An update on thoron exposure in Canada with simultaneous 222Rn and 220Rn measurements in Fredericton and Halifax

Abstract

Naturally occurring isotopes of radon in indoor air are identified as the second leading cause of lung cancer after tobacco smoking. Radon-222 (radon gas) and radon-220 (thoron gas) are the most common isotopes of radon. While extensive radon surveys have been conducted, indoor thoron data are very limited. To better assess thoron exposure in Canada, radon/thoron discriminating detectors were deployed in 45 homes in Fredericton and 65 homes in Halifax for a period of 3 months. In this study, radon concentrations ranged from 16 to 1374 Bq m(-3) with a geometric mean (GM) of 82 Bq m(-3) and a geometric standard deviation (GSD) of 2.56 in Fredericton, and from 4 to 2341 Bq m(-3) with a GM of 107 Bq m(-3) and a GSD of 3.67 in Halifax. It is estimated that 18 % of Fredericton homes and 32 % of Halifax homes could have radon concentrations above the Canadian indoor radon guideline of 200 Bq m(-3). This conclusion is significantly higher than the previous estimates made 30 y ago with short-term radon measurements. Thoron concentrations were below the detection limit in 62 % of homes in both cities. Among the homes with detectable thoron concentrations, the values varied from 12 to 1977 Bq m(-3) in Fredericton and from 6 to 206 Bq m(-3) in Halifax. The GM and GSD were 86 Bq m(-3) and 3.19 for Fredericton, and 35 Bq m(-3) and 2.35 for Halifax, respectively. On the basis of these results, together with previous measurements in Ottawa, Winnipeg and the Mont-Laurier region of Quebec, it is estimated that thoron contributes ∼8 % of the radiation dose due to indoor radon exposure in Canada.

The Concept of Equivalent Radon Concentration for Practical Consideration of Indoor Exposure to Thoron

“…A total of 370 Canadian homes have been tested for thoron in addition to radon [7,8,9,10] with thoron detected in about half of those. Among the homes with detectable thoron concentrations, the values varied from 6 to 1977 Bq·m −3 with a population weighted average of 56 Bq·m −3 .…”

“…Research on thoron and its contribution to the total radiation exposure from radon isotopes (both radon-222 and radon-220) has been carried out since the beginning of the National Radon Program in 2007. Results of several small scale Canadian thoron surveys have been published [7,8,9,10]. It is estimated that thoron contributes about 8% of the radiation dose attributed to indoor exposure to both radon-222 and radon-220 in Canada.…”

“…However, the variation is large for various geographical locations and there are situations where exposure to thoron is much more significant. Simultaneous radon and thoron measurements were conducted in a total of 370 Canadian homes in five cities/communities [7,8,9,10]; the ratios between thoron and radon concentrations in individual homes varied widely with an average ratio of 0.67. Three point eight percent (3.8%) of homes had thoron concentrations more than five times the radon concentration.…”

An Extended Study on the Correlation between 210Pb in Household Dust and Indoor Radon Concentration

“…RADUET detectors were placed on the lowest floor of 110 private homes randomly distributed in two Canadian cities, 45 in Fredericton and 65 in Halifax. Details of detector characteristics and radon measurements were given in a previous publication (Chen et al, 2011).…”

Radiological data on building stones from a Spanish region: Castilla y León

“…The carcinogenic effects of radon gas on the human population have been clearly established (Lubin et al, 1994;Darby et al, 1995;Krewski et al, 2006;Chen et al, 2011), and this has prompted many countries to address the question of the presence of radon inside dwellings in their territories (Gillmore and Jabarivasal, 2010). It is also well known that radon is the largest single contributor to exposure of the public to natural radiation (UNSCEAR, 1993).…”