Choosing the number of images and image position when analyzing the UNC Passive Aerosol Sampler for occupational exposure assessment.

The University of North Carolina passive aerosol sampler (UNC sampler) could be an alternative when measuring occupational dust exposure, but the time required for microscopic imaging of the sampler needs to be reduced to make it more attractive. The aims of this study were to (1) characterize the effect on precision when reducing imaging, in order to shorten analysis time and (2) assess if the position of the images makes a difference. Eighty-eight samplers were deployed in different locations of an open pit mine. Sixty images were captured for each UNC sampler, covering 51% of its collection surface, using scanning electron microscopy. Bootstrapped samples were generated with different image combinations, to assess the within-sampler coefficient of variation (CVws) for different numbers of images. In addition, the particle concentration relative to the distance from the center of the sampler was studied. Reducing the number of images collected from the UNC sampler led to up to 8.3% CVws for 10 images when calculating respirable fraction. As the overall CV has previously been assessed to 36%, the additional contribution becomes minimal, increasing the overall CV to 37%. The mean concentrations of the images were modestly related to distance from the center of the sampler. The CVws changed from 8.26% to 8.13% for 10 images when applying rules for the image collection based on distance. Thus, the benefit of these rules on the precision is small and the images can therefore be chosen at random. In conclusion, reducing the number of images analyzed from 60 to 10, corresponding to a reduction of the imaged sampling area from 51% to 8.5%, results in a negligible loss in precision for respirable fraction dust measurements in occupational environments.

Can we explain the exposure variability found in hand-arm vibrations when using angle grinders? A round robin laboratory study.

OBJECTIVES: To quantify variance components of hand-arm vibration exposure from data collected in a laboratory study of four different angle grinders. METHODS: Four different angle grinders were sent to seven laboratories for grinding tests by three operators at each laboratory. Vibration in both the throttle and support handles was measured. For one grinder, the experimental set-up was repeated and two measurements were collected for that specific grinder. RESULTS: At least one-third of the estimated variability is attributable to the wheel and less than one-third to the operator. In repeated experiments, between-occasion, operator and wheel factors explained 4, 29 and 17% of the total variability, respectively. CONCLUSIONS: Since measured vibrations in the support and throttle handles are significantly differed, measurements should be taken at both locations. Factors influencing vibration variability include the presence/absence of an auto balance unit, wheel and operator, but other factors remain to be elucidated.

Dermal and inhalation exposure to methylene bisphenyl isocyanate (MDI) in iron foundry workers.

Diisocyanates are a group of chemically reactive agents, which are used in the production of coatings, adhesives, polyurethane foams, and parts for the automotive industry and as curing agents for cores in the foundry industry. Dermal and inhalation exposure to methylene bisphenyl isocyanate (MDI) is associated with respiratory sensitization and occupational asthma. However, limited research has been performed on the quantitative evaluation of dermal and inhalation exposure to MDI in occupationally exposed workers. The objective of this research was to quantify dermal and inhalation exposure levels in iron foundry workers. Workers involved in mechanized moulding and mechanized production of cores were monitored: 12 core makers, 2 core-sand preparers, and 5 core installers. Personal breathing-zone levels of MDI were measured using impregnated filter sampling. Dermal exposure to MDI was measured using a tape-strip technique. Three or five consecutive tape-strip samples were collected from five exposed skin areas (right and left forefingers, left and right wrists, and forehead). The average personal air concentration was 0.55 microg m(-3), 50-fold lower than the Swedish occupational exposure limit of 30 microg m(-3). The core makers had an average exposure of 0.77 microg m(-3), which was not significantly different from core installers' and core-sand preparers' average exposure of 0.16 microg m(-3) (P = 0.059). Three core makers had a 10-fold higher inhalation exposure than the other core makers. The core makers' mean dermal exposure at different skin sites varied from 0.13 to 0.34 microg while the two other groups' exposure ranged from 0.006 to 0.062 microg. No significant difference was observed in the MDI levels between the skin sites in a pairwise comparison, except for left forefinger compared to left and right wrist (P < 0.05). In addition, quantifiable but decreasing levels of MDI were observed in the consecutive tape strip per site indicating MDI penetration into the skin. This study indicates that exposure to MDI can be quantified on workers' skin even if air levels are close to unquantifiable. Thus, the potential for uncured MDI to deposit on and penetrate into the skin is demonstrated. Therefore, dermal exposure along with inhalation exposure to MDI should be measured in the occupational settings where MDI is present in order to shed light on their roles in the development of occupational isocyanate asthma.

Exposure assessment of monoterpenes and styrene: a comparison of air sampling and biomonitoring.

BACKGROUND: Within- and between-worker variance components have seldom been reported for both environmental and biological data collected from the same persons. AIMS: To estimate these variance components and their ratio for air contaminants and urinary metabolites in two different work environments and to predict the attenuation of exposure-response relationships based on these measures. METHODS: Parallel measurements of air and urine were performed among workers exposed to monoterpenes in sawmills (urinary metabolite: verbenol) and styrene in reinforced plastics factories (urinary metabolite: mandelic acid). RESULTS: Among the sawmill workers, variance components of the air and urinary verbenol results were similar; for the reinforced plastics workers the estimated between-worker variance component was greater for styrene in air than mandelic acid in urine. This suggests that attenuation bias would be about equal if air or biological monitoring were employed for monoterpene exposures, but would be greater if urinary mandelic acid were used instead of airborne styrene in an investigation of styrene exposure. CONCLUSIONS: Personal air samplers provide data with similar or superior quality to urinary metabolites as measures of exposure to these monoterpenes in sawmills and styrene in reinforced plastics factories.

Comparison of self-assessment and expert assessment of occupational exposure to chemicals.

OBJECTIVES: Occupational assessments of chemical exposure are often inadequate because of difficulties in obtaining sufficient numbers of measurements by trained professionals (experts). The objective of this study was to determine whether workers can provide unbiased data via self-assessments of exposure facilitated by the use of simple passive monitors for personal sampling. METHODS: Untrained workers obtained personal measurements of their exposures to gaseous contaminants (terpenes in sawmills and styrene in reinforced plastics factories) with passive monitors and written instructions. To study the validity of the self-assessments, an occupational hygienist performed exposure measurements on the same occupational groups after the workers had obtained two or more measurements independently. The potential bias of the self-assessments was evaluated by comparing the self-assessments with the expert assessments in mixed-effects statistical models. RESULTS: A total of 153 terpene (97 self and 56 expert) and 216 styrene (159 self and 57 expert) measurements were obtained from four sawmills and six reinforced plastics factories, respectively. No significant differences in the geometric mean exposures were observed between the self-assessments and the expert assessments in 3 of 4 sawmills and 5 of 6 reinforced plastics factories (P > 0.10). The potential bias of the self-assessments of exposure ranged from less than 0.1% to 102% and was less than 17% in 9 of the 10 groups investigated. CONCLUSIONS: The results indicate that untrained, unsupervised workers are able to collect consistently unbiased exposure data by employing currently available passive monitors.

Self-assessment of exposure--a pilot study of assessment of exposure to benzene in tank truck drivers.

Occupational hygienists or safety engineers perform exposure assessments, mostly with very little participation by the workers. The objective of our study is to involve the workers themselves in the assessment and measurement procedure, the self-assessment method (SAE). A pilot study has been carried out involving tank truck drivers at a company transporting gasoline. The drivers were supposed to decide themselves when, and how often, they wanted to measure benzene exposure by using diffusive samplers that were then sent by mail for analysis. After every measurement they received their own results in a personal document for interpretation. The company management also received a document, which summarized all the drivers' measurements. Expert measurements, with the same type of sampler, were also accomplished to evaluate the self-assessments. The geometric mean and the 95 percent confidence intervals of the measurements made by the drivers (29 measurements) was 0.17 (0.11-0.26), and by an occupational hygienist (8 measurements) 0.12 mg/m3 (0.04-0.37). The results show that the drivers technically can perform SAE. Interviews with the workers and the management indicated that some kind of organizational support within the company is needed to implement the method into the regular internal control of the working environment.