Radon gas exposure: sources, health effects, and mitigation strategies

Radon Exposure

Radon is present everywhere in the air both in the outdoor and the indoor settings but the levels of radon in the indoors especially the basements and lower floors is higher. Exposure to significantly high levels of radon gas causes lung cancer in humans. The correlation of lung cancer related deaths and exposure has been shown by several studies conducted on instances of lung cancers among miners of uranium. There are hazardous effects of radon exposure in the homes in particular in the confined spaces like basement even though there isn't yet conclusive evidence of direct link lung cancers and radon levels in the home. This paper will describe the radon gas, its production and exposure. The various health effects will be analyzed in relation to the different case studies which have been conducted on the radon related health effects. Finally the ways to mitigate the effect of radon gas will be presented forth.

Radon gas

Radon is a naturally occurring radioactive gas that is odorless and colorless. The uranium natural breakdown in the rocks and soil usually produces the gas. It cannot be felt, smelt or heard and still poses cancer causing hazards. The element was discovered in 1899 by Rutherford and credited by Friedrich. It is nine times heavier than air and practically the heaviest known gas. Its high penetration abilities through leather, paper, low density plastics and building materials like concrete block, sheathing paper and gypsum is attributed to its property of being a gas of single atom. Radon dissolves fairly in organic solvents and water and even though it is considered inert, it is not entirely so because it reacts with several materials that are highly electronegative forming stable molecules. The inhalation of radon is due to rapid attachment of the radioisotopes formed from the decay products to dust and other airborne materials.

Production and exposure

Radon occurs naturally from uranium break down with its presence common in almost all the air. Radon is breathed everyday by people at quite low levels though there is increased lung cancer risk for those who inhale high levels. The main source of radon is the ingenious soil and rock though there are some instances where it is found in water. The entry of radon into homes is through cracks in walls, floors or foundations and eventually collects indoors. Building materials or well water can also release radon. Well insulated homes, houses built on soil rich with uranium or tightly sealed homes have higher levels of radon. First floor and the basements usually have the highest levels of radon because of their proximity to the ground. Radon is primarily exposed to humans through inhalation and ingestion. Radon from the ground water, ground and building materials fragments into its decaying products after the entering the living and the working spaces. Radon released from water and then inhaled is the most important although radon exposure can also result from ingestion from the high concentration present in the ground water ("Radon, It's your health").

Case studies

The inhalation of radon gas and decay products which are highly reactive and mostly stick to the airborne dust is the principal danger of the radon. Whenever the delicate cells found on the passageways to the lungs are affixed with these elements. There was reported evidence by IARC working Group for the radon carcinogenicity and its related decay products in humans. Many epidemiological studies conducted on miners of underground hard rock who are exposed to radon in high doses due to the nature of their occupation have shown incremented instances of lung cancer. The group under study consisted of iron-ore, uranium, and other metal miners and another one group of fluorspar. Despite the uncertainties that have effect on the exposure estimates of the population being studied to the decay products from radon, strong evidence on have been obtained on the exposure response relationships. There have been suggestions on the increased risk in people residing in houses with high radon levels from various lung cancer case-control studies than those peoples inhabiting houses with less exposure. There is no simple conclusion with regards to lung cancer in the cigarette smoking interaction with radon and its related decay products. Largest study has shown data that is coherent with sub-multiplicative and multiplicative synergism model where by an additive model is rejected. A higher number unexpected fraction of cases of lung cancers was accounted for by the small cell cancers in various studies conducted on the miners and one where domestic exposure was presumed. There has been reducing fraction of these miners over time. Experience from the miners has been used to make the risk quantification due to limited number of epidemiological study conducted on radon decay products exposure which is not occupational. There is no decisive conclusion regarding the tobacco smoking and the exposure to radon as considerations of the epidemiologic evidence by the IARC Working Group. There are usually inadequate or variable interaction assessment approaches and the epidemiologic studies are not of large numbers cases ("Cancer and radon: Studies on the carcinogenicity of radon").

A study was conducted in Colorado where 80 miners for underground uranium and 20 controls had their Peripheral lymphocyte chromosomes studied. Diagnostic radiation and cigarette smoking were some of the confounding factors taken into consideration. There was selection of groups whose radon exposure was increased. Through sputum cell cytology, there was observation of high number of chromosomes aberrations in miners who exhibited abnormal bronchial cell cytology, carcinoma or suspected carcinoma in situ than those miners with regular abnormal cells. In experimental animals, there has been witnessed enough evidence of carcinogenicity of isotropic form of radon i.e. radon-220 and radon 222. Adenocarcinomas, pulmonary adenomas, squamous cell carcinomas and pulmonary adenomas were induced by radon when it was administered through inhalation followed by cerium hydroxide dust exposure in the male rats. Bronchio-alveolar or bronchiolar was believed to the origin of most of the tumors.

Male hamsters exposed to the inhalation of radon which had uranium ore dust combined with it induced a development of activity that led to malignant tumors in the bronchioles from unit basal cell hyperplasia. There was also observed lung tumors which included adenocarcinomas, adenomas and squamous cell carcinomas; alveolar and bronchiolar metaplasia. There was also observation of fibrosis, adenomatous lesions, and interstitial pneumoniaDogs which had the exposure through inhalation administration exhibited nasal carcinomas, bronchio-alveolar carcinomas, epidermoid carcinomas and fibrosarcoma. Dogs and rats which had the exposure exhibited tumors of the respiratory tracts than those which had not been exposed. Testing for radon experiments in rats produced a dose response relationship.

Mitigating radon gas exposure

The radon levels in the homes can be lowered through various methods which either prevent the actual entry of radon into the homes or reduce the radon levels once they have entered the house. Prevention of entry technique is the most recommended method. For instance, Soil suction technique prevents the entry by sucking the radon beneath the house and using pipes, this is vented outside to the air above the building and fast dilution takes place. Visual and diagnostic tests of the house are performed before the actual reduction so that information like air flow is obtained. The reduction system will be affected by the house type. For basement and Slab- on -- Grade houses, the reduction is done through any of the four methods of soil suction: drain tile suction, sump-hole suction, drain tile suction or block wall suction. For claw-space houses, the radon levels are reduced effectively by using high-density plastic sheet to cover the floor. Radon is vented to the outdoor by drawing it under the sheet using fans and vent pipe. Other method of radon reduction is sealing of the cracks found in the foundation that limit the radon flow into the house ("How to reduce radon levels in your home").

Conclusion

Association between lung cancer and exposure in the residential houses has been shown by many studies conducted by scientists In the United States and other parts of the world though not all studies has shown this association. The reason for this inconsistencies in the different studies is because of disparate radon levels in the homes, some studies were smaller and complexity of radon's exposure measuring in a person over time. Analysis of combined data from studies conducted on radon in the U.S. And Canada where data from thousands of people was considered, has shown exposure from the radon in the house hold has demonstrated increased lung cancer risk. There are consistencies to the risk levels increases for the estimation on the underground miner's studies (Field 1091).