Experiencing a probabilistic approach to clarify and disclose uncertainties when setting occupational exposure limits.

OBJECTIVES: Assessment factors (AFs) are commonly used for deriving reference concentrations for chemicals. These factors take into account variabilities as well as uncertainties in the dataset, such as inter-species and intra-species variabilities or exposure duration extrapolation or extrapolation from the lowest-observed-adverse-effect level (LOAEL) to the noobserved- adverse-effect level (NOAEL). In a deterministic approach, the value of an AF is the result of a debate among experts and, often a conservative value is used as a default choice. A probabilistic framework to better take into account uncertainties and/or variability when setting occupational exposure limits (OELs) is presented and discussed in this paper. MATERIAL AND METHODS: Each AF is considered as a random variable with a probabilistic distribution. A short literature was conducted before setting default distributions ranges and shapes for each AF commonly used. A random sampling, using Monte Carlo techniques, is then used for propagating the identified uncertainties and computing the final OEL distribution. RESULTS: Starting from the broad default distributions obtained, experts narrow it to its most likely range, according to the scientific knowledge available for a specific chemical. Introducing distribution rather than single deterministic values allows disclosing and clarifying variability and/or uncertainties inherent to the OEL construction process. CONCLUSIONS: This probabilistic approach yields quantitative insight into both the possible range and the relative likelihood of values for model outputs. It thereby provides a better support in decision-making and improves transparency. Int J Occup Med Environ Health 2018;31(4):475-489.

Assessment of occupational exposure to asbestos fibers: Contribution of analytical transmission electron microscopy analysis and comparison with phase-contrast microscopy.

From November 2009 to October 2010, the French general directorate for labor organized a large field-study using analytical transmission electron microscopy (ATEM) to characterize occupational exposure to asbestos fibers during work on asbestos containing materials (ACM). The primary objective of this study was to establish a method and to validate the feasibility of using ATEM for the analysis of airborne asbestos of individual filters sampled in various occupational environments. For each sampling event, ATEM data were compared to those obtained by phase-contrast optical microscopy (PCOM), the WHO-recommended reference technique. A total of 265 results were obtained from 29 construction sites where workers were in contact with ACM. Data were sorted depending on the combination of the ACM type and the removal technique. For each "ACM-removal technique" combination, ATEM data were used to compute statistical indicators on short, fine and WHO asbestos fibers. Moreover, exposure was assessed taking into account the use of respiratory protective devices (RPD). As in previous studies, no simple relationship was found between results by PCOM and ATEM counting methods. Some ACM, such as asbestos-containing plasters, generated very high dust levels, and some techniques generated considerable levels of dust whatever the ACM treated. On the basis of these observations, recommendations were made to measure and control the occupational exposure limit. General prevention measures to be taken during work with ACM are also suggested. Finally, it is necessary to continue acquiring knowledge, in particular regarding RPD and the dust levels measured by ATEM for the activities not evaluated during this study.

SYN-JEM: A Quantitative Job-Exposure Matrix for Five Lung Carcinogens.

OBJECTIVE: The use of measurement data in occupational exposure assessment allows more quantitative analyses of possible exposure-response relations. We describe a quantitative exposure assessment approach for five lung carcinogens (i.e. asbestos, chromium-VI, nickel, polycyclic aromatic hydrocarbons (by its proxy benzo(a)pyrene (BaP)) and respirable crystalline silica). A quantitative job-exposure matrix (JEM) was developed based on statistical modeling of large quantities of personal measurements. METHODS: Empirical linear models were developed using personal occupational exposure measurements (n = 102306) from Europe and Canada, as well as auxiliary information like job (industry), year of sampling, region, an a priori exposure rating of each job (none, low, and high exposed), sampling and analytical methods, and sampling duration. The model outcomes were used to create a JEM with a quantitative estimate of the level of exposure by job, year, and region. RESULTS: Decreasing time trends were observed for all agents between the 1970s and 2009, ranging from -1.2% per year for personal BaP and nickel exposures to -10.7% for asbestos (in the time period before an asbestos ban was implemented). Regional differences in exposure concentrations (adjusted for measured jobs, years of measurement, and sampling method and duration) varied by agent, ranging from a factor 3.3 for chromium-VI up to a factor 10.5 for asbestos. CONCLUSION: We estimated time-, job-, and region-specific exposure levels for four (asbestos, chromium-VI, nickel, and RCS) out of five considered lung carcinogens. Through statistical modeling of large amounts of personal occupational exposure measurement data we were able to derive a quantitative JEM to be used in community-based studies.

TEXAS: a Tool for EXposure ASsessment-Statistical models for estimating occupational exposure to chemical agents.

Measurements of occupational exposure to chemical agents are performed by sampling and analyzing workplace atmospheres. In France, this is done by the industrial hygienists of the prevention network of the Social Security Service, who collect and then enter the data in the COLCHIC database. More than 900000 measurements performed in French companies over the past 25 years have been collected. Using this amount of data is major challenge for obtaining knowledge and predicting occupational exposures. This study presents the way in which statistical models are built and used on the basis of almost 19000 recent measurements of 26 frequent chemical substances. For a given substance, the models use 13 exposure determinants as inputs, such as the task performed, the occupation of the operator or the type of process employed. The models permit to estimate two parameters: the geometric mean and geometric standard deviation. These parameters are used to build an exposure profile. By combining them with the limit value, an exposure index is estimated using a Bayesian network. A decision rule based on the interpretation of this probability is proposed to qualify the predicted situation as 'well-controlled situation', 'controlled situation', and 'poorly controlled situation'. On the basis of this decision rule, 62% of predictions are true for all substances confounded, an average of 36% of predictions are approximate and only 2% of them are wrong. The result of this study led to the development of a pragmatic software tool named TEXAS, tool for exposure assessment, which enables industrial hygienists to obtain a rapid estimation of the level of exposure control as a function of simple determinants of work situations.

Occupational exposure to chrome VI compounds in French companies: results of a national campaign to measure exposure (2010-2013).

A campaign to measure exposure to hexavalent chromium compounds was carried out in France by the seven CARSAT chemistry laboratories, CRAMIF laboratory, and INRS over the 2010-2013 period. The survey included 99 companies involved in various activity sectors. The inhalable fraction of airborne particles was sampled, and exposure levels were determined using ion chromatography analysis combined with post-column derivatization and UV detection. The quality of the measurement results was guaranteed by an inter-laboratory comparison system involving all the laboratories participating in this study. Exposure levels frequently exceeded the French occupational exposure limit value (OELV) of 1 µg m(-3), in activities such as thermal metallization and manufacturing and application of paint in the aeronautics sector. The results also reveal a general trend for a greater proportion of soluble Chromium VI (Cr VI) compounds compared with insoluble compounds. Qualitative and quantitative information relating to the presence of other metallic compounds in the air of workplaces is also provided, for example for Cr III, Ni, Fe, etc. The sampling strategy used and the measurement method are easy to implement, making it possible to check occupational exposure with a view to comparing it to an 8 h-OELV of 1 µg m(-3).

Assessment of occupational exposure to chemicals by air sampling for comparison with limit values: the influence of sampling strategy.

This study was aimed at quantifying the impact of sampling duration and the number of measurements taken on the quality of assessing occupational exposure to toluene. To this end, a measurement database was built, based on four campaigns carried out in an industrial printing facility. Five homogeneous exposure groups (HEGs) were set up and between 120 and 290 individual measurements lasting from 2 to 8 h were collected for each of them. These measurements were performed with the objective of comparing them to the 8-h Occupational Exposure Limit (8-h OEL). The resulting data were used to define a reference exposure profile per HEG: the 'gold standard'. This exposure profile corresponds to a log-normal distribution of measurements from which compliance/non-compliance with the 8-h OEL decision is derived. To simulate the possible sampling strategies used by industrial hygienists, six scenarios were defined, each containing a different number of measurements: 2, 3, 4, 6, 9, and 12 measurements performed per HEG, over different working days and different seasons of the year. The measurement values per scenario were simulated by sampling from the real measurement per HEG. For each scenario, 1000 simulated exposure profiles and corresponding simulated compliance decisions were computed. They were compared to the gold standard compliance decision using statistical indicators. Three methods were used for computing the simulated compliance decision: (i) the 95th percentile must be lower than the 8-h OEL, (ii) the exceedance fraction with respect to the 8-h OEL must be <0.1% (as defined by standard CEN 689, Appendix D), and (iii) the 70% upper confidence limit of the exceedance fraction with respect to the 8-h OEL must be <5% (as defined by French regulations). The results show that exposure assessment quality increases with both the number of measurements and sampling duration when using the 95th percentile and exposure assessment based on French regulations, whereas it decreases when using the standard. Moreover, guidelines for the efficient evaluation of chemical exposure in the workplace can be drawn up to help professional occupational hygienists. Indeed, boundaries can be recommended regarding the number of measurements and sampling duration necessary to obtain a reliable exposure assessment while minimizing effort devoted to sampling and analysis.

Sensitivity analyses of exposure estimates from a quantitative job-exposure matrix (SYN-JEM) for use in community-based studies.

OBJECTIVES: We describe the elaboration and sensitivity analyses of a quantitative job-exposure matrix (SYN-JEM) for respirable crystalline silica (RCS). The aim was to gain insight into the robustness of the SYN-JEM RCS estimates based on critical decisions taken in the elaboration process. METHODS: SYN-JEM for RCS exposure consists of three axes (job, region, and year) based on estimates derived from a previously developed statistical model. To elaborate SYN-JEM, several decisions were taken: i.e. the application of (i) a single time trend; (ii) region-specific adjustments in RCS exposure; and (iii) a prior job-specific exposure level (by the semi-quantitative DOM-JEM), with an override of 0 mg/m(3) for jobs a priori defined as non-exposed. Furthermore, we assumed that exposure levels reached a ceiling in 1960 and remained constant prior to this date. We applied SYN-JEM to the occupational histories of subjects from a large international pooled community-based case-control study. Cumulative exposure levels derived with SYN-JEM were compared with those from alternative models, described by Pearson correlation ((Rp)) and differences in unit of exposure (mg/m(3)-year). Alternative models concerned changes in application of job- and region-specific estimates and exposure ceiling, and omitting the a priori exposure ranking. RESULTS: Cumulative exposure levels for the study subjects ranged from 0.01 to 60 mg/m(3)-years, with a median of 1.76 mg/m(3)-years. Exposure levels derived from SYN-JEM and alternative models were overall highly correlated (R(p) > 0.90), although somewhat lower when omitting the region estimate ((Rp) = 0.80) or not taking into account the assigned semi-quantitative exposure level (R(p) = 0.65). Modification of the time trend (i.e. exposure ceiling at 1950 or 1970, or assuming a decline before 1960) caused the largest changes in absolute exposure levels (26-33% difference), but without changing the relative ranking ((Rp) = 0.99). CONCLUSIONS: Exposure estimates derived from SYN-JEM appeared to be plausible compared with (historical) levels described in the literature. Decisions taken in the development of SYN-JEM did not critically change the cumulative exposure levels. The influence of region-specific estimates needs to be explored in future risk analyses.

Development of an exposure measurement database on five lung carcinogens (ExpoSYN) for quantitative retrospective occupational exposure assessment.

BACKGROUND: SYNERGY is a large pooled analysis of case-control studies on the joint effects of occupational carcinogens and smoking in the development of lung cancer. A quantitative job-exposure matrix (JEM) will be developed to assign exposures to five major lung carcinogens [asbestos, chromium, nickel, polycyclic aromatic hydrocarbons (PAH), and respirable crystalline silica (RCS)]. We assembled an exposure database, called ExpoSYN, to enable such a quantitative exposure assessment. METHODS: Existing exposure databases were identified and European and Canadian research institutes were approached to identify pertinent exposure measurement data. Results of individual air measurements were entered anonymized according to a standardized protocol. RESULTS: The ExpoSYN database currently includes 356 551 measurements from 19 countries. In total, 140 666 personal and 215 885 stationary data points were available. Measurements were distributed over the five agents as follows: RCS (42%), asbestos (20%), chromium (16%), nickel (15%), and PAH (7%). The measurement data cover the time period from 1951 to present. However, only a small portion of measurements (1.4%) were performed prior to 1975. The major contributing countries for personal measurements were Germany (32%), UK (22%), France (14%), and Norway and Canada (both 11%). CONCLUSIONS: ExpoSYN is a unique occupational exposure database with measurements from 18 European countries and Canada covering a time period of >50 years. This database will be used to develop a country-, job-, and time period-specific quantitative JEM. This JEM will enable data-driven quantitative exposure assessment in a multinational pooled analysis of community-based lung cancer case-control studies.

Modelling of occupational respirable crystalline silica exposure for quantitative exposure assessment in community-based case-control studies.

We describe an empirical model for exposure to respirable crystalline silica (RCS) to create a quantitative job-exposure matrix (JEM) for community-based studies. Personal measurements of exposure to RCS from Europe and Canada were obtained for exposure modelling. A mixed-effects model was elaborated, with region/country and job titles as random effect terms. The fixed effect terms included year of measurement, measurement strategy (representative or worst-case), sampling duration (minutes) and a priori exposure intensity rating for each job from an independently developed JEM (none, low, high). 23,640 personal RCS exposure measurements, covering a time period from 1976 to 2009, were available for modelling. The model indicated an overall downward time trend in RCS exposure levels of -6% per year. Exposure levels were higher in the UK and Canada, and lower in Northern Europe and Germany. Worst-case sampling was associated with higher reported exposure levels and an increase in sampling duration was associated with lower reported exposure levels. Highest predicted RCS exposure levels in the reference year (1998) were for chimney bricklayers (geometric mean 0.11 mg m(-3)), monument carvers and other stone cutters and carvers (0.10 mg m(-3)). The resulting model enables us to predict time-, job-, and region/country-specific exposure levels of RCS. These predictions will be used in the SYNERGY study, an ongoing pooled multinational community-based case-control study on lung cancer.

Used tire recycling to produce granulates: evaluation of occupational exposure to chemical agents.

Exposure was assessed in four facilities where used tires are turned into rubber granulates. Particulate exposure levels were measured using filter samples and gravimetric analysis. In parallel, volatile organic compounds (VOCs) screening was carried out using samples taken on activated carbon supports, followed by an analysis using a gas chromatograph coupled to a spectrometric detector. The exposure level medians are between 0.58 and 3.95 mg m(-3). Clogging of the textile fiber separation systems can lead to worker exposure; in this case, the measured concentrations can reach 41 mg m(-3). However, in contrast to the data in the literature, VOC levels >1 p.p.m. were not detected. The particulate mixtures deposited on the installation surfaces are complex; some of the chemical agents are toxic to humans. The results of this study indicate significant exposure to complex mixtures of rubber dust. Optimizing exhaust ventilation systems inside the shredders, with a cyclone for example, is essential for reducing the exposure of workers in this rapidly developing sector.

Occupational exposure to beryllium in French enterprises: a survey of airborne exposure and surface levels.

An assessment survey of occupational exposure to beryllium (Be) was conducted in France between late 2004 and the end of 2006. Exposure estimates were based on the analytical results of samples collected from workplace air and from work surfaces in 95 facilities belonging to 37 sectors of activity. The results of this study indicated airborne Be concentrations in excess of the occupational exposure limit value of 2 microg m(-3) recommended in France. Metallurgy and electronic component manufacturing represented the activities and occupations where workers had the highest arithmetic mean exposures to Be. Surface contamination levels were also high and frequently exceeded thresholds recommended by different bodies. These results should prompt the development of prevention programmes that include Be substitution, process control and surface decontamination, in conjunction with suitable medical surveillance.

Formaldehyde exposure in U.S. industries from OSHA air sampling data.

National occupational exposure databanks have been cited as sources of exposure data for exposure surveillance and exposure assessment for occupational epidemiology. Formaldehyde exposure data recorded in the U.S Integrated Management Information System (IMIS) between 1979 and 2001 were collected to elaborate a multi-industry retrospective picture of formaldehyde exposures and to identify exposure determinants. Due to the database design, only detected personal measurement results (n = 5228) were analyzed with linear mixed-effect models, which explained 29% of the total variance. Short-term measurement results were higher than time-weighted average (TWA) data and decreased 18% per year until 1987 (TWA data 5% per year) and 5% per year (TWA data 4% per year) after that. Exposure varied across industries with maximal estimated TWA geometric means (GM) for 2001 in the reconstituted wood products, structural wood members, and wood dimension and flooring industries (GM = 0.20 mg/m(3). Highest short-term GMs estimated for 2001 were in the funeral service and crematory and reconstituted wood products industries (GM = 0.35 mg/m(3). Exposure levels in IMIS were marginally higher during nonprogrammed inspections compared with programmed inspections. An increasing exterior temperature tended to cause a decrease in exposure levels for cold temperatures (-5% per 5 degrees C for T < 15 degrees C) but caused an increase in exposure levels for warm temperatures (+15% per 5 degrees C for T >15 degrees C). Concentrations measured during the same inspection were correlated and varied differently across industries and sample type (TWA, short term). Sensitivity analyses using TOBIT regression suggested that the average bias caused by excluding non-detects is approximately 30%, being potentially higher for short-term data if many non-detects were actually short-term measurements. Although limited by availability of relevant exposure determinants and potential selection biases in IMIS, these results provide useful insight on formaldehyde occupational exposure in the United States in the last two decades. The authors recommend that more information on exposure determinants be recorded in IMIS.

Occupational exposure to mineral fibres: analysis of results stored on colchic database.

The aim of this paper is to present fibre exposure data recorded on the COLCHIC database. This database consolidates all occupational exposure data collected in French companies by the Caisses Régionales d'Assurance Maladie (regional health insurance funds, CRAM) and the Institut National de Recherche et de Sécurité (national institute for research and safety, INRS). A total of 8029 concentration results, expressed in number of fibres measured by phase-contrast optical microscopy, are available for exposure to asbestos fibres, ceramic fibres and man-made mineral fibres other than ceramic fibres. Presentation of base data by activity branch, activity sector or workplace permits identification of situations, for which prevention efforts are most essential. Analysis of exposure levels during the 1986-2004 period show that these are broadly influenced by changes in the exposure limit values. Wearing of respiratory protection equipment by employees is also discussed. The data may be helpful to occupational physicians performing occupational screening of exposed workers and to epidemiologists seeking information for building job-exposures matrices. In this respect, a database (FIBREX) will be available on the INRS web site (www.inrs.fr) at the beginning of 2007. This database will provide a higher level of detail in activity and workplace description than that which was possible for practical reasons in this paper.

Occupational exposure to inhalable wood dust in the member states of the European Union.

The aim of this study was to estimate occupational exposure to inhalable wood dust by country, industry, the level of exposure and type of wood dust in 25 member states of the European Union (EU-25) for the purposes of hazard control, exposure surveillance and assessment of health risks. National labour force statistics, a country questionnaire (in 15 member states, EU-15), a company survey (in Finland, France, Germany and Spain), exposure measurements (from Denmark, Finland, France, Germany, The Netherlands and the United Kingdom) and expert judgements were used to generate preliminary estimates of exposure to different types of wood dust. The estimates were generated according to industrial class (six wood industries, four other sectors) and level of exposure (five classes). These estimates were reviewed and finalized by national experts from 15 member states. Crude estimates were generated also for 10 new member states (EU-10). The basic data and final estimates were included in the WOODEX database. In 2000-2003, about 3.6 million workers (2.0% of the employed EU-25 population) were occupationally exposed to inhalable wood dust. Of those, construction employed 1.2 million exposed workers (33%), mostly construction carpenters. The numbers of exposed workers were 700,000 (20%) in the furniture industry, 300,000 (9%) in the manufacture of builders' carpentry, 200,000 (5%) in sawmilling, 150,000 (4%) in forestry and <100,000 in other wood industries. In addition, there were 700,000 exposed workers (20%) in miscellaneous industries employing carpenters, joiners and other woodworkers. The numbers of exposed workers varied by country ranging from <3,000 in Luxembourg and Malta to 700,000 in Germany. The highest exposure levels were estimated to occur in the construction sector and furniture industry. Due to limited exposure data there was considerable uncertainty in the estimates concerning construction woodworkers. About 560,000 workers (16% of the exposed) may be exposed to a level exceeding 5 mg m(-3). Mixed exposure to more than one species of wood and dust from wooden boards was very common, but reliable data on exposure to different species of wood could not be retrieved. This kind of assessment procedure integrating measurement data, company data, country-specific data and expert judgement could also serve as one model for the assessment of other occupational exposures.

Statistical modelling of formaldehyde occupational exposure levels in French industries, 1986-2003.

Occupational exposure databanks (OEDBs) have been cited as sources of exposure data for exposure surveillance and exposure assessment in epidemiology. In 2003, an extract was made from COLCHIC, the French national OEDB, of all concentrations of formaldehyde. The data were analysed with extended linear mixed-effects models in order to identify influent variables and elaborate a multi-sector picture of formaldehyde exposures. Respectively, 1401 and 1448 personal and area concentrations were available for the analysis. The fixed effects of the personal and area models explained, respectively, 57 and 53% of the total variance. Personal concentrations were related to the sampling duration (short-term higher than TWA levels), decreased with the year of sampling (-9% per year) and were higher when local exhaust ventilation was present. Personal levels taken during planned visits and for occupational illness notification purpose were consistently lower than those taken during ventilation modification programmes or because the hygienist suspected the presence of significant risk or exposure. Area concentrations were related to the sampling duration (short-term higher than TWA levels), and decreased with the year of sampling (-7% per year) and when the measurement sampling flow increased. Significant within-facility (correlation coefficient 0.4-0.5) and within-sampling campaign correlation (correlation coefficient 0.8) was found for both area and personal data. The industry/task classification appeared to have the greatest influence on exposure variability while the sample duration and the sampling flow were significant in some cases. Estimates made from the models for year 2002 showed elevated formaldehyde exposure in the fields of anatomopathological and biological analyses, operation of gluing machinery in the wood industry, operation and monitoring of mixers in the pharmaceutical industry, and garages and warehouses in urban transit authorities.