Health effects of acid aerosols formed by atmospheric mixtures.

Under ambient conditions, sulfur and nitrogen oxides can react with photochemical products and airborne particles to form acidic vapors and aerosols. Inhalation toxicological studies were conducted, exposing laboratory animals, at rest and during exercise, to multicomponent atmospheric mixtures under conditions favorable to the formation of acidic reaction products. Effects of acid and ozone mixtures on early and late clearance of insoluble radioactive particles in the lungs of rats appeared to be dominated by the oxidant component (i.e., the mixture did cause effects that were significantly different from those of ozone alone). Histopathological evaluations showed that sulfuric acid particles alone did not cause inflammatory responses in centriacinar units of rat lung parenchyma (expressed in terms of percent lesion area) but did cause significant damage (cell killing followed by a wave of cell replication) in nasal respiratory epithelium, as measured by uptake of tritiated thymidine in the DNA of replicating cells. Mixtures of ozone and nitrogen dioxide, which form nitric acid, caused significant inflammatory responses in lung parenchyma (in excess of effects seen in rats exposed to ozone alone), but did not damage nasal epithelium. Mixtures containing acidic sulfate particles, ozone, and nitrogen dioxide damaged both lung parenchyma and nasal epithelia. In rats exposed at rest, the response of the lung appeared to be dominated by the oxidant gas-phase components, while responses in the nose were dominated by the acidic particles. In rats exposed at exercise, however, mixtures of ozone and sulfuric acid particles significantly (2.5-fold) elevated the degree of lung lesion formation over that seen in rats exposed to ozone alone under an identical exercise protocol.

Airway permeability in rats exposed to ozone or treated with cytoskeleton-destabilizing drugs.

Ozone (O3) exposure of rats increases airway epithelial permeability. We hypothesized that this increased permeability may be mediated by the epithelial cell cytoskeleton. To test this hypothesis, we studied the effect of cytoskeletal disruption on the transmucosal transport of tracers from airway lumen to blood and compared the results with the effects of O3 exposure. No increase in transport occurred following disruption of microtubules by vinblastine, but disruption of microfilaments with cytochalasin D resulted in increased transport of radiolabeled tracers [99mTc- and 111In-labeled diethylenetriamine-pentacetate (DTPA) and 125I-labeled bovine serum albumin (BSA)]. In control rats, both horseradish peroxidase (HRP) and BSA, localized by cytochemistry and autoradiography, respectively, were detected on the epithelial cell surfaces and in endocytic vesicles. In rats treated with cytochalasin D or exposed to O3, the tracer molecules also penetrated the intercellular spaces, though the apical tight junctions remained devoid of the tracers. Increased numbers of endocytic vesicles containing HRP and aggregation of 125I-labeled BSA autoradiographic grains in the subepithelial region were also seen after either treatment. We conclude that destabilization of cytoskeletal elements following O3 exposure is a possible mechanism of increased transmucosal transport, which may be a combined effect of accelerated transport through both endocytic and paracellular pathways.

Effects of exercise exposure on toxic interactions between inhaled oxidant and aldehyde air pollutants.

Respiratory tract injury resulting from inhalation of mixtures of ozone (O3) and nitrogen dioxide (NO2) and of O3 and formaldehyde (HCHO) was studied in Sprague-Dawley rats under exposure conditions of rest and exercise. Focal inflammatory injury induced in lung parenchyma by O3 exposure was measured morphometrically and HCHO injury to the nasal respiratory epithelium was measured by cell turnover using tritium-labeled thymidine. Mixtures of O3 (0.35 or 0.6 ppm) with NO2 (respectively 0.6 or 2.5 ppm) doubled the level of lung injury produced by O3 alone in resting exposures to the higher concentrations and in exercising exposures to the lower concentrations. Formaldehyde (10 ppm) mixed with O3 (0.6 ppm) resulted in reduced lung injury compared to O3 alone in resting exposures, but exercise exposure to the mixture did not show an antagonistic interaction. Nasal epithelial injury from HCHO exposure was enhanced when O3 was present in a mixture. Mixtures of O3 and NO2 at high and low concentrations formed respectively 0.73 and 0.02 ppm nitric acid (HNO3) vapor. Chemical interactions among the oxidants, HNO3, and other reaction products (N2O5 and nitrate radical) and lung tissue may be the basis for the O3-NO2 synergism. Increased dose and dose rate associated with exercise exposure may explain the presence of synergistic interaction at lower concentrations than observed in resting exposure. No oxidation products were detected in O3-HCHO mixtures, and the antagonistic interaction observed in lung tissue during resting exposure may result from irritant breathing pattern interactions.

Tracheal and bronchoalveolar permeability changes in rats inhaling oxidant atmospheres during rest or exercise.

Permeability of tracheal and bronchoalveolar airways of rats was measured and used to examine the effects of inhaled oxidant-containing atmospheres. The atmospheres studied were (a) ozone (O3) at 0.6 ppm (1.2 mg/m3) or 0.8 ppm (1.6 mg/m3); (b) nitrogen dioxide (NO2) at 6 ppm (11.3 mg/m3) or 12 ppm (22.6 mg/m3); (c) O3 + NO2 at 0.6 ppm (1.2 mg/m3) and 2.5 ppm (4.7 mg/m3), respectively; and (d) a 7-component particle and gas mixture (complex atmosphere) representing urban air pollution in a photochemical environment. The rats were exposed for 2 h. The effects of exercise during exposure were evaluated by exposing additional groups in an enclosed treadmill. Exposure of resting rats to 0.8 ppm O3 increased tracheal permeability to DTPA and bronchoalveolar permeability to diethylenetriamine pentaacetate (DTPA) and bovine serum albumin (BSA) at 1 h after the exposure. Bronchoalveolar, but not tracheal, permeability remained elevated at 24 h after the exposure. Exercise during exposure to O3 increased permeability to both tracers in the tracheal and the bronchoalveolar zones, and prolonged the duration of increased permeability in the tracheal zone from 1 h to 24 h, and in the bronchoalveolar zone from 24 h to 48 h. Permeability in the tracheal and bronchoalveolar zones of rats exposed at rest to 6 or 12 ppm NO2 did not differ from controls. However, rats exposed during exercise to 12 ppm NO2 for 2 h developed a significant increase in tracheal and bronchoalveolar permeability to DTPA and BSA at 1 h, but not at 24 or 48 h, after exposure. Exposure at rest to 0.6 ppm O3 plus 2.5 ppm NO2 significantly increased bronchoalveolar permeability at 1 and 24 h after exposure, although exposure at rest to 0.6 ppm O3 alone increased bronchoalveolar permeability only at 1 h after exposure. Exposure to O3 + NO2 during exercise led to significantly greater permeability to DTPA than did exercising exposure to O3 alone. Resting rats exposed to a complex gas/aerosol atmosphere composed of the above O3 and NO2 concentrations, plus 5 ppm (13.1 mg/m3) sulfur dioxide (SO2) and an aerosol of insoluble colloidal Fe2O3 with an aerosol of manganese, ferric, and ammonium salts, demonstrated increased permeability at 1 and 24 h after exposure. Nitric acid vapor was formed in both the O3 + NO2 atmosphere and the complex gas/aerosol atmosphere.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulmonary epithelial permeability in rats exposed to O3.

Measurements of pulmonary epithelial permeability were made in rats exposed for 2 h to either purified air or ozone (O3) at concentrations of 0.8 or 2 ppm. [99mTc]Diethylenetriaminepentaacetate ([99mTc]DTPA) (492 daltons) and 125I-labeled bovine serum albumin ([125I]BSA) (69,000 daltons) were injected intravenously, and the lungs were lavaged 6 min later. In rats exposed to air, transfer of the larger tracer molecule (BSA) from blood to the lavage fluid was less than that of the smaller molecule (DTPA) when the amount of tracer in the lavage fluid was calculated as percent of the counts in femoral artery blood 5 min after injection, i.e., 1 min prior to lavage. In rats exposed to O3, alveolar permeability increased in a dose-related fashion, the increase under all exposure conditions was greater for the smaller molecule than for the larger one, and the permeability was reversible with time. The increase in permeability from blood to air was comparable to the increase from air to blood reported earlier (Bhalla et al., 1986). The increased permeability provided an early and reliable indicator of short-term O3 exposure effect in rats. Autoradiography by electron microscopy identified multiple pathways for BSA transfer from blood to the alveolar space. Grains produced by [125I]BSA were localized over endothelial and epithelial cell surfaces, were associated with cytoplasmic vesicles, were over cell surface invaginations, and were found in the cytoplasm of apparently degenerating cells. Although defects in tight junctions of alveolar type I cells were observed in lungs of rats exposed to O3, autoradiographic grains also appeared in intercellular spaces, with the intercellular junctions remaining intact.

Tracheal permeability in rats exposed to ozone. An electron microscopic and autoradiographic analysis of the transport pathway.

Exposure of rats to ozone (O3), 0.8 ppm increases the tracheal permeability to 99mTc-diethylenetriaminepentaacetate (99mTc-DTPA) about twofold but to 125I-bovine serum albumin (125I-BSA) to a lesser extent. It is generally believed that exposure to air pollutants causes perturbation of tight junctions and formation of intercellular channels for the passage of molecules from airway lumen to blood. We now report that a second mechanism, vesicular transport, is operative in the transepithelial movement of molecules, that this mechanism is speeded in tracheas of O3-exposed rats, and that there is a concurrent delay in movement of BSA from connective tissue to capillaries after O3 exposure. Horseradish peroxidase (HRP) instilled in trachea was taken up by endocytic vesicles, which could be localized in apical as well as basal regions of ciliated and nonciliated cells. A count of HRP-positive vesicles and measurement of their surface area revealed an approximate twofold increase in O3-exposed rats over that in control animals breathing clean air; this paralleled a twofold increase in transport of 99mTc-DTPA from tracheal lumen to blood. An autophagocytic process induced in tracheal epithelial cells by O3 is proposed. Despite the difference in the size of HRP and BSA, the 2 molecules migrated through common pathways and were colocalized in the luminal membranes as well as in endocytic vesicles and intercellular spaces in double labeling experiments involving simultaneous detection of HRP by cytochemistry and 125I-BSA by autoradiography. This procedure proved particularly useful in detecting a dramatic accumulation of 125I-BSA autoradiographic grains in subepithelial connective tissue and HRP accumulation in intercellular spaces and at the basal membrane-connective tissue junction in O3-exposed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport of macromolecules and particles at target sites for deposition of air pollutants.

This study analyzed rats' nasal, tracheal and bronchoalveolar epithelial permeability to macromolecules after they were exposed, in 2- or 4-hour periods of rest or exercise, to ozone (O3) (0.6, 0.8 or 2 ppm), nitrogen dioxide (NO2) (2.5, 6 or 12 ppm) or formaldehyde (10 ppm). Exercise was performed on a treadmill operated at a speed that led to a 2-fold increase in oxygen consumption. Histopathologic and electron microscopic cytochemical and autoradiographic studies were performed to identify the structural aspects of mucosal response. In rats not exposed to pollutants, the quantity of macromolecular tracers (99mTc-DTPA, 125I-BSA) in blood sampled 6, 7, 8, 9 and 10 minutes after a slow 5-minute instillation of comparable quantities of tracer molecules in the lumen of each zone, was lowest in nasal, highest in tracheal, and intermediate in the bronchoalveolar region. Exposure of resting rats to O3 did not affect nasal permeability, but tracheal and bronchoalveolar permeabilities increased by 2-fold 1 hour after the exposure. In rats exposed at rest to O3, tracheal permeability was no longer elevated 24 hours after exposure, but bronchoalveolar permeability remained elevated at 24 hours after exposure and was normal at 48 hours. Exposure during exercise increased the effect of O3 in the trachea and in the bronchoalveolar zone. However, exercise also prolonged the duration of the O3 effect on the tracheal zone from 1 hour to 24 hours and, in the bronchoalveolar zone, from 24 hours to 48 hours. Histologically, focal inflammatory lesions in the alveolar zone were maximal at 48 hours after a 4-hour resting exposure to O3. After exposure during exercise, the area of lung involved by lesions increased 4- to 7-fold above the lesion-bearing area in rats exposed while resting. By electron microscopy, horseradish peroxidase (HRP) was localized in epithelial intercellular spaces, but not in the apical tight junctions, of tracheal epithelial cells from O3-exposed rats; no HRP was found in intercellular spaces in controls. The number of HRP-containing endocytic vesicles in tracheal epithelial cells was 2-fold greater in rats exposed to O3 than in control rats. This 2-fold increase in vesicles presumed to be transporting HRP matches the 2-fold increase in transfer of DTPA from the tracheal lumen to the blood. Electron microscopic autoradiography revealed 125I-BSA accumulation in subepithelial connective tissue, and electron microscopic cytochemistry identified accumulation of HRP not only between cells but also at the basal lamina.(ABSTRACT TRUNCATED AT 400 WORDS)

Relative permeability of nasal, tracheal, and bronchoalveolar mucosa to macromolecules in rats exposed to ozone.

Nasal, tracheal and bronchoalveolar injuries resulting from acute ozone exposure of rats were investigated by permeability changes. 99mTc-labeled diethylenetriaminepentaacetate (DPTA) and 125I-labeled bovine serum albumin (BSA) were selectively instilled into localized airway regions of anesthetized rats exposed to 0.8 ppm 03 or clean air for 2 h. Transmucosal transfer of the radiolabeled tracers was detected by counting the radioactivity in blood samples collected at short postinstillation time intervals. Permeability measurements were made on d 0, 1, and 2 after O3 exposure to analyze the extent and persistence of tissue injury in the nasal, tracheal, and bronchoalveolar regions. Normal mucosal permeability was low in nose, intermediate in bronchoalveolar zone, and high in trachea. The O3-related injury, reflected by elevated permeability, was substantial in the trachea and bronchoalveolar zone but was minimal in the nose immediately after the exposure. Abnormal permeability persisted for less than 24 h in the trachea but for more than 24 h in the bronchoalveolar zone. The results are consistent with the properties of O3 of causing greater injury in the smaller airways and the alveolar zone than in the trachea.

Effect of ozone on mean linear intercept in the lung of young beagles.

Although photochemical air pollutants are believed to be associated with respiratory illness, there is also a need to consider their possible effects on postnatal lung maturation. The purpose of this study was to determine whether the maturation of lungs of young beagle dogs might be altered by an inhalation exposure to ozone that represents a severe 5-d episode of photochemical oxidant air pollution. Exposures were at 6 wk of age to purified air, 1 or 2 ppm ozone for 4 h/d on 5 consecutive days. After holding for 6 wk in clean air, lungs were removed and weighed, and the left lung was fixed both by inflation at 30 cm pressure and immersion using buffered formalin. Histologic sections were used for morphometric measurements. Statistical analysis showed that the mean linear intercept (inversely related to lung surface area) was greater than controls (up to about 5%) in the 1 ppm ozone-exposed group. This effect was not seen at 2 ppm ozone, apparently due to large variations in mean linear intercept. No significant differences were seen in body weight, chest girth, lung weight, or volumes of the fixed, inflated lungs. It is concluded that if anatomic maturation of the lung was retarded by this brief regimen of ozone exposure, the effect was small and not likely to have major health consequences.

Polychlorinated biphenyl concentrations in the blood plasma of a selected sample of non-occupationally exposed southern California working adults.

Blood samples from 738 employees of the Southern California Edison Company were analyzed for PCBs prior to their starting work, as part of a pre-employment medical examination. Blood PCB concentrations of the pre-employment sample had a median of 4 ppb and a mean of 5 +/- 4 ppb. These data are comparable to previously published values for blood PCB concentrations in people without occupational exposure. Plasma PCB concentrations are also sorted by demographic characteristics of the sample (age/race/sex/education). Since the demographic properties of the newly hired employees are reasonably similar to those of the Los Angeles-Long Beach work force, as determined in the 1980 census, we conclude that the low PCB concentrations present in the blood of a sample of new electric utility employees is representative of the regional work force and arise from exposures to PCBs present in the general environment.

Polychlorinated biphenyls in the blood of personnel from an electric utility.

Because polychlorinated biphenyls (PCBs) have been implicated as potentially toxic to humans and because the electric utility industry is thought to have significant opportunity for occupational exposure, a study was performed to identify electric utility personnel with the highest PCB exposure potential and to assess their current blood PCB concentrations. For currently employed personnel, a median PCB plasma value of 3 ppb with a mean of 4 +/- 3.65 ppb was found; for a preemployment sample the median was 4 ppb with a mean of 5 +/- 4.25 ppb. PCB concentrations in blood of these personnel are similar to concentrations reported for other populations without occupational exposure. No adverse health impacts would be expected to result from these blood concentrations. These data indicate that no significant occupational exposure has occurred in this utility. This study shows the importance of assessing exposure potential at specific worksites prior to making general exposure or hazard assessments.

Postnatal enlargement of human tracheobronchial airways and implications for particle deposition.

In support of predictions for inhaled particle deposition, morphometric measurements were taken on 20 replica airway casts of people aged 11 days to 21 years. Measurements of right upper lobe airway lengths, diameters, and branching angles were made such that a growth model suitable as input to predictive equations for particle deposition efficiency was obtained. The tracheobronchial airways growth was describable by linear regressions on body length. The length-to-diameter ratio of growing airways did not change in any simple way as a function of airway generation. Airflow rates for a given state of physical activity for various ages were found from previously published data to be describable by linear regressions on body mass. Three states of physical exertion-low activity, light exertion, and heavy exertion-were used for modeling purposes. The computed particle deposition efficiencies indicate that under most circumstances smaller (younger) people will have greater tracheobronchial deposition efficiencies than larger (older) people. For example, tracheobronchial dose on a per kilogram body mass basis for 5-micron-diameter particles may be more than 6 times higher in the resting newborn than in the resting adult assuming equivalent deposition efficiencies above the larynx.

Enhancement of ozone-induced lung injury by exercise.

Rats were exposed for up to 3.75 h to 0.20-0.80 ppm O3 under conditions of rest and treadmill exercise up to 30 m/min, 20% grade, to assess the importance of exposure duration, O3 concentration, and exercise on lung tissue injury. Focal lung parenchymal lesions increased in abundance and severity in response to the three variables; however, exercise was the most important. Lesion response to exercise was greater than that predicted by a simple proportion to estimated effective dose of O3. The results emphasize the importance of including exercise in assessment of possible adverse health effects of exposure to airborne pollutants.

Effect of sulfur dioxide-sulfate exposure on rat respiratory tract clearance.

The effects of a 4 hour exposure to a model sulfur pollutant atmosphere on the clearance of inhaled insoluble tracer particles from the lungs of rats has been studied. The pollutant combination consisted of 5 ppm of sulfur dioxide gas and 1.5 mg/m3 of sulfate aerosol at 80-85% relative humidity. The exposure atmosphere was aged for 30 minutes upstream of the exposure chamber in an aging line in order to provide for gas/ particle interactions such as those occurring in industrial and environmental atmosphere. Results indicate that the sulfur pollutant atmosphere did not produce a statistically significant alteration in early (nasopharyngeal and tracheobronchial) or late (parenchymal) clearance rates such as those which have been identified in this laboratory following exposure to ozone-containing atmospheres.

Effects of sulfate aerosols in combination with ozone on elimination of tracer particles inhaled by rats.

Several inhaled atmospheres were tested for effects on the rat respiratory defense system. Materials studied included ozone and aerosols of ammonium sulfate, ferric sulfate, and sulfuric acid; relative humidity was also a controlled experimental variable. Each sulfate was studied alone as a submicrometer aerosol at a concentration of 3.5 mg/m3 in air and combined with ozone at 0.8 ppm. Results were compared with those for sham-exposed animals and for rats exposed to ozone alone. Air pollutant exposures, inside stainless steel chambers, were one time only for 4 h. The end points for evaluation of effects were measurements of early and late rates of clearance of radiolabeled insoluble tracer particles. Tracer particles were inhaled before air pollutant exposures and particle clearance was followed for about 2 wk. Ozone alone slowed the early (0-50 h after exposure) particle clearance and stimulated clearance during the later phase (2-17 d). High humidity usually amplified these effects of ozone as well as many of the other atmospheres studied. Sulfate aerosols alone tended to produce relatively small effects on early or late clearance. Combinations of ozone and aerosols resulted in effects that were similar to those of ozone alone. The data do not support the hypotheses that sulfate aerosols synergize with ozone in altering respiratory tract clearance, sulfuric acid being a probable exception. These data alone cannot be used to predict the overall health effects of the materials studied.

Laboratory production of ammonium and ferric sulfate aerosols.

Since sulfate aerosol particles are an environmental factor of possible concern, laboratory studies are being conducted to determine their health effects. It is important in such studies that aerosols be controlled and monitored. Submicron sulfate aerosols at high (greater than 80%) and low (30-40%) relative humidities were generated and characterized in support of animal inhalation experiments. Aqueous solutions of ammonium sulfate and ferric sulfate were aerosolized with a compressed air nebulizer, dried, discharged and passed into an aerosol chamber. Aerosol characterization was performed using cascade impactors, electron microscopy, filter samples and an electrical mobility analyzer. Parameters measured included particle size distribution and mass concentration. Instruments used for sizing the aerosols were compared. The electrical mobility analyzer provided useful information on the time stability of the particle size and the mass concentration, but agreement between this instrument and electron microscopy or cascade impaction was poor.

Labeling of monodisperse polystyrene microspheres with tightly bound 51Cr.

Monodisperse radioactive polystyrene latex microspheres have been prepared by attachment of chromium-51 to latex spheres. Labeling was by emulsion polymerization of chromium acetylacetonate dissolved in styrene monomer using commercially available microspheres. This was accomplished with two successive polymerization steps: radiation excitation and radical polymerization initiated with potassium persulfate. After attachment of the label the particle suspension was purified by repeated centrifugation wash cycles to remove labile radioactivity. Results indicate a radioactive binding yield of greater than 80% to the particles. The stability of the label was tested in in vivo and in vitro leaching studies. In these tests, the activity leaching rate was estimated to be less than 0.2% per day.