Quantification of historical exposures in occupational cohort studies

Occupational asbestos exposure after the ban: a job exposure matrix developed in Italy

Background

Asbestos is a well-known carcinogen for humans. The aim of this study is to develop a tool to estimate occupational asbestos exposure in Italy after the ban using information collected in a national dataset.

Methods

Data were collected from firm registries of workers exposed to asbestos in the period 1996–2016. Descriptive statistics (arithmetic mean, standard deviation, geometric mean and geometric standard deviation) were calculated for the main exposure-related variables (activity sector, occupational group and exposure period). An estimate of workers potentially exposed to asbestos was also performed.

Results

A total of 19 704 airborne measurements of asbestos exposure was selected from the national database of occupational exposures in the sectors of asbestos abatement. Overall, a geometric mean of 7.93 f l−1 was found, and chrysotile was the asbestos type that had more exposures (41%). A total of 46 422 workers was estimated to be potentially at asbestos exposure risk. Exposure data were summarized by calendar period, activity sector and occupational group.

Conclusions

The construction of a job exposure matrix for different occupation/industry combinations may allow the assessment of occupational exposure to asbestos in several removal and disposal activities, and the estimate of the risks associated with asbestos-related diseases in epidemiological studies.

Use and Reliability of Exposure Assessment Methods in Occupational Case-Control Studies in the General Population: Past, Present, and Future

Introduction

Retrospective occupational exposure assessment has been challenging in case-control studies in the general population. We aimed to review (i) trends of different assessment methods used in the last 40 years and (ii) evidence of reliability for various assessment methods.

Methods

Two separate literature reviews were conducted. We first reviewed all general population cancer case-control studies published from 1975 to 2016 to summarize the exposure assessment approach used. For the second review, we systematically reviewed evidence of reliability for all methods observed in the first review.

Results

Among the 299 studies included in the first review, the most frequently used assessment methods were self-report/assessment (n = 143 studies), case-by-case expert assessment (n = 139), and job-exposure matrices (JEMs; n = 82). Usage trends for these methods remained relatively stable throughout the last four decades. Other approaches, such as the application of algorithms linking questionnaire responses to expert-assigned exposure estimates and modelling of exposure with historical measurement data, appeared in 21 studies that were published after 2000. The second review retrieved 34 comparison studies examining methodological reliability. Overall, we observed slightly higher median kappa agreement between exposure estimates from different expert assessors (~0.6) than between expert estimates and exposure estimates from self-reports (~0.5) or JEMs (~0.4). However, reported reliability measures were highly variable for different methods and agents. Limited evidence also indicates newer methods, such as assessment using algorithms and measurement-calibrated quantitative JEMs, may be as reliable as traditional methods.

Conclusion

The majority of current research assesses exposures in the population with similar methods as studies did decades ago. Though there is evidence for the development of newer approaches, more concerted effort is needed to better adopt exposure assessment methods with more transparency, reliability, and efficiency.

Metalworking Fluids and Colon Cancer Risk: Longitudinal Targeted Minimum Loss-based Estimation

Metalworking fluids (MWFs) are a class of complex mixtures of chemicals and oils, including several known carcinogens that may pose a cancer hazard to millions of workers. Reports on the relation between MWFs and incident colon cancer have been mixed.

METHODS

We investigated the relation between exposure to straight, soluble, and synthetic MWFs and the incidence of colon cancer in a cohort of automobile manufacturing industry workers, adjusting for time-varying confounding affected by prior exposure to reduce healthy worker survivor bias. We used longitudinal targeted minimum loss-based estimation (TMLE) to estimate the difference in the cumulative incidence of colon cancer comparing counterfactual outcomes if always exposed above to always exposed below an exposure cutoff while at work. Exposure concentration cutoffs were selected a priori at the 90th percentile of total particulate matter for each fluid type: 0.034, 0.400, and 0.003 for straight, soluble, and synthetic MWFs, respectively.

RESULTS

The estimated 25-year risk differences were 3.8% (95% confidence interval [CI] = 0.7, 7.0) for straight, 1.3% (95% CI = -2.3, 4.8) for soluble, and 0.2% (95% CI = -3.3, 3.7) for synthetic MWFs, respectively. The corresponding risk ratios were 2.39 (1.12, 5.08), 1.43 (0.67, 3.04), and 1.08 (0.51, 2.30) for straight, soluble, and synthetic MWFs, respectively.

CONCLUSIONS

By controlling for time-varying confounding affected by prior exposure, a key feature of occupational cohorts, we were able to provide evidence for a causal effect of straight MWF exposure on colon cancer risk that was not found using standard analytical techniques in previous reports.

Assessment of occupational risks to extremely low frequency magnetic fields: Validation of an empirical non-expert approach

The expert method of exposure assignment involves relying on chemists or hygienists to estimate occupational exposures using information collected on study subjects. Once the estimation method for a particular contaminant has been made available in the literature, it is not known whether a non-expert, briefly trained by an expert remaining available to answer ad hoc questions, can provide reliable exposure estimates. We explored this issue by comparing estimates of exposure to extremely low frequency magnetic fields (ELF-MF) obtained by an expert to those from a non-expert. Using a published exposure matrix, both the expert and non-expert independently calculated a weekly time-weighted average exposure for 208 maternal jobs by considering three main determinants: the work environment, magnetic field sources, and duration of use or exposure to given sources. Agreement between assessors was tested using the Bland-Altman 95% limits of agreement. The overall mean difference in estimates between the expert and non-expert was 0.004 μT (standard deviation 0.104). The 95% limits of agreement were − 0.20 μT and + 0.21 μT. The work environments and exposure sources were almost always similarly identified but there were differences in estimating exposure duration. This occurred mainly when information collected from study subjects was not sufficiently detailed. Our results suggest that following a short training period and the availability of a clearly described method for estimating exposures, a non-expert can cost-efficiently and reliably assign exposure, at least to ELF-MF.

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Retrospective occupational exposure assessment often relies on the expert method.

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Using a published job-exposure matrix, a trained non-expert can correctly estimate an individual's specific exposure.

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Non-expert method is a feasible, practical, and based on our study, a valid approach to code exposure.

An Icon-based Interview for the Assessment of Occupational Pesticide Exposure in a Case–Control Study of Childhood Leukemia

An icon-calendar interview form (ICF) for a case-control study of childhood leukemias and parental exposures to pesticides is described. It includes calendar sheets, icons for life events, crops, jobs, regions, non-agricultural jobs, application techniques and personal protection, markers for durations of exposure patterns, and checklists of pesticides. The ICF collects monthly data from two years before birth until diagnosis of cancer (index children) or until either the interview date or age 15 (controls). Data ascertainment was easy in 62% of interviews, moderately easy in 32%, and difficult in 6%. Seventy-eight subjects delivered data on specific pesticides with pesticide checklists, which improved identification of pesticides. ICF performs satisfactorily for crops, tasks, and other determinants of exposure. Data on pesticides will be further improved by introducing external data use on different crops, time periods, and regions, and by exposure modeling for 27 pesticides.

Dust exposure is associated with increased lung function loss among workers in the Norwegian silicon carbide industry

OBJECTIVES

To investigate the relationship between dust exposure and annual change in lung function among employees in Norwegian silicon carbide (SiC) plants using a quantitative job exposure matrix (JEM) regarding total dust.

METHODS

All employees, 20-55 years of age by inclusion (n=456), were examined annually for up to 5 years (1499 examinations). Spirometry was performed at each examination, and a questionnaire encompassing questions of respiratory symptoms, smoking status, job and smoking history, and present job held was completed. A JEM was constructed based on 1970 personal total dust exposure measurements collected during the study period. The association between lung function and total dust exposure was investigated using linear mixed models.

RESULTS

The annual change in forced expiratory volume (FEV) in one second per squared height, FEV1/height(2), per mg/m(3) increase in dust exposure was -2.3 (95% CI -3.8 to -0.79) (mL/m(2))×year(-1). In an employee of average height (1.79 m) and exposure (1.4 mg/m(3)) the estimated contribution to the annual change in FEV1 associated with dust was 10.4 mL/year. The annual change in FEV1/height(2) in current, compared with non-smokers was -1.9 (-7.2 to 3.4) (mL/m(2))×year(-1). The estimated overall annual decline in FEV1 among current and non-smokers in the highest exposed group was -91.2 (-124.3 to -58.1) (mL/m(2))×year(-1) and -49.0 (-80.2 to -17.8) (mL/m(2))×year(-1), respectively.

CONCLUSIONS

Dust exposure, expressed by a quantitative JEM, was found to be associated with an increased yearly decline in FEV1 in employees of Norwegian SiC plants.

Assessing occupational exposure to chemicals in an international epidemiological study of brain tumours

The INTEROCC project is a multi-centre case-control study investigating the risk of developing brain cancer due to occupational chemical and electromagnetic field exposures. To estimate chemical exposures, the Finnish Job Exposure Matrix (FINJEM) was modified to improve its performance in the INTEROCC study and to address some of its limitations, resulting in the development of the INTEROCC JEM. An international team of occupational hygienists developed a crosswalk between the Finnish occupational codes used in FINJEM and the International Standard Classification of Occupations 1968 (ISCO68). For ISCO68 codes linked to multiple Finnish codes, weighted means of the exposure estimates were calculated. Similarly, multiple ISCO68 codes linked to a single Finnish code with evidence of heterogeneous exposure were refined. One of the key time periods in FINJEM (1960-1984) was split into two periods (1960-1974 and 1975-1984). Benzene exposure estimates in early periods were modified upwards. The internal consistency of hydrocarbon exposures and exposures to engine exhaust fumes was improved. Finally, exposure to polycyclic aromatic hydrocarbon and benzo(a)pyrene was modified to include the contribution from second-hand smoke. The crosswalk ensured that the FINJEM exposure estimates could be applied to the INTEROCC study subjects. The modifications generally resulted in an increased prevalence of exposure to chemical agents. This increased prevalence of exposure was not restricted to the lowest categories of cumulative exposure, but was seen across all levels for some agents. Although this work has produced a JEM with important improvements compared to FINJEM, further improvements are possible with the expansion of agents and additional external data.

An analysis of workplace exposures to benzene over four decades at a petrochemical processing and manufacturing facility (1962-1999)

Benzene, a known carcinogen, can be generated as a by-product during the use of petroleum-based raw materials in chemical manufacturing. The aim of this study was to analyze a large data set of benzene air concentration measurements collected over nearly 40 years during routine employee exposure monitoring at a petrochemical manufacturing facility. The facility used ethane, propane, and natural gas as raw materials in the production of common commercial materials such as polyethylene, polypropylene, waxes, adhesives, alcohols, and aldehydes. In total, 3607 benzene air samples were collected at the facility from 1962 to 1999. Of these, in total 2359 long-term (>1 h) personal exposure samples for benzene were collected during routine operations at the facility between 1974 and 1999. These samples were analyzed by division, department, and job title to establish employee benzene exposures in different areas of the facility over time. Sampling data were also analyzed by key events over time, including changes in the occupational exposure limits (OELs) for benzene and key equipment process changes at the facility. Although mean benzene concentrations varied according to operation, in nearly all cases measured benzene quantities were below the OEL in place at the time for benzene (10 ppm for 1974-1986 and 1 ppm for 1987-1999). Decreases in mean benzene air concentrations were also found when data were evaluated according to 7- to 10-yr periods following key equipment process changes. Further, an evaluation of mortality rates for a retrospective employee cohort (n = 3938) demonstrated that the average personal benzene exposures at this facility (0.89 ppm for the period 1974-1986 and 0.125 ppm for the period 1987-1999) did not result in increased standardized mortality ratio (SMRs) for diseases or malignancies of the lymphatic system. The robust nature of this data set provides comprehensive exposure information that may be useful for assessing human benzene exposures at similar facilities. The data also provide a basis for comparable measured exposure levels and the potential for adverse health effects. These data may also prove beneficial for comparing relative exposure potential for production versus nonproduction operations and the relationship between area and personal breathing zone samples.

Lung function and respiratory symptoms in hard metal workers exposed to cobalt

OBJECTIVE

To follow-up lung function and airway symptoms in workers exposed to cobalt dust at a hard metal plant.

METHODS

A total of 582 employees underwent spirometry and completed a questionnaire. A historical exposure matrix was created, assigning figures for historical and recent work-related exposure.

RESULTS

At the time of employment, 5% reported symptoms from respiratory tract. At follow-up, 5% suffered from persistent coughing and 7% reported asthma; 20% were daily smokers. Among nonsmokers without asthma, an evident, statistically nonsignificant, dose-response effect was seen between increasing cobalt exposure and decline in FEV1 (forced expiratory volume in the first second). In all exposure categories, the FEV1 in smokers declined 10 mL more per year than for nonsmokers.

CONCLUSIONS

Even low levels of cobalt exposure seem to hamper lung function both in smokers and nonsmokers. This impact is considered low in relation to the effect of aging.

Solvent exposures and Parkinson disease risk in twins

OBJECTIVE

Several case reports have linked solvent exposure to Parkinson disease (PD), but few studies have assessed associations with specific agents using an analytic epidemiologic design. We tested the hypothesis that exposure to specific solvents is associated with PD risk using a discordant twin pair design.

METHODS

Ninety-nine twin pairs discordant for PD ascertained from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort were interviewed regarding lifetime occupations and hobbies using detailed job task-specific questionnaires. Exposures to 6 specific solvents selected a priori were estimated by expert raters unaware of case status.

RESULTS

Ever exposure to trichloroethylene (TCE) was associated with significantly increased risk of PD (odds ratio [OR], 6.1; 95% confidence interval [CI] 1.2-33; p = 0.034), and exposure to perchloroethylene (PERC) and carbon tetrachloride (CCl(4) ) tended toward significance (respectively: OR, 10.5; 95% CI, 0.97-113; p = 0.053; OR, 2.3; 95% CI, 0.9-6.1; p = 0.088). Results were similar for estimates of exposure duration and cumulative lifetime exposure.

INTERPRETATION

Exposure to specific solvents may increase risk of PD. TCE is the most common organic contaminant in groundwater, and PERC and CCl(4) are also ubiquitous in the environment. Our findings require replication in other populations with well-characterized exposures, but the potential public health implications are substantial.

A novel strategy for retrospective exposure assessment in the Norwegian silicon carbide industry

The objective was to construct a retrospective job-exposure matrix (JEM) for the Norwegian silicon carbide industry. More than 3300 historical total dust measurements were available (1967-2005); however, there were few measurements of other agents. Total dust measurements were therefore used as the basis for the JEM, and a novel method was developed to estimate exposure to other agents. Multiple linear regression models were developed to describe historical exposure to total dust. Exposure estimates were extrapolated backward to periods without exposure data by adjustments for process and work-hour related changes. An exposure assessment study was performed where total dust was sampled in parallel with fibers or respirable dust. The respirable dust was analyzed for the content of quartz, cristobalite, and silicon carbide. Mixed-effect models were developed to estimate the exposure to these agents from total dust exposure, plant, and job group. Exposure to asbestos and polycyclic aromatic hydrocarbons was assigned qualitatively. Multiple linear regression models of total dust described historical exposure best in the furnace department (R(2) (adj) = 0.49-0.74). Models in the other departments explained less variance (R(2) (adj) = 0.12-0.32). Exposure determinants and total dust explained a substantial proportion of the between- (70-100%) and within-worker (8.0-54%) variance in the mixed-effect models. The relative bias between available historical measurements and the estimated exposure to dust components varied between -39% (fiber) and 40% (quartz). However, corrections were not considered necessary due to limitations in the historical data. The component-specific metrices were sufficiently different from each other (r(Pearson) < 0.7), with the exception of total and respirable dust (r(Pearson) = 0.84) and total dust and cristobalite (r(Pearson) = 0.72), and will enable component-specific epidemiologic analyses in the future. Improved and less correlated estimates of exposure levels for the different components in the dust were obtained with the updated exposure assessment. Due to limitations in the measurement data, assumptions had to be made, especially in the period before 1967. [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: a file containing tables outlining multiple linear regression models for prediction of total dust exposure in the processing departments of Norwegian SiC producing plants, evaluation of the predictive abilities of the reduced total dust models, and mixed models for pedicting exposure to fibers and respirable quartz, cristobalite, non-fibrous silicon carbide and respirable dust from total dust exposure.].

Exposure assessment and modeling of quartz in Swedish iron foundries for a nested case-control study on lung cancer

Exposure assessment of quartz in Swedish iron foundries was performed based on historical and current measurement data. To evaluate the exposure-response relationship between quartz exposure and lung cancer, we modeled quartz exposure from our database of measurements using determinants job title, time period, and company. Based on these modeled exposure data, we conducted a nested case-control evaluation. In our database, the overall individual, daily time-weighted average (TWA) quartz concentrations of current and historical data varied between 0.0018 and 4.9 mg/m(3), averaging 0.083 mg/m(3). Job titles with mean TWAs for the whole study period exceeding the European Union recommended occupational exposure limit of 0.05 mg/m(3) were fettlers (0.087 mg/m(3)), furnace and ladle repair (0.42 mg/m(3)), and maintenance (0.054 mg/m(3)) workers. The mixed model analysis demonstrated significant determinants on the job level for furnace and ladle repair (β = 4.06; 95% confidence interval [CI] 2.78-5.93). For all jobs, significantly higher exposure levels occurred only during the first time period, 1968-1979 (β = 2.08; 95% CI 1.75-2.47), and a decreasing but not significant trend was noted for the three following 10-year time periods up to 2006 (β = 1.0, 0.96 and 1, respectively). Two iron foundries had significantly higher quartz concentration levels than the others (β = 1.31; 95% CI 1.00-1.71 and β = 1.63; 95% CI 1.00-2.65, respectively). The individual cumulative quartz exposure measures were categorized in low, medium, and high exposure (0.5-<1, 1-1.9 and ≥ 2 mg/m(3)*years, respectively). In the nested case-control analysis, we found the highest odds ratios of lung cancer (OR 1.17; 95% CI 0.53-2.55) for the medium exposure group. No dose-response trend or significantly increased risk was determined for our high exposed group (≥2 mg/m(3)), representing 40 years of exposure at >0.05 mg/m(3) of quartz. To conclude, certain foundry workers are still exposed to high levels of quartz, but an increased risk of lung cancer caused by quartz exposure in these Swedish iron foundries could not be confirmed at our exposure levels.

Cohort mortality study of roofing granule mine and mill workers. Part I: Estimation of historical crystalline silica exposures

A study was conducted to construct a job exposure matrix for the roofing granule mine and mill workers at four U.S. plants. Each plant mined different minerals and had unique departments and jobs. The goal of the study was to generate accurate estimates of the mean exposure to respirable crystalline silica for each cell of the job exposure matrix, that is, every combination of plant, department, job, and year represented in the job histories of the study participants. The objectives of this study were to locate, identify, and collect information on all exposure measurements ever collected at each plant, statistically analyze the data to identify deficiencies in the database, identify and resolve questionable measurements, identify all important process and control changes for each plant-department-job combination, construct a time line for each plant-department combination indicating periods where the equipment and conditions were unchanged, and finally, construct a job exposure matrix. After evaluation, 1871 respirable crystalline silica measurements and estimates remained. The primary statistic of interest was the mean exposure for each job exposure matrix cell. The average exposure for each of the four plants was 0.042 mg/m(3) (Belle Mead, N.J.), 0.106 mg/m(3) (Corona, Calif.), 0.051 mg/m(3) (Little Rock, Ark.), and 0.152 mg/m(3) (Wausau, Wis.), suggesting that there may be substantial differences in the employee cumulative exposures. Using the database and the available plant information, the study team assigned an exposure category and mean exposure for every plant-department-job and time interval combination. Despite a fairly large database, the mean exposure for > 95% of the job exposure matrix cells, or specific plant-department-job-year combinations, were estimated by analogy to similar jobs in the plant for which sufficient data were available. This approach preserved plant specificity, hopefully improving the usefulness of the job exposure matrix.

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.

The role of exposure reconstruction in occupational human health risk assessment: current methods and a recommended framework

Exposure reconstruction for substances of interest to human health is a process that has been used, with various levels of sophistication, as far back as the 1930s. The importance of robust and high-quality exposure reconstruction has been recognized by many researchers. It has been noted that misclassification of reconstructed exposures is relatively common and can result in potentially significant effects on the conclusions of a human health risk assessment or epidemiology study. In this analysis, a review of the key exposure reconstruction approaches described in over 400 papers in the peer-reviewed literature is presented. These approaches have been critically evaluated and classified according to quantitative, semiquantitative, and qualitative approaches. Our analysis indicates that much can still be done to improve the overall quality and consistency of exposure reconstructions and that a systematic framework would help to standardize the exposure reconstruction process in the future. The seven recommended steps in the exposure reconstruction process include identifying the goals of the reconstruction, organizing and ranking the available data, identifying key data gaps, selecting the best information sources and methodology for the reconstruction, incorporating probabilistic methods into the reconstruction, conducting an uncertainty analysis, and validating the results of the reconstruction. Influential emerging techniques, such as Bayesian data analysis, are highlighted. Important issues that will likely influence the conduct of exposure reconstruction into the future include improving statistical analysis methods, addressing the issue of chemical mixtures, evaluating aggregate exposures, and ensuring transparency with respect to variability and uncertainty in the reconstruction effort.

Cumulative exposure estimates for polychlorinated biphenyls using a job-exposure matrix

PCB exposure has been associated with increased risk for cancer, neurological disease, and for birth defects in children exposed in utero. Because of the long half-lives of PCB congeners, they remain a public health problem in the United States 30 years after being banned. Workers (n=3569) at an Indiana capacitor manufacturing plant were exposed to polychlorinated biphenyls (PCBs) from 1957 to 1977. The purpose of this work was to develop a period-specific job-exposure matrix (JEM) for a follow-up epidemiologic study investigating the increased risks for cancer previously observed in the cohort.

METHODS

We used eight exposure determinants to estimate PCB exposures systematically. Work history, job description, capacitor production factors, PCB usage trends, and air sample data were used to develop the JEM in four steps: (1) all job titles (n=884) were assessed for exposure determinants, (2) jobs with similar exposure determinants were grouped, (3) for each job exposure category, exposure intensity (high-medium-low-background) and frequency (continuous-intermittent) were qualitatively rated separately for inhalation and dermal exposure, and (4) for each job exposure category, the product of intensity (based on air sampling data) and frequency (fraction of day exposed) was calculated. The JEM was then modified for two eras of different PCB exposure conditions.

RESULTS

The resulting JEM consists of inhalation and dermal exposure values for 19 job exposure categories.

CONCLUSION

The JEM showed an exposure-response trend associated with increased brain cancer mortality in the epidemiologic study.

Cancer mortality in a synthetic spinning plant in Besançon, France

OBJECTIVES

To assess the mortality of a cohort of workers in a synthetic textile spinning plant and to evaluate the relationship between mortality from lung, liver and bladder cancer and the processes or the products used.

METHODS

The study population consisted of male workers present for at least 6 months in the plant from 1968 to 1984. The cohort was followed until 1999. Vital status and the causes of death were determined by consulting national registries. The population of the Franche-Comté region was used for comparison. In total, 17 groups of exposure were assessed by the industrial hygienist, based on the consensus of an expert group that determined the exposure levels of each job to selected occupational hazards. Each worker was assigned to one or several groups, according to his occupational history. Confounding factors could not be assessed. Standardised mortality ratios (SMR) and 95% bilateral confidence intervals were calculated based on an assumed Poisson distribution of the number of cases to compare the plant mortality and the population mortality. Internal analyses were performed with Cox models in order to assess the risks of death related to the various exposures.

RESULTS

In the whole cohort, mortality from all malignant neoplasms was lower than expected, but this was not significant. All the estimated SMRs were lower than or close to 1. The "hot -line fitters" (RR = 2.13; n = 9; 1.06 to 4.29) and the "fibre-drawing workers" (RR = 1.83; n = 20;1.09 to 3.07) experienced a statistically significant excess in mortality from lung cancer. A slightly elevated but not significant risk of death related to lung cancer (RR = 1.5; n = 41; 0.8 to 2.7) was observed in the groups with the highest exposure to mineral fibres. A statistically significant increase in cancer deaths was observed for workers with high exposure to dust (higher intensity: RR = 1.42; n = 79; 1.06 to 1.89).

CONCLUSION

Some findings, mainly of lung cancer, justify further exploration in other plants in this industry.

Exposure assessment methods for a study of mortality and cancer morbidity in relation to specific petroleum industry exposures

In 1987 a Canadian company implemented an exposure tracking and health information system. The exposure tracking method aligned closely with published concepts for describing workplace exposure, with over 1800 similar exposure groups being used to describe occupational exposures. The database has been actively maintained and is subject to a number of quality checks. Recently, the company initiated a cancer morbidity study, with one objective being to examine whether the exposure tracking data could be used to reconstruct exposure estimates for the cohort. Five agents--hydrogen sulfide, petroleum coke/spent catalyst, hydrocarbon solvents and fuels, hydrocarbon lubricants, and an index for exposure to operations derived from noise exposure--were selected for development of occupational exposure estimates for each cohort member. The cohort consisted of workers first employed between January 1964 and December 1994 and who were employed for at least 1 year. Work history records were associated with a similar exposure group, using human resources data and knowledge of local industrial hygienists. Only employees with >90% duration of their work history assigned were kept in the cohort (25,292 people out of a possible 25,617). For each similar exposure group inventory, the substances were identified that contributed to each of the five agents being studied. Exposure estimates before 1987 were modified using historic occupational exposure limits. Rules were created to sum the exposure from multiple substances found in any one similar exposure group. The validity of exposure estimates was tested via comparison with results documented in industrial hygiene survey reports. Industrial hygienists who were unaware of the derived exposure estimates evaluated several hundred industrial hygiene surveys and prepared benchmark information. The two lists were then evaluated for concordance, which was found to be significantly different from that occurring by chance. We conclude that the process described can create valid exposure estimates for use in epidemiology studies.

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.

Estimating historical occupational exposure to airborne hexavalent chromium in a chromate production plant: 1940--1972

This article presents a retrospective exposure assessment for 493 workers who were occupationally exposed to airborne hexavalent chromium, Cr(VI), at a Painesville, Ohio, chromate production plant from 1940-1972. Exposure estimates were reconstructed using a job-exposure matrix approach that related job titles with area monitoring data from 21 industrial hygiene surveys conducted from 1943 to 1971. No personal monitoring data were collected. Specifically, airborne Cr(VI) concentration profiles for 22 areas of the plant, termed job-exposure group (JEG) areas, were constructed for three distinct time periods (1940-1949, 1950-1964, and 1965-1972), with cut points based on known major plant and process changes. Average airborne Cr(VI) concentrations were the highest for the bridge crane operators (5.5 mg/m3) prior to 1965, although only four cohort members held this job title. Airborne concentrations for the rest of the production areas of the plant ranged from 1.9 mg/m3 for packers in the 1940s to 0.012 mg/m3 for ore mill operators after 1964. For nearly all JEG areas, exposures decreased over time, particularly after 1964. For example, average airborne concentrations in production areas of the plant decreased from 0.72 mg/m3 in the 1940s to 0.27 mg/m3 from 1950 to 1964, and the average was 0.039 mg/m3 after 1964. Former workers were interviewed to determine activity patterns in the plant by job title. This information was combined with Cr(VI) monitoring data to calculate cumulative occupational exposure for each worker. Cumulative exposures ranged from 0.003 to 23 (mg/m3) x years. The highest monthly 8-hour average exposure concentration for each worker ranged from 0.003 to 4.1 mg/m3. These exposure estimates have been combined with mortality data for this cohort to assess the lung cancer risk associated with inhaled Cr(VI), and a positive dose-response relationship was observed for increases in lung cancer mortality with measures of cumulative exposure and highest monthly exposure.

Dose-response and risk assessment of airborne hexavalent chromium and lung cancer mortality

This study evaluates the dose-response relationship for inhalation exposure to hexavalent chromium [Cr(VI)] and lung cancer mortality for workers of a chromate production facility, and provides estimates of the carcinogenic potency. The data were analyzed using relative risk and additive risk dose-response models implemented with both Poisson and Cox regression. Potential confounding by birth cohort and smoking prevalence were also assessed. Lifetime cumulative exposure and highest monthly exposure were the dose metrics evaluated. The estimated lifetime additional risk of lung cancer mortality associated with 45 years of occupational exposure to 1 microg/m3 Cr(VI) (occupational exposure unit risk) was 0.00205 (90%CI: 0.00134, 0.00291) for the relative risk model and 0.00216 (90%CI: 0.00143, 0.00302) for the additive risk model assuming a linear dose response for cumulative exposure with a five-year lag. Extrapolating these findings to a continuous (e.g., environmental) exposure scenario yielded an environmental unit risk of 0.00978 (90%CI: 0.00640, 0.0138) for the relative risk model [e.g., a cancer slope factor of 34 (mg/kg-day)-1] and 0.0125 (90%CI: 0.00833, 0.0175) for the additive risk model. The relative risk model is preferred because it is more consistent with the expected trend for lung cancer risk with age. Based on statistical tests for exposure-related trend, there was no statistically significant increased lung cancer risk below lifetime cumulative occupational exposures of 1.0 mg-yr/m3, and no excess risk for workers whose highest average monthly exposure did not exceed the current Permissible Exposure Limit (52 microg/m3). It is acknowledged that this study had limited power to detect increases at these low exposure levels. These cancer potency estimates are comparable to those developed by U.S. regulatory agencies and should be useful for assessing the potential cancer hazard associated with inhaled Cr(VI).

Performance of different exposure assessment approaches in a study of bitumen fume exposure and lung cancer mortality

BACKGROUND

We compared performance of different exposure assessment approaches in a cohort study of cancer risk among European asphalt workers.

METHODS

Three bitumen fume exposure indices (duration of exposure (years), average exposure (mg/m3) and cumulative exposure (mg/m3*years)) and two latency models (with and without a 15 year lag) were considered for an association between lung cancer mortality and bitumen fume.

RESULTS

There was no association between lung cancer risk and either duration or cumulative exposure. However, there was the suggestion of an increase in lung cancer risk accompanying rise in average exposure. Only models with average bitumen fume exposure (with or without lag) improved model fit, albeit to the same extent.

CONCLUSIONS

Constructing quantitative indices of exposure intensity was justified because they produced the greatest improvement in fit of models that explored possible relationship between bitumen fume exposure and lung cancer risk. The identified associations require further investigation.

Development of quantitative exposure data for a pooled exposure-response analysis of 10 silica cohorts

BACKGROUND

Comprehensive quantitative silica exposure estimates over time, measured in the same units across a number of cohorts, would make possible a pooled exposure-response analysis for lung cancer. Such an analysis would help clarify the continuing controversy regarding whether silica causes lung cancer.

METHODS

Existing quantitative exposure data for 10 silica-exposed cohorts were retrieved from the original investigators. Occupation- and time-specific exposure estimates were either adopted/adapted or developed for each cohort, and converted to milligram per cubic meter (mg/m(3)) respirable crystalline silica.

RESULTS

Quantitative exposure assignments were typically based on a large number (thousands) of raw measurements, or otherwise consisted of exposure estimates by experts (for two cohorts). Median exposure level of the cohorts ranged between 0.04 and 0.59 mg/m(3) respirable crystalline silica. Exposure estimates were partially validated via their successful prediction of silicosis in these cohorts.

CONCLUSIONS

Existing data were successfully adopted or modified to create comparable quantitative exposure estimates over time for 10 silica-exposed cohorts, permitting a pooled exposure-response analysis. The difficulties encountered in deriving common exposure estimates across cohorts are discussed.

Evaluation of concurrent personal measurements of acrylonitrile using different sampling techniques

In a retrospective assessment of employee exposure to acrylonitrile (AN) for an epidemiological study, investigators from the National Cancer Institute (NCI) and the National Institute for Occupational Safety and Health (NIOSH) evaluated the feasibility of using historic acrylonitrile air samples without modification. The evaluation discussed here was to determine whether the air sampling results across plants were comparable. During site visits to each plant conducted between 1984 and 1986, study investigators collected personal air samples for four days on approximately ten jobs per day. During these visits, IHs at seven of the eight plants also collected personal samples to compare their sample values to the study-collected sample values. Each plant's IH collected these concurrent measurements for their own use and independent of the IHs at the other plants. The plant IHs had no common sampling protocol but, rather, used professional judgment in deciding sampling logistics for their concurrent measurement. In addition, each plant IH used a different laboratory to analyze samples (the study industrial hygienists used one laboratory). Three sampling methods were used by plant industrial hygienists to collect concurrent measurements: charcoal tubes, passive monitors, and porous polymer tubes. The study investigators only used charcoal tubes. Two hundred and sixty four (264) pairs of concurrent measurements were collected. To assess the +/- comparability of the data sets, paired-observation tests were used. The two sets of charcoal tubes were found to compare favorably with each other. The study's charcoal tubes were 1.2 times higher than results from plant passive monitors. No correlation was found between the study's charcoal tube results and plant porous polymer tube results, although the means for 34 pairs of samples were equivalent. As a result of this evaluation, the investigators decided that no adjustments would be made to the plant measurements. This type of evaluation should be considered when using measurement data in multisite epidemiological studies.

Cumulative exposure to styrene and visual functions

BACKGROUND

Results from a 1990-1992 longitudinal study of several reinforced plastics plants showed that for those workers whose styrene exposure had decreased, color vision (CV) improved; while near visual contrast sensitivity (CS) was poorer.

METHODS

In 1999, we retested these visual functions in 18 workers with good visual acuity. A cumulative exposure index (CEI), corrected for respirator use, was calculated for each worker.

RESULTS

Intra-individual comparison of mandelic acid (MA) showed a significant decrease over time (Friedman; P = 0.015), but current values were not related to CEI. For CV, no significant difference was observed between 1992 and 1999; present results were not related to MA or CEI. The CS profile decreased over time, with significant differences at 3 cpd (Friedman; P < 0.05). CS did not vary with MA levels, but was significantly depressed at the intermediate frequencies among those in the upper CEIH category (Kruskal-Wallis; P < 0.05).

CONCLUSIONS

These findings suggest that CS loss increases with long-term cumulative exposure, reflecting chronic damage to the neuro-optic pathways.

Exposure Assessment: Industrial Hygiene and Safety

Poison information specialists use a wide variety of consultants in the process of fielding calls. One group with whom they may appear to have the least in common is the industrial safety and health specialists. By knowing more about their respective backgrounds, both these specialists can benefit, ultimately making better clinical decisions on any given patient exposure event that they may be responding to. In terms of training, there are some important differences to note with respect to the poison information specialist and industrial safety and health specialist.

Use of miniradiographs to detect silicosis. Comparison of radiological with autopsy findings

Radiological and routine autopsy findings from 241 South African gold miners were compared, using pathology as the "gold standard." Previous annual screening miniradiographs were read independently by two readers, using the International Labor Office (ILO) grading system, without reference to personal identifiers. Individual and consensus silicosis grades were recorded for each subject. When pathological and radiological silicosis were defined as any abnormal grade, the sensitivity and specificity of the radiological diagnosis was 67.5% and 80%, with positive and negative predictive values of 63% and 83%. Most undetected autopsy silicosis was early-grade. Using higher pathological and radiological grades to define silicosis (5 nodules or more and ILO grades 1/1 and above), sensitivity and specificity increased to 71% and 96%, and positive and negative predictive values increased to 76% and 95%, respectively. Use of a consensus grade made little difference to results from individual readers. For each radiological definition, sensitivity was considerably higher than, but specificity was similar to, that found in a previous study of South African gold miners which used the same pathology source and standard sized films. The difference between these two study findings, and unexpected demonstration of higher sensitivity from miniradiographs, suggests that further research is required into factors affecting radiological interpretation before silicosis grading can be considered to be adequately standardized.

Study of cancer incidence among 8530 male workers in eight Norwegian plants producing ferrosilicon and silicon metal

OBJECTIVES

To examine the association between cancer incidence, in particular incidence of lung cancer, and duration of work among employees in eight Norwegian plants producing ferrosilicon and silicon metal.

METHODS

Among men first employed during 1933-91 and with at least 6 months in these plants, the incident cases of cancer during 1953-91 were obtained from The Cancer Registry of Norway. The numbers of various cancers were compared with expected figures calculated from age and calendar time specific rates for Norwegian men during the same period. Internal comparisons of rates were performed with Poisson regression analysis. The final cohort comprised 8530 men.

RESULTS

A total of 832 cases of cancer were observed against 786 expected (standardised incidence ratio (SIR) 1.06). Among the furnace workers an increased incidence of lung cancer (SIR 1.57) and testicular cancer (SIR 2.30) was found. Internal comparisons of rates by Poisson regression analysis among the rural furnace workers showed a positive trend between incidence of lung cancer and duration of work of 1.05 (95% confidence interval (95% CI) 1.00 to 1.10)/work-year. Excess cases of prostate and kidney cancer were found among blue collar non-furnace workers, in particular among the mechanics.

CONCLUSION

The results suggest associations between furnace work and lung and testicular cancer, and between non-furnace work and prostate cancer.

Occupational cancer among women: research status and methodologic considerations

Occupational causes of cancer have not been well-evaluated among women. An increase in the number of women in the work force in jobs with potentially hazardous exposures during the past few decades raises the question as to whether there is a need to enhance our efforts in this area. The inability to evaluate occupational causes of female gynecologic tumors in studies of men, plus the potential for variation in outcome responses between men and women because of gender-based exposure and susceptibility differences, underscore the need for investigations specifically focused on women. Investigations of occupational exposures and cancer risk among women may require design considerations that differ somewhat from studies of men. Issues to consider include the impact of studying outcomes with high survival (e.g., breast cancer), gender-specific exposure patterns and toxicokinetic processing of some chemicals, special limitations in the use of the general population as the referent, and the need to control for established risk factors for gynecologic tumors.

Exposure to PAH and fluoride in aluminum reduction plants in Norway: historical estimation of exposure using process parameters and industrial hygiene measurements

BACKGROUND

In this study, we describe the methodology used for historical estimation of exposure to fluoride and to PAH in vertical stud Søderberg (VSS) potrooms at two Norwegian aluminum smelters. The assessment was performed in order to develop exposure data for epidemiological studies of cause-specific mortality and cancer incidence.

METHODS

The estimation was performed in several steps. In the first step, we estimated the area concentrations of fluoride and PAH in periods with no measurements. Relationships between measured area concentrations and process parameters were investigated by statistical modeling. Process parameters and the models were then used to estimate area concentrations in periods lacking area measurement data. In the second step, the relationships between the area measurements and job specific exposure (personal measurements) were investigated by use of a measurement model. In the last step, the obtained relationships were used to estimate job specific exposure in different periods.

RESULTS

The range for the annual exposure estimates in the VSS-potrooms was 0.05-1.7 mg/m3 for fluoride and 3-3,437 micrograms/m3 for PAH.

CONCLUSIONS

Despite limitations of available measurements in the early production period, we have concluded that the exposure estimates from this study provide a reasonable tool for the estimation of dose-response relations in subsequent epidemiological analyses.

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

OBJECTIVES

To explore the effects of various factors related to the industry, the contaminant, and the period and type of sampling on long term declining trends in occupational exposure.

METHODS

Linear regression analyses were used to assess the relation between reductions in exposure and geographical location, industrial sector, type of contaminant, type of monitoring, carcinogenic classification, calendar period, duration of sampling, and number of reductions in the threshold limit value during the sampling period. Both univariable and multivariable models were applied.

RESULTS

Based on univariable analyses, the findings suggest that exposures declined more rapidly in manufacturing than in mining, more rapidly for aerosol contaminants than for vapours, and more rapidly when biological, rather than airborne, monitoring was conducted. Exposures collected more recently (first year of sampling in 1972 or later) fell more rapidly than exposures first evaluated during earlier periods. Irrespective of when the data were collected, the results also suggest that the longer the duration of sampling the slower the rate of decline. Taken together, we found that characteristics related to the contaminant, the industry, the sampling period, and the type of sampling explained a substantial proportion of the variability for exposures evaluated before 1972 (R2 = 0.78) and for sites evaluated both before and after 1972 (R2 = 0.91), but explained essentially no variation for data gathered exclusively after 1972 (R2 = 0.04).

CONCLUSIONS

By identifying factors that have affected the rates of reduction in a consistent fashion, the results should guide investigators in estimating historical levels when studies assessing exposure-response relations are carried out.