Modeling the intraurban variability of ambient traffic pollution in Toronto, Canada.

The objective of this paper is to model determinants of intraurban variation in ambient concentrations of nitrogen dioxide (NO2) in Toronto, Canada, with a land use regression (LUR) model. Although researchers have conducted similar studies in Europe, this work represents the first attempt in a North American setting to characterize variation in traffic pollution through the LUR method. NO2 samples were collected over 2 wk using duplicate two-sided Ogawa passive diffusion samplers at 95 locations across Toronto. Independent variables employed in subsequent regression models as predictors of NO2 were derived by the Arc 8 geographic information system (GIS). Some 85 indicators of land use, traffic, population density, and physical geography were tested. The final regression model yielded a coefficient of determination (R2) of .69. For the traffic variables, density of 24-h traffic counts and road measures display positive associations. For the land use variables, industrial land use and counts of dwellings within 2000 m of the monitoring location were positively associated with NO2. Locations up to 1500 m downwind of major expressways had elevated NO2 levels. The results suggest that a good predictive surface can be derived for North American cities with the LUR method. The predictive maps from the LUR appear to capture small-area variation in NO2 concentrations. These small-area variations in traffic pollution are probably important to the exposure experience of the population and may detect health effects that would have gone unnoticed with other exposure estimates.

A cohort study of mortality among Ontario pipe trades workers.

AIMS: To study mortality in a cohort of members of the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry of the United States and Canada and to compare results with two previous proportional mortality studies. METHODS: A cohort of 25,285 workers who entered the trade after 1949 was assembled from records of the international head office. Mortality was ascertained by linkage to the Canadian Mortality Registry at Statistics Canada. Standardised mortality ratios were computed using Ontario general population mortality rates as the reference. RESULTS: There were significant increases in lung cancer mortality rates (SMR 1.27; 95% CI 1.13 to 1.42). Increased lung cancer risk was observed among plumbers, pipefitters, and sprinkler fitters. Increased risk was observed among workers joining the Union as late as the 1970s. A random effects meta-analysis of this study and the two PMR studies found significant increases in oesophageal (RR 1.24; 95% CI 1.00 to 1.53), lung (RR 1.31; 95% CI 1.19 to 1.44), and haematological/lymphatic (RR 1.21; 95% CI 1.08 to 1.35) malignancies. CONCLUSIONS: The mortality pattern is consistent with the effects of occupational exposure to asbestos. Increased risk due to other respiratory carcinogens such as welding fume cannot be excluded. There are substantial amounts of asbestos in place in industrial and commercial environments. The education and training of workers to protect themselves against inhalation hazards will be necessary well into the future.

Do factors other than need determine utilization of physicians' services in Ontario?

BACKGROUND: Universal health care systems seek to ensure access to care on the basis of need, rather than income, but there are concerns about preferential access to cardiovascular and specialist care for high income patients. In this study, I used population-based, individual-level health, income and utilization data to determine whether whether there is evidence for differential access to physician care in relation to household income. METHODS: I studied data for 2170 Ontario respondents to the 1995 National Population Health Survey (aged 40 to 79 years) who had approved linkage of their survey responses to the administrative databases of the Ontario Health Insurance Plan and for whom income data were available. I used linear and generalized linear regression to model the mean per capita expenditures on physician care and the probability of referral to a specialist in relation to income and self-reported health status. RESULTS: Residents of higher income households incurred lower per capita expenditures for physicians' services than those in lower income households; for example, the mean per capita expenditure in the upper middle income group was $220 less (95% confidence interval -$87 to -$334) than the mean per capita expenditure in the lowest income group. Expenditures were significantly related to self-reported health status; for example, the mean per capita expenditure among those reporting fair health status was $590 higher (95% confidence interval $465 to $737) than among those reporting excellent health. After adjustment for health status, there was no association between income and the expenditures on all physician services, out-of-hospital services or specialist care. INTERPRETATION: Utilization of physicians' services in Ontario is based on need, rather than income.

Exposure estimation in the presence of nondetectable values: another look.

A common problem faced by industrial hygienists is the selection of a valid way of dealing with those samples reported to contain nondetectable values of the contaminant. In 1990, Hornung and Reed compared a maximum likelihood estimation (MLE) statistical method and two methods involving the limit of detection, L. The MLE method was shown to produce unbiased estimates of both the mean and standard deviation under a variety of conditions. That method, however, was complicated, requiring difficult mathematical calculations. Two simpler alternatives involved the substitution of L/2 or L/square root of 2 for each nondetectable value. The L/square root of 2 method was recommended when the data were not highly skewed. Although the MLE method produces the best estimates of the mean and standard deviation of an industrial hygiene data set containing values below the detection limit, it was not practical to recommend this method in 1990. However, with advances in desktop computing in the past decade the MLE method is now easily implemented in commonly available spreadsheet software. This article demonstrates how this method may be implemented using spreadsheet software.

Obesity, cigarette smoking and the cost of physicians' services in Ontario.

BACKGROUND: This report uses population-based individual-level data to compute direct estimates of the costs of physicians' services in Ontario in relation to Body Mass Index (BMI) and smoking. METHODS: Subjects were 2,170 respondents to the National Population Health Survey who approved linkage to the Ontario Health Insurance Plan. RESULTS: The mean per capita cost of physicians' services in Ontario increased by $8.90 (95% CI: $1.90-$15.60) for each unit increase in BMI and by $1.75 (95% CI: $0.11-$3.40) for every year of daily smoking. The annual attributable cost of smoking and overweight among residents of Ontario, aged 40-79, was estimated at $275,000,000. CONCLUSIONS: Overweight and smoking are responsible for large costs to the health care system. The cost of public health initiatives could be easily recovered if they were successful in making only moderate changes to the levels of smoking and body weight in the population.

Body mass index and quality of life in a survey of primary care patients.

BACKGROUND: The prevalence of overweight and obesity is increasing and contributes to the burden of ill health in the community. The impact of obesity on health-related quality of life has been less well studied than how it affects physical morbidity and mortality. METHODS: A survey of health-related quality of life using the 12-item Short Form (SF-12) of the Medical Outcomes Study Short Form-36 was mailed to patients attending a family medicine clinic. Multiple regression analyses were used to investigate the relationships between scores on the mental and physical components of the SF-12 and body mass index (BMI) while controlling for age, sex, and family income. RESULTS: Responses were received from 565 subjects (53%). The relationships among BMI and quality of life in the mental and physical domains were nonlinear. Quality of life scores were optimal when BMI was in the range of 20 to 25 kg per m2. CONCLUSIONS: The National Heart, Lung, and Blood Institute has published evidence-based clinical guidelines for the identification, evaluation, and treatment of overweight and obesity in adults. Subjects with BMI in the range 18.5 to 24.9 kg per m2 are classified as having normal weight. These observations suggest that achieving a weight in this range will maximize the patient's subjective sense of well-being.

Leukemia after exposure to benzene: temporal trends and implications for standards.

BACKGROUND: Benzene is a human leukemogen. Risk assessment, and the setting of occupational and environmental standards, has assumed that risk is constant in time after a unit of exposure. Leukemia risk is known to vary with time after exposure to ionizing radiation. METHODS: A matched case-control study of leukemia risk in relation to the temporal pattern of benzene exposures was performed using data from the National Institute of Occupational Safety and Health. RESULTS: Leukemia risk following exposure to benzene varied with time in a manner similar to that following exposure to ionizing radiation. More recent exposures were more strongly associated with risk than were more distant ones. There was no significant relation between leukemia death and benzene exposures incurred more than 20 years previously. CONCLUSIONS: Recent analyses of specific occupational and environmental carcinogens, including benzene and radon, have indicated that cancer risk tends to decline as the time from exposure increases. This suggests that standards for the control of occupational or public risk must be selected to control exposures over a narrower time frame than the usual lifetime one. In the case of benzene, it would appear that risk is attributable primarily to exposures incurred during the previous 10 to 20 years, with exposures in the most recent 10 years being the most potent. To limit risk, exposures must be controlled during that interval. It is important that epidemiologists explore the temporal pattern of risk in their studies to facilitate the risk assessment of other carcinogens.

Silica, silicosis, and lung cancer: a risk assessment.

BACKGROUND: To investigate exposure-response relationships for silica, silicosis, and lung cancer. METHODS: Quantitative review of the literature identified in a computerized literature search. RESULTS: The risk of silicosis (ILO category 1/1 or more) following a lifetime of exposure at the current OSHA standard of 0.1 mg/m(3) is likely to be at least 5-10% and lung cancer risk is likely to be increased by 30% or more. The exposure-response relation for silicosis is nonlinear and reduction of dust exposures would have a greater than linear benefit in terms of risk reduction. Available data suggests that 30 years exposure at 0.1 mg/m(3) might lead to a lifetime silicosis risk of about 25%, whereas reduction of the exposure to 0.05 mg/m(3) might reduce the risk to under 5%. CONCLUSIONS: The lifetime risk of silicosis and lung cancer at an exposure level of 0.1 mg/m(3) is high. Lowering exposures to the NIOSH recommended limit if 0.05 mg/m(3) may have substantial benefit.

Mesothelioma and lung tumors attributable to asbestos among petroleum workers.

BACKGROUND: Asbestos exposure has been definitively found to be associated with both mesothelioma and lung cancer. Nevertheless, in the overall population of oil refinery workers potentially exposed to asbestos, many studies clearly show a definitely increased risk of mesothelioma, but no proven excess of lung cancer after comparison to the general population. Through the presentation of new data and the re-appraisal of two recent and independent epidemiological studies conducted in Liguria, Italy, and Ontario, Canada, we attempt to shed light on this apparently paradoxical finding. METHODS: Lung cancer mortality was studied among maintenance workers exposed to asbestos, and among two other subgroups of refinery employees: blue collar and white collar workers. The comparison with blue collar workers was performed in order to take into account the role of healthy worker effect, smoking habit, and the socioeconomic level. The comparison with white collar workers was performed to control for other occupational lung carcinogens. RESULTS AND CONCLUSIONS: Results reveal a consistency between the two studies and show that 96-100% of the mesotheliomas and 42-49% of the lung tumors arising among maintenance workers were attributable to asbestos exposure. Our new analysis, estimating two cases of asbestos-related lung cancer for each case of mesothelioma, confirms published findings on the magnitude of asbestos-related tumors in oil refineries.

Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers.

BACKGROUND: The health effects of asbestos are intimately related to the fate of inhaled fibers in the lungs. The kinetics of asbestos fibers have been studied primarily in rodents. The objective of this study was to explore the application of these kinetic models to human autopsy data. METHODS: We analyzed the asbestos fiber content of the lungs of 72 Quebec chrysotile miners and millers and 49 control subjects using analytical transmission electron microscopy. Statistical methods included standard multivariate linear regression and locally weighted regression methods. RESULTS: The lung burdens of asbestos bodies and chrysotile and tremolite fibers were correlated, as were the concentrations of short, medium, and long fibers of each asbestos variety. There were significant associations between the duration of occupational exposure and the burdens of chrysotile and tremolite. The concentration of chrysotile decreased with the time since last exposure but the concentration of tremolite did not. The clearance rate varied inversely with the length of chrysotile fibers. For fibers greater than 10 mu in length the clearance half-time was estimated to be 8 years. CONCLUSIONS: The patterns in our data are compatible with both of the hypotheses suggested from rodent experiments; the existence of a long-term sequestration compartment and overload of clearance mechanisms in this compartment.