Tracing airborne micro-particles released by Al-industry using actinides

Laurent Pourcelot (1) , Olivier Masson (1) , Beatrice Boulet (2)

1 IRSN/PSE-ENV/SEREN/LEREN - Laboratoire d'étude et d'expertise sur la radioactivité de l'environnement
2 IRSN/PSE-ENV/SAME/LMRE - Laboratoire de métrologie de la radioactivité dans l'environnement

Industry remains an important source of environmental contamination by heavy metals and metalloids which may pose a serious threat to the ecosystems and the population. Especially the alumina production from bauxite ore gives rise to large amount of liquid and solid wastes since the production of 1 kg of alumina involves same weight of solid residue, the well-known red muds enriched in iron and heavy metals. Up to now, without any valorization of by-products, the red muds are stored in artificial ponds which are a potential source of pollutants for the surroundings due to the uplift of red dust under strong wind conditions. The study of plants allows filling the gap of knowledge concerning air quality over a wide potentially contaminated area. Thus, the current work aims to compare the activity concentration of natural radionuclides (238U, decay products and 232Th) in plants leaves (quercus robur and lettuces), in grains (wheat) and leaf vegetables with those of aerosols and the potential sources of atmospheric particles from soils and above all the red dust emitted from the dried ponds and from the piles of bauxite. The activity concentration of natural radionuclides such as 238U, some decay products and 232Th was determined in plants samples taken according to the two dominant wind directions, at plots located 100 to 1,500 m from the basins. Furthermore, the atmospheric particles were taken in the same areas, using a high-volume aerosol sampler. The increase of 232Th and 238U activity concentration in a few trees leaves (a factor 9 and 4, respectively) and in some aerosols samples is accompanied by a decrease of 238U/232Th activity ratio of these matrices. Such low ratio suggests that the airborne particles emitted by bauxite piles and red mud basins - those latter’s are also characterized by low 238U/232Th - first contaminate the atmosphere and then the leaves surface, after deposition. Available at distance greater than 1,000 m from the ponds, locally produced foodstuffs do not show any excess of radionuclides, suggesting low influence of airborne micro particles from the alumina production. Thus, the actinides measured in leaf vegetables rather derived from the soil micro-particles deposited onto leaves than from an anthropogenic source.

Mots clés: actinides; aerosols; tree leaves; red muds

Domaines: Sciences de l'environnement

Laurent Pourcelot, Olivier Masson, Beatrice Boulet. Tracing airborne micro-particles released by Al-industry using actinides. 3rd International Conference on Radioanalytical and Nuclear Chemistry (RANC-3), American Nuclear Society, May 2023, Budapest, Hungary. ⟨irsn-04113866⟩