Pulmonary Retention Research Articles

A prototype passive samples for trace metals in submicron particles

A passive sampler, designed to simulate pulmonary retention of submicron particles is described. The device can accumulate lead from ambient air over a period of four weeks with a precision of 15%.

Pulmonary retention of inhaled diesel particles after prolonged exposures to diesel exhaust

The effect of continuous exposure to diluted diesel exhaust on the pulmonary retention of inhaled diesel particles was studied in male Fischer 344 rats. Test animals were first exposed to clean air or diluted diesel exhaust in exposure chambers at nominal particulate concentrations of 250 μg/m 3 or 6 mg/m 3 for 20 hr/day, 7 days/week, for periods lasting from 7 to 112 days, followed by a nose-only exposure to 14C-tagged diesel particles for 45 min. At preselected time intervals after the radioactive exposure, the 14C-activities in the lungs of groups of four animals were measured to determine the clearance of the 14C-diesel particles up to 1 year. The pulmonary retention of the radioactive diesel particles was greater in animals which had been preexposed to diesel exhaust. The slower alveolar clearance of particle-laden macrophages and leukocytes can be described by a normal biphasic clearance model. Since some of the macrophages were found sequestered as aggregates in the pulmonary region, a slow-clearing residual component was included in a modified lung retention model. When these residual fractions were determined and excluded from the active particulate transport within the lungs, normal alveolar clearance rates were calculated for the animals with a preexposure diesel particulate dose less than 0.8 mg. Slower clearance was observed at a dose of 6.5 mg and no clearance was evident at a dose of 11.8 mg in their lungs. In effect, the greater retention of inhaled particles can be interpreted as a sign of impaired lung clearance attributable to the prolonged exposures to high concentrations of diesel exhaust gases and/or the presence of accumulated carbonaceous particles residing in sequestered macrophage aggregates in the lungs.

Toxicological data on NOx: an overview.

This overview is based on experimental and epidemiological studies of NOx toxicity during the past decade. Approximately 130 published studies are cited and about one-fourth of these are discussed briefly under one of the following headings: acute and subacute studies, chronic low-level studies, human studies, and special studies. The latter section examines a selection of comparatively unique investigations, including several devoted to the pulmonary uptake and retention of NO2, and several examining the potential tumorigenicity of NO2. For each major section of the overview, a critical evaluation is attempted in terms of the impact of the appropriate studies on the extant NOx toxicological data base and on the current and planned air quality standards for NOx.

Bioavailability in rabbits of formaldehyde from durable-press textiles.

Carbon-14-labeled formaldehyde was used per se, or was used in the synthesis of dimethyloldihydroxyethyleneurea (DMDHEU), which was incorporated into cotton or cotton/polyester blend fabric. Patches of the fabric containing known quantities of radioactive DMDHEU were applied to the backs of New Zealand White rabbits for periods up to 48 h. The rabbits were placed in specially constructed metabolism chambers designed to prevent either inhalation of volatile material emanating from the fabric or interference of any volatile material from the fabric with trapping of expired carbon dioxide. The results of the studies indicate that aqueous formaldehyde covered with a latex barrier is absorbed and retained in the layers of skin in direct contact with the formaldehyde. Approximately 65% of a dose of [14C] formaldehyde was recovered in skin 4 h after application. Skin samples from the backs of rabbits to which durable-press fabric prepared from radiolabeled DMDHEU had been applied were found to have 0.09-2.61% of the total 14C contained in the cloth patches. The levels of radioactivity recovered from the skin varied with degree of occlusion of the cloth, presence or absence of perspiration, type of synthesis used for the preparation of DMDHEU, and whether cotton or cotton/polyester blend fabric was used. Other tissues and organs had only low levels of radioactivity. Injected [14C] formaldehyde was rapidly expired as 14CO2 (28.6% of the dose within 4 h; 37.0% within 48 h). Metabolism and distribution of formaldehyde was found to be dependent on route of administration: i.e., topical application resulted in high skin levels, whereas intravenous injection led to rapid pulmonary and renal excretion and retention of radioactivity in liver, kidney, and blood.

Pulmonary Retention of Inhaled Diesel Particles after Prolonged Exposures to Diesel Exhaust

Pulmonary Retention of Inhaled Diesel Particles after Prolonged Exposures to Diesel Exhaust CHAN, T. L., LEE, P. S., AND HERING, W. E. (1984). Fundam. Appl. Toxicol. 4, 624–631. The effect of continuous exposure to diluted diesel exhaust on the pulmonary retention of inhaled diesel particles was studied in male Fischer 344 rats. Test animals were first exposed to clean air or diluted diesel exhaust in exposure chambers at nominal particulate concentrations of 250 μg/m3 or 6 mg/m3 for 20 hr/day, 7 days/week, for periods lasting from 7 to 112 days, followed by a nose-only exposure to l4C-tagged diesel particles for 45 min. At preselected time intervals after the radioactive exposure, the 14C-activities in the lungs of groups of four animals were measured to determine the clearance of the l4C-diesel particles up to 1 year. The pulmonary retention of the radioactive diesel particles was greater in animals which had been preexposed to diesel exhaust The slower alveolar clearance of particle-laden macrophages and leukocytes can be described by a normal Diphasic clearance model. Since some of the macrophages were found sequestered as aggregates in the pulmonary region, a slow-clearing residual component was included in a modified lung retention model. When these residual fractions were determined and excluded from the active particulate transport within the lungs, normal alveolar clearance rates were calculated for the animals with a preexposure diesel particulate dose less than 0.8 mg. Slower clearance was observed at a dose of 6.5 mg and no clearance was evident at a dose of 11.8 mg in their lungs. In effect, the greater retention of inhaled particles can be interpreted as-a sign of impaired lung clearance attributable to the prolonged exposures to high concentrations of diesel exhaust gases and/or the presence of accumulated carbonaceous particles residing in sequestered macrophage aggregates in the lungs.

Beneficial effects of implanted muscle tissue on pulmonary particulate retention and survival following splenectomy.

Following splenectomy (SPLY) there is increased retention in the lung of injected particulate matter and an increased mortality from sepsis in experimental animals. Since it has been shown that autotransplanted splenic tissue (AST) decreased elevated pulmonary particulate retention after SPLY and improved the survival of animals following SPLY and sepsis, we attempted to determine whether the protective effect offered by AST was specific to the spleen. To determine this, four groups of rats were studied: Group I--sham; Group II--SPLY; Group III--received 100 mg of heterotopic AST in an omental pocket after SPLY; and Group IV--received 100 mg of heterotopic muscle tissue from the abdominal wall (AMT) in an omental pocket after SPLY. Six days after the above procedure, reticuloendothelial (RES) function was evaluated. The results indicate that both AST and AMT significantly decrease the abnormal pulmonary retention of particulate matter following SPLY. However, hepatic lipid retention was greater in the AMT than the AST group. Survival following sepsis was studied in other animals from Group I, II, III, and IV. At 7 days after the original operation, the cecum was ligated and punctured (CLP) and then removed 16 hours later. The splenic-as well as muscle-implanted animals showed significantly higher survival rates than the splenectomized animals. We therefore conclude that survival after SPLY can be improved by implanting either a fragment of the spleen or the muscle in the omental pocket. Since both tissues appeared necrotic at 7 days following implantation, the decreased pulmonary particulate retention and improved survival following SPLY and sepsis appear to be due to the presence of a necrotic tissue irrespective of its origin. These results suggest that the early effect of an implanted tissue is a nonspecific stimulation of phagocytosis.

Influence of elastase-induced emphysema and the inhalation of an irritant aerosol on deposition and retention of an inhaled insoluble aerosol in Fischer-344 rats

The purpose of this study was to assess the effects of elastase-induced pulmonary emphysema and the inhalation of an irritant aerosol (Triton X-100, a nonionic surfactant similar to those used in a number of pressurized consumer products) on pulmonary deposition and retention of an insoluble test aerosol, 59Fe-labeled Fe 2O 3. Untreated rats or rats pretreated by intratracheal instillation with elastase were exposed to an aerosol of 59Fe-labeled Fe 2O 3 either 18 hr or 7 days after exposure to aerosolized Triton X-100 which was administered in doses of 20, 100, or 200 μg/g of lung. Rats pretreated with elastase had significantly lower pulmonary deposition of 59Fe than the untreated controls ( p < 0.005). Pulmonary deposition of Fe 2O 3 was unaffected by pretreatment with Triton X-100. Elastase treatment alone had no effect on retention of Fe 2O 3. Triton X-100 administered 18 hr prior to exposure of rats to Fe 2O 3 aerosol resulted in dose-related increases in whole-body retention of 59Fe. When rats were exposed to Triton X-100 7 days before exposure to Fe 2O 3, increased retention of 59Fe was noted only in those treated at the highest Triton X-100 dose level (200 μg/g).

Cadmium concentrations in tobacco and tobacco smoke

The amount of cadmium in tobacco depends on the variety and origin of the plant as well as on the analytical method used to determine cadmium. In the literature, cadmium concentrations in tobacco of between 0.5 and 5 ppm are reported. Modern German cigarette tobacco contains about 0.5–1.5 μg cadmium/cigarette. Of importance for the smoker is the amount of the metal in the mainstream smoke. The cadmium level in the mainstream smoke of modern cigarettes is reduced by means of filters and other construction features. The average Cd value of German filter cigarettes is less than 0.1 μg/cigarette in mainstream smoke. An average daily intake of about 1 μg cadmium by smoking 20 cigarettes can be calculated on the basis of an experimentally proved pulmonary retention rate of 50%. Pulmonary resorption rates relevant to uptake rates of cadmium by smoking are discussed. It can be assumed that cadmium uptake by smoking modern cigarettes has been reduced because of modifications in tobacco processing and cigarette construction in the last few decades.

Right ventricular performance during increased afterload impaired by hypercapnic acidosis in conscious dogs.

Since heart failure may occur in the setting of lung dysfunction and CO2 retention with only modest increases in cardiac work load, we questioned whether myocardial function is impaired by hypercapnic acidosis. To determine the influence of hypercapnic acidosis on right ventricular function, we measured the effects of acute (2 hours) and chronic (2 weeks) hypercapnic acidosis on right ventricular performance during normal and increased right ventricular afterload in five conscious dogs. Systemic hemodynamic and right ventricular functions were unaltered during normal right ventricular afterload by acute hypercapnic acidosis (PaCO2 = 49 +/- 3 mm Hg, pH = 7.27 +/- 0.003). As right ventricular afterload was increased by progressive balloon occlusion of the right ventricular outflow tract during acute hypercapnic acidosis, the rise (slope) in right ventricular end-diastolic pressure was increased 4-fold (P less than 0.01) over that observed in normocapnic control. Maximum isovolumic right ventricular dP/dt rose (P less than 0.05) comparably with increasing right ventricular afterload during normocapnic control and acute hypercapnic acidosis. Chronic hypercapnic acidosis (PaCO2 = 55 +/- 2 mm Hg, pH = 7.28 +/- 0.01) resulted in systemic vasodilation and increased (P less than 0.05) heart rate and cardiac output during normal right ventricular afterload. As right ventricular afterload was increased during chronic hypercapnic acidosis, the rate of rise in right ventricular end-diastolic pressure was 2-fold (P less than 0.01) above normocapnic control but maximum isovolumic right ventricular dP/dt was unchanged in contrast to normocapnic control and acute hypercapnic acidosis. Moreover, cardiac output fell and stroke work was unchanged with increasing afterload during chronic hypercapnic acidosis. beta-Adrenergic blockade resulted in an increased (P less than 0.01) rate of rise in right ventricular end-diastolic pressure with afterload during normocapnic control and chronic hypercapnic acidosis. We conclude that hypercapnic acidosis results in diminished right ventricular performance during increased right ventricular afterload, evidenced by accentuated rise in right ventricular end-diastolic pressure, and may contribute to the congestive heart failure and edema observed in patients with pulmonary hypertension and CO2 retention.

Long-term pulmonary retention of inhaled particles in man

Long-term pulmonary retention of inhaled particles in man

The disposition of coal dusts in the lungs and tracheobronchial lymph nodes of dogs

The pulmonary disposition, histopathology and lymphatic uptake of anthracite (Tamaqua) and bituminous (Lower Kittaning) cost dusts were measured as part of a pulmonary retention study which revealed a mean half-time of 1.92 years in dogs (Morrow et al. 1981). After brief (1–2.5 hr) exposures to either natural or neutron-activated coals having an average airborne mass concentration of ∼90 mg m −3 and a 1.8 μm mass median aerodynamic diameter (og 2.5), dogs (n=12) were serially sacrificed up to 52 weeks after exposure. Coal dusts were found only in the lungs and pulmonary lymph nodes. The coals were considered indistinguishable as to their pulmonary clearance and disposition and lymphatic uptake. All coals in the lung were associated mainly with the peribronchiolar and perivascular lymphatics or connective tissue spaces, and some were found in alveolar macrophages. The lymphatic uptake of coal dusts followed the powder function 0.55 t 0.513 where t is in weeks and uptake is expressed as percent of the initial alveolar burden. In terms of pulmonary dust clearance, only 4 percent of the initial alveolar burden appeared to have been translocated to the tracheobronchial lymph nodes in the first 50 weeks, but this constituted ∼14 percent of the total alveolar clearance. Histopathologically, one distinction was found: animals exposed to the highest level of neutron-activated anthracite showed patchy hyaline thickening of some small blood vessels and alveolar septa. The response was low grade, probably exposure-related, but otherwise unremarkable.

Deposition, retention, and biological fate of inhaled benzo( a)pyrene adsorbed onto ultrafine particles and as a pure aerosol

The effect of ultrafine, airborne, carrier particles on the deposition, retention, and biological fate of inhaled polycyclic aromatic hydrocarbons (PAHs) was studied. Using a radiolabeled model PAH, [ 3H]benzo( a)pyrene ([ 3H]BaP), Fischer-344 rats were exposed by nose-only inhalation (30 min) to this compound, as a coating (15% by mass) on insoluble 67Ga 2O 3 particles or as a pure aerosol. These aerosols were produced by vapor condensation methods in a dynamic aerosol generation system. The concentrations of [ 3H]BaP in the coated and homogeneous aerosols were 0.6 and 1.0 μg/liter of air, respectively, while the mass median diameter of both these aerosols was approximately 0.1 μm. Pulmonary retention of 3H radioactivity was longer in animals exposed to the [ 3H]BaP coated on the 67Ga 2O 3 particles. The time required to clear 90% of the initial lung burden of 67Ga 2O 3-associated 3H radioactivity detected 30 min postexposure was approximately 1 day as compared to 4 hr for animals exposed to the pure [ 3H]BaP aerosol. Tracheal clearance of 90% of the 67Ga 2O 3-associated 3H radioactivity (as a fraction of the amount detected 30 min postexposure) required 1 day, while only 1.5 hr were required to clear the same percentage of 3H radioactivity from the tracheas of rats exposed to the pure [ 3H]BaP aerosol. The rates of clearance of this 3H material to other tissues suggested that a substantial amount of the [ 3H]BaP coated on 67Ga 2O 3 was cleared from lungs by mucociliary clearance and subsequent ingestion, whereas the majority of the pure [ 3H]BaP aerosol was cleared by direct absorption into blood. In both cases, the ultimate fate of the majority of the [ 3H]BaP and its metabolites was excretion in feces. However, clearance of the 67Ga 2O 3-associated [ 3H]BaP by ingestion may have been the cause for the higher levels and longer retention times of 3H radioactivity in stomach, liver, and kidneys when compared to the levels found in these same tissues from animals exposed to the pure [ 3H]BaP aerosol. Thus, particle association of BaP not only increased the respiratory tract retention of this PAH, but also increased the dose of this compound and its metabolites to stomach, liver, and kidneys.

Renal and cardiovascular responses to acute hypercapnic acidosis in conscious dogs: role of renin--angiotensin.

Patients with pulmonary dysfunction and CO2 retention have renal hemodynamic abnormalities accompanied by increased plasma renin activity. To determine if hypercapnia impairs renal function, particularly through the renin-angiotensin system, the effects of acute hypercapnic acidosis (HC), using 8.5% CO2, were measured in five unanesthetized dogs during (a) the intact state; (b) renin-angiotensin antagonism using either 1-sarcosine, 8-glycine angiotensin II ( [Sar1, Gly8] AII) or SQ 14,225; and (c) exogenous angiotensin II infusion. As partial arterial carbon dioxide pressure (PaCO2) increased (p less than 0.05) from control (C) of 35 +/- 1 (SEM) to 48 +/- 1 mm Hg during HC, arterial pH fell (p less than 0.05) from 7.36 +/- 0.01 to 7.24 +/- 0.005. Renal function was uncompromised with HC, and glomerular filtration rate (GFR) and urinary sodium excretion increased (p less than 0.05) despite a fourfold rise in plasma renin activity from C of 0.6 +/- 0.3 to 2.2 +/- 0.8 ng AI ml-1 h-1 during HC. Administration of [Sar1, Gly8] AII during HC did not consistently alter systemic or renal hemodynamic responses, and effects of SQ 14,225 during HC were also observed during normocapnia. Although systemic vascular responses to exogenous AII infusion were similar, the renal vasoconstrictor response was antagonized during HC with unchanged GFR and renal blood flow. These findings indicate that despite activation of the renin-angiotensin system, acute hypercapnic acidosis is unassociated with impairment of renal function in unanesthetized dogs. This may be related to diminished renal vascular AII responsiveness during hypercapnia.

PULMONARY RETENTION OF COAL DUSTS &lt;xref ref-type="fn" rid="fn1"&gt;&lt;sup&gt;*&lt;/sup&gt;&lt;/xref&gt;

The principal objectives of this study were: to determine, quantitatively, coal dust retention times in the dog lung; to test the appropriateness of a pulmonary retention model which incorporates first order rate coefficients obtained from in vitro and in vivo experiments on neutron-activated coal; to acquire a temporal description of the pulmonary disposition of the retained coal dust, and to compare the behavior of two different Pennsylvania coals in the foregoing regards. The principal findings include: retention half-times for both coals of approximately 2 years following single, hour-long exposures; a vivid association of the retained coal dust with the pulmonic lymphatics; and a general validation of the retention model.

MAGNETOPNEUMOGRAPHY AS A TOOL FOR THE STUDY OF DUST RETENTION IN THE LUNGS

Magnetopneumography is a sensitive non-invasive technique for measuring the concentration and distribution of the magnetizable ferrimagnetic fraction of occupationally acquired lung dust. It was used to measure pulmonary retention of ferrimagnetic dust in several different occupational groups. Data from a study of deep bituminous miners indicated ferrimagnetic dust accumulation in 17 of 71 miners at a level greater than 22 of 23 control subjects. Magnetopneumographic measurement of 26 steel arc welders revealed marked pulmonary retention of welding fume in all workers at concentrations far above that seen in 26 control subjects (p < 0.001). Ferrimagnetic dust content in welders correlated with years of welding and radiographic abnormality (p < 0.01), but not with smoking history. Accumulation of ferrimagnetic dust above normal was also noted in seven machinists (p<0.01), but was not found in a group of 16 insulators with remote exposure to asbestos. All subjects with elevated levels of ferrimagnetic dust manifested a pattern of hilar concentration. Magnetic mapping of freeze-dried autopsied lungs from nine coal miners and four non-miners confirmed the pattern of lymphatic accumulation of ferrimagnetic dust. The capabilities and uses of magnetopneumography will be discussed.

The Disposition of Coal Dusts in the Lungs and Tracheobronchial Lymph Nodes of Dogs

The Disposition of Coal Dusts in the Lungs and Tracheobronchial Lymph Nodes of Dogs. Morrow, P.E. and Yuile, C.L. (1982). Fundam. Appl. Toxicol. 2:300–305. The pulmonary disposition, histopathology and lymphatic uptake of anthracite (Tamaqua) and bituminous (Lower Kittaning) coal dusts were measured as part of a pulmonary retention study which revealed a mean half-time of 1.92 years in dogs (Morrow et al. 1981). After brief (1-2.5 hr) exposures to either natural or neutron-activated coals having an average airborne mass concentration of ˜90 mg m−3 and a 1.8 μm mass median aerodynamic diameter (σg 2.5), dogs (n=12) were serially sacrificed up to 52 weeks after exposure. Coal dusts were found only in the lungs and pulmonary lymph nodes. The coals were considered indistinguishable as to their pulmonary clearance and disposition and lymphatic uptake. All coals in the lung were associated mainly with the peribronchiolar and perivascular lymphatics or connective tissue spaces, and some were found in alveolar macrophages. The lymphatic uptake of coal dusts followed the powder function 0.55 t0.613 where t is in weeks and uptake is expressed as percent of the initial alveolar burden. In terms of pulmonary dust clearance, only 4 percent of the initial alveolar burden appeared to have been translocated to the tracheobronchial lymph nodes in the first 50 weeks, but this constituted ˜14 percent of the total alveolar clearance. Histopathologically, one distinction was found: animals exposed to the highest level of neutron-activated anthracite showed patchy hyaline thickening of some small blood vessels and alveolar septa. The response was low grade, probably exposure-related, but otherwise unremarkable.

Effects of drugs on mucociliary transport in the trachea and bronchial airways.

Pharmacologically active agents may change transport rates regionally within the airways of the lung, as well as affect the overall magnitude of the clearance of inhaled deposited radioaerosols. To investigate these possibilities the response of ethanol on pulmonary retention was determined and the responses of both the trachea and bronchial airways were measured after either oral administration of metaproterenol or inhalation of sulfuric acid mist. In the healthy nonchallenged lung, the velocity of mucociliary transport in the trachea was related to the percentage of activity cleared from the lung in two hours. Indices representing different portions of the pulmonary retention curve were also correlated. Changes in this interdependence of mucociliary transport within airways were produced by all agents. Metaproterenol increased tracheal mucus velocity but not lung clearance. Alcohol changed pulmonary retention in both magnitude and direction depending on the individual, resulting in an increase in variability of pulmonary mucociliary clearance between persons. Thus, to evaluate the effects of drugs or pollutants on the lower respiratory tract, measurements of mucociliary transport should be made in both the trachea and the bronchial airways.

Bacteremia

Pulmonary effects, lung clearance, and tissue retention of blood-borne Pseudomonas aeruginosa were compared in dogs (n = 5) and pigs (n = 5) during continuous 6-hour intravenous infusion of 1.2(10(9)) bacteria/min/20 kg. Control pigs received an equal volume of sterile saline. In contrast to controls, experimental pigs developed pulmonary artery (PA) hypertension (mean, 30 +/- SE 3; baseline, 17 mm Hg) and pulmonary failure manifested by hypoxemia (mean PaO2, 49 +/- 4; baseline, 78 +/- 2 mm Hg; p less than 0.001), increased intrapulmonary shunting (40 to 50%), noncardiogenic pulmonary edema, and congestive atelectasis, a pattern of pulmonary failure very similar to sepsis-induced ARDS in humans. In dogs, PA pressures wee unchanged from baseline, no edema was detected, and comparable hyperventilation was associated with an increase in PaO2 from 77 +/- 4 (baseline) to 87 +/- 2 mm Hg (p less than 0.001). Tissue retention of viable blood-borne organisms in pigs was greatest in the lungs. In dogs, lung retention was minimal and greatest tissue retention occurred in the liver and spleen. We conclude that both lung clearance of blood-borne organisms and bacteremia-induced pulmonary failure are quite host dependent.

Effect of splenectomy on reticuloendothelial function and survival following sepsis.

It is well known that splenectomy causes immunologic impairment and increases susceptibility to infection; however, the time course of reticuloendothelial depression and of alterations in hepatic and pulmonary retention of injected lipid emulsion following splenectomy is not known. To determine this, rats were splenectomized and reticuloendothelial function evaluated at various intervals following splenectomy by measuring the intravascular clearance of 131I-triolein gelatinized lipid emulsion. The intravascular clearance (T/2) and lung uptake of the lipid emulsion increased and hepatic uptake of emulsion decreased 4 to 8 hours following splenectomy. One day followng splenectomy, although the T/2 appeared normal, the lung uptake was 1,123% higher and hepatic uptake was still 33% lower than control. The T/2 and hepatic retention returned to normal 2 days following splenectomy; however, the lung retention was higher than controls even 10 days following splenectomy. In another set of experiments, splenectomy was performed following which sepsis in rats was produced by cecal ligation and puncture. Ten hours following cecal ligation and puncture, the gangrenous cecum was removed and survival was measured over 5 days. The mortality rate in these animals was 57% (12/21) compared to 0% (0/8) in nonsplenectomized cecal ligated and punctured animals. These results suggest that splenectomy may not only have deleterious effects in terms of the host defense system, but may also cause prolonged pulmonary changes.

Pulmonary retention of lead: An experimental study in man

This human investigation of lead absorption from the lungs utilized two forms of lead, lead chloride and lead hydroxide; the former was used in picogram amounts and the latter at microgram levels. These two species of lead were selected in an attempt to simulate the range of physicochemical properties found in atmospheric lead (urban air). Aerosols labeled with lead-203 were made of comparable aerodynamic size (MMAD 0.25 μm ± 0.1) by using sodium chloride as the deposition-determining aerosol. After brief, mouthpiece exposures, 17 subjects were followed by serial counting with a thoracic array of 12 2-in. scintillation detectors and two 2-in. leg counters, all coupled to single channel analyzers. Serial blood samples were also taken. The two exposure groups showed similar total deposition values (23 vs 26%) and the same biological retention halftimes, viz., 22.6 hr. When the retention data were “corrected” for blood-borne 203Pb, the biological halftimes for lung lead retention averaged 13.1 and 14.2 hr, respectively, and were not significantly different. Blood build-up data were also indistinguishable in the two groups. The authors discuss these findings in relation to other inhalation studies and conclude the collective evidence supports the view that atmospheric lead is rapidly and completely absorbed from the human lungs.