Occupational Carcinogens

Occupational carcinogens are subset of environmental carcinogens which occur in workplace. Occupational carcinogens can be detected easily. It is obvious an individual can develop cancer when exposed to carcinogenic substances or due to genetic traits. Classified examples of occupational carcinogen are asbestos, coal tar and aromatic amines. Cancer bioassay helps in detection of those cancerous substance quantities proven to be carcinogen. Depending on the cluster of events it is possible to identify the occupational carcinogens. This study helps in establishing a link between carcinogenic agents and how the cancer develops. By Cohort study it is easy to compare the cancer occurrence among the populations exposed to carcinogen.Ward et al draw attention by highlighting the potency and limitations of occupational carcinogens.

Classification of occupational carcinogens

International agency for research on cancer (IARC) made remarkable classification as follows.

• Group I or human carcinogens: 38 chemicals that are used in industries
• Group 2A carcinogen: Probably human carcinogenic
• Group 2B carcinogen: Possibly human carcinogenic

These classifications are sufficient enough to detect carcinogen in animals; but in case of epidemiologic studies these classifications are not adequate enough. Major classified human carcinogens are diet control and cigarette smoking. Occupational carcinogens like poly aromatic hydrocarbons (PAH), pesticide, arsenic, dioxins and asbestos are considered below.

Poly aromatic hydrocarbon (PAH)

PAH is a carcinogen which is widely distributed in gasoline, crude oil and coal and is generated when fossil fuel burns. It is also prevalent in motor exhaust emissions, smoke, stoves emission, fire stations, charbroiling meat and tobacco smoke. Human may acquire occupational carcinogens by air, water and food contamination with PAH. However it is widely spread by air. When PHA is inhaled it interacts with DNA thereby quinones are metabolized which end up in formation of reactive oxygen species (ROS). Carcinogenesis spreads via DNA thereby proliferation of cells occur or cell cycle is altered. Non smoking individuals can also develop cancer is confirmed by epidemiologic study of PAH.  PAH is abundant in industrial runoff, ground water, and coal tar leachate and distribution pipe lines. It is more in food like charbroiled meat and vegetables when compared to water. Plants can easily acquire PAH from water and soil contact.

Pesticides

Pesticide is a chemical used to control the growth of pests, rodents and other insects. They are biologically active compounds and can interact with organism normal function. Main exposure to pesticide is by food ingestion and water either by absorption or inhalation of pesticides. So far 165 pesticides are known to cause possible human carcinogens. A pesticides retard cell proliferation thereby resulting in cell death and disturbs cell communication. For instance glycophosphate based pesticides result in lymphocyte. DDT, organochlorine pesticides are potential human carcinogen. It can interfere with endocrine pathway thereby inducing prostrate and breast cancer. It can also endanger the oxidative metabolism.

Arsenic

Potential human carcinogens of arsenic are inorganic type. First cancer evidence was found in the year 1977. During 1977 arsenic was used for topological apply as ointment which resulted in skin cancer. Production of arsenic was stopped in the year 1985.Major exposure to arsenic is through water and food. Industries that manufacture pesticide, cigarette tobacco, fossil fuel and smelting release arsenic compounds that cause skin, bladder, colon, rectum, liver, kidney damage and lung cancer. Mode of interaction is not clearly understood still. However it does not interact with DNA; however it ends in chromosome aberrations. Arsenic alters the DNA repair mechanism, signal transduction pathway and progression of cell cycle. Arsenic interaction result in cell death, differentiation and transformation.

Dioxins

Dioxins are byproducts of smelting operations, paper and pulp manufacturing, incineration of coal, tar, oil and waste products. Natural releases of dioxins are volcanic eruptions and forest fires. Epidemiologic study shows that cancer like lymphoma, leukemia, sarcomas and Hodgkin diseases may develop if dioxins interact with tissues. For instance TCDD is potential carcinogen of dioxin type. It interferes with signal transduction pathway of epithelial cells thereby causing lung cancer.

Asbestos

Asbestos release is from both natural source and anthropogenic source. Asbestos induces lung cancer, pleural disorders, pleural plague, thickening and effusions of pleural. Depending on the dose, size, geometry and chemical content of the fiber asbestos induces lung cancer in human. Cigarette smoking causes cancer by releasing asbestos compounds. Asbestos fiber has a direct effect on mesothelial cells. Asbestos damages DNA by ROS generation and interrupting signal transduction pathways.

Questions:

• What are occupational carcinogens?
• Describe briefly about occupational carcinogens types.
• How occupational carcinogens are different form environmental carcinogens?
• Define mechanism of action of asbestos fibers.
• Give general aspects of exposure to occupational carcinogens.