The World Health Organization has recommended a radon reference concentration of 100 Bq/m3 (2.7 pCi/L).[98] The European Union recommends that action should be taken starting from concentrations of 400 Bq/m3 (11 pCi/L) for older dwellings and 200 Bq/m3 (5 pCi/L) for newer ones.[99] After publication of the North American and European Pooling Studies, Health Canada proposed a new guideline that lowers their action level from 800 to 200 Bq/m3 (22 to 5 pCi/L).[100] The United States Environmental Protection Agency (EPA) strongly recommends action for any dwelling with a concentration higher than 148 Bq/m3 (4 pCi/L),[51] and encourages action starting at 74 Bq/m3 (2 pCi/L).