The School of Public Health at the University of Alberta is always looking for field practicum opportunities for Master of Public Health students specializing in Environmental & Occupational Health. Some students are interested in Workplace Health and Safety broadly  others in Occupational Hygiene specifically. We are interested in connections with companies/institutions interested in hosting these MPH students. The practicum is a minimum of 13 weeks full-time and is typically completed during the spring/summer term – beginning in early May. Occupational Hygiene placements should be supervised by a qualified occupational hygienist. Workplace Health & Safety placements could be supervised by other appropriate individuals. Companies or institutions interested in exploring this are encouraged to contact either Bernadette Quemerais at  or Ruth Wolfe at .”

The Fort McMurray wildfire that started in Alberta, Canada, on May 1, 2016 burned more than 2,300 square miles, caused the evacuation of close to 90,000 people, and destroyed nearly 2,000 structures and damaged another 19,000. Two fatalities were indirectly tied to the fire. Early financial estimates put the insurance cost at between $2.6 and $4.7 billion dollars. By June 10, the fire was nearly 73 percent contained.

By contrast, the 2003 Cedar Fire in San Diego County, Calif., while only one-fourth the size of the Fort McMurray fire, displaced more than 300,000 people, caused 14 fatalities, and destroyed 2,400 structures due to higher population density in the urban-wildland interface. As the effects of climate change on seasonal weather become more evident, frequent and severe wildfires in proximity to residential areas are expected to expose greater numbers of homes and people to smoke and debris from the fire and its aftermaths.

As of mid-June, Fort McMurray was under a boil-water order. Air quality throughout the region was significantly affected. Arsenic and heavy metals contamination in some undamaged homes made them unsafe to reoccupy. The alkaline ash—one of the main components of wildfires—acts as a corrosive agent, and dust suppression compounds sprayed on burned structures contain crystalline silica. Reconstruction activities can cause these substances to become airborne. Labor authorities urged employers to take all necessary steps to protect the health and safety of their workers and mitigate hazards once recovery begins.

Wildfires can impact property, the environment, and public health from the immediate vicinity of the fire up to several hundred miles from the source. Insurance claims for property damage are the driving force behind most investigations of damage from wildfire smoke. In many cases, these investigations take place several months to a year after the incident. Investigative, sampling, and analytical techniques are primarily intended to confirm the presence or absence of wildfire residues and determine the degree of damage to property and assets. The potential human health effects of wildfire smoke and residues often remain unanswered. Does wildfire residue pose a human health hazard? How do we evaluate the potential health hazard posed by wildfire residue? What are the background levels of similar products of combustion in homes? And what is the appropriate level of remediation and clean up?

Modeling Exposure to Wildfire Residues

Smoke inhalation can have acute and chronic effects on the health of wildland firefighters. Heating and cooking with wood can also have recognized adverse health effects on household residents. However, there is little information on the health risk to residents from exposure to wildfire residues in homes that are reoccupied after being affected or damaged by smoke. 

A conceptual model can serve to explore the potential adverse health effects of residential exposure to wildfire residues. In this model, the wildfire does not reach a structure. Instead, smoke from the wildfire descends upon a residential area and enters the home through roof penetrations, make-up air vents, and seams around doors and windows. Gaseous and particulate smoke contaminants entering the building settle on solid surfaces, including HVAC units and ductwork, and some are adsorbed onto carpets, floors, walls, and furnishings. When residents return home days or weeks after the fire, the smoke is no longer a direct hazard. Combustion gases and the more volatile smoke constituents dissipate and become diluted by passive or active ventilation to reduce odors.

The fate and transport of the residual contaminants depends in part on housekeeping practices, the chemicals’ partition coefficients, and the type of ventilation. The larger-size fractions of settled dust are removed by regular cleaning, while the respirable-size particulates may remain longer in the absence of HEPA filtration. Adsorbed semi-volatile organic compounds (sVOCs) continue to off-gas following their gas-solid phase equilibrium kinetics for days, weeks, and even months. At this stage, the potential health risk from the wildfire residuals is most likely from inhalation, skin contact, and ingestion of particulates—mainly char and ash deposited by the smoke, as well as the polycyclic aromatic hydrocarbons (PAHs) that have become adsorbed onto the fire particulates and onto surfaces in the home.

Evaluating Health Hazards

Wildfire smoke is a veritable cocktail of products of incomplete combustion. Ash and char, the main components of wildfires, may contain heavy metals, PAHs, and dioxins and furans. Research on firefighter exposure to smoke has identified a number of constituents of potential concern: combustion gases, such as carbon monoxide; volatile organic compounds (VOCs), particularly benzene; aldehydes such as formaldehyde and acrolein; a wide variety of PAHs, including pyrene, phenanthrene, benzo(a)anthracene, benzo(a)pyrene, and benzo(b)fluoranthene resulting from combustion of organic matter; and particulate matter, principally in the PM_2.5-size range. 

The health effects of wood smoke inhalation range from acute irritation, inflammatory responses, asthma triggers, and immune system suppression to changes in lung function (measured as increased airway resistance); reduced lung function capacity; chronic illnesses, including bronchitis, obstructive pulmonary disease, and cardiac disease; and cancers of the lung, skin, and bladder.

Concentrations of VOCs, PAHs, and particulates measured at wildfire suppression and prescribed burning operations suggest that the primary sources of cancer risk in the range of one-in-one-thousand to one-in-one-million derive from exposure to benzene and formaldehyde, and that non-cancer adverse health effects above a level of concern (hazard quotient > 1) result from exposure to acrolein and respirable particulate matter. In studies of wildland firefighter risk assessment models, neither carbon monoxide nor any of the PAHs detected reached levels of concern.

Many of these compounds have also been identified inside homes, which complicates the evaluation of health hazards from wildfire smoke residues. Background sources of PAHs in urban outdoor air and in homes not affected by wildfire smoke include smoke from fireplaces and cigarettes, asphalt pavement sealers containing coal tar, and vehicle exhaust. Background PAH levels in indoor air range from 0.00027 µg/m³ to 0.05 µg/m³, approximately twice the background levels found in outdoor air.

PAHs exist in equilibrium between a vapor and a solid phase, and have a strong affinity for organic matter like charcoal. They attach to building materials and furnishings, such as carpet, gypsum wallboard, and even stainless steel, and slowly off-gas for time periods ranging from hours to weeks or months. As a result, PAHs are commonly found as a component of household dust. Typical background levels are in the range of 0.15 to 1.64 micrograms per gram (µg/g) of dust. Dust ingestion by children is the second most important route of exposure to carcinogenic PAHs, after inhalation exposure. However, household dust needs to contain more than 150 times the typical PAH background levels to pose a lifetime cancer risk above one-in-one-million.

Sampling and Analysis

The residential post-wildfire exposure scenario discussed in this article illustrates some of the uncertainties that must be addressed when evaluating human health risk from wildfire residuals. These include the composition of the wildfire smoke inside a home; concentration of chemical constituents in the smoke; fate and transport of persistent wildfire residual chemicals in the interior environment; partition coefficients of PAHs in char, ash, construction materials, and furnishings; background levels from non-wildfire sources; and the effects of ventilation and housekeeping practices on contaminant deposition and removal rates.

The wildfire impact investigator needs to have a clear understanding of the sampling technique and analytical methods to ensure that they are compatible with each other and meet the desired objectives. Various techniques for particulates, metals, VOCs, sVOCs, or gases are applicable to wildfire residue investigations. 

Depending on the objective of the investigation, particulate analysis of soot, char, and ash can be conducted through optical microscopy using reflected and transmitted light, transmission or scanning electron microscopy (TEM or SEM) supported by X-ray diffraction techniques for material composition, or a combination of methods. Sample collection techniques need to consider the desired analysis to maintain sample integrity. For instance, wipe sampling with water or solvents can dissolve ash particles and render them invisible to microscopic examination. By the same token, some lab preparation techniques can destroy the sampling media, or the sample itself.

Some of the most common sampling techniques in wildfire property damage claims are tape lifts and micro-vacuum sampling for particulate microscopy analysis, often used as part of Visual Area Estimation (VAE) analysis. This method identifies various types of particles in the sample, such as soot, ash, char, mold, cellulose, soil minerals, and other opaque particles, and reports them as percentages or numbers of each component particle in the observed field. The laboratory interprets the percentage or count in a range from normal background to uncommon, and makes recommendations as to the source of the particles or the level of cleaning needed. The results and interpretation of this particle characterization method can vary between laboratories. Because VAE analysis does not determine actual surface or mass concentrations of the identified particle types in the home, it is not appropriate for human health risk assessments. 

Air sampling methods for gases, VOCs, and sVOCs used in traditional industrial hygiene or indoor air quality investigations can be used in wildfire residue assessments. The objective of the investigation will dictate the sampling and analytical technique. Direct-reading instruments for combustion gases and VOCs can be used for initial screening. Bulk samples of furnishings or building materials can be analyzed in environmental chambers for off-gassing chemicals to identify persistent odors. Due to the long time lag between the fire and the smoke damage investigation, sampling methods that can detect residual concentrations in the parts per billion range (ppb)—such as EPA TO-15 and TO-17 for VOCs, and XAD-coated samplers for sVOCs—followed by gas chromatography and mass spectrometry are often necessary. These methods can detect hundreds of chemicals at ppb and sub-ppb concentrations.

The experienced laboratory can help sort through the background “noise” to identify the signature chemical compound combinations that indicate the presence of a particular wildfire residue. Choosing experienced and qualified wildfire residue laboratories and working closely with the analysts to develop the sampling strategy is essential to produce usable and defensible data to support the interpretation of results. This is especially important in wildfire residue investigations due to existing gaps in published standard methods in this emerging area of practice.

Sampling and analytical methods specifically designed to quantify concentration and distribution of the wildfire residuals in the building and allow calculation of dose by the major routes of exposure are necessary to evaluate the human health risk from wildfire smoke. Industrial hygienists involved in wildfire residual impact investigations from the health risk perspective need to utilize sampling and analytical methods that can evaluate potential health hazards. This data can also inform the development of clean-up levels and post-remediation verification protocols.

ENRIQUE MEDINA, MS, CIH, CSP, FAIHA, is president of Alliance Consulting International in San Diego, Calif., and a member of the AIHA Environmental Issues Committee. He can be reached at (619) 297-1469 or .

Dozens of groups are pressing Ottawa to join more than 50 countries in banning asbestos, a move the Liberal Party supported while in opposition.

A letter sent to Prime Minister Justin Trudeau this month notes that Canada still allows the use of asbestos and lacks a comprehensive strategy to phase out the substance or to promote safe substitutes.

Separately, the Canadian Cancer Society has also sent a letter to the government, a copy of which was given to The Globe and Mail, calling for a nationwide ban on all asbestos products, a rare step for the country’s largest national health charity.

“It’s time to send a clear message and establish clear policy to end asbestos, end any confusion about its dangers, any confusion about the toll it’s taken, and any debate there is about a mythical ‘safe’ exposure level, and most importantly, [end] the exposure of Canadian workers and families to this potentially deadly substance,” said Gabriel Miller, director of public issues at the Canadian Cancer Society.

In an e-mailed statement, Health Canada said it will carefully consider whether further controls of asbestos are necessary, in addition to the measures the government has in place to protect Canadians from exposure.

Adding to a sense of urgency is the federal government’s plans to boost spending on infrastructure. Those plans raise concerns that asbestos in pipes, cement or other building materials could wind up in new construction.

“Given the huge investment that the federal government is going to make around infrastructure, this is the time to say ‘we’re not going to repeat past mistakes,’ ” said Hassan Yussuff, president of the Canadian Labour Congress, the county’s largest labour organization, which is also calling for a comprehensive ban on asbestos.

Backed by nurses’ associations, building trades councils, unions and some city councils, the letter to the Prime Minister makes 11 recommendations, among them: passing legislation that bans the use of asbestos; prohibiting the use of asbestos-containing materials in federal infrastructure projects; and ensuring safer disposal and creating a national registry of asbestos exposure locations and diseases. It also wants to see a broad public-health response to asbestos diseases.

The World Health Organization says all types of asbestos cause lung cancer, mesothelioma and other types of cancers along with asbestosis. It says the most efficient way to eliminate these diseases is to stop the use of asbestos.

But Statistics Canada trade data show asbestos-related imports rose to a six-year high last year – $8.3-million in 2015 from $6-million a year earlier. About half of that was in brake pads and linings, while this country also imported raw asbestos, sheets and pipes, clothing and fabricated products. Exports have markedly declined, but Canada still exported $1.2-million to other countries in clothing, building materials and fabricated products.

Asbestos is the top on-the-job killer in Canada. New cases of mesothelioma – a cancer caused almost exclusively by asbestos exposure – have more than doubled in the past two decades. Each year, more than 2,000 people are diagnosed with asbestos cancers and other diseases, according to Cancer Care Ontario. About 150,000 Canadian workers are exposed to asbestos in their workplaces, Carex Canada estimates, among them construction workers and contractors, mechanics, shipbuilders and engineers.

Canada was once one of the world’s top producers of asbestos, and shut its last mine in 2011. The federal government in the past had defended the industry and maintained a position of “safe and controlled use,” a stand that was harshly criticized by doctors, scientists, advocates and those who have been affected by asbestos-related diseases. Countries including Australia, Germany and Britain have banned the mineral.

In an interview a year ago, Liberal MP Geoff Regan – now Speaker of the House – told The Globe and Mail he speaks for the party in favouring a ban of all asbestos use in Canada.

That’s what Renée Guay is hoping to see soon. She watched her father pass away in “unbearable” pain in 2011 from mesothelioma at age 59. He was exposed at a manufacturing plant in St. Catharines, Ont., where he worked as an engineer. Her uncle, who worked in the same facility, was diagnosed with asbestosis last year.

“It’s discouraging … and it just goes back to that Canada doesn’t have a plan, and how is this okay? We’ve known this is an issue for years, and no one’s doing anything. It doesn’t make any sense.”

The number of new mesothelioma cases rose to a record 580 in 2013, according to Statscan. Mesothelioma has a long latency period, of 10 to 50 years, and researchers expect new cases will continue to climb.

“There is no sign that we have reached the peak,” said Paul Demers, director at the Occupational Cancer Research Centre, who estimates that about 80 per cent of these cancers stemmed from workplace exposure to asbestos, and almost all of the rest “due to exposure at home from the clothes of a family member who worked with asbestos” or through other forms of environmental exposure.

His team’s analysis, based on studies of exposed workers, pegs the number of lung cancers attributable to occupational asbestos exposure at about 2,000 in 2013.

“This government stated clearly when they got elected, they’re going to be relying on science-based decisions, and there’s no question that the WHO and even now Health Canada have come to realize that asbestos is a carcinogen,” said Mr. Yussuff, himself exposed to asbestos dust when he worked at a General Motors truck plant, and wonders about the impact that has had on his health. Given the body of evidence. “I hope the government will do the right thing, because knowing that fact, why would you allow this substance to be imported, and why would you allow Canadians to be exposed to it?”

Asbestos was the most common source in workplace death claims in 2014, cited in 388 cases, most-recent data from the Association of Workers’ Compensation Boards of Canada show. In that year, mesothelioma was the No. 1 cause of death in accepted fatality claims.

“When you look at the No. 1 [occupational] disease that people are going to die from, asbestos is right up there,” said Dr. Andréane Chénier, national health and safety specialist with the Canadian Union of Public Employees. Hundreds of people are dying from asbestos-related diseases every year, “and you know this is going to be a very slow, very painful death. It’s heart wrenching to watch, and there’s no cure. But it’s preventable – we know this stuff is bad.”

“There is no safe use. People keep saying oh no, there are safe ways to use it – no there aren’t. There aren’t because it’s not fibres you can see, it’s the fibres you can’t see.”

In Ottawa, Michaela Keyserlingk says she’s tired of waiting. “I’m deeply disappointed” no action has been taken, said Ms. Keyserlingk, whose husband of 47 years died in 2009 of mesothelioma, after exposure as a cadet in the Canadian navy. “We lived this perfect life. And then suddenly, my husband who ran marathons and played tennis couldn’t get enough air … he survived [with mesothelioma] for the next 2 1/2 years. This cancer and lack of oxygen, he had real anxiety attacks … he was skin and bones. I terribly miss not being able to talk to him.”

“I had thought when the Liberals were elected I could now relax and think everything would be in good hands. And I’m not convinced any longer that this is the case.”

 

This article originally published in the Globe and Mail newspaper: 

Health Canada completed the Human Health Risk Assessment for Diesel Exhaust, a comprehensive review and analysis of the potential adverse health effects associated with diesel fuel use in Canada. The report focuses on diesel exhaust (DE) emissions from on-road and off-road vehicles (excluding rail and marine applications) and targets impacts resulting from general population exposures. The assessment includes a review of diesel fuels, engines and emissions, a review of exposure to DE, an evaluation of the health effects associated with DE exposure, as well as a quantitative analysis of the population health impacts associated with the contribution of DE to criteria air contaminant concentrations in Canada. This report does not address the health risks of diesel fuel itself, which is under review as part of the Chemicals Management Plan of the Government of Canada and will be reported elsewhere.

Internationally, the potential health effects of DE exposure have long been recognized, and great effort has resulted in substantial reductions in diesel emissions, including in Canada. A key accomplishment has been the introduction of stringent emission regulations for new diesel vehicles and engines, resulting in improved engine and emission control technologies in both the off-road and on-road diesel fleets. In addition, the quality of diesel fuel used in on-road, off-road, rail, marine and stationary engines has improved, particularly in terms of the sulphur content. Some jurisdictions have undertaken additional initiatives to mitigate in-use diesel engine emissions and human exposure to them, such as inspection and maintenance programs, retrofit and scrappage programs and idling restrictions. However, the Canadian in-use diesel fleet is still dominated by engines pre-dating the most recent emission standards.

Diesel-powered vehicles are pervasive on major roadways and in urban centres in Canada. It is reasonable to assume that most Canadians are regularly exposed to DE. Because of the variable and complex nature of DE and the fact that DE constituents are emitted by other pollution sources, it has been difficult to quantify general population exposure to DE. Several surrogates have been used to represent DE, all of which have had their limitations. The respirable fraction of elemental carbon is considered to be one of the better options used to date.

This risk assessment considered the reviews and conclusions of the California Environmental Protection Agency (1998)^Footnote1 and the United States Environmental Protection Agency (2002)^Footnote2 human health risk assessments for DE and provided detailed review of the health effects literature published since 2000. The available information supports the conclusion that DE emissions have direct effects on human health.

The newly published health studies along with supporting evidence from work published prior to 2000 provide sufficient evidence to conclude that DE is carcinogenic in humans and is specifically associated with the development of lung cancer. Although the risk estimates are generally small, the population health risks are considered to be significant given the ubiquitous presence of DE emissions in Canada. The evidence is also suggestive that DE may be implicated in the development of cancer of the bladder in humans, but further research is required to allow definitive conclusions to be drawn. A limited number of studies have investigated other cancers in association with DE exposure, but the evidence is inadequate to draw conclusions regarding causality. Overall, these conclusions are consistent with the categorization of DE as a human carcinogen (Group 1) by the International Agency for Research on Cancer.^{Footnote3,Footnote4}

Regarding non-cancer health effects and the potential causal role of DE in their development, a number of conclusions are drawn from the existing literature. The evidence supports a causal relationship between acute exposure to DE at relatively high concentrations and effects on the respiratory system, including increases in airway resistance and respiratory inflammation. Under conditions of chronic exposure, DE exposure is likely to be causal in the development of respiratory effects. It was concluded that DE exposure is likely to be causal in the development of adverse cardiovascular outcomes following acute exposure and in the development of adverse immunological responses. The evidence reviewed is suggestive of a causal relationship between DE and 1) adverse cardiovascular outcomes following chronic exposure, 2) adverse reproductive and developmental effects and 3) central nervous system effects following acute exposure to DE. Currently, there is inadequate evidence to draw conclusions regarding the potential neurological impacts of chronic DE exposure.

Based on traditional risk assessment methodologies and with regard to general population exposures, a short-term exposure guidance value of 10 µg/m³ and a chronic exposure guidance value of 5 µg/m³ have been derived based on diesel exhaust particulate matter (PM) to protect against adverse effects on the respiratory system. The available evidence indicates that respiratory effects occur at lower concentrations of DE than those associated with other non-cancer adverse effects, and so these guidance values are considered protective against the non-cancer health impacts of DE exposure. However, it is recognized that there have not been adequate large scale epidemiological studies of non-cancer effects associated with either short-term or chronic DE exposure to conclusively characterize the exposure-response relationships. More research is needed to elucidate this and to evaluate the potential role of DE in the observed non-threshold population health effects of fine particulate matter (PM_2.5).

In general, it has been shown that sensitive subpopulations, such as the elderly, children and asthmatics, can be at greater risk of adverse respiratory effects due to DE exposure. Exposure of the elderly and asthmatics to traffic-related DE has been shown to increase respiratory inflammation. Also, pulmonary function decrements have been demonstrated in asthmatics exposed to traffic-related DE. Furthermore, traffic-related DE exposure in children has been implicated in potential asthma development later in life. The guidance values for short-term and chronic DE exposure presented above account for the enhanced sensitivity of subgroups in the population.

Overall, it is concluded that DE is associated with significant population health impacts in Canada and efforts should continue to further reduce emissions of and human exposures to DE.

As part of this assessment, efforts were also made to quantify the population health impacts associated with the contribution of DE to criteria air contaminant concentrations in Canada. The analysis of population health impacts was conducted in a stepwise manner with the use of computer simulation tools to 1) estimate emissions from the Canadian diesel fleet, 2) estimate the impact of those emissions on ambient concentrations of criteria air contaminants across the country and 3) estimate population health impacts resulting from the incremental contribution of DE to air pollution levels. This was undertaken for calendar year 2015, and results were assessed on a national, provincial/territorial and regional basis. This analysis is complementary to the traditional risk assessment approach presented above.

The air quality scenarios modelled with A Unified Regional Air Quality Modelling System (AURAMS) and the Air Quality Benefits Assessment Tool (AQBAT) were selected in order to provide an indication of the potential air quality and health impacts associated with diesel fuel use in on-road and off-road applications in Canada. On-road and off-road diesel applications are responsible for substantial levels of pollutant emissions. Compared with other mobile sources, diesel vehicles and engines contribute significantly to nitrogen dioxide (NO₂) and PM_2.5 emissions, whereas gasoline mobile sources contribute the majority of carbon monoxide (CO) and volatile organic compound (VOC) emissions. Diesel source emissions are notably important in large urban areas, such as Greater Vancouver, Toronto and Montréal, where a large fraction of the Canadian population resides. Diesel emissions are also important along major trucking routes and roadways connecting major cities (e.g. Windsor-Québec corridor), as well as in agricultural and mining areas (e.g. Alberta). The characteristics of the mobile fleet and the dominating economic sectors in a particular region determine the influence of diesel emissions. The concentration of diesel emissions in specific geographic areas leads to distinct air quality impacts across Canada.

Diesel emissions are estimated to contribute significantly to ambient concentrations of NO₂, PM_2.5 and ground level ozone (O₃). The air quality modelling results show that on-road diesel emissions contribute significantly to air pollutant concentrations in urban and economically active areas and along major transportation routes. Off-road diesel emissions, which are more widely distributed than on-road diesel emissions, affect air quality in both rural and urban areas. The combination of on-road and off-road emissions leads to greater air quality impacts in the largest Canadian urban centres, notably Greater Vancouver, Edmonton, Calgary, Winnipeg, Toronto and Montréal. Off-road diesel emissions also have a relatively large impact in less developed areas characterized by few other sources of pollutant emissions (e.g. remote mining communities).

Based on the current health impact analysis, on-road and off-road diesel emissions result in significant and substantial population health impacts and societal costs in Canada via the contribution of DE to ambient concentrations of criteria air contaminants. The modelling undertaken estimates that on-road diesel emissions are associated with 320 premature mortalities for 2015 (valued at $2.3 billion), with 65% and 35% of the estimated mortalities attributable to ambient PM_2.5 and NO₂, respectively. On-road and off-road diesel emissions are associated with 710 premature mortalities (valued at $5.1 billion), with 65%, 32% and 3% of the estimated mortalities being attributable to ambient PM_2.5, NO₂ and O₃, respectively. Diesel emissions are also associated with significant numbers of 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. Results from the AQBAT simulations for the current assessment suggest that on-road and off-road emissions each contribute approximately equally to population health impacts. The results also indicate that both on-road and off-road diesel applications have significant health impacts in major Canadian urban centres. Diesel emissions have higher health impacts in the most populated provinces, such as British Columbia, Alberta, Ontario and Quebec, and in the most populated census divisions, which correspond to the Greater Vancouver, Calgary, Winnipeg, Toronto and Montréal areas. The greatest air quality impacts are also observed in those areas. Overall, it is concluded that efforts should continue to further reduce emissions of DE in Canada, particularly in areas with large populations.

To obtain an electronic copy of the Human Health Risk Assessment for Diesel Exhaust, please contact .