Driver exposure to combustion particles in the U.S. Trucking industry

Exposure to diesel engine exhaust and alterations to the Cys34/Lys525 adductome of human serum albumin

We investigated whether exposure to carcinogenic diesel engine exhaust (DEE) was associated with altered adduct levels in human serum albumin (HSA) residues. Nano-liquid chromatography-high resolution mass spectrometry (nLC-HRMS) was used to measure adducts of Cys34 and Lys525 residues in plasma samples from 54 diesel engine factory workers and 55 unexposed controls. An untargeted adductomics and bioinformatics pipeline was used to find signatures of Cys34/Lys525 adductome modifications. To identify adducts that were altered between DEE-exposed and unexposed participants, we used an ensemble feature selection approach that ranks and combines findings from linear regression and penalized logistic regression, then aggregates the important findings with those determined by random forest. We detected 40 Cys34 and 9 Lys525 adducts. Among these findings, we found evidence that 6 Cys34 adducts were altered between DEE-exposed and unexposed participants (i.e., 841.75, 851.76, 856.10, 860.77, 870.43, and 913.45). These adducts were biologically related to antioxidant activity.

Inequalities in occupational exposures among people using popular commute modes

Several recent studies have looked into the differences in air qualities inside popular commute modes. The impact of daily commuting patterns and work-related trips on inhalation doses, however, are not investigated. The purpose of this study is to quantify the variation in air pollutants within popular commute modes in Mumbai, India, and to estimate the variation in exposure as a result of occupational or work-related trips across different sub-groups. Real-time pollutants, both gaseous and particulate matters (PM), were measured on a pre-defined route during rush and non-rush hours on buses, cars, auto-rickshaws, sub-urban trains, and motorbikes through several trips (N = 98). Household surveys were conducted to estimate the exposures of different occupational subgroups (cab-driver, auto-rickshaw drivers, delivery persons) and people commuting to their offices daily. Participants (N = 800) from various socioeconomic backgrounds in the city were asked about their job categories, work-activity patterns, and work-related commute trips. Mass concentrations of particles in different size ranges (PM₁, PM_2.5, and PM₁₀) were substantially higher (p < 0.05) inside auto-rickshaws (44.6 μg/m³, 84.7 μg/m³, and 138.3 μg/m³) compared to other modes. Inside cars, gaseous pollutants such as carbon monoxide (CO) and total volatile organic compounds (TVOC) were significantly higher (p < 0.05). Although both gaseous and particulate concentrations were lower (p < 0.05) inside buses, bus-commuters were found to be highly exposed to the pollutants due to the extended trip time (∼1.2 times longer than other modes) and driving conditions. Office commuters inhale a large fraction of their daily doses (25-30%) during their work-related travel. Occupational sub-groups, on the other hand, inhale ∼90% of the pollutants during their work. In a day, an auto-rickshaw driver inhales 10-15% more (p < 0.05) pollutants than cab driver or delivery personnel. Therefore, this study highlights the inequalities in occupational exposure as a combined effect of in-cabin air qualities and commute patterns due to occupational obligations.

Elevated urinary mutagenicity among those exposed to bituminous coal combustion emissions or diesel engine exhaust

Urinary mutagenicity reflects systemic exposure to complex mixtures of genotoxic/carcinogenic agents and is linked to tumor development. Coal combustion emissions (CCE) and diesel engine exhaust (DEE) are associated with cancers of the lung and other sites, but their influence on urinary mutagenicity is unclear. We investigated associations between exposure to CCE or DEE and urinary mutagenicity. In two separate cross-sectional studies of nonsmokers, organic extracts of urine were evaluated for mutagenicity levels using strain YG1041 in the Salmonella (Ames) mutagenicity assay. First, we compared levels among 10 female bituminous (smoky) coal users from Laibin, Xuanwei, China, and 10 female anthracite (smokeless) coal users. We estimated exposure-response relationships using indoor air concentrations of two carcinogens in CCE relevant to lung cancer, 5-methylchrysene (5MC), and benzo[a]pyrene (B[a]P). Second, we compared levels among 20 highly exposed male diesel factory workers and 15 unexposed male controls; we evaluated exposure-response relationships using elemental carbon (EC) as a DEE-surrogate. Age-adjusted linear regression was used to estimate associations. Laibin smoky coal users had significantly higher average urinary mutagenicity levels compared to smokeless coal users (28.4 ± 14.0 SD vs. 0.9 ± 2.8 SD rev/ml-eq, p = 2 × 10-5 ) and a significant exposure-response relationship with 5MC (p = 7 × 10-4 ). DEE-exposed workers had significantly higher urinary mutagenicity levels compared to unexposed controls (13.0 ± 10.1 SD vs. 5.6 ± 4.4 SD rev/ml-eq, p = .02) and a significant exposure-response relationship with EC (p-trend = 2 × 10-3 ). Exposure to CCE and DEE is associated with urinary mutagenicity, suggesting systemic exposure to mutagens, potentially contributing to cancer risk and development at various sites.

Diesel Engine Exhaust Exposure in the Ontario Civil Infrastructure Construction Industry

OBJECTIVES

Diesel engine exhaust (DEE) is a known lung carcinogen and a common occupational exposure in Canada. The use of diesel-powered equipment in the construction industry is particularly widespread, but little is known about DEE exposures in this work setting. The objective of this study was to determine exposure levels and identify and characterize key determinants of DEE exposure at construction sites in Ontario.

METHODS

Elemental carbon (EC, a surrogate of DEE exposure) measurements were collected at seven civil infrastructure construction worksites and one trades training facility in Ontario using NIOSH method 5040. Full-shift personal air samples were collected using a constant-flow pump and SKC aluminium cyclone with quartz fibre filters in a 37-mm cassette. Exposures were compared with published health-based limits, including the Dutch Expert Committee on Occupational Safety (DECOS) limit (1.03 µg m-3 respirable EC) and the Finnish Institute of Occupational Health (FIOH) recommendation (5 µg m-3 respirable EC). Mixed-effects linear regression was used to identify determinants of EC exposure.

RESULTS

In total, 149 EC samples were collected, ranging from <0.25 to 52.58 µg m-3 with a geometric mean (GM) of 3.71 µg m-3 [geometric standard deviation (GSD) = 3.32]. Overall, 41.6% of samples exceeded the FIOH limit, mostly within underground worksites (93.5%), and 90.6% exceeded the DECOS limit. Underground workers (GM = 13.20 µg m-3, GSD = 1.83) had exposures approximately four times higher than below grade workers (GM = 3.56 µg m-3, GSD = 1.94) and nine times higher than above ground workers (GM = 1.49 µg m-3, GSD = 1.75). Training facility exposures were similar to above ground workers (GM = 1.86 µg m-3, GSD = 4.12); however, exposures were highly variable. Work setting and enclosed cabins were identified as the key determinants of exposure in the final model (adjusted R2 = 0.72, P < 0.001). The highest DEE exposures were observed in underground workplaces and when using unenclosed cabins.

CONCLUSIONS

This study provides data on current DEE exposure in Canadian construction workers. Most exposures were above recommended health-based limits, albeit in other jurisdictions, signifying a need to further reduce DEE levels in construction. These results can inform a hazard reduction strategy including targeted intervention/control measures to reduce DEE exposure and the burden of occupational lung cancer.

Diesel Exhaust Exposure during Farming Activities: Statistical Modeling of Continuous Black Carbon Concentrations

OBJECTIVES

Daily driving of diesel-powered tractors has been linked to increased lung cancer risk in farmers, yet few studies have quantified exposure levels to diesel exhaust during tractor driving or during other farm activities. We expanded an earlier task-based descriptive investigation of factors associated with real-time exposure levels to black carbon (BC, a surrogate of diesel exhaust) in Iowa farmers by increasing the sample size, collecting repeated measurements, and applying statistical models adapted to continuous measurements.

METHODS

The expanded study added 43 days of sampling, for a total of 63 sample days conducted in 2015 and 2016 on 31 Iowa farmers. Real-time, continuous monitoring (30-s intervals) of personal BC concentrations was performed using a MicroAeth AE51 microaethelometer affixed with a micro-cyclone. A field researcher recorded information on tasks, fuel type, farmer location, and proximity to burning biomass. We evaluated the influence of these variables on log-transformed BC concentrations using a linear mixed-effect model with random effects for farmer and day and a first-order autoregressive structure for within-day correlation.

RESULTS

Proximity to diesel-powered equipment was observed for 42.5% of the overall sampling time and on 61 of the 63 sample days. Predicted geometric mean BC concentrations were highest during grain bin work, loading, and harvesting, and lower for soil preparation and planting. A 68% increase in BC concentrations was predicted for close proximity to a diesel-powered vehicle, relative to far proximity, while BC concentrations were 44% higher in diesel vehicles with open cabins compared with closed cabins. Task, farmer location, fuel type, and proximity to burning biomass explained 8% of within-day variance in BC concentrations, 2% of between-day variance, and no between-farmer variance.

CONCLUSION

Our findings showed that farmers worked frequently near diesel equipment and that BC concentrations varied between tasks and by fuel type, farmer location, and proximity to burning biomass. These results could support the development of exposure models applicable to investigations of health effects in farmers associated with exposure to diesel engine exhaust.

Characteristics of Occupational Exposure to Diesel Engine Exhaust for Shipyard Transporter Signal Workers

Background: Workers performing signal work for a heavy-duty shipyard transporter are exposed to diesel engine exhaust (DEE), which is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. Here, we evaluate DEE exposure levels for workers engaged in shipyard transporter signal work through measurement of respirable elemental carbon (EC), organic carbon (OC), and total carbon (TC), and identify the factors affecting exposure. Methods: Sixty signal workers were selected, and measured samples were analyzed by thermo-optical transmittance. Results: The mean EC exposure level of a transporter signal worker was 4.16 µg/m3, with a range of 0.69 to 47.81 µg/m3. EC, OC, and TC exposure levels did not show statistically significant differences for individual variables except the measurement date. This was influenced by meteorological factors such as wind speed, and it was confirmed that the work position, number carried, and load capacity in the multiple regression analysis after minimizing the meteorological effects were factors influencing the EC exposure level of the signalman. Conclusions: Meteorological conditions influenced DEE exposure of transporter signal workers who work outdoors. The mean EC exposure level was not high, but exposures to high concentrations of EC were recorded by meteorological factors.

Characteristics of PM2.5 and Black Carbon Exposure Among Subway Workers

This study aimed to assess the characteristics of exposure to both PM_2.5 and black carbon (BC) among subway workers. A total of 61 subway workers, including 26, 23, and 12 subway station managers, maintenance engineers, and train drivers, respectively, were investigated in 2018. Real-time measurements of airborne PM_2.5 and BC were simultaneously conducted around the breathing zones of workers. Maintenance engineers had the highest average levels of exposure to both PM_2.5 and BC (PM_2.5, 76 µg/m³; BC, 9.3 µg/m³), followed by train drivers (63.2 µg/m³, 5.9 µg/m³) and subway station managers (39.7 µg/m³, 2.2 µg/m³). In terms of the relationship between mass concentrations of PM_2.5 and BC, train drivers demonstrated the strongest correlation (R = 0.72), indicating that the proportion of BC contained in PM_2.5 is relatively steady. The average proportion of BC in PM_2.5 among maintenance engineers (13.0%) was higher than that among train drivers (9.4%) and subway station managers (6.4%). Univariate and mixed effect multiple analyses demonstrated the type of task and worksite to be significant factors affecting exposure levels in maintenance engineers and subway station managers. The use of diesel engine motorcars in tunnel maintenance was found to be a key contributor to PM_2.5 and BC exposure levels among subway workers.

A task-based analysis of black carbon exposure in Iowa farmers during harvest

Diesel exhaust has been associated with adverse human health effects. Farmers are often exposed to diesel exhaust; however, their diesel exposure has not been well characterized. In this descriptive study, we measured black carbon concentrations as a proxy for diesel exhaust exposure in 16 farmers over 20 sampling days during harvest in southeast Iowa. Farmers wore a personal aethalometer which measured real-time black carbon levels throughout the working day, and their activities were recorded by a field researcher. Black carbon concentrations were characterized for each farmer, and by activity, vehicle fuel type, and microenvironment. Overall, 574 discrete tasks were monitored with a median task duration of 5.5 min. Of these tasks, 39% involved the presence of a diesel vehicle. Farmers' daily black carbon geometric mean exposures ranged from 0.1-2.3 µg/m³, with a median daily geometric mean of 0.3 µg/m³. The highest black carbon concentrations were measured on farmers who used or worked near diesel vehicles (geometric mean ranged from 0.5 µg/m³ while harvesting to 4.9 µg/m³ during animal work). Higher geometric means were found for near vs. far proximity to diesel-fueled vehicles and equipment (2.9 vs. 0.3 µg/m³). Indoor, bystander proximity to diesel-operated vehicles resulted in the highest geometric mean black carbon concentrations (18 µg/m³). Use of vehicles with open cabs had higher mean black carbon concentrations than closed cabs (2.1-3.2 vs. 0.4-0.9 µg/m³). In summary, our study provided evidence that farmers were frequently exposed to black carbon associated with diesel-related activities at levels above urban ambient concentrations in their daily work during harvest.

Occupational Exposure to Diesel Particulate Matter in Municipal Household Waste Workers

OBJECTIVE

The purposes of this study were to determine the following: 1) the exposure levels of municipal household waste (MHW) workers to diesel particulate matter (DPM) using elemental carbon (EC), organic carbon (OC), total carbon (TC), black carbon (BC), and fine particulate matter (PM 2.5) as indicators; 2) the correlations among the indicators; 3) the optimal indicator for DPM; and 4) factors that influence personal exposure to DPM.

METHODS

A total of 72 workers in five MHW collection companies were assessed over a period of 7 days from June to September 2014. Respirable EC/OC samples were quantified using the thermal optical transmittance method. BC and PM 2.5 were measured using real-time monitors, an aethalometer and a laser photometer. All results were statistically analyzed for occupational and environmental variables to identify the exposure determinants of DPM.

RESULTS

The geometric mean of EC, OC, TC, BC and PM 2.5 concentrations were 4.8, 39.6, 44.8, 9.1 and 62.0 μg/m3, respectively. EC concentrations were significantly correlated with the concentrations of OC, TC and BC, but not with those of PM 2.5. The exposures of the MHW collectors to EC, OC, and TC were higher than those of the drivers (p<0.05). Workers of trucks meeting Euro 3 emission standard had higher exposures to EC, OC, TC and PM 2.5 than those working on Euro 4 trucks (p<0.05). Multiple regression analysis revealed that the job task, European engine emission standard, and average driving speed were the most influential factors in determining worker exposure.

CONCLUSIONS

We assessed MHW workers' exposure to DPM using parallel sampling of five possible indicators. Of these five indicators, EC was shown to be the most useful indicator of DPM exposure for MHW workers, and the job task, European emission standard, and average driving speed were the main determinants of EC exposure.

Occupational exposure to roadway emissions and inside informal settlements in sub-Saharan Africa: A pilot study in Nairobi, Kenya

Few studies examine urban air pollution in sub-Saharan Africa (SSA), yet urbanization rates there are among the highest in the world. In this study, we measured 8-hr average occupational exposure levels of fine particulate matter (PM_2.5), black carbon (BC), ultra violet active-particulate matter (UV-PM), and trace elements for individuals who worked along roadways in Nairobi, specifically bus drivers, garage workers, street vendors, and women who worked inside informal settlements. We found BC and re-suspended dust were important contributors to PM_2.5 levels for all study populations, particularly among bus drivers, while PM_2.5 exposure levels for garage workers, street vendors, and informal settlement residents were not statistically different from each other. We also found a strong signal for biomass emissions and trash burning, which is common in Nairobi's low-income areas and open-air garages. These results suggest that the large portion of urban residents in SSA who walk along roadways would benefit from air quality regulations targeting roadway emissions from diesel vehicles, dust, and trash burning. This is the first study to measure occupational exposure to urban air pollution in SSA and results imply that roadway emissions are a serious public health concern.

Lung cancer risk in professional drivers in Korea: A population-based proportionate cancer incidence ratio study

OBJECTIVES

Professional drivers are exposed to diesel engine exhaust and outdoor air pollution while driving. Diesel engine exhaust and outdoor air pollution are known carcinogens causing lung cancer. However, previous epidemiological studies examining lung cancer risk in professional drivers have not shown a consistent association. In the present study, we evaluated lung cancer risk among Korean professional drivers.

METHODS

Subjects consisted of male drivers aged 30-59 registered in the Korea Central Cancer Registry for lung cancer between 1999 and 2011. Proportionate cancer incidence ratios (PCIRs) for lung cancer were calculated and indirectly age standardized with the male general population. Additional PCIRs were calculated by indirectly adjusting for the effect of cigarette smoking.

RESULTS

The PCIR for lung cancer in professional drivers during the study period increased significantly (1.20, 95% CI: 1.13-1.26). The increased risk was generally consistent throughout study years and age categories. Adjusting for the effect of cigarette smoking did not change the significance of the associations (1.09, 95% CI: 1.03-1.15).

CONCLUSIONS

Our findings support an association between lung cancer and driver jobs in the Korean male population. However, the association should be further evaluated in a study with a longitudinal design and a quantitative exposure assessment.

A structural approach to address the healthy-worker survivor effect in occupational cohorts: an application in the trucking industry cohort

BACKGROUND

Occupational cohort studies are often challenged by the Healthy Worker Survivor Effect, which may bias standard methods of analysis. G-estimation of structural failure time models is an approach for reducing this type of bias. Accelerated failure time models have recently been applied in an occupational cohort but cumulative failure time models have not.

METHODS

We used g-estimation of a cumulative failure time model to assess the effect of working as a long-haul driver on ischaemic heart disease mortality in a cohort of 30 448 men employed in the unionised US trucking industry in 1985. Exposure was defined by job title and based on work records. We also applied g-estimation of an accelerated failure time model as a sensitivity analysis and approximated HRs from both models to compare them.

RESULTS

The risk ratio (RR) obtained from the cumulative failure time model, comparing the observed risk under no intervention to the risk had nobody ever been exposed as a long-haul driver, was 1.09 (95% CI 1.02 to 1.16). The RR comparing the risk had everyone been exposed as long-haul driver for 8 years to the risk had nobody ever been exposed was 1.20 (95% CI 1.04 to 1.46). After HR approximations, accelerated failure time model results were similar.

CONCLUSIONS

The cumulative failure time model can effectively control time-varying confounding by Healthy Worker Survivor Effect, and provides an easily interpretable effect estimate. RRs estimated from the cumulative failure time model indicate an elevated ischaemic heart disease mortality risk for long-haul drivers in the US trucking industry.

Different occupations associated with amyotrophic lateral sclerosis: is diesel exhaust the link?

The cause of sporadic amyotrophic lateral sclerosis (SALS) remains unknown. We attempted to find out if occupational exposure to toxicants plays a part in the pathogenesis of this disease. In an Australia-wide case-control study we compared the lifetime occupations of 611 SALS and 775 control individuals. Occupations were coded using country-specific as well as international classifications. The risk of SALS for each occupation was calculated with odds ratios using logistic regression. In addition, the literature was searched for possible toxicant links between our findings and previously-reported occupational associations with SALS. Male occupations in our study that required lower skills and tasks tended to have increased risks of SALS, and conversely, those occupations that required higher skills and tasks had decreased risks of SALS. Of all the occupations, only truck drivers, where exposure to diesel exhaust is common, maintained an increased risk of SALS throughout all occupational groups. Another large case-control study has also found truck drivers to be at risk of SALS, and almost two-thirds of occupations, as well as military duties, that have previously been associated with SALS have potential exposure to diesel exhaust. In conclusion, two of the largest case-control studies of SALS have now found that truck drivers have an increased risk of SALS. Since exposure to diesel exhaust is common in truck drivers, as well as in other occupations that have been linked to SALS, exposure to this toxicant may underlie some of the occupations that are associated with SALS.

Genotoxic bioactivation of constituents of a diesel exhaust particle extract by the human lung

The ability of the human lung to catalyze genotoxic bioactivation of constituents of diesel exhaust particle (DEP) extract (DEPE) and the identity of the lung enzymes involved in the bioactivation were investigated using human lung tissues obtained from surgical resections. Genotoxicity was determined by lung S9-catalyzed mutagenicity of DEPE constituents to Salmonella typhimurium TA98NR in the Ames test and by DEPE-induced pneumocyte DNA damage response as determined by γH2Ax expression in ex vivo tissues. S9 was prepared from lung explants treated ex vivo with either DEPE to induce pulmonary enzymes (DEPE-S9) or vehicle only (CON-S9). TA98NR served as the tester strain for the purpose of enhancing and minimizing the contribution of lung S9 and Salmonella, respectively, to DEPE bioactivation. DEPE-S9 was 2.2-fold more active than CON-S9 or rat liver S9 in DEPE bioactivation and the bioactivation was inhibited 58, 45, 22, and 16% by α-naphthoflavone, dicumarol, ketoconazole, and ticlopidine, respectively. Alveolar S9 was less active than bronchioalveolar S9 in DEPE bioactivation. DEPE and diesel exhaust particles (DEP) induced γ-pH2Ax expression in pulmonary cells. Pulmonary CYP1A1 and NQO1 were induced by DEPE treatment, with the constitutive and induced CYP1A1 distributed throughout all peripheral lung regions, whereas NQO1 was limited in distribution to bronchiolar epithelium. The results show that the human lung is highly active in catalyzing genotoxic bioactivation of diesel emission constituents and that CYP1A and NQO1 play major roles in the reaction. The findings underscore the usefulness of human lung tissues in studies of the pneumotoxicity potential of chemicals to humans.

Plasma fluorescent oxidation products and short-term occupational particulate exposures

BACKGROUND

Evidence suggests that fine particulate air pollution results in oxidative induced tissue damage.

METHODS

A global fluorescent oxidation products (FLOx) assay (fluorescent intensity (FI) units per milliliter of plasma) was measured in blood samples collected from 236 nonsmoking, Caucasian, male trucking industry workers either prior to, during, or after their work shifts. Occupational exposures to particulate matter (PM)(2.5) were based on job-specific area-level sampling. Generalized linear models were used to determine associations between FLOx levels and PM(2.5) , adjusted for age, time since last meal, alcohol consumption, aspirin, and cholesterol medications.

RESULTS

The mean (standard deviation) level of FLOx was 265.9 FI/ml (96.0). Levels of FLOx were higher among older individuals and lower among those who had consumed alcohol in the past 24 hr. However, no associations were observed between FLOx and PM(2.5) .

CONCLUSIONS

Our results indicate no association between occupational PM(2.5) exposure and this marker of global oxidative stress.

Ischaemic heart disease mortality and years of work in trucking industry workers

OBJECTIVES

Evidence from general population-based studies and occupational cohorts has identified air pollution from mobile sources as a risk factor for cardiovascular disease. In a cohort of US trucking industry workers, with regular exposure to vehicle exhaust, the authors previously observed elevated standardised mortality ratios for ischaemic heart disease (IHD) compared with members of the general US population. Therefore, the authors examined the association of increasing years of work in jobs with vehicle exhaust exposure and IHD mortality within the cohort.

METHODS

The authors calculated years of work in eight job groups for 30,758 workers using work records from four nationwide companies. Proportional hazard regression was used to examine relationships between IHD mortality, 1985-2000, and employment duration in each job group.

RESULTS

HRs for at least 1 year of work in each job were elevated for dockworkers, long haul drivers, pick-up and delivery drivers, combination workers, hostlers, and shop workers. There was a suggestion of an increased risk of IHD mortality with increasing years of work as a long haul driver, pick-up and delivery driver, combination worker, and dockworker.

CONCLUSION

These results suggest an elevated risk of IHD mortality in workers with a previous history of regular exposure to vehicle exhaust.

Lung cancer and elemental carbon exposure in trucking industry workers

BACKGROUND

Diesel exhaust has been considered to be a probable lung carcinogen based on studies of occupationally exposed workers. Efforts to define lung cancer risk in these studies have been limited in part by lack of quantitative exposure estimates.

OBJECTIVE

We conducted a retrospective cohort study to assess lung cancer mortality risk among U.S. trucking industry workers. Elemental carbon (EC) was used as a surrogate of exposure to engine exhaust from diesel vehicles, traffic, and loading dock operations.

METHODS

Work records were available for 31,135 male workers employed in the unionized U.S. trucking industry in 1985. A statistical model based on a national exposure assessment was used to estimate historical work-related exposures to EC. Lung cancer mortality was ascertained through the year 2000, and associations with cumulative and average EC were estimated using proportional hazards models.

RESULTS

Duration of employment was inversely associated with lung cancer risk consistent with a healthy worker survivor effect and a cohort composed of prevalent hires. After adjusting for employment duration, we noted a suggestion of a linear exposure-response relationship. For each 1,000-µg/m³ months of cumulative EC, based on a 5-year exposure lag, the hazard ratio (HR) was 1.07 [95% confidence interval (CI): 0.99, 1.15] with a similar association for a 10-year exposure lag [HR = 1.09 (95% CI: 0.99, 1.20)]. Average exposure was not associated with relative risk.

CONCLUSIONS

Lung cancer mortality in trucking industry workers increased in association with cumulative exposure to EC after adjusting for negative confounding by employment duration.

Health effects research and regulation of diesel exhaust: an historical overview focused on lung cancer risk

The mutagenicity of organic solvent extracts from diesel exhaust particulate (DEP), first noted more than 55 years ago, initiated an avalanche of diesel exhaust (DE) health effects research that now totals more than 6000 published studies. Despite an extensive body of results, scientific debate continues regarding the nature of the lung cancer risk posed by inhalation of occupational and environmental DE, with much of the debate focused on DEP. Decades of scientific scrutiny and increasingly stringent regulation have resulted in major advances in diesel engine technologies. The changed particulate matter (PM) emissions in "New Technology Diesel Exhaust (NTDE)" from today's modern low-emission, advanced-technology on-road heavy-duty diesel engines now resemble the PM emissions in contemporary gasoline engine exhaust (GEE) and compressed natural gas engine exhaust more than those in the "traditional diesel exhaust" (TDE) characteristic of older diesel engines. Even with the continued publication of epidemiologic analyses of TDE-exposed populations, this database remains characterized by findings of small increased lung cancer risks and inconsistent evidence of exposure-response trends, both within occupational cohorts and across occupational groups considered to have markedly different exposures (e.g. truckers versus railroad shopworkers versus underground miners). The recently published National Institute for Occupational Safety and Health (NIOSH)-National Cancer Institute (NCI) epidemiologic studies of miners provide some of the strongest findings to date regarding a DE-lung cancer association, but some inconsistent exposure-response findings and possible effects of bias and exposure misclassification raise questions regarding their interpretation. Laboratory animal studies are negative for lung tumors in all species, except for rats under lifetime TDE-exposure conditions with durations and concentrations that lead to "lung overload." The species specificity of the rat lung response to overload, and its occurrence with other particle types, is now well-understood. It is thus generally accepted that the rat bioassay for inhaled particles under conditions of lung overload is not predictive of human lung cancer hazard. Overall, despite an abundance of epidemiologic and experimental data, there remain questions as to whether TDE exposure causes increased lung cancers in humans. An abundance of emissions characterization data, as well as preliminary toxicological data, support NTDE as being toxicologically distinct from TDE. Currently, neither epidemiologic data nor animal bioassay data yet exist that directly bear on NTDE carcinogenic potential. A chronic bioassay of NTDE currently in progress will provide data on whether NTDE poses a carcinogenic hazard, but based on the significant reductions in PM mass emissions and the major changes in PM composition, it has been hypothesized that NTDE has a low carcinogenic potential. When the International Agency for Research on Cancer (IARC) reevaluates DE (along with GEE and nitroarenes) in June 2012, it will be the first authoritative body to assess DE carcinogenic health hazards since the emergence of NTDE and the accumulation of data differentiating NTDE from TDE.

Comparing gravimetric and real-time sampling of PM(2.5) concentrations inside truck cabins

As part of a study on truck drivers' exposure and health risk, pickup and delivery (P&D) truck drivers' on-road exposure patterns to PM(2.5) were assessed in five, weeklong sampling trips in metropolitan areas of five U.S. cities from April to August of 2006. Drivers were sampled with real-time (DustTrak) and gravimetric samplers to measure average in-cabin PM(2.5) concentrations and to compare their correspondence in moving trucks. In addition, GPS measurements of truck locations, meteorological data, and driver behavioral data were collected throughout the day to determine which factors influence the relationship between real-time and gravimetric samplers. Results indicate that the association between average real-time and gravimetric PM(2.5) measurements on moving trucks was fairly consistent (Spearman rank correlation of 0.63), with DustTrak measurements exceeding gravimetric measurements by approximately a factor of 2. This ratio differed significantly only between the industrial Midwest cities and the other three sampled cities scattered in the South and West. There was also limited evidence of an effect of truck age. Filter samples collected concurrently with DustTrak measurements can be used to calibrate average mass concentration responses for the DustTrak, allowing for real-time measurements to be integrated into longer-term studies of inter-city and intra-urban exposure patterns for truck drivers.

A retrospective assessment of occupational exposure to elemental carbon in the U.S. trucking industry

BACKGROUND

Despite considerable epidemiologic evidence about the health effects of chronic exposure to vehicle exhaust, efforts at defining the extent of risk have been limited by the lack of historical exposure measurements suitable for use in epidemiologic studies and for risk assessment.

OBJECTIVES

We sought to reconstruct exposure to elemental carbon (EC), a marker of diesel and other vehicle exhaust exposure, in a large national cohort of U.S. trucking industry workers.

METHODS

We identified the predictors of measured exposures based on a statistical model and used this information to extrapolate exposures across the cohort nationally. These estimates were adjusted for changes in work-related conditions over time based on a previous exposure assessment of this industry, and for changes in background levels based on a trend analysis of historical air pollution data, to derive monthly estimates of EC exposure for each job and trucking terminal combination between 1971 and 2000.

RESULTS

Occupational exposure to EC declined substantially over time, and we found significant variability in estimated exposures both within and across job groups, trucking terminals, and regions of the United States. Average estimated EC exposures during a typical work shift ranged from < 1 μg/m³ in the lowest exposed category in the 1990s to > 40 μg/m³ for workers in the highest exposed jobs in the 1970s.

CONCLUSIONS

Our results provide a framework for understanding changes over time in exposure to EC in the U.S. trucking industry. Our assessment should minimize exposure misclassification by capturing variation among terminals and across U.S. regions, and changes over time.

Long-term ambient multipollutant exposures and mortality

RATIONALE

population-based studies have demonstrated associations between ambient air pollution exposures and mortality, but few have been able to adjust for occupational exposures. Additionally, two studies have observed higher risks in individuals with occupational dust, gas, or fume exposure.

OBJECTIVES

we examined the association of ambient residential exposure to particulate matter less than 10 microm in diameter (PM(10)), particulate matter less than 2.5 microm in diameter (PM(2.5)), NO(2), SO(2), and mortality in 53,814 men in the U.S. trucking industry.

METHODS

exposures for PM(10), NO(2), and SO(2) at each residential address were assigned using models combining spatial smoothing and geographic covariates. PM(2.5) exposures in 2000 were assigned from the nearest available monitor. Single and multipollutant Cox proportional hazard models were used to examine the association of an interquartile range (IQR) change (6 microg/m(3) for PM(10), 4 microg/m(3) for PM(2.5), 4ppb for SO(2), and 8ppb for NO(2)) and the risk of all-cause and cause-specific mortality.

MEASUREMENTS AND MAIN RESULTS

an IQR change in ambient residential exposures to PM(10) was associated with a 4.3% (95% confidence interval [CI], 1.1-7.7%) increased risk of all-cause mortality. The increase for an IQR change in SO(2) was 6.9% (95% CI, 2.3-11.6%), for NO(2) was 8.2% (95% CI, 4.5-12.1%), and for PM(2.5) was 3.9% (95% CI, 1.0-6.9%). Elevated associations with cause-specific mortality (lung cancer, cardiovascular and respiratory disease) were observed for PM(2.5), SO(2), and NO(2), but not PM(10). None of the pollutants were confounded by occupational exposures. In multipollutant models, overall, the associations were attenuated, most strongly for PM(10). In sensitivity analyses excluding long-haul drivers, who spend days away from home, larger hazard ratios were observed.

CONCLUSIONS

in this population of men, residential ambient air pollution exposures were associated with mortality.

Exposure assessment of PM2.5 and urinary 8-OHdG for diesel exhaust emission inspector

Animal studies have shown exposure to diesel exhaust particles (DEPs) to induce production of reactive oxygen species (ROSs) and increase levels of 8-hydroxydeoxyquanosine (8-OHdG). Controversial results have been obtained regarding the effects of workplace exposure on urinary 8-OHdG level. This study assessed concentrations of environmental PM(2.5) in DEP (DEP(2.5)), personal DEP(2.5) and urinary 8-OHdG of diesel engine exhaust emission inspector (inspector) at a diesel vehicle emission inspection station (inspection station). The analysis specifically focuses on the factors that influence inspector urinary 8-OHdG. Repeated-measures study design was used to sample for five consecutive days. A total of 25 environmental PM(2.5) measurements were analyzed at 5 different locations by using a dichotomous sampler, and a total of 55 personal PM(2.5) measurements were analyzed from inspectors by using PM(2.5) personal sampler. During the sampling period, a total of 110 pre- and post-work urine samples from inspectors, and 32 samples from the control group were collected. Following age and sex matching between the inspectors and the control group, levels of urinary 8-OHdG were analyzed. Environmental and personal concentrations of DEP(2.5) were 107.25+/-39.76 (mean+/-SD) and 155.96+/-75.70 microg/m(3), respectively. Also, the concentration of urinary 8-OHdG differed significantly between inspector and control non-smokers, averaging 14.05+/-12.71 and 6.58+/-4.39 microg/g creatinine, respectively. Additionally, urinary 8-OHdG concentrations were associated with diesel exposure after controlling for smoking and cooking at home. Compared with the control group, the inspector displayed significantly increased levels of urinary 8-OHdG. Diesel exhaust is the single pollutant involved in the exposure of DEP(2.5) at the inspection station, as confirmed by the final results.

Occupational exposure to diesel engine exhaust: a literature review

Diesel exhaust (DE) is classified as a probable human carcinogen. Aims were to describe the major occupational uses of diesel engines and give an overview of personal DE exposure levels and determinants of exposure as reported in the published literature. Measurements representative of personal DE exposure were abstracted from the literature for the following agents: elemental carbon (EC), particulate matter (PM), carbon monoxide (CO), nitrogen oxide (NO), and nitrogen dioxide (NO(2)). Information on determinants of exposure was abstracted. In total, 3528 EC, 4166 PM, 581 CO, 322 NO, and 1404 NO(2) measurements were abstracted. From the 10,001 measurements, 32% represented exposure from on-road vehicles and 68% from off-road vehicles (30% mining, 15% railroad, and 22% others). Highest levels were reported for enclosed underground work sites in which heavy equipment is used: mining, mine maintenance, and construction (EC: 27-658 microg/m(3)). Intermediate exposure levels were generally reported for above-ground (semi-) enclosed areas in which smaller equipment was run: mechanics in a shop, emergency workers in fire stations, distribution workers at a dock, and workers loading/unloading inside a ferry (generally: EC<50 microg/m(3)). Lowest levels were reported for enclosed areas separated from the source, such as drivers and train crew, or outside, such as surface mining, parking attendants, vehicle testers, utility service workers, surface construction and airline ground personnel (EC<25 microg/m(3)). The other agents showed a similar pattern. Determinants of exposure reported for enclosed situations were ventilation and exhaust after treatment devices. Reported DE exposure levels were highest for underground mining and construction, intermediate for working in above-ground (semi-) enclosed areas and lowest for working outside or separated from the source. The presented data can be used as a basis for assessing occupational exposure in population-based epidemiological studies and guide future exposure assessment efforts for industrial hygiene and epidemiological studies.

Identification of surrogate measures of diesel exhaust exposure in a controlled chamber study

Exposure to diesel exhaust (DE) has been associated with acute cardiopulmonary and vascular responses, chronic noncancer health effects, and respiratory cancers in humans. To better understand DE exposures and eventually their related health effects, we established a controlled chamber experiment wherein human volunteer subjects were exposed to approximately 100 microg/m3 DE. In general, human exposure assessment for DE is based on ambient air measurements of surrogates such as elemental carbon (EC) or total organic carbon (OC) collected on filters. As specific health effect mechanisms and dose-response are obscured bythe complex composition of DE, the linkage from exposure to internal dose can presumably be improved by use of specific biomarkers and metabolites in blood, breath, or urine. Because EC and OC are not suitable as biomarkers, in this study, we focus on identifying compounds that are demonstrated indicators of DE and can also be found in biological fluids. We measured an assortment of volatile, semivolatile, and particle-bound aromatic compounds in the chamber air and report their airborne concentrations in DE and purified air, as well as the estimated values of the corresponding exposure ratios (mean DE air concentration:mean purified air concentration). These estimated exposure ratios were used to identify naphthalene (Nap) and phenanthrene (Phe) as potentially useful surrogates for DE exposure that could also serve as biomarkers. Estimated mean levels of Nap and Phe associated with the nominal 100 microg/m3 DE were 2600 and 765 ng/m3 with estimated exposure ratios of 252 and 92.4, respectively. Nap levels were significantly correlated with OC and total particle-bound polycyclic aromatic hydrocarbons (PAHs); Phe levels were significantly correlated with total volatile + semivolatile PAHs. These results suggest that Nap and Phe may be particularly useful surrogates for DE concentrations. While Nap and Phe are not validated here as internal biomarkers of DE exposure, we are currently assessing human biological specimens collected during this study and will discuss those results in ensuing papers.

Lung cancer and vehicle exhaust in trucking industry workers

BACKGROUND

An elevated risk of lung cancer in truck drivers has been attributed to diesel exhaust exposure. Interpretation of these studies specifically implicating diesel exhaust as a carcinogen has been limited because of limited exposure measurements and lack of work records relating job title to exposure-related job duties.

OBJECTIVES

We established a large retrospective cohort of trucking company workers to assess the association of lung cancer mortality and measures of vehicle exhaust exposure.

METHODS

Work records were obtained for 31,135 male workers employed in the unionized U.S. trucking industry in 1985. We assessed lung cancer mortality through 2000 using the National Death Index, and we used an industrial hygiene review and current exposure measurements to identify jobs associated with current and historical use of diesel-, gas-, and propane-powered vehicles. We indirectly adjusted for cigarette smoking based on an industry survey.

RESULTS

Adjusting for age and a healthy-worker survivor effect, lung cancer hazard ratios were elevated in workers with jobs associated with regular exposure to vehicle exhaust. Mortality risk increased linearly with years of employment and was similar across job categories despite different current and historical patterns of exhaust-related particulate matter from diesel trucks, city and highway traffic, and loading dock operations. Smoking behavior did not explain variations in lung cancer risk.

CONCLUSIONS

Trucking industry workers who have had regular exposure to vehicle exhaust from diesel and other types of vehicles on highways, city streets, and loading docks have an elevated risk of lung cancer with increasing years of work.