An Airborne Gamma Ray Survey of Parts of SW Scotland in February 1993. Final Report

An airborne gamma ray survey was conducted for the Scottish Office Environment Department of coastal and inland parts of SW Scotland to define existing background levels, to locate features worthy of further attention, and to demonstrate the emergency response capabilities of radiometric methods. Coastal areas were surveyed with 500 m line spacing. Inland areas were specified to 2 km line spacing, however it was possible to achieve 1 km line spacing in the majority of the inland zone. Fieldwork was conducted between the 1st and 16th February 1993. A total of over 17,000 gamma ray spectra were recorded, using a 16 litre NaI spectrometer mounted in a helicopter flying at 50-75m ground clearance and 120kph. A total area of 3650 km2 was surveyed in 41.6 flying hours, from roughly 4370 line kilometres. The data were reduced in the field using standard SURRC procedures for background subtraction, stripping of spectral interferences, altitude correction, and calibration. Preliminary maps of the distribution of 137Cs, 40K, 214Bi, 208Tl, and estimated ground level gamma dose rate were produced during the fieldwork period using working calibration values derived from previous surveys. A set of core samples was collected from Wigtown Merse, Longbridgemuir and Caerlaverock merse for calibration purposes, and aerial observations were performed at these sites. Further soil sampling and ground level in-situ gamma spectrometry was performed in the summer of 1993 to investigate the applicability of the calibration to a range of upland soil types and topographical environments. These locations received peak deposition from the Chernobyl accident, are vulnerable to wet deposition, and are difficult to monitor rapidly using ground based methods. A total of 76 soil cores, subdivided into 168 separate samples was thus collected for high resolution gamma spectrometry in the laboratory. This was conducted from April to November 1993. For the terrestrial sites the aerial survey estimates based on the working calibration, were in good agreement with both in-situ gamma spectrometry and the results of core analysis. This validates the preliminary maps in these contexts, and confirms that a general calibration is sufficient for fallout mapping under emergency response conditions. On coastal salt marsh sites (merse), where aged deposits of Sellafield derived activity have accumulated, subsurface activity profiles for 137Cs and 241Am and the presence of superficial levels of 134Cs were observed from the soil cores. Similar features have been observed in previous surveys. In these cases the effects of source burial must be taken into account to avoid underestimation of activity levels by both ground-based and aerial gamma spectrometry. A separate set of detailed maps for the principal merse sites was therefore prepared using a calibration factor derived from the soil cores from this context. There are prospects for developing spectral analysis procedures to account for source depth in aerial surveys. Source burial on the merse also has implications for sampling techniques, and for dose rate measurement, which would merit further consideration. The radiometric maps show clearly the distributions of each individual nuclide and indicate the contribution which individual localised features make to the overall gamma ray dose rate. Naturally occurring nuclides reflect the underlying geological and geomorphological contexts of the landscape. The main granite intrusions, most notably at Cairnsmore of Fleet, the Loch Doon Granodiorite, Glencairn of Carsphairn, the Dalbeattie granite, and Criffel Pluton are readily visible in 40K, 214Bi and 208Tl maps, and control their local radiation environments. A number of areas of enhanced 214Bi, which may reflect radon potential, were noted. A transient radon associated 214Bi signal was observed on the west of the Wigtown peninsular during the survey. Examination of spectral data in the vicinity of Dundrennan has confirmed that there is no evidence of widespread terrestrial contamination arising from the use of depleted uranium projectiles on the range. The 137Cs map indicates the environmental distribution of this nuclide in considerable detail. Levels of 137Cs range from approximately 2 kBq m-2, a level consistent with global weapons’ testing fallout, from 2-40kBq m-2 on terrestrial sites affected by deposition from the Chernobyl accident, and from 40 kBq m-2 to over 200 kBq m-2 on tide washed pastures which have accumulated marine sediments from the Irish Sea. All three levels are represented within the survey zone, in a manner which is consistent with the findings of previous aerial surveys in adjacent areas, and with ground based studies. The main Chernobyl deposition in Dumfries and Galloway appears to have occurred between an area just east of the Nith, and Glenluce. The northern limit has not yet been defined, and there may be grounds for considering extension of the northern and particularly eastern limits of the inland survey zone. Within the survey zone the deposition pattern is complex, including both upland and lowland components. The plume trajectories for deposition inferred from these observations are oriented northwards rather than in the NW directions predicted by meteorological derived estimates. This may explain the contradiction between results from the Central Highlands and the estimated fallout patterns. The data presented here both add to previous knowledge, and serve as a baseline against which any future changes can be measured. The survey provides systematic coverage of the sedimentary and terrestrial coastal system for the first time, and has identified a number of merse sites which have accumulated radioactivity from past marine discharges from Sellafield, and which are not routinely monitored under existing Scottish Office arrangements. Some of these locations are extensive and fall within SSI’s; furthermore they are key sites for studying future deposition trends. It would seem prudent to review radiological assessments in the light of this work to ensure that the patterns of occupancy and sensitive ecologies of the merse are taken fully into account. The emergency response potential of aerial radiometrics has been clearly demonstrated in this project. It provides the only practical means of providing comprehensive environmental measurements of remote and upland landscapes on a short time scale, with an effective area sampling density some 106-107 times greater than soil sampling. Results are compatible with ground based approaches, and could focus ground based efforts effectively under emergency conditions. Modern approaches to data recording and analysis are able to produce maps during the survey period. National baseline mapping in Scotland, at 1 km resolution, would require less than 800 flying hours; 20 km line spacing would take roughly 40 hours of flight time. A long term programme of high resolution national baseline mapping, coupled to an emergency response standby arrangement, would provide an extremely cost effective way of preserving the capability developed since the Chernobyl accident, while producing high quality environmental data for research purpos

An Aerial Gamma Ray Survey of Torness Nuclear Power Station on 27-30 March 1994

<p>An aerial gamma-ray survey of the environment of Torness Nuclear Power Station was commissioned by Scottish Nuclear Limited, and conducted by the Scottish Universities Research and Reactor Centre. The area surveyed encloses a 31km square, with Torness Nuclear Power Station at the centre, flown with a line spacing of 500m. A secondary area, in closer proximity to the nuclear site, was flown with 250m spacing.</p> <p>Over 6000 gamma ray spectra were recorded with a high volume spectrometer operated from a helicopter over a three day period in March 1994. Spectral data were recorded together with satellite navigation (GPS) and radar altimetry data. The results provide a comprehensive record of the radiation environment around Torness and have been used to map the distribution of natural and man-made radionuclides, forming a baseline to enable future environmental changes may be assessed.</p> <p>The natural radionuclides 40K, 214Bi and 208Tl are highly correlated with each other and show a distribution which reflects both the underlying geological and geomorphological features of the area. The main structural boundaries of the Dunbar-Gifford and Lammermuir faults can be partly discerned in the maps, as can some igneous intrusions. Areas with peat or alluvium cover appear as negative features in the radiometric maps.</p> <p>Radiocaesium 137Cs levels range from below 4 kBq m-2 to over 20 kBq m-2. Upland areas near Coldingham Common, Black Castle Hill and Dunbar Common show the highest values, similar in deposition pattern and level to Chernobyl activity observed in the West of Scotland and elsewhere. Published national maps derived from meteorological and ground sampling data predicted much lower levels for these locations. However core samples taken after the survey have confirmed the presence of the activity, and the attribution to Chernobyl. This finding demonstrates both the effectiveness of the method for rapid location of radioactive deposition, and the need for baseline studies to determine present levels. Count rates from a spectral window corresponding to 60Co were also mapped. The results are close to detection limits and show a slight correlation with natural sources. Therefore they are more probably due to residuals remaining after separation of spectral interferences than to low level 60Co contamination.</p> <p>Gamma ray dose rates range from approximately 0.1 to 0.6 mGy a-1 with a mean value of 0.34 mGy a-1, and are derived mainly from natural sources. Ground level measurements were taken at nine district monitoring points within the area using a 3x3" NaI spectrometer and a survey meter (Series 6/80) used routinely by SNL. Both ground based data sets were in good agreement with each other and with the aerial survey after accounting for instrumental and cosmic ray background contributions.</p> <p>There is no evidence that Torness Power Station has affected the surrounding radiation environment, within the operational and sensitivity limits of the aerial survey.</p> <p>The longer term impact of the site can be assessed by future surveys. Moreover under emergency conditions it would be possible to utilise this method for rapid mapping of the area on a timescale which cannot be matched using alternative approaches. </p&gt

The Use of Aerial Radiometrics for Epidemiological Studies of Leukaemia: a Preliminary Investigation in SW England

The report presents the results and conclusions of a pilot study designed to evaluate the potential use of aerial gamma ray measurements in epidemiological investigations of leukaemia. The sources of natural radiation were reviewed and associations between U, Th and K and dose to the human population noted. The association between leukaemia and radiation exposure was also noted, in particular the clear evidence from high dose studies, the potential importance of radium and radon, and the difficulties of achieving statistical significance in case-control studies at environmental dose rates due to the need for large area surveys covering large populations. Aerial surveys were conducted in three disjoint grids selected by the Leukaemia Research Fund Clinical epidemiology unit at Leeds University. The areas covered some 2,500 km, and were surveyed in a 50 hour fieldwork period in September 1989. Over 4800 gamma spectra were recorded, representing between 200 and 400 times the number of measurements per unit area of the NRPB national maps, and an area sampling density some 106 times greater. The data were used to estimate specific activities of potassium, uranium and thorium. Environmental infinite matrix alpha and beta dose rates were calculated using equilibrium assumptions and gamma ray dose rates were estimated directly from the spectra. Mean values for gamma dose rates were compatible with NRPB estimates for the counties. The detailed gamma ray maps demonstrate that both radiation levels, and quality show local variations within each survey grid of a magnitude comparable with that observed in whole of the UK in national maps. Considerable caution is thus needed in using national data for epidemiological studies. Local variations, which can be clearly associated with underlying geological and geomorphological structures should be taken into account in such work. No significant enhancements were noted due to activities at the Devonport Dockyard, in keeping with published ground based monitoring. The main enhancement in the vicinity of Hinkley Point was due to the authorised discharge of 41Ar, which was clearly detected in the survey. Two methods for associating the radiometric results with epidemiological data were developed and applied. A case-control study was performed by matching case and control locations to individual spatially averaged radiometric results and comparing the associated radiation levels. The second method evaluated radiation stratified incidence rates by combining stratified case radiometric data with similar information estimated from a population density surface constructed for the grids. Weighted regression analysis was used to assess any associations. The results are in general limited by the low number of leukaemia cases within the study area, resulting in statistically weak or insignificant links. However positive associations between equivalent uranium and leukaemia, particularly in the grid including the rivers Tavy and Tamar, were observed in both case-control and incidence rate analyses. A negative association with equivalent Thorium observed in the incidence rate analysis was not reproduced in case-control comparisons. This approach could be extended to larger area studies to increase statistical power. In parallel investigations of the relationship between environmental and individual radiation exposure, and investigation of the potential association between radium, or radon and leukaemia following the trends observed here would be appropriate

Commercial Nucleic-Acid Amplification Tests for Diagnosis of Pulmonary Tuberculosis in Respiratory Specimens: Meta-Analysis and Meta-Regression

BACKGROUND: Hundreds of studies have evaluated the diagnostic accuracy of nucleic-acid amplification tests (NAATs) for tuberculosis (TB). Commercial tests have been shown to give more consistent results than in-house assays. Previous meta-analyses have found high specificity but low and highly variable estimates of sensitivity. However, reasons for variability in study results have not been adequately explored. We performed a meta-analysis on the accuracy of commercial NAATs to diagnose pulmonary TB and meta-regression to identify factors that are associated with higher accuracy. METHODOLOGY/PRINCIPAL FINDINGS: We identified 2948 citations from searching the literature. We found 402 articles that met our eligibility criteria. In the final analysis, 125 separate studies from 105 articles that reported NAAT results from respiratory specimens were included. The pooled sensitivity was 0.85 (range 0.36-1.00) and the pooled specificity was 0.97 (range 0.54-1.00). However, both measures were significantly heterogeneous (p<.001). We performed subgroup and meta-regression analyses to identify sources of heterogeneity. Even after stratifying by type of commercial test, we could not account for the variability. In the meta-regression, the threshold effect was significant (p = .01) and the use of other respiratory specimens besides sputum was associated with higher accuracy. CONCLUSIONS/SIGNIFICANCE: The sensitivity and specificity estimates for commercial NAATs in respiratory specimens were highly variable, with sensitivity lower and more inconsistent than specificity. Thus, summary measures of diagnostic accuracy are not clinically meaningful. The use of different cut-off values and the use of specimens other than sputum could explain some of the observed heterogeneity. Based on these observations, commercial NAATs alone cannot be recommended to replace conventional tests for diagnosing pulmonary TB. Improvements in diagnostic accuracy, particularly sensitivity, need to be made in order for this expensive technology to be worthwhile and beneficial in low-resource countries

The Use of Aerial Radiometrics for Epidemiological Studies of Leukaemia: a Preliminary Investigation in SW England

The report presents the results and conclusions of a pilot study designed to evaluate the potential use of aerial gamma ray measurements in epidemiological investigations of leukaemia. The sources of natural radiation were reviewed and associations between U, Th and K and dose to the human population noted. The association between leukaemia and radiation exposure was also noted, in particular the clear evidence from high dose studies, the potential importance of radium and radon, and the difficulties of achieving statistical significance in case-control studies at environmental dose rates due to the need for large area surveys covering large populations. Aerial surveys were conducted in three disjoint grids selected by the Leukaemia Research Fund Clinical epidemiology unit at Leeds University. The areas covered some 2,500 km, and were surveyed in a 50 hour fieldwork period in September 1989. Over 4800 gamma spectra were recorded, representing between 200 and 400 times the number of measurements per unit area of the NRPB national maps, and an area sampling density some 106 times greater. The data were used to estimate specific activities of potassium, uranium and thorium. Environmental infinite matrix alpha and beta dose rates were calculated using equilibrium assumptions and gamma ray dose rates were estimated directly from the spectra. Mean values for gamma dose rates were compatible with NRPB estimates for the counties. The detailed gamma ray maps demonstrate that both radiation levels, and quality show local variations within each survey grid of a magnitude comparable with that observed in whole of the UK in national maps. Considerable caution is thus needed in using national data for epidemiological studies. Local variations, which can be clearly associated with underlying geological and geomorphological structures should be taken into account in such work. No significant enhancements were noted due to activities at the Devonport Dockyard, in keeping with published ground based monitoring. The main enhancement in the vicinity of Hinkley Point was due to the authorised discharge of 41Ar, which was clearly detected in the survey. Two methods for associating the radiometric results with epidemiological data were developed and applied. A case-control study was performed by matching case and control locations to individual spatially averaged radiometric results and comparing the associated radiation levels. The second method evaluated radiation stratified incidence rates by combining stratified case radiometric data with similar information estimated from a population density surface constructed for the grids. Weighted regression analysis was used to assess any associations. The results are in general limited by the low number of leukaemia cases within the study area, resulting in statistically weak or insignificant links. However positive associations between equivalent uranium and leukaemia, particularly in the grid including the rivers Tavy and Tamar, were observed in both case-control and incidence rate analyses. A negative association with equivalent Thorium observed in the incidence rate analysis was not reproduced in case-control comparisons. This approach could be extended to larger area studies to increase statistical power. In parallel investigations of the relationship between environmental and individual radiation exposure, and investigation of the potential association between radium, or radon and leukaemia following the trends observed here would be appropriate