Mean Exposure Levels Research Articles

Characterization of Model Error in a Simulation of Fine Particulate Matter Exposure Distributions of the Working Age Population in Helsinki, Finland

Exposure models are needed for comparison of scenarios resulting from alternative policy options. The reliability of models used for such purposes should be quantified by comparing model outputs in a real situation with the corresponding observed exposures. Measurement errors affect the observations, but if the distribution of these errors for single observations is known, the bias caused for the population statistics can be corrected. The current paper does this and calculates model errors for a probabilistic simulation of 48-hr fine particulate matter (PM2.5) exposures. Direct and nested microenvironment-based models are compared. The direct model requires knowledge on the distribution of the indoor concentrations, whereas the nested model calculates indoor concentrations from ambient levels, using infiltration factors and indoor sources. The model error in the mean exposure level was <0.5gm–3 for both models. Relative errors in the estimated population mean were +1% and −5% for the direct and nested models, respectively. Relative errors in the estimated SD were –9% and −23%, respectively. The magnitude of these errors and the errors calculated for population percentiles indicate that the model errors would not drive general conclusions derived from these models, supporting the use of the models as a tool for evaluation of potential exposure reductions in alternative policy scenarios.

Eye blinks as indicator for sensory irritation during constant and peak exposures to 2-ethylhexanol

Two experiments were performed to re-evaluate the sensory irritating properties of 2-ethylhexanol in relation to dose and time and to examine the usability of electromyographic eye blink recordings as indicator of sensory irritation. Mean exposure levels of 1.5, 10 and 20 ppm were realized in experimental models simulating either constant or variable 4 h exposure. Each study was carried out with two subject samples, healthy young men with self-reported multiple chemical sensitivity (sMCS) and age matched controls. Although 2-ethylhexanol exposure was below the occupational threshold limit value of 50 ppm, the study revealed strong dose–response relationships between airborne solvent concentrations and blink rates. During 40 ppm peak exposures the blink rate increased threefold. In the course of 4 h, exposure blink rates increased significantly showing no adaptation. Subjects with sMCS revealed, with one exception at start of exposure, no significantly higher blink rates than controls. The results indicate that the irritative potential of 2-ethylhexanol is higher than commonly expected. In both exposure scenarios with either constant or peak exposures, electromyographic eye blink recordings were an appropriate method for the examination of acute sensory irritations in time.

A meta-analytical approach to neurobehavioural effects of occupational toluene exposure

Twenty-two studies investigating neurobehavioural effects of toluene were reviewed. Repeatedly applied neuropsychological performance tests and appropriately documented results allowed to include 10 of the studies into a meta-analysis based on effect sizes. Mean exposure level of the studies was 57 ppm (range 20–117 ppm) toluene. Five of the six analyses of neuropsychological tests obtained effect sizes suggesting a negative impact of toluene, but for none of the analyses a significant effect size was estimated at averaged exposure levels between 33 and 89 ppm. The tests represented the psychological domains of attention and constructional performance. Additionally, the relation between exposure conditions (level of exposure, length of exposure), potential confounders (age, verbal intelligence), and effect sizes was analysed. Only pre-exposure intellectual capacity showed a consistent relation to effect sizes. The study suggests that homogenisation of study groups with respect to intelligence, cultural background and practice trials is important when investigating low-level exposure. Efforts to homogenize studies should be completed by a thorough documentation of feasible influences.

Biologic Markers of Oxidative Stress and Nephrotoxicity as Studied in Biomonitoring of Adverse Effects of Occupational Exposure to Lead and Cadmium

In this work, we studied impregnation levels of workers occupationally exposed to lead (Pb) and cadmium (Cd), usefulness of early urinary markers of nephrotoxicity, and occurrence of oxidative stress as the underlying mechanism involved in Pb- or Cd-induced adverse effects. Thirty-five men were recruited from a nonferrous metal smelter. Pb and Cd in blood (B-Pb, B-Cd) and urine (U-Pb, U-Cd) were measured. Relations between oxidative stress markers (malondialdehyde, superoxide dismutase, glutathione peroxidase, selenium, glutathione reductase, glutathione status, 8-hydroxy-2'-deoxyguanosine) and exposure levels, on the one hand, and early urinary markers (alpha-1-microprotein, beta-2-microglobulin, retinol binding protein, alpha and pi-glutathione S-transferases) and exposure levels, on the other hand, were evaluated. Mean exposure levels were moderate (B-Pb = 395.71 microg Pb/L; U-Pb = 95.19 microg Pb/g creatinine; B-Cd = 5.83 microg Cd/L; U-Cd = 4.67 microg Cd/g creatinine). Changes in malondialdehyde, glutathione status, 8-hydroxy-2'-deoxyguanosine, and alpha-glutathione S-transferases were closely correlated with exposure levels and did not depend on tobacco consumption. We showed that these workers showed moderate Pb and Cd exposure levels. Taken together, the data suggests the use of alpha-glutathione S-transferases excretion in urine as a hallmark of early changes in the proximal tubular integrity that could later lead to clinical disease if exposure is not reduced.

The impact of exposure categorisation for grouped analyses of cohort data

Background: Poisson regression is routinely used in occupational and environmental epidemiology. For typical Poisson regression analyses, person-time and events are tabulated by categorising predictor variables that were originally measured on...

Point-of-sale glass bottle recycling: indoor airborne exposures and symptoms among employees

Aims: To assess the impact of newly introduced point-of-sale glass bottle recycling on indoor air quality and employee health. Methods: Airborne exposures and both chronic and acute respiratory and somatic...

BOES CCD 카메라 II. 카메라의 특성

The characteristics of the BOES (Bohyunsan Observatory Echelle Spectrograph) CCD camera is presented. In order to get optimum gain and readout noise of the CCD, we examine the variation of the gain and readout noise by changing the value of output drain voltage of the CCD and measuring the gain using transfer curve, which is defined as the plot of variance versus mean exposure level of a homogeneous light onto the CCD surface. The gain and readout noises are optimised to be 0.5e/ADU and 3e, which is good for highest signal-to-noise ratio and contrast for the low light level characteristics of the BOES. We also measure the dark count of the CCD by getting five dark images with 3600 seconds exposure time. The mean dark count from median stacked dark images is essentially zero. A table of positions of defected pixels is also presented.

Preliminary measurements of aromatic VOCs in public transportation modes in Guangzhou, China

This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou, China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/ p-xylene and o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the benzene measured, the mean exposure level in taxis (33.6 μg/m 3) was the highest and was followed by air-conditioned buses (13.5 μg/m 3) and non-air-conditioned buses (11.3 μg/m 3). The exposure level in the subway (7.6 μg/m 3) is clearly lower than that in roadway transports. The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.

Time to pregnancy among partners of men exposed to di(2-ethylhexyl)phthalate.

This study assessed paternal occupational exposure to di(2-ethylhexyl)phthalate (DEHP) in association with reduced fertility. Men working in three plants with DEHP exposure were studied retrospectively. Male and female employees and their partners were invited to participate if they had reported a pregnancy or an attempt to achieve a pregnancy. Postal questionnaires and telephone interviews were used to collect additional data from the men and women, respectively. Information on time to pregnancy was eligible for 326 pregnancies fathered by 193 men. Male exposure to DEHP during every month of their time to pregnancy was classified into one of three exposure categories. The exposure ranged from <0.1 to 2.1 mg/m3. The fathers of only four pregnancies had DEHP exposure of >0.5 mg/m3 during the time to pregnancy. The pregnancies of employed women with unexposed partners or pregnancies of employed men unexposed during the time to pregnancy formed the reference group. The fecundability ratio for time to pregnancy was 1.07 [95% confidence interval (95% CI) 0.84-1.35] for those with low exposure and 0.97 (95% CI 0.70-1.33) for the highly exposed after adjustment for the father's age, mother's age, and length of recall. When the analyses were restricted to first pregnancy, the fecundability ratio was 1.13 (95% Cl 0.83-1.56) for low exposure and 1.02 (95% CI 0.66-1.59) for high exposure. Time to pregnancy is not prolonged among couples with paternal exposure to DEHP at a mean exposure level of <0.5 mg/m3.

Respiratory symptoms and dust exposure among male workers in small-scale wood industries in Tanzania.

Few studies have assessed respiratory symptoms and dust exposure levels in small-scale wood industry workers in Africa. We interviewed 546 workers exposed to wood dust and 565 control subjects using a respiratory health questionnaire. Inhalable dust measurements were collected for 106 workers. The dust exposure was high, and job title-based geometric mean exposure levels ranged from 2.9 to 22.8 mg/m3. Prevalence of respiratory symptoms in the previous 12 months was significantly higher in the exposed group compared with the nonexposed office workers. Allergy and sensitivity symptoms were reported regularly in the exposed group with Odds ratios and 95% confidence intervals (CIs) varying from 2.4 (95% CI = 1.8-3.1) for low- and 2.7 (1.8-4.0) for high-exposure groups compared with controls. We conclude that working in the small-scale wood industry in Tanzania is associated with an increased prevalence of respiratory symptoms.

Exposure levels and determinants of softwood dust exposures in BC lumber mills, 1981-1997.

Measurements of personal exposure to wood dust (n = 1237) collected by the Workers' Compensation Board of British Columbia, Canada, over the period 1981-1997 were used to construct an empirical model to identify broad determinants of softwood dust exposure. Potential determinants of exposure examined included species of tree processed; company; geographic location of lumber mill; department; job title; calendar year; and production factors such as board feet of lumber produced per year. A determinants of exposure model was built using multiple linear regression. Nested within this compliance database was a subset of samples collected for a research study. These enabled the authors to explore whether differences in exposure measurements can in part be explained by sampling strategy (research versus compliance). Potential differences were examined by examining differences in means for each job title, stratified by sampling strategy; and by offering "sampling strategy" as a categorical predictor variable to the empirical model. Multiple linear regressions revealed the most important determinants of increased wood dust exposure to be mill location away from the coast, earlier calendar year, and indoor jobs. The empirical model had an R2 of 0.39 and a predictive range from 0.02 to 25.45 mg/m3. Research and compliance sampling strategies showed no difference in mean exposure and distribution in the empirical model (p < 0.05), suggesting that regulatory exposure databases may be of utility for exposure assessment in epidemiology. This research indicates that compliance-sampling strategies do not result in an overestimation of mean exposure levels within jobs, but they do focus on a biased sample of jobs-those most highly exposed.

Assessment of road users’ elemental carbon personal exposure levels, London, UK

Little is known about particulate elemental carbon (EC) personal exposure levels, a key component of diesel exhaust, specifically in transport microenvironments. A method utilizing the optical properties of EC particles has been applied to personal exposure measurement filter samples. In a series of field studies carried out in London, UK, during 1999–2000 over 400 fine particle (PM 2.5) personal exposure level measurements were taken for journeys in bicycle, bus, car and underground rail transport microenvironments, along three main fixed routes. The particulate EC contribution to the PM 2.5 personal exposure was assessed indirectly by means of an optical technique and with the development and use of a size fraction specific and site-specific calibration curve. In this first EC personal exposure study of transport users geometric mean exposure levels in the summer field campaign were 11.2 μg m −3 (GSD=2.7) for cyclists, 13.6 μg m −3 (GSD=1.9) for bus passengers and 21.6 μg m −3 (GSD=2.1) for car drivers; corresponding exposure levels in the winter were 16.4 μg m −3 (GSD=1.8), 18.6 μg m −3 (GSD=2.3) and 27.3 μg m −3 (GSD=2.0), respectively. EC/PM 2.5 ratios were approximately 0.5–0.6 for bicycle and bus modes and 0.7–0.8 for the car mode. EC/PM 2.5 ratios for different routes ranged from approximately 0.7 for Route 1 to 0.4 for Route 3. Cyclists had the lowest exposure to EC, and car occupants the highest exposure. A large difference in exposure levels between a central high traffic density route and the other less central routes was observed. Particulate EC was a very significant proportion of the total PM 2.5 personal exposure and EC personal exposure levels were considerably higher than reported fixed site monitor EC concentrations.

Assessment of variability in biomonitoring data using a large database of biological measures of exposure.

Although intra- and interindividual sources of variation in airborne exposures have been extensively studied, similar investigations examining variability in biological measures of exposure have been limited. Following a review of the world's published literature, biological monitoring data were abstracted from 53 studies that examined workers' exposures to metals, solvents, polycyclic aromatic hydrocarbons, and pesticides. Approximately 40% of the studies also reported personal sampling results, which were compiled as well. In this study, the authors evaluated the intra- and interindividual sources of variation in biological measures of exposure collected on workers employed at the same plant. In 60% of the data sets, there was more variation among workers than variation from day to day. Approximately one-fourth of the data were homogeneous with small differences among workers' mean exposure levels. However, an almost equal number of data sets exhibited moderate to extreme levels of heterogeneity in exposures among workers at the same facility. In addition, the relative magnitude of the intra- to interindividual source of variation was larger for biomarkers with short compared to long half-lives, which suggests that biomarkers with half-lives of 7 days or longer exhibit physiologic dampening of fluctuations in external levels of the workplace contaminant and thereby may offer advantages when compared to short-lived biomarkers or exposures assessed by air monitoring. The use of biological indices of exposure, however, places an additional burden on the strategy used to evaluate exposures, because data may be serially correlated as evidenced in this study, which could result in biased estimates of the variance components if autocorrelation is undetected or ignored in the statistical analyses.

Apartment residents' and day care workers' exposures to tetrachloroethylene and deficits in visual contrast sensitivity.

Tetrachloroethylene (also called perchloroethylene, or perc), a volatile organic compound, has been the predominant solvent used by the dry-cleaning industry for many years. The U.S. Environmental Protection Agency (EPA) classified perc as a hazardous air pollutant because of its potential adverse impact on human health. Several occupational studies have indicated that chronic, airborne perc exposure adversely affects neurobehavioral functions in workers, particularly visual color discrimination and tasks dependent on rapid visual-information processing. A 1995 study by Altmann and colleagues extended these findings, indicating that environmental perc exposure at a mean level of 4,980 microg/m(3) (median=1,360 microg/m(3)) alters neurobehavioral functions in residents living near dry-cleaning facilities. Although the U.S. EPA has not yet set a reference concentration guideline level for environmental exposure to airborne perc, the New York State Department of Health set an air quality guideline of 100 microg/m(3). In the current residential study, we investigated the potential for perc exposure and neurologic effects, using a battery of visual-system function tests, among healthy members of six families living in two apartment buildings in New York City that contained dry-cleaning facilities on the ground floors. In addition, a day care investigation assessed the potential for perc exposure and effects among workers at a day care center located in the same one-story building as a dry-cleaning facility. Results from the residential study showed a mean exposure level of 778 microg/m(3) perc in indoor air for a mean of 5.8 years, and that perc levels in breath, blood, and urine were 1-2 orders of magnitude in excess of background values. Group-mean visual contrast sensitivity (VCS), a measure of the ability to detect visual patterns, was significantly reduced in the 17 exposed study participants relative to unexposed matched-control participants. The groups did not differ in visual acuity, suggesting that the VCS deficit was of neurologic origin. Healthy workers in the day care investigation were chronically exposed to airborne perc at a mean of 2,150 microg/m(3) for a mean of 4.0 years. Again, group-mean VCS, measured 6 weeks after exposure cessation, was significantly reduced in the nine exposed workers relative to matched controls, and the groups did not differ significantly in visual acuity. These results suggested that chronic, environmental exposure to airborne perc adversely affects neurobehavioral function in healthy individuals. Further research is needed to assess the susceptibility of the young and elderly to perc-induced effects, to determine whether persistent solvent-induced VCS deficits are a risk factor for the development of neurologic disease, and to identify the no observable adverse effect level for chronic, environmental, perc exposure in humans.

Fine particle (PM 2.5) personal exposure levels in transport microenvironments, London, UK

In order to investigate a specific area of short-term, non-occupational, human exposure to fine particulate air pollution, measurements of personal exposure to PM 2.5 in transport microenvironments were taken in two separate field studies in central London, UK. A high flow gravimetric personal sampling system was used; operating at 16 l min −1; the sampler thus allowed for sufficient sample mass collection for accurate gravimetric analysis of short-term travel exposure levels over typical single commute times. In total, samples were taken on 465 journeys and 61 volunteers participated. In a multi-transport mode study, carried out over 3-week periods in the winter and in the summer, exposure levels were assessed along three fixed routes at peak and off-peak times of the day. Geometric means of personal exposure levels were 34.5 μg m −3 (G.S.D.=1.7, n s=40), 39.0 μg m −3 (G.S.D.=1.8, n s=36), 37.7 μg m −3 (G.S.D.=1.5, n s=42), and 247.2 μg m −3 (G.S.D.=1.3, n s=44) for bicycle, bus, car and Tube (underground rail system) modes, respectively, in the July 1999 (summer) measurement campaign. Corresponding levels in the February 2000 (winter) measurement campaign were 23.5 μg m −3 (G.S.D.=1.8, n s=56), 38.9 μg m −3 (G.S.D.=2.1, n s=32), 33.7 μg m −3 (G.S.D.=2.4, n s=12), and 157.3 μg m −3 (G.S.D.=3.3, n s=12), respectively. In a second study, exposure levels were measured for a group of 24 commuters travelling by bicycle, during August 1999, in order to assess how representative the fixed route studies were to a larger commuter population. The geometric mean exposure level was 34.2 μg m −3 (G.S.D.=1.9, n s=105). In the fixed-route study, the cyclists had the lowest exposure levels, bus and car were slightly higher, while mean exposure levels on the London Underground rail system were 3–8 times higher than the surface transport modes. There was significant between-route variation, most notably between the central route and the other routes. The fixed-route study exposure was similar in level and in variability to the ‘real’ commuters study, suggesting that the routes chosen and the number of samples taken provided a reasonably good estimate of the personal exposure levels in the transport microenvironments of Central London. This first comprehensive PM 2.5 multi-mode transport user exposure assessment study in the UK also showed that mean personal exposure levels in road transport modes were approximately double that of the PM 2.5 concentration at an urban background fixed site monitor.

Influence of Data Elements in OSHA Air Sampling Database on Occupational Exposure Levels

The influence of five variables in the Occupational Safety and Health Administration (OSHA) sampling data collected from 1979-1997 in three exposure groups were examined for their association with the reported levels of occupational exposure to airborne chemicals. The exposure groups evaluated were: 1) asbestos abatement workers exposed to asbestos fibers; 2) automotive body repair shop workers exposed to toluene during spray painting; and 3) embalmers exposed to formaldehyde. The variables (data elements) examined were type, year and scope of inspection, size of the employer, and union status. Multiple linear regression was used to investigate, using three statistical models, the influence of these variables on occupational exposure levels. In the asbestos and toluene exposure groups, a consistent time-related trend in mean exposures was observed with decreasing exposure levels being seen under each statistical model. By contrast, no consistent relationship between year of inspection and exposure levels was seen for the formaldehyde exposure group. Higher exposures were detected during comprehensive inspections than during partial scope inspections in each exposure group under all three regression models, suggesting that scope may be a source of bias in this data. Higher mean exposures were measured during complaint inspections than planned inspections across all regression models in the toluene and formaldehyde exposure groups. However, this trend was reversed for the asbestos case study, in which higher mean exposures were measured during planned inspections under each model. Type of inspection and union status were not consistently found to be associated with mean exposure levels in any of the exposure groups. The strengths and limitations of the OSHA sampling data in providing insights regarding occupational exposures, as well as their utility beyond assessing regulatory compliance are discussed. The results of this study are compared with those obtained in a previous study of OSHA compliance data that examined the potential association of the same variables with exposure levels in three different exposure groups.

Household appliance use and residential exposure to 60-hz magnetic fields.

We characterized the distribution of exposure to magnetic fields (MFs) during daily activities and during household appliance use, and estimated the relative contribution of various activities and appliances to total daily exposure. One hundred sixty-two subjects provided information on their patterns of appliance use and wore personal monitors for 24 h to collect MF exposure data. Of total exposure, 27% accumulated while subjects were in bed; 41% while at home but not in bed; 9% at work; and 24% elsewhere. Less than 2% of the total MF exposure accumulated during the use of each of the eight individual appliances considered, except computers, during the use of which 9% of the total exposure accumulated. Of the time subjects spent at exposure levels higher than 2 microT, 8% accumulated while they were using microwave ovens, and 4% and 3% while using computers and electric stoves, respectively. Mean MF measurements tended to be lowest when subjects were in bed and highest at work and during the use of microwave ovens, coffee grinders, hair dryers, and electric shavers. Results from questionnaires on household appliance use in the past year were not useful in predicting the total mean exposure level and over-threshold exposures measured by 24-h personal monitors. Significant MF exposure accumulates at home, at work, and elsewhere; therefore, accurate exposure assessment needs to consider residential, occupational, and other sources together. Questionnaire-based information on appliance use has limited value in the assessment of average and over-threshold exposure to MFs.

Organic dust-related respiratory and eye irritation in Norwegian farmers.

Information on exposure to organic dust and work-related symptoms in farmers is sparse. An exposure study was nested in a survey of 8,482 farmers and spouses. Task-related respiratory and eye symptoms were recorded by questionnaire. Personal exposure to total dust, fungal spores, bacteria, endotoxins, and ammonia during 12 different tasks was measured in a random sample of 127 farms (288 measurements). The prevalence of work-related symptoms occurring "often" was 31% and "seldom" 35%. Specific tasks provoking symptoms were reported by 5-55% of the farmers. Task mean exposures ranged from 0.04 to 2 mg dust/m(3), 0.02 x 10(6) to 2 x 10(6) fungal spores/m(3), 0.2 x 10(6) to 48 x 10(6) bacteria/m(3), 0.5 x 10(3) to 28 x 10(3) endotoxin units/m(3), and 0 to 8 ppm ammonia. Task mean exposure levels were positively correlated with task-specific symptom prevalences for total dust, fungal spores, and endotoxins but not for bacteria and ammonia. Work-related symptoms are common in farmers and are associated with exposure to total dust, fungal spores, and endotoxins.

Biases in estimating the effect of cumulative exposure in log-linear models when estimated exposure levels are assigned

Exposure-response trends in occupational studies of chronic disease are often modeled via log-linear models with cumulative exposure as the metric of interest. Exposure levels for most subjects are often unknown, but can be estimated by assigning known job-specific mean exposure levels from a sample of workers to all workers. Such assignment results in (nondifferential) measurement error of the Berkson type, which does not bias the estimate of exposure effect in linear models but can result in substantial bias in log-linear models with dichotomous outcomes. This bias was explored in estimated exposure-response trends using cumulative exposure. Simulations were conducted under the assumptions that (i) exposure level is assigned to all workers based on the job-specific means from a sample of workers, (ii) exposure level and duration are log-normal, (iii) the true exposure-response model is log-linear for cumulative exposure, (iv) the disease is rare, and (v) the variance of job-specific exposure level increases with its job-specific mean. Results Assignment of job-specific mean exposure levels from a sample of workers causes an upward bias in the estimated exposure-response trend when there is little variance in the duration of exposure but causes a downward bias when duration has a large variance. This bias can be substantial (eg, 30-50%). Berkson errors in exposure result in little bias in estimating exposure-response trends when the standard deviation of duration is approximately equal to its mean, which is common in many occupational studies. No bias occurs when the variance of exposure level is constant across jobs, but such conditions are probably uncommon.

Development of an eight-hour occupational exposure limit for beryllium.

This article recommends an 8-hour occupational exposure limit (OEL) for beryllium. It responds to growing concerns about the continuing incidence of chronic beryllium disease despite the long-standing OEL for beryllium: 2 micrograms of beryllium per cubic meter of air (microgram/m3), 8-hour time-weighted average (TWA). Current 8-hour TWA beryllium OELs are not based on chronic beryllium disease toxicology and an increasing number of studies report incidence of chronic beryllium disease at exposure levels apparently below 2 micrograms/m3. The experience of the beryllium-exposed population of Lorain, Ohio, in the late 1940s, and the ambient air regulatory standards derived from that event provide evidence that establishing a protective level is possible. These levels are used as the basis for a new recommended beryllium exposure standard. A correspondingly protective 8-hour TWA level of 0.1 microgram/m3 has been derived, which, for commonly encountered workplace conditions (in terms of geometric standard deviation and percent-compliance), should provide long-term mean exposure protection comparable to that received by the unaffected Lorain subpopulation and provided by the Environmental Protection Agency (EPA) ambient standard. It is concluded that an exposure limit of 0.1 microgram/m3 combined with exposure monitoring to assure a high rate of day-to-day compliance would provide better control of both long-term mean exposure levels and short-term levels than do current occupational exposure limits. The health data available, while certainly not conclusive, support further reductions in exposure levels to help minimize the incidence of chronic beryllium disease.