Diesel Engine Exhaust Environmental Exposures

Diesel Engine Exhaust Environmental Exposures

Overview

The primary source of exposure to the general population is from outdoor and indoor air.[1] CAREX Canada’s environmental estimates for diesel exhaust suggest that levels in both indoor and outdoor air result in increased risks of cancer at a population level (data quality very low). Because diesel engine exhaust is not directly measured in Canada, our estimates are developed based on the assumption that 12% of total outdoor fine particles (PM2.5) are attributable to diesel engine emissions.

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The three major sources of diesel exhaust are mobile sources (e.g. vehicles, ships, locomotives); stationary area sources (e.g. oil and gas production facilities, stationary engines, repair yards, shipyards); and stationary point sources (e.g. chemical manufacturing, electric utilities). Non-road sources can double the exposure to diesel exhaust in nearby locations.[1]

Data from a Health Canada assessment of respirable particulate matter estimated that over 80% of PM10 emitted from the transportation sector was attributable to diesel engines.[2] Regulating engine performance and fuel formulation has decreased exhaust emissions, however the contributions of increased numbers of vehicles, and increased use of sports utility vehicles (SUVs) in particular, are ongoing concerns.[3]

Diesel engine exhaust also contributes to smog, which is composed primarily of ground level ozone (formed when nitrous oxides and volatile organic compounds, or VOCs, react in sunlight) and particulate matter.[4]

Cancer Risk Estimates

Potential lifetime excess cancer risk (LECR) is an indicator of Canadians’ exposure to known or suspected carcinogens in the environment. When potential LECR is more than 1 per million in a single pathway, a more detailed risk assessment may be useful for confirming the need to reduce individual exposure. If measured levels of diesel engine exhaust in relevant exposure pathways (outdoor air and indoor air) decrease, the risk will also decrease.

Potential LECR is calculated by multiplying lifetime average daily intake (the amount inhaled or ingested) by a cancer potency factor or unit risk factor. More than one cancer potency factor may be available, because agencies interpret the underlying health studies differently, or use a more precautionary approach. Our results use cancer potency factors from Health Canada, the US Environmental Protection Agency (US EPA), and/or the California Office of Environmental Health Hazard Assessment (OEHHA).

The calculated lifetime daily intake and LECR results for diesel engine exhaust are provided in the tables below. For more information on supporting data and sources, click on the Methods and Data tab below.

Calculated Lifetime Daily Intake

Lifetime Excess Cancer Risk (per million people)

*LECR based on average intake x cancer potency factor from each agency
NOTE: DIESEL ENGINE EXHAUST (DEE) ESTIMATES ASSUME THAT 12% OF TOTAL FINE PARTICULATES MEASURED IN OUTDOOR AIR ARE FROM DEE AND 60% OF FINE PARTICULATES FROM DEE IN OUTDOOR AIR INFILTRATE TO INDOOR AIR. 

Compare substances: Canadian Potential Lifetime Excess Cancer Risk, 2011

The data in this table are based on average intake and Health Canada’s cancer potency factor, assuming no change in measured levels. When Health Canada values are not available, United States Environmental Protection Agency values are used.
Click the second tab to view LECR data. 

**Exposure not applicable: For indicated pathways, substance not present, not carcinogenic, or exposure is negligible
**Gap in data: No cancer potency factor or unit risk factor, or no data available
IARC Group 1 = Carcinogenic to humans, IARC Group 2A = Probably carcinogenic to humans, IARC Group 2B = Possibly carcinogenic to humans
NOTE: Chromium (hexavalent) estimates assume that 5% of total chromium measured in outdoor air is hexavalent and 8% total chromium measured in indoor dust is hexavalent. 

Potential LECR assumes exposure occurs at the same level, 24 hours per day, for 70 years. This is rarely true for any single individual, but using a standard set of assumptions allows us to provide a relative ranking for known and suspected carcinogens across different exposure routes. While ongoing research continually provides new evidence about cancer potency and whether there is a safe threshold of exposure, our approach assumes there are no safe exposure levels.

Mapping

This map shows predicted levels of diesel engine exhaust in outdoor air at residential locations in Canada in 2011. The average concentration of diesel engine exhaust measured in outdoor air in 2011 was 0.8 µg/m3, but concentrations of diesel engine exhaust can be higher or lower than average in many locations.

2011 Predicted Annual Average Diesel Engine Exhaust Concentrations in Outdoor Air at Residential Locations

*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Methods and Data

Our Environmental Approach page outlines the general approach used to calculate lifetime excess cancer risk estimates and includes documentation on our mapping methods.

Data sources and data quality for diesel engine exhaust can be found in the PDF below.

Supplemental data – Diesel Engine Exhaust [PDF]

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