Exposure-response relationship of bronchial mucociliary clearance in rabbits following acute inhalations of sulfuric acid mist

Eight rabbits underwent 1 h oral inhalations of submicrometer sulfuric acid mist at concentrations ranging from approx. 100-1084 micrograms/m3, followed by measurement of the mucociliary clearance of a tracer aerosol from the bronchial tree. These data, plus those from a previous study, were used to construct an exposure concentration-response relationship for alterations in clearance produced by H2SO4. The response pattern is characterized by transient acceleration of clearance at low concentration exposures, and retardation at higher concentrations. In addition, comparison of these results with those from a similar study using human volunteers supports use of the rabbit as an appropriate model for studying mucociliary clearance alterations produced by inhaled irritants.

Molecular dosimetry of DNA damage caused by alkylation. II. The induction and repair of different classes of single-strand breaks in cultured mammalian cells treated with ethylating agents

Cultured Chinese hamster ovary cells were treated with ethylating agents. DNA lesions giving rise to single-strand breaks (SSB) or alkali-labile sites were measured by elution through membrane filters at pH 12.0 and pH 12.6, and by centrifugation in alkaline sucrose gradients after 1 h and 21 h lysis in alkali. Two agents with different tendencies to ethylate preferentially either at N or O atoms were compared, namely N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) and diethyl sulphate (DES). The compounds differed greatly in their potency to induce lesions, but the ratios of SSB, measured with different methods after a treatment for 30 min, did not differ significantly. This suggested that the spectrum of lesions induced by the two compounds is very similar. However, when both agents were studied with alkaline elution at pH 12.0 after a short treatment time (5 min) only ENNG was found to induce rapidly-repairable SSB. Most of these were rejoined already within 5 min after treatment. These results suggest that rapidly-repairable lesions occurring in DNA after treatment of mammalian cells with ethylating agents are due mainly to alkylation at O-atoms.

Measurement of respiratory tract ammonia in the rabbit and implications to sulfuric acid inhalation studies

Ammonia (NH3) in the respiratory tract has the potential to neutralize inhaled acid vapors and aerosols. Levels of exhaled (nasal) NH3 were measured in rabbits at different times on the same day, on different days, and in rabbits in a normal fed state, or in a fasted or fed state in which the teeth were brushed and the mouth cleansed. The variability of NH3 levels within any individual rabbit was found to be of the same order as the variability found between different animals. In addition, rabbits which were fasted and had their teeth brushed exhaled significantly less NH3 than did fed animals. Levels in the former group ranged from 4 to 236 micrograms/m3, while those in the latter group ranged from 10 to 758 micrograms/m3. Although brushing the teeth of fed animals compressed the observable range of NH3 levels (22-404 micrograms/m3), this was not a significant reduction compared to fed, unbrushed animals. Thus, fasting likely minimized foodstuff in the mouth; the latter may contribute to NH3 formation through bacterial degradation, which appears to be a significant source of NH3 exhaled through the nose. The NH3 concentrations observed may produce variable degrees of neutralization of inhaled H2SO4 droplets before they deposit in the lungs.

Dose-dependent effects of submicrometer sulfuric acid aerosol on particle clearance from ciliated human lung airways

We previously showed that 1 hr exposures to submicrometer sulfuric acid (H2SO4) aerosol at 100 and 1000 micrograms/m3 altered the bronchial mucociliary clearance of monodisperse 7.6 micron MMAD 99mTc-labelled ferric oxide (Fe2O3) in healthy, nonsmoking humans. The 7.6 micron particles were primarily deposited in the larger bronchial airways, where submicrometer H2SO4 has very little deposition. To determine the extent that submicrometer H2SO4 aerosol affects clearance from the more distal ciliated airways, we measured the clearance of a monodisperse 4.2 micron MMAD Fe2O3 aerosol in eight other healthy nonsmoking subjects. A greater fraction of 4.2 micron particles deposited in distal conductive airways. Bronchial mucociliary clearance was slower following 1 h nasal H2SO4 inhalations at 100, 300 and 1000 micrograms/m3 than after sham exposures, while mucociliary transport rates within the trachea and indices of respiratory mechanics were unchanged. A comparison of the effects of 1 h exposures at 100 micrograms/m3 on the clearance of 7.6 and 4.2 micron particles suggests greater physiological response in distal ciliated airways than in larger central airways.

Evaluation of concentration-response relationships for histamine and sulfuric acid aerosols in unanesthetized guinea pigs for their effects on ventilatory response to CO2

Through the addition of aerosols to 10% CO2 mixtures, acute respiratory responses can be detected in unanesthetized guinea pigs. This conclusion was supported by results from a previous study conducted in our laboratory in which animals were exposed to nebulized histamine or sulfuric acid while placed in a whole-body plethysmograph. In that study, only one concentration of each agent was examined. The present data were collected over a wider range of histamine and sulfuric acid exposure concentrations and the results served to reinforce the previous conclusion regarding the ease in detecting acute responses with this approach. Again, inspiratory volume (VI) and pressure changes (delta P), proportional to inspired volume, were measured continously and significant decreases in these parameters occurred during aerosol challenges. In addition, respiratory frequency (f) was evaluated during all exposures but few changes in frequency were observed other than the increases induced by 10% CO2 alone. Measurements of VI and delta P indicated similar levels of response to the tested aerosols, except during intense bronchoconstriction evoked by higher concentrations of histamine. In such constricted states, VI was a more sensitive indicator. Concentration-response relationships for histamine and sulfuric acid using VI measurements were comparable to those of other investigators who measured airflow resistance. Therefore, the new method offers many advantages over previous methods through its noninvasive and simple features yet there is comparable sensitivity to detect acute responses, as demonstrated by this study.

Response of the bronchial mucociliary clearance system in rabbits to inhaled sulfite and sulfuric acid aerosols

A group of eight rabbits was exposed (orally) for 1 hr to a distilled water aerosol (sham control) or to submicrometer aerosols of either a transition metal sulfite complex (Fe(III)-S(IV], sodium sulfite (Na2SO3), or sulfuric acid (H2SO4). Mucociliary clearance was evaluated by external retention measurements of radioactively tagged tracer particles from the bronchial tree. Fe(III)-S(IV) in the range of 238 to 1227 micrograms/m3 (as SO2-3) produced no significant change from sham control in the mean residence time (MRT) of the tracer, indicating no effect upon mucociliary clearance rate. On the other hand, Na2SO3 at levels greater than or equal to 1200 micrograms/m3 (as SO2-3) resulted in clearance acceleration; the lack of effect of Fe(III)-S(IV) is possibly due to its stability. H2SO4 at 260 to 2155 micrograms/m3 produced a significant dose-related response, indicating clearance acceleration at low concentrations and a depression at higher levels.

The pathogenesis of synergistic lung damage in mice by an environmental irritant (H2SO4) and particulate antigen

Daily inhalation by mice of an environmental irritant (H2SO4) followed by consequent respiratory immunization with a particulate antigen (sheep red blood cells, SRBC) induced severe interstitial pneumonitis. Inhalation of H2SO4 per se resulted in accumulation of i.v. injected globulin in the lungs of mice, without significant change in lung weight. In addition, when marker colloidal carbon particles were injected i.v. following H2SO4 inhalation, the carbon was rapidly trapped in the capillary wall in the lungs. Homologous anti-SRBC serum instilled into the respiratory tract followed by subsequent SRBC inhalation produced inflammation and injury similar to that generated by H2SO4 in combination with particulate antigen. It is postulated that following irritant inhalation, the permeability of alveolocapillary membranes increases, so that immune complexes formed by pre-existing circulating antibodies and inhaled antigen can initiate subsequent lung injury.

Physiological and histological alterations in the bronchial mucociliary clearance system of rabbits following intermittent oral or nasal inhalation of sulfuric acid mist

Rabbits were exposed to submicometer sulfuric acid mist (H2SO4) for 1 h/d, 5 d/w for 4 wk, during which time mucociliary clearance was monitored by external in vivo measurements of tagged tracer aerosol retention. One group was exposed orally to 250 micrograms/m3, another to the same concentration via the nose, and a third to 500 micrograms/m3 also via nasal breathing. Clearance was accelerated on specific individual days during the course of the acid exposures, especially at 500 micrograms/m3. In all series, clearance was significantly faster, compared to preexposure controls, during a 2-wk follow-up period after acid exposures had ceased. At the end of this period, the rabbits were sacrificed, and histological sections were obtained from the tracheobronchial tree. Significantly increased epithelial thickness of small conducting airways, compared to sham exposure controls, occurred in rabbits exposed orally at 250 micrograms/m3 or nasally at 500 micrograms/m3, and additionally the lumen of the smallest airways of the former group was narrower than control. The number of airways containing epithelial secretory cells was also significantly greater in these acid exposure groups compared to sham controls. The only change in the rabbits exposed nasally at 250 micrograms/m3 was a significant increase in the number of airways with epithelial secretory cells in the smallest airway classification. The histological alterations provide a basis for observed changes in clearance, and are similar to those found in chronic bronchitis in humans and experimental animals. Differences in site and degree of histological response and degree of physiological change between the two groups exposed to identical acid concentrations appear to have been due to differences in exposure mode, with resultant effects on breathing pattern, aerosol size distribution, and concentration penetrating beyond the upper respiratory tract to specific lung sites.

Mutagenicity and cytotoxicity of dimethyl and monomethyl sulfates in the CHO/HGPRT system

It has recently been shown that coal fly ash collected from coal-fired plants contains dimethyl sulfate (DMS) and monomethyl sulfate (MS) at concentrations as high as 830 ppm. Both these compounds were tested in the CHO/HGPRT system, and it was found that only DMS was cytotoxic and mutagenic to CHO cells. On a molar basis, DMS is twice a mutagenic as methyl methanesulfonate (MMS). Under our treatment conditions, maximum mutation induction and cytotoxicity were obtained after approximately 1 h. The Mutagenic potency of DMS was more stable in aqueous solutions at 4 degrees C than at the ambient temperature of 22 degrees C, but was least stable in DMSO solutions at 22 degrees C. Near-ultraviolet (near-UV) light caused an approximately twofold decrease in the mutagenic and cytotoxic effects of DMS. Although DMS produced by coal combustion could be rendered innocuous by environmental agents in a short span of time, this compound could still pose a health risk to workers closely involved in coal-combustion technology.

Pulmonary function and bronchial reactivity in human subjects with exposure to ozone and respirable sulfuric acid aerosol

The effect of 0.3 ppm ozone with a subsequent exposure to 100 micrograms/m3 sulfuric acid aerosol was studied in 12 nonsmoking subjects to determine if preexposure to ozone would sensitize them to sulfuric acid aerosol. Pulmonary function and bronchial reactivity measurements were made after single and sequential exposures to these pollutants. No significant changes in pulmonary function or bronchial reactivity to methacholine were observed. However, a decrease in bronchial reactivity approaching significance occurred after the 4-h exposure to 100 micrograms/m3, 0.13 microns sulfuric acid aerosol. We conclude that there are no readily apparent risks from sequential exposures of nonsmokers to low concentrations of ozone and sulfuric acid aerosol during light-to-moderate exercise.

Pulmonary host defense responses to inhalation of sulfuric acid and ozone

The effects of simultaneous exposure to ozone (O3) and sulfuric acid [H2SO4, 0.23 microns volume median diameter (VMD)] and a single exposure to ultrafine (less than 0.1 micron VMD) H2SO4 under various conditions were studied using the infectivity/mortality and the ciliary beating frequency model systems. A 3-h exposure to a combined aerosol of 196 micrograms O3/m3 and 483 or 241 micrograms H2SO4/m3 significantly increased the susceptibility of mice to a laboratory-induced respiratory infection. However, exposure to 543 micrograms ultrafine H2SO4/m3 for 2 h or 365 micrograms/m3 2 h/d for 5 d did not significantly affect this parameter. Upper airway response, as measured by changes in hamster tracheal ciliary beating frequency, was not affected by either a 3-h combined exposure to 196 micrograms O3/m3 and 847 micrograms H2SO4/m3 or a 2-h exposure to 458 micrograms ultrafine H2SO4/m3.

Methylation of chromosomal DNA by two alkylating agents differing in carcinogenic potential

The affinity of 2 methylating agents, N-methyl-N-nitrosourea (MNU), a potent carcinogen, and dimethyl sulfate (DMS), a very weak or non-carcinogen, for specific structural or functional regions of DNA has been studied in an in vitro system using rat liver nuclei. The release of alkylated nucleotides from nuclei following limited nuclease digestion was measured. Under restrictive conditions, pancreatic DNase I preferentially digests DNA sequences active in RNA transcription while micrococcal nuclease digests spacer DNA between nucleosome cores. Nucleotides methylated by methylnitrosourea were preferentially released early during the digestions, suggesting a localization in both actively transcribing regions and spacer DNA. DMS alkylation, on the other hand, showed a random distribution in chromosomal DNA as measured by micrococcal nuclease and only limited accumulation in transcribing DNA.

Effects of sulfuric acid aerosols on pulmonary function of guinea pigs

Forty-seven Hartley guinea pigs were exposed for 1 h to approximately 1-micrometer (mass median aerodynamic diameter) sulfuric acid aerosols at concentrations that ranged from 1.2 to 48.3 mg/m3. Ten animals (controls) were exposed to filtered room air only. Eight H2SO4-exposed animals exhibited marked increases in total pulmonary resistance and marked decreases in dynamic compliance. Four of these eight "responsive" animals died during exposure. All other H2SO4-exposed animals exhibited no major difference from controls and were termed nonresponsive. The proportion of responsive to nonresponsive animals increased with exposure concentration, but the magnitude of pulmonary function change was similar for all responsive animals regardless of concentration. Compared to nonresponders, responsive animals had higher preexposure values of tidal transpulmonary pressure excursions and total pulmonary resistance and lower values of dynamic compliance. Preexposure transpulmonary pressure excursions were positively correlated with minute volume only for nonresponsive animals; transpulmonary pressure excursions were positively correlated with total pulmonary resistance in responsive animals. The results suggest that the Hartley guinea pig reacts to inhaled H2SO4 with an essentially all-or-none airway constrictive response and that an animal's sensitivity to this response may be related to its preexposure airway caliber.

Biochemical effects of sulfuric acid mist inhalation by human subjects while at rest

This study evaluated the effect of sulfuric acid aerosol exposure for 2 consecutive days on seven human biochemical blood parameters. A total of 20 human subjects were exposed to 100 micrograms/m3 (0.033 microM) sulfuric acid aerosol (0.5 microns mean mass diameter) for 4 hr/day for 2 consecutive days. A total of 17 human subjects were exposed to 4 hr of ambient air on both exposure days. The chemical blood parameters were measured pre- and post-exposure, and 20 hr after the second exposure: serum glutathione, red blood cell glutathione reductase, red blood cell glucose-6-phosphate dehydrogenase, lysozyme, serum glutamic oxaloacetic acid transaminase, serum vitamin E, and 2, 3-diphosphoglycerate. The results indicate no significant response in any of the seven biochemical blood parameters measured. At this level, repeated exposure did not over-burden the upper airway defenses against acid aerosol.

Potential carcinogenic and mutagenic industrial chemicals. I. Alkylating agents

A variety of alkylating agents, acylating agents, peroxides, halogenated derivatives, and nitrogen derivatives have been reviewed, principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, population at risk, metabolism, carcinogenicity, and mutagenicity.

Biochemical changes in humans upon exposure to sulfuric acid aerosol and exercise

This study evaluated the effect of a single exposure to sulfuric acid aerosol on six human biochemical blood parameters. A total of 18 human subjects were exposed to ambient air for 4 hr on the first day of exposure and to 100 microgram/m3 (0.033 microM) sulfuric acid aerosol (0.5 micrometer mean mass diameter) for 4 hr on the second day. A total of 17 human subjects were exposed for 4 hr to ambient air on both exposure days. On each exposure day, at 30 min and 90 min after exposure was initiated, all subjects engaged in a 15-min exercise period (walking 4 mph on a treadmill inclined at 10 degrees). Six biochemical blood parameters were measured before and after exposure: glutathione, lysozyme, glutathione reductase, serum glutamic oxaloacetic acid transaminase, serum vitamin E, and 2, 3-diphosphoglyceric acid. The results indicate no significant effect of one 4-hr exposure of humns to 100 microgram/m3 sulfuric acid aerosol. One significant post-exposure effect did occur--an increase in glutathione reductase--for both the control and acid-exposed group. It is concluded that at the levels studied, sulfuric acid aerosol is neutralized in the upper airways; consequently, no cellular damage is measurable.

Studies on the enhancement of allergic lung sensitization by inhalation of ozone and sulfuric acid aerosol

Air pollutants were found to enhance the allergic sensitization of mice to an inhaled antigen. Aerosolized ovalbumin was used to mimic the inhalation of an environmental allergen. In three experiments the antigenic contact was repeated at 4 to 7 times over a period of approximately a month. Groups of mice were intermittently exposed to ozone at 0.5 and 0.8 ppm, sulfuric acid aerosol (1 mg/m3), and a combination of the two air pollutants. Antigenically sensitized mice showed some evidence of atopic reactivity to the inhaled antigen, but the interpretation of these responses was difficult to evaluate by observation alone. Clear evidence of allergic sensitization was obtained by injecting the antigen intravenously and recording the instances of systemic anaphylaxis. Allergic mice demonstrated anaphylactic shock within a few minutes of the injection, and fatally shocked animals died within 20 to 40 min. Significant increases in the levels of sensitization were obtained in animals exposed to ozone and the combination of ozone and sulfuric acid aerosol.

Genetic effects of dimethyl sulfate, diethyl sulfate, and related compounds

DMS and DES are monofunctional alkylating agents that have been shown to induce mutations, chromosomal aberrations, and other genetic alterations in a diversity of organisms. They have also been shown to be carcinogenic in animals. As an alkylating agent, DMS is a typical SN2 agent, attacking predominantly nitrogen sites in nucleic acids. DES is capable of SN1 alkylations as well as SN2 and thereby causes some alkylation on oxygen sites including the O6-position of guanine which is thought to be significant in mutagenesis by direct mispairing. The mutagenicity of DMS is better explained in terms of indirect, repair-dependent processes. With respect to both alkylating activity and genetic effects, striking similarities are found between DMS and MMS and between DES and EMS. In most systems where they have been tested, both DMS and DES are mutagenic. Results of many of the mutagenesis studies involving these compounds and other alkylating sulfuric acid esters are summarized in Tables 6, 7, 8, 9 and 10 of this review. Most data are consistent with these agents acting primarily as base-pair substitution mutagens. In the case of DES, strong specificity for G.C to A.T transitions has been reported in some systems but has not been clearly supported in some others. Low levels of frameshift mutations of the deletion type are also likely. In addition to the induction of mutations, recombinogenic and clastogenic effects have been described.