust releases of motor vehicles. Hexachlorobenzene, PCBs, dioxins, and PAHs contaminating animal fat foods impose significant cancer risk upon these same populations. These by products of combustion are emitted by sources in the transportation, manufacturing and energy sectors of the economy. It is the cumulative effect of exposure to many relatively small amounts of pollutant carcinogens over a lifetime that results in initiation and promotion of cancer cells. A greater amount of life-long exposure imposes a higher risk of developing cancer.
During the past several decades, scientific research into the matter of how much cancer risk is imposed by exposure to certain carcinogenic substances has progressed to a considerable extent. Much of this research has dealt with occupational exposures to carcinogenic chemicals and cigarette smoking. Particularly extensive bodies of research literature exist for dioxins and dioxin-like compounds, diesel engine exhaust, cigarette smoke and arsenic.
The cancer risk of exposure to dioxins and dioxin-like compounds has been carefully assessed by the United States Environmental Protection Agency (US EPA). By studying "Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds", it is possible to acquire a clear conception of how EPA has quantified the cancer risk of exposure to this class of chemical substances (US EPA, 2003).
No quantification of the cancer risk associated with background exposure to diesel engine exhaust has yet been published. The cancer risk of occupational exposure to diesel engine exhaust is more fully understood. This subject area is thoroughly covered in the "Health Assessment Document for Diesel Engine Exhaust" (US EPA, 2002).
The amount of cancer risk associated with exposure to arsenic has been calculated based upon lifelong exposure to naturally occurring arsenic in drinking water. Using this knowledge it has been possible to make an estimate of the cancer risk resultant from a child's exposure to arsenic by way of play on CCA pressure treated lumber playground structures (Environmental Working Group, 2001).
There are several categories into which cancer risk factors can be grouped: (1) pesticides contaminating grains, fruits, nuts and vegetables; (2) exhaust from internal combustion engines; (3) fat-soluble carcinogens contaminating animal fat foods; (4) cigarette smoke; (5) ultraviolet radiation from the sun; (6) ionizing radiation from radionuclides; and (7) pesticides in materials other than foods, including arsenic in CCA pressure treated lumber. At the current time, only an incomplete understanding of the relative potency of carcinogens exists. Furthermore, we do not know how much exposure to every specific carcinogen is taking place. A reasonable approach to preventing cancer at this stage of our knowledge is to reduce exposure within each of the above listed categories. By taking the following steps, a person can readily accomplish such exposure reduction.
Eat only organic grains, fruits, nuts and vegetables
Minimize the amount of exhaust that you inhale by avoiding as much as possible concentrated exhaust fumes
Significantly reduce consumption of animal fat foods
Do not smoke cigarettes or spend time where others are smoking
Avoid excessive exposure to sunlight
Avoid occupational and health care exposures to ionizing radiation
Do not allow children to have contact with CCA pressure treated lumber
Prevention of cancer involves avoidance of exposure and reduction of releases of carcinogenic pollutants to the environment. It will be the changes in human activity, which result in lower levels of carcinogens in the air, water and food that yield the most satisfactory and effective form of cancer prevention. An environment that has been cleaned-up by pollutant minimization will provide cancer prevention for people and wildlife. This is what we must work to create.
Environmental Working Group, 2001; Poisoned Playgrounds
US EPA, 2003; Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds
US EPA, 2002; Health Assessment Document for Diesel Engine Exhaust
Doc. No. EPA/600/8-90/057F, May 2002
Deborah Elaine Barrie
4 Catherine Street
Smiths Falls, On
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