Chris J Groves-Kirkby

Lorenz Curve and Gini Coefficient: novel tools for analysing seasonal variation of environmental radon gas.

Using a methodology derived from Economics, the Lorenz Curve and Gini Coefficient are introduced as tools for investigating and quantifying seasonal variability in environmental radon gas concentration. While the Lorenz Curve presents a graphical view of the cumulative exposure during the course of the time-frame of interest, typically one year, the Gini Coefficient distils this data still further, to provide a single-parameter measure of temporal clustering. Using the assumption that domestic indoor radon concentrations show annual cyclic behaviour, generally higher in the winter months than in summer, published data on seasonal variability of domestic radon concentration levels, in various areas of the UK, Europe, Asia and North America, are analysed. The results demonstrate significantly different annual variation profiles between domestic radon concentrations in different countries and between regions within a country, highlighting the need for caution in ascribing seasonal correction factors to extended geographical areas. The underlying geography, geology and meteorology of a region have defining influences on the seasonal variability of domestic radon concentration, and some examples of potential associations between the Gini Coefficient and regional geological and geographical characteristics are proposed. Similar differences in annual variation profiles are found for soil-gas radon measured as a function of depth at a common site, and among the activity levels of certain radon progeny species, specifically (214)Bi deposited preferentially in human body-fat by decay of inhaled radon gas. Conclusions on the association between these observed measures of variation and potential underlying defining parameters are presented.

Tidal synchronicity of built-environment radon levels in the UK

In our recent work on radon in UK homes the authors have observed tidal-periodic variations in built-environment radon levels and here report results from our ongoing investigations. These tidal variations have been quantified using a variety of analytical techniques, including a novel correlation technique developed as part of this investigation. The observed variations are cyclic at the 14-15 day tidal period and lag new/full moons by varying periods of days, the magnitude of the variation and lag being dependent on factors such as location, underlying geology and rock/soil hydration. As well as quantification and discussion of tidal effects on radon levels, the potential effects of such phenomena on the reliability of short-term radon measurements are discussed.

Using the European Community Radon Software to estimate the individual health benefits of a domestic radon remediation programme

Radon can be present in domestic properties at high enough levels to pose a health risk. Such levels can usually be reduced by simple means. Studies on a group of radon-remediated homes in Northamptonshire, a radon affected area, have estimated the health benefits and cost effectiveness from remediation and have shown that remediation can be justified. These assessments have been based on collective population-average risk coefficients. The advent of the European Community Radon Software (ECRS) permits the consideration of individual risk. In particular, it can take into account individual smoking habits, which significantly affect risk, as current scientific opinion is that risks from radon and smoking are multiplicative. This note indicates how the software can be used, and the usefulness of this approach.

The cost effectiveness of radon reduction programmes in domestic housing in England and Wales: the impact of improved radon mapping and housing trends

In the UK, excessive levels of radon gas have been detected in domestic housing. Areas where 1% of existing homes were found to be over the Action Level of 200Bq·m(-3) were declared to be Radon Affected Areas. Building Regulations have been introduced which require that, for areas where between 3% and 10% of existing houses are above the Action Level, new homes should be built with basic radon protection using a membrane, and that, where 10% or more of existing homes exceed this level, new homes should be built with full radon protection. Initially these affected areas followed administrative boundaries, known as Counties. However, with increasing numbers of measurements of radon levels in domestic homes recorded in the national database, these areas have been successively refined into smaller units - 5km grid squares in 1999, down to 1km grid squares in 2007. One result is the identification of small areas with raised radon levels within regions where previously no problem had been identified. In addition, some parts of areas that were previously considered radon affected are now considered low, or no, risk. Our analysis suggests that the net result of improved mapping is to increase the number of affected houses. Further, the process is more complex for local builders, and inspectors, who need to work out whether radon protection in new homes is appropriate. Our group has assessed the cost-effectiveness of radon remediation programmes, and has applied this analysis to consider the cost-effectiveness of providing radon protection in both new and existing homes. This includes modelling the potential failure rate of membranes, and whether testing radon levels in new homes is appropriate. The analysis concludes that it is more cost effective to provide targeted radon protection in high radon areas, although this introduces more complexity. The paper also considers the trend in housing to a greater proportion of apartments, the regional variations in types of housing and the decreasing average number of occupants in each dwelling, and concludes that data and methods are now available to respond to the health risks of radon at a local level, in keeping with a general initiative to prioritise responses to health and social welfare issues at a more local level.

Radon remediation of a two-storey UK dwelling by active sub-slab depressurisation: effects and health implications of radon concentration distributions.

Radon concentration levels in a two-storey detached single-family dwelling in Northamptonshire, UK, were monitored continuously throughout a 5-week period during which active sub-slab depressurisation remediation measures were installed. Remediation of the property was accomplished successfully, with both the mean radon levels and the diurnal variability greatly reduced both upstairs and downstairs. Following remediation, upstairs and downstairs radon concentrations were 33% and 18% of their pre-remediation values respectively: the mean downstairs radon concentration was lower than that upstairs, with pre- and post-remediation values of the upstairs/downstairs concentration ratio, R(U/D), of 0.81 and 1.51 respectively. Cross-correlation between upstairs and downstairs radon concentration time-series indicates a time-lag of the order of 1 h or less, suggesting that diffusion of soil-derived radon from downstairs to upstairs either occurs within that time frame or forms a relatively insignificant contribution to the upstairs radon level. Cross-correlation between radon concentration time-series and the corresponding time-series for local atmospheric parameters demonstrated correlation between radon concentrations and internal/external pressure difference prior to remediation; this correlation disappears following remediation. Overall, these observations provide further evidence that radon concentration levels within a dwelling are not necessarily wholly determined by the effects of soil-gas advection, and further support the suggestion that, depending on the precise content of the building materials, upstairs radon levels, in particular, may be dominated by radon exhalation from the walls of the dwelling, especially in areas of low soil-gas radon.

Lowering the UK domestic radon Action Level to prevent more lung cancers—is it cost-effective?

Case studies have shown that radon gas can accumulate within domestic properties at sufficiently high levels that it can cause lung cancer, and recent studies have suggested that this risk remains significant below the UK domestic Action Level of 200 Bq m(-3). Raised radon levels can be reduced by engineering measures, and it has been shown that domestic radon remediation programmes in UK Affected Areas can result in reduced risks to the population and can be cost-effective. We consider here the benefits and costs of the domestic radon remediation programme in Northamptonshire, UK, and consider the implications for that programme of reducing the UK Action Level below its present value. A radon remediation programme based on an Action Level above 200 Bq m(-3) will cost less and will target those most at risk, but will be less cost-effective and will lead to higher residual dose and greater risk of cancer in the remaining population. Reducing the Action Level below 200 Bq m(-3) will prevent more cancers, but at significantly higher cost. It will also be less cost-effective, because remediation of a significant number of houses with moderate radon levels will provide only a modest health benefit to occupants. Overall, a completed radon remediation programme of the type implemented in Northamptonshire is most cost-effective for an Action Level between 200 and 300 Bq m(-3). The implications for future health policy are discussed.

A detailed evaluation of the individual health benefits arising in a domestic property following radon remediation – a case-study in Northamptonshire, U.K.

Radon gas occurs naturally in the environment with variable distribution, concentrating sufficiently in the built environment in some areas to pose a public health risk. Radon levels can be successfully reduced in affected buildings, and large-scale remediation programmes have been justified in terms of accrued costs and benefits. We present results from a house where radon levels in the main living-room and master bedroom were monitored on an hourly basis over extended periods before and after radon remediation by sub-slab depressurisation. These results were combined with results from a recent occupancy survey to estimate the health impact on occupants spending varying times in the home. Prior to remediation, mean hourly radon exposure is moderately linearly correlated (R(2)=0.66-0.78) with time spent in the house. Following remediation, correlation is significantly enhanced (R(2)=0.91-0.95), but the exposure reduction of an occupant following remediation is less than that predicted using the NRPB protocol.