Are current biomarkers suitable for the assessment of manganese exposure in individual workers?

BACKGROUND: Whole blood and urinary manganese have been measured in occupational and environmental studies for the assessment of exposure. The aim of this study was to assess the relationship between the airborne concentrations of manganese and these biological indicators. METHODS: Environmental and biological monitoring was performed in a group of 94 employees in a ferroalloy production, who were exposed to manganese (Mn) oxides (MnO(2) and Mn(3)O(4)). The results were compared with those from a control group of 87 subjects not exposed to Mn. RESULTS: Mn exposure levels ranged between 5 and 740 micrograms/m(3), with arithmetic and geometric mean and median values being 202.6, 97.6, and 150 micrograms/m(3), respectively. Arithmetic and geometric means for Mn in total blood (MnB) were, respectively, 10.3+/-3.8 and 9.7 micrograms/L in the exposed and 5.9+/-1.7 and 5.7 micrograms/L in the controls. For urinary Mn (MnU), arithmetic and geometric means were, respectively, 4.9+/-3.6 and 3. 8 micrograms/L in the exposed and 1.2+/-1.4 and 0.7 micrograms/L in the controls. On a group comparison, a significant relationship was found between high and low exposed subgroups, identified according to Mn atmospheric concentrations (MnA), for both MnB (F value=38.0, P > 0.0001) and MnU (F value=36.1, P > 0.0001). On a linear relationship, a correlation was observed between MnA and MnB (r=0. 34; r(2)=0.112; P=0.001), whereas no association was found between MnA and MnU. A significant relationship emerged also between MnB and MnU (r=0.48, r(2)=0.23, P < 0.0001). No association was observed between an index of cumulative exposure and the biological indicators of exposure. CONCLUSIONS: These results confirm that MnB and MnU can discriminate groups of occupationally exposed workers from groups of nonexposed subjects. MnB is also related to the intensity of external exposure on a linear relationship, but given a high variability, it is not suitable for individual biological monitoring. Therefore, further research should focus on more accurate biomarkers of Mn exposure.     

Respirable dust and silica exposure among World Trade Center cleanup workers

The cleanup effort following the destruction of the World Trade Center (WTC) was unprecedented and involved removal of 1.8 million tons of rubble over a nine-month period. Work at the site occurred 24 hr a day, 7 days a week and involved thousands of workers during the process. The Occupational Safety and Health Administration (OSHA) conducted personal and area exposure sampling during the cleanup of the site. Secondary data analysis was performed on OSHA air sampling data for respirable dust and silica from September 2001 to June 2002 at the WTC recovery site to characterize workers' exposure. Results for silica and respirable particulate were stratified by area and personal samples as well as job task for analysis. Of 1108 samples included in the analysis, 693 were personal and 415 were area. The mean result for personal silica samples was 42 μg/m³ (Range: 4.2–1800 μg/m³). Workers identified as drillers had the highest mean silica exposure (72 μg/m³; range: 5.8–800 μg/m³) followed by workers identified as dock builders (67 μg/m³; range: 5.8–670 μg/m³). The mean result for personal samples for respirable particulate was 0.44 mg/m³ (range: 0.00010–13 mg/m³). There were no discernable trends in personal respirable dust and silica concentrations with date.     

Levels and predictors of airborne and internal exposure to manganese and iron among welders

We investigated airborne and internal exposure to manganese (Mn) and iron (Fe) among welders. Personal sampling of welding fumes was carried out in 241 welders during a shift. Metals were determined by inductively coupled plasma mass spectrometry. Mn in blood (MnB) was analyzed by graphite furnace atom absorption spectrometry. Determinants of exposure levels were estimated with multiple regression models. Respirable Mn was measured with a median of 62 (inter-quartile range (IQR) 8.4-320) μg/m(3) and correlated with Fe (r=0.92, 95% CI 0.90-0.94). Inhalable Mn was measured with similar concentrations (IQR 10-340?μg/m(3)). About 70% of the variance of Mn and Fe could be explained, mainly by the welding process. Ventilation decreased exposure to Fe and Mn significantly. Median concentrations of MnB and serum ferritin (SF) were 10.30?μg/l (IQR 8.33-13.15?μg/l) and 131?μg/l (IQR 76-240?μg/l), respectively. Few welders were presented with low iron stores, and MnB and SF were not correlated (r=0.07, 95% CI -0.05 to 0.20). Regression models revealed a significant association of the parent metal with MnB and SF, but a low fraction of variance was explained by exposure-related factors. Mn is mainly respirable in welding fumes. Airborne Mn and Fe influenced MnB and SF, respectively, in welders. This indicates an effect on the biological regulation of both metals. Mn and Fe were strongly correlated, whereas MnB and SF were not, likely due to higher iron stores among welders.     

Reduction in welding fume and metal exposure of stainless steel welders: an example from the WELDOX study

Purpose

In a plant where flux-cored arc welding was applied to stainless steel, we investigated changes in airborne and internal metal exposure following improvements of exhaust ventilation and respiratory protection.

Methods

Twelve welders were examined at a time in 2008 and in 2011 after improving health protection. Seven welders were enrolled in both surveys. Exposure measurement was performed by personal sampling of respirable welding fume inside the welding helmets during one work shift. Urine and blood samples were taken after the shift. Chromium (Cr), nickel (Ni), and manganese (Mn) were determined in air and biological samples.

Results

The geometric mean of respirable particles could be reduced from 4.1 mg/m³ in 2008–0.5 mg/m³ in 2011. Exposure to airborne metal compounds was also strongly reduced (Mn: 399 vs. 6.8 μg/m³; Cr: 187 vs. 6.3 μg/m³; Ni: 76 vs. 2.8 μg/m³), with the most striking reduction inside helmets with purified air supply. Area sampling revealed several concentrations above established or proposed exposure limits. Urinary metal concentrations were also reduced, but to a lesser extent (Cr: 14.8 vs. 4.5 μg/L; Ni: 7.9 vs. 3.1 μg/L). Although biologically regulated, the mean Mn concentration in blood declined from 12.8 to 8.9 μg/L.

Conclusion

This intervention study demonstrated a distinct reduction in the exposure of welders using improved exhaust ventilation and welding helmets with purified air supply in the daily routine. Data from area sampling and biomonitoring indicated that the area background level may add considerably to the internal exposure.     

Lead Exposure and Blood Pressure among Workers in Diverse Industrial Plants in Kenya

The study evaluated airborne exposures and blood lead (BPb) levels in 233 production workers at six diverse industrial plants in Kenya. Blood and personal breathing zone air samples were collected and analyzed for lead (Pb) using atomic absorption spectroscopy. Blood pressure (BP) levels were measured using a standard mercury sphygmomanometer. The results indicated mean airborne Pb levels ± standard deviation (SD) as follows: 183.2 ± 53.6 μg/m³ in battery recycling, 133.5 ± 39.6 μg/m³ in battery manufacturing, 126.2 ± 39.9 μg/m³ in scrap metal welding, 76.3 ± 33.2 μg/m³ in paint manufacturing, 27.3 ± 12.1 μg/m³ in a leather manufacturing, and 5.5 ± 3.6 μg/m³ in a pharmaceutical plant. The mean airborne Pb levels exceeded the U.S. Occupational Safety and Health Administration (OSHA) 8-hr time-weighted average (TWA) permissible exposure limit (PEL) for Pb of 50 μg/m³ in the battery manufacturing, battery recycling, welding, and paint manufacturing plants. Similarly, mean BPb concentrations exceeded the American Conference of Governmental Industrial Hygienists (ACGIH®) biological exposure index (BEI) for Pb of 30 μg/dl. A significant positive association was observed between BPb and breathing zone air Pb (R² = 0.73, P < 0.001). Approximately 30% of the production workers (N = 233) were in the hypertensive range with an average systolic and diastolic blood pressure (BP) of 134.7 ± 12.7 mmHg and 86.4 ± 8.9 mmHg, respectively. In the multivariate regression analysis, age, duration of work, airborne Pb and BPb levels were significantly associated (P < 0.05) with a change in BP. We recommend improved engineering controls, work practices, and personal hygiene to reduce Pb exposures. In addition, workers should undergo comprehensive medical surveillance to include BPb and BP testing, and airborne Pb assessments in all industries with significant lead exposures.     

Intellectual function in Mexican children living in a mining area and environmentally exposed to manganese

Background

Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children.

Objective

This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children.

Methods

Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure.

Results

Exposed children had significantly higher median values for MnH (12.6 μg/g) and MnB (9.5 μg/L) than did nonexposed children (0.6 μg/g and 8.0 μg/L, respectively). MnH was inversely associated with Verbal IQ [β = −0.29; 95% confidence interval (CI), −0.51 to −0.08], Performance IQ (β = −0.08; 95% CI, −0.32 to 0.16), and Total Scale IQ (β = −0.20; 95% CI, −0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants.

Conclusions

The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.     

Air,hand wipe,and surface wipe sampling for Bisphenol A (BPA) among workers in industries that manufacture and use BPA in the United States

For decades, bisphenol A (BPA) has been used in making polycarbonate, epoxy, and phenolic resins and certain investment casting waxes, yet published exposure data are lacking for U.S. manufacturing workers.

In 2013–2014, BPA air and hand exposures were quantified for 78 workers at six U.S. companies making BPA or BPA-based products. Exposure measures included an inhalable-fraction personal air sample on each of two consecutive work days (n = 146), pre- and end-shift hand wipe samples on the second day (n = 74 each), and surface wipe samples (n = 88). Potential determinants of BPA air and end-shift hand exposures (after natural log transformation) were assessed in univariate and multiple regression mixed models.

The geometric mean (GM) BPA air concentration was 4.0 µg/m³ (maximum 920 µg/m³). The end-shift GM BPA hand level (26 µg/sample) was 10-times higher than the pre-shift level (2.6 µg/sample). BPA air and hand exposures differed significantly by industry and job. BPA air concentrations and end-shift hand levels were highest in the BPA-filled wax manufacturing/reclaim industry (GM_Air = 48 µg/m³, GM_Hand-End = 130 µg/sample) and in the job of working with molten BPA-filled wax (GM_Air = 43 µg/m³, GM_Hand-End = 180 µg/sample), and lowest in the phenolic resins industry (GM_Air = 0.85 µg/m³, GM_Hand-End = 0.43 µg/sample) and in the job of flaking phenolic resins (GM_AIR = 0.62 µg/m³, GM_Hand-End = 0.38 µg/sample). Determinants of increased BPA air concentration were industry, handling BPA containers, spilling BPA, and spending ≥50% of the shift in production areas; increasing age was associated with lower air concentrations. BPA hand exposure determinants were influenced by high values for two workers; for all other workers, tasks involving contact with BPA-containing materials and spending ≥50% of the shift in production areas were associated with increased BPA hand levels. Surface wipe BPA levels were significantly lower in eating/office areas (GM = 9.3 µg/100 cm²) than in production areas (GM = 140 µg/100 cm²).

In conclusion, worker BPA exposure was associated with tasks and conditions affecting both inhalation and dermal exposure. The potential for BPA-related health effects among these workers is unknown.     

A methodology for the determination of fugitive dust emissions from landfill sites

This study focuses on the development of a methodology for the determination of the contribution of fugitive dust emissions from landfill sites to ambient PM₁₀ concentrations and the subsequent exposure to working personnel. Fugitive dust emissions in landfills mainly originate from resuspension due to truck traffic on paved and unpaved roads and from wind-blown dust from landfill cover soil. The results revealed that exposure to PM_10, originating from fugitive dust emissions in the landfill site, was exceeding the health protection standards (50 μg m^?3). The higher average daily PM₁₀ concentration (average value) for weekdays was equal to 275 μg m^?3 and was computed for the areas nearby the unpaved road located inside the landfill facilities that lead to the landfill cell. The percentage contributions of road and wind-blown dust to the PM₁₀ concentrations on weekdays were equal to 76 and 1?%, respectively. The influence of the background concentration is estimated close to 23?%.     

Sources of trace metals in PM<Subscript>10</Subscript> from a petrochemical industrial complex in Northern Mexico

Concentrations, sources, and relative contributions of Cd, Cr, Cu, Fe, Mn, Pb, Ni, Ti, V, and Zn observed in PM₁₀ in the petrochemical industrial zone of Altamira in Northern Mexico are reported for the first time. Results show that oil refining, alloys, fertilizer, mining, metallurgical processes, and steel production industries are important contributions to PM₁₀ and metal concentrations. PM₁₀ concentrations ranged from 21 to 92 μg m^?3 and exceeded the revised 24-h average Mexican standard NOM-025-SSA1-2014 of 75 μg m^?3 12 % of the study period. The highest metal concentrations were Fe (1.64 μg m^?3), Mn (0.57 μg m^?3), and Ti (0.29 μg m^?3) and were associated with two dominant wind directions. Ti and Fe were associated with NNW winds (natural sources), and Mn and Fe were associated with SSW winds (ferromanganese industry). An average V/Ni ratio of 8.5 was found in this study with highest ratios associated to two dominant wind directions, NNW-NW and SE-SSE, suggesting origins from a fuel oil thermoelectric power plant and a refinery fuel oil, respectively. Pb was associated with industrial activity and never exceeded the Mexican standard of 1.5 μg m^?3 in 24 h. Zn and Cd were correlated with a dominant easterly wind, suggesting the presence of vehicle exhaust pollutants. The study of the size and shape of PM₁₀ particles by scanning electronic microscopy and energy-dispersive spectroscopy (SEM-EDS) allowed us to confirm the presence of trace metals associated to natural soils and clays, combustion, and industrial processes. The results presented here constitute the first efforts to evaluate toxic metals in a heavily industrialized area in Mexico and can be used to develop air quality management programs.     

Exposure to respirable dust and manganese and prevalence of airways symptoms,among Swedish mild steel welders in the manufacturing industry

Purpose

Welding fume consists of metal fumes, e.g., manganese (Mn) and gases, e.g., ozone. Particles in the respirable dust (RD) size range dominate. Exposure to welding fume could cause short- and long-term respiratory effects. The prevalence of work-related symptoms among mild steel welders was studied, and the occupational exposure to welding fumes was quantified by repeated measurements of RD, respirable Mn, and ozone. Also the variance components were studied.

Method

A questionnaire concerning airway symptoms and occupational history was answered by 79 % of a cohort of 484 welders. A group of welders (N = 108) were selected and surveyed by personal exposure measurements of RD and ozone three times during 1 year.

Results

The welders had a high frequency of work-related symptoms, e.g., stuffy nose (33 %), ocular symptoms (28 %), and dry cough (24 %). The geometric mean exposure to RD and respirable Mn was 1.3 mg/m³ (min–max 0.1–38.3 mg/m³) and 0.08 mg/m³ (min–max <0.01–2.13 mg/m³), respectively. More than 50 % of the Mn concentrations exceeded the Swedish occupational exposure limit (OEL). Mainly, low concentrations of ozone were measured, but 2 % of the samples exceeded the OEL. Of the total variance for RD, 30 and 33 % can be attributed to within-worker variability and between-company variability, respectively.

Conclusions

Welders had a high prevalence of work-related symptom from the airways and eyes. The welders’ exposure to Mn was unacceptably high. To reduce the exposure further, control measures in the welding workshops are needed. Correct use of general mechanical ventilation and local exhaust ventilation can, for example, efficiently reduce the exposure.     

Determinants of respirable quartz exposure in farming

The objectives of this article are to quantify personal respirable quartz exposure on sandy, sandy loam, and clay soil farms and to identify exposure determinants. The methods applied included observing and examining the variables soil type, commodity farmed, activity, process, quartz % in respirable dust, and weather variables. Multiple linear regression was used to identify determinants of respirable quartz concentration and logistic regression was applied to identify determinants of respirable quartz concentration > 50 µg.m^?3 (a commonly used reference value of over-exposure). The highest quartz concentration was 626 µg.m^?3 and 30%, 22%, and 31% of measurements were > 50 µg.m^?3 for sandy, sandy loam, and clay soil farms, respectively. In general, the commodities livestock farming and cereal grains as well as the activity cereal planter operator, decreased humidity on the day of measurement, the mechanical processes, and quartz % in respirable dust (in a confounding way) were associated with higher respirable quartz concentrations (p ≤ 0.10) as well as season (p = 0.14). Variables associated with quartz levels above 50 µg.m^?3 were cereal planter operator, increased quartz % in respirable dust, decreased humidity on day of measurement, and increased respirable dust concentration. Cereal planter operator (Multivariate Odds Ratio (OR) 4.56, 95% CI: 1.79–8.89) and levels of quartz % > 10 µg.m^?3 (Multivariate OR 6.01, 95% CI: 3.52–9.71 if quartz % > 10 but ≤ 20 µg.m^?3, and Multivariate OR 5.32, 95% CI: 2.56–8.34 if quartz % > 20 µg.m^?3) were clear determinants of quartz over-exposure. It can therefore be concluded that over-exposure to quartz in farming is possible. Joint influences of more farming characteristics and weather variables should be included, together with soil type in future farming exposure assessments.     

Occupational Exposure to Crystalline Silica at Alberta Work Sites

Although crystalline silica has been recognized as a health hazard for many years, it is still encountered in many work environments. Numerous studies have revealed an association between exposure to respirable crystalline silica and the development of silicosis and other lung diseases including lung cancer. Alberta Jobs, Skills, Training and Labour conducted a project to evaluate exposure to crystalline silica at a total of 40 work sites across 13 industries. Total airborne respirable dust and respirable crystalline silica concentrations were quite variable, but there was a potential to exceed the Alberta Occupational Exposure Limit (OEL) of 0.025 mg/m³ for respirable crystalline silica at many of the work sites evaluated. The industries with the highest potentials for overexposure occurred in sand and mineral processing (GM 0.090 mg/m³), followed by new commercial building construction (GM 0.055 mg/m³), aggregate mining and crushing (GM 0.048 mg/m³), abrasive blasting (GM 0.027 mg/m³), and demolition (GM 0.027 mg/m³). For worker occupations, geometric mean exposure ranged from 0.105 mg/m³ (brick layer/mason/concrete cutting) to 0.008 mg/m³ (dispatcher/shipping, administration). Potential for GM exposure exceeding the OEL was identified in a number of occupations where it was not expected, such as electricians, carpenters and painters. These exposures were generally related to the specific task the worker was doing, or arose from incidental exposure from other activities at the work site. The results indicate that where there is a potential for activities producing airborne respirable crystalline silica, it is critical that the employer include all worker occupations at the work site in their hazard assessment. There appears to be a relationship between airborne total respirable dust concentration and total respirable dust concentrations, but further study is require to fully characterize this relationship. If this relationship holds true, it may provide a useful hazard assessment tool for employers by which the potential for exposure to airborne respirable silica at the work site can be more easily estimated.     

Long-term exposure to air pollution and the incidence of asthma: meta-analysis of cohort studies

We quantified the association between long-term exposure to air pollution and the incidence of asthma by conducting a systematic review and meta-analysis of cohort studies. Incidence was defined as the incidence of diagnosed asthma or of new wheeze symptom between two assessments or, in birth cohorts followed up to 10 years of age, a lifetime prevalence estimate of asthma or wheeze symptom. We identified 17 cohorts (eight birth cohorts and nine child/adult cohorts) with a total of 99 population-based risk estimates. The studies were heterogeneous in their design and methods of measurement. Follow-up ranged from 3 to 23 years. Most studies were based on within-community exposure contrasts dominated by traffic pollution. Twelve of the cohorts reported at least one positive statistically significant association between air pollution and a measure of incidence. Of the total of 99 estimates, only a minority (29) were positive and statistically significant. Estimates for meta-analysis were chosen a priori using a protocol. For the 13 studies with estimates for nitrogen dioxide (NO₂), the random effects odds ratio was 1.07 (95% CI 1.02 to 1.13) per 10 μg/m³. For five studies with estimates for particulate matter with aerodynamic diameter <2.5 μm (PM_2.5), the random effects estimate was 1.16 (95% CI 0.98 to 1.37) per 10 μg/m³. These estimates were reduced in size and statistical significance by adjustment for publication bias but remained positive. The results are consistent with an effect of outdoor air pollution on asthma incidence. Future meta-analyses would benefit from greater standardisation of cohort methods.     

Fine particulate matter (PM2.5) association with peripheral artery disease admissions in northeastern United States

Background: Current evidence, on the association of PM_2.5 and peripheral artery disease (PAD) is very sparse. Methods: We use novel PM_2.5 prediction models to investigate associations between chronic and acute PM_2.5 exposures and hospital PAD admissions across the northeast USA. Poisson regression analysis was preformed where daily admission counts in each zip code are regressed against both chronic and acute PM_2.5 exposure, temperature, socio-economic characteristics and time to control for seasonal patterns. Results: Positive significant associations were observed between both chronic and acute exposure to PM_2.5 and PAD hospitalizations. Every 10-μg/m³ increase in acute PM_2.5 exposure was associated with a 0.26 % increase in admissions (CI = 0.08 – 0.45 %) and every 10-μg/m³ increase in chronic PM _2.5 exposure was associated with a 4.4 % increase in admissions (CI = 3.50 – 5.35 %). Conclusions: The study supports the hypothesis that acute and chronic exposure to PM_2.5 can increase the risk of PAD.     

Air quality at outdoor community events: findings from fine particulate (PM2.5) sampling at festivals in Edmonton,Alberta

Exposure to fine particulate matter (PM_2.5) is associated with a broad range of health risks. This study assessed the impacts of cooking smoke and environmental tobacco smoke on air quality at outdoor community events in Edmonton, Alberta (Canada). Data were collected at three festivals in July–August 2011 using a portable real-time airborne particle monitor. The pooled mean PM_2.5 level was 12.41?μg/m³. Peak readings varied from 52 to 1877?μg/m³. Mean PM_2.5 near food stalls was 35.42?μg/m³, which exceeds the WHO limit for 24?h exposure. Mean PM_2.5 levels with smokers present were 16.39?μg/m³ (all points) and 9.64?μg/m³ (excluding points near food stalls). Although some smokers withdrew from common spaces, on average 20 smokers/hour were observed within 3?m. Extending smoking bans would improve air quality and address related concerns. However, food preparation is a more pressing area for policy action to reduce PM_2.5 exposure at these community events.     

Urinary excretion of platinum (Pt) following skin and respiratory exposure to soluble Pt at South African precious metals refineries

Adverse respiratory and skin health effects have been associated with occupational exposure to soluble platinum (Pt). However, the relationship between skin exposure and urinary Pt excretion has not yet been investigated. In this study we examined the relationship between skin and respiratory exposure to soluble Pt and urinary Pt excretion at two South African precious metals refineries.The skin and respiratory exposure to soluble Pt as well as the urinary Pt excretion of forty precious metals refinery workers was assessed simultaneously using Ghostwipes?, Methods for the Determination of Hazardous Substances method 46/2 and spot urine tests, respectively.The geometric mean for skin exposure to soluble Pt on four anatomical positions (palm, wrist, neck and forehead) was 0.008?μg/cm² [95% confidence interval (CI): 0.005-0.013?μg/cm²], while the geometric mean for respiratory exposure was 0.301?μg/m³ (95%CI: 0.151-0.601?μg/m³) and the geometric mean for urinary Pt excretion was 0.212?μg/g creatinine (95%CI: 0.169-0.265?μg/g creatinine). Partial correlations identified significant positive correlations between skin exposure, respiratory exposure and urinary Pt excretion (r?=?0.580 to 0.754).Skin and respiratory exposures to soluble Pt were both positively correlated with urinary Pt excretion, and both exposure routes should be considered when investigating occupational exposure to soluble Pt.     

Occupational exposure to airborne mercury during gold mining operations near El Callao, Venezuela

Objective: The National Institute for Occupational Safety and Health (NIOSH) recently conducted a cross–sectional study during gold mining operations near El Callao, Venezuela. The purpose of the study was to assess mercury exposures and mercury-related microdamage to the kidneys. The study consisted of concurrent occupational hygiene and biological monitoring, and an examination of the processing techniques employed at the different mining facilities. Mercury was used in these facilities to remove gold by forming a mercury-gold amalgam. The gold was purified either by heating the amalgam in the open with a propane torch or by using a small retort. Methods: Thirty-eight workers participated in this study. Some participants were employed by a large mining company, while others were considered “informal miners” (self-employed). Mercury exposure was monitored by sampling air from the workers' breathing zones. These full-shift air samples were used to calculate time-weighted average (TWA) mercury exposure concentrations. A questionnaire was administered and a spot urine sample was collected. Each urine sample was analyzed for mercury, creatinine, and N-acetyl-ß-d-glucosaminidase (NAG). Results: The range for the 8-h TWA airborne mercury exposure concentrations was 0.1 to 6,315?μg/m³, with a mean of 183?μg/m³. Twenty percent of the TWA airborne mercury exposure measurements were above the NIOSH recommended exposure limit (REL) of 50?μg/m³, and 26% exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 25?μg/m³. The mean urine mercury concentration was 101?μg/g creatinine (μg/g-Cr), and the data ranged from 2.5 to 912?μg/g-Cr. Forty–two percent of the study participants had urine mercury concentrations that exceeded the ACGIH biological exposure index (BEI) of 35?μg/g-Cr. Urinary NAG excretion is considered a biological marker of preclinical, nonspecific microdamage to the kidney's proximal tubule cells. The mean urine NAG concentration was 3.6 International Units/g-Cr (IU/g-Cr) with a range of 0.5 to 11.5?IU/g-Cr. Three workers had urine NAG levels in excess of the reference values. Correlation analyses found statistically significant correlations between airborne mercury exposure and urine mercury level (P=0.01), and between urine mercury level and urine NAG excretion (P=0.01). In addition, the airborne mercury exposure data and urine mercury data were segregated by job tasks. A Wilcoxon rank sum test revealed significant correlations between tasks and mercury exposure (P=0.03), and between tasks and urine mercury level (P=0.02). Conclusions: The tasks with the highest mean airborne mercury exposures were “burning the mercury-gold amalgam” and “gold refining/smelting”. Recommendations were provided for improving the retort design to better contain mercury, for ventilation in the gold shops, and for medical surveillance and educational programs.     

Dust exposure in workers from grain storage facilities in Costa Rica

Background

About 12 million workers are involved in the production of basic grains in Central America. However, few studies in the region have examined the occupational factors associated with inhalable dust exposure.

Effect of ventilation velocity on hexavalent chromium and isocyanate exposures in aircraft paint spraying

Exposure control system performance was evaluated during aircraft paint spraying at a military facility. Computational fluid dynamics (CFD) modeling, tracer gas testing, and exposure monitoring examined contaminant exposure vs. crossflow ventilation velocity. CFD modeling using the RNG k-? turbulence model showed exposures to simulated methyl isobutyl ketone of 294 and 83.6 ppm, as a spatial average of five worker locations, for velocities of 0.508 and 0.381 m/s (100 and 75 fpm), respectively. In tracer gas experiments, observed supply/exhaust velocities of 0.706/0.503 m/s (136/99 fpm) were termed full-flow, and reduced velocities were termed 3/4-flow and half-flow. Half-flow showed higher tracer gas concentrations than 3/4-flow, which had the lowest time-averaged concentration, with difference in log means significant at the 95% confidence level. Half-flow compared to full-flow and 3/4-flow compared to full-flow showed no statistically significant difference. CFD modeling using these ventilation conditions agreed closely with the tracer results for the full-flow and 3/4-flow comparison, yet not for the 3/4-flow and half-flow comparison. Full-flow conditions at the painting facility produced a velocity of 0.528 m/s (104 fpm) midway between supply and exhaust locations, with the supply rate of 94.4 m³/s (200,000 cfm) exceeding the exhaust rate of 68.7 m³/s (146,000 cfm). Ventilation modifications to correct this imbalance created a midhangar velocity of 0.406 m/s (80.0 fpm). Personal exposure monitoring for two worker groups—sprayers and sprayer helpers (“hosemen”)—compared process duration means for the two velocities. Hexavalent chromium (Cr[VI]) exposures were 500 vs. 360 µg/m³ for sprayers and 120 vs. 170 µg/m³ for hosemen, for 0.528 m/s (104 fpm) and 0.406 m/s (80.0 fpm), respectively. Hexamethylene diisocyanate (HDI) monomer means were 32.2 vs. 13.3 µg/m³ for sprayers and 3.99 vs. 8.42 µg/m³ for hosemen. Crossflow velocities affected exposures inconsistently, and local work zone velocities were much lower. Aircraft painting contaminant control is accomplished better with the unidirectional crossflow ventilation presented here than with other observed configurations. Exposure limit exceedances for this ideal condition reinforce continued use of personal protective equipment.