Comprehensive evaluation of long-term trends in occupational exposure: Part 2. Predictive models for declining exposures

Temporal risk assessment - 20th century Pb emissions to air and exposure via inhalation in the Swedish glass district

The objective of the present study was to assess historical emissions of Pb to air around a number of glassworks sites in southeastern Sweden, and the possible implications for human exposure. To do so, a four-step method was applied. First, emissions of Pb to air around 10 glassworks were modelled for the 20th century. Second, an assessment of the resulting exposure was made for a number of scenarios. Third, the number of people potentially exposed at different times was estimated, and fourth, measurements of "current" Pb concentrations in PM₁₀ material from four sites were conducted in 2019. The results show that the highest emissions, and exposures, occurred from 1970 to1980. It coincides with the time period when the highest number of people resided in the villages. At this time, the average Pb concentration in air around the six largest factories was about 2.4 μg Pb/m³, i.e. 16 times the present US national ambient air quality standard (NAAQS) of 0.15 μg Pb/m³. By year 2000 the modelled average concentration had dropped to 0.05 μg Pb/m³, a level that is normal for urban regions today. The PM₁₀ measurements from 2019 indicate a further decline, now with a mean value of about 0.02 μg Pb/m³. Over the entire study period, inhalation hazard quotients (HQs) exceeded the dietary HQ by many orders of magnitude, indicating that inhalation has been the most prevalent exposure pathway in the past. At present, both pathways are judged to be associated with low exposures. Even if only roughly approximated, a picture of the historical exposure can increase our understanding of the connection between exposure and disease, and can be valuable when risks are to be communicated to residents near contaminated areas.

Reconstructing Historical Exposures to Respirable Dust and Respirable Silica in the Taconite Mining Industry for 1955-2010

The goal of this study was to reconstruct the historical respirable silica (RS) and respirable dust (RD) exposures of workers in the Minnesota taconite industry from 1955 to 2010 as part of several epidemiological studies for assessing the association between exposure to components of taconite dusts and the development of respiratory diseases. A job-exposure matrix (JEM) was developed that uses 9127 RS and 19 391 RD occupational hygiene historical measurements. Historical RS and RD data were extracted from several sources and were grouped into seven mines and then into eight departments [Concentrating, Crushing, Janitor, Mining, Office/control room, Pelletizing, Shop (mobile), and Shop (stationary)]. Within each department, we applied a two-level random-intercept regression model which assumes that the natural log of Y (RD or RS concentration) changes over time at a constant rate. Among all predicted RD and RS values, we found that larger RD values were located in the following departments: Crushing, Concentrating, Pelletizing, and Shop (mobile). Larger RS values were located only in either Crushing or Shop (mobile). The annual rates of change for historical RD and RS exposures were between -3.3 and 3.2%. The silica percentage in the dust varied by mine/department with the highest value of 29.3% in Mine F (Crushing) and the lowest value of 2.1% in Mine B (Pelletizing). The predicted historical RD and RS arithmetic mean exposures ranged between <0.075 and 3.14 mg m-3, and between <0.005 and 0.36 mg m-3, respectively. The result of this study is a JEM by mine, department, and year for RD and RS for epidemiological studies.

A Quantitative General Population Job Exposure Matrix for Occupational Noise Exposure

Occupational noise exposure is a known risk factor for hearing loss and also adverse cardiovascular effects have been suggested. A job exposure matrix (JEM) would enable studies of noise and health on a large scale. The objective of this study was to create a quantitative JEM for occupational noise exposure assessment of the general working population. Between 2001–2003 and 2009–2010, we recruited workers from companies within the 10 industries with the highest reporting of noise-induced hearing loss according to the Danish Working Environment Authority and in addition workers of financial services and children day care to optimize the range in exposure levels. We obtained 1343 personal occupational noise dosimeter measurements among 1140 workers representing 100 different jobs according to the Danish version of the International Standard Classification of Occupations 1988 (DISCO 88). Four experts used 35 of these jobs as benchmarks and rated noise levels for the remaining 337 jobs within DISCO 88. To estimate noise levels for all 372 jobs, we included expert ratings together with sex, age, occupational class, and calendar year as fixed effects, while job and worker were included as random effects in a linear mixed regression model. The fixed effects explained 40% of the total variance: 72% of the between-jobs variance, −6% of the between-workers variance and 4% of the within-worker variance. Modelled noise levels showed a monotonic increase with increasing expert score and a 20 dB difference between the highest and lowest exposed jobs. Based on the JEM estimates, metal wheel-grinders were among the highest and finance and sales professionals among the lowest exposed. This JEM of occupational noise exposure can be used to prioritize preventive efforts of occupational noise exposure and to provide quantitative estimates of contemporary exposure levels in epidemiological studies of health effects potentially associated with noise exposure.

Burden of lung cancer attributable to occupational diesel engine exhaust exposure in Canada

Objective

To estimate the population attributable fraction (PAF) and number of incident and fatal lung cancers in Canada from occupational exposure to diesel engine exhaust (DEE).

Methods

DEE exposure prevalence and level estimates were used with Canadian Census and Labour Force Survey data to model the exposed population across the risk exposure period (REP, 1961–2001). Relative risks of lung cancer were calculated based on a meta-regression selected from the literature. PAFs were calculated using Levin’s equation and applied to the 2011 lung cancer statistics obtained from the Canadian Cancer Registry.

Results

We estimated that 2.4% (95% CI 1.6% to 6.6%) of lung cancers in Canada are attributable to occupational DEE exposure, corresponding to approximately 560 (95% CI 380 to 1570) incident and 460 (95% CI 310 to 1270) fatal lung cancers in 2011. Overall, 1.6 million individuals alive in 2011 were occupationally exposed to DEE during the REP, 97% of whom were male. Occupations with the highest burden were underground miners, truck drivers and mechanics. Half of the attributable lung cancers occurred among workers with low exposure.

Conclusions

This is the first study to quantify the burden of lung cancer attributable to occupational DEE exposure in Canada. Our results underscore a large potential for prevention, and a large public health impact from occupational exposure to low levels of DEE.

Cancer Incidence Among Hardmetal Production Workers: The Swedish Cohort

: The cancer incidence was determined for 3713 workers from three plants from 1958 to 2011. The exposure measures were ever/never exposed, duration, cumulative, and mean cobalt concentrations.The incidence of all malignant neoplasms was increased at one plant, but standardized incidence ratio (SIR) was 0.96 for all workers. Lung cancer incidence was increased for all workers, SIR 1.38 (1.01 to 1.85). The lung cancer incidence was associated with shorter employment time and showed no exposure-response. There was decreased incidence for skin cancer. Increased lip cancer incidence found at one of the production plants might be related to diagnostic intensity.Lung cancer incidence showed no correlation to cobalt exposure based on internal comparison. The increased SIR for all workers might be associated with other factors.

Retrospective benzene exposure assessment for a multi-center case-cohort study of benzene-exposed workers in China

Quality of exposure assessment has been shown to be related to the ability to detect risk of lymphohematopoietic disorders in epidemiological investigations of benzene, especially at low levels of exposure. We set out to build a statistical model for reconstructing exposure levels for 2898 subjects from 501 factories that were part of a nested case-cohort study within the NCI-CAPM cohort of more than 110,000 workers. We used a hierarchical model to allow for clustering of measurements by factory, workshop, job, and date. To calibrate the model we used historical routine monitoring data. Measurements below the limit of detection were accommodated by constructing a censored data likelihood. Potential non-linear and industry-specific time-trends and predictor effects were incorporated using regression splines and random effects. A partial validation of predicted exposures in 2004/2005 was performed through comparison with full-shift measurements from an exposure survey in facilities that were still open. Median cumulative exposure to benzene at age 50 for subjects that ever held an exposed job (n=1175) was 509 mg/m(3) years. Direct comparison of model estimates with measured full-shift personal exposure in the 2004/2005 survey showed moderate correlation and a potential downward bias at low (<1 mg/m(3)) exposure estimates. The modeling framework enabled us to deal with the data complexities generally found in studies using historical exposure data in a comprehensive way and we therefore expect to be able to investigate effects at relatively low exposure levels.

Evaluating temporal trends from occupational lead exposure data reported in the published literature using meta-regression

OBJECTIVES

The published literature provides useful exposure measurements that can aid retrospective exposure assessment efforts, but the analysis of this data is challenging as it is usually reported as means, ranges, and measures of variability. We used mixed-effects meta-analysis regression models, which are commonly used to summarize health risks from multiple studies, to predict temporal trends of blood and air lead concentrations in multiple US industries from the published data while accounting for within- and between-study variability in exposure.

METHODS

We extracted the geometric mean (GM), geometric standard deviation (GSD), and number of measurements from journal articles reporting blood and personal air measurements from US worksites. When not reported, we derived the GM and GSD from other summary measures. Only industries with measurements in ≥2 time points and spanning ≥10 years were included in our analyses. Meta-regression models were developed separately for each industry and sample type. Each model used the log-transformed GM as the dependent variable and calendar year as the independent variable. It also incorporated a random intercept that weighted each study by a combination of the between- and within-study variances. The within-study variances were calculated as the squared log-transformed GSD divided by the number of measurements. Maximum likelihood estimation was used to obtain the regression parameters and between-study variances.

RESULTS

The blood measurement models predicted statistically significant declining trends of 2-11% per year in 8 of the 13 industries. The air measurement models predicted a statistically significant declining trend (3% per year) in only one of the seven industries; an increasing trend (7% per year) was also observed for one industry. Of the five industries that met our inclusion criteria for both air and blood, the exposure declines per year tended to be slightly greater based on blood measurements than on air measurements.

CONCLUSIONS

Meta-analysis provides a useful tool for synthesizing occupational exposure data to examine exposure trends that can aid future retrospective exposure assessment. Data remained too sparse to account for other exposure predictors, such as job category or sampling strategy, but this limitation may be overcome by using additional data sources.

Historical occupational trichloroethylene air concentrations based on inspection measurements from Shanghai, China

PURPOSE

Trichloroethylene (TCE) is a carcinogen that has been linked to kidney cancer and possibly other cancer sites including non-Hodgkin lymphoma. Its use in China has increased since the early 1990s with China's growing metal, electronic, and telecommunications industries. We examined historical occupational TCE air concentration patterns in a database of TCE inspection measurements collected in Shanghai, China to identify temporal trends and broad contrasts among occupations and industries.

METHODS

Using a database of 932 short-term, area TCE air inspection measurements collected in Shanghai worksites from 1968 through 2000 (median year 1986), we developed mixed-effects models to evaluate job-, industry-, and time-specific TCE air concentrations.

RESULTS

Models of TCE air concentrations from Shanghai work sites predicted that exposures decreased 5-10% per year between 1968 and 2000. Measurements collected near launderers and dry cleaners had the highest predicted geometric means (GM for 1986 = 150-190 mg m(-3)). The majority (53%) of the measurements were collected in metal treatment jobs. In a model restricted to measurements in metal treatment jobs, predicted GMs for 1986 varied 35-fold across industries, from 11 mg m(-3) in 'other metal products/repair' industries to 390 mg m(-3) in 'ships/aircrafts' industries.

CONCLUSIONS

TCE workplace air concentrations appeared to have dropped over time in Shanghai, China between 1968 and 2000. Understanding differences in TCE concentrations across time, occupations, and industries may assist future epidemiologic studies in China.

Essential Occupational Safety and Health Interventions for Low- and Middle-income Countries: An Overview of the Evidence

There is still a considerable burden of occupational diseases and injuries in the world. It is not well known which interventions can effectively reduce the exposures at work that cause this burden. The objective of this article is to summarize evidence from systematic reviews of interventions to prevent occupational diseases and injuries. We included systematic reviews of interventions to reduce the incidence of work-related cancer, dust-related diseases, occupational asthma, chronic obstructive pulmonary disease, noiseinduced hearing loss, back pain, and occupational injuries. We searched Medline and Embase with predefined search strategies to locate systematic reviews of these interventions. We found 23 systematic reviews of which the results are also applicable to low- and middle income countries. Effective measures to reduce exposure leading to work-related cancer, dust-related diseases, asthma, chronic obstructive pulmonary disease, noise, and injuries are available. However, better implementation of these measures is needed. Regulation, enforcement of regulation, and incentives for employers are effective interventions to achieve this goal. There is evidence that feedback and rewards for workers help in reducing occupational injuries. There is no evidence in many studies that back pain can be prevented. Personal protective equipment technically has the potential to reduce exposure but this is difficult to put into effect. There is no evidence in the studies regarding the effectiveness of education and training, preventive drugs, or health examinations. There is evidence that the implementation of technical measures enforced by regulation can prevent occupational diseases and injuries. For other interventions such as education or health examinations, there is no evidence that supports their effectiveness. More systematic reviews are needed in the area of injury prevention.

Occupational cancer in Britain. Exposure assessment methodology

To estimate the current occupational cancer burden due to past exposures in Britain, estimates of the number of exposed workers at different levels are required, as well as risk estimates of cancer due to the exposures. This paper describes the methods and results for estimating the historical exposures. All occupational carcinogens or exposure circumstances classified by the International Agency for Research on Cancer as definite or probable human carcinogens and potentially to be found in British workplaces over the past 20-40 years were included in this study. Estimates of the number of people exposed by industrial sector were based predominantly on two sources of data, the CARcinogen EXposure (CAREX) database and the UK Labour Force Survey. Where possible, multiple and overlapping exposures were taken into account. Dose-response risk estimates were generally not available in the epidemiological literature for the cancer-exposure pairs in this study, and none of the sources available for obtaining the numbers exposed provided data by different levels of exposure. Industrial sectors were therefore assigned using expert judgement to 'higher'- and 'lower'-exposure groups based on the similarity of exposure to the population in the key epidemiological studies from which risk estimates had been selected. Estimates of historical exposure prevalence were obtained for 41 carcinogens or occupational circumstances. These include exposures to chemicals and metals, combustion products, other mixtures or groups of chemicals, mineral and biological dusts, physical agents and work patterns, as well as occupations and industries that have been associated with increased risk of cancer, but for which the causative agents are unknown. There were more than half a million workers exposed to each of six carcinogens (radon, solar radiation, crystalline silica, mineral oils, non-arsenical insecticides and 2,3,7,8-tetrachlorodibenzo-p-dioxin); other agents to which a large number of workers are exposed included benzene, diesel engine exhaust and environmental tobacco smoke. The study has highlighted several industrial sectors with large proportions of workers potentially exposed to multiple carcinogens. The relevant available data have been used to generate estimates of the prevalence of past exposure to occupational carcinogens to enable the occupational cancer burden in Britain to be estimated. These data are considered adequate for the present purpose, but new data on the prevalence and intensity of current occupational exposure to carcinogens should be collected to ensure that future policy decisions be based on reliable evidence.

Combining a job-exposure matrix with exposure measurements to assess occupational exposure to benzene in a population cohort in shanghai, china

BACKGROUND

Generic job-exposure matrices (JEMs) are often used in population-based epidemiologic studies to assess occupational risk factors when only the job and industry information of each subject is available. JEM ratings are often based on professional judgment, are usually ordinal or semi-quantitative, and often do not account for changes in exposure over time. We present an empirical Bayesian framework that combines ordinal subjective JEM ratings with benzene measurements. Our aim was to better discriminate between job, industry, and time differences in exposure levels compared to using a JEM alone.

METHODS

We combined 63 221 short-term area air measurements of benzene exposure (1954-2000) collected during routine health and safety inspections in Shanghai, China, with independently developed JEM intensity ratings for each job and industry using a mixed-effects model. The fixed-effects terms included the JEM intensity ratings for job and industry (both ordinal, 0-3) and a time trend that we incorporated as a b-spline. The random-effects terms included job (n = 33) and industry nested within job (n = 399). We predicted the benzene concentration in two ways: (i) a calibrated JEM estimate was calculated using the fixed-effects model parameters for calendar year and JEM intensity ratings; (ii) a job-/industry-specific estimate was calculated using the fixed-effects model parameters and the best linear unbiased predictors from the random effects for job and industry using an empirical Bayes estimation procedure. Finally, we applied the predicted benzene exposures to a prospective population-based cohort of women in Shanghai, China (n = 74 942).

RESULTS

Exposure levels were 13 times higher in 1965 than in 2000 and declined at a rate that varied from 4 to 15% per year from 1965 to 1985, followed by a small peak in the mid-1990s. The job-/industry-specific estimates had greater differences between exposure levels than the calibrated JEM estimates (97.5th percentile/2.5th percentile exposure level, (B)(G)R(95)(B): 20.4 versus 3.0, respectively). The calibrated JEM and job-/industry-specific estimates were moderately correlated in any given year (Pearson correlation, r(p) = 0.58). We classified only those jobs and industries with a job or industry JEM exposure probability rating of 3 (>50% of workers exposed) as exposed. As a result, 14.8% of the subjects and 8.7% of the employed person-years in the study population were classified as benzene exposed. The cumulative exposure metrics based on the calibrated JEM and job-/industry-specific estimates were highly correlated (r(p) = 0.88).

CONCLUSIONS

We provide a useful framework for combining quantitative exposure data with expert-based exposure ratings in population-based studies that maximized the information from both sources. Our framework calibrated the ratings to a concentration scale between ratings and across time and provided a mechanism to estimate exposure when a job/industry group reported by a subject was not represented in the exposure database. It also allowed the job/industry groups' exposure levels to deviate from the pooled average for their respective JEM intensity ratings.

Exposure to rubber process dust and fume since 1970s in the United Kingdom; influence of origin of measurement data

The objective of this study was to compare measured concentrations of rubber process dust and rubber fume originating from different sources in the British rubber manufacturing industry. Almost 8000 exposure measurements were obtained from industry-based survey results collected by the British Rubber Manufacturers' Association (BRMA), and covering the years 1977 to 2002, and from a series of small surveys contained in the Health and Safety Executive's (HSE) National Exposure Database (HSE-NEDB) from 1980 to 2002. The analysis investigated temporal trends in the exposure concentrations and the underlying main factors responsible for these changes. Analyses were carried out using hierarchical linear mixed effects models. Average personal exposures to rubber process dust and rubber fumes were respectively a factor 2 and 4 higher for the HSE-NEDB data when compared to data originating from the industry (BRMA data). Personal exposure to rubber process dust decreased on average by 4.1% (95% CI 4.7-3.6) annually for the BRMA data and slightly less at 2.3% (95% CI 5.2-0.7%) per annum for the HSE-NEDB data. Personal exposure to rubber fume also showed a downward temporal trend of 2.9% (95% CI 3.6-2.3%) and 4.8% (95% CI 7.4-2.1%) annually for the BRMA and HSE-NEDB data, respectively. These trends differed considerably between departments. No major changes in the estimated temporal trends in exposure concentrations were observed after including the presence of local exhaust ventilation in the models for any department in the BRMA and HSE-NEDB datasets. Lack of information on the quality and status of the local exhaust ventilation is the most likely explanation for this. In conclusion, even though there were relatively similar downward time trends in both rubber process dust and fume concentrations in both datasets, the source of exposure data was an important determinant of average exposure concentrations present in the British rubber manufacturing industry. Lack of detailed auxiliary information on company size, reason for sampling, measurement strategy and other potentially important determinants of exposure prevented an explanation for the observed differences in exposure level.

Occupation and cancer in Britain

Background:

Prioritising control measures for occupationally related cancers should be evidence based. We estimated the current burden of cancer in Britain attributable to past occupational exposures for International Agency for Research on Cancer (IARC) group 1 (established) and 2A (probable) carcinogens.

Methods:

We calculated attributable fractions and numbers for cancer mortality and incidence using risk estimates from the literature and national data sources to estimate proportions exposed.

Results:

5.3% (8019) cancer deaths were attributable to occupation in 2005 (men, 8.2% (6362); women, 2.3% (1657)). Attributable incidence estimates are 13 679 (4.0%) cancer registrations (men, 10 063 (5.7%); women, 3616 (2.2%)). Occupational attributable fractions are over 2% for mesothelioma, sinonasal, lung, nasopharynx, breast, non-melanoma skin cancer, bladder, oesophagus, soft tissue sarcoma, larynx and stomach cancers. Asbestos, shift work, mineral oils, solar radiation, silica, diesel engine exhaust, coal tars and pitches, occupation as a painter or welder, dioxins, environmental tobacco smoke, radon, tetrachloroethylene, arsenic and strong inorganic mists each contribute 100 or more registrations. Industries and occupations with high cancer registrations include construction, metal working, personal and household services, mining, land transport, printing/publishing, retail/hotels/restaurants, public administration/defence, farming and several manufacturing sectors. 56% of cancer registrations in men are attributable to work in the construction industry (mainly mesotheliomas, lung, stomach, bladder and non-melanoma skin cancers) and 54% of cancer registrations in women are attributable to shift work (breast cancer).

Conclusion:

This project is the first to quantify in detail the burden of cancer and mortality due to occupation specifically for Britain. It highlights the impact of occupational exposures, together with the occupational circumstances and industrial areas where exposures to carcinogenic agents occurred in the past, on population cancer morbidity and mortality; this can be compared with the impact of other causes of cancer. Risk reduction strategies should focus on those workplaces where such exposures are still occurring.

A comprehensive review of the literature on exposure to metalworking fluids

An extensive literature review was conducted of studies with exposure measurements to metalworking fluids (MWFs). A database of 155 arithmetic means based on 9379 aerosol measurements from published studies was compiled. Weighted arithmetic means (WAMs) and their variance calculated across studies were summarized based on decade (prior to 1970s through 2000s), industry (auto, auto parts, small job shops, and others), operation (grinding and machining), and fluid type (straight, soluble, synthetic, and semisynthetic). Total mass and total extractable mass measurements that were simultaneously collected were compared. Average concentrations by size fractions and mass median aerodynamic diameters (MMADs) were also analyzed. Analysis of the WAMs indicated a reduction in exposure levels over time regardless of industry or type of operation or fluid, with mean levels prior to the 1970s of 5.4 mg/m(3), which dropped to 2.5 mg/m(3) in the 1970s, to 1.2 mg/m(3) in the 1980s, and to 0.5 mg/m(3) in the 1990s. No further reduction was seen in the 2000s. A comparison by industry, operation, and fluid type found no consistent patterns in the measurement results. The percent extractable mass in the total aerosol samples varied by fluid type, with an average 84% in straight fluids, 58% in synthetic fluids, 56% in soluble fluids, and 42% in the semisynthetic fluids. Exposure means from the thoracic fraction (0.3-0.5 mg/m(3)) were slightly less than those for total aerosol for both the 1990s and 2000s, the only decades for which thoracic data were available. Respirable means did not change from the 1980s to the 2000s (generally about 0.2-0.3 mg/m(3)). The MMADs of the MWF aerosols averaged 4-6 microm. These measurement data indicate a clear reduction of exposure levels over time. They will be used for the retrospective assessment of exposure levels to MWFs in a population-based, case-control study of bladder cancer.

Issues when modeling benzene, toluene, and xylene exposures using a literature database

A database of benzene, toluene, and xylene measurements was compiled from an extensive literature review that contained information on several exposure determinants, including job type, operation, mechanism of release, process type, ventilation, temperature, distance from the source, quantity, and location. The database was used to develop statistical models for benzene, toluene, and xylene exposure as a function of operation and other workplace determinants. These models can be used to predict exposure levels for subjects enrolled in community-based case-control studies. This article presents the derived parameter estimates for specific operations and additional workplace exposure determinants and describes a number of statistical and data limitation issues that are inherent in determinants modeling of historical published data. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource(s): a PDF file of QQ plots and a Word file with references used in the benzene/toluene/xylene exposure database].

A review of historical exposures to asbestos among skilled craftsmen (1940-2006)

This article provides a review and synthesis of the published and selected unpublished literature on historical asbestos exposures among skilled craftsmen in various nonshipyard and shipyard settings. The specific crafts evaluated were insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers, maintenance workers, and abatement workers. Over 50 documents were identified and summarized. Sufficient information was available to quantitatively characterize historical asbestos exposures for the most highly exposed workers (insulators), even though data were lacking for some job tasks or time periods. Average airborne fiber concentrations collected for the duration of the task and/or the entire work shift were found to range from about 2 to 10 fibers per cubic centimeter (cm3 or cc) during activities performed by insulators in various nonshipyard settings from the late 1960s and early 1970s. Higher exposure levels were observed for this craft during the 1940s to 1950s, when dust counts were converted from millions of particles per cubic foot (mppcf) to units of fibers per cubic centimeter (fibers/cc) using a 1:6 conversion factor. Similar tasks performed in U.S. shipyards yielded average fiber concentrations about two-fold greater, likely due to inadequate ventilation and confined work environments; however, excessively high exposure levels were reported in some British Naval shipyards due to the spraying of asbestos. Improved industrial hygiene practices initiated in the early to mid-1970s were found to reduce average fiber concentrations for insulator tasks approximately two- to five-fold. For most other crafts, average fiber concentrations were found to typically range from <0.01 to 1 fibers/cc (depending on the task or time period), with higher concentrations observed during the use of powered tools, the mixing or sanding of drywall cement, and the cleanup of asbestos insulation or lagging materials. The available evidence suggests that although many historical measurements exceeded the current OSHA 8-h time-weighted average (TWA) permissible exposure limit (PEL) of 0.1 fibers/cc, average fiber concentrations generally did not exceed historical occupational exposure limits in place at the time, except perhaps during ripout activities or the spraying of asbestos in enclosed spaces or onboard ships. Additionally, reported fiber concentrations may not have represented daily or actual human exposures to asbestos, since few samples were collected beyond specific short-term tasks and workers sometimes wore respiratory protective equipment. The available data were not sufficient to determine whether the airborne fiber concentrations represented serpentine or amphibole asbestos fibers, which would have a pronounced impact on the potential health hazards posed by the asbestos. Despite a number of limitations associated with the available air sampling data, the information should provide guidance for reconstructing asbestos exposures for different crafts in specific occupational settings where asbestos was present during the 1940 to 2006 time period.

Retrospective exposure assessment of airborne asbestos related to skilled craftsmen at a petroleum refinery in Beaumont, Texas (1940-2006)

Despite efforts over the past 50 or more years to estimate airborne dust or fiber concentrations for specific job tasks within different industries, there have been no known attempts to reconstruct historical asbestos exposures for the many types of trades employed in various nonmanufacturing settings. In this paper, 8-h time-weighted average (TWA) asbestos exposures were estimated for 12 different crafts from the 1940s to the present day at a large petroleum refinery in Beaumont, TX. The crafts evaluated were insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers, and maintenance workers. This analysis quantitatively accounts for (1) the historical use of asbestos-containing materials at the refinery, (2) the typical workday of the different crafts and specific opportunities for exposure to asbestos, (3) industrial hygiene asbestos air monitoring data collected at this refinery and similar facilities since the early 1970s, (4) published and unpublished data sets on task-specific dust or fiber concentrations encountered in various industrial settings since the late 1930s, and (5) the evolution of respirator use and other workplace practices that occurred as the hazards of asbestos became better understood over time. Due to limited air monitoring data for most crafts, 8-h TWA fiber concentrations were calculated only for insulators, while all other crafts were estimated to have experienced 8-h TWA fiber concentrations at some fraction of that experienced by insulators. A probabilistic (Monte Carlo) model was used to account for potential variability in the various data sets and the uncertainty in our knowledge of selected input parameters used to estimate exposure. Significant reliance was also placed on our collective professional experiences working in the fields of industrial hygiene, exposure assessment, and process engineering over the last 40 yr. Insulators at this refinery were estimated to have experienced 50th (and 95th) percentile 8-h TWA asbestos exposures (which incorporated 8-h TWA fiber concentrations, respirator use and effectiveness, and time spent working with asbestos-containing materials) of 9 (16) fibers/cc (cubic centimeter) from 1940 to 1950, 8 (13) fibers/cc from 1951 to 1965, 2 (5) fibers/cc from 1966 to 1971, 0.3 (0.5) fibers/cc from 1972 to 1975, and 0.005 (0.02) fibers/cc from 1976 to 1985 (estimated exposures were <0.001 fibers/cc after 1985). Estimated 8-h TWA exposures for all other crafts were at least 50- to 100-fold less than that of insulators, with the exception of laborers, whose estimated 8-h TWA exposures were approximately one-fifth to one-tenth of those of insulators. In spite of the data gaps, the available evidence indicates that our estimates of 8-h TWA asbestos exposures reasonably characterize the typical range of values for these categories of workers over time.

Occupational exposure to NDMA and NMor in the European rubber industry

Many nitrosamines are suspected of being human carcinogens, with the highest concentrations in the environment being measured in the rubber industry. Time trends of personal exposure to N-nitrosodimethylamine (NDMA) and to N-nitrosomorpholine (NMor) during the past two decades in the German rubber industry were analysed and compared with cross-sectional studies in the same period in the Netherlands, Poland, the UK and Sweden. In the majority of the surveyed departments exposures reduced over time, but considerable heterogeneity was present between departments and sectors. Significant reductions were primarily found in curing and post-treating departments and ranged from -3% year(-1) to -19% year(-1). In contrast, NDMA levels increased (+13% year(-1)) in maintenance and engineering in the tyres industry. Average NDMA-levels in general rubber goods (GRG) and NMor-levels in tyre production in Germany did not decrease significantly in the past two decades, whereas NDMA-levels in tyre production (-10% year(-1)) and NMor-levels in GRG (-7% year(-1)) declined significantly after the introduction of an exposure limit for total nitrosamines in Germany in 1988. Confidence intervals of average exposures in other studied countries largely overlap trends observed in Germany. Exposure to N-nitrosamines decreased on average two-to-five fold in the German rubber industry with comparable concentration levels in other European countries. Although average levels are well below the current limits exposure has not been eliminated, and incidental high exposures do still occur.

From expert-based to quantitative retrospective exposure assessment at a Soderberg aluminum smelter

OBJECTIVES

Expert judgement of exposure levels is often only poorly or moderately correlated with directly measured levels. For a follow-up of a historical cohort study at a Söderberg aluminum smelter we updated an expert-based semiquantitative job exposure matrix of coal tar pitch volatiles (CTPV) to quantitative estimates of CTPV and benzo(a)pyrene (BaP).

METHODS

Mixed effects models to predict exposure for potroom operation and maintenance jobs were constructed from personal CTPV and BaP measurements. Mean exposures of jobs in non-potroom locations were directly calculated when measurements were available. Exposure estimates for jobs/time periods with no measurements were based on proportion of time spent in exposed areas compared to jobs where exposure was modeled or measured. For pre-1977, the original expert exposure assignments were calibrated using the updated 1977 estimates.

RESULTS

The rate of change in exposure levels varied by time period and was accounted for in mixed models with a linear spline time trend. Other variables significant in the models were job, potroom group and season as fixed effects, and worker as a random effect. The models for potroom operations explained 45 and 27% of the variability in the CTPV and BaP measurements, respectively. The models for maintenance jobs explained 40 and 19% of the variability in the CTPV and BaP measurements, respectively. For 1977-2000 model estimates, direct calculation of means and extrapolation from modeled/measured exposures accounted for 57, 6 and 37% of the exposed person-years, respectively.

CONCLUSIONS

The above methodology maximized the use of exposure measurements and largely replaced the original expert-based estimates. Finer discrimination between exposure levels was possible with the updated exposure assessment. The new estimates are expected to reduce exposure misclassification and help better assess the exposure-response relationships.

Occupational exposure to n-hexane in Italy--analysis of a registry of biological monitoring

OBJECTIVE

This study assesses 2,5-hexanedione (2,5-HD) in the urine of subjects exposed to n-hexane solvent between 1991 and 1998, from details obtained from the Registry of Biological Monitoring (BM) at the Florence Local Health Unit, and its development over time.

METHODS

The Registry contains 15,925 samples from 6,650 subjects occupationally exposed to n-hexane, especially in leather (9,099 samples; 3,607 subjects) and shoe (3,865 samples; 1,938 subjects) production.

RESULTS

Over the time span studied there was a total reduction of 31.9% in urinary 2,5-HD level. The yearly decrease over the entire period was 5.4%. Dividing the 8 years into three periods: before the introduction of the new legislation for health protection in the workplace (1991-1993), during its transition (1994-1996) and after its complete enforcement (1997-1998), respectively, we observed a marked decrease in the last period. Women and young people (under 30 years) experienced significantly higher absorption levels (respectively, 7.1% and 24.4%).

CONCLUSION

The data suggest that monitoring was more frequent in subjects with higher starting values, and the greatest decrease was reported in this group. Reduction may be due to less n-hexane in the products used, better structural conditions in the factories, and the effectiveness of inspections carried out by the authority for hygiene and safety in the workplace. The results confirm the usefulness of the reporting of risk levels of exposure to industrial toxicants by routine biological monitoring.

Exposure of Danish workers to trichloroethylene, 1947-1989

The aim of this study was to investigate the exposure of Danish workers to trichloroethylene (TCE) and the factors that affected such exposure. Data from Danish health authorities were evaluated for use in an epidemiological study of possible adverse health effects of TCE. The paper files relating to 1,075 air measurements taken between 1947 and 1989 at 150 companies were examined to extract information about calendar year, company, industry, type of measurement, and worker. Multiple regression models were used to analyze the effects of various factors on the concentration of TCE. TCE concentrations decreased over the four decades studied. The geometric mean was 329 mg/m3 for measurements taken 1947-1959, and 260 mg/m3, 53 mg/m3, and 23 mg/m3, respectively, for the three subsequent decades. Regression analyses showed that 1) TCE concentrations decreased on average 4 percent per year before 1964 and 15 percent per year afterward; 2) area and personal measurements gave similar concentrations (for the same calendar period, industry, and duration of measurement); 3) longer-duration measurements were associated with lower TCE concentrations; 4) high TCE concentrations occurred in the iron and metal industry; and, 5) in this industry men were exposed to concentrations two times those of women. Moreover, this study indicated that both the exposure level and the proportion of exposed workers in Danish companies increased with decreasing number of employees. Epidemiological studies of health effects of TCE may benefit from evaluating potential risk within different strata of calendar time, number of company employees, sex, and type of industry.

Comprehensive evaluation of long-term trends in occupational exposure: Part 1. Description of the database

OBJECTIVES

To conduct a comprehensive evaluation of long term changes in occupational exposure among a broad cross section of industries worldwide.

METHODS

A review of the scientific literature identified studies that reported historical changes in exposure. About 700 sets of data from 119 published and several unpublished sources were compiled. Data were published over a 30 year period in 25 journals that spanned a range of disciplines. For each data set, the average exposure level was compiled for each period and details on the contaminant, the industry and location, changes in the threshold limit value (TLV), as well as the type of sampling method were recorded. Spearman rank correlation coefficients were used to identify monotonic changes in exposure over time and simple linear regression analyses were used to characterise trends in exposure.

RESULTS

About 78% of the natural log transformed data showed linear trends towards lower exposure levels whereas 22% indicated increasing trends. (The Spearman rank correlation analyses produced a similar breakdown between exposures monotonically increasing or decreasing over time.) Although the rates of reduction for the data showing downward trends ranged from -1% to -62% per year, most exposures declined at rates between -4% and -14% per year (the interquartile range), with a median value of -8% per year. Exposures seemed to increase at rates that were slightly lower than those of exposures which have declined over time. Data sets that showed downward (versus upward) trends were influenced by several factors including type and carcinogenicity of the contaminant, type of monitoring, historical changes in the threshold limit values (TLVs), and period of sampling.

CONCLUSIONS

This review supports the notion that occupational exposures are generally lower today than they were years or decades ago. However, such trends seem to have been affected by factors related to the contaminant, as well as to the period and type of sampling.