Human Health Risk Assessment for Gasoline Exhaust – Summary

Health Canada completed the Human Health Risk Assessment for Gasoline Exhaust, a comprehensive review and analysis of the potential adverse health effects associated with gasoline fuel use in Canada. The report focuses on gasoline exhaust (GE) and vehicle emissions from on-road and off-road mobile sources (excluding rail, marine and aviation applications). The assessment includes a review of gasoline fuels, engines, and emissions, a review of exposure to GE, an evaluation of scientific literature on the health effects associated with GE exposure, as well as a quantitative analysis of the population health impacts associated with the contribution of gasoline vehicle and engine emissions to ambient air pollution concentrations in Canada. This report does not address the health risks of gasoline fuel itself, which is under review as a part of the Chemicals Management Plan of the Government of Canada and will be reported elsewhere.

Gasoline, or spark ignition, engines are used throughout Canada, representing 92% of on-road vehicles and 87% of off-road engines or equipment. It is reasonable to assume that exposure to GE is nearly ubiquitous, particularly for Canadians living in urban areas or in close proximity to a major roadway: it is estimated that approximately 2 million people live within 50 m of a major road in Canada. GE is a highly variable and complex mixture of particulate and gaseous pollutants, the composition of which depends on numerous factors including fuel quality, engine and pollution control technologies, vehicle operating conditions and ambient temperature. GE is an important source of criteria air contaminants associated with adverse effects on human health, including fine particulate matter (PM2.5), ground-level ozone (O3), nitrogen dioxide (NO2), volatile organic compounds (VOCs) and carbon monoxide (CO). In addition, GE constituents include air toxics that are recognized internationally as carcinogens, such as benzene and polycyclic aromatic hydrocarbons (PAHs).

Gasoline fuel, vehicles and engines are subject to multiple federal regulations which have successfully reduced air pollutant emissions from gasoline mobile sources, representing a major success in the management of air quality in Canada and the protection of human health. However, given the number of vehicles and engines in use, the age structure of the in-use fleets, and the vehicle kilometres travelled by Canadians, gasoline engines remain a key source of air pollution. The adverse health effects of individual pollutants in GE or produced secondarily in the atmosphere from primary GE emissions (e.g. PM2.5, O3, NO2, benzene and PAHs), are well characterized in the scientific literature and include increased risk of cardiorespiratory mortality and morbidity and of cancer, among other outcomes.

This report is a comprehensive review and analysis of the potential adverse health effects associated with gasoline fuel use in Canada. Two distinct approaches are used. Part A provides an evaluation of scientific studies that have examined the health effects associated with exposure to GE as a mixture. Studies on the health effects of individual GE constituents, such as PM2.5 and benzene, were not considered, as these substances have been extensively reviewed by Health Canada elsewhere. Part B provides a quantitative assessment of the contribution of on-road and off-road gasoline mobile source emissions to individual air pollutant concentrations in Canada and the population health impacts associated with that incremental contribution. The health impact analysis in Part B, which is based on well-established quantitative estimates of risk of adverse health impacts associated with incremental changes in air concentrations of individual pollutants, is complementary to the traditional risk assessment approach presented in Part A.

Following a weight of evidence analysis in Part A of this document, it is concluded that the available literature database of studies that have examined the health effects of GE as a mixture is limited in both study quality and quantity. It is inherently difficult to examine the health effects of GE as a mixture in epidemiological studies, given that most populations are co-exposed to GE and diesel exhaust, and that a unique surrogate for GE exposure has not been identified. Overall, the database of studies examining the role of the GE mixture in adverse health effects (including cancer, cardiovascular, immunological, reproductive, developmental and neurological outcomes) is inadequate. The weight of evidence suggests that GE affects the respiratory system, which is consistent with the known health effects of air pollution to which GE contributes, but the available data examining the GE mixture itself are limited and further study is required. These causality determinations do not preclude the known and well-documented carcinogenicity of individual compounds found in GE, such as benzene and PAHs, nor the well-established non-cancer health effects of GE constituents.

In Part B, analyses were conducted in a stepwise manner: (1) estimation of emissions from gasoline on-road vehicles and off-road applications in Canada; (2) estimation of the impact of those emissions on ambient concentrations of PM2.5, NO2, O3, CO, sulphur dioxide (SO2), benzene, formaldehyde and acetaldehyde across the country using air quality models; and (3) estimation of population health impacts or risks resulting from the incremental contribution of gasoline emissions to ambient concentrations of these pollutants. Modelling was conducted for calendar year 2015.

On-road and off-road gasoline applications represent an important source of air pollutant emissions (e.g. 11% of nitrogen oxides (NOx), 67% of CO and 20% of VOC emissions), especially in populated urban areas, where a large fraction of the Canadian population resides and where personal vehicle use is ubiquitous. Furthermore, on-road gasoline vehicles contribute 98% of CO, 46% of NOx, 28% of PM2.5, 83% of SO2 and 91% of VOC emissions from all on-road vehicles (all fuel types). Off-road gasoline vehicles and engines contribute 94% of CO, 14% of NOx, 27% of PM2.5, 32% of SO2 and 89% of VOC emissions from all off-road vehicles and engines (all fuel types).

Air quality modelling results indicate that gasoline emissions influence ambient concentrations of PM2.5, NO2, O3 and CO. On-road gasoline emissions contribute to air pollutant concentrations in urban areas (e.g. Greater Vancouver, Calgary, Winnipeg, Toronto and Montréal) and along major transportation routes. Specifically, on-road gasoline emissions are estimated to contribute 0.5-2 micrograms per cubic metre (µg/m3) to PM2.5 concentrations, 0.5-5.5 parts per billion (ppb) to NO2 concentrations, and 100 to over 500 ppb to CO concentrations in and around urban areas. On-road gasoline emissions decrease summer O3 concentrations by 0.01-4 ppb within large urban centres, and increase summer O3 concentrations by 0.5-4 ppb in areas surrounding urban centres. These seemingly opposite effects are due to the complex photochemical reactions between O3 and NOx, and the associated impact of high levels of NOx emissions in urban centres. The impact on ambient air pollutant concentrations of off-road gasoline emissions appears more widely distributed geographically, affecting air quality in both rural and urban areas, but lower in magnitude than that of on-road gasoline emissions.

The health effects of individual air pollutants are well-recognized by Health Canada and internationally. The current health impact analysis estimates that on-road and off-road gasoline emissions, via their contributions to ambient concentrations of criteria air contaminants, lead to population health impacts and societal costs in Canada. For calendar year 2015, on-road gasoline emissions are associated with 700 premature mortalities (valued at $5.0 billion), where 69%, 20%, 6%, and 5% of the estimated mortalities are attributable to ambient PM2.5, NO2, CO, and O3, respectively. On-road and off-road gasoline emissions are associated with 940 premature mortalities (valued at $6.8 billion), where 66%, 17%, 11% and 6% of the estimated mortalities are attributable to ambient PM2.5, NO2, and O3 and CO, respectively. The mortality endpoints considered result from both acute and chronic exposure to air pollutants, and include cardiovascular, respiratory and lung cancer mortalities. Gasoline emissions are also associated with acute respiratory symptom days, restricted activity days, asthma symptom days, hospital admissions, emergency room visits, child acute bronchitis episodes and adult chronic bronchitis cases across Canada. The total societal cost associated with on-road and off-road gasoline emissions for calendar year 2015 is estimated to be $7.3 billion.

A similar health impact analysis was previously undertaken by Health Canada for on-road and off-road diesel emissions in Canada, also for calendar year 2015. For that assessment, it was estimated that on-road diesel emissions were associated with 320 premature mortalities and combined on-road and off-road diesel emissions were associated with 710 premature mortalities. Hence, the population health impacts from gasoline emissions are estimated to be greater than those from diesel emissions, based on these model-based analyses. This finding highlights the important contribution of gasoline emissions to ambient air pollution, including the contribution of NOx and VOCs to the secondary production of PM2.5. It also highlights that the geographic distribution of gasoline emission sources and human populations are closely aligned, increasing population exposures.

Recent amendments to the Canadian On-Road Vehicle and Engine Emission RegulationsFootnote 1, Sulphur in Gasoline RegulationsFootnote 2 and Off-Road Small Spark-Ignition Engine Emission RegulationsFootnote 3 will result in reductions in air pollutant emissions from gasoline engines over the next decade, and associated population health benefits. These amendments were not reflected in the current analysis, which targeted calendar year 2015.

This assessment report was undertaken to provide Canadian jurisdictions, regulators and policy makers with a comprehensive evaluation of the potential health effects of gasoline emissions.Footnote 4 It is intended that the report be used to inform further efforts to mitigate emissions and population health impacts associated with this key source of air pollution in Canada. Overall, it is concluded that air pollutants from gasoline sources continue to pose a risk to human health in Canada.

To obtain an electronic copy of the Human Health Risk Assessment for Gasoline Exhaust, please contact hc.air.sc@canada.ca. The report is also available for download.

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