RESUMEN
The manufacture and use of radium in the early to mid-20th century within industrial, medicinal and recreational products have 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 has 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 subsample of sixty sources was 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 ((226)Ra) and lead-210 ((210)Pb; driven by Polonium solubility) are dissolved from sources in artificial 'stomach' solutions compared with 'lower intestine' solutions. The combined 'gut' solubility for (226)Ra and apparent (210)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 100mSv committed effective dose to an infant. Using the solubility of 35% as a worst case, minimum source activities necessary to deliver 100mSv to the full age range of users of the foreshore were estimated. All the estimated activities have been detected and recovered through routine monitoring.
Asunto(s)
Relación Dosis-Respuesta en la Radiación , Exposición a Riesgos Ambientales/legislación & jurisprudencia , Radio (Elemento)/normas , Contaminantes Radiactivos del Suelo/normas , Ingestión de Alimentos , Humanos , Intestino Grueso , Radio (Elemento)/análisis , Contaminantes Radiactivos del Suelo/análisis , Estómago , Reino UnidoRESUMEN
The transport of ammonium and methylammonium was studied in a strain of Ochrobactrum anthropi, a microorganism isolated from garden soil and able to degrade methyleneureas which are used as slow-release nitrogen fertilizer. The activity of both transport systems was determined using [14C]methylammonium. Differences between the two transport systems were observed with regard to their pH- and temperature dependence as well as their kinetic parameters and regulation during growth with various nitrogen sources. Ammonium transport was subject to repression by ammonium and to derepression in its absence, while the methylammonium carrier was induced in the presence of methylamine. The ammonium but not the methylammonium transport system was severely inhibited by ammonium, and metabolic poisons inhibited both uptake systems. The analysis of intracellular metabolites using thin-layer chromatography and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry indicated that methylammonium was rapidly metabolized to N-methylglutamate via gamma-N-methylglutamine.