Radon levels in South African homes - design elements for a national survey and initial results from directed sampling

Date
2021-03
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Radon (222Rn) is an inert, colourless, odourless radioactive gas that is generated by the alpha decay of radium (226Ra), a radionuclide in the uranium (238U) decay series. Radon (222Rn) is the primary source of environmental radiation exposure posing significant risks to human health. The World Health Organization (WHO) estimates that between 3 and 14% of lung cancers are attributable to radon and its progeny. There are a number of factors contributing in a multiplicative manner to the radon levels inside dwellings (e.g. underlying soil and geology, building materials, building construction). An overview of existing data on indoor radon levels across South Africa and national radon surveys conducted around the world is presented. The approach strategies adopted to achieve public acceptance of radon detectors in dwellings is presented and discussed. An investigation into the most appropriate technology to use for short- and long-term indoor radon measurements was undertaken. As part of this, results from measurements with track-etch, electret ion-chamber and Airthings™ detectors were critically compared. Radon measurements were carried in workplaces, homes and schools. The radon concentration recorded in workplaces (offices and laboratories) ranged from 32.2 5.2 Bqm􀀀3 to 87.0 10.1 Bqm􀀀3. The levels recorded in Gauteng homes ranged from 2.4 0.3 Bqm􀀀3 to 102.5 11.7 Bqm􀀀3. The levels recorded in schools and homes in Western Cape ranged from 12.3 2.8 Bqm􀀀3 to 143.7 17.0 Bqm􀀀3 and from 0.0 0.0 Bq m􀀀3 to 126.9 14.6 Bqm􀀀3, respectively. Results of the surveys showed that radon concentration levels in most of the dwellings were low, whilst in areas close to granite outcrops the levels were found to be relatively high. The overall annual mean effective dose rate from radon and its decay progenies was estimated to be 0.6 0.4 mSvy􀀀1 which yields an excess lifetime cancer risk of around 1.7 1.1 x 10􀀀3. These values are below the recommended action levels. The study recommends that the highly populated areas, especially those close to granite outcrops, should be prioritised for the future indoor radon survey. The radon measurements should preferably be made during the winter seasons using electret ion-chamber and track-etch detectors. Access to homes can be gained through the door-to-door approach, invitations and school outreach.
AFRIKAANSE OPSOMMING: Radon (222Rn) is ’n inerte, kleurlose, reuklose radioaktiewe gas wat ontstaan deur die alfaverval van radium (226Ra), ’n radionuklied in die uraan (238U) vervalreeks. Radon (222Rn) is die primêre bron van blootstelling aan die omgewingstraling wat beduidende risikos vir die mens se gesondheid inhou. Die Wêreldgesondheidsorganisasie (WGO) skat dat tussen 3 en 14% van longkanker gevalle aan radon en sy afvalprodukte te wyte is. Daar is ’n aantal faktore wat op ’n vermenigvuldigende manier bydra tot die radonvlakke in huise (bv. onderliggende grond en geologie, boumateriaal, boukonstruksie). ’n Oorsig van bestaande data oor radonvlakke regoor Suid Afrika en nasionale radonopnames wat oor die hele wêreld gedoen word, word aangebied. Die benaderingsstrategieë wat aangewend word om openbare aanvaarding van radondetektore in wonings te bewerkstellig, word aangebied en bespreek. ’n Ondersoek na die mees geskikte tegnologie om vir kort- en langtermyn radonmetings binnenshuis te gebruik, is onderneem. As deel hiervan is resultate van metings met spoor-ets, elektret ioonkamer en Airthings™ detektore krities vergelyk. Radonmetings is by werkplekke, binne huise en by skole. Die radonkonsentrasie wat by werkplekke (kantore en laboratoriums) aangeteken is, wissel van 32.2 5.2 Bqm􀀀3 tot 87.0 10.1 Bqm􀀀3. Die vlakke wat in Gautengse huise aangeteken is, het gewissel van 2.4 0.3 Bqm􀀀3 tot 102.5 11.7 Bqm􀀀3. Die vlakke wat in skole en huise in die Wes-Kaap aangeteken is, wissel van 12.3 2.8 Bqm􀀀3 tot 143.7 17.0 Bqm􀀀3 en van 0.0 0.0 Bqm􀀀3 tot 126.9 14.6 Bqm􀀀3, onderskeidelik. Resultate van die opnames het getoon dat die radonkonsentrasievlakke in die meeste wonings laag was, terwyl die vlakke relatief hoog in gebiede naby graniet “outcrops” was. Die totale jaarlikse gemiddelde effektiewe dosis as gevolg van radon en sy afvalprodukte word beraam op 0.6 0.4 mSvy􀀀1 wat ’n oormaat lewenslange kankerrisiko oplewer van ongeveer 1.7 1.1 x 10 􀀀3. Hierdie waardes is laer as die aanbevole aksievlakke. Die studie beveel aan dat die meer bevolkte gebiede, veral die naby graniet “outcrops” voorkeur moet geniet in toekomstige binnenshuise radonopnames. Radon metings moet verkieslik gedurende die winterseisoen geskied met behulp van elektriese ioonkamer-en spoor-etsdetektors. Toegang tot huise kan verkry word deur die deur-tot-deur-benadering, uitnodigings en skooluitreike.
Description
Thesis (MSc)--Stellenbosch University, 2021.
Keywords
Radon -- Measurement, Radon mitigation, Dwellings -- South Africa -- Radioactive contamination, Radioactive contamination of houses -- South Africa -- Sampling, Sampling (Statistics), UCTD
Citation