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.

Domestic radon remediation of UK dwellings by Sub-Slab Depressurisation: evidence for a baseline contribution from constructional materials.

To quantify the effectiveness of Sub-Slab Depressurisation, widely used in the United Kingdom (U.K.) to mitigate indoor radon gas levels in residential properties, a study was made of radon concentration data collected from a set of 170 homes situated in Radon Affected Areas in Northamptonshire and neighbouring counties, remediated using conventional sump/pump technology. A high incidence of satisfactory remediation outcomes was achieved, with 100% of the houses remediated demonstrating post-remediation radon concentrations below the U.K. domestic Action Level of 200 Bq m(-3), while more than 75% of the sample exhibited radon mitigation factors (defined as the ratio of radon concentrations following and prior to remediation) <0.2. Two systematic trends are identified. Firstly, absolute radon concentration reduction following remediation is directly proportional to initial radon concentration, with a mean reduction factor of 0.96 and a residual component of around 75 Bq m(-3). Secondly, houses with lower initial radon concentrations demonstrate poorer (higher) mitigation factors. These observations support a model in which the total indoor radon concentration within a dwelling can be represented by two principal components, one susceptible to mitigation by sub-slab depressurisation, the other remaining essentially unaffected. The first component can be identified with radon emanating from the subsoil and bedrock geologies, percolating through the foundations of the dwelling as a component of the soil-gas, and potentially capable of being attenuated by sub-slab depressurisation or radon-barrier remediation technologies. The second contribution can be identified with radon emanating from materials used in the construction of the dwelling with a further contribution from the natural background level, and is essentially unaffected by ground-level remediation strategies. Modelling of a multi-component radon dependency using ground-radon attenuation factors derived from the experimental data, in conjunction with typical background and structural-radon levels, yields behaviour in good agreement with the observed dependence of mitigation factor on initial radon concentration.

Predation as a landscape effect: the trading off by prey species between predation risks and protection benefits.

1. Predators impose costs on their prey but may also provide benefits such as protection against other (e.g. nest) predators. The optimal breeding location in relation to the distance from a nesting raptor varies so as to minimize the sum of costs of adult and nest predation. We provide a conceptual model to account for variation in the relative predation risks and derive qualitative predictions for how different prey species should respond to the distance from goshawk Accipiter gentilis nests. 2. We test the model predictions using a comprehensive collection of data from northern Finland and central Norway. First, we carried out a series of experiments with artificial bird nests to test if goshawks may provide protection against nest predation. Second, we conducted standard bird censuses and nest-box experiments to detect how the density or territory occupancy of several prey species varies with distance from the nearest goshawk nest. 3. Nest predation rate increased with distance from goshawk nest indicating that goshawks may provide protection for birds' nests against nest predation. Abundance (or probability of presence) of the main prey species of goshawks peaked at intermediate distances from goshawk nests, reflecting the trade-off. The abundance of small songbird species decreased with distance from goshawk nests. The goshawk poses little risk to small songbirds and they may benefit from goshawk proximity in protection against nest predation. Finally, no pattern with distance in pied flycatcher territory (nest box) occupation rate or the onset of egg-laying was detected. This is expected, as flycatchers neither suffer from marked nest predation risk nor are favoured goshawk prey. 4. Our results suggest that territory location in relation to the nest of a predator is a trade-off situation where adult birds weigh the risk of themselves being predated against the benefits accrued from increased nest survival. Prey species appear able to detect and measure alternative predation risks, and respond adaptively. From the prey perspective, the landscape is a mosaic of habitat patches the quality of which varies according to structural and floristic features, but also to the spatial distribution of predators.

Radon mitigation in domestic properties and its health implications--a comparison between during-construction and post-construction radon reduction.

Although United Kingdom (UK) Building Regulations applicable to houses constructed since 1992 in Radon Affected Areas address the health issues arising from the presence of radon in domestic properties and specify the installation of radon-mitigation measures during construction, no legislative requirement currently exists for monitoring the effectiveness of such remediation once construction is completed and the houses are occupied. To assess the relative effectiveness of During-Construction radon reduction and Post-Construction remediation, radon concentration data from houses constructed before and after 1992 in Northamptonshire, UK, a designated Radon Affected Area, was analysed. Post-Construction remediation of 73 pre-1992 houses using conventional fan-assisted sump technology proved to be extremely effective, with radon concentrations reduced to the Action Level, or below, in all cases. Of 64 houses constructed since 1992 in a well-defined geographical area, and known to have had radon-barrier membranes installed during construction, 11% exhibited radon concentrations in excess of the Action Level. This compares with the estimated average for all houses in the same area of 17%, suggesting that, in some 60% of the houses surveyed, installation of a membrane has not resulted in reduction of mean annual radon concentrations to below the Action Level. Detailed comparison of the two data sets reveals marked differences in the degree of mitigation achieved by remediation. There is therefore an ongoing need for research to resolve definitively the issue of radon mitigation and to define truly effective anti-radon measures, readily installed in domestic properties at the time of construction. It is therefore recommended that mandatory testing be introduced for all new houses in Radon Affected Areas.

Analysis of the individual health benefits accruing from a domestic radon remediation programme.

Although radon can be present within buildings at sufficient levels to pose a health risk, levels can be reduced relatively easily. Recent studies on a group of radon-remediated homes, based on assessment of collective population-average risk coefficients, have estimated the benefits and cost effectiveness accruing from remediation and have confirmed that domestic remediation in UK radon Affected Areas would result in significantly reduced cancer risks to the population in those areas. Although the population-average approach used hitherto has applied occupancy and lung-cancer risk factors, these are potentially misleading in assessing discrete populations. The study reported here uses the recently developed European Community Radon Software (ECRS) to quantify individual risks in a sample of householders who remediated their homes following indications that radon levels exceeded the action level. The study proceeds from population-averaged to 'individual risk' evaluation, successfully comparing individual and collective risk assessments, and demonstrates that those who remediate are not representative of the general population. Health benefits accruing from remediation are three times lower than expected, largely because remediators are older, live in smaller households, and smoke less than the population average, leading to the conclusion that the current strategy employed in the UK is failing to target those most at risk.

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 costs and benefits of radon remediation programmes in existing homes: case study of action level selection.

Radon gas can be present within buildings at sufficiently high levels that it becomes a health risk. Such levels can be reduced, and so radon remediation programmes in the home in UK Affected Areas should result in reduced risks to the population. This paper considers the benefits and costs of the domestic radon remediation programme in Northamptonshire, UK, and considers the implications of the choice of Action Level, in view of the adoption of different levels in many countries. A programme with a higher Action Level will cost less, and target those most at risk, but will be less cost effective. In addition, a higher Action Level leaves a higher residual dose and risk to the remaining population. Such doses are higher than and inconsistent with the radiation dose limits for the general public in the EU Basic Standards Directive.

Changes in diet and morphology of Finnish goshawks from 1960s to 1990s.

We studied the morphology of the goshawk in northern Finland by measuring skin and skeletal characters of 258 museum specimens dated between 1961 and 1997. We predicted a decrease in the size of male goshawks from the 1960s because availability of their main prey, grouse, has decreased since then and grouse have been replaced in the diet by smaller prey during the breeding season. Based on the assumption that winter is the most critical period for females, we predicted that female size should have increased because their winter diet consisted of more and more mountain hare, which is a prey generally larger than grouse. Analyses revealed that male size has indeed decreased since the 1960s, while adult females have increased in size. Our data suggest that these morphological shifts were the result of selective pressures due to changes in diet. We also found changes in the (size-independent) shape of the hawks. Relative wing and tail lengths of adult hawks became longer between 1980 and 1990 compared with the 1960-1970 period, while relative juvenile wing and tail lengths tended to decrease. As a result of these morphological changes size dimorphism between the sexes increased from the 1960s to the 1990s.