Deposition fraction

Respiratory Tract Clearance. This portion of the model identifies the principal clearance pathways within the respiratory tract. The model was developed to predict the retention of various radioactive materials. Figure 3-4 presents the compartmental model and is linked to the deposition model (see Figure 3-2) and to reference values presented in Table 3-5. This table provides clearance rates, expressed as a fraction per day and also as half-time (Part A), and deposition fractions (Part B) for each compartment for insoluble... 

The USTUR proposed modifications to the ICRP americium model, based on post-mortem americium measurements in human exposure cases (Kathren 1994). The major modifications are 1) the initial deposition fraction is assumed to be skeleton 45%, liver 25%, muscle 20%, other tissues 10% 2) the half-... 

Unidirectional, first-order transfer rates (day1) between compartments were developed for 6 age groups, and intermediate age-specific values are obtained by linear interpolation. The range of age-specific transfer rate values are given in Table 2-8. The total transfer rate from diffusible plasma to all destinations combined is assumed to be 2,000 day"1, based on isotope tracer studies in humans receiving lead via injection or inhalation. Values for transfer rates in various tissues and tissue compartments are based on measured deposition fractions, or instantaneous fractional outflows of lead between tissue compartments (Leggett 1993). 

The Leggett Model simulates the age-dependence of lead kinetics on such factors as bone turnover rates, partitioning between soft tissues and excreta, removal half-times in liver, kidneys, and red blood cells, and the deposition fraction in brain. The model structure represents a compromise between biological realism and practical considerations regarding the quantity and quality of information available to determine parameter values (Leggett 1993). 

The ratios of the experimental to the calculated values for deposition efficiency for each generation are shown for each of the experiments in Figures 2-4. The error bars represent the standard error derived from the mean measured deposition fraction for the generation. A coefficient of variation was calculated for the measured deposition in each generation which was used to obtain an estimate of the standard error of the ratio. It was assumed that no additional variability in the ratio was introduced by the calculated deposition fraction. The mean ratio for all six sets of cast measurements is shown in Figure 5. The error bars in Figure 5 represent the standard error of the mean of the six experiments. 

Figure 2. Ratio of measured to calculated deposition fraction 0.2 pm particles.

Radiocerium absorbed into the systemic circulation will be transported by blood proteins and be deposited predominantly in liver and bone. Deposition fractions will be about 0.45 for liver, 0.35 for bone, and 0.1 for other soft tissues with the remainder excreted in urine and feces. The retention times in liver and bone are long compared to the radioactive half-lives of the cerium isotopes. Therefore, their effective biological half-times in these organs will be approximately equal to their physical half-lives. Experimental data on internal organ distri-... 

Fractions of absorbed cerium depositing in gonads were calculated from data in Table 20 by taking average ratios of radioactivity in testes or ovaries to that in liver and skeleton and multiplying these by the above liver and skeletal deposition fraction. 

Keywords molybdenite, rhenium, granite, ore deposit, fractionation... 

An alternative method which could be used to establish the fraction of protein that actually reaches the alveoli is the so-called co-aerosohzation. If a protein is aerosolized from a solution that also contains another low molecular weight substance (deposition marker), it can be assumed that the fractions of protein and deposition marker reaching the alveoli will be the same. The deposition marker should be a substance with a known alveolar epithelial membrane passage (e.g. tobramycin or a decapeptide) which does not undergo absorption after oral administration. The fraction of the deposition marker that is deposited in the alveoli can be established from plasma (and urine) measurements of the deposition marker. The maximum fraction of protein that can pass the alveolar membrane whl then be known. The ratio between the deposited fraction and the fraction that has been absorbed into the systemic circulation (as can be estabhshed form plasma or urine analysis) will provide an estimation of the protein passage across the alveolar membrane. 

Figure 2.13 shows the deposition of particles in various regions of the respiratory tract as a function of particle diameter (Phalen, 1984 Phalen et al., 1991 Yeh et al., 1996). The deposition fraction of PM1() in the pulmonary and tracheobronchial regions can be quite large, so it is not surprising that health effects could be associated with these particles. Deposition in the upper portions of the respiratory system is dominated primarily by the large particles, which are readily taken out in the nose and upper airways. 

Fig. 5 Typical respiratory deposition doses in different European cities. Standard deviation values are derived used the average PNCs plotted in Fig. 3 and the standard deviation values of deposition fraction (i.e. 0.03)...

Eecent work by L. M. Dermis2 and his co-workers has shown that electrolysis may be of considerable value in effecting a complete or partial separation of the oxides of the rare earth metals. Prom a neutral solution of the nitrates of neodymium, praseodymium, lanthanum, and samarium, nearly all the lanthanum is deposited as hydroxide in the last fractions discharged on the cathode. The hydroxides are deposited fractionally in order of their basicity, and the deposition is not dependent upon the... 

Bennett, W. D. (1988), Human variation in spontaneous breathing deposition fraction A review, /. Aerosol Med., 1, 67-80. 

To obtain infrared spectra of the depositable fraction of the particles, the particles were deposited on the crystal of an internal reflectance attachment to an infrared spectrophotometer using MSI. The IR spectra were then taken with a Perkin-Elmer model 337 grating infrared spectrophotometer. 

The penetration of inhaled particles in human airways depends on their size. As defined by new standards (European EN 481 and International ISO 7708), the cut-off aerodynamic diameter of the total thoracic fraction is 10 pm it is related to the smallest particles penetrating beyond the larynx. Because these particles are strongly responsible for the inhalation risk, their on-line measurement must be representative. The variations in intensities of deposited fractions as a function of particle diameter is shown in Fig. 9.11. 

Physical and chemical properties of the ultrafine (< 100 nm) fraction of ambient PM give this fraction the highest potential for toxic effects. These particles readily reach the alveolar region, have a high deposited fraction, are present in high numbers with high... 

Porous microsphere technology is another area with considerable potential. Porous microspheres have a large physical diameter but, because they are not solid, have a relatively low aerodynamic diameter, which is the physical property that determines deposition fraction and site. They also have... 

This figure shows the mass deposition fraction plotted against the initial geometric particle size. Martonen et al (1985) argued that a critical particle size could be defined Dc. For hygroscopic particles initially smaller than this size, hygroscopic growth would be expected to reduce... 

A part of this lead is then taken up by the gastrointestinal tract. For particles inhaled via the mouth, and with a size of 0.05 pm and a respiratory rate of 15 breaths per min, about 40% of the inhaled lead is deposited in the airways (Chamberlain 1985). For smaller particles, the deposited fractions are lower. 

Deposit fraction wt % Various crudes API 34° Light crudes API >40... 

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