Radon Gas
In the 1930’s a French engineer Pierie Cody who lived in the sea-port of Le Havre  knew of local ‘cancer houses’ in the port where many people had died from cancer over the years. He decided to investigate the matter using a gold leaf electroscope.
[The leaves statically charged to open slowly closed up again. The faster the leaves collapsed, the greater the ionization in the air]
After checking large numbers of these dwellings, Cody concluded that the air in these ‘Cancer Houses’ were ionized to an unusual degree. From various other tests Cody concluded that the ionization radiation consisted of positively charged Alpha Particles. [Each consisting of two protons and two neutrons] The only known source of alpha particle emission in dwellings was from a radioactive gas called Radon
[Cody later verified this assumption by carbon absorption and re emission, behaviour only shown by Radon.]

The National Radiological Protection Board (NRPB) estimate that out of 50.000 lung cancer deaths a year in Great Britain Radon gas is responsible for about 2,500 cases.

When we breathe the gas into our lungs the radon 222 atoms behave like miniature cannons bombarding the cells within their alpha particles large enough to slice through both strands of the double helix DNA molecule. (Mass of Gamma particle too small to damage both strands. A single strand is easily repaired, whereas double break very difficult if not impossible to repair). Even after radon 222 atoms have fired their alpha particles, the newly formed Polonium –218 atoms decay very quickly into other daughter isotopes which also eject alpha particles followed by high speed electrons and high energy gamma rays increasing the chances of lungs and other organs to succumb to cancer. Cody’s early research seemed to backup Baron Von Pohl’s findings  that noxious vapours/energy from underground water baring fissures were responsible for many of the cases of cancer.