|
WHAT ARE DIESEL EMISSIONS?
Diesel engines emit a complex mixture of air pollutants, composed of both solid and gaseous material. The visible emissions you can see in diesel exhaust are known as particulate matter. These include many carbon particles (also called soot), as well as gases that become visible as they cool. Diesel particulate matter (diesel PM) has been identified as having the potential to cause cancer, as well as many other adverse health effects. In addition to particulate matter, emissions from diesel-fueled engines include over 40 other cancer-causing substances.
WHAT ARE THE MAJOR SOURCES OF DIESEL PM?
The major sources of diesel PM are on-road and off-road vehicles powered by diesel engines. In addition to cars, trucks, and buses, diesel engines are used in construction vehicles, agricultural equipment, trains, and marine vessels. Diesel engines are also used to generate electricity on both an emergency and routine basis, and are also found on cranes, drilling equipment, and portable pumps.
EMISSIONS FROM STATIONARY SOURCES
There are hundreds of diesel engines in New Jersey (and many more around the country) that are used to produce power for small-scale operations or are kept to generate electricity in an emergency. Emissions from these diesel engines are not accounted for in USEPA’s diesel PM inventory. In New Jersey, we have been making efforts to quantify these emissions. Preliminary results show that these numerous small sources can contribute significant amounts of pollutants to the air that we breathe. As the larger engines apply for Air Pollution Control Permits, they will be required to include particulate control measures in their design.
WHAT IS BEING DONE TO REDUCE EXPOSURE TO DIESEL EMISSIONS?
For more information on what New Jersey is doing to reduce emissions of and exposure to diesel particulate matter, see Stop The Soot.
DIESEL PM HEALTH RISK AND THE 1999 NATA RESULTS
NJDEP evaluated the health risk from diesel PM in the air that we breathe based on concentrations that were estimated by USEPA for the 1999 NATA. NJDEP looked at both cancer and noncancer effects. In the past, NJDEP had been using a noncancer reference concentration (RfC) from USEPA, divided by a safety factor of ten to account for possible cancer-causing effects that are otherwise not accounted for in the RfC.
NJDEP has now decided to estimate cancer risk from diesel PM using a unit risk factor (URF) that California has been using for a number of years. Also, we have decided to evaluate noncancer effects by using the original reference concentration from USEPA (5 ug/m3), with no adjustment (since we are accounting for the cancer risk by using the URF). Results are given in the table below.
(For a discussion of how the diesel risk assessment was done for the 1996 NATA, see the NJDEP 1996 NATA page.
NJDEP’s analysis of the 1999 NATA data for diesel indicates that, throughout the state, the cancer risk from exposure to diesel PM exceeds the targeted one in a million risk level. Countywide average risks range from a high of 1408 in a million in Hudson County, to a low of 248 in a million in Cape May County. The statewide average risk is 633 in a million.
CARCINOGENICITY OF DIESEL PM
USEPA has determined that diesel particulate matter is likely to be carcinogenic to humans through inhalation. The International Agency for Research on Cancer (IARC) also considers diesel engine exhaust to be “probably carcinogenic to humans.” In 1990, California identified diesel exhaust as a chemical known to cause cancer under its Proposition 65. In 1998, the California Air Resources Board added particulate emissions from diesel-fueled engines to its list of Toxic Air Contaminants.
To quantify cancer risk from diesel PM for its Air Toxics Hot Spots Program, California’s Office of Environmental Health Hazard Assessment (OEHHA) developed a unit risk factor that has been used in the program for a number of years. In its “Technical Support Document for Describing Available Cancer Potency Factors” (see below), OEHHA gives an estimated range of lung cancer risk of 1.3 x 10-4 to 1.5 x 10-3 per ug/m3, with a “reasonable estimate” of 3 x 10-4.” This “reasonable estimate” unit risk factor is used here by NJDEP to estimate cancer risk for diesel PM from the 1999 NATA. In the table above, it has been converted to a “Cancer Health Benchmark” that is equal to the air concentration that gives a one in a million cancer risk.
For more diesel information from California, see:
USEPA’s RISK EVALUATION
For NATA, USEPA looked only at noncancer effects, using a reference concentration from its toxics database (Integrated Risk Information System, or IRIS). This RfC is based on specific noncancer effects found in several animal studies, which showed adverse changes in lungs such as inflammation and lesions. The 1999 NATA results show population exposures above this level. USEPA states that “there is a significant potential for noncancer health effects… based on the contribution of diesel particulate matter to ambient levels of fine particles. Exposure to fine particles has been linked to significant public health impacts, including respiratory and cardiovascular effects, as well as premature mortality”. For more information see “What About Diesel PM?”
Although USEPA has determined that diesel particulate matter is likely to be carcinogenic to humans by inhalation from environmental exposures, it does not quantify the cancer risk. USEPA has concluded that the available data are not sufficient to develop a confident estimate of cancer potency. In its “Health Assessment Document for Diesel Engine Exhaust” (May 2002; EPA/600/8-90/057F), USEPA states that available data are inadequate to confidently derive a cancer unit risk estimate for diesel exhaust or diesel particulate matter. However, on page 8-16, they also state that “an exploratory risk analysis shows that environmental cancer risks possibly range from 10-5 to nearly 10-3.” The California unit risk factor used by NJDEP falls within this range.
USEPA’s explanation of why it does not evaluate cancer risk from diesel PM for NATA can be found at its 1999 NATA web site under “Frequent Questions” (question number 13).
back to top
|
