The radium legacy: Contaminated land and the committed effective dose from the ingestion of radium contaminated materials

Abstract

The manufacture and use of radium in the early to mid-20 th century within industrial, medicinal and recreational products has resulted in a large number of contaminated sites across a number of countries with notable examples in the USA and Europe. These sites, represent a significant number of unregulated sources of potential radiological exposure that have collectively and hitherto not been well characterised. In 2007, the Radioactive Contaminated Land (RCL) regulations came into force in the UK, providing the statutory guidance for regulators to classify and deal with RCL. Here we report on results derived from digestion experiments to estimate committed effective dose, a key aspect of the RCL regulations, from the ingestion of radium contaminated sources that can be found in the environment. This case study includes particles, clinker and artefacts that arise from past military activities on a site that was once an airfield at Dalgety Bay on the Firth of Forth, UK. Since 2011 the number of radium contaminated finds have increased by one order of magnitude on the foreshore areas of Dalgety Bay. The increase in finds may in large part be attributed to a change in monitoring practice. A sub sample of sixty sources were selected, on the basis of their activity and dimensions, and subjected to digestion in simulated stomach and lower intestine solutions. The study demonstrated that more radium-226 ( Pb varied from less than 1 % to up to 35 % ICRP 72 conversion factors were used to convert the activities measured in solution to committed effective dose. A little over 10 % of the sources tested dissolved sufficient radioactivity to result in 100 mSv committed effective dose to an infant. Using the solubility of 35 % as a worst case, minimum source activities necessary to deliver 100 mSv to the full age range of users of the foreshore were estimated. All the estimated activities have been detected and recovered through routine monitoring.

Characterising radium-226 particles from legacy contamination to support radiation dose assessments

“…Simulated gastrointestinal digestion was undertaken using sixty particles for calculating doses from inadvertent ingestion and found a wide range of gastrointestinal solubility (1 -35% of particle activity) but, due to the lack of particle characterisation data, the cause of such a wide range could not be investigated. The percentage solubilities reported are also subject to significant uncertainty due to the 25% uncertainty on the particle activity measurements (Tyler et al, 2013). A sample of nine particles was radiologically, physically and chemically characterised with the aim of investigating their origin, deposition and transport within the local environment at Dalgety Bay (Wilson et al, 2013).…”

“…The analyses reported a range of activities, sizes, shapes and chemical composition, and alluded to the presence of distinct sub-populations, but the limited sample size did not allow for statistically robust conclusions. Additionally, these particles were different to those used in the skin and ingestion dose studies (Charles, 2008;Charles and Gow, 2010;Tyler et al, 2013), therefore the influence of particle characteristics on skin and ingestion doses could not be investigated. An improved understanding of the hazard presented by the Ra-226 particles is not only important for the work ongoing at Dalgety Bay but also other sites potentially contaminated due to past practices using radium as well as existing exposure situations involving radioactive particles from other sources.…”

“…Due to the irregular geometries of the Ra-226 particles, efficiency calibrations associated with standard sample geometries, such as Marinelli beakers, are not appropriate. To minimise the impact of the irregular geometries, an efficiency calibration has been derived that is as independent from sample geometry as possible (Tyler et al, 2013). Using two gamma reference point sources, Ra-226 (100kBq, UR371, Eckert & Ziegler) and Pb-210 (231kBq, KU654, AEA Technology), a particle-specific efficiency calibration has been derived at distance from the detector (20cm), allowing the Ra-226 particles to behave as point sources, minimising the effect of sample geometry.…”

Characterising the morphological properties and surface composition of radium contaminated particles: a means of interpreting origin and deposition

“…The method for achieving this is presented in Tyler et al 20 and summarised here. An IAEA RGU (uranium reference material) sample was pelletized into a disk 48 mm in diameter and 11 mm in thickness and sealed within a petri dish of similar geometry allowed to equilibrate with the 95 daughters through 222Rn.…”

“…The activity order in the 150 particles is III > VI > II > VIII > V > IX > I > IV > VII (907 Bq). Particle III was imaged following simulated stomach digestion work 20 . Table 3 presents a summary of size and shape results.…”