Evidence from temperate regions have often suggested a link between lung cancer deaths and radon exposure. A tasteless, odourless gas about eight times heavier than air, radon seeps out of the earth all over the world, but levels in the air outdoors vary significantly from place to place; exposure to radon mainly occurs indoors.

In the colder regions of the world, the concentration of radon indoors is five to 10 times higher than it is outdoors. In tropical countries, as buildings are kept well ventilated in the hotter climate, there is probably less difference in the indoor and the outdoor concentrations.

In Kinnaur, Himachal Pradesh, a steady rise due to lung cancer deaths had been observed about two years back. In severe winters, people in the district remain indoors. Alongwith carbon monoxide and carbon dioxide -emitted from the coal-burning bukharis (tin hearths) -radon (generated due to local rock-formation) too entered the houses. Opening the windows for brief intervals had no effect on the gas which is heavy and settles in the lower levels of the room.

Radon was also detected in other villages in the state in the course of a research project titled 'Radon Pollution Studies in Human Environment', undertaken by Surinder Singh, head of the department of physics in Guru Nanak Dev University, Amritsar (Punjab) and sponsored by the Union ministry of environment and forests in 1993. The acceptable limit (to the human body) for radioactive elements in the atmosphere prescribed by the US Environmental Protection Agency as safe is four pico curie per litre of air. The study, which used radon metres and plastic track detectors, found that in these villages, the measure of radioactive particles was much higher than this limit.

Radon, despite being an inert gas, spells doom as it is radioactive. In many countries, radon in homes is the largest single source of chronic exposure to radiation. The common building materials - wood, bricks and concrete - emit relatively little radon, but granite and pumice stone are much more radioactive, and are used in the CIS and Germany.

Radon levels in houses can be reduced by sealing floors and walls. out by far the most effective way to reduce levels is to use fans to ventilate crawl spaces, as most radon gets in through the floor.