Results of the national survey on radon indoors in all the 21 Italian regions

The National Survey on Radon Indoors was designed to estimate the distribution of annual radonconcentration in Italian dwellings, on the basis of a representative sample of about 5000 dwellings. Itstarted in 1989 and ended in 1994, involving all Italian Regions except Sicilia and Calabria, due toorganizational problems in these two regions of Southern Italy. After the official conclusion, tworegional surveys were also carried out in Sicilia and Calabria, using the same experimental apparatusand protocols as in the other Regions. The final sample size was of 5631 dwellings distributed in 232towns, i.e. all the 50 large towns (with more than 100,000 inhabitants) and a random sample of thesmaller towns. The results in Sicilia and Calabria were characterized by quite low radonconcentrations, thus moving the national radon distribution towards somewhat lower values. Theupdated national average, weighted by the population of each Region, of the annual radonconcentration decreases from 75 Bq/m3 to 70 Bq/m3, the geometric mean decreases from 57 Bq/m3 to52 Bq/m3, while the geometric standard deviation slightly increases from 2.0 to 2.1. The estimatednational average values of the fraction of dwellings with radon concentration above the referencelevels of 150 Bq/m3, 200 Bq/m3, 400 Bq/m3, and 600 Bq/m3 are 7.7%, 4.1% and 0.9%, and 0.2%,respectively. Regional averages range from about 25 Bq/m3 to about 120 Bq/m3. However, theuncertainty of regional values can be relevant in case of small Regions, where a low number of smalltowns were sampled, although such uncertainties do not affect significantly national values. In fact,while results in large Regions were generally confirmed by the more detailed regional surveys carriedout in schools and/or in dwellings after the National Surveys, for three less populated Regions thereare strong indications that the results from the National Survey were probably characterized by arelevant underestimation of regional radon concentration levels, although with a very limited effect(up to about 2 Bq/m3) on the national average. In conclusion, the complete results of National Surveyprovided a reliable estimate of the radon national distribution in Italian dwellings, and represent thebasis for more detailed regional surveys, some of which have already been carried out.