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Cancer-causing substance found in Seoul subway stations

A total of 30 subway stations in the capital city of Seoul contained higher-than-allowed levels of cancer-causing substances over the last decade, the municipal government said Monday.

The city's regular checks between 1998 and 2004 found that the level of radon in 30 out of 285 stations in Seoul from Line No. 1 through 7, including Gwanghwamun Station in downtown Seoul, exceeded the standard, or 4 picocuries, at least one time, according to the Seoul Metropolitan Government.

A picocurie is one trillionth of a curie, which is a standard measure for the intensity of radioactivity contained in a sample of radioactive material.

Radon is a radioactive gas that is chemically inert and naturally occurring, and is known as one of the main risks of ionizing radiation, causing tens of thousands of deaths from lung cancer each year globally, according to the World Health Organization.