Animal Exposure Chamber Research Articles

Durational Effect of Cement Dust Exposure on Haematological Profile of Albino Rat

Background: This research work studied the durational effects of cement dust inhalation on the haematological parameters of exposed Albino rats. In this study, a glass house animal exposure chamber was fabricated using a plexi-glass and two blowing fans of adjustable revolution.
 Methodology: Twenty five Albino rats were divided into five groups. Group A served as the control, while group B, C, D and E served as the test, and were exposed for 15, 30, 45 and 60 days interval respectively, for one hour daily to cement dust (200g), at a revolution of 3000rpm of the fans. At the end of the exposure, the animals were sacrificed, blood collected in EDTA bottle and was analysed for some haematological variables.
 Results: The result showed that there were significant durational increase (p < 0.05) in the levels of Packed Cell Volume (PCV), Haemoglobin (Hb), Red Blood Cell (RBC), Lymphocyte, Monocytes and Eosinophils of the test group compared to control group but there was no significant difference in the Wbc, Basophils, Platelets and Neutrophils levels among the groups (p >0.05).
 Conclusion: There is a durational exposure haematotoxic effect of cement dust inhalation on rat exposed to cement dust.

Exposure-Time Effect of Cement Dust on Liver Organ in Rat (Rattus norvegicus)

Background: The purpose of this research was to compare the effect of duration of cement dust on the liver organ of albino rats. In this study, a glass house animal exposure chamber was fabricated using a plexi-glass and two blowing fans of adjustable revolution.
 Methodology: A total of twenty five rats averagely weighing 135g were used and categorized into five groups composed of 5 rats each: A group (without cement exposure); B group (exposed to 200g of cement dust for 1 hour daily for 15days); C group (exposed to 200g of cement dust for 1 hour daily for 30 days); D group (exposed to 200g of cement dust for 1 hour daily for 45 days) and E group (exposed to 200g of cement dust for 1 hour daily for 60 days). The means of exposure was by inhalation. After the exposure periods, the animals were sacrificed, blood collected in plain bottle and analyzed for some liver function.
 Results: The ANOVA result showed that there were significant changes (p < 0.05) in the levels of some liver function markers such as alkaline phosphatase (ALP), Total protein (TP), Albumin and Conjugated bilirubin (CB), and the alteration patterns were irregular. On the other hand, there were no changes (p>0.05) in the levels of Aspartate amino transferase (AST), Alanine amino transferase (ALT) and Total bilirubin (TB) among the groups.
 Conclusion: This study has therefore shown that exposure to cement may cause some decrease of liver injury in rats regardless of the duration of the exposure.

Establishment and characterization of a multi-purpose large animal exposure chamber for investigating health effects.

Air pollution poses a significant threat to the environment and human health. Most in vivo health studies conducted regarding air pollutants, including particulate matter (PM) and gas phase pollutants, have been either through traditional medical intranasal treatment or using a tiny chamber, which limit animal activities. In this study, we designed and tested a large, whole-body, multiple animal exposure chamber with uniform dispersion and exposure stability for animal studies. The chamber simultaneously controls particle size distribution and PM mass concentration. Two different methods were used to generate aerosol suspension through either soluble material (Alternaria extract), liquid particle suspension (nanosilica solution), or dry powder (silica powder). We demonstrate that the chamber system provides well controlled and characterized whole animal exposures, where dosage is by inhalation of particulate matter.

A dry powder combination of pyrazinoic acid and its n-propyl ester for aerosol administration to animals

Combining the advantage of higher efficacy due to local pulmonary administration of pyrazinoic acid (POA) and potent effect of pyrazinoic acid ester (PAE) delivered as an aerosol would aid in tuberculosis therapy. A combination spray dried dry powder, composed of POA, PAE (n-propyl POA), maltodextrin and leucine, was prepared for aerosol delivery to animals. Solid-state characteristics of morphology (scanning electron microscopy) crystallinity (X-ray powder diffraction), thermal properties (thermogravimetric analysis and differential scanning calorimetry) and moisture content (Karl Fisher) were evaluated. Particle size distributions, by volume (laser diffraction) for the dispersed powder and by mass (inertial impaction) were determined. Efficient delivery of the powder to a nose only animal exposure chamber employed a novel rotating brush/micro-fan apparatus. Spherical, crystalline particles were prepared. The volume median diameter, ∼1.5μm, was smaller than the mass median aerodynamic diameter, ∼3.0μm, indicating modest aggregation. Drug content variations were observed across the particle size distribution and may be explained by PAE evaporative losses. Delivery to the nose-only exposure chamber indicated that boluses could be administered at approximately 3min intervals to avoid aerosol accumulation and effect uniform dose delivery with successive doses suitable for future pharmacokinetic and pharmacodynamic studies.

Design, Construction, and Characterization of a Novel Robotic Welding Fume Generator and Inhalation Exposure System for Laboratory Animals

Respiratory effects observed in welders have included lung function changes, metal fume fever, bronchitis, and a possible increase in the incidence of lung cancer. Many questions remain unanswered regarding the causality and possible underlying mechanisms associated with the potential toxic effects of welding fume inhalation. The objective of the present study was to construct a completely automated, computer-controlled welding fume generation and inhalation exposure system to simulate real workplace exposures. The system comprised a programmable six-axis robotic welding arm, a water-cooled arc welding torch, and a wire feeder that supplied the wire to the torch at a programmed rate. For the initial studies, gas metal arc welding was performed using a stainless steel electrode. A flexible trunk was attached to the robotic arm of the welder and was used to collect and transport fume from the vicinity of the arc to the animal exposure chamber. Undiluted fume concentrations consistently ranged from 90–150 mg/m3 in the animal chamber during welding. Temperature and humidity remained constant in the chamber during the welding operation. The welding particles were composed of (from highest to lowest concentration) iron, chromium, manganese, and nickel as measured by inductively coupled plasma atomic emission spectroscopy. Size distribution analysis indicated the mass median aerodynamic diameter of the generated particles to be approximately 0.24 μm with a geometric standard deviation (σ g ) of 1.39. As determined by transmission and scanning electron microscopy, the generated aerosols were mostly arranged as chain-like agglomerates of primary particles. Characterization of the laboratory-generated welding aerosol has indicated that particle morphology, size, and chemical composition are comparable to stainless steel welding fume generated in other studies. With the development of this novel system, it will be possible to establish an animal model using controlled welding exposures from automated gas metal arc and flux-cored arc welding processes to investigate how welding fumes affect health.

Development of an animal model to study the potential neurotoxic effects associated with welding fume inhalation

Serious questions have been raised regarding a possible causal association between neurological effects in welders and the presence of manganese in welding fume. An experimental model is needed that could examine the potential neurotoxic effect of manganese after pulmonary exposure to welding fume. The National Institute for Occupational Safety and Health (NIOSH) has recently finished construction of a completely automated, computer controlled welding fume generation and inhalation exposure system for laboratory animals. The system is comprised of a programmable six-axis robotic welding arm and a water-cooled arc welding torch. A flexible trunk has been attached to the robotic arm of the welder and is used to collect and transport fume from the vicinity of the arc to the animal exposure chamber. Preliminary fume characterization studies have indicated that particle morphology, size, and chemical composition were comparable to welding fume generated in the workplace. Animal inhalation studies are currently underway. With the development of this novel system, an animal model has been established using controlled welding exposures to investigate the possible mechanisms by which welding fume may affect the central nervous system.

Urinary benzo[a]pyrene and its metabolites as molecular biomarkers of asphalt fume exposure characterized by microflow LC coupled to hybrid quadrupole time-of-flight mass spectrometry.

As a step to study the health effects of asphalt fume exposure, an analytical method was developed to characterize benzo[a]pyrene and its hydroxy metabolites in the urine of asphalt fume-exposed rats. This method is based on microflow liquid chromatography (LC) coupled to hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometry (Q-TOFMS). Twenty-four female Sprague-Dawley rats were used in the experiment, with 8 as controls and 16 exposed to asphalt fumes in a whole-body inhalation chamber for 10 days (4 h/day). Generated at 150 degrees C, the asphalt fume concentration in the animal exposure chamber ranged 76-117 mg/m(3). In the urine of the asphalt fume-exposed rats, benzo[a]pyrene and its metabolites of 3-hydroxybenzo[a]pyrene, benzo[a]pyrene-7,8-dihydrodiol(+/-), and benzo[a]pyrene-7,8,9,10-tetrahydrotetrol(+/-) were identified, and their concentrations were determined at 2.19 +/- 0.49, 16.17 +/- 0.3, 6.28 +/- 0.36, and 29.35 +/- 0.26 ng/100 mL, respectively. The metabolite concentrations from the controlled group, however, were either under the detection limits or at a relatively very low level (0.19 +/- 0.41 ng/100 mL for benzo[a]pyrene-7,8,9,10-tetrahydrotetrol metabolite). The results clearly indicate that the benzo[a]pyrene and its hydroxy metabolites were significantly elevated (p < 0.001) in the urine of asphalt fume-exposed rats relative to controls. The study also demonstrated that the combination of microflow LC separation and collision-induced dissociation leading to a characteristic fragmentation pattern by hybrid Q-TOFMS offers a distinct advantage for the identifications and characterizations of the benzo[a]pyrene metabolites.

Characterization of DNA adducts from lung tissue of asphalt fume-exposed mice by nanoflow liquid chromatography quadrupole time-of-flight mass spectrometry

A bioanalytical method based on nanoflow liquid chromatography coupled to a hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometry was developed to characterize selected polyaromatic hydrocarbon (PAH)–DNA adducts. The collision-induced dissociation of analytes results in characteristic fragmentation patterns that can be utilized to identify the DNA adducts. In the experiment, 32 B6C3F1 mice were exposed daily (4 h/day) to asphalt fume in a whole-body inhalation chamber for 10 days; 16 nonexposed mice served as controls. The asphalt fume was generated at 180 °C and the concentrations of PAHs in the animal exposure chamber ranged from 152 to 198 mg/m 3. The DNA adducts N 2-deoxyguanosine-benzo( a)pyrene-7,8-dihydrodiol-9,10-epoxide ( N 2-dG-BPDE); N 6-deoxyadenosine-benzo( a)pyrene-7,8-dihydrodiol-9,10-epoxide ( N 6-dA-BPDE), and N 4-deoxycytidine-benzo( a)pyrene-7,8-dihydrodiol-9,10-epoxide ( N 4-dC-BPDE) were identified. The concentrations of N 2-dG-BPDE, N 6-dA-BPDE, and N 4-dC-BPDE adducts were determined to be 1.17, 0.97, and 0.68 pmol/mg DNA, respectively, in the lung tissue of exposed mice using the nanoflow technique. The total DNA adducts in exposed lung tissue was determined to be 8.35 pmol/mg DNA by 32P-postlabeling assay. In total, the results indicated that PAH–DNA adducts were significantly elevated ( p<0.001) in the lung tissue of asphalt-fume-exposed mice relative to tissue from control animals.

Identification and quantification of urinary benzo[a]pyrene and its metabolites from asphalt fume exposed mice by microflow LC coupled to hybrid quadrupole time-of-flight mass spectrometry.

Prolonged, extensive exposure to asphalt fume has been associated with several adverse health effects. Inhaled polycyclic aromatic hydrocarbons (PAHs) from asphalt fume exposure have been suspected of inducing such effects. In this study, a bioanalytical method was proposed and evaluated to identify and quantify benzo[a]pyrene and its hydroxy-metabolites. This method is based on coupling a microflow liquid chromatography (LC) to a hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometry (Q-TOFMS). In the experiment, thirty-two B6C3FI mice were exposed to asphalt fume in a whole body inhalation chamber for 10 days (4 h day(-1)) and twelve other mice were used as controls. The asphalt fume was generated at 180 degrees C and the concentrations in the animal exposure chamber ranged 175-182 mg m(-3). Benzo[a]pyrene and its metabolites of 3-hydroxybenzo[a]pyrene, benzo[a]pyrene-7,8-dihydrodiol(+/-), benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide(+/-), and benzo[a]pyrene-7,8,9,10-tetrahydrotetrol(+/-) in the urine of asphalt fume exposed mice were identified and found at 3.18 ng 100 mL(-1), 31.36 ng 100 mL(-1), 11.56 ng 100 mL(-1), 54.92 ng 100 mL(-1), and 45.23 ng 100 mL(-1) respectively. The results revealed that the urinary benzo[a]pyrene and its hydroxy-metabolites from exposed mice were at significantly higher levels (p < 0.001) than those from the control groups. Compared with several other technologies such as HPLC-UV and HPLC-fluorescence, the new method is more sensitive and selective, and it can also provide additional useful information on the structures of the metabolites. Hence, this method can be used to perform the assessment and to study the mechanisms of the adverse health effects. The fragmentation patterns established in this study can also be used to identify and quantify PAH metabolites in other biological fluids.

Development and validation of a new bitumen fume generation system which generates polycyclic aromatic hydrocarbon concentrations proportional to fume concentrations.

Bitumen fumes emitted during road paving and roofing contain polycyclic aromatic compounds (PACs) of potential health concern. Little information is available for an experimental device devoted to inhalation experiments with animals exposed to bitumen fumes, and in all studies the systems were never validated for a range of fume concentrations, which prohibited their use for toxicological concentration-effect studies. Therefore, the purpose of this study was to validate a new experimental device able to generate bitumen fumes at different total particulate matter (TPM) concentrations with a linear correlation between TPM and the concentrations of different PACs, thus allowing toxicological dose-response studies with fumes representative of those in the field. Atmosphere samples collected from an animal exposure chamber allowed the determination of TPM, toluene soluble matter, polycyclic aromatic hydrocarbons (PAHs) and semi-volatiles. The particulate size distributions were determined in order to assess the deposition pattern in the respiratory tract. The temperature of 170 degrees C was chosen by analogy with the upper range of the temperature used during paving operations. The temperature of the air passing over the fume emission area was regulated to 20 degrees C and stirring of the heated bitumen was restricted to 90 r.p.m. The data show that the objective of developing a static fume generation system that reproducibly produces fumes in the inhalation chamber for specified target concentrations (TPM) were successful. The within-day variation coefficients for TPM were between 2.5 and 6.1%. The day-to-day variations for TPM concentration were between 4.1 and 5.8%. The concentrations of the 4-5 ring PAHs and the polycyclic aromatic sulphur heterocycles were proportional to the TPM concentration. The 2 and 3 ring PAH concentrations showed a deviation from proportionality with the TPM, probably due to their re-evaporation during sampling. The mass median aerodynamic diameter of airborne particles varied from 1.4 micro m at a fume concentration of 5 mg/m(3) to 3.2 micro m at 100 mg/m(3). In conclusion, this equipment was suitable for nose-only inhalation studies in the 5-100 mg/m(3) range of TPM. Bitumen fumes were generated with a good reproducibility under well-controlled conditions. Finally, the PAH profiles from atmospheric samples were in good agreement with those measured during road paving.

Improvement in high altitude hypoxic stress tolerance in albino rats on oral glutamate supplementation

Hypoxia results in body weight loss due to anorexia and hypophagia and reduced human performance. The present study was undertaken to evaluate the role of oral glutamate administration with food and water in improvement in hypoxic tolerance, if any. The placebo controlled study revealed that supplementation of optimal dose of glutamate (Glu) promoted hypoxic tolerance in male Sprague Dawley Albino rats fed one dose daily for 5 days and exposed to continuous intermittent hypoxia of 6 hrs per day at 10,668m in an animal exposure chamber. Effect of varying dose of Glu on body weight (bw),food intake and water uptake were studied which revealed the optimal dose of Glu to be 27mgKg bw. Oral feeding of Glu resulted in improved tolerance of combined stress of cold and hypoxia as measured by fall in rectal temperature from 37’C to 23’C and faster rewarming. It enhanced 5.8 times hypoxic tolerance 36% bw gain and 24% food intake in hypoxia possibly by acting as a conditionally essential amino acid under hypoxia.

Development and Evaluation of a Prototype Ambient Particle Concentrator for Inhalation Exposure Studies

A number of studies have underlined the importance of the acute and chronic effects of ambient particles on respiratory health. Because fine particles are capable of penetrating deeply into the respiratory system, most of the health studies have focused on the res-pirable portion of the particle size spectrum. Previous studies to examine exposureJ response relationships between particle exposure and adverse respiratory effects have been based on artificial preparations, or collected and resuspended ambient particles, rather than the natural material found in ambient air. Artificial particles may not be representative, and collected particles may be difficult to redisperse. In addition, the chemical and physical characteristics of ambient particles may change upon resuspension. We have developed a new technique that enables us to increase the concentration of ambient particles to levels about 10 times higher (or more, if desirableJ than their ambient values and supply them to an exposure chamber. Ambient aerosol containing particles in the size range 0.1–2.5 Aim can be concentrated using a series of two slit-nozzle virtual impactors. The intake flow rates are 1 m3Jmin and 200 Umin in the first and second virtual impactors, respectively. The virtual impactors were characterized in terms of their cutpoints and interstage losses using artificial monodisperse fluorescent aerosols as well as indoor ambient aerosols. Since the concentrated particles are maintained airborne, they can be supplied to a human or animal exposure chamber for conduction of exposure studies. The supply flow rate in the prototype concentrator is 40 Umin. Higher flow rates can be achieved by using more than one such system in parallel.

Computer Automation of a Dry-Dust Generating System

AbstractAn automated system to minimize variability in an aerosol concentration over time in an animal exposure chamber was developed. This system includes a microprocessor-controlled stepper motor to regulate the speed of a dust generator, a real-time aerosol monitor to instantaneously measure chamber aerosol concentrations, and a personal computer with an analog-to-digital (A/D) converter, serial port, and relay board for signal input and output. A computer program was written to use these devices to produce a chamber concentration near a level chosen by the operator. This program was also written to start and stop an exposure after a specified time period and to continuously display the data received from the aerosol monitor on the computer screen during the exposure. A combination of operating conditions, which include a moderately high chamber flow rate (0.32 m3/min) and high generator rotation speed while using a small scraper blade, optimized the performance of the automated system by minimizing th...

The Toxicity of Smoke from Fires Involving Perfluoropolymers: Full-Scale Fire Studies

The combustion or pyrolysis of perfluorinated resins, under cer tain laboratory conditions (e.g., the "NIST" smoke toxicity test), produces fumes which are 2-3 orders of magnitude more toxic than the smoke from common plastics or wood. To determine whether these materials show the same high level of toxicity under realistic fire conditions, a series of twenty full-scale test burns was carried out at the facilities of the Laboratory for Heat Transfer and Fuel Technology, State University of Ghent, Belgium. A metal tray holding up to 30 kg of 25-pair telecommunications cable in sulated and jacketed with fluorinated materials (Teflon® FEP and/or Teflon® PFA) was exposed to fires involving 110 kg wood cribs, or energetically equiva lent amounts of diesel fuel or polyurethane foam. The burn facility was an 8' × 12' × 8' high (2.4 m × 3.7 m × 2.4 m) masonry room connected to a 43- foot (13 m) corridor. Smoke flowed out of the burn room, down the corridor, and into a smoke collection stack. Near the end of the corridor, a portion of the smoke was extracted, diluted and cooled, and passed through one of a series of stainless steel exposure chambers, each containing ten male Sprague-Dawley rats. Temperature and fuel weight loss were measured at regular time inter vals in the burn room, as were smoke temperature and composition (CO, CO2 and fluorine analysis), as it passed down the hallway and into the smoke collec tion stack. Carbon monoxide, oxygen, fluorine content and temperature of the smoke were also monitored in the animal exposure chambers. Fires were allowed to burn for 30-40 minutes. Animals were exposed to smoke for 30 minutes, after which the surviving animals were observed for a two-week post-exposure period. Selected animals were killed and tested for blood carboxyhemoglobin (COHb) content and tissue samples from the respira tory tract were subsequently examined for histopathological characteristics. Smoke reaching the end of the corridor contained only about one-third of the theoretical amount of fluorine. Additional losses were incurred during dilution and in the animal chamber. The fluorine loss is probably attributable to deposi tion of hydrogen fluoride in the high-humidity conditions associated with com bustion. The exposed animals showed some of the effects previously attributed to combustion products of fluoropolymers, but also showed near-lethal amounts of blood COHb, attributable to carbon monoxide from the principal fuel. Simi lar results were obtained whether the fire fuel was wood or diesel fuel. Use of polyurethane foam as a fuel was found to be unsuitable. The lethal smoke con centration of the cable smoke alone, i.e., without the effects of the carbon monoxide contributed by the principal fuel, is estimated to be 1.6 mg/l, or about 80 times less toxic than would be expected based on the NIST test. This toxicity is within a factor to two of what would be expected if the princi pal toxic agent (in addition to CO) were hydrogen fluoride or carbonyl fluoride. No evidence was found for the highly toxic agent present in the NIST test, which either did not form or existed only transiently in these experiments.

Determination of Vapors of Cumene-Propanol Mixtures by Single-Beam Infrared Spectrophotometry

Abstract This investigation shows that the vapor concentration of a mixture of cumene and propanol in an animal exposure chamber can be determined by single-beam infrared spectrophotometry. The method is not influenced by deviations from Beer's law and is not dependent on the possibility of selecting wavelengths where only one of the substances absorbs the light. The determination was based on a calibration with the substances in four combinations of concentrations at two different wavelengths. A chamber trial (i.e., operating the exposure system without the presence of animals) was carried out, and the absorbance of the gas-air mixture was measured at the two wavelengths. The exposure experiment with animals was then carried out under exactly the same conditions, and the concentration in air was monitored at one of the wavelengths to ensure that no change occurred in the experimental conditions. The method was evaluated in a real toxicological investigation dealing with interactions between two solvents and was found valuable. As the analytical method is in no way limited to the two substances in case, we consider that infrared spectrophotometry offers an easy analytical method when dealing with experiments involving two-component gas mixtures.

An aerosol generator for the resuspension of cotton dust

An aerosol generator, the Pitt 3 model, was designed, fabricated, and characterized for the resuspension of inhalable particles from bulk cotton dust. The generator was constructed around a loudspeaker whose energy is transferred into an air column through latex rubber dams. This action tumbles the bulk dust, and small particles are loosened which can then be carried out of the column with the air passing through it. Thirty to forty grams of bulk cotton dust produced a stable aerosol concentration for at least 90 min. The maximum output of about 100 mg/m 3 can be reduced to lower concentrations by adding dilution air. In one application, the generator produced a stable aerosol cloud in the range of 2 to 30 mg/m 3 with a mass median aerodynamic diameter (MMAD) of about 3 μm and a geometric standard deviation (σ g) of about 1.5. In another application the concentration in an animal exposure chamber was kept at 20.8 mg/m 3 with an MMAD = 2.5 μm and a σ g = 1.8 for over 6 months. The Pitt 3 generator proved to be trouble-free and produced large amounts of inhalable particles from bulk cotton dust. The generator was also used to generate dust clouds from silica powder, fly ash, and cellulose dust. The only requirement for successful resuspension of any dust with this generator is the presence of small particles in the bulk feed dust.

Aerosol mixing in an animal exposure chamber having three levels of caging with excreta pans

Aerosol mixing in an animal exposure chamber having three levels of caging with excreta pans

Aerosol mixing in an animal exposure chamber having three levels of caging with excreta pans

To achieve uniform movement of air within an animal aerosol exposure chamber, and to meet animal husbandry requirements, we modified existing chambers in three ways: 1) air was introduced along the walls of the chamber; 2) catch pans were suspended away from chamber walls (except for the lowest level, which extended to the walls); 3) space between pans was allowed for exhaust flow. Each tier in the chamber acted like a perfectly-mixing box, resulting in clearance half-times of 3 to 6 minutes at a flow of 10 chamber equivalent volumes/hour. Concentration uniformity and aerosol buildup were measured in a full-scale chamber. We also demonstrated that measurements of flow visualization made in a reduced-scale, dynamically similar model were applicable to a full-scale chamber.

Static electrification of airborne asbestos: a study of its causes, assessment and effects on deposition in the lungs of rats.

The paper describes a series of experiments carried out in the laboratory to investigate how asbestos fibres might become electrostatically charged during the process of being made airborne, the magnitude and polarity of the charge per fibre, and the effect on lung deposition in rats. Measurements of the penetration of fibres through an electrostatic elutriator enabled the magnitude and distribution of charge in a cloud of fibres to be quantitatively assessed. Thus it was found that a typical fibre of UICC amosite, as dispersed in a typical animal exposure chamber, carried a net charge of magnitude equivalent to about 60 electrons. The distribution of charge was bimodal, suggesting that two charging mechanisms were taking place, the main one producing net negative charge and the lesser one producing net positive charge. These were attributed to materials in the dust dispenser used and with which the fibres came into contact during dispersal. It was found that the magnitude of charge on a typical fibre could be significantly reduced by the introduction of equal numbers of positive and negative gaseous ions from an a.c. corona discharge ioniser. Finally it was found that enhancement by up to 40% of the dust deposited into the slowest clearing part of the respiratory tract of experimental rats was brought about by the electrostatic charge on the airborne fibres. The implications of this finding in the field of occupational hygiene are briefly discussed.

Facilities for diesel exhaust studies

It is the major intent of this report to examine the animal inhalation facilities at the EPA Health Effects Research Laboratory in Cincinnati, Ohio, associated with the exposure to the exhaust of diesel-powered equipment. The facility serves as a center for toxicologic evaluation, in relevant animal models, of potentially hazardous environmental pollutants from diesel engine exhaust. Briefly, the entire engine exhaust is mixed with filtered and conditioned air in a dilution tube. That diluted exhaust enters a large volume mixing chamber and a portion passes through dynamic flow irradiation chambers (to simulate sunlight) and is then conducted to animal exposure chambers. The system provides nonirradiated exhaust in the same concentration (directly from the mixing chamber) and also filtered, conditioned ambient air for control animal exposure. The major physical components of the diesel emission system include: air purifiers, animal exposure chambers, engine-dynamometers, irradiation chambers, monitoring instrumentation and data acquisition systems.