title: Characterisation of airborne uranium and thorium contamination in northern England through measurement of U, Th and 235U/238U in tree bark.
abstract: Samples of tree bark were collected from four locations in Northern England (a typical rural site, a coal-fired power station, a uranium (isotopic) enrichment plant and a nuclear fuel fabrication facility), to assess the nature and extent of airborne uranium and thorium contamination. The U and Th concentrations of bark were determined by inductively coupled plasma mass spectrometry after conventional nebulisation of bark digests, whilst measurement of 235U/238U isotopic ratio utilised high efficiency nebulisation. Uranium concentrations varied between and within the sites (range, 0.01-12 micrograms g-1), with maximum values recorded within 1 km of the nuclear fuel fabrication plant (Springfields). In comparison, the concentration of Th in bark was low (mean, 0.018 microgram g-1) at all sites with the exception of the area affected by coal combustion (0.2-0.8 microgram g-1). The U/Th ratio varied from 0.5 to 3900 compared with the average crustal ratio of 0.3. Low values (< 2) were recorded at the 'coal' and 'rural' sites whilst Capenhurst and Springfields showed high values indicating the relative magnitude of uranium elevation. Significant enrichment of the natural 235U/238U ratio (0.00725) was observed near the nuclear installations, in particular, the enrichment plant (Capenhurst).
authors.affiliation: Centre for Analytical Sciences, Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield, UK S3 7HF.
authors.forename: D J
authors.initials: DJ
authors.lastname: Bellis
authors.forename: R
authors.initials: R
authors.lastname: Ma
authors.forename: C W
authors.initials: CW
authors.lastname: McLeod
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D003031:Coal; D004739:England; D004784:Environmental Monitoring / Q000379:methods; D017745:Incineration; D011210:Power Plants; D013910:Thorium / Q000032:analysis*; D014197:Trees / Q000737:chemistry*; D014501:Uranium / Q000032:analysis*
chemical_list: D000396:Air Pollutants, Radioactive; D003031:Coal; D014501:Uranium; D013910:Thorium