Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Threshold Limit Values”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources
PubMedDate not supplied

A structure-activity relationship of some chlorinated hydrocarbons.

Partition coefficients of water/air, blood/air, oil/air, and oil/water for twenty chlorianted hydrocarbons, which were determined by means of a vial-equilibration method, were examined in relation to their chemical structures and threshold limit values (TLVs) recommended by the American Conference of Governmental Industrial Hygienists. The TLV was correlated closely with the blood/air partition coefficient and with the product of the water/air and the oil/air partition coefficient except for carbon tetrachloride and o-dichlorobenzene. A relation between partition coefficients and toxicity of these hydrocarbons is also described.

Air↗
PubMedDate not supplied

Effect of hydrogen sulfide on bacterial inactivation in the rat lung.

This study evaluated the effect of a low concentration of hydrogen sulfide on the rat antibacterial defense system. Rats exposed to 45 ppm hydrogen sulfide (threshold limit value for hydrogen sulfide = 10 ppm) for 4 or 6 hr exhibited a significant (P less .01) reduction in the inactivation of viable staphylococci deposited in the lungs during a bacterial aerosol challenge. Pre-exposure of rats to 46 ppm hydrogen sulfide for 2 hr, however, did not alter intrapulmonary staphylococcal inactivation. We hypothesize that impairment of the alveolar macrophage is the basis of these findings.

Aerosols↗
PubMedDate not supplied

Epidemiologic health study of workers in an aluminum smelter in Kitimat, B.C. II. Effects on musculoskeletal and other systems.

A health study was carried out on 2066 workers in an aluminum smelter in Kitimat, British Columbia to study the effects of exposure to fluoride and other air contaminants encountered on the potlines on the musculoskeletal system, hemopoietic tissue, liver, and renal function. Three hundred seventy-two railway repair workers from Squamish, British Columbia served as an "external" control group. Examination of the spine and sacroiliac joints and pelvic X-ray were conducted on long-term potline workers and a number of "internal" control workers in the smelter not exposed to any air contaminants. Urinary fluoride measurements and personal sampling for airborne fluoride were also carried out. Blood samples were collected for routine blood count and liver and renal function test. Definite cases of skeletal fluorosis were not found in any potroom workers. Some of the changes of early skeletal fluorosis described on pelvic X-rays, e.g., increased density, calcification of ligaments, and periosteal changes, were found in a few workers who were employed on the potlines for more than 10 yr. There was, however, poor agreement in the findings of the two radiologists who read the films. The entity "musculoskeletal fluorosis" does not exist in this smelter where the potroom workers were exposed to total fluoride levels below the currently accepted threshold limit value of 2.5 mg/m3. No ill effects on the hematopoietic tissue or liver and renal function were found.

Air Pollutants↗
PubMedDate not supplied

Occupational exposure to 1,3-dichloropropene (Telone II) in Hawaiian pineapple culture.

1,3-dichloropropene (DCP), the primary constituent of Telone II, is a subsoil fumigant that has supplanted 1,2-dibromo-3-chloropropane (DBCP) and ethylene dibromide (EDB) as primary fumigant in Hawaiian pineapple culture. To determine the potential for adverse health effects, an environmental survey was done to assess worker exposures. Exposures were predominantly below 1 ppm, which is the no-effect level determined with experimental animals, and the Threshold Limit Value (TLV) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH).

Agriculture↗
PubMedDate not supplied

Epidemiological study of the systemic ophthalmological effects of carbon disulfide.

A total of 123 male viscose rayon workers who were exposed to carbon disulfide, and an additional 67 workers who were not exposed to any toxic agent in the working environment, underwent a thorough ophthalmological examination. The relationship between exposure and ophthalmological results was analyzed with univariate and multivariate methods. The most striking findings were strong associations between exposure and the 100-HUE color vision score and excess of microaneurysms in the exposed group. The current threshold limit value appeared to protect against these effects.

Adult↗
PubMed1995

Effects of thermal, personal and behavioural factors on the physiological strain, thermal comfort and productivity of Australian shearers in hot weather.

Multiple-regression analyses were used to evaluate the separate and combined effects of factors that are commonly expected to influence strain and productivity in a hot workplace. Forty-three men were studied throughout 54 man-days of shearing sheep and pressing wool bales, in air temperatures 19-41 degrees C and Wet-bulb Globe Temperature index (WBGT) 16-29 degrees C; 43% of the observations of WBGT exceeded 26.7 degrees C, the Threshold Limit Value (TLV) for the subjects' work rate of 400 W. Subjects were men of age 18-59 years, fat-free mass 44-77 kg, and body fat content 11-26%, who had drunk an estimated 0-207 g alcohol the previous evening. Afternoon mean values of rectal temperature (Tre) exceeded 38.0 degrees C (maximum 38.4 degrees C) in 4 of the 15 observations made when WBGT > TLV, and in none of those made when WBGT < TLV. Over the 10 h work day the subjects sweated 2.4-9.9 kg, but they replaced their sweat losses so successfully that warmer weather and heavier sweating were not accompanied by significantly greater dehydration. Surprisingly, the fatter men felt cooler, and those who had drunk more alcohol the previous evening had lower Tre and tended to be more productive. Age was not associated with any measured response. All factors together explained barely half the observed variation in Tre and thermal comfort, and almost none of the variation in productivity. The findings highlight the uncertainty inherent in attempts to define safe limits for occupational heat stress; they show how such uncertainty could restrict the usefulness in the shearing industry of the current heat-stress guidelines; and they demonstrate the effectiveness of the behavioural responses that permit shearers to perform sustained strenuous work in a hot environment without excessive physiological strain.

Adolescent↗
PubMed2002

Airborne concentrations of benzene due to diesel locomotive exhaust in a roundhouse.

Concentrations of airborne benzene due to diesel exhaust from a locomotive were measured during a worst-case exposure scenario in a roundhouse. To understand the upper bound human health risk due to benzene, an electromotive diesel and a General Electric four-cycle turbo locomotive were allowed to run for four 30-min intervals during an 8-h workshift in a roundhouse. Full-shift and 1-h airborne concentrations of benzene were measured in the breathing zone of surrogate locomotive repairmen over the 8-h workshift on 2 consecutive days. In addition, carbon monoxide was measured continuously; elemental carbon (surrogate for diesel exhaust) was sampled with full-shift area samples; and nitrogen dioxide/nitric oxide was sampled using full-shift and 15-min (nitrogen dioxide only) area samples. Peak concentrations of carbon monoxide ranged from 22.5 to 93 ppm. The average concentration of elemental carbon for each day of the roundhouse study was 0.0543 and 0.0552 microg/m(3 )for an 8-h workshift. These were considered "worst-case" conditions since the work environment was intolerably irritating to the eyes, nose, and throat. Short-term nitrogen dioxide concentrations ranged from 0.81 to 2.63 ppm during the diesel emission events with the doors closed. One-hour airborne benzene concentrations ranged from 0.001 to 0.015 ppm with 45% of the measurements below the detection limit of 0.002-0.004 ppm. Results indicated that the 8-h time-weighted average for benzene in the roundhouse was approximately 100-fold less than the current threshold limit value (TLV) of 0.5 ppm. These data are consistent with other studies, which have indicated that benzene concentrations due to diesel emissions, even in a confined environment, are quite low.

Air Pollution, Indoor↗
PubMed2006

The toxicological response of Brazilian chrysotile asbestos: a multidose subchronic 90-day inhalation toxicology study with 92-day recovery to assess cellular and pathological response.

Inhalation toxicology studies with chrysotile asbestos have in the past been performed at exceedingly high doses without consideration of fiber number or dimensions. As such, the exposures have exceeded lung overload levels, making quantitative assessment of these studies difficult if not impossible. To assess the cellular and pathological response in the rat lung to a well-characterized aerosol of chrysotile asbestos, a 90-day subchronic inhalation toxicology study was performed using a commercial Brazilian chrysotile (CA 300). The protocol was based on that established by the European Commission for the evaluation of synthetic vitreous fibers. The study was also designed to assess the potential for reversibility of any such changes and to permit association of responses with fiber dose in the lung and the influence of fiber length. Wistar male rats were randomly assigned to an air control group and to 2 CA 300 exposure groups at mean fiber aerosol concentrations of 76 fibers L > 20 microm/cm3 (3413 total fibers/cm3; 536 WHO fibers/cm3) or 207 fibers L > 20 microm/cm3 (8941 total fibers/cm3; 1429 WHO fibers/cm3). The animals were exposed using a flow-past, nose-only exposure system for 5 days/wk, 6 h/day, during 13 consecutive weeks (65 exposures), followed by a subsequent nonexposure period lasting for 92 days. Animals were sacrificed after cessation of exposure and after 50 and 92 days of nonexposure recovery. At each sacrifice, subgroups of rats were assessed for the determination of the lung burden; histopathological examination; cell proliferation response; bronchoalveolar lavage with the determination of inflammatory cells; clinical biochemistry; and for analysis by confocal microscopy. Through 90 days of exposure and 92 days of recovery, chrysotile at a mean exposure of 76 fibers L > 20 microm/cm3 (3413 total fibers/cm3) resulted in no fibrosis (Wagner score 1.8 to 2.6) at any time point. The long chrysotile fibers were observed to break apart into small particles and smaller fibers. In vitro modeling has indicated that these particles are essentially amorphous silica. At an exposure concentration of 207 fibers L > 20 microm/cm3 (8941 total fibers/cm3) slight fibrosis was observed. In comparison with other studies, chrysotile produced less inflammatory response than the biosoluble synthetic vitreous fiber CMS. As predicted by the recent biopersistence studies on chrysotile, this study clearly shows that at that at an exposure concentration 5000 times greater than the U.S. threshold limit value of 0.1 f(WHO)/cm3, chrysotile produces no significant pathological response.

Aerosols↗
PubMed2006

Generation, sampling, and analysis for low-level GB (Sarin) and GF (Cyclosarin) vapor for inhalation toxicology studies.

This study tested and optimized various methodologies to generate, sample, and characterize GB and GF test atmospheres in an inhalation chamber, particularly at low vapor levels. A syringe drive/spray atomization system produced vapor concentrations at a range of 1-50 mg/m3. A saturator cell was used to generate vapor at sub-lethal concentrations ranging from 1 mg/m3 down to low levels approaching the threshold limit value time-weighted average (TLV-TWA) of 0.0001 mg/m3 for GB. Both generation techniques demonstrated the ability to produce stable vapor concentrations over extended exposure periods. This capability was important to determine sublethal nerve agent effects, such as miosis, for inhalation toxicology studies. In addition, the techniques employed for producing and maintaining low-level agent vapor would lay the foundation for testing less volatile chemical warfare agents such as VX.

Cholinesterase Inhibitors↗
PubMed2000

Review of occupational standards and guidelines for hand-arm (segmental) vibration syndrome (HAVS).

This article reviews the health effects, treatment, prevention strategies, and international standards for hand-arm vibration syndrome (HAVS). It draws attention to the proposed International Standards Organization (ISO) 1998 revision requirement to base the assessment of vibration on the root-sum-of-squares for all directions rather than the dominant direction; the European Economic Commission (EEC) directives with their threshold, action, and ceiling levels; and the intent of the EEC, United Kingdom, and Japanese jurisdictions to propose action levels to prevent the incidence of vibration-induced Raynaud's phenomenon (VWF) from exceeding the background level in their countries. Proposals for the revision of the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) are presented.

Arm↗
PubMed2000

The use of a task-based exposure assessment model (T-BEAM) for assessment of metal fume exposures during welding and thermal cutting.

Elevated disease rates have been documented among construction workers for cancer, pneumonoconiosis, asbestosis, and silicosis. However, methodologies for exposure assessment in construction are not well described in the U.S. literature. Working through a cooperative agreement with the National Institute for Occupational Safety and Health (NIOSH), the Center to Protect Workers' Rights--a research arm of the Building and Construction Trades Department, AFL-CIO--has developed and used a "Task-Based Exposure Assessment Model (T-BEAM)" for construction. The characteristic elements of T-BEAM are: (1) an emphasis on the identification, implementation, and evaluation of engineering and work practice controls; and (2) use of experienced, specially trained construction workers (construction safety and health specialists) in the exposure assessment process. A task-based approach was used because tasks, or specialized skills, form the single greatest thread of continuity in the dynamic environment of construction. Workers in the construction industry come from several crafts and are typically employed by a large number of contractors throughout their career. Project types (e.g., residential or industrial rehabilitation) are also highly variable and present unique health risks. Finally, because construction involves building, renovating, or dismantling physical surroundings, the work site is constantly changing. Between 1995 and 1996, T-BEAM was applied to the collection of approximately 200 personal exposure measurements associated with "hot work tasks"--welding and thermal cutting. Data were collected with the assistance of specially trained, journeyman ironworkers, pipe fitters, and boilermakers on nine construction sites located throughout the United States. Portable local exhaust ventilation was provided to participating contractors with the intent of measuring its impact on exposure. Results indicate that data collected in a standardized, systematic fashion from multiple work sites can be used to characterize exposures among sampled trades. Comparison of results to American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs) demonstrate a significant health hazard among sampled trades posed by welding and thermal cutting fume, manganese, nickel, and chromium VI. Direct estimates of the probability of exceeding the ACGIH TLV for respirable particulate suggests that boilermakers (100%) and ironworkers (71%) are at greatest risk. Other task variables evaluated with respect to exposure include task, whether work was performed indoors or outdoors, intermittency of work, and use of ventilation. Use of local or mechanical ventilation reduced mean exposures to fumes significantly.

Adult↗
PubMed2000

Manganese dioxide exposures and respirator performance at an alkaline battery plant.

Two industrial hygiene studies were conducted at an alkaline battery plant to evaluate worker exposures to manganese dioxide particulate and the effectiveness of filtering facepiece respirators. The work areas studied included the plant's powder-processing tower and press rooms where manganese was blended, compacted with graphite, and inserted into battery cans. Full-shift personal breathing zone monitoring was conducted to estimate manganese dust exposures of press operators, mechanics, and material handlers. In-facepiece and personal breathing zone air sampling pairs were also collected using a program protection factor protocol to estimate the protection provided by the respirators. Particle size evaluations were made using nylon cyclones and Marple personal multi-stage impactors. All samples were analyzed for manganese by inductively coupled argon plasma, atomic emission spectroscopy via NIOSH analytical method 7300 utilizing a modified acid digestion procedure. Fifty-four, full-shift, time-weighted average (TWA) exposures to total manganese ranged from 0.1 to 5.4 milligrams per cubic meter (mg/m3); worker exposures were substantially lower during a follow-up study due to engineering control improvements. Concurrent area sample comparisons of total and respirable manganese revealed that the respirable particulate mass fractions ranged from 6 to 32 percent, and mass median aerodynamic diameters determined from personal breathing zone air samples were mostly greater than 10 micrometers. Fifteen respirator performance evaluations were conducted using Moldex 2200 respirators fitted with 25 millimeter cassettes and light weight sampling probes. Protection factors ranged from 5 to 220, with a geometric mean and standard deviation of 31 and 2.97, respectively. The 5th percentile protection factor estimate was 5, as calculated from the protection factor distribution for this sample set. In 1995, the American Conference of Governmental Industrial Hygienists (ACGIH) lowered the elemental and inorganic manganese dust Threshold Limit Value (TLV) from 5 mg/m3 to 0.2 mg/m3 to address adverse pulmonary and central nervous system effects and male infertility. Although most personal breathing zone concentrations were above 0.2 mg/m3, none of the in-facepiece concentrations exceeded this concentration. Parkinson's-like symptoms have been reported in the literature for high manganese dust and fume exposures, but the importance of low dust exposures for producing neurological effects is uncertain.

Adult↗
PubMed2000

Exposures to 1,6-hexamethylene diisocyanate during polyurethane spray painting in the U.S. Air Force.

1,6-Hexamethylene diisocyanate (HDI) exposures were measured during polyurethane enamel spray painting at four Air Force bases. Breathing zone samples were collected for HDI monomer and polyisocyanates (oligomers) using three sampling methods: NIOSH Method 5521, the Iso-Chek sampler, and the total aerosol mass method (TAMM). Exposures to HDI monomer are low when compared to current occupational exposure limits; the highest 8-hr time-weighted average (TWA) exposure found was 3.5 micrograms/m3, below the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 34 micrograms/m3. HDI oligomer levels were higher; mean task exposures indicated by either the Iso-Chek sampler or TAMM are above the Oregon ceiling limit of 1 mg/m3. Eight-hour TWA exposures, however, were much lower, with only one exceeding the Oregon standard of 0.5 mg/m3. Poor worker practices commonly observed during this study included: standing in downwind positions so paint overspray passed through breathing zones; spraying toward other painters; and using excessive paint spray gun air cap pressures. Workers should stand in upwind orientation relative to the aircraft being painted, causing overspray to move away from the painter's breathing zone; adjust their position to prevent spraying other painters or limit paint application to one worker at a time; and use air cap pressure gauges prior to spraying to limit spray gun air cap pressures and reduce paint overspray generation rates. These improved techniques will result in reduced worker exposures to isocyanates.

Aerosols↗
PubMed2000

Assessment of exposure to manganese in welding operations during the assembly of heavy excavation machinery accessories.

Welder exposure to metals in various industrial sectors is poorly characterized. We had the opportunity to carry out an exploratory study to characterize manganese exposure in welding operations in a recently established Quebec factory that assembled accessories for heavy excavation machinery. Ten workers were sampled for total manganese for at least two consecutive days out of three followed by two consecutive days for respirable manganese (with a size selective sampler with a median cut-off of 4 microns), during a typical week in the summer of 1998. Parts being welded were characterized as large or small. Small parts were those being welded on tables during subassembly. Workers were divided into two groups according to the parts they were welding. Seventy-eight percent of the total manganese exposure levels of welding operations during the assembly of large accessories of heavy excavation machinery exceeded the manganese American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 0.20 mg/m3 (GM 0.24 mg/m3, n = 14) while none exceeded the TLV during the assembly of small pieces (GM 0.06 mg/m3, n = 8). Welding operations during the assembly of large heavy excavation machinery accessories may pose a significant health hazard. Considering the importance of task-related variables affecting exposure among workers, further studies are needed to better characterize exposure determinants of welding operations during the assembly of heavy excavation machinery accessories.

Adult↗
PubMed2000

Metal exposure among abrasive blasting workers at four U.S. Air Force facilities.

Button Aerosol Samplers were used to monitor the personal exposure of workers performing abrasive blasting operations at four U.S. Air Force facilities. Inhalable aerosols containing 25 metals, including cadmium, lead, and chromium, were investigated. The Button Aerosol Sampler was chosen because of its ability to successfully withstand mechanical stress, prevent very large particles from collection, and protect the filter from overloading and shredding by rebound particles. In addition, previous studies have shown that the sampling efficiency of this personal Aerosol Sampler exhibits low sensitivity to the ambient air conditions and that it adequately follows the inhalability convention. Inductively coupled plasma (ICP) was used to analyze the collected samples for all 25 metals. In addition, visual absorption spectrophotometry (VAS) was used to analyze for hexavalent chromium because of the presence of strontium chromate. The collected samples yielded 8-hr time-weighted average (TWA) concentrations that were up to 250, 6, and 5 times higher than the permissible exposure limits (PELs) for cadmium, lead, and hexavalent chromium, respectively. Also, the chromium levels measured by the ICP and VAS exceeded the strontium chromate threshold limit value (TLV) by up to 640 and 950 times, respectively. No correlation was found between the ICP and VAS hexavalent chromium concentrations. The likely reasons of this were the presence of Cr (II) and (III) that cannot be detected by the VAS, and the chemical interference from iron and some other metals in the samples. The Button Aerosol Sampler was shown to be useful for the monitoring of workers' exposure to heavy metals during abrasive blasting operations.

Aerosols↗
PubMed2001

Evaluation of organic-vapor respirator cartridge efficiency for hexamethylene diisocyanate vapor in the presence of organic solvents.

Hexamethylene diisocyanate (HDI)-based polyisocyanates are widely used in formulating polyurethane coatings. These polyisocyanates contain a small amount of HDI monomer and the American Conference of Governmental Industrial Hygienists (ACGIH) recommends an eight-hour time-weighted average (TWA) threshold limit value (TLV) of 5 ppb for HDI. Some polyurethane (PU) paint applicators have used air-purifying paint spray respirators with organic vapor cartridges and particulate pre-filters. In this study, the effect of typical paint solvents on the efficiency of organic vapor cartridges (OVC) for HDI vapor was tested. A Teflon-coated polycarbonate exposure chamber was constructed. Three OVCs were simultaneously tested in an atmosphere containing HDI vapor and solvents. The test atmosphere was generated by evaporating a mixture of paint solvents containing n-butyl acetate, propylene glycol mono methyl ether acetate, toluene and methyl ethyl ketone, and neat HDI. The target challenge concentrations were 20 times the TLV for HDI and 10 times the combined TLV for the solvent mixture. The test atmosphere, with 20 or 80 percent relative humidity and at room temperature, was drawn through each cartridge at 32 L/min for 40 hours. However, in the last 8 hours of the test, the atmosphere had only HDI vapor. The pre- and the post-cartridge atmospheres were periodically sampled for HDI and the solvents. The study concluded that under the test conditions there was no detectable breakthrough of HDI from the OVCs. The average calculated efficiency of the OVCs, based on the HDI analytical limit of quantitation, was >99.4 percent for the 40 hours tested. The overall average challenge concentration of HDI was 105 ppb and the average combined solvent concentration was 3,176 mg/m3. The cartridges were saturated with solvents within the first 10 hours of testing; nevertheless, continued challenging with HDI vapor and solvents did not show any HDI breakthrough. Solvent breakthrough and breathing resistance, rather than HDI breakthrough, would be the key parameters in life expectancy calculations for cartridge change out schedules.

Cyanates↗
PubMed2001

The effects of temperature and pressure on airborne exposure concentrations when performing compliance evaluations using ACGIH TLVs and OSHA PELs.

Occupational hygienists perform air sampling to characterize airborne contaminant emissions, assess occupational exposures, and establish allowable workplace airborne exposure concentrations. To perform these air sampling applications, occupational hygienists often compare an airborne exposure concentration to a corresponding American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) or an Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL). To perform such comparisons, one must understand the physiological assumptions used to establish these occupational exposure limits, the relationship between a workplace airborne exposure concentration and its associated TLV or PEL, and the effect of temperature and pressure on the performance of an accurate compliance evaluation. This article illustrates the correct procedure for performing compliance evaluations using airborne exposure concentrations expressed in both parts per million and milligrams per cubic meter. In so doing, a brief discussion is given on the physiological assumptions used to establish TLVs and PELs. It is further shown how an accurate compliance evaluation is fundamentally based on comparison of a measured work site exposure dose (derived from the sampling site exposure concentration estimate) to an estimated acceptable exposure dose (derived from the occupational exposure limit concentration). In addition, this article correctly illustrates the effect that atmospheric temperature and pressure have on airborne exposure concentrations and the eventual performance of a compliance evaluation. This article also reveals that under fairly moderate conditions of temperature and pressure, 30 degrees C and 670 torr, a misunderstanding of how varying atmospheric conditions affect concentration values can lead to a 15 percent error in assessing compliance.

Air Pollution, Indoor↗
PubMed2001

Identifying an apppropriate occupational exposure limit (OEL) for beryllium: data gaps and current research initiatives.

The occupational exposure limit of 2.0 microg/m3 for beryllium has been used in the workplace since the late 1940s. In particular, the adequacy of the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for beryllium has recently come into question. The symposium "Beryllium: Effect on Worker Health" was convened in September 1999, to bring together leading scientists to present and discuss current research activities on beryllium exposure and chronic beryllium disease (CBD). One of the key questions to be resolved at the symposium was, "Is there a sufficient understanding of exposure and the cause of CBD that would allow us to develop a TLV that we believe would prevent disease?" Seven scientists presented information regarding the current understanding of the disease, possible causes, and ongoing research. The topics were (1) biomonitoring approaches and their relationship with clinical effects, (2) historical and current exposure assessments, (3) sampling methods and aerosol characterization, and (4) epidemiology. Six basic hypotheses regarding the relationship between exposure to beryllium and CBD were generated from the information presented at the symposium. The six hypotheses that are related to issues such as beryllium form, particle size, industrial hygiene practices, extrapulmonary routes of exposure, and genetic susceptibility also appear to be the focus of ongoing and likely future research initiatives. This article summarizes both the presentations made at the meeting and the hypotheses generated. It is expected that an understanding of these issues should explain the inconsistent dose-response relationship observed between exposure and CBD. The ongoing and planned research is anticipated to provide sufficient data within two to three years to develop one or more scientifically sound TLVs for the different chemical forms of beryllium.

Air Pollutants, Occupational↗