Environmental carcinogens and their effect on life

Cancer is a group of related diseases that begin in cells of the body. Normally cells divide to produce more cells when body needs them for development, growth and repair of cell damage. Process of continuous division and growth of cells keeps the body healthy and normal. However, at times cells keep on dividing even when new cells are not required.

These cells form a mass of tissue known as a tumour. The tumours can be either benign or malignant. The benign tumours are not harmful. Generally they can be removed surgically and do not reappear. Further, cells from these tumours do not move to other parts of the body and rarely endanger life. On the other hand, malignant tumours are cancerous.

Cells of these tumours are abnormal and they divide and re-divide without any control. They can invade and damage nearby tissues and organs. Cells from these tumours can break away and enter the blood stream or lymphatic system and spread from the original site to form new tumours in other organs.

Leukaemia and lymphoma are cancers which are initiated in blood-forming cells. Most cancers are named after the organ concerned e.g. Cancer that begins in lungs is lung cancer and the one in skin is known as melanoma. The cancer-causing agents are known as carcinogens. Agents present in the environment are the environmental carcinogens.

Tobacco

Smoking tobacco or being regularly exposed to tobacco smoke is responsible for about 85 per cent of all cancer deaths. Smoking may increase the chances of getting cancers of stomach, liver, prostate, colon and rectum. Using smokeless tobacco and chewing tobacco cause mouth and throat cancer. Exposure to environmental tobacco smoke, termed passive smoking also increases the risk of lung cancer for non-smokers. The risk of cancer begins to decrease soon after quitting smoking and chewing tobacco. This risk continues to decline gradually after quitting.

Ultraviolet (UV) radiation

Environmental Science Senior Secondary Course UV radiation coming from sun can cause premature aging of and skin damage prolonged exposure to UV radiation may lead to skin cancer. The formation of ozone hole by compounds like chlorofluorocarbons and others, increase the incidence of UV radiation reaching the earth.

This is because ozone layer acts as a shield to prevent passage of UV radiations preventing melanoma. Avoiding exposure to direct midday sun light (from 10 a.m. to 3 p.m.) is perhaps the best way of reducing the risk of skin cancer. Wearing of a broad-brimmed hat, use of UV absorbing sunglasses and clothing to cover the body adequately also offers protection against UV.

Ionising radiation

High levels of radiation like those from radiation therapies and X-rays, and from radioactive substances can damage normal (somatic) cells and increase the risk of developing leukaemia and cancers of the breast, thyroid, lung, stomach and other organs. Studies with survivors of the atomic bomb in Japan showed that ionizing radiation increases the risk of leukaemia and other cancers. It is always desirable to minimize diagnostic and therapeutic exposure to ionising radiation and protect other parts of the body during such procedures.

Chemicals and other substances

Pesticides: Excessive use of pesticides particularly herbicides like 2,4dichlorophenoxyacetic acid (2, 4-D) has been associated with a 200-800% increase of NHL (Non-Hodgkin’s Lymphoma) – one type of cancer in Sweden. Pesticides such as toxaphene, hexachlorocyclohexane (BHC), trichlorophenol, dieldrin, DDT are known to cause lymphatic cancer in rats and mice. The danger is increased due to the persistent nature of the residues of these pesticides in the environment resulting in chronic exposure to low levels of pesticides.

The use of all these pesticides has now either been banned or restricted. Organic farming and emphasis on Integrated Pest Management (IPM) as an alternate and environment friendly method of pest control. Asbestos, nickel, cadmium, radon, vinyl chloride, benzidine and benzene are well known carcinogens. Reduction in exposure to these will reduce the incidence of various types of cancer.

Allergens and allergy

Substances in the environment that cause allergic reactions are known as allergens. Allergens stimulate within the body an immune response which may be in the form of a reaction. An allergic person’s immune system believes allergens to be damaging and so produces a special type of antibody immunoglobulin E (IgE) to attack the invading material. This leads other blood cells to release further chemicals (including histamine) which together cause the symptoms of an allergic reaction.

The most common symptoms are sneezing, runny nose, itchy eyes and ears, severe wheezing, coughing, breathlessness, sinus problems, a sore palate and nettle- like rash. Other commonly known problems could include asthma, eczema and headaches.The most common allergens are pollen from specific trees and grasses, house dust mites,moulds, cats, dogs, insects like wasps and bees, industrial and household chemicals,medicines and foods such as milk and eggs.

Allergens contain protein which is often regarded as a constituent of the food we eat. There are some non-protein allergens including drugs like penicillin- but they need to be bound to a protein once they are in the body. The best method to combat allergy is to identify the allergen (often difficult) and avoid coming into contact with it.

Blue Baby disease

Modern agriculture uses a lot of nitrogenous fertilizers and manures. This leads to increasedlevels of nitrates in the ground water as nitrates being soluble in water easily leach into thesoil. Once the level exceeds 10 ppm it may become harmful. In areas where ground wateris the only source of drinking water, this causes methaemoglobinaemia particularly in bottle fed infants who are very sensitive to this pollutant.

Babies drink large quantities of water; water is used to mix powdered or concentrated recipes or juices. When water containing nitrates is consumed and it reaches intestines, the intestinal bacteria convert nitrates into nitrites. The nitrite ions combine with haemoglobin to form methaemoglobin which inhibits the oxygen carrying capacity of the blood causing a kind of anaemia known as methaemoglobinaemia.

Methaemoglobin is formed when iron in the haemoglobin molecule is oxidized from Fe (ferrous) (ferric) form. Due to reduced carrying capacity for oxygen the babiesgradually acquire a blue tinge and hence the name – “Blue Baby disease”. Symptoms are sleeping, poor feeding, decreased energy, etc. Nitrates can be removed from thewater by processes like electro dialysis and reverse osmosis.Nitrites in the water can beoxidised to nitrates by introducing a strong oxidant like ozone in the water.

Asthma

It is a chronic (long term) disease of the respiratory passages. It is characterized by reversible airflow obstruction (tightening of the smooth muscles around airways), inflammation (swelling) and mucous production when airways are exposed to variousstimuli (triggers). Asthma has no cure but there are effective medications to control the symptoms and prevent asthma attacks.

Asthma can be life threatening, requiring emergencyroom care or hospital admission. Asthma can develop at any age. What exactly causes bronchial tubes to become swollen is still not known. However, possible risk factors for developing asthma in childhood includes-

• family history of allergy and allergic disorders
• high exposure of airborne allergy causing substances (pet dander, house dust mites,cockroaches, moulds, etc) among susceptible children in the first year of life
• exposure to tobacco smoke and
• frequent respiratory infections early in life
• Symptoms of asthma are breathlessness, wheezing, chest tightness or pain around the chest, persistent cough that can last several weeks.