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cancer detection programs ( e . g ., 40 % of Canadian patients ), as they have used tobacco to only a limited extent (~ 20 % of patients ), or have never used tobacco at all ( another ~ 20 % of patients ) 22 – 28 .
At a population and individual level , radon exposure arises from a complex convergence of geologic , built environment , demographic , lifestyle , and behavioural factors 19 – 21 , 29 – 36 . In Canada , evolving building practices over the 20th to 21st century have increasingly and unintentionally captured , contained , and concentrated alpha radiation emitting radionuclides from radon within the residential built environment to unnaturally high and unsafe levels 29 , 31 , 37 . Radiation doses from radon inhalation are also a function of decision making factors and socioeconomics relating to radon awareness , testing , and reduction ( i . e ., how fast an individual is able to understand and reduce radon exposure as a personal risk factor ) 20 , 21 , 30 , 38 , 39 , as well as lifestyle factors such as occupation that dictate activity patterns ( i . e ., the amount of time spent between environments ) 19 – 21 . Based on current residential radon levels and activity patterns , radiation doses from radon in Canada are estimated to be at historic highs , with radon-vulnerable populations in Canada including younger people with children living at home , who are employed or in education , and / or whose occupations are more amenable to telecommuting 19 . In part , this phenomenon is driven by younger ( those under age 45 ) Canadian adults being more likely to live in newer , more affordable residential buildings that have innately higher radon levels , and / or who are less able to afford radon reduction services due to comparatively lower household incomes 21 .
Socioeconomic disparities in lung cancer risk have been documented previously and are often linked to community types , with people living in more rural area ( i . e . less populated ) communities being more likely to use tobacco , earn less income , be exposed to different and / or higher amounts of environmental lung carcinogens throughout life , and have reduced access to health care and / or higher education 40 – 42 . In the context of radon exposure , disparities between urban and rural communities are documented and intriguing , but still ambiguous . Certainly , there are many reports of disparate rural versus urban indoor air radon levels across the globe 37 , 43 – 48 , highlighting a potentially serious issue with an ambiguous origin . One theory has been that domestic water supplies from rural-area groundwater wells often contain higher amounts of dissolved radon relative to ( already de-gassed ) supplies entering houses from urban-area municipal water treatment plants 49 , 50 . However , the contribution of water-borne radon to indoor air radon levels assessed in recent decades has typically been found to be relatively minor (~ 1 – 2 % of total , equating to microsievert ( μSv ) doses ) 51 – 57 ; this is most likely because the equilibration ratio of radon from air to water is 1:10,000 , meaning 10,000 Bq / L of radon degassing from water contributes only 1 Bq / m 3 to air 49 . Thus , an important question becomes : if radon being released directly from groundwater to indoor air is not the biggest contributor to the phenomenon of higher rural radon exposure , as current research indicates , then what might it be ?
How ( and to what extent ) radon exposure contributes to elevated lung cancer risks in diverse rural areas currently remains mechanistically unclear . In part , this is because earlier studies documenting radon differences between urban and rural areas were based on ( i ) smaller-scale datasets with limited statistical power ( a few hundred radon readings ), ( ii ) geogenic radon potentials ( i . e ., not empirical measurements of radon in indoor air ), ( iii ) data without matched urban controls from the same region , ( vi ) data that were potentially confounded by uncontrolled differences in radon-modifying property metrics between the urban and rural built environment , and / or findings that could not connect individual exposures to lung cancer risk 37 , 52 – 57 . To address these knowledge gaps in a systematic manner , we surveyed indoor air radon levels in residential properties across a broad geographic region with a highly diverse urban to rural paradigm , controlling for differences in regional building metrics that influence radon , and deriving radon exposure outcomes , radiation doses , and increased cancer risks based on the activity patterns of people living in these diverse communities .
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The study region included all Canadian provinces and territories , spanning a total land area of 9,984,670 km 2 with ( as of 2021 ) a population of 36.99 million people living in 16.28 million private dwellings . Based on Statistics Canada data , 17.8 % of the Canadian population ( 6.6 million people in 2021 ) lived in a community of less than 1000 people ( including isolated properties such as farm residences ). Our study cohort encompassed 42,051 households who provided building , demographic , and radon test data to the ‘ Evict Radon National Study ’, a publicly funded project led by investigators at multiple Canadian universities 19 – 21 , 29 – 31 , 58 . All radon level outcomes were from alpha track style radon tests conducted for an average of 124.2 days and performed by citizen scientist participants with oversight of the study team . For the purposes of this work , all households were assigned a ‘ community type ’ identifier by combining the precise geographic information system ( GIS ) coordinates of the residential property tested for radon with contemporary Statistics Canada ( StatCan ) definitions of population centres . More specifically , the community types include large urban population centres (‘ Cities ’, ≥ 100,000 inhabitants ), medium population centres (‘ Large towns ’, 30,000 – 99,999 inhabitants ), small population centres (‘ Small towns ’, 1000 – 29,999 inhabitants ), and entirely rural populations (“ Villages , hamlets and isolated properties ”, ( 1 – 999 inhabitants ) ( Fig . 1A ). Based on these geographically derived designations , our cohort encompassed 2032 unique civic areas with 14.9 % properties in villages , hamlets and isolated properties , 11.9 % in small towns , 10.1 % in large towns , and 63.1 % in cities ( Fig . 1B ). Importantly , the distribution of communities in our cohort was highly symmetric with the outcomes of the 2021 StatCan national census , indicating that , overall , our sample of communities reflected Canada during the period of radon testing . To understand social perspectives of a civic area ’ s population relative to our GIS-associated classifications , we asked participants to report how they described the identity of the community in which their home was located . We found strong agreement between the perceptions of individuals about their community and the impartial designations produced by our team ( Fig . 1C ), supporting our classification system .
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