Priority Substances List Assessment Report for Respirable Particulate Matter

Click here or on the pdf file to learn more from Health Canada or read an excerpt below.



Particulate matter (PM) refers in this assessment to particles of less than or equal to 10 µm mass median aerodynamic diameter (PM10). PM10 generally includes a fine fraction of particles 2.5 µm or less (PM2.5) and a coarse fraction of particles larger than 2.5 µm (PM10-2.5). Particulate matter can be emitted directly into the atmosphere or formed secondarily from precursor gases as a result of physical and chemical transformations. Particulate matter may include a broad range of chemical species, such as elemental carbon and organic carbon compounds, oxides of silicon, aluminum and iron, trace metals, sulphates, nitrates and ammonia.

Particulate matter is ubiquitous, being emitted from both natural and anthropogenic sources. The fine fraction of particulate matter and its precursor gases originate typically from combustion processes – motor vehicles, industrial processes and vegetative burning. In contrast, the coarse fraction of PM10 is associated with mechanical processes, such as wind erosion, breaking ocean waves and grinding operations. The available data indicate that source contributions to primary particulate matter emissions and precursor gases in Canada vary by province/territory and by region. Industrial sources provide a major contribution in most provinces, followed by non-industrial fuel combustion and the transportation sector. Forest fires and prescribed burning are the largest estimated sources of particulate matter in some provinces and in the territories. Long-range transport from industrial regions of the United States makes a major contribution to levels of particulate matter in some regions of Canada.

Concentrations of particulate matter typically vary by time of day, day of the week, season and year. Based on fixed-site monitoring of 24-hour concentrations in ambient air, long-term mean PM10 concentrations during the mid-1980s to mid-1990s ranged from 11 to 42 µg/m3 at urban sites and during the mid-1990s ranged from 11 to 17 µg/m3 at rural sites. The corresponding values for PM2.5 were 6.9-20.2 µg/m3 and 7.0-10.5 µg/m3, respectively. The values for both PM10 and PM2.5 are above estimated background levels, indicating that anthropogenic activities make an important contribution to ambient particulate matter loadings. On a national scale, average particulate matter concentrations decreased by approximately 2-3% annually between 1984 and 1995.

In numerous epidemiological studies from around the world, including Canada, positive associations have been observed between ambient levels of particulate matter (as PM10, PM2.5 or other particle metrics) and a range of health outcomes, including daily mortality, respiratory and cardiovascular hospitalizations, impaired lung function, adverse respiratory symptoms and medication use, restricted activity days and the frequency of reported chronic respiratory disease. These associations could not be explained by the influence of weather, season, yearly trends, day-to-day variations or variations due to holidays, epidemics or other non-pollutant factors. While the populations studied were always exposed to other air pollutants in addition to particulate matter, associations of a similar magnitude were observed across numerous locations with differing air pollutant mixtures, and the association with particulate matter remained in analyses that adjusted for the effects of various other pollutants. These particulate matter-related health effects were observed at ambient concentrations that currently occur in Canada.

Therefore, the epidemiological evidence for mortality and morbidity in response to current levels of particulate air pollution meets a number of the criteria for causality, including consistency, dose-response relationship, coherence, temporal relationship and specificity of both outcome and agent. With respect to the biological plausibility of the association, the results of experimental studies in animals and humans provide some limited support for the epidemiological findings. However, both animal and experimental human work are constrained by the technological difficulties in reproducing environmentally relevant particulate matter, and this work has generally been conducted at high levels with artificial particles. Some of this work, specifically the most recent work with concentrated ambient particles, has provided initial evidence of the particulate matter-induced effects on the cardiorespiratory system, particularly in individuals with pre-existing respiratory and cardiovascular disease, and has provided preliminary indications of possible mechanisms. The database supports, therefore, a causal relation between current ambient PM10 and PM2.5 exposure and adverse health effects and provides a reasonable basis for preventive action.

Based principally on the sufficient weight of evidence of mortality and morbidity in the general population exposed to ambient concentrations of PM10 and PM2.5examined in recent extensive epidemiological analyses in Canada and in other countries (at ambient concentrations currently occurring in Canada), as well as on some limited supporting data in experimental animal and controlled human exposure studies, PM10 and particularly PM2.5 are considered to be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health. Therefore, PM10 and particularly PM2.5 are considered to be “toxic” as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999).

Based on available data on the health effects of particulate matter, investigations of options to reduce exposure to particulate matter should be focussed on the fine fraction (PM2.5). They should also be designed to reduce mid-range (24-hour average) rather than peak (i.e., <24-hour periods) exposures, since, on the basis of available data, 24-hour average exposure is associated with increases in mortality and morbidity.

The available data clearly indicate that relative source contributions to PM10 and PM2.5 vary by province/territory and by region. There are ongoing initiatives in risk management designed to accommodate these regional variations. Under the Canada-wide Standards subagreement of the Harmonization Accord signed by the Environment Ministers in January 1998, federal and provincial/territorial governments will develop numerical air quality standards for PM10 and PM2.5, with each jurisdiction developing a plan of action to achieve the standards in a specified time frame. Any investigations of options to reduce exposure as a result of the assessment of particulate matter as a Priority Substance under CEPA 1999 will complement those for this ongoing initiative.

The conclusion of this assessment is based on estimated and measured ambient levels of PM10. However, the assessment acknowledges that this substance can be emitted directly into the atmosphere or formed secondarily from precursors as a result of physical or chemical transformations. It is recommended that stakeholders be consulted on the need to add precursors to PM10 to the List of Toxic Substances in Schedule 1 and on the form of the Schedule 1 listing.

Table of Contents

List of Tables

  • Table 1 Sources of particulate matter
  • Table 2 The 1995 Criteria Air Contaminants emission inventory for Canada (tonnes)
  • Table 3 Provincial/territorial distribution of particulate matter and precursor emissions (tonnes), 1995
  • Table 4 Average, median and standard deviation of the 24-hour PM10, PM2.5 and sulphate measurements sorted by trajectory group
  • Table 5 Frequency distributions of 24-hour average PM10 concentrations (µg/m3) from dichotomous sampler sites (1984-1995) and SSI sites (1988-1994) – national network
  • Table 6 Frequency distributions of 24-hour average PM2.5 concentrations (µg/m3) from dichotomous sampler sites (1984-1995) – national network
  • Table 7 Combined summary statistics for 14 urban NAPS sites in operation between 1986 and 1994
  • Table 8 Summary of relative risks for particulate matter from time-series studies: Total mortality
  • Table 9 Summary of results of time-series studies of hospital admissions and emergency department visits in relation to particulate matter
  • Table 10 Summary of adverse health effects associated with particulate matter (epidemiological studies)

List of Figures

  • Figure 1 Generalized chemical composition of particulate matter
  • Figure 2 Distributions of the ratio of PM2.5 to PM10 mass at the NAPS dichotomous sampler sites
  • Figure 3 Comparison of the distributions of TSP, PM10, PM2.5 and sulphate at 11 urban sites (1984-1993)

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