J.D. Appleton

Mapping variation in radon potential both between and within geological units.

Previously, the potential for high radon levels in UK houses has been mapped either on the basis of grouping the results of radon measurements in houses by grid squares or by geological units. In both cases, lognormal modelling of the distribution of radon concentrations was applied to allow the estimated proportion of houses above the UK radon Action Level (AL, 200 Bq m(-3)) to be mapped. This paper describes a method of combining the grid square and geological mapping methods to give more accurate maps than either method can provide separately. The land area is first divided up using a combination of bedrock and superficial geological characteristics derived from digital geological map data. Each different combination of geological characteristics may appear at the land surface in many discontinuous locations across the country. HPA has a database of over 430,000 houses in which long-term measurements of radon concentration have been made, and whose locations are accurately known. Each of these measurements is allocated to the appropriate bedrock--superficial geological combination underlying it. Taking each geological combination in turn, the spatial variation of radon potential is mapped, treating the combination as if it were continuous over the land area. All of the maps of radon potential within different geological combinations are then combined to produce a map of variation in radon potential over the whole land surface.

Mercury contamination associated with artisanal gold mining on the island of Mindanao, the Philippines.

The Agusan River basin of eastern Mindanao, the Philippines, hosts several centres of artisanal gold mining, the most important of which, Diwalwal, is a significant gold producer in global terms. An investigation of the environmental impacts of artisanal mining in the Agusan system, with particular reference to mercury contamination, was initiated in 1995 following reports of several incidents of human Hg poisoning in the province of Davao del Norte. Results show drainage downstream of Diwalwal is characterised by extremely high levels of Hg both in solution (maximum 2906 micrograms/l) and in bottom sediments (> 20 mg/kg). Filtered surface water Hg levels exceed the WHO Drinking Water guideline and the US-EPA Water Quality Criteria for the Protection of Aquatic Life for a downstream distance of more than 14 km, including channel sections utilised for fishing and potable water supply. The Environment Canada sediment quality Hg Toxic Effect Threshold for the Protection of Aquatic Life is exceeded for a downstream distance of 20 km. Hair Hg data indicate that ballmill and CIP plant operators processing Hg contaminated tailings at eastern Mindanaos principal gold beneficiation centre, Apokon, may be subject to enhanced occupational Hg exposure. It appears that the wider population of this area has not been affected.

A statistical evaluation of the geogenic controls on indoor radon concentrations and radon risk

ANOVA is used to show that approximately 25% of the total variation of indoor radon concentrations in England and Wales can be explained by the mapped bedrock and superficial geology. The proportion of the total variation explained by geology is higher (up to 37%) in areas where there is strong contrast between the radon potential of sedimentary geological units and lower (14%) where the influence of confounding geological controls, such as uranium mineralisation, cut across mapped geological boundaries. When indoor radon measurements are grouped by geology and 1-km squares of the national grid, the cumulative percentage of the variation between and within mapped geological units is shown to be 34-40%. The proportion of the variation that can be attributed to mapped geological units increases with the level of detail of the digital geological data. This study confirms the importance of radon maps that show the variation of indoor radon concentrations both between and within mapped geological boundaries.

Background exposure rates of terrestrial wildlife in England and Wales

It has been suggested that, when assessing radiation impacts on non-human biota, estimated dose rates due to anthropogenically released radionuclides should be put in context by comparison to dose rates from natural background radiation. In order to make these comparisons, we need data on the activity concentrations of naturally occurring radionuclides in environmental media and organisms of interest. This paper presents the results of a study to determine the exposure of terrestrial organisms in England and Wales to naturally occurring radionuclides, specifically (40)K, (238)U series and (232)Th series radionuclides. Whole-body activity concentrations for the reference animals and plants (RAPs) as proposed by the ICRP have been collated from literature review, data archives and a targeted sampling campaign. Data specifically for the proposed RAP are sparse. Soil activity concentrations have been derived from an extensive geochemical survey of the UK. Unweighted and weighted absorbed dose rates were estimated using the ERICA Tool. Mean total weighted whole-body absorbed dose rates estimated for the selected terrestrial organisms was in the range 6.9 x 10(-2) to 6.1 x 10(-1) microGy h(-1).

Comparison of Northern Ireland radon maps based on indoor radon measurements and geology with maps derived by predictive modelling of airborne radiometric and ground permeability data

Publicly available information about radon potential in Northern Ireland is currently based on indoor radon results averaged over 1-km grid squares, an approach that does not take into account the geological origin of the radon. This study describes a spatially more accurate estimate of the radon potential of Northern Ireland using an integrated radon potential mapping method based on indoor radon measurements and geology that was originally developed for mapping radon potential in England and Wales. A refinement of this method was also investigated using linear regression analysis of a selection of relevant airborne and soil geochemical parameters from the Tellus Project. The most significant independent variables were found to be eU, a parameter derived from airborne gamma spectrometry measurements of radon decay products in the top layer of soil and exposed bedrock, and the permeability of the ground. The radon potential map generated from the Tellus data agrees in many respects with the map based on indoor radon data and geology but there are several areas where radon potential predicted from the airborne radiometric and permeability data is substantially lower. This under-prediction could be caused by the radon concentration being lower in the top 30 cm of the soil than at greater depth, because of the loss of radon from the surface rocks and soils to air.

Modelling lead bioaccessibility in urban topsoils based on data from Glasgow, London, Northampton and Swansea, UK

Predictive linear regression (LR) modelling between bioaccessible Pb and a range of total elemental compositions and soil properties was executed for the Glasgow, London, Northampton and Swansea urban areas in order to assess the potential for developing a national urban bioaccessible Pb dataset for the UK. LR indicates that total Pb is the only highly significant independent variable for estimating the bioaccessibility of Pb. Bootstrap resampling shows that the relationship between total Pb and bioaccessible Pb is broadly the same in the four urban areas. The median bioaccessible fraction ranges from 38% in Northampton to 68% in London and Swansea. Results of this study can be used as part of a lines of evidence approach to localised risk assessment but should not be used to replace bioaccessibility testing at individual sites where local conditions may vary considerably from the broad overview presented in this study.

Radon: Sources, Health Risks, and Hazard Mapping

There are three naturally occurring radon (Rn) isotopes: 219Rn (actinon), 220Rn (thoron) and 222Rn, which is commonly called radon. Radon-222 is a natural radioactive gas produced by the radioactive decay of radium (226Ra), which in turn is derived from the radioactive decay of uranium. Uranium is found in small quantities in all soils and rocks, although the amount varies from place to place. 222Rn (radon) occurs in the uranium-238 decay series, has a half-life of 3.82 days and provides about 50% of the total radiation dose to the average person. Radon concentrations1 in outdoor air are generally low (4 to 8 Bq m-3) whilst radon in indoor air ranges from less that 20 Bq m-3 to about 110,000 Bq m-3 with a population-weighted world average of 39 Bq m-3. Country averages range from 9 in Egypt, 20 Bq m-3 in the UK, 46 Bq m-3 in the US, 108 Bq m-3 in Sweden and 140 Bq m-3 in the Czech Republic (1). Radon in soil air (the air that occupies the pores in soil) commonly varies from 5 to 50 Bq L-1 but may be <1 or more than 2500 Bq L-1. The amount of radon dissolved in ground water ranges from about 3 to nearly 80,000 Bq L-1. This synopsis describes the kinds of rocks and unconsolidated deposits that radon is associated with; how radon moves through the ground and into buildings; the associated health risks, and how to produce radon hazard maps. It is an updated summary of (2).

Ammonium geochemistry in mineral exploration—a comparison of results from the American cordilleras and the southwest Pacific

Abstract Ammonium concentrations in the host rocks to circum-Pacific epithermal precious metal and exhalative base metal deposits vary from 0 to 25,000 ppm. High ammonium concentrations in mineralizing fluids are probably derived from the breakdown of organic matter in sediments or sedimentary rocks within the hydrothermal system. Shales are particularly good ammonium source rocks. Ammonium substitutes for K and other alkali elements in crystal lattices. Host rocks with K-bearing minerals therefore have the highest potential for the development of ammonium haloes. Both surface and subsurface rocks can contain high concentrations of ammonium and substantial haloes have been found associated with precious metal veins, particularly in the hanging wall. Such haloes are well developed at mines in Mexico, Bolivia and Peru and ammonium geochemistry thus provides a potentially useful exploration tool, especially for vein-type epithermal precious metal deposits.

Pilot study of the application of Tellus airborne radiometric and soil geochemical data for radon mapping

The scope for using Tellus Project airborne gamma-ray spectrometer and soil geochemical data to predict the probability of houses in Northern Ireland having high indoor radon concentrations is evaluated, in a pilot study in the southeast of the province, by comparing these data statistically with in-house radon measurements. There is generally good agreement between radon maps modelled from the airborne radiometric and soil geochemical data using multivariate linear regression analysis and conventional radon maps which depend solely on geological and indoor radon data. The radon maps based on the Tellus Project data identify some additional areas where the radon risk appears to be relatively high compared with the conventional radon maps. One of the ways of validating radon maps modelled on the Tellus Project data will be to carry out additional indoor measurements in these areas.

Anthropogenic and geogenic impacts on arsenic bioaccessibility in UK topsoils.

Predictive linear regression (LR) modelling between bioaccessible arsenic (B-As) and a range of total elemental compositions and soil properties was executed in order to assess the potential for developing a national B-As dataset for the UK. LR indicates that total arsenic (As) is the only highly significant independent variable for estimating B-As in urban areas where it explains 75-92% of the variance. The broad compatibility of the London, Glasgow and Swansea regression models suggests that application of these models to estimate bioaccessible As in UK soils impacted by diffuse anthropogenic urban contamination and non-ferrous metal processing should be relatively accurate. In areas dominated by Jurassic ironstones and associated clays and limestones, total As, P and pH are significant, accounting for 53, 14 and 5%, respectively, of the B-As variance. Models based on total As as the sole predictor in the combined Jurassic and Cretaceous sedimentary ironstones datasets explain about 40% of the B-As variance. The median As bioaccessible fraction (%As-BAF) is 19 to 28% in the anthropogenic contamination impacted urban domains, but much lower (5-9%) in geogenic terrains dominated by ironstones. Results of this study can be used as part of a lines of evidence approach to localised risk assessment but should not be used to replace bioaccessibility testing at individual sites where local conditions may vary considerably from the broad overview presented in this study.