Lung cancer mortality in a Dutch cohort of asphalt workers: evaluation of possible confounding by smoking

A Comparative Review of Hot and Warm Mix Asphalt Technologies from Environmental and Economic Perspectives: Towards a Sustainable Asphalt Pavement

The environmental concerns of global warming and energy consumption are among the most severe issues and challenges facing human beings worldwide. Due to the relatively higher predicted temperatures (150-180 °C), the latest research on pavement energy consumption and carbon dioxide (CO₂) emission assessment mentioned contributing to higher environmental burdens such as air pollution and global warming. However, warm-mix asphalt (WMA) was introduced by pavement researchers and the road construction industry instead of hot-mix asphalt (HMA) to reduce these environmental problems. This study aims to provide a comparative overview of WMA and HMA from environmental and economic perspectives in order to highlight the challenges, motivations, and research gaps in using WMA technology compared to HMA. It was discovered that the lower production temperature of WMA could significantly reduce the emissions of gases and fumes and thus reduce global warming. The lower production temperature also provides a healthy work environment and reduces exposure to fumes. Replacing HMA with WMA can reduce production costs because of the 20-75% lower energy consumption in WMA production. It was also released that the reduction in energy consumption is dependent on the fuel type, energy source, material heat capacity, moisture content, and production temperature. Other benefits of using WMA are enhanced asphalt mixture workability and compaction because the additives in WMA reduce asphalt binder viscosity. It also allows for the incorporation of more waste materials, such as reclaimed asphalt pavement (RAP). However, future studies are recommended on the possibility of using renewable, environmentally friendly, and cost-effective materials such as biomaterials as an alternative to conventional WMA-additives for more sustainable and green asphalt pavements.

Cancer Risk Associated With Exposure to Bitumen and Bitumen Fumes: An Updated Systematic Review and Meta-Analysis

OBJECTIVE

To evaluate whether cancer risks are increased among bitumen (asphalt) workers.

METHODS

Systematic review and meta-analysis of cancer risks (lung, upper aerodigestive tract (UADT), esophagus, bladder, kidney, stomach, and skin) and bitumen exposure. Certainty in the epidemiological evidence that bitumen-exposed workers experience increased cancer risks was rated using Grading of Recommendations Assessment, Development and Evaluation criteria.

RESULTS

After excluding lower-quality studies, lung cancer risks were not increased among bitumen-exposed workers (meta-relative risk [RR] 0.94, 95% CI 0.74 to 1.20, eight studies). Increased risks of UADT and stomach cancers were observed (meta-RR 1.31, 95% CI 1.03 to 1.67, 10 studies and meta-RR 1.29, 95% CI 1.03 to 1.62, seven studies, respectively).

CONCLUSIONS

Except for lung cancer, evidence for increased cancer risks among bitumen-exposed workers was judged to be of low certainty, due to inadequate exposure characterization and unmeasured confounders (coal tar exposure, smoking, and alcohol consumption).

Elevated cancer mortality in a German cohort of bitumen workers: extended follow-up through 2004

The mortality follow-up in a cohort of German asphalt workers covered an additional 6 years. Male workers (N = 7919) were classified into four exposure categories: (1) exposure to bitumen only, (2) to bitumen and coal tar, (3) neither to tar nor to bitumen, and (4) unknown exposure. Exposure-specific standardized mortality ratios (SMR) and associated 95% confidence intervals (CI) based on age- and calendar period-specific national mortality rates were calculated. To compare exposed and unexposed workers, relative risks were estimated by Poisson regression. By the end of 2004, 835 workers had died. The SMR for lung cancer was 1.77 (95% CI 1.46-2.16). Head and neck cancer showed an SMR of 2.36 (95% CI 1.78-3.07). Bladder cancer mortality was elevated threefold. Significantly elevated cancer-related SMRs were also found for all malignant tumors. In addition, elevated mortality rates of nonmalignant causes such as alcoholism, liver cirrhosis, and unnatural causes of deaths including accidents were observed. After stratification by exposure group, cancer mortality was elevated among bitumen-exposed and unexposed subjects. In the internal analysis, the association between lung cancer and bitumen exposure was weakened as compared with the previous follow-up (relative risk [RR] = 1.15; 95% CI 0.72-1.84). The follow-up demonstrated an excess of cancer in this cohort of asphalt workers. However, the observed mortality patterns were not clear. Although exposure to bitumen cannot be ruled out as being responsible for the observed results, a higher prevalence of alcohol and tobacco consumption may partially explain the observed risk increases. Exposure assessment in future studies should account for multiple occupational agents and nonoccupational factors to rule out that the observed differences in SMR are not due simply to random variation.

Sensitivity of the association between increased lung cancer risk and bitumen fume exposure to the assumptions in the assessment of exposure

PURPOSE

A multi-centre IARC-coordinated European cohort study provided evidence of an association between lung cancer risk and bitumen fume exposure. Sensitivity analyses were conducted to assess whether these associations were robust to assumptions in the exposure assessment for which support could not be obtained due to lack of either measurements or direct observations.

METHODS

New exposure estimates were generated by changing assumptions on exposure levels, specific tasks, lags, and coal tar use. Subsequently, Poisson regression models estimated relative risks (RRs); change in fit of models was evaluated.

RESULTS

The influence of these assumptions was minimal, with log-likelihood deviations between -5.0 and 4.7% and similar patterns in dose-dependent increases of lung cancer risk. In the highest exposure categories, point estimates of RRs ranged 2.07-2.83 for average, and 1.22-2.23 for cumulative exposure.

CONCLUSIONS

The small increase in lung cancer risk associated with bitumen fume exposure depends only to a limited extent on the subjective judgments made in the exposure assessment for this cohort.

Bladder cancer incidence and exposure to polycyclic aromatic hydrocarbons among asphalt pavers

OBJECTIVES

To investigate the association between exposures to polycyclic aromatic hydrocarbons (PAH) that arises during asphalt paving, and risk of bladder cancer.

METHODS

7298 men included in the historical cohort were first employed between 1913 and 1999 in companies applying asphalt in Denmark, Norway, Finland and Israel. The minimal duration of employment for inclusion in the cohort was two seasons of work. Occupational histories were extracted from personnel files. A follow-up for cancer incidence was conducted through national cancer registries. The authors estimated exposures to benzo(a)pyrene as a marker for 4-6 ring PAH. Exposures were reconstructed by using information about changes in asphalt paving technology in each company over time, the modelled relation between production characteristics and exposure levels, and job histories. Relative risks and associated 95% confidence intervals were estimated using Poisson regression.

RESULTS

48 bladder cancers among asphalt paving workers were detected; of these, 39 cases were exposed at least 15 years before the diagnosis. Cumulative exposure to PAH was not associated with the incidence of bladder cancer. The association with average exposure became stronger when 15-year lag was considered, revealing a twofold increase in relative bladder cancer risk in the two higher exposure categories. There was an indication of exposure-response association with lagged averaged exposure. Risk estimates were adjusted for age, country, duration of employment and calendar period, did not show heterogeneity among countries and did not materially change when re-estimated after excluding non-primary cancers from follow-up. Previously conducted sensitivity analysis indicates that confounding by cigarette smoking is an unlikely explanation for the observed exposure-response trends.

CONCLUSIONS

The authors were unable to control for all possible sources of confounding and bias. The results do not allow conclusion on the presence or absence of a causal link between exposures to PAH and risk of bladder cancer among asphalt workers.

Polycyclic Aromatic Hydrocarbons and Fatal Ischemic Heart Disease

BACKGROUND

Several toxicologic and epidemiologic studies have produced evidence that occupational exposure to polycyclic aromatic hydrocarbons (PAH) is a risk factor for ischemic heart disease (IHD). However, a clear exposure-response relation has not been demonstrated.

METHODS

We studied a relation between exposure to PAH and mortality from IHD (418 cases) in a cohort of 12,367 male asphalt workers from Denmark, Finland, France, Germany, Israel, The Netherlands and Norway. The earliest follow up (country-specific) started in 1953 and the latest ended in 2000, averaging 17 years. Exposures to benzo(a)pyrene were assessed quantitatively using measurement-driven exposure models. Exposure to coal tar was assessed in a semiquantitative manner on the basis of information supplied by company representatives. We carried out sensitivity analyses to assess potential confounding by tobacco smoking.

RESULTS

Both cumulative and average exposure indices for benzo(a)pyrene were positively associated with mortality from IHD. The highest relative risk for fatal IHD was observed for average benzo(a)pyrene exposures of 273 ng/m or higher, for which the relative risk was 1.64 (95% confidence interval=1.13-2.38). Similar results were obtained for coal tar exposure. Sensitivity analysis indicated that even in a realistic scenario of confounding by smoking, we would observe approximately 20% to 40% excess risk in IHD in the highest PAH-exposure categories.

CONCLUSIONS

Our results lend support to the hypothesis that occupational PAH exposure causes fatal IHD and demonstrate a consistent exposure-response relation for this association.

Quantitative risk assessment for lung cancer after exposure to bitumen fume

An international cohort of asphalt workers was assembled to study cancer risk after bitumen exposure. This article describes the combination of the exposure assessment with the exposure-response for a quantitative risk assessment for lung cancer mortality within the Dutch component of the study. We identified a retrospective cohort of 3,709 workers with at least one season of employment. Semi-quantitative exposure to bitumen fume was estimated by a job-exposure matrix. Exposure-response relations were fitted by Poisson regression, and excess lifetime risks through age 75 were calculated by a life table method. Working lifetime cumulative exposure to bitumen fume was calculated under different scenarios, representing past and future exposures. For workers with exposures accumulated in the past, excess risks for lung cancer varied from 7.8 to 14.3%. Calculations for future exposures resulted in considerably lower excess risks ranging from 0.6 to 2.6%. The calculated excess risks for lung cancer mortality after working lifetime exposure to bitumen fume depend strongly on when exposure was experienced and to some extent on the exposure-response model chosen, while confounding by smoking cannot be ruled out. Nevertheless, the excess lifetime risk for lung cancer in this Dutch cohort of asphalt workers is above benchmark risks as applied by the Dutch Health Council. Current exposure levels have decreased this risk considerably, but further exposure control may be required.

Cancer mortality among European asphalt workers: an international epidemiological study. I. Results of the analysis based on job titles

BACKGROUND

Inhalation of bitumen fumes is potentially carcinogenic to humans.

METHODS

We conducted a study of 29,820 male workers exposed to bitumen in road paving, asphalt mixing and roofing, 32,245 ground and building construction workers unexposed to bitumen, and 17,757 workers not classifiable as bitumen workers, from Denmark, Finland, France, Germany, Israel, the Netherlands, Norway, and Sweden, with mortality follow-up during 1953-2000. We calculated standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) based on national mortality rates. Poisson regression analyses compared mortality of bitumen workers to that of building or ground construction workers.

RESULTS

The overall mortality was below expectation in the total cohort (SMR 0.92, 95% CI 0.90-0.94) and in each group of workers. The SMR of lung cancer was higher among bitumen workers (1.17, 95% CI 1.04-1.30) than among workers in ground and building construction (SMR 1.01, 95% CI 0.89-1.15). In the internal comparison, the relative risk (RR) of lung cancer mortality among bitumen workers was 1.09 (95% CI 0.89-1.34). The results of cancer of the head and neck were similar to those of lung cancer, based on a smaller number of deaths. There was no suggestion of an association between employment in bitumen jobs and other cancers.

CONCLUSIONS

European workers employed in road paving, asphalt mixing and other jobs entailing exposure to bitumen fume might have experienced a small increase in lung cancer mortality risk, compared to workers in ground and building construction. However, exposure assessment was limited and confounding from exposure to carcinogens in other industries, tobacco smoking, and other lifestyle factors cannot be ruled out.

Cancer mortality among European asphalt workers: an international epidemiological study. II. Exposure to bitumen fume and other agents

BACKGROUND

An increased risk of lung cancers among asphalt workers has been suggested in epidemiological studies based on large scale statistical analyses.

METHODS

In a multi-country study of 29,820 male workers employed in road paving, asphalt mixing and roofing, 32,245 ground and building construction workers and 17,757 other workers from Denmark, Finland, France, Germany, Israel, the Netherlands, Norway, and Sweden, with mortality that was documented from 1953-2000. Exposures to bitumen fume, coal tar, 4-6 ring polycyclic aromatic hydrocarbons, organic vapor, diesel exhaust, asbestos, and silica dust were assessed via a job-exposure matrix. Standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) based on national mortality rates, as well as relative risks (RRs) based on Poisson regression models were calculated.

RESULTS

The SMR of lung cancer among workers exposed to bitumen fume (1.08, 95% CI 0.99-1.18) was comparable to that of non-exposed workers (SMR 1.05, 95% CI 0.92-1.19). In a sub-cohort of bitumen-exposed workers without exposure to coal tar, the SMR of lung cancer was 1.23 (95% CI 1.02-1.48). The analysis based on the semi-quantitative, matrix-based exposures in the whole cohort did not suggest an increased lung cancer risk following exposure to bitumen fume. However, in an analysis restricted to road pavers, based on quantitative estimate of bitumen fume exposure, a dose-response was suggested for average level of exposure, applying a 15-year lag, which was marginally reduced after adjustment for co-exposure to coal tar. The results for cancer of the head and neck were similar to those of lung cancer, although they were based on a smaller number of deaths. There was no clear suggestion of an association with bitumen fume for any other neoplasm.

CONCLUSIONS

The results of the analysis by bitumen fume exposure do not allow us to conclude on the presence or absence of a causal link between exposure to bitumen fume and risk of cancer of the lung and the head and neck.

Performance of different exposure assessment approaches in a study of bitumen fume exposure and lung cancer mortality

BACKGROUND

We compared performance of different exposure assessment approaches in a cohort study of cancer risk among European asphalt workers.

METHODS

Three bitumen fume exposure indices (duration of exposure (years), average exposure (mg/m3) and cumulative exposure (mg/m3*years)) and two latency models (with and without a 15 year lag) were considered for an association between lung cancer mortality and bitumen fume.

RESULTS

There was no association between lung cancer risk and either duration or cumulative exposure. However, there was the suggestion of an increase in lung cancer risk accompanying rise in average exposure. Only models with average bitumen fume exposure (with or without lag) improved model fit, albeit to the same extent.

CONCLUSIONS

Constructing quantitative indices of exposure intensity was justified because they produced the greatest improvement in fit of models that explored possible relationship between bitumen fume exposure and lung cancer risk. The identified associations require further investigation.