The P.E.I. Department of Health has found two more schools with high levels of radon.
Rooms at the Spring Park Elementary School in Charlottetown and Queen Elizabeth Elementary School in Kensington had levels of the colourless, odourless radioactive gas that are above the national guideline.
Health Canada lowered the acceptable level of radon from 800 becquerels per cubic metre to 200 in 2007. A becquerel is a measure of radioactive decay.
Radon comes from the natural breakdown of uranium in soil, rock and water, and is usually found at higher concentrations in the lower levels of buildings.
Long-term exposure to high levels of radon gas can cause lung cell damage, which increases the risk of developing lung cancer.
Since 2007, the Department of Health has been testing provincial buildings, including schools, seniors housing and correctional centres for radon gas.
In 2008, the department found 20 buildings throughout the province with radon levels higher than the national guideline, including schools. When those buildings were tested again this year, four buildings were still found to be over the national guideline.
The department said if people have concerns about radon levels in their own homes, they should conduct tests over a three-month period.