Mount st. Helens ash from the 18 may 1980 eruption: chemical, physical, mineralogical, and biological properties.

Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic.

When nanoparticles get in the way: impact of projected area on in vivo and in vitro macrophage function.

Previous reports by others establish that particle surface area is related to a change in macrophage function as measured by the ability to clear particles from the alveolar spaces. However, for nanoparticles the relation may not be strictly due to surface chemistry: The cumulative projected area of the particles may reflect the degree to which the inner or outer surface of the macrophage is shielded from other objects or molecules. We apply this alternative interpretation to in vitro measurements of macrophage uptake of 26-nm-diameter fluorescent beads and to in vivo data presented in a classic inhalation toxicology paper on nano-sized TiO2 particles. In their paper, Oberdörster et al. (Environ. Health Perspect. 102[suppl. 5]:173-179, 1994) reported that following inhalation exposure to 20-nm or 250-nm TiO2 particles, the half-times for alveolar clearance of polystyrene test particles were proportional to square centimeters of TiO2 particle surface per million macrophages; macrophage toxicity from TiO2 particle surface was assumed to be the cause of the decrease in the clearance rate of polystyrene test particles. When TiO2 particle projected area was incorporated into the in vivo macrophage dosimetry calculations, particle projected areas ranged in value from covering only a fraction (0.1) of the macrophage surface to covering the cell surface 4 times over. The observed decrease in macrophage mediated alveolar clearance of polystyrene test particles was directly related to the potential for TiO2 particles to mask the surface of the macrophage-a possibility that was visualized in vitro with confocal laser scanning microscopy.

Influence of exhaled air on inhalation exposure delivered through a directed-flow nose-only exposure system.

In order to conserve material that is available in limited quantities, "directed-flow" nose-only exposure systems have at times been run at flow rates close to the minute ventilation of the animal. Such low-flow-rate conditions can contribute to a decrease of test substance concentration in inhaled air; near the animal nose, exhaled air and the directed flow of exposure air move in opposite directions. With a Cannon "directed-flow" nose-only exposure system (Lab Products, Maywood, NJ), we investigated the extent to which exposure air plus exhaled air can be inhaled by an animal. A mathematical model and a mechanical simulation of respiration were adopted to predict for a male Fischer 344 rat the concentration of test substance in inhaled air. The mathematical model was based on the assumption of instantaneous mixing. The mechanical simulation of respiration used a Harvard respirator. When the system was operated at an exposure air flow rate greater than 2.5 times the minute ventilation of the animal, the concentration of test substance in the inhaled air was reduced by less than 10%. Under these conditions, the circular jet of air exiting the exposure air delivery tube tended to reach the animal's nose with little dispersion. For exposure air flow rates less than 2 times the minute ventilation, we predict that the interaction of exhaled air and exposure air can be minimized by proportionally reducing the delivery tube diameter. These findings should be applicable to similar "directed-flow" nose-only exposure systems.

Dosimetry counts: molecular hypersensitivity may not drive pulmonary hyperresponsiveness.

Airway hyperresponsiveness is one measure of allergic asthma. One such test, the methacholine challenge, uses an inhaled aerosol to induce changes in resistance to breathing. The test is also used to test hyperresponsiveness in rodent models of asthma. For two varieties of mice, the B6C3F1 and the Balb/c, exposure to aerosolized methacholine demonstrates that the Balb/c is 12x more responsive based on the concentration of methacholine in the solution used to produce the inhaled aerosol (the normally accepted dose-metric). Here we show that the 12x difference in exposure disappears when measurements of airway dimensions of generations 1-6 are used first to calculate deposited mass of methacholine; and second to account for the physiology of airway constriction and pressure drop. These observations in mice provide one explanation of how some hyperresponsive subjects can have no underlying molecular sensitivity; and how constriction in the upper airways can have greater impact on breathing than constriction of airway generations 6-16.

Comparison of pleural responses of rats and hamsters to subchronic inhalation of refractory ceramic fibers.

In the present subchronic study, we compared pleural inflammation, visceral pleural collagen deposition, and visceral and parietal pleural mesothelial cell proliferation in rats and hamsters identically exposed to a kaolin-based refractory ceramic fiber, (RCF)-1 by nose-only inhalation exposure, and correlated the results to translocation of fibers to the pleural cavity. Fischer 344 rats and Syrian golden hamsters were exposed to 650 fibers/cc of RCF-1, for 4 hr/day, 5 days/week for 12 weeks. Following 4 and 12 weeks of exposure, and after a 12-week recovery period, pleural lavage fluid was analyzed for cytologic and biochemical evidence of inflammation. Visceral and parietal pleural mesothelial cell proliferation was assessed by immunocytochemical detection of bromodeoxyuridine incorporation. Pleural collagen was quantitated using morphometric analysis of lung sections stained with Sirius Red. Fiber-exposed rats and hamsters had qualitatively similar pleural inflammation at each time point. Mesothelial cell proliferation was more pronounced in hamsters than in rats at each time point and at each site. In both species, the mesothelial cell labeling index was highest in the parietal pleural mesothelial cells lining the surface of the diaphragm at each time point. Hamsters but not rats had significantly elevated collagen in the visceral pleura at the 12-week postexposure time point. Fibers were found in the pleural cavities of both species at each time point. These fibers were generally short and thin. These results suggest that mesothelial cell proliferation and fibroproliferative changes in the pleura of rodents following short-term inhalation exposure are associated with fiber translocation to the pleura and may be predictive of chronic pleural disease outcomes following long-term exposure.

Comparison of pulmonary and pleural responses of rats and hamsters to inhaled refractory ceramic fibers.

The present study was designed to determine whether pleural fiber burdens or subchronic pleural fibroproliferative and inflammatory changes can help explain the marked interspecies differences in pleural fibrosis and mesothelioma that are observed following long-term inhalation of RCF-1 ceramic fibers by rats and hamsters. Fischer 344 rats and Syrian golden hamsters were exposed to RCF-1 for 4 h per day, 5 days per week, for 12 consecutive weeks. Lung and pleural fiber burdens were characterized during and after exposure. For all time points, approximately 67% of fibers associated with lung tissues from both rats and hamsters were longer than 5 microns in length. In comparison, fibers longer than 5 microns recovered from the pleural compartment, following a 12-week exposure and 12 weeks of recovery, accounted for 13% (hamsters) and 4% (rats) of the distribution. In the 12 weeks after the cessation of exposure, the number of fibers longer than 5 microns in length remained constant in the hamster at approximately 150 fibers per cm2 pleura. This was 2 to 3 times the corresponding fiber surface density in the rat. Significant pulmonary and pleural inflammation was detected at all time points and for both species. DNA synthesis by pleural mesothelial cells was quantified by bromodeoxyuridine uptake following 3 days of labeling. Labeling indices were higher in hamsters than in rats, both for RCF-1-exposed and filtered air-control animals and was highest for the parietal surface of the pleura. Significantly greater collagen deposition was measured in the visceral pleura of hamsters 12 weeks post-exposure but was not significantly elevated in rats. These findings demonstrate that subchronic inhalation exposure to RCF-1 induces pleural inflammation, mesothelial-cell turnover, pleural fibrosis, and an accumulation of fibers with a length greater than 5 microns in the hamster. The accumulation of long fibers in the pleural space may contribute to the pathology observed in the hamster following chronic inhalation of RCF-1, whereas the presence of short, thin fibers may play a role in the acute-phase biological response seen in both species.

Assessment of 1,3-butadiene mutagenicity in the bone marrow of B6C3F1 lacI transgenic mice (Big Blue): a review of mutational spectrum and lacI mutant frequency after a 5-day 625 ppm 1,3-butadiene exposure.

1,3-Butadiene (BD) is a carcinogen that is bioactivated to at least two genotoxic metabolites. In the present article, we review briefly our previous studies on the in vivo mutagenicity and mutational spectra of BD in bone marrow and extend these studies to examine the effect of exposure time (5-days vs. 4-week exposure to 625 ppm BD used in previous studies) on the lacI mutant frequency in the bone marrow. Inhalation exposure to BD at 625 ppm and 1,250 ppm mutagenic in vivo, inducing an increase in the transgene mutant and mutation frequency in the bone marrow. Analysis of the mutational spectrum in BD-exposed and air control mice demonstrated that BD exposure induced an increased frequency of mutations at A:T base pairs. There was no difference in the lacI mutant frequency determined in the bone marrow between a short-term exposure to BD (5 days) and a longer-term exposure (4 weeks). These data taken together demonstrate that inhalation exposure to BD induces in vivo somatic cell mutation.

Toxicity of formaldehyde vapor in B6C3F1 mice exposed for 13 weeks.

Groups of 10 male and 10 female B6C3F1 mice were exposed to 0, 2, 4, 10, 20, or 40 ppm of formaldehyde vapor 6 h/day, 5 days/week for 13 weeks. Clinical abnormalities (dyspnea, listlessness, and hunched posture), significant mortality, and body weight loss were observed in the 40 ppm groups. Pathologic changes were observed in the nose, larynx, trachea, and bronchi of treated males and females and in the uterus and ovaries of treated females. Squamous metaplasia and inflammation were present in the nasal tissues of male and female mice in the 10, 20, and 40 ppm groups and in the larynx of males and females in the 20 and 40 ppm groups. The trachea had squamous metaplasia and hyperplasia of the epithelium in addition to submucosal fibrosis and inflammation in the 20 and 40 ppm groups. In some mice, epithelial-lined, irregular connective tissue bands spanned the tracheal lumen. Metaplasia of the bronchial epithelium was confined to the 40 ppm exposure groups. These effects on the respiratory system were more prevalent in male than in female mice. Hypoplasia of the uterus and ovaries, probably secondary to body weight loss, was confined to the 40 ppm exposure group. In conclusion, 13-week inhalation exposures of B6C3F1 mice to 10, 20, and 40 ppm of formaldehyde vapor induced histologic lesions in the upper respiratory system and concentrations of 40 ppm were lethal to those mice.

Pharmacokinetics of methanol and formate in female cynomolgus monkeys exposed to methanol vapors.

The 1990 Clean Air Act Amendments contain mandates for reduced automotive emissions and add new requirements for the use of alternative fuels such as methanol to reduce certain automotive pollutants. Methanol is acutely toxic in humans at relatively low doses, and the potential for exposure to methanol will be increased if it is used in automotive fuel. Formate is the metabolite responsible for neurotoxic effects of acute methanol exposure. Since formate metabolism is dependent on folate, potentially sensitive folate-deficient subpopulations, such as pregnant women, may accumulate formate and be at higher risk from low-level methanol exposure. Our objective was to determine the pharmacokinetics of 14C-methanol and 14C-formate in normal and folate-deficient monkeys after exposure to 14C-methanol vapors at environmentally relevant concentrations: below the threshold limit value (TLV), at the TLV of 200 parts per million (ppm), and above the TLV. Four normal adult female cynomolgus monkeys were individually anesthetized with isoflurane, and each was exposed by endotracheal intubation to 10, 45, 200, or 900 ppm 14C-methanol for 2 hours. Concentrations of the inhaled and exhaled 14C-methanol, blood concentrations of 14C-methanol and 14C-formate, exhaled 14C-carbon dioxide (14CO2), and respiratory parameters were measured during exposure. After exposure, 14C-methanol and 14CO2 exhaled, 14C-methanol and 14C-formate excreted in urine, and 14C-methanol and 14C-formate in blood were quantified. The amounts of exhaled 14C-methanol and 14CO2, blood concentrations of 14C-methanol and 14C-formate, and 14C-methanol and 14C-formate excreted in urine were linearly related to methanol exposure concentration. For all exposures, blood concentrations of 14C-methanol-derived formate were 10 to 1000 times lower than endogenous blood formate concentrations (100 to 200 mM) reported for monkeys and were several orders of magnitude lower than levels of formate known to be toxic. Since the metabolism of formate in primates depends on the availability of tetrahydrofolate, the same four monkeys were next placed on a folate-deficient diet until folate concentrations in red blood cells consistent with moderate folate deficiency (29 to 107 ng/mL) were achieved. Monkeys were then reexposed to the highest exposure concentration, 900 ppm 14C-methanol, for a similar 2-hour period, and again the pharmacokinetic data described above were obtained. Even with a reduced folate status, monkeys exposed to 900 ppm methanol for 2 hours had peak concentrations of methanol-derived formate that were well below the endogenous levels of formate. Although these results represent only a single exposure and therefore preclude broad generalizations, they do suggest the body contains sufficient folate stores to effectively detoxify small doses of methanol-derived formate from exogenous sources, such as those that might occur during normal use of automotive fuel.

Respiratory tract toxicity in rats exposed to Mexico City air.

The rat has been used extensively as a health sentinel, indicator, or monitor of environmental health hazards, but this model has not been directly validated against human exposures. Humans in Mexico City show upper respiratory tract lesions and evidence of pulmonary damage related to their environmental inhalation exposure. In this study, male and female F344 rats were exposed (23 hr/day) in Mexico City to local Mexico City air (MCA)* for up to seven weeks. Controls were maintained at the same location under filtered air. Prior to these exposures, several steps were taken. First, the nasal passages of normal male rats shipped from the United States and housed in Mexico City were examined for mycoplasma infection; no evidence of infection was found. In addition, a mobile exposure and monitoring system was assembled and, with an ozone (O3) exposure atmosphere, was tested along with supporting histopathology techniques and analysis of rat nasal and lung tissues. Last, the entire exposure model (equipment and animals) was transported to Mexico City and validated for a three-week period. During the seven-week study there were 18 one-hour intervals during which the average O3 concentration of MCA in the exposure chamber exceeded the US National Ambient Air Quality Standard (NAAQS) of 0.120 ppm 03 (hourly average, not to be exceeded more than once per year). This prolonged exposure of healthy F344 rats to MCA containing episodically low to moderate concentrations of 03 (as well as other urban air pollutants) did not induce inflammatory or epithelial lesions in the nasal airways or lung as measured by qualitative histologic techniques or quantitative morphometric techniques. These findings agree with those of previous controlled O3 inhalation studies, but they are in contrast to reports indicating that O3-polluted MCA causes significant nasal mucosal injury in adults and children living in southwestern Mexico City. Taken together, these findings may suggest that human airways are markedly more susceptible to the toxic effects of MCA than are the airways of the F344 rat.

An inhalation exposure chamber designed for animal handling.

A whole-body inhalation exposure chamber was designed and constructed that provided for uniform distribution of aerosols within the chamber and facilitated animal care. Animals were permanently housed in the chamber while on experiment. The entire chamber (including cage units) was sanitized in our cagewashing unit. Animals and their feed were easily observed since cages were mounted in pull-out drawers. The chamber accommodated 360 mice, 196 rats (depending on size), 312 hamsters, 60 guinea pigs, or 30 rabbits (the latter for exposure only). A special feature of the design was that cages and their associated excreta pans were equally spaced from chamber walls and arranged in vertical columns which were offset. This arrangement prevented excreta from dropping on animals in lower tiers.

Comparison of the aerodynamic size distribution of chain-like aggregates measured with a cascade impactor and a spiral centrifuge.

Several authors have suggested that chain-like aggregates fragment in the jets of cascade impactors and that the impactor consequently underestimates the median aerodynamic diameter and overestimates the geometric standard deviation (GSD). The aerodynamic size distribution of (Pu0.14U0.86)02.2 aggregates were measured simultaneously with two Mercer cascade impactors and a LAPS spiral centrifuge to investigate this problem. Although the median aerodynamic diameters were generally in good agreement, the impactor consistently measured higher values for the GSD than did the spiral centrifuge. Based on experiments in which losses in the centrifuge inlet were measured, it was concluded that the centrifuge had measured the aerodynamic size distribution more accurately than the impactor. Interception of chain-like aggregates on the first few impactor stages may have been the primary reason for the disparity between the impactor and centrifuge measurements.

Controlled-delivery vapor generator for animal exposures.

A vapor generation system is described which provides long-term stable vapor concentrations for inhalation bioassay tests with laboratory animals. Liquid is pumped from a reservoir by a micrometering pump to the surface of a cylindrical vaporizer covered with a glass fiber wick. An 80-watt heater and temperature sensor, embedded in the cylinder, control the vaporizer temperature. Pump rates of 0.01 to 20 mL/min and surface temperatures greater than 100 degrees C can be achieved. To minimize condensation on delivery-tube walls, the vaporizer is positioned in the dilution air inlet tube leading directly into the 2-m3 exposure chamber. During exposure of rats, mice and rabbits to eleven different chemicals for periods ranging from 4 hours to over 400 daily 6-hour exposure periods, concentrations from 25 to 10,000 ppm were achieved with a dilution air flow of 280 L/min. Chamber concentrations were routinely maintained within 10% of target levels. Stable pump rates provide a method of calculating vapor concentration independent of chemical analysis. Long-term generation stability and ease of operation reduce labor requirements compared to previous generation techniques.

DNA-protein cross-links and cell replication at specific sites in the nose of F344 rats exposed subchronically to formaldehyde.

Chronic exposures to high concentrations (> or = 6 ppm) of formaldehyde (HCHO) induce cell proliferation, squamous metaplasia, and squamous cell carcinomas in F344 rats. To assess the cancer risk associated with HCHO exposure, DNA-protein cross-links (DPX) formed in a single exposure of naive (previously unexposed) rats and monkeys have been used as a surrogate for the internal dose. Since the quantity of DPX may differ in subchronically exposed animals, the effects of preexposure to HCHO on the acute DPX yield (concentration of DPX following a single exposure) and the cumulative DPX yield (concentration of DPX following repeated exposures) were determined. Male F344 rats were preexposed (PE) to 0.7, 2, 6, or 15 ppm of HCHO (6 hr/day, 5 days/week, 11 weeks + 4 days). Naive (N) rats were exposed to room air. On the 5th day of the 12th week, PE and N rats were simultaneously exposed (3 hr) to H14CHO at the same concentrations used for preexposure. Acute DPX yields and cell replication (incorporation of 14C into DNA) were determined in the mucosal lining of the nasal lateral meatus (LM) (high tumor site in HCHO bioassay) and the medial and posterior meatuses (M:PM) (low tumor site in bioassay). DPX yields in the LM were approximately sixfold higher than in the M:PM. At 0.7 and 2 ppm, no differences between PE and N rats were detected in either tissue. At 6 and 15 ppm, acute DPX yields in the LM of PE rats were approximately half those of N rats, but no differences were detected in the M:PM. Cell proliferation was induced in PE rats at 6 ppm (LM only) and especially at 15 ppm (LM and M:PM). Cumulative DPX yields were measured indirectly by determining the decrease in extractability of DNA from proteins. PE rats were preexposed to 6 or 10 ppm as above, while N rats were exposed to room air. Both groups (PE and N) were then exposed (3 hr) to the same concentration of unlabeled HCHO. DPX yields increased in a concentration-dependent manner in both groups, but the yields were smaller in PE than N rats, suggesting that no accumulation of DPX occurred in PE rats. The results demonstrate that at concentrations < or = 2 ppm, N and PE rats are equivalent with respect to the formation of DPX.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetics of inhaled manganese phosphate in male Sprague-Dawley rats following subacute (14-day) exposure.

Methylcyclopentadienyl manganese tricarbonyl (MMT) is used as a gasoline octane enhancer. Manganese phosphate is the primary respirable (PM(2.5)) MMT-combustion product emitted from the automobile tailpipe. The goal of this study was to determine the exposure-response relationship for inhaled manganese phosphate in adult male CD rats. Rats were exposed 6-h/day for either 5 days/week (10 exposures) or 7 days/week (14 exposures) to manganese phosphate at 0, 0.03, 0.3, or 3 mg Mn/m(3) (MMAD congruent with 1.5 micrometer). The following tissues collected at the end of the 2-week exposure: plasma, erythrocytes, olfactory bulb, striatum, cerebellum, lung, liver, femur, and skeletal muscle (n = 6 rats/exposure group) were analyzed for manganese content by neutron activation analysis. Intravenous (54)MnCl(2) tracer studies were also conducted following the 14th exposure (n = 6 rats/concentration), and whole-body gamma spectrometry was performed immediately after injection and at 1, 2, 4, 8, 12, and 16 weeks after (54)MnCl(2) administration. Increased manganese concentrations were observed in olfactory bulb, lung, femur, and skeletal muscle following exposure to 3 mg Mn/m(3) (10 or 14 exposures). Increased manganese concentrations were also observed in olfactory bulb, striatum, and lung following exposure to 0.3 mg Mn/m(3) (14 exposures only). Red blood cell and plasma manganese concentrations were increased only in rats exposed to 3 mg Mn/m(3) (10 exposures). Rats exposed to 3 mg Mn/m(3) also had an increased whole-body manganese clearance rate when compared to air-exposed control animals. Our results suggest that the rat olfactory bulb may accumulate more manganese than other brain regions following inhalation exposure.

Pleural lesions in Syrian golden hamsters and Fischer-344 rats following intrapleural instillation of man-made ceramic or glass fibers.

The mesothelium is a target of the toxic and carcinogenic effects of certain natural mineral and man-made fibers. Long-term inhalation of a ceramic fiber (RCF-1) results in a high incidence of pleural mesotheliomas in Syrian golden hamsters but not in identically exposed Fischer-344 rats. The present study compared the histopathology of the early pleural response in rats and hamsters instilled with artificial fibers. Groups of Syrian golden hamsters and Fischer-344 rats were instilled with ceramic (RCF-1) or glass (MMVF-10) fibers directly into the pleural space. Each species received approximately equal numbers of long, thin fibers per g body weight. Fiber-induced lesions were compared 7 and 28 days postinstillation. Both hamsters and rats developed qualitatively similar dose-dependent inflammatory lesions that were not fiber-type specific. Both species developed fibrosis in conjunction with inflammation in the visceral pleura, but a striking interspecies difference was noted in the pattern of mesothelial cell response. Hamsters developed greater surface mesothelial cell proliferation and had focal aggregates of mesothelial cells embedded deep within regions of visceral pleural fibrosis. It is hypothesized from the present study that the marked fiber-induced proliferative mesothelial cell response of the hamster visceral pleura may explain the high number of pleural mesotheliomas found in long-term fiber studies in this species.