Mortality and cancer morbidity in workers from an aluminium smelter with prebaked carbon anodes--Part III: Mortality from circulatory and respiratory diseases

A review of the epidemiological and laboratory evidence of the role of aluminum exposure in pathogenesis of cardiovascular diseases

The objective of the present study was to review the epidemiological and laboratory evidence on the role of aluminum (Al) exposure in the pathogenesis of cardiovascular diseases. Epidemiological data demonstrated an increased incidence of cardiovascular diseases (CVD), including hypertension and atherosclerosis in occupationally exposed subjects and hemodialysis patients. In addition, Al body burden was found to be elevated in patients with coronary heart disease, hypertension, and dyslipidemia. Laboratory studies demonstrated that Al exposure induced significant ultrastructural damage in the heart, resulting in electrocardiogram alterations in association with cardiomyocyte necrosis and apoptosis, inflammation, oxidative stress, inflammation, and mitochondrial dysfunction. In agreement with the epidemiological findings, laboratory data demonstrated dyslipidemia upon Al exposure, resulting from impaired hepatic lipid catabolism, as well as promotion of low-density lipoprotein oxidation. Al was also shown to inhibit paraoxonase 1 activity and to induce endothelial dysfunction and adhesion molecule expression, further promoting atherogenesis. The role of Al in hypertension was shown to be mediated by up-regulation of NADPH-oxidase, inhibition of nitric oxide bioavailability, and stimulation of renin-angiotensin-aldosterone system. It has been also demonstrated that Al exposure targets cerebral vasculature, which may be considered a link between Al exposure and cerebrovascular diseases. Findings from other tissues lend support that ferroptosis, pyroptosis, endoplasmic reticulum stress, and modulation of gut microbiome and metabolome are involved in the development of CVD upon Al exposure. A better understanding of the role of the cardiovascular system as a target for Al toxicity will be useful for risk assessment and the development of treatment and prevention strategies.

Cancer and noncancer mortality among aluminum smelting workers in Badin, North Carolina

BACKGROUND

Badin, North Carolina, hosted an aluminum smelting plant from 1917 to 2007. The Concerned Citizens of West Badin reported suspected excess cancer mortality among former employees. This study aimed to investigate these concerns.

METHODS

The study cohort was enumerated from United Steel Workers' records of workers employed from 1980 to 2007. Cause-specific mortality rates in the cohort were compared with North Carolina population mortality rates using standardized mortality ratios (SMRs), standardized by age, sex, race, and calendar period. We estimated cause-specific adjusted standardized mortality ratios (aSMRs) using negative controls to mitigate healthy worker survivor bias (HWSB). Standardized rate ratios (SRRs) were calculated to compare mortality rates between workers ever employed vs never employed in the pot room.

RESULTS

All-cause mortality among Badin workers was lower than in the general population (SMR: 0.81, 95% confidence interval [CI]: 0.71-0.92). After adjusting for HWSB, excesses for all cancers (aSMR: 1.55, 95% CI: 1.10-2.21), bladder cancer (3.47, 95% CI: 1.25-9.62), mesothelioma (17.33, 95% CI: 5.40-55.59), and respiratory cancer (1.24, 95% CI: 0.77-1.99) were observed. Black males worked the highest proportion of their employed years in the pot room. Potroom workers experienced higher respiratory cancer (SRR: 2.99, 95% CI: 1.23-7.26), bladder cancer (SRR: 1.58, 95% CI: 0.15-15.28), and mesothelioma (SRR: 3.36, 95% CI: 0.21-53.78) mortality rates than never workers in the pot room.

CONCLUSIONS

This study responds to concerns of a group of former aluminum workers. The results, while imprecise, suggest excess respiratory and bladder cancers among pot room workers in a contemporary cohort of union employees at a US smelter.

Potential role of polycyclic aromatic hydrocarbons as mediators of cardiovascular effects from combustion particles

Air pollution is the most important environmental risk factor for disease and premature death, and exposure to combustion particles from vehicles is a major contributor. Human epidemiological studies combined with experimental studies strongly suggest that exposure to combustion particles may enhance the risk of cardiovascular disease (CVD), including atherosclerosis, hypertension, thrombosis and myocardial infarction.In this review we hypothesize that adhered organic chemicals like polycyclic aromatic hydrocarbons (PAHs), contribute to development or exacerbation of CVD from combustion particles exposure. We summarize present knowledge from existing human epidemiological and clinical studies as well as experimental studies in animals and relevant in vitro studies. The available evidence suggests that organic compounds attached to these particles are significant triggers of CVD. Furthermore, their effects seem to be mediated at least in part by the aryl hydrocarbon receptor (AhR). The mechanisms include AhR-induced changes in gene expression as well as formation of reactive oxygen species (ROS) and/or reactive electrophilic metabolites. This is in accordance with a role of PAHs, as they seem to be the major chemical group on combustion particles, which bind AhR and/or is metabolically activated by CYP-enzymes. In some experimental models however, it seems as PAHs may induce an inflammatory atherosclerotic plaque phenotype irrespective of DNA- and/or AhR-ligand binding properties. Thus, various components and several signalling mechanisms/pathways are likely involved in CVD induced by combustion particles.We still need to expand our knowledge about the role of PAHs in CVD and in particular the relative importance of the different PAH species. This warrants further studies as enhanced knowledge on this issue may amend risk assessment of CVD caused by combustion particles and selection of efficient measures to reduce the health effects of particular matters (PM).

Occupational Exposure to PM2.5 and Incidence of Ischemic Heart Disease: Longitudinal Targeted Minimum Loss-based Estimation

BACKGROUND

We investigated the incidence of ischemic heart disease (IHD) in relation to accumulated exposure to particulate matter (PM) in a cohort of aluminum workers. We adjusted for time varying confounding characteristic of the healthy worker survivor effect, using a recently introduced method for the estimation of causal target parameters.

METHODS

Applying longitudinal targeted minimum loss-based estimation, we estimated the difference in marginal cumulative risk of IHD in the cohort comparing counterfactual outcomes if always exposed above to always exposed below a PM2.5 exposure cut-off. Analyses were stratified by sub-cohort employed in either smelters or fabrication facilities. We selected two exposure cut-offs a priori, at the median and 10th percentile in each sub-cohort.

RESULTS

In smelters, the estimated IHD risk difference after 15 years of accumulating PM2.5 exposure during follow-up was 2.9% (0.6%, 5.1%) using the 10th percentile cut-off of 0.10 mg/m. For fabrication workers, the difference was 2.5% (0.8%, 4.1%) at the 10th percentile of 0.06 mg/m. Using the median exposure cut-off, results were similar in direction but smaller in size. We present marginal incidence curves describing the cumulative risk of IHD over the course of follow-up for each sub-cohort under each intervention regimen.

CONCLUSIONS

The accumulation of exposure to PM2.5 appears to result in higher risks of IHD in both aluminum smelter and fabrication workers. This represents the first longitudinal application of targeted minimum loss-based estimation, a method for generating doubly robust semi-parametric efficient substitution estimators of causal parameters, in the fields of occupational and environmental epidemiology.

Incident Ischemic Heart Disease After Long-Term Occupational Exposure to Fine Particulate Matter: Accounting for 2 Forms of Survivor Bias

Little is known about the heart disease risks associated with occupational, rather than traffic-related, exposure to particulate matter with aerodynamic diameter of 2.5 µm or less (PM2.5). We examined long-term exposure to PM2.5 in cohorts of aluminum smelters and fabrication workers in the United States who were followed for incident ischemic heart disease from 1998 to 2012, and we addressed 2 forms of survivor bias. Left truncation bias was addressed by restricting analyses to the subcohort hired after the start of follow up. Healthy worker survivor bias, which is characterized by time-varying confounding that is affected by prior exposure, was documented only in the smelters and required the use of marginal structural Cox models. When comparing always-exposed participants above the 10th percentile of annual exposure with those below, the hazard ratios were 1.67 (95% confidence interval (CI): 1.11, 2.52) and 3.95 (95% CI: 0.87, 18.00) in the full and restricted subcohorts of smelter workers, respectively. In the fabrication stratum, hazard ratios based on conditional Cox models were 0.98 (95% CI: 0.94, 1.02) and 1.17 (95% CI: 1.00, 1.37) per 1 mg/m(3)-year in the full and restricted subcohorts, respectively. Long-term exposure to occupational PM2.5 was associated with a higher risk of ischemic heart disease among aluminum manufacturing workers, particularly in smelters, after adjustment for survivor bias.

Annual decline in forced expiratory volume is steeper in aluminum potroom workers than in workers without exposure to potroom fumes

Background

Aluminum potroom exposure is associated with increased mortality of COPD but the association between potroom exposure and annual decline in lung function is unknown. We have measured lung volumes annually using spirometry from 1986 to 1996. The objective was to compare annual decline in forced expiratory volume in 1 s (dFEV1) and forced vital capacity (dFVC).

Methods

The number of aluminum potroom workers was 4,546 (81% males) and the number of workers in the reference group was 651 (76% males). The number of spirometries in the index group and the references were 24,060 and 2,243, respectively.

Results

After adjustment for confounders, the difference in dFEV1 and dFVC between the index and reference groups were 13.5 (P < 0.001) and −8.0 (P = 0.060) ml/year.

Conclusion

Aluminum potroom operators have increased annual decline in FEV1 relative to a comparable group with non‐exposure to potroom fumes and gases. Am. J. Ind. Med. 59:322–329, 2016. © 2016 The Authors. American Journal of Industrial Medicine Published by Wiley Periodicals, Inc.

Construction of a Job Exposure Matrix to Dust, Fluoride, and Polycyclic Aromatic Hydrocarbons in the Norwegian Aluminum Industry using Prediction Models

BACKGROUND

The Norwegian aluminum industry developed and implemented a protocol for prospective monitoring of employees' exposure using personal samplers. We analyzed these data to develop prediction lines to construct a job exposure matrix (JEM) for the period 1986-1995.

METHODS

The protocol for personal monitoring of exposure was implemented in all seven Norwegian aluminum plants in 1986 and continued until 1995. Personal samplers were used to collect total dust, fluorides, and total polycyclic aromatic hydrocarbons (PAH). In addition, exposure could be categorized according to process, i.e. prebake, Søderberg, and 'other'. We constructed four-dimensional JEMs characterized by: Plant, Job descriptor, Process, and Year. Totally 8074, 6734, and 3524 measurements were available for dust, fluorides, and PAH, respectively. The data were analyzed using linear mixed models with two-way interactions. The models were assessed using the Akaike criterion (AIC) and unadjusted R (2). The significance level was set to 10% (two-sided) for retaining variables in the model.

RESULTS

In 1986, the geometric mean (95% confidence interval in parentheses) for total dust, total fluorides, and PAH were 3.18 (0.46-22.2) mg m(-3), 0.58 (0.085-4.00) mg m(-3), and 33.9 (2.3-504) µg m(-3), respectively. During 10 years of follow-up, the exposure to total dust, fluorides, and PAH decreased by 9.2, 11.7, and 14.9% per year, respectively. Each model encompassed from 49 to 72 significant components of the interaction terms. The interaction components were at least as important as the main effects, and 65 to 91% of the significant components of the interaction terms were time-dependent.

CONCLUSION

Our prediction models indicated that exposures were highly time-dependent. We expect that the time-dependent changes in exposure are of major importance for longitudinal studies of health effects in the aluminum industry.

Fluoride as a factor initiating and potentiating inflammation in THP1 differentiated monocytes/macrophages

It is well known that exposure to fluorides lead to an increased ROS production and enhances the inflammatory reactions. Therefore we decided to examine whether cyclooxygenases (particular COX-2) activity and expression may be changed by fluoride in THP1 macrophages and in this way may change the prostanoids biosynthesis. In the present work we demonstrate that fluoride increased concentration of PGE2 and TXA2 in THP1 macrophages. Following exposure to 1-10 μM NaF, COX-2 protein and COX-2 transcript increased markedly. COX-2 protein up-regulation probably is mediated by ROS, produced during fluoride-induced inflammatory reactions. Additional fluoride activates the transcription factor, nuclear factor (NF)-kappaB, which is involved in the up-regulation of COX-2 gene expression. This study indicated that even in small concentrations fluoride changes the amounts and activity of COX-1 and COX-2 enzymes taking part in the initiating and development of inflammatory process.

Respiratory disorders in aluminum smelter workers

Objectives:

Summarizing the knowledge status, including the morphology, possible etiological factors, and clinical expression of aluminum potroom asthma and chronic obstructive pulmonary disease related to aluminum potroom exposure.

Methods:

A review of the literature from the last two decades as it appears in PubMed.

Results:

There is substantial evidence for the existence of potroom asthma, although the incidence seems to decline over the last 10 years. Increased mortality from chronic obstructive pulmonary disease and longitudinal decline in forced expiratory volume in the first second of expiration has been shown in aluminum potroom workers. Morphological manifestations in bronchial biopsies and the inflammatory markers NO and eosinophils in airway tissue and blood are consistent with asthma in general. The causative agent(s) is (are) not known.

Conclusions:

Reduction of exposure and cessation of smoking seem to be the major preventive measures to avoid respiratory disorders in the aluminum industry.

Marginal structural models in occupational epidemiology: application in a study of ischemic heart disease incidence and PM2.5 in the US aluminum industry

Marginal structural models (MSMs) and inverse probability weighting can be used to estimate risk in a cohort of active workers if there is a time-varying confounder (e.g., health status) affected by prior exposure-a feature of the healthy worker survivor effect. We applied Cox MSMs in a study of incident ischemic heart disease and exposure to particulate matter with aerodynamic diameter of 2.5 μm or less (PM2.5) in a cohort of 12,949 actively employed aluminum workers in the United States. The cohort was stratified by work process into workers in smelting facilities, herein referred to as "smelters" and workers in fabrication facilities, herein referred to as "fabricators." The outcome was assessed by using medical claims data from 1998 to 2012. A composite risk score based on insurance claims was treated as a time-varying measure of health status. Binary PM2.5 exposure was defined by the 10th-percentile cutoff for each work process. Health status was associated with past exposure and predicted the outcome and subsequent exposure in smelters but not in fabricators. In smelters, the Cox MSM hazard ratio comparing those always exposed above the cutoff with those always exposed below the cutoff was 1.98 (95% confidence interval: 1.18, 3.32). In fabricators, the hazard ratio from a traditional Cox model was 1.34 (95% confidence interval: 0.98, 1.83). Results suggest that occupational PM2.5 exposure increases the risk of incident ischemic heart disease in workers in both aluminum smelting and fabrication facilities.

Incident ischemic heart disease and recent occupational exposure to particulate matter in an aluminum cohort

Fine particulate matter (PM(2.5)) in air pollution, primarily from combustion sources, is recognized as an important risk factor for cardiovascular events but studies of workplace PM(2.5) exposure are rare. We conducted a prospective study of exposure to PM(2.5) and incidence of ischemic heart disease (IHD) in a cohort of 11,966 US aluminum workers. Incident IHD was identified from medical claims data from 1998 to 2008. Quantitative metrics were developed for recent exposure (within the last year) and cumulative exposure; however, we emphasize recent exposure in the absence of interpretable work histories before follow-up. IHD was modestly associated with recent PM(2.5) overall. In analysis restricted to recent exposures estimated with the highest confidence, the hazard ratio (HR) increased to 1.78 (95% CI: 1.02, 3.11) in the second quartile and remained elevated. When the analysis was stratified by work process, the HR rose monotonically to 1.5 in both smelter and fabrication facilities, though exposure was almost an order of magnitude higher in smelters. The differential exposure-response may be due to differences in exposure composition or healthy worker survivor effect. These results are consistent with the air pollution and cigarette smoke literature; recent exposure to PM(2.5) in the workplace appears to increase the risk of IHD incidence.

Exposure to polycyclic aromatic hydrocarbons and serum inflammatory markers of cardiovascular disease

Polycyclic aromatic hydrocarbons (PAHs) are environmental and occupational carcinogens produced by the incomplete combustion of organic materials, such as coal and petroleum product combustion, tobacco smoking, and food cooking, that may be significant contributors to the burden of cardiovascular disease in human populations. The purpose of this study was to investigate associations between ten monohydroxy urinary metabolites of four PAHs and three serum biomarkers of cardiovascular disease (fibrinogen, homocysteine, and white blood cell count). Using data on 3219 participants aged 20 years and older from the National Health and Nutrition Examination Survey (NHANES) 2001-2004 dataset, the associations between PAH metabolites and serum inflammatory markers were analyzed using the Spearman correlations and multiple linear regression modeling. The PAH metabolites of naphthalene, fluorene, phenanthrene, and pyrene each showed both positive and negative correlations with homocysteine, fibrinogen, and white blood cell count (correlation coefficient range: -0.077-0.143) in nonsmoking participants. Using multiple linear regression models adjusted for age, gender, race/ethnicity, and body mass index, estimates of weighted geometric means of inflammatory marker levels were not significantly different between high and low levels (75th vs. 25th percentiles) for all PAH metabolites in nonsmoking subjects. The results of this study do not provide evidence for a relationship between PAH exposure (as measured by urinary levels of PAH metabolites) and serum biomarkers of cardiovascular disease after controlling for tobacco use.

Fluoride in low concentration modifies expression and activity of 15 lipoxygenase in human PBMC differentiated monocyte/macrophage

Epidemiological and experimental evidences demonstrate positive correlation between environmental and occupational fluoride exposure and risk to various cardio-respiratory disorders. That fore we decided to examine the effect of fluorides on activity and expression of 15LOX enzyme which is implicated in biosynthesis of inflammatory mediators. Expression of 15LOX-1 and -2 enzymes mRNA and protein was analyzed using RT PCT and immunoblotting methods respectively whereas HPLC method was used to measure the levels of 15 lipoxygenases end products. Additionally AA and LA concentration in cells was measured using GC method. We observed that fluoride in small concentration may significantly decrease activity of 15LOX-1 and -2 in human PBMC macrophages and then concentration of its end products: 15-HETE, 12-HETE and 9+13-HODE, what may cause development of inflammation through the cholesterol arrest into the macrophages and its differentiation to foam cell. Noted by our team overexpression of the 15LOX-1 enzyme in macrophages after addition of lowest fluoride concentrations (1 and 3 μM) may be aimed at fighting inflammation development and excessive intracellular lipid accumulation. But highest fluoride concentrations (6 and 10 μM) added to cell culture slowly declined expression of this enzyme probably because of developing inflammation. Additional 15LOX-2 expression in macrophages after fluoride addition was low in 1 and 3 μM concentrations, but increased significantly after 10 μM fluoride addition what may suggest developing acute inflammation, because 15LOX-2 is associated to increased local hypoxia. This study indicated that even in small concentrations fluorides changes the amounts and activity of 15 LOX-1 and -2 enzymes taking part in the development of inflammatory process.

Activation of phospholipase A(2) by low levels of fluoride in THP1 macrophages via altered Ca(2+) and cAMP concentration

Phospholipases (PLA's) participate in the regulation of physiological and pathological processes in the cell, including the release of pro-inflammatory mediators and stimulation of inflammatory processes. It is also well known that fluoride can increase the inflammatory reactions. Therefore we decided to examine the effect of fluorides in concentrations determined in human serum on cPLA(2) and sPLA(2) activity. The incubation of macrophages in fluoride solutions significantly increased the amount of synthesized cellular cAMP, intracellular calcium and sPLA(2) activity in a dose-dependent pattern. The cPLA(2) activity, estimated by the amount of released arachidonic acid, increased significantly when 10 μM NaF was used. The results of our study suggest that fluoride may change the activity of phospholipases in macrophage cells. Probably, increased cAMP concentration activates protein kinase C (PKC) and thus stimulates PLA(2). cAMP also regulates the passage of Ca(2+) through ion channels, which additionally influence PLA(2) throughout Ca(2+)-calmodulin dependent protein kinase.

Chronic and acute effects of coal tar pitch exposure and cardiopulmonary mortality among aluminum smelter workers

Air pollution causes several adverse cardiovascular and respiratory effects. In occupational studies, where levels of particulate matter and polycyclic aromatic hydrocarbons (PAHs) are higher, the evidence is inconsistent. The effects of acute and chronic PAH exposure on cardiopulmonary mortality were examined within a Kitimat, Canada, aluminum smelter cohort (n = 7,026) linked to a national mortality database (1957-1999). No standardized mortality ratio was significantly elevated compared with the province's population. Smoking-adjusted internal comparisons were conducted using Cox regression for male subjects (n = 6,423). Ischemic heart disease (IHD) mortality (n = 281) was associated with cumulative benzo[a]pyrene (B(a)P) exposure (hazard ratio = 1.62, 95% confidence interval: 1.06, 2.46) in the highest category. A monotonic but nonsignificant trend was observed with chronic B(a)P exposure and acute myocardial infarction (n = 184). When follow-up was restricted to active employment, the hazard ratio for IHD was 2.39 (95% confidence interval: 0.95, 6.05) in the highest cumulative B(a)P category. The stronger associations observed during employment suggest that risk may not persist after exposure cessation. No associations with recent or current exposure were observed. IHD was associated with chronic (but not current) PAH exposure in a high-exposure occupational setting. Given the widespread workplace exposure to PAHs and heart disease's high prevalence, even modest associations produce a high burden.

Occupational causes of chronic obstructive pulmonary disease

The relation between Chronic Obstructive Pulmonary Disease (COPD, including chronic bronchitis and emphysema (CBE), and exposure to coal dust is well established. This paper reviews the evidence relating to other occupational causes of COPD, including industries associated with exposure to fumes, chemical substances, and dusts. A review of key literature has been carried out with a focus on the magnitude of risks and levels of exposure causing disabling health effects. The literature suggests that elevated risks of developing COPD are clearly associated with several occupations, with risk estimates being high in some, even after taking into account the effect of confounders, such as smoking. Of particular concern are agricultural workers who can be exposed to a variety of gases and organic dusts, among whom CBE is clearly elevated, particularly for pig farmers and exposure to endotoxins, with an increased annual decline in lung function. Similarly, cotton textile workers are exposed to a mixture of substances affecting development of atopy, byssinosis, and CBE, and across-shift and long-term decline in lung function. Atopy also has an important role in the development of COPD in flour mill workers and bakers, with those sensitized to bakery allergens having a greater lung function decline than non-sensitized individuals. Welding processes involve a range of potential chemical, physical and radiation hazards. The average reduction in FEV1 associated with welding fumes is similar to that associated with smoking. Challenges in assessing the evidence include variation in diagnostic methods; concurrent exposure to cigarette smoke (direct or second-hand) and multiple work-place irritants; healthy worker selection/survivor effects; poor exposure definition. Raising awareness of occupational causes of COPD among employers, employees, and health service professionals is important.

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.

Outdoor air pollution and stroke in Sheffield, United Kingdom: a small-area level geographical study

BACKGROUND AND PURPOSE

Current evidence suggests that stroke mortality and hospital admissions should be higher in areas with elevated levels of outdoor air pollution because of the combined acute and chronic exposure effects of air pollution. We examined this hypothesis using a small-area level ecological correlation study.

METHODS

We used 1030 census enumeration districts as the unit of analysis and examined stroke deaths and hospital admissions from 1994 to 1998, with census denominator counts for people > or =45 years. Modeled air pollution data for particulate matter (PM10), nitrogen oxides (NO(x)), and carbon monoxide (CO) were interpolated to census enumeration districts. We adjusted for age, sex, socioeconomic deprivation, and smoking prevalence.

RESULTS

The analysis was based on 2979 deaths, 5122 admissions, and a population of 199 682. After adjustment for potential confounders, stroke mortality was 37% (95% CI, 19 to 57), 33% (95% CI, 14 to 56), and 26% (95% CI, 10 to 46) higher in the highest, relative to the lowest, NO(x), PM10, and CO quintile categories, respectively. Corresponding increases in risk for admissions were 13% (95% CI, 1 to 27), 13% (95% CI, -1 to 29), and 11% (95% CI, -1 to 25).

CONCLUSIONS

The results are consistent with an excess risk of stroke mortality and, to a lesser extent, hospital admissions in areas with high outdoor air pollution levels. If causality were assumed, 11% of stroke deaths would have been attributable to outdoor air pollution. Targeting policy interventions at high pollution areas may be a feasible option for stroke prevention.

Stroke Mortality Associated With Living Near Main Roads in England and Wales

Background and Purpose— Air pollution is associated with stroke, and road traffic is a major source of outdoor air pollution. Using proximity to roads as a proxy for exposure to road traffic pollution, we examined the hypothesis that living near main roads increases the risk of stroke mortality.

Methods— We used a small-area ecological study design based on 113 465 census enumeration districts in England and Wales. Stroke mortality ( International Classification of Disease , 9th revision, codes 430 through 438) in England and Wales from 1990 to 1992 for people ≥45 years of age was examined through the use of 1991 population denominators. Exposure was calculated as distance from each enumeration district population centroid to the nearest main road. We adjusted for age, sex, socioeconomic deprivation (using Carstairs index), regional variation, urbanization, and metropolitan area using Poisson regression.

Results— The analysis was based on 189 966 stroke deaths and a population of 19 083 979. After adjustment for potential confounders, stroke mortality was 7% (95% confidence interval [CI], 4 to 9) higher in men living within 200 m of a main road compared with men living ≥1000 m away. The corresponding increase in risk for women was 4% (95% CI, 2 to 6) and the risk for men and women combined was 5% (95% CI, 4 to 7). These raised risks diminished with increasing distance from main roads.

Conclusions— Living near main roads is associated with excess risk of mortality from stroke, and if causality were assumed, ≈990 stroke deaths per year would have been attributable to road traffic pollution.

Nicotine does not influence arterial lipid deposits in rabbits exposed to second-hand smoke

BACKGROUND

Second-hand smoke (SHS) accelerates atherogenesis and impairs vascular function. The role of nicotine in this process has not been defined.

METHODS AND RESULTS

To examine the potential effects of nicotine on atherogenesis and vascular function, 48 rabbits receiving a 0.5% cholesterol diet were randomized to control (cholesterol diet only), SHS from nicotine-standard research cigarettes (SHS-ST), and SHS from nicotine-free research cigarettes (SHS-NF). The SHS rabbits were exposed to 48 nicotine-standard (12 animals) or nicotine-free (12 animals) cigarettes/d, 5 d/wk for 10 weeks. Air carbon monoxide and particulates and plasma carboxyhemoglobin were significantly higher in the 2 SHS groups than the control group (P<0.001). The SHS-ST group had significant increases in plasma nicotine and cotinine compared with the other groups (P<0.001). There was no difference in serum lipids. Lipid lesions were increased in both SHS groups (54+/-5% [SEM] aorta and 66+/-4% pulmonary artery, 53+/-7% and 69+/-4%, and 39+/-4% and 43+/-3% in the SHS-ST, SHS-NF, and control groups, respectively; P=0.049 aorta and P<0.001 pulmonary artery).

CONCLUSIONS

SHS exposure increased arterial lipid lesions, but nicotine did not contribute significantly to this effect. This effect is presumably due to other combustion products in the smoke.

Cancer incidence and cause specific mortality among workers in two Norwegian aluminum reduction plants

BACKGROUND

Concern about the health hazards in the aluminum industry has initiated this study where we have investigated associations between exposure to polycyclic aromatic hydrocarbons (PAH) and fluorides, and cancer incidence and cause specific mortality among workers in two Norwegian aluminum plants in operation since 1954 and 1957, respectively.

METHODS

The study was designed as a historical cohort study and comprised 5627 identified men employed for more than six months. Cancer incidence was investigated from start of employment to 1995, and cause specific mortality was investigated from 1962 to 1995. The observed cases of cancers and observed deaths were compared with expected numbers calculated from national rates. Internal comparisons were made using Poisson regression with age and smoking included in the models. Historical exposure to PAH and fluoride had been estimated previously by use of statistical modeling on industrial hygiene measurements and process parameters. A job exposure matrix was used to investigate possible associations between cumulative exposures, and cancer incidence and cause specific mortality. Smoking habits were identified for 92% of the cohort members.

RESULTS

The study showed a significant excess risk for urinary bladder cancer among workers exposed to PAH, but no clear dose-response relationship. When using a 30-year lag period, a significant excess of bladder cancer in the highest exposure category (> 2000 microg/m(3);year PAH) was shown (SIR 4.08). The data also suggested an association between exposure to PAH and pancreatic cancer, but no association with lung cancer was seen. The mortality analysis indicated an association between exposure to pot-room emissions (fluorides) and mortality from chronic bronchitis, emphysema and asthma, but no associations with cardiovascular diseases.

CONCLUSIONS

The study findings are compatible with an excess risk for bladder cancer for aluminum plant workers exposed to PAH. The increased risk for cancer of the pancreas indicated, should be further evaluated in larger exposed populations.

Health survey of former workers in a Norwegian coke plant: Part 2. Cancer incidence and cause specific mortality

OBJECTIVES

A Norwegian coke plant that operated from 1964 to 1988 was investigated to ascertain whether the male workers in this plant had increased morbidities of cancer or increased mortality from specific causes, particularly associated with specific exposures at the coke plant.

METHODS

Personal data on all the employees of the plant were obtained from the plant's archives. With additional data from the Norwegian Bureau of Statistics we identified 888 male former workers at the plant. Causes of death were obtained from the Norwegian Bureau of Statistics, and cancer diagnoses from the Norwegian Cancer Registry. The results were compared with national averages adjusted for age. Specific exposures were estimated with records of actual measurements done at the plant and interviews with former workers at the plant.

RESULTS

A significant excess of stomach cancer (standardised incidence ratio (SIR) 2.22, 95% confidence interval (95% CI) 1.01 to 4.21) was found. Mortality from ischaemic heart disease and sudden death was positively associated with work in areas which entailed peak exposures to CO. When considering work in such areas the past 3 years before death, the association was significant (p = 0.01). The last result is based on only two deaths.

CONCLUSIONS

Considering the short follow up time and the small size of the cohort the results should be interpreted with a certain caution. The positive results would justify a re-examination of the cohort at a later date.

Occupational exposure to dust: inflammation and ischaemic heart disease

OBJECTIVES

To review the possible association between occupational exposure to dust and ischaemic heart disease (IHD).

METHODS

A literature search was performed of relevant studies regarding IHD in specific exposures to dust. The chosen exposures were arsenic, asbestos, beryllium, lead, polycyclic aromatic hydrocarbons, and quartz. The chosen occupations were farmers, paper and paper pulp workers, sawyers, and welders.

DISCUSSION

A theory was launched in 1995 that urban particulate air pollution may provoke alveolar inflammation, with release of mediators capable of increasing blood coagulability in susceptible people and cause cardiovascular deaths. The present review expands this hypothesis and links occupational exposure to inhaled particles with the occurrence of ischaemic heart disease.

CONCLUSION

This hypothesis should be tested by comparing the concentrations of fibrinogen in workers exposed and nonexposed to particles with control for other possible confounders such as smoking habits.

Metal workers and repairmen at risk for prostate cancer: a review

BACKGROUND

The objective is to summarize the results of studies of prostate cancer risk among metal workers, mechanics, and repairmen in order to evaluate the magnitude of risk and to investigate the role of specific work-related hazards in the development of this disease.

METHODS

Review of literature.

RESULTS

In most of the studies reviewed, a slight excess risk of prostate cancer incidence or mortality was observed among metal workers and repairmen. It is as yet unclear, however, whether this excess risk is caused by particular occupational exposures or by risk factors in personal life style (e.g., dietary habits). Hardest evidence is found of a relationship to exist between the use of cutting oils or other metal-work liquids and prostate cancer risk.

CONCLUSIONS

It would appear that metal workers, mechanics, and repairmen run a slightly elevated risk of prostate cancer. However, the actual risk factors are still unknown.

Relation between decline in FEV1 and exposure to dust and tobacco smoke in aluminium potroom workers

OBJECTIVES

To investigate the relation between pulmonary function and occupational exposure in aluminium pot operators.

METHODS

2795 observations were obtained in 630 workers over six years of follow up. An autoregressive method of analysis was used.

RESULTS

After adjustment for FEV1 in the three previous years, the effect of smoking v no smoking on FEV1 was -43.1 ml, 95% confidence interval (95% CI) -72.3 to -13.9. Similarly, an increase in the exposure to particulates by 1 mg/m3 corresponded to a decrease in FEV1 of -11.9 ml, 95% CI -19.9 to -3.9. Age was a significant predictor of both FEV1 and FVC.

CONCLUSION

Exposure to particulates in aluminium potrooms seems to increase the decline in FEV15 thereby increasing the risk of development of chronic obstructive lung disease in pot operators.

Mortality and cancer morbidity in workers from an aluminium smelter with prebaked carbon anodes--Part I: Exposure assessment

OBJECTIVES

To design a job-exposure matrix for epidemiological studies of men who had worked in a Norwegian aluminium smelter between 1922 and 1975.

METHODS

Jobs held by cohort members were identified from personnel records. Tasks and their locations were determined for all jobs, and information was gathered about changes in exposure conditions over time. The jobs were combined into categories thought to have experienced similar exposure conditions, and time weighted average exposures were estimated on a relative scale. The results were reviewed by a panel of former smelter employees and an experienced industrial hygienist.

RESULTS

96 different jobs could be identified from the cohort members' work histories. These were grouped into 18 categories, and relative exposure intensities were estimated for 31 different combinations of category and period. The most prevalent exposure in the cohort was pot emissions (fluorides, sulphur dioxide, and carbon monoxide; 74% ever exposed), followed by magnetic fields and heat stress (65-68%), asbestos (40%), and coal tar pitch volatiles (33%).

CONCLUSIONS

Although the use of this job-exposure matrix in the subsequent epidemiological studies may result in some misclassification of exposure, this is unlikely to seriously attenuate true risks in a stratified analysis based on cumulative exposure.

Mortality and cancer morbidity in workers from an aluminium smelter with prebaked carbon anodes--Part II: Cancer morbidity

OBJECTIVE

To investigate associations between cancer incidence and exposure to coal tar pitch volatiles, asbestos, pot emissions (fluorides, sulphur dioxide), heat stress, and magnetic fields in workers from a Norwegian aluminium smelter that operated from 1914 to 1975.

METHODS

Cancer incidence between 1953 and 1991 was recorded in a cohort of 1137 men hired between 1922 and 1975. The expected number of cancer cases was calculated from incidence rates in Norwegian men. A job exposure matrix with semiquantitative exposure estimates was used to investigate associations between cumulative exposure estimates was used to investigate associations between cumulative exposure and cancer incidence through exploring temporal relations by considering exposures only within specific time windows.

RESULTS

A significant excess of cancer cases, 90 observed v 59.0 expected, was found in workers who had been employed for less than three years. No such excess was found in men with at least three years' employment, with 120 cases observed v 129.7 expected. In this subcohort an association was found between the incidence of bladder cancer and exposure to coal tar pitch volatiles 40 years or more before each person-year under observation, and between incidence of lung cancer and tar exposure 35-50 years before observation. An association was also found between incidence of kidney cancer and exposure to heat stress 20-35 years before observation.

CONCLUSIONS

The results support previous findings that exposure to coal tar pitch volatiles in the aluminium industry has been associated with increased risk of bladder and lung cancer. They also add information about temporal relations, suggesting that exposure to tar in this smelter has acted on an early stage in the development of these cancers, followed by a latency period of 30-40 years.