Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic.

SARS-CoV-2 can spread by close contact through large droplet spray and indirect contact via contaminated objects. There is mounting evidence that it can also be transmitted by inhalation of infected saliva aerosol particles. These particles are generated when breathing, talking, laughing, coughing or sneezing. It can be assumed that aerosol particle concentrations should be kept low in order to minimize the potential risk of airborne virus transmission. This paper presents measurements of aerosol particle concentrations in a gym, where saliva aerosol production is pronounced. 35 test persons performed physical exercise and aerosol particle concentrations, CO2 concentrations, air temperature and relative humidity were obtained in the room of 886 m³. A separate test was used to discriminate between human endogenous and exogenous aerosol particles. Aerosol particle removal by mechanical ventilation and mobile air cleaning units was measured. The gym test showed that ventilation with air-change rate ACH = 2.2 h-1, i.e. 4.5 times the minimum of the Dutch Building Code, was insufficient to stop the significant aerosol concentration rise over 30 min. Air cleaning alone with ACH = 1.39 h-1 had a similar effect as ventilation alone. Simplified mathematical models were engaged to provide further insight into ventilation, air cleaning and deposition. It was shown that combining the above-mentioned ventilation and air cleaning can reduce aerosol particle concentrations with 80 to 90% , depending on aerosol size. This combination of existing ventilation supplemented with air cleaning is energy efficient and can also be applied for other indoor environments.

Allergic contact dermatitis: epidemiology, molecular mechanisms, in vitro methods and regulatory aspects. Current knowledge assembled at an international workshop at BfR, Germany.

Contact allergies are complex diseases, and one of the important challenges for public health and immunology. The German 'Federal Institute for Risk Assessment' hosted an 'International Workshop on Contact Dermatitis'. The scope of the workshop was to discuss new discoveries and developments in the field of contact dermatitis. This included the epidemiology and molecular biology of contact allergy, as well as the development of new in vitro methods. Furthermore, it considered regulatory aspects aiming to reduce exposure to contact sensitisers. An estimated 15-20% of the general population suffers from contact allergy. Workplace exposure, age, sex, use of consumer products and genetic predispositions were identified as the most important risk factors. Research highlights included: advances in understanding of immune responses to contact sensitisers, the importance of autoxidation or enzyme-mediated oxidation for the activation of chemicals, the mechanisms through which hapten-protein conjugates are formed and the development of novel in vitro strategies for the identification of skin-sensitising chemicals. Dendritic cell cultures and structure-activity relationships are being developed to identify potential contact allergens. However, the local lymph node assay (LLNA) presently remains the validated method of choice for hazard identification and characterisation. At the workshop the use of the LLNA for regulatory purposes and for quantitative risk assessment was also discussed.

Human volunteer study with PGME: eye irritation during vapour exposure.

The objective of this study was to establish the possible occurrence of eye irritation and subjective symptoms in human volunteers exposed to propylene glycol monomethyl ether (PGME) vapour at concentrations of 0, 100 and 150 ppm. Testing was conducted in 12 healthy male volunteers using a repeated measures design. Each subject was exposed for 2.5 h to each of the three exposure conditions that were spaced 7 days apart. The exposure sequences were counterbalanced and the exposure to the test substance and the effect measurements were conducted in a double-blind fashion. During all exposure sessions, 20 ppm diethyl ether was used as a 'masking agent' for vapour exposure. Measurements of pre- and post exposure eye redness, corneal thickness, tear film break-up time, conjunctival epithelial damage, blinking frequency, and subjective ratings on discomfort were used to evaluate the possible irritating effects of PGME. The results indicated no significant treatment effects for any of the objective parameters. Results of the subjective ratings indicated very slight effects on the eyes in the 150 ppm PGME condition only. No significant effects of treatment were found for the remaining questions concerning the perceived intensity of the smell in the room, the (un)pleasantness of the smell, the perceived effects on the skin, effects on the throat, shivering, muscle aching, and intestinal cramps. In conclusion, the results of the present study indicated minimal subjective eye effects at 150 ppm only, and no impact on the objective measures of eye irritation at either of the two exposure levels. It was concluded that the no adverse effect concentration for eye irritation due to PGME vapour was at least 150 ppm.

Pulmonary effects of ultrafine and fine ammonium salts aerosols in healthy and monocrotaline-treated rats following short-term exposure.

In the present study the effects of a 3-day inhalation exposure to model compounds for ambient particulate matter were investigated: ammonium bisulfate, ammonium ferrosulfate, and ammonium nitrate, all components of the secondary aerosol fraction of ambient particulate matter (PM), and carbon black (CB, model aerosol for primary PM). The objective of this study was to test the hypothesis that secondary model aerosols exert acute pulmonary adverse effects in rats, and that rats with pulmonary hypertension (PH), induced by monocrotaline (MCT), are more sensitive to these components than normal healthy animals. An additional aim was to test the hypothesis that fine particles exert more effects than ultrafines. Healthy and PH rats were exposed to ultrafine (mass median diameter [MMD] approximate, equals 0.07-0.10 microm; 4 x 10(5) particles/cm(3)) and fine (MMD approximate, equals 0.57-0.64 micro;m; 9 x 10(3) particles/cm(3)) ammonium aerosols during 4 h/day for 3 consecutive days. The mean mass concentrations ranged from 70 to 420 microg/m(3), respectively, for ultrafine ammonium bisulfate, nitrate, and ferrosulfate and from 275 to 410 microg/m(3) for fine-mode aerosols. In an additional experiment, simultaneous exposure to a fine CB aerosol (0.6 microm; 2-9 mg/m(3)) and ammonium nitrate (0.4-18 mg/m(3)) was performed. Bronchoalveolar lavage fluid (BALF) analysis and histopathological examination were performed on animals sacrificed 1 day after the last exposure. Histopathology of the lungs did not reveal test atmosphere-related abnormalities in either healthy or PH rats exposed to the ammonium salts, or to a combination of CB + nitrate. Alveolar macrophages in rats exposed to CB only revealed the presence of black material in their cytoplasm. There were no signs of cytotoxicity due to the aerosol exposures (as measured with lactate dehydrogenase [LDH], protein, and albumin contents in BALF). Macrophages were not activated after MCT treatment or the test atmospheres, since no changes were observed in N-acetyl glucosaminidase (NAG). Cell differentiation profiles were inconsistent, partly caused by an already present infection with Haemophilus sp. However, we believe that the test atmospheres did not affect cell differentiation or total cell counts. The results show that at exposure levels of ammonium salts at least one order of magnitude higher than ambient levels, marked adverse health effects were absent in both healthy and PH rats.

An analysis of human response to the irritancy of acetone vapors.

Studies on the irritative effects of acetone vapor in humans and experimental animals have revealed large differences in the lowest acetone concentration found to be irritative to the respiratory tract and eyes. This has brought on much confusion in the process of setting occupational exposure limits for acetone. A literature survey was carried out focusing on the differences in results between studies using subjective (neuro)behavioral methods (questionnaires) and studies using objective measurements to detect odor and irritation thresholds. A critical review of published studies revealed that the odor detection threshold of acetone ranges from about 20 to about 400 ppm. Loss of sensitivity due to adaptation and/or habituation to acetone odor may occur, as was shown in studies comparing workers previously exposed to acetone with previously unexposed subjects. It further appeared that the sensory irritation threshold of acetone lies between 10,000 and 40,000 ppm. Thus, the threshold for sensory irritation is much higher than the odor detection limit, a conclusion that is supported by observations in anosmics, showing a ten times higher irritation threshold level than the odor threshold found in normosmics. The two-times higher sensory irritation threshold observed in acetone-exposed workers compared with previously nonexposed controls can apart from adaptation be ascribed to habituation. An evaluation of studies on subjectively reported irritation at acetone concentrations < 1000 ppm shows that perception of odor intensity, information bias, and exposure history (i.e., habituation) are confounding factors in the reporting of irritation thresholds and health symptoms. In conclusion, subjective measures alone are inappropriate for establishing sensory irritation effects and sensory irritation threshold levels of odorants such as acetone. Clearly, the sensory irritation threshold of acetone should be based on objective measurements.

Respiratory irritation by trimellitic anhydride in Brown Norway and Wistar rats.

Several acid anhydrides are known for their sensitizing and irritative properties. Since both irritation and respiratory allergy can cause changes of lung function, proper testing of allergen-dependent effects on the respiratory tract requires knowledge of the respiratory irritant effects. To study the latter effects, groups of female Brown Norway (BN) and Wistar rats were exposed for 30 min to a range of concentrations (10 to 300 mg/m(3)) of the well-known respiratory allergen trimellitic anhydride (TMA). Breathing pattern and frequency were monitored before, during, and after exposure. Animals were necropsied and lung weights were determined 1 day after exposure. In BN rats, changes in breathing pattern were seen at levels of 29 mg/m(3) and higher and decreases in frequency at 60 mg/m(3) and higher, whereas in Wistar rats changes in both pattern and frequency (increases followed by decreases) were seen at levels of 34 mg/m(3) and higher. Changes in breathing pattern consisted of a spiked form instead of a wave form of the respiratory cycle, with a pause between breaths at the end of expiration. The length of the pause increased with increasing concentrations of TMA while the duration of the respiratory cycle decreased slightly, implying that breathing frequency was mainly determined by the magnitude of the increase in pause. These reversible changes in breathing pattern and frequency were considered to be suggestive of lower airway irritation, rather than upper airway irritation. No concentration-related changes in lung weights were observed. The highest level at which no acute airway irritation as based on both breathing pattern and frequency was observed in both rat strains was 14 mg/m(3).

Health risks associated with inhaled nasal toxicants.

Health risks of inhaled nasal toxicants were reviewed with emphasis on chemically induced nasal lesions in humans, sensory irritation, olfactory and trigeminal nerve toxicity, nasal immunopathology and carcinogenesis, nasal responses to chemical mixtures, in vitro models, and nasal dosimetry- and metabolism-based extrapolation of nasal data in animals to humans. Conspicuous findings in humans are the effects of outdoor air pollution on the nasal mucosa, and tobacco smoking as a risk factor for sinonasal squamous cell carcinoma. Objective methods in humans to discriminate between sensory irritation and olfactory stimulation and between adaptation and habituation have been introduced successfully, providing more relevant information than sensory irritation studies in animals. Against the background of chemoperception as a dominant window of the brain on the outside world, nasal neurotoxicology is rapidly developing, focusing on olfactory and trigeminal nerve toxicity. Better insight in the processes underlying neurogenic inflammation may increase our knowledge of the causes of the various chemical sensitivity syndromes. Nasal immunotoxicology is extremely complex, which is mainly due to the pivotal role of nasal lymphoid tissue in the defense of the middle ear, eye, and oral cavity against antigenic substances, and the important function of the nasal passages in brain drainage in rats. The crucial role of tissue damage and reactive epithelial hyperproliferation in nasal carcinogenesis has become overwhelmingly clear as demonstrated by the recently developed biologically based model for predicting formaldehyde nasal cancer risk in humans. The evidence of carcinogenicity of inhaled complex mixtures in experimental animals is very limited, while there is ample evidence that occupational exposure to mixtures such as wood, leather, or textile dust or chromium- and nickel-containing materials is associated with increased risk of nasal cancer. It is remarkable that these mixtures are aerosols, suggesting that their "particulate nature" may be a major factor in their potential to induce nasal cancer. Studies in rats have been conducted with defined mixtures of nasal irritants such as aldehydes, using a model for competitive agonism to predict the outcome of such mixed exposures. When exposure levels in a mixture of nasal cytotoxicants were equal to or below the "No-Observed-Adverse-Effect-Levels" (NOAELs) of the individual chemicals, neither additivity nor potentiation was found, indicating that the NOAEL of the "most risky chemical" in the mixture would also be the NOAEL of the mixture. In vitro models are increasingly being used to study mechanisms of nasal toxicity. However, considering the complexity of the nasal cavity and the many factors that contribute to nasal toxicity, it is unlikely that in vitro experiments ever will be substitutes for in vivo inhalation studies. It is widely recognized that a strategic approach should be available for the interpretation of nasal effects in experimental animals with regard to potential human health risk. Mapping of nasal lesions combined with airflow-driven dosimetry and knowledge about local metabolism is a solid basis for extrapolation of animal data to humans. However, more research is needed to better understand factors that determine the susceptibility of human and animal tissues to nasal toxicants, in particular nasal carcinogens.

Short-Term Inhalation Exposure of Healthy and Compromised Rats and Mice to Fine and Ultrafine Carbon Particles.

Epidemiological studies have consistently shown associations between acute pulmonary effects and relatively low levels of ambient particulate matter (PM). The present study was carried out to examine the pulmonary toxicity of inhaled fine (FCB) and ultrafine carbon (UFC) particles as model compounds for carbonaceous (primary) PM, and to identify whether particle size, particle number, and/or mass could be critical in inducing the deleterious effects. Healthy and compromised rats and mice were exposed for 4 h/day during 3 consecutive days to 10(4) or 10(5) fine carbon black (~300-500 nm), or 10(5) or 10(6) ultrafine carbon (∼30-60 nm) particles/cm(3), covering a mass range of about 10 to 10,000 µ/m(3). Separate groups of rats were also exposed to a combination of FCB and fine ammonium nitrate at similar number and mass concentrations. Animals were sacrificed the day after the last exposure to determine their pulmonary responses using bronchoalveolar lavage fluid (BALF) analysis and lung histopathology. Exposure to FCB resulted in early signs of lung injury. Effects were not enhanced in compromised animals when compared to healthy animals. Exposure to UFC particles at similar and higher number concentrations did not induce any biologically relevant changes. These data may indicate that at number concentrations occurring in ambient air, the size of the particles (in air) is more important than their number.

Pathological and immunological effects of respirable coal fly ash in male Wistar rats.

In this study the effects of inhalatory exposure to coal fly ash on lung pathology and the immune system in rats were examined. Rats were exposed to 0, 10, 30, or 100 mg/m(3) coal fly ash (6 h/day, 5 days/wk) for 4 wk, or to 0 and 100 mg/m(3) for 1 wk, and for 1 wk followed by a recovery in clean air of 3 wk. A concentration-related increase in lung weight was found starting from 30 mg/m(3) coal fly ash. After exposure to 100 mg/m(3), a time-related deposition of free particles in the lungs was observed as well as a time-related number of coal fly ash particles phagocytized in alveolar macrophages. Histological examination revealed increased cellularity in alveolar septa, consisting mainly of mononuclear cell infiltrate, proliferated type II cells, and a slight fibrotic reaction. After a recovery period of 3 wk the histological picture was identical to that after 1 wk of exposure, indicating no significant recovery. No toxicological significant changes were found in the hematological, clinical chemistry, or urine parameters. Effects both on nonspecific defense mechanisms and on specific immune responses were noted. With regard to the immune function in the draining lymph nodes of the lung, a significantly increased number of both T and B lymphocytes was observed. The ratio of both cell types was not changed in either of the groups. In serum of exposed rats a significant increase of up to 150% of the immunoglobulin A (IgA) content was found. The number and phagocytic capacity of macrophages were significantly increased, while the killing of Listeria bacteria per cell ex vivo/in vitro remained unchanged. Natural killer (NK) activity in pulmonary cell suspensions was slightly stimulated in rats exposed for 4 wk to 10 and 30 mg/m(3), whereas an exposure to 100 mg/m(3) resulted in a slight decrease; however, both changes were not significant. In conclusion, the alterations in lung histopathology and immunity, observed in a dose and exposure time relation at concentrations up to and including 100 mg/m(3) coal fly ash, may be considered an adverse response of the host to inhalation of particulate matter. Whether these observed alterations may effect the host resistance must be learned from infection studies.

Airway morphology and function of rats following dermal sensitization and respiratory challenge with low molecular weight chemicals.

Local lymph node activation and increased total serum IgE levels are suggested to be predictive parameters of airway hypersensitivity caused by low molecular weight (LMW) chemicals. Whether increases of total serum IgE are indicative of actual induction of specific airway reactions (morphological and functional) after inhalation challenge was examined in the present study. In Brown Norway (BN) and Wistar rats, serum IgE concentrations were examined following topical exposure of chemicals with known diverse sensitization potential in humans: trimellitic anhydride (TMA), a dermal and respiratory sensitizer; dinitrochlorobenzene (DNCB), a dermal sensitizer with no known potential to cause respiratory allergy; and methyl salicylate, a skin irritant devoid of sensitizing properties. Functional and histopathological changes in the respiratory tract were examined after subsequent inhalatory challenge with these chemicals. Of the three tested chemicals, only topical exposure to TMA resulted in a significant increase in total serum IgE concentrations in the high-IgE-responding BN rat. Upon subsequent inhalatory challenge of these rats, TMA induced specific airway reactions which included a sharp decrease in respiratory rate during challenge, followed by an increase in breathing rate with a concomitant decrease in tidal volume 24 and 48 h after inhalatory challenge, and histopathological changes in the larynx and lungs of animals necropsied 48 h after challenge. Interestingly, despite low IgE levels, TMA induced histopathological changes in the larynx and lungs of Wistar rats too. Laryngeal changes were also observed in Wistar rats upon sensitization and challenge with DNCB. These data suggest that increased total serum IgE after topical sensitization is associated with immediate-type specific airway reactivity after inhalation challenge in BN rats and thus may be a valuable parameter in testing for respiratory sensitization potential of LMW compounds. Histopathological examination upon subsequent inhalation challenge of sensitized low-IgE-responders may provide information on other allergic inflammatory airway reactions.

Weight changes and serum sodium concentrations after an ultradistance multisport triathlon.

OBJECTIVE: This study describes the incidence of hyponatremia and the weight changes during an ultradistance multisport triathlon. DESIGN: Descriptive research. SETTING: A 1-day triathlon in which each athlete kayaks 67 km, cycles 148 km, and runs 23.8 km. PARTICIPANTS: Forty-eight athletes competing in the race were studied. INTERVENTIONS: None. MAIN OUTCOME MEASURES: All subjects were weighed before the race and on completion of the race. A blood sample for serum sodium was taken at the finish of the race. RESULTS: The mean weight change over the course of the race was a loss of 2.5 kg (SD +/- 1.7, n = 48), or a mean percentage loss of body weight of 3.1% (SD +/- 2.07). This was highly statistically significant (p < 0.0001) using the Student paired t test. No athletes gained weight, and six athletes maintained their same weight. Only one athlete was hyponatremic (Na = 134 mEq/L). This athlete maintained his weight over the course of the race and he did not seek medical attention. The mean serum sodium concentration at the end of the race was 139.3 mEq/L (SD = 2.28, n = 47). There was a significant correlation (r = 0.30, p = 0.04) between sodium levels and weight change during the race: the greater the weight loss, the higher the serum sodium concentration. There was no significant correlation between the degree of weight loss and athletes' finishing times (r = 0.11, p = 0.45). CONCLUSIONS: Symptomatic hyponatremia did not occur in the 1996 Coast to Coast multisport triathlon, although one athlete had borderline hyponatremia. Athletes lose significant amounts of weight over the course of this multisport event, but nevertheless manage to complete the race.

Local lymph node activation and IgE responses in brown Norway and Wistar rats after dermal application of sensitizing and non-sensitizing chemicals.

The local lymph node assay (LLNA) and the IgE test in the mouse are proposed models for predictive recognition of low molecular weight chemicals causing IgE-mediated allergic airway reactions in man. Since rats are commonly used in routine toxicity studies and a previous study (Arts et al. (1996) Food Chem. Toxicol. 34, 55-62) has shown that several rat strains were found appropriate for the LLNA, the suitability of the rat for the IgE test was examined in the present study. Serum IgE concentrations were examined following topical exposure of Brown Norway (BN) and Wistar rats to each of four chemicals with known diverse sensitization potential in humans: trimellitic anhydride (TMA), a dermal and respiratory sensitizer, dinitrochlorobenzene (DNCB), a dermal sensitizer with no or limited potential to cause respiratory allergy; formaldehyde (FA), a skin irritant and dermal sensitizer with equivocal evidence for respiratory sensitizing potential; methyl salicylate (MS), a skin irritant devoid of sensitizing properties. Of the four tested chemicals, only exposure to TMA resulted in a significant increase in serum IgE concentration and this response was only evoked in the high-IgE-responding BN rat. The latter two chemicals were also tested for lymph node activation, in casu the ear-draining lymph nodes. FA caused a dose-dependent activation of the draining lymph nodes whereas MS was inactive. The results as obtained with TMA, DNCB and MS in the rat are in agreement with human data. The results with FA though, indicate the need for further studies of chemicals that have both irritant and sensitizing properties at about similar concentrations or may act through non-IgE-mediated immune mechanisms.

Local lymph node activation in rats after dermal application of the sensitizers 2,4-dinitrochlorobenzene and trimellitic anhydride.

Five rat strains were compared for their performance in the local lymph node assay (LLNA), a promising test system for the identification of the skin-sensitizing potential of chemicals in the mouse. The contract sensitizer 2,4-dinitrochlorobenzene (DNCB) and the contact and respiratory sensitizer trimellitic anhydride (TMA) were used as model chemicals and responses in rats were compared with those in BALB/c mice. The chemicals were applied to the dorsum of both ears, once daily for three consecutive days; 2 days (mice) or 3 days (rats) thereafter, proliferating cells were labelled by i.p. injection of BrdU 2 hr before the animals were killed. Systemic effects were subsequently assessed by determination of spleen, liver and kidney weights, skin effects by determination of swelling and inflammatory cell infiltration of the ears, and immune effects by determination of weight and proliferative activity of the local lymph nodes (LLN). Following application (x 3) of DNCB or TMA, minor systemic effects were observed, as indicated by slightly elevated spleen and liver weights in a few rat strains and the mice. Skin effects, consisting of increased ear thickness and presence of mononuclear inflammatory cell infiltrates, were observed in all rat strains treated with DNCB or TMA, LLN weights had increased, as had the proliferative activity in these nodes. It was concluded that effects induced by DNCB and TMA in all five rat strains were comparable with those in mice.

Sensory irritation to mixtures of formaldehyde, acrolein, and acetaldehyde in rats.

Sensory irritation of formaldehyde (FRM), acrolein (ACR) and acetaldehyde (ACE) as measured by the decrease in breathing frequency (DBF) was studied in male Wistar rats using nose-only exposure. Groups of four rats were exposed to each of the single compounds separately or to mixtures of FRM, ACR and/or ACE. Exposure concentrations of the mixtures were chosen in such a way that summation of the effects of each chemical would be expected not to exceed 80% reduction of the breathing frequency. FRM, ACR and ACE appeared to act as sensory irritants as defined by Alarie (1966, 1973). With FRM and ACR desensitization occurred, whereas with ACE the breathing frequency gradually decreased with increasing exposure time (up to 30 min). For mixtures, the observed DBF was more pronounced than the DBF for each compound separately, but was less than the sum of the DBFs for the single compounds. A model for three compounds competing for the same receptor was applied to predict the DBF of mixtures of FRM, ACE and ACR. The results also showed that with mixtures no desensitization occurred; in fact, the breathing frequency further decreased in the last 15 min of exposure. These observations were similar to those found for ACE alone, and might have been caused by effects on the upper respiratory tract. The results of the present study allow the conclusion that sensory irritation in rats exposed to mixtures of irritant aldehydes is more pronounced than that caused by each of the aldehydes separately, and that the DBF as a result of exposure to a mixture could well be predicted using a model for competitive agonism, thus providing evidence that the combined effect of these aldehydes is basically a result of competition for a common receptor (trigeminal nerve).

Safety evaluation of the mixture of chemicals at a specific workplace: theoretical considerations and a suggested two-step procedure.

Procedures for the selection of compounds with high health hazard potential are reviewed, and major aspects of the assessment of health risks associated with exposure to mixtures of chemicals are discussed. Examples are given of additivity and synergism of effects following exposure to mixtures. Using these data from the literature a two-step procedure for the safety evaluation of the mixture of chemicals occurring at a specific workplace is suggested. The first step consists of estimating the relative health risk associated with each chemical; the estimation is based on the ratio between exposure level and degree of toxicity. Those chemicals representing a high risk are then selected for further consideration. The second step comprises the risk assessment, focusing on prediction of the risk associated with exposure to the mixture of selected chemicals. To allow such prediction the (presumable) mode of action of the selected compounds should be considered. A practical way to find out whether exposure to chemicals at a specific workplace is of serious health concern, could be the conduct of both a 4-week toxicity study in rats and 2 different types of genotoxicity studies with the mixture of selected chemicals, using exposure concentrations related to those occurring in practice.

Acute and subacute inhalation toxicity of germanium dioxide in rats.

Two acute (4 hr) and one subacute (4 wk) inhalation toxicity studies on germanium dioxide (purity > or = 99%, mean particle size 1.7-2.6 microns) were conducted in young adult Wistar rats. In the acute studies, exposure of two groups of five rats of each sex to maximum attainable concentrations of either 3.10 g amorphous or 1.42 g hexagonal germanium dioxide/m3 for 4 hr was not lethal. In the subacute study, four groups of five rats of each sex were exposed to 0, 16, 72 and 309 mg hexagonal germanium dioxide/m3 for 6 hr/day, 5 days/wk during 4 wk. Two additional groups of 5 rats per sex, exposed either to 0 or to 309 mg/m3, were kept for a 33-day post-exposure period. At the end of the treatment period, changes were observed only in rats of the high concentration group: these changes were decreased body weight gain (both sexes), decreases in haematocrit (females) and thrombocyte count (both sexes), and increases in neutrophil count (both sexes) and white blood cell count (females). On clinical chemistry evaluation, decreased fasting blood glucose (females), decreased total protein concentration (both sexes), increased plasma alanine aminotransferase and aspartate aminotransferase activities (females), increased plasma urea nitrogen (males) and increased plasma bilirubin level (females) were observed. In addition, urinary volume was elevated, and urine density and pH were lowered in both sexes. Relative weights of kidneys, spleen, heart and lungs were higher than in controls. Microscopic examination revealed effects on renal tubular epithelium. Effects on growth, kidneys, and liver were still present at the end of the 33-day recovery period. It was concluded that the 4-hr LC50 value of amorphous germanium dioxide was greater than 3.10 g/m3 and that of the hexagonal form greater than 1.42 g/m3. The no-adverse-effect-level in the 4-wk study using hexagonal germanium dioxide was 72 mg/m3.

Airway responses during and directly after single-time exposure to ozone.

Breathing pattern and lung mechanical parameters were measured in 7 female Wistar rats (ca. 200 g) during exposure to 1.0 (n = 5) or 1.3 (n = 2) ppm ozone in air for 2 h and during a 2-h post-exposure observation period. Changes in breathing pattern showed a gradual decrease from 3 to 2 Hz at constant minute ventilation during the first hour of exposure. During the second hour of exposure 6 out of 7 animals developed post-expiratory apnoea (resulting from interstitial oedema), which took about half the breathing cycle concomitant with a decrease of ca. 50% of the minute volume. The breathing pattern returned to normal at the end of the post-exposure observation period. Lung mechanical properties were determined by the forced oscillation method in the restrained, unanaesthetized, spontaneously breathing rats. Airway resistance, inertia and compliance were calculated at regular time intervals during exposure and during the observation period. Overall resistance increased significantly by a factor of 1.76 (P < 0.05); compliance decreased significantly by a factor of 3 (P < 0.05). Airway inertia showed individual increases or decreases. The mean increase (1.23) did not reach the level of significance. At the end of the exposure period the stable changes were interrupted by short-lasting periods of bronchospasms during which the airway resistance increased by a factor of 8 or more.

Chronic inhalation toxicity and carcinogenicity study of respirable polymeric methylene diphenyl diisocyanate (polymeric MDI) aerosol in rats.

Four groups of 60 Wistar rats of each sex were exposed by inhalation to 0, 0.2, 1.0, or 6.0 mg/m3 respirable polymeric methylene diphenyl diisocyanate (polymeric MDI) aerosol (93.5% < 4.2 microns) for 6 hr a day, 5 days a week for up to 24 months. In addition, satellite groups of 10 rats/sex/group received the same treatment for 12 months. There was no adverse effect on general health, survival, body weight, or hematological or clinical chemistry parameters. Lung weights were increased in both males and females exposed to 6.0 mg polymeric MDI/m3 for 12 or 24 months. Gross examination at autopsy of males exposed to 6.0 mg polymeric MDI/m3 for 24 months revealed an increased incidence of spotted and discolored lungs. Increased incidences of degeneration and basal cell hyperplasia of the nasal olfactory epithelium, often accompanied by hyperplasia of Bowman's glands, were found in the 1.0 and 6.0 mg/m3 groups. Light and electron microscopic studies of the lungs revealed accumulations of alveolar macrophages containing polymeric MDI-associated refractile yellowish material at the level of the alveolar duct in all exposed groups. Alveolar duct epithelialization as well as fibrosis of tissues surrounding the macrophage accumulations occurred at the 1.0 and 6.0 mg/m3 exposure levels. In addition, increased incidences of calcareous deposits and localized alveolar bronchiolization were seen in the 6.0 mg/m3 group. Moreover, eight pulmonary adenomas (six in males and two in females) and one pulmonary adenocarcinoma (in a male) were observed in the 6.0 mg/m3 exposure group. The time sequence of the spectrum of pulmonary changes indicates that recurrent alveolar wall damage by polymeric MDI and/or polymeric MDI-containing alveolar macrophages leads to alveolar bronchiolization and ultimately to bronchioloalveolar tumors. No lung tumors were found in the lower concentration groups and in the control group. The incidence and distribution of other types of tumors were not influenced by polymeric MDI. It was concluded that in the present study, the "no-observed-adverse-effect level" of polymeric MDI was 0.2 mg/m3, and that chronic exposure to polymeric MDI at a level of 6.0 mg/m3 was related to the occurrence of pulmonary tumors. It was also concluded that exposure to polymeric MDI at concentrations not leading to recurrent lung tissue damage will not produce pulmonary tumors.

Alternative acute inhalation toxicity testing by determination of the concentration-time-mortality relationship: experimental comparison with standard LC50 testing.

A new design for acute inhalation toxicity testing was evaluated and compared with results obtained according to OECD guideline 403. The new design consists of a range-finding test, which is compatible with a conventional limit test, and can be followed by determination of a concentration-time-mortality relationship, enabling calculation of LC50 (50% mortality exposure concentration) values. By exposing pairs of rats for different periods of time to about four different test concentrations in a nose-only exposure unit, LT50 (50% mortality exposure time) values were obtained for five pairs of animals per concentration. The mortality data of the approximate 20 time-concentration combinations were used to calculate the probit relationship. Estimated mortality responses from these probit relations were compared with mortality figures obtained by exposing groups of five male rats and five female rats whole-body according to conventional toxicity testing. In general, there was good correspondence between the estimated and the observed mortality response. In our hands, the determination of the concentration-time-mortality relationship takes about the same number of animals (40-50) as the conventional LC50 procedure according to the OECD guideline 403. However, the new method has several additional advantages such as: (A) LC50 values are obtained over a 10-fold range in time, with the potential of decreasing the number of animals used when regulations require acute toxicity data for different periods of exposure. (B) The obtained relationship contains considerably more valuable information for risk assessment than the LC50 value.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute and sub-acute inhalation toxicity of germanium metal powder in rats.

An acute (4-hr) and a sub-acute (4-wk) inhalation toxicity study of germanium metal powder (purity 99.8%, mean particle size 2.0-2.4 microns) were carried out in young adult Wistar rats. Exposure of five male and five female rats to 3.86 or 5.34 g/m3 for 4 hr resulted in the death of one rat at each exposure level. Four groups of five male and five female rats were exposed to 0, 9.9, 65.1 or 251.4 mg/m3 for 6 hr/day, 5 days/wk for 30 days. Two additional (recovery) groups of five male and five female rats exposed to 0 or 251.4 mg/m3 were kept untreated for 31 days after exposure. At the end of the treatment period, fasting blood glucose was decreased in males exposed to the high concentration. In females of this group, blood creatinine and urea levels, and urine volumes were increased, but urine density was decreased. Increased blood creatinine levels and urine volume and decreased urine density were also observed in females exposed to 65.1 mg/m3. The absolute and relative lung weights were increased in rats in the mid-and high-concentration groups. Histopathological examination revealed: accumulation of particulate material in the lungs of all treated groups, accumulation of alveolar macrophages in the mid- and high-concentration groups, and alveolitis mainly in the high-concentration group. After the 4-wk recovery period, urine volume was increased in males that had been exposed to germanium. In exposed rats of both sexes, lung weights were still increased and histopathological changes were present, but to a lesser extent than at the end of the exposure period. It was concluded that the 4-hr LC50 value of germanium metal powder in rats is greater than 5.34 g/m3. The no-adverse-effect level in the 4-wk study was 9.9 mg/m3 air.