An environmental case-study of depleted uranium particulate contamination

A factory in Colonie (NY, USA) emitted c. 4.8 ± 1 tonnes of depleted uranium (DU) particulates into a suburban environment during 1958 – 1984. These particulates were initially dispersed by prevailing winds. Quadrupole inductively coupled plasma mass spectrometry (ICP-MS), laser ablation multicollector (LA-MC-) ICP-MS, scanning electron microscopy (SEM) and microfocus extended X-ray absorption fine structure (μEXAFS) spectroscopy have been used to characterise soils, dusts, vegetation, and individual particles. The concentration range of natural uranium in Colonie soils is 0.7 — 2.1 μg g-1; with total uranium up to 500 ± 40 μg g-1 in DU contaminated soils. Bioturbation can account for dispersal of contaminant from the soil surface. Primary morphologies are described for uraniferous particles from soils and dusts. Polycrystalline, often hollow microscopic uranium oxide spheres are similar to particles produced by DU munitions impacting armoured targets. These survive as UO2+x and U3O8, the least bioaccessible oxides of uranium. Fruit and wood samples were contaminated by DU, demonstrating limited bioavailability. Deviation of 235U/238U from the natural isotope ratio allows detection of DU in soils to at least 5.6 km from site. The average DU ‘end-member’ composition aggregated in soil samples comprises (2.05 ± 0.06) x10-3 235U/238U, (3.2 ± 0.1) x10-5 236U/238U, and (7.1 ± 0.3) x10-6 234U/238U. Individual uranium oxide grains were analysed by LA-MC-ICP-MS, all of which were from DU, with variable isotopic compositions (236U/238U, 235U/238U & 234U/238U). There is no evidence of enriched uranium in Colonie soils and dusts. The isotopic compositions of the Colonie particles can be explained by the inhomogeneous mixing of at least seven batches of tails from the Paducah gaseous diffusion plant, which are identified as the origins of the DU feedstocks used by National Lead Industries at Colonie. LA-MC-ICP-MS is recommended for nuclear forensic applications. This case-study is an attractive analogue for battlefield contamination.