Activity Median Aerodynamic Diameter Research Articles

Beryllium-7 aerosols in ambient air

The aerodynamic size distribution of 7Be in ambient aerosol particles was determined using l-ACFM cascade impactors. The activity distribution of 7Be measured by gamma spectrometry (Eγ = 477 keV) was largely associated with submicrometer aerosols in the accumulation mode (0.4 to 2.0 μm). The activity median aerodynamic diameter (AMAD) ranged from 0.76 to 1.18 μm (average 0.90 μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, σ g, ranged from 1.86 to 2.77 (average 2.24). In 65% of the cascade impactor measurements, the activity distributions of 7Be showed maxima in the 0.7 to 1.1 μm size range. Low AMADs as low as 0.62 to 0.74 μm of 7Be aerosols have been observed at locations characterized with relatively low pollution. Some dependency of AMADs on height has been also observed. In marine environments, the 7Be activity size distribution was dominant in the upper size range of aerosol particles.

Influence of Air Pollutants in the7Be Size Distribution of Atmospheric Aerosols

ABSTRACT The atmospheric behavior of 7Be aerosols was studied by using 1-ACFM cascade impactors. The activity distribution of Be measured by gamma spectrometry (E γ=477 keV), was largely associated with submicron aerosols in the accumulation mode (0.4–2.0 μm). The activity median aerodynamic diameter, AM AD ranged from 0.62 to 1.00 yam (average 0.80 μm). The geometric standard deviation, σg ranged from 1.87 to 2.50 (average 2.22). Low AMADs of 7Be aerosols have been observed at locations characterized with relatively low pollution. Some dependency of AMADs on height has been also observed. In near marine environment the 7Be activity size distribution was observed in higher size range of aerosol particles (AMAD 0.82 μm).

Long-term retention of inhaled fused aluminosilicate particles in the trachea and first bifurcation of the rat

Rats inhaled by nose-only exposure an aerosol of fused aluminosilicate particles, 3.95 μm activity median aerodynamic diameter, labelled with 57Co. The amount remaining on the airway surface at 7, 28 and 112 days after inhalation was determined at sacrifice by measuring the 57CO content in successive washes of trachea and of the region of the first bifurcation. Similar low levels were found in both cases. From 57Co excretion measurements, the rate at which particles were being cleared through the trachea was calculated, and hence the amount on the tracheal surface that was expected from rapid mucociliary clearance, T f. As expected, T f decreased markedly during the study period. However, at all times the amount of 57Co washed from the tracheal surface was greater than T f. The difference was a measure of the amount remaining on the surface long-term, T s. At 7 and 28 days after inhalation, T s was approx. 4 x 10 −4 of the thoracic content at 1 day, decreasing to 7 × 10 −5 after 112 days. The fraction sequestered in the tracheal wall, T w, remained approximately constant at around 1 × 10 −4 At 7 days, T s and T w were 1.81 and 0.45%, respectively, of the estimated amount deposited on the trachea. Much of the 57Co activity in the tracheal washes was associated with macrophages, the proportion increasing with time.

Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny 218Po and 214Pb, size distributions for both unattached 218Po and 214Pb, and attached 214Pb and 214Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached 218Po and 214Pb) are nearly similar. The diffusion equivalent diameters ( d f) of 218Po and 214Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations ( σ g) of 1.65 and 2.1, respectively. The latter distributions (attached 214Pb and 214Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of 214Pb and 214Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of 214Pb shows a broader activity distribution than 214Bi ( σ g = 2.2 for 214 Pb and σ g = 2.05 for 214 Bi ).

Particle Size Distributions of Radioactive Aerosols Measured in Workplaces

A survey of published values of Activity Median Aerodynamic Diameter (AMAD) measured in working environments was conducted to assist in the selection of a realistic default AMAD for occupational exposures. Results were compiled from 52 publications covering a wide variety of industries and workplaces. Reported values of AMAD from all studies ranged from 0.12 µm to 25 µm, and most were well fitted by a log-normal distribution with a median value of 4.4 µm. This supports the choice of a 5 µm default AMAD, as a realistic rounded value for occupational exposures, by the ICRP Task Group on Human Respiratory Tract Models for Radiological Protection and its acceptance by ICRP. Both the nuclear power and nuclear fuel handling industries gave median values of approximately 4 µm. Uranium mills gave a median value of 6.8 µm with AMADs frequently greater than 10 µm. High temperature and arc saw cutting operations generated submicron particles and occasionally, bimodal log-normal particle size distributions. It is concluded that in view of the wide range of AMADs found in the surveyed literature, greater emphasis should be placed on air sampling to characterise aerosol particle size distributions for individual work practices, especially as doses estimated with the new 5 µm default AMAD will not always be conservative.

Aerodynamic size association of 7Be in ambient aerosols

The aerodynamic size distribution of 7Be in ambient aerosol particles was determined by using 1-ACFM cascade impactors. The activity distribution of 7Be measured by γ-spectrometry ( E γ = 447 keV), was largely associated with submicron aerosols in the accumulation mode (0.4–2.0 μm). The activity median aerodynamic diameter, AM AD ranged from 0.76 to 1.18μm (average 0.90μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, gs g ranged from 1.86 to 2.77 (average 2.24). In 65% of the cascade impactor measurements the activity distributions of 7Be showed maxima in the 0.7 to 1.1 μm size range. In estimating lifetimes of 7Be aerosols in ambient air, a mean residence time of about 8 days averaged for tropospheric aerosols of 0.90 μm AM AD size.

Etude de l'exposition industrielle à des aérosols d'uranium dans le procédé d'enrichissement par laser. Méthodes et résultats

Comprehensive studies of the radiotoxicological risk at new uranium enrich­ ment processing facilities using laser isotopic separation, were particularly moti­ vated by the generation of a uranium oxide aerosol identified as UC>2+U metaj. Taking the new ICRP 66 recommendatio ns into account, the following study on this uranium oxide mixture, was aimed at determining the physico-chemical and biokinetic specific parameters required in order to calculate the effective dose. The activity median aerodynamic diameters (AMAD) ranged between 5.2 and 10 um with, in some cases, up to 20 % of submicron size particles, while concen­ tration values at the workplace ranged from 1.8 to 125 Bq m -3 and biological half-time calculations gave a 48 d period with in vitro dissolution test and a 77 d period with in vivo inhalation experiments. Transfer rates and dissolution rates obtained from both in vitro and in vivo experiments intend to emphasize a class W behaviour in term of ICRP 30 and M in term of ICRP 66.

Industrial Exposure to Uranium Aerosols at Laser Enrichment Processing Facilities

Comprehensive studies of the radiotoxicological risk at a new uranium enrichment processing facility using laser isotopic separation were motivated by the formation of industrial uranium oxide aerosols identified at UO2+Umetal and U3O8. Taking the new ICRP recommendations into account, this study was aimed at determining for each of those uranium oxides the physicochemical and biokinetics parameters which are required in order to calculate committed dose per unit of intake (DPUI). Activity median aerodynamic diameter was measured between 5.2 and 10 µm with the presence of fine particles under 1µm reaching, in some cases, up to 20%, concentration at the workstation varied from 1.8 to 125 Bq.m-3 and biological half-times were calculated from in vitro and in vivo experiments, leading to a main biological half-time of 77 days for UO2+Umetal particles and 187 days for U3O8 particles. DPUI values using these experimental results were assessed between 1.7x10-6 and 2.9 x 10-6 Sv.Bq-1 for UO2+Umetal and between 1.8x10-6 and 3.2x1-6 Sv.Bq-1 for U3O8.

Longer Lung Retention of PuO2 Particles Observed in Rats Measured Using Periodic In Vivo Counting

The object of this study is to establish a lung clearance curve for PuO 2 in rats, which provides basic information on lung dosimetry. Rats were exposed to polydisperse aerosols of PuO 2 having a size of 0.47 μm activity median aerodynamic diameter. The initial lung burden (ILB) was between 1990 Bq and 2960 Bq. In vivo counting of low energy L X rays with thin NaI(Tl) scintillation detectors was applied to follow the lung retention of Pu. Our results showed that 77% of PuO 2 deposited deep in the lung was cleared with a half-time of 53 days, whereas the residual 23% stayed there for a longer period (a half-time of 794 days)

Long-term Clearance of Accidentally Inhaled 60Co Aerosols in Humans

Long-term body retention was measured in six workers who accidentally inhaled 60Co aerosols during manipulation with a high-activity 60Co source. Improved whole body counting and calibration techniques provided good conditions to follow body clearance over 5 y. A two-detector profile scanning arrangement was used to measure the activity distribution in vivo over the lung region. The observed whole body retention followed a two-exponential time function between 10 and 1,850 d. Based on the profile measurements, the shorter exponent of 25-78 d was associated with activity leaving the pulmonary region while the long-term exponential should be interpreted as the clearance of the slowest component of the systemic burden with a biological half-time of 500-1,100 d. These observations classify the 60Co aerosols encountered in this incident as inhalation class W. The agreement of the measured retention pattern with the ICRP inhalation model was investigated assuming different aerosol size distributions characterized by an activity median aerodynamic diameter = 0.25 micron, 1 micron, and 4 microns. It was found that the ICRP model with an activity median aerodynamic diameter = 4 microns could describe the retention of our investigated cases reasonably well.

Fate of Inhaled Nickel Oxide and Nickel Subsulfide in F344/N Rats

AbstractThe fates of inhaled nickel oxide (NiO, green oxide calcined at 1200°C) and nickel subsulfide (Ni3S2), two occupationally relevant nickel compounds, have been studied in male F344/N rats. Groups of rats underwent pernasal exposure to 9.9 mg NiO/m3 or to 5.7 mg Ni3S2/m3 for 70 and 120 min, respectively. The activity median aerodynamic diameters (geometric standard deviation) of the NiO and Ni3S2 aerosols were 1.3 μm (2.0) and 1.3 μm (1.5), respectively. End points evaluated included total and regional respiratory tract deposition of the aerosols, lung clearance of deposited material, distribution of solubilized material to extrarespiratory tract tissue, and pathways of Ni excretion from the body. The fractions of the inhaled NiO and Ni3S2 aerosols that deposited in the respiratory tract were 0.11 and 0.13, respectively. The fractions of the inhaled aerosol that deposited in the lungs were 0.05 for both aerosols. Inhaled NiO cleared slowly from the lungs, with a half-life of approximately 120 days. ...

Lung retention of Pu following inhalation of PuO2 in rats measured using a whole body counter.

A lung retention function on the amount of PuO2 in rats was determined. Five rats were exposed to polydisperse aerosols of PuO2 having a size of 0.47 micron activity median aerodynamic diameter. The initial lung burden was between 1990 Bq and 2960 Bq. Instead of serial-sacrifice study, in vivo counting of low energy L X-rays with thin NaI(Tl) scintillation detectors was used to follow the lung retention of Pu at various intervals up to 468 days after inhalation. The calibration of this counting system was made by measuring lung activity of rats sacrificed for other experimental purposes. It was confirmed that the potential skin contamination and the Pu translocated to the other organs was not counted at the present counting geometry. Our results showed that 77% of PuO2 deposited deep in the lung was cleared with a half-time of 53 days, whereas the residual 23% stayed there for a longer period (a half-time of 795 days).

Difference in inhaled aerosol deposition patterns in the lungs due to three different sized aerosols.

Deposition patterns of inhaled aerosol in the lungs were studied in five normal subjects and 20 patients with lung disease by inhaling radioaerosols with three different particle size distributions. These aerosols were generated from BARC, UltraVent, and Mistogen-EN-142. Particle size distributions generated by these three nebulizers were 0.84, 1.04 and 1.93 microns in activity median aerodynamic diameter (AMAD) with its geometric standard deviation (sigma g) of 1.73, 1.71 and 1.52, respectively. Deposition patterns of inhaled aerosols were compared qualitatively and quantitatively by studying six different parameters: alveolar deposition ratio (ALDR), Xmax, Xmean, standard deviation (S.D.), skewness and kurtosis of the radioactive distribution in the lungs following inhalation. It has been found that aerosol deposition patterns varied with particle size. The unevenness of aerosol deposition, Xmax, Xmean and the number of 'hot spots' became more prominent with the increase in particle size, whereas values of ALDR and S.D. decreased as particle size increased. Knowing these deposition characteristics would facilitate a judicious application of aerosol inhalation to medical use.

ネブライザで発生させた酸化プルトニウムエアロゾルの粒子性状

Characteristics of plutonium oxide aerosols, 239PuO2, were investigated. Plutonium oxide aerosols were generated by nebulizing the Pu (OH)4 dispersed in HCl and passing the resultant droplets through a high temperature furnace to produce the PuO2. When a nebulizer solution containing plutonium of 3.21×105Bq/cm3 was used, aerosols with air concentration of 0.088Bq/cm3 were produced. Size distributions of these aerosols were determined with a cascade impactor to be 0.17μm AMAD (Activity Median Aerodynamic Diameter) and 2.1 geometric standard deviation. When a nebulizer solution with plutonium concentration of 3.95×106Bq/cm3 was used, 0.47μm AMAD was observed as expected roughly for the higher concentrated plutonium solutions. Observations of alpha trucks by autoradiograph and particle shape by scanning eletcron microscopy were also made for selected filter samples.

An Evaluation of Radiation and Dust Hazards at a Mineral Sand Processing Plant

This three-part article discusses the results of a 2-y study on radiation and dust hazards in a mineral sand processing plant involving: (1) evaluation of external gamma radiation levels and determination of isotopic composition of the different sand products; (2) evaluation of radiation carried in long-lived radioactive dust (LLRD) particles; (3) evaluation of Rn gas concentrations within the working environs of the plant. Gamma radiation levels had a mean value of approximately 40 nSv h-1, and monazite sand returned the highest activity concentrations of 0.16% and 3.4% for 238U and 232Th, respectively. Low volume gross respirable dust sampling revealed an average long-lived airborne alpha activity concentration of 0.07 +/- 0.02 Bq m-3 and an average dust mass concentration of 3.3 +/- 2 mg m-3. Gamma spectroscopy applied to high-volume air samples showed average airborne 232Th and 238U activities of 0.012 +/- 0.004 Bq m-3 and 0.005 +/- 0.002 Bq m-3, respectively, giving an airborne 232Th: 238U ratio of 2.4:1. Air sampling using a high volume, five-stage cascade impactor indicated an average activity median aerodynamic diameter (AMAD) of 3.2 microns with an associated average geometric standard deviation (GSD) of 2.8. Average radiation dose arising from the inhalation of LLRD was estimated to be 7 mSv per annum. CR-39 (polycarbonate plastic) nuclear track detectors indicated that Rn gas concentrations in the environs of the processing plant dry mill and main product warehouse ranged from 30 Bq m-3 to 220 Bq m-3, with an average value of 100 Bq m-3, which presents a possible inhaled dose from Rn daughters of 1.5 mSv y-1 (assuming an equilibrium ratio of 0.5).

Mean residence times of atmospheric aerosols in the boundary layer as determined from 210Bi/ 210Pb activity ratios

Concentrations of radioactive 210Pb and 210Bi were measured in surface air after chemical separation and radiochemical analysis in an annual cycle and were used to determine aerosol residence times in the lower atmosphere. It was concluded that residence times of 8 days would apply to aerosols of 0.3 μm activity median aerodynamic diameter (AMAD). Cascade impactor data are also presented in relating the residence times and the AMAD of atmospheric aerosols.

Particle-size distributions of atmospheric 129I and 127I aerosols

Atmospheric aerosols were collected with an Andersen sampler in the periods of November 1987–May 1988 and July 1988–June 1989 in order to determine the particle-size distributions of atmospheric 129I and 127I aerosols. Fine fractions (FF), defined as FF = (fine(<1 μm) mode) /(fine and coarse (>1 μm) modes), of 129I were 0.95 and 0.79, and those of 127I were 0.64 and 0.79, respectively. The particle-size distribution of 129I aerosols, which was rich in the fine-mode, was similar to that of 127I aerosols. Activity median aerodynamic diameters of 129I were 0.4 and <0.4 μm in each of the samples, and approximated to mass median aerodynamic diameters of 127I. The coarse-mode 129I and 127I were assumed to be the contribution of resuspension from the soil.

Long-term Clearance of Inhaled UO2 Particles from the Pulmonary Region of the Rat

This paper reports on an enriched uranium dioxide (UO2) mass clearance study undertaken with Fischer-344 rats. The UO2 had a uranium (U) isotopic composition of 0.79% 234U, 92.8% 235U, 0.34% 236U and 6.06% 238U, by mass, with an alpha-particle activity of 1.91 Bq micrograms-1. Forty-six rats were exposed to an enriched UO2 aerosol that had an activity median particle aerodynamic diameter ranging from 2.7 to 3.2 microns. The rats were killed from 1 to 720 d post-inhalation (PI). The mass of enriched UO2 present in the trachea, lung lobes, thoracic lymph nodes, kidneys, liver, spleen, gut, and the remainder of the carcass was assessed at death. At 720 d after exposure, 82% of the total body burden of enriched UO2 was in the lung, with a further 10% in the thoracic lymph nodes. This represented 17% and 2% of the original (5 d PI) lung burden. The mass clearance of enriched UO2 from the lung was fitted to a single exponential function, normalized to 100% at 5 d PI. The rate constant (k) was 2.8 X 10(-3) d-1, giving a clearance half-time of 247 d. Although statistical comparisons with the majority of published data were not possible, it appeared that both enriched UO2 and natural UO2 particles cleared at rates that were broadly similar, with a t1/2 in the rat lung of 150 to 300 d over the 5- to 720-d PI period. As a consequence of the 234U component in the inhaled UO2 particles, the rats killed at 720 d PI received a total mean accumulated alpha-particle dose averaged over the whole lung of 5.7 Gy. Histologic investigations of the rat lungs found that widespread lung disease was only observed in animals killed at 720 d PI.

Size distribution of airborne particulates in monazite dust

A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.

A biokinetic model of inhaled Cm compounds in dogs: application to human exposure data.

Curium isotopes are major by-products in irradiated nuclear reactor fuel and comprise a significant fraction of the alpha-emitting radionuclide inventory. Although little use is currently being made of purified Cm sources, such usage is possible if reprocessing of spent fuel becomes feasible. Because little information is available on the biokinetics and dosimetry of inhaled Cm compounds, a study was conducted in which adult beagle dogs received a single inhalation exposure to either a monodisperse aerosol of 244Cm2O3 (1.4 micron activity median aerodynamic diameter [AMAD]; sigma g = 1.16) or a polydisperse aerosol of 244Cm (NO3)3 (1.1 micron AMAD; sigma g = 1.74). At times ranging from 4 h to 2 y after exposure, animals were sacrificed and their tissues analyzed for Cm content. The data describing the uptake and retention of 244Cm in the different organs and tissues and the measured rates of excretion of these dogs formed the basis on which a biokinetic model of Cm metabolism was constructed. This Cm model was based on a previously published model of the biokinetics of 241Am that was shown to be applicable to data from human cases of inhalation exposure to 241Am aerosols. This Cm model was found to be adequate to describe the biological distribution of Cm in dogs and was also applied to the sparse data from humans. Reasonable agreement was found between the model predictions for lung retention of Cm and for urinary excretion patterns in humans.