Assessing whole body vibration exposure for use in epidemiological studies of back injuries: measurements, observations and self-reports.

Improved assessment of whole body vibration exposure is needed for epidemiological studies investigating the causes of low back disorders. Vibration was measured on 54 worker-days in five heavy industries, with data collected on observed and self-reported driving conditions, demographics, and vehicle characteristics. Variables significant at p < 0.1 in simple linear regressions (20 of 34) were retained for mixed effects multiple regressions to determine the best prediction of rms vibration level and 8-h equivalent vibration exposure. Vibration was measured, on average, for 205 min per work shift (SD 105). Means and standard deviations in m · s⁻² were: x-axis 0.35 (0.19); y-axis 0.34 (0.28); z-axis 0.54 (0.23); vector sum 0.90 (0.49); and 8-h equivalent vector sum 0.70 (0.37). The final three regression models retained only 2 or 3 of the 34 variables (driving speed (<20 km/h and/or 20-40 km/h) and industry and/or vehicle type and explained up to 60% of the variance (R² = 0.26-0.6). PRACTITIONER SUMMARY: The purpose of the project was to create a model that can predict whole body vibration exposure from a number of observed or self-reported variables. This could eliminate the need for costly and time-consuming field measurements of WBV in epidemiological studies. Despite a large number of variables included in the model (34) and 54 worker-days of WBV measurement, the final models contained only two or three variables, and explained 60% of the variance. While this is an improvement over use of job title in epidemiological studies, it still leaves a considerable amount of WBV variance unexplained.

Development and evaluation of an observational Back-Exposure Sampling Tool (Back-EST) for work-related back injury risk factors.

We developed and evaluated an observational Back-Exposure Sampling Tool. A literature review suggested 53 exposure variables; these were reduced to 20 following field trials. Kappas for agreement beyond chance between six observers assessing exposures in 72 photos ranged from 0.21 to 1.0, with the highest values for posture type, trunk angle, manual materials handling, hands on item, and load weight. Intraclass correlations for agreement between pairs observing 17 workers once per minute for a full-shift were >0.74 for most postural, trunk angle, and manual materials handling variables. In validity testing, the proportions of shifts in flexion/extension and lateral bending observed for 169 full-shifts were compared to inclinometer measurements. Pearson correlations were 0.42 for 45-60 degrees flexion and 0.9 for >60 degrees flexion, but only 0.11-0.19 for lateral bending and trunk flexion less than 45 degrees . When lower flexion angles were collapsed to include trunk extension, correlations increased to >0.5.

A retrospective assessment of occupational noise exposures for a longitudinal epidemiological study.

OBJECTIVES: Chronic exposure to high levels of noise may be associated with increased risk of cardiovascular disease. We therefore undertook a quantitative retrospective exposure assessment using predictive statistical modelling to estimate historical exposures to noise among a cohort of 27,499 sawmill workers as part of an investigation of acute myocardial infarction mortality. METHODS: Noise exposure data were gathered from research, industry and regulatory sources. An exposure data matrix was defined and exposure level estimated for job title/mill/time period combinations utilising regression analysis to model determinants of noise exposure. Cumulative exposure and duration of exposure metrics were calculated for each subject. These were merged with work history data, and exposure-response associations were tested in subsequent epidemiological studies, reported elsewhere. RESULTS: Over 14,000 noise measurements were obtained from British Columbia sawmills. A subset, comprising 1901 full-shift dosimetry measurements from cohort mills was used in producing a predictive model (R(2) = 0.51). The model was then used to estimate noise exposures for 3809 "cells" of an exposure data matrix representing 81 jobs at 14 mills over several decades. Various exposure metrics were then calculated for subjects; mean cumulative exposure was 101 dBA*year. Mean durations of employment in jobs with exposure above thresholds of 85, 90 and 95 dBA, were 9.9, 7.0 and 3.2 years, respectively. CONCLUSIONS: The utility of predictive statistical modelling for occupational noise exposure was demonstrated. The model required input data that were relatively easily obtained, even retrospectively. Remaining issues include adequate handling of the use of hearing protectors that likely bias exposure estimation.

From measures to models: an evaluation of air pollution exposure assessment for epidemiological studies of pregnant women.

OBJECTIVES: To evaluate exposure estimation methods such as spatially resolved land-use regression models and ambient monitoring data in the context of epidemiological studies of the impact of air pollution on pregnancy outcomes. METHODS: The study measured personal 48 h exposures (NO, NO(2), PM(2.5) mass and absorbance) and mobility (time activity and GPS) for 62 pregnant women during 2005-2006 in Vancouver, Canada, one to three times during pregnancy. Measurements were compared to modelled (using land-use regression and interpolation of ambient monitors) outdoor concentrations at subjects' home and work locations. RESULTS: Personal NO and absorbance (ABS) measurements were moderately correlated (NO: r = 0.54, ABS: r = 0.29) with monitor interpolations and explained primarily within-subject (temporal) variability. Land-use regression estimates including work location improved correlations for NO over those based on home postal code (for NO: r = 0.49 changed to NO: r = 0.55) and explained more between-subject variance (4-20%); limiting to a subset of samples (n = 61) when subjects spent >65% time at home also improved correlations (NO: r = 0.72). Limitations of the GPS equipment precluded assessment of including complete GPS-based mobility information. CONCLUSIONS: The study found moderate agreement between short-term personal measurements and estimates of ambient air pollution at home based on interpolation of ambient monitors and land-use regression. These results support the use of land-use regression models in epidemiological studies, as the ability of such models to characterise high resolution spatial variability is "reflected" in personal exposure measurements, especially when mobility is characterised.

Predicting historical dust and wood dust exposure in sawmills: model development and validation.

Nonspecific dust measurements are used as a surrogate for wood dust exposure in sawmills. However, the wood dust component of dust has been found to vary by job and work area. Thus, the use of nonspecific dust exposure levels in epidemiologic studies may introduce exposure misclassification when assessing wood-related health effects. To improve exposure assessment in a retrospective cohort of 28,000 sawmill workers, we developed and evaluated the validity of two empirical models of exposure: one for nonspecific dust and one for wood dust. The dust model was constructed using 1,395 dust measurements collected in 13 sawmills for research or regulatory purposes from 1981 to 1997. Inter-sampler conversion factors were used to obtain inhalable dust equivalents if necessary. The wood dust model was constructed after applying adjustment factors to subtract nonwood components of the dust from the original measurements. The validity of the two models was tested against measurements (n = 213) from a technologically similar mill that was not part of the cohort study. The proportions of variability explained by the dust and wood dust models were 35% and 54%, respectively. When tested against the validation mill, the biases in the dust model were -33% for outdoor jobs and 2% for indoor jobs. The biases in the wood dust model were 2% for outdoor jobs and -3% for indoor jobs. Strong correlations were observed between the predicted and observed geometric means of jobs (0.79 and 0.70 for the dust model and wood dust model, respectively). Testing the validity of predictive models examines the generalizability of the models. The low overall bias, especially in the wood-specific model, increases our confidence in the use of these models for all sawmills to assess both nonspecific particulate and wood-related health effects in the historical cohort study.

Considering risks to healthcare workers from glutaraldehyde alternatives in high-level disinfection.

Due to concerns over glutaraldehyde's toxicity, two substitutes have recently been introduced; ortho-phthalaldehyde (OPA), and a mixture of hydrogen peroxide and peracetic acid. There is limited information about the health effects for employees from these products. This study assesses the current practices regarding the use of high-level disinfectants in British Columbian hospitals and predicts the relative toxicities of each product. Industry practices were compiled using a comprehensive survey of current practices and decision processes in all hospitals in British Columbia. Of 95 hospitals, 64 returned surveys; 80% of these used high-level disinfection. Among user hospitals, 49% used glutaraldehyde alone and 51% had introduced alternatives. Concern about staff health was the most common reason for substituting, but this was frequently not considered when choosing specific alternatives. Hospitals that involved occupational health, infection control or regional staff in high-level disinfectant decisions used glutaraldehyde alternatives less often. In most hospitals, it was difficult to find individuals who were knowledgeable about the use of disinfectants. Potential health effects associated with each type of high-level disinfectant were assessed by review of the published literature and available manufacturers' data along with qualitative structure-activity relationship analysis. Results indicated that although all products irritate the skin and respiratory tract, OPA is a potential dermal and respiratory sensitizer but hydrogen peroxide and peracetic acid do not cause allergic reactions. Despite little being known about the risks to employees from glutaraldehyde alternatives, their use is widespread. The potential risks of all high-level disinfectants are serious; thus regulators and users are faced with important risk management decisions before and after they have been introduced into the workplace.

Occupational exposure to chemical agents in the paper industry.

As part of an International Agency for Research on Cancer (IARC) international epidemiological study of workers in the pulp and paper industry, previously unpublished exposure measurements were assembled in a database. This article summarizes the results of 3,873 measurements carried out in the production departments of paper and paperboard mills and recycling plants in 12 countries. In the paper and paperboard mills, most of the agents were measured in the pulping and refining departments and in on-machine coating and winding of paper/paperboard. Exposures to asbestos, carbon monoxide, formaldehyde, fungal spores, bacteria, nitrogen dioxide, minerals dusts, paper dust, sulphuric acid and different solvents sometimes exceeded exposure limit values. In the re-pulping and de-inking departments of recycling plants high exposures to formaldehyde, fungal spores, bacteria and paper dust were observed. High exposures to asbestos, bioaerosols, carbon monoxide and paper dust were found in many departments; ammonia, formaldehyde, mineral and paper dust and solvents were found in coating machines; and diphenyl and polychlorobiphenyls (PCBs) were found in some special circumstances. Measurements in the newsprint and uncoated paper machine departments revealed only a few elevated exposures. In nearly all departments, measurements of epichlorohydrin, PCBs, sulphur dioxide, hydrogen sulphide and mercaptans tended to be low, often even below their detection limits. In spite of some uncertainties in the measurement data, the study provides new insights into the level and variation of occupational exposures of production workers in the paper and paperboard industry.

A field comparison of four samplers for enumerating fungal aerosols I. Sampling characteristics.

UNLABELLED: This study compared the performance of four bioaerosol samplers, the Reuter Centrifugal Air Sampler, the Andersen N6 single stage, the Surface Air System 90, and the Air-o-Cell, in measurements for airborne fungal propagules collected in 75 public building sites without prior knowledge of water damage or mold problems in British Columbia, Canada. The samplers had differences in detection limits, reproducibility, and overall yield. However, high and significant correlations between samplers (indoor samples: Pearson r = 0.60-0.85, P < 0.001) suggest that relative performances between samplers were reasonably consistent. These results indicate that fungal airborne concentration data are dependent on the methods used for assessment, and introduce additional variability in exposure assessment studies. PRACTICAL IMPLICATIONS: In the absence of a standard protocol for sampling bioaerosols, the interpretation of aerosol data reported in indoor air quality studies is entirely dependent on an appreciation of the sampling characteristics of commonly used instrumentation. Although a number of comparative studies have been undertaken in the laboratory, only a few studies have made reported comparison data under field conditions. This study compared three culturable sampling devices, the Andersen N6, SAS 90, and RCS, and one particulate sampling device, the Air-o-Cell, in offices and public areas in a variety of buildings, under conditions of forced air or natural ventilation. The concentrations of fungal aerosols collected during simultaneous sample collection were highly correlated, yet varied by orders of magnitude. The performance of these devices must be carefully considered before a standard protocol can be promulgated.

A field comparison of four fungal aerosol sampling instruments: inter-sampler calibrations and caveats.

UNLABELLED: Four bioaerosol samplers (Reuter Centrifugal, Andersen N6 Single Stage, Surface Air System Super 90, and Air-o-Cell) were used to take c. 300 side-by-side measurements at 75 public building sites. Regression models were developed to examine the relationships between each method pair. The models demonstrate that measurements from these instruments are not directly comparable, requiring inter-instrument calibration. Sampling location (indoor vs. outdoor) was a confounder in all the pairwise comparisons between samplers. In addition, the slopes of the relationships between all method pairs except one differed in indoor vs. outdoor locations. These results emphasize that direct comparisons between methods should not be undergone without prior calibration. Where measurement circumstances are similar to those of this study, the regression models might serve as a basis to convert measurements made with one instrument to those made with another. However, the robustness and generalizability of the models in different measurement settings needs to be assessed. PRACTICAL IMPLICATIONS: Many different bioaerosol sampling devices are in common use for indoor air quality studies. If data from research studies are to be compared, an approximation of the relationships between the equipment would be useful. A comparison of three culturable sampling devices (Andersen N6, SAS 90, RCS) and one particulate sampling device (Air-o-Cell) collecting simultaneous samples under field conditions showed high linear correlations between methods. However, while direct comparisons between sampling data were not possible, the regression models reported here explained 60-85% of the variance in fungal concentrations, and underscored the importance of the effect of environment on measurement.

The prevalence of Parkinson's disease in British Columbia, Canada, estimated by using drug tracer methodology.

OBJECTIVE: To estimate the prevalence of Parkinson's disease (PD) in British Columbia utilizing the prescription database of the College of Pharmacists. METHODS: Patients receiving anti-parkinsonian drug (anti-PD) prescriptions between 1996 and 1998 were stratified by year, age, gender, drug use category, and geographic location. The numbers of patients on levodopa alone, or levodopa and/or other anti-PD drugs were adjusted using published data which gave estimates of the proportion of undiagnosed patients with PD, the proportion of those treated for parkinsonism with definite PD, the proportion of patients with PD not being treated with anti-PD medications, and the proportion of patients treated with anti-PD medications who have PD. Use of the anti-PD drug bromocriptine for other purposes in women under 50 years of age was also considered. RESULTS: The estimated prevalences of PD based on all anti-PD medications used were 109, 121, and 125 per 100,000 population in 1996, 1997, and 1998, respectively. Estimated prevalences of PD based on levodopa use were 126, 134, and 144, respectively. The prevalence in both prescription groups increased with age. The male to female ratio of prevalence ranged from 1.16 to 1.21. CONCLUSIONS: Using a large, accurate database, it is possible to estimate the prevalence of PD in a large population, though the assumptions built into the estimate remain to be validated in the subject population.

Occupational exposure assessment in case-control studies: opportunities for improvement.

Community based case-control studies are an efficient means to study disease aetiologies, and may be the only practical means to investigate rare diseases. However, exposure assessment remains problematic. We review the literature on the validity and reliability of common case-control exposure assessment methods: occupational histories, job-exposure matrices (JEMs), self reported exposures, and expert assessments. Given the variable quality of current exposure assessment techniques, we suggest methods to improve assessments, including the incorporation of hygiene measurements: using data from administrative exposure databases; using results of studies identifying determinants of exposure to develop questionnaires; and where reasonable given latency and biological half life considerations, directly measuring exposures of study subjects.

Effect of de-industrialisation on working conditions and self reported health in a sample of manufacturing workers.

STUDY OBJECTIVE: To explore the impact of de-industrialisation over a 20 year period on working conditions and health among sawmill workers, in the province of British Columbia (BC), Canada. DESIGN AND SETTING: This investigation is based on a sample of 3000 sawmill workers employed in 1979 (a year before the beginning de-industrialisation) and interviewed in 1998. The sample was obtained by random selection from an already gathered cohort of approximately 28 000 BC sawmill workers. Change in working conditions from 1979 to 1998 are described. Self reported health status, in 1998, was used as a dependent variable in logistic regression after controlling for confounders. MAIN RESULTS: Downsizing in BC sawmills eliminated 60% of workers between 1979 and 1998. Working conditions in 1998 were better for those who left the sawmill industry and obtained re-employment elsewhere. Workers who remained employed in restructuring sawmills were approximately 50% more likely to report poor health than those re-employed elsewhere. CONCLUSIONS: Working conditions and health status were better for workers who, under pressure of de-industrialisation, left the sawmill industry and obtained re-employment outside this sector.

Occupational and environmental risk factors for Parkinson's disease.

The etiology of Parkinson's disease (PD) remains obscure. Current research suggests that a variety of occupational and environmental risk factors may be linked to PD. This paper provides an overview of major occupational and environmental factors that have been associated with the development of PD and tries to assess current thinking about these factors and their possible mechanisms of operation. While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD.

A model for predicting endotoxin concentrations in metalworking fluid sumps in small machine shops.

METHODS: In British Columbia, Canada, nineteen small machine shops which used water-based metalworking fluids (MWF) were examined. One bulk MWF sample was taken from each independent sump (N=140) and tested for endotoxin using the Limulus Amoebocyte Lysate assay. Factors that might influence the MWF sump endotoxin concentration were investigated using mixed effect multiple regression modelling to control for repeated measures within shops. RESULTS: The geometric mean (GM) endotoxin concentration was 6791 EU/ml. Contamination of MWF with tramp oil, MWF pH, MWF temperature, and MWF type were significant predictors of sump fluid endotoxin concentration (model P=0.0001, ordinary least squares R(2) =0.36). Concentrations of endotoxin in sump fluids were increased by MWF contamination with tramp oils such as hydraulic oils, preservative oils, spindle oils, slidway lubricants, gear lubricants, and greases (model predicted GM=17400 EU/ml vs. 1600 EU/ml without tramp oil). Concentrations were also elevated where pH was lower than 8.5 (predicted GM=10600, vs 3600 EU/ml for pH 8.5 to 9.5), where soluble fluids were used (predicted GM=11800 vs. 2800 EU/ml for synthetic fluids), and where sump fluid temperatures were higher (predicted GM=2600 EU/ml at 11 degrees C vs. 21500 EU/ml at 32 degrees C). The within-shop correlation of sump bulk fluid endotoxin concentrations was 38%. CONCLUSIONS: Minimizing tramp oil contamination, using synthetic fluids, and monitoring pH and temperature would be valuable tools for controlling endotoxin contamination in MWF sumps. In addition, since there was correlation within-shop, contamination of one sump in a shop may suggest changing the fluids in all.

Parental occupational exposures to electromagnetic fields and radiation and the incidence of neuroblastoma in offspring.

We examined parental occupational exposures to electromagnetic fields and radiation and the incidence of neuroblastoma in offspring. Cases were 538 children diagnosed with neuroblastoma between 1992 and 1994 in the United States or Canada. Age-matched controls were selected by random-digit dialing. Occupational exposures to electrical equipment and radiation sources were classified by an industrial hygienist, and average exposures to extremely low frequency magnetic fields were estimated using a job exposure matrix. Maternal exposure to a broad grouping of sources that produce radiofrequency radiation was associated with an increased incidence of neuroblastoma (odds ratio = 2.8; 95% confidence interval = 0.9-8.7). Paternal exposure to battery-powered forklifts was positively associated with neuroblastoma (odds ratio = 1.6; 95% confidence interval = 0.8-3.2), as were some types of equipment that emit radiofrequency radiation (odds ratios congruent with 2.0); however, the broad groupings of sources that produce ELF fields, radiofrequency radiation, or ionizing radiation were not associated with neuroblastoma. Paternal average extremely low frequency magnetic field exposure >0.4 microTesla was weakly associated with neuroblastoma (odds ratio = 1.6; 95% confidence interval = 0.9-2.8), whereas maternal exposure was not. Overall, there was scant supportive evidence of strong associations between parental exposures in electromagnetic spectrum and neuroblastoma in offspring.

Parental occupational exposures to chemicals and incidence of neuroblastoma in offspring.

To evaluate the effects of parental occupational chemical exposures on incidence of neuroblastoma in offspring, the authors conducted a multicenter case-control study, using detailed exposure information that allowed examination of specific chemicals. Cases were 538 children aged 19 years who were newly diagnosed with confirmed neuroblastoma in 1992-1994 and were registered at any of 139 participating hospitals in the United States and Canada. One age-matched control for each of 504 cases was selected through random digit dialing. Self-reported exposures were reviewed by an industrial hygienist, and improbable exposures were reclassified. Effect estimates were calculated using unconditional logistic regression, adjusting for child's age and maternal demographic factors. Maternal exposures to most chemicals were not associated with neuroblastoma. Paternal exposures to hydrocarbons such as diesel fuel (odds ratio (OR) = 1.5; 95% confidence interval (CI): 0.8, 2.6), lacquer thinner (OR = 3.5; 95% CI: 1.6, 7.8), and turpentine (OR = 10.4; 95% CI: 2.4, 44.8) were associated with an increased incidence of neuroblastoma, as were exposures to wood dust (OR = 1.5; 95% CI: 0.8, 2.8) and solders (OR = 2.6; 95% CI: 0.9, 7.1). The detailed exposure information available in this study has provided additional clues about the role of parental occupation as a risk factor for neuroblastoma.

Comparison of assessment methods for pesticide exposure in a case-control interview study.

In epidemiologic studies, much of the variation in disease risk estimates associated with occupational pesticide exposure may be due to variation in exposure classification. The authors compared five different methods of using interview information to assess occupational pesticide exposure in a US-Canada case-control study of neuroblastoma (1992-1994). For each method, exposure assignment was compared with that of a reference method, and neuroblastoma effect estimates were calculated. Compared with the reference method, which included a complete review of occupation, industry, job tasks, and exposure-specific activities, the use of occupation-industry groups alone or in combination with general job task information diluted the exposed group by including individuals who were unlikely to have been truly exposed. The effect estimates representing associations between each exposure method and neuroblastoma were different enough to influence the study's conclusions, especially when the exposure was rare (for maternal occupational pesticide exposure, the odds ratio was 0.7 using the reference exposure assessment method and 3.2 using the occupation-industry group exposure assessment method). Exposure-specific questions about work activities can help investigators distinguish truly exposed individuals from those who report exposure but are unlikely to have been exposed above background levels and from those who have not been exposed but are misclassified as exposed because of their employment in an occupation-industry group determined a priori to be exposed.

An application of hierarchical regression in the investigation of multiple paternal occupational exposures and neuroblastoma in offspring.

BACKGROUND: We used hierarchical regression to study the effects of 46 paternal occupational exposures on the incidence of neuroblastoma in offspring. METHODS: The study population included 405 cases and 302 controls. The effect of each exposure was estimated using both conventional maximum likelihood and hierarchical regression. RESULTS: Using hierarchical regression, overall precision was greatly enhanced compared to the conventional analysis. In addition, adjustment of effect estimates based on prespecified prior distributions of the true effect parameters allowed a more consistent interpretation across the entire panel of exposures. Estimates for several metals and solvents were shrunk close to the null value, whereas estimates for several thinner solvents, diesel fuel, solders, wood dust, and grain dust remained moderately elevated. CONCLUSIONS: Hierarchical regression may mitigate some of the problems of the conventional approach by controlling for correlated exposures, enhancing the precision of estimates, and providing some adjustment of estimates based on prior knowledge.

Measuring psychosocial job strain with the job content questionnaire using experienced job evaluators.

BACKGROUND: A union/management system of job evaluation has been in place in the British Columbia (BC) sawmill industry since the late 1960s. This system uses an instrument, very similar to the job content questionnaire (JCQ) to evaluate psychosocial work conditions for sawmill jobs. METHODS: Four experienced evaluators, one from the union and three from industry, independently estimated psychosocial work conditions for 54 current job titles in a "typical" coastal sawmill using a shortened, 18-question version of the JCQ questionnaire. RESULTS: Inter-rater reliability was acceptable for control but not for co-worker social support, physical demand, or psychological demand. Reliability was least for psychological demand. CONCLUSIONS: Experienced job evaluators in the sawmill industry were able to reliably estimate only the control dimension of the JCQ. The observed lowest reliability for psychological job demand may be due to the imprecise construct definition in the domain of the JCQ instrument.

Comparison of expert-rater methods for assessing psychosocial job strain.

OBJECTIVES: This study tested the reliability and validity of industry- and mill-level expert methods for measuring psychosocial work conditions in British Columbia sawmills using the demand-control model. METHODS: In the industry-level method 4 sawmill job evaluators estimated psychosocial work conditions at a generic sawmill. In the mill-level method panels of experienced sawmill workers estimated psychosocial work conditions at 3 sawmills. Scores for psychosocial work conditions were developed using both expert methods and applied to job titles in a sawmill worker database containing self-reported health status and heart disease. The interrater reliability and the concurrent and predictive validity of the expert rater methods were assessed. RESULTS: The interrater reliability and concurrent reliability were higher for the mill-level method than for the industry-level method. For all the psychosocial variables the reliability for the mill-level method was greater than 0.90. The predictive validity results were inconclusive. CONCLUSIONS: The greater reliability and concurrent validity of the mill-level method indicates that panels of experienced workers should be considered as potential experts in future studies measuring psychosocial work conditions.