Aerosol release fraction by concrete scarifying operations and its implications on the dismantling of nuclear facilities.

The sanitation of concrete structures through dismantling of nuclear buildings is complicated by the radiological threat associated with the airborne release of fine dust. This is the reason why the aerosol release fraction (ARF) associated with mechanical removal of concrete structure containing radioactivity needs to be accurately evaluated to implement efficient radiological survey and containment techniques. We characterize experimentally the ARF resulting from milling operations on a standard non-radioactive concrete slab in a confined experimental chamber using an industrial scarifying machine. Our results reveal a significant production of fine aerosol particles with a mass median aerodynamic diameter close to 4 µm and which mineralogical composition is dominated by calcium and silica compounds. The ARF measured when a vacuum suction device is used to confine the dust production close to the source is on the order of 5 × 10-4; the maximum ARF estimated when no suction device is used is on the order of 0.5. As the study is focused on non-radioactive concrete, transposition of aerosol characteristics investigated in this study to assess radioactive airborne release is only relevant for in-depth neutron activation on elemental compounds of concrete.

Aerosolization of Mycotoxins after Growth of Toxinogenic Fungi on Wallpaper.

Many fungi can develop on building material in indoor environments if the moisture level is high enough. Among species that are frequently observed, some are known to be potent mycotoxin producers. This presence of toxinogenic fungi in indoor environments raises the question of the possible exposure of occupants to these toxic compounds by inhalation after aerosolization. This study investigated mycotoxin production by Penicillium brevicompactum, Aspergillus versicolor, and Stachybotrys chartarum during their growth on wallpaper and the possible subsequent aerosolization of produced mycotoxins from contaminated substrates. We demonstrated that mycophenolic acid, sterigmatocystin, and macrocyclic trichothecenes (sum of 4 major compounds) could be produced at levels of 1.8, 112.1, and 27.8 mg/m2, respectively, on wallpaper. Moreover, part of the produced toxins could be aerosolized from the substrate. The propensity for aerosolization differed according to the fungal species. Thus, particles were aerosolized from wallpaper contaminated with P. brevicompactum when an air velocity of just 0.3 m/s was applied, whereas S. chartarum required an air velocity of 5.9 m/s. A. versicolor was intermediate, since aerosolization occurred under an air velocity of 2 m/s. Quantification of the toxic content revealed that toxic load was mostly associated with particles of size ≥3 µm, which may correspond to spores. However, some macrocyclic trichothecenes (especially satratoxin H and verrucarin J) can also be found on smaller particles that can deeply penetrate the respiratory tract upon inhalation. These elements are important for risk assessment related to moldy environments.IMPORTANCE The possible colonization of building material by toxinogenic fungi in cases of moistening raises the question of the subsequent exposure of occupants to aerosolized mycotoxins. In this study, we demonstrated that three different toxinogenic species produce mycotoxins during their development on wallpaper. These toxins can subsequently be aerosolized, at least partly, from moldy material. This transfer to air requires air velocities that can be encountered under real-life conditions in buildings. Most of the aerosolized toxic load is found in particles whose size corresponds to spores or mycelium fragments. However, some toxins were also found on particles smaller than spores that are easily respirable and can deeply penetrate the human respiratory tract. All of these data are important for risk assessment related to fungal contamination of indoor environments.

Characterisation of exposure to airborne fungi: measurement of ergosterol.

In order to gain a clearer understanding of the level of fungal air contamination in indoor environments, we have adapted and tested a method to evaluate fungal biomass. Liquid phase chromatography (HPLC) of ergosterol, a component of the cell membrane of microscopic fungi, was employed. This method permits the detection and identification of ergosterol molecules at a concentration of 40 microg/ml (n=33, sigma=5). By combining this assay with a rotating cup collection apparatus, it was possible to measure fungal flora levels with a limit of quantification of 0.4 ng/m3 or a theoretical value of 150 spores per cubic meter (m3). Measurements of ergosterol levels performed on different sites showed that this method reflected the different situations of exposure of occupants to airborne fungal flora.