Clean Air Reports

Dangers Of Diesel: How Diesel Soot And Other Air Toxics Increase Americans' Risk Of Cancer

2002-10-30

Executive Summary

Toxic chemicals in the air pose a serious threat to public health. Although levels of many air toxics have declined over the last decade, concentrations of these hazardous substances in the outdoor air remain far above health-protective guidelines established under the Clean Air Act. Congress has identified 188 of these pollutants, including substances that cause cancer, birth defects, neurological damage, and respiratory effects, but a very small number of the chemicals, most of which are emitted from cars, trucks, and non-road engines, such as diesel construction and farm equipment, appear to account for the majority of the potential cancer risk associated with the pollutants.

This report estimates the potential cancer risk associated with exposure to 33 hazardous air pollutants in order to better understand the magnitude of the cancer risk posed by air toxics. Given the dominant role played by toxic emissions from cars, trucks, and non-road engines, collectively referred to as “mobile sources,” the report also provides detailed estimates regarding the potential cancer risks posed by five priority mobile source air toxics nationally and in every state and county in the continental U.S. Specifically, the report documents the extent to which emissions of diesel soot, acetaldehyde, benzene, 1,3-butadiene, and formaldehyde compromise public health by increasing Americans’ risk of developing cancer in their lifetimes. However, the report does not consider the serious non-cancer health effects associated with the pollutants and, as a result, underestimates their health impacts.

Key findings include the following:

• The national average cancer risk from breathing hazardous air pollutants in the outdoor air was one-in-2,100 in 1996, the most recent year for which data are available. This is nearly 500 times greater than the one-in-one-million health-protective threshold for cancer established in the Clean Air Act. Emissions from cars, trucks, and non-road engines accounted for 93 percent of the added cancer risk, while stationary and background sources accounted for the remaining seven percent of the risk. Diesel emissions alone contributed 89 percent of the risk, with 28 percent from on-road sources, such as freight trucks, and 60 percent from non-road sources, such as construction, industrial, and farm equipment.

• Americans in every state and county in the continental U.S. and the District of Columbia were exposed to diesel soot at levels that exceeded the California EPA’s cancer benchmark concentration in 1996. In New York, the statewide average human exposure concentration for diesel particulate exceeded the cancer benchmark concentration by 1,200 times, meaning that residents of New York face a one-in-850 chance of developing cancer in their lifetimes simply as a result of breathing diesel soot in the outdoor air. Non-road engines released from 41-88 percent of total diesel emissions by state.

• Americans in 10 states in the continental U.S. And the District of Columbia were exposed to acetaldehyde emissions at levels that exceeded the cancer benchmark concentration in 1996. Cars, trucks, and non-road engines released from 32-99 percent of total acetaldehyde emissions by state.

• Americans in every state in the continental U.S. And the District of Columbia were exposed to benzene emissions at levels that exceeded the cancer benchmark concentration in 1996. In Maryland, the statewide average human exposure concentration for benzene exceeded the cancer benchmark concentration by 14 times. Cars, trucks, and non-road engines released from 53-96 percent of total benzene emissions by state.

• Americans in 27 states in the continental U.S. And the District of Columbia were exposed to 1,3-butadiene emissions at levels that exceeded the cancer benchmark concentration in 1996. Cars, trucks, and non-road engines released from 29-100 percent of total 1,3-butadiene emissions by state.

• Americans in every state in the continental U.S. And the District of Columbia were exposed to formaldehyde emissions at levels that exceeded the cancer benchmark concentration in 1996. In Virginia, Minnesota, Delaware, Ohio, Colorado, and Florida, the statewide average human exposure concentration for formaldehyde exceeded the cancer benchmark concentration by a factor of 10. Cars, trucks, and non-road engines released 21-95 percent of total formaldehyde emissions by state.

These findings add a new urgency to the need for the U.S. EPA to take swift action to reduce toxic emissions from cars, trucks, and non-road engines to levels that do not adversely impact public health. Specifically, EPA immediately should move to:

• Fully implement clean air standards for diesel trucks and buses. Reducing exposure to diesel soot is an essential component of reducing the public health risk from toxic air pollution. In 2001, EPA issued landmark standards to clean up dirty diesel trucks and buses, comparable to the advent of the catalytic converter on cars over 25 years ago. In addition to reducing the cancer risk from exposure to diesel exhaust, EPA estimates that the standards will prevent more than 360,000 asthma attacks and 8,300 premature deaths each year.

The Bush administration backed the landmark standards after taking office but now is considering allowing diesel engine makers to trade emission credits rather than produce cleaner trucks and buses. The administration should reject this flawed approach and honor its commitment to fully implement clean air standards for diesel trucks and buses.

• Pass equivalent standards for dirty diesel construction and farm equipment.

This report finds that much of the cancer risk from diesel exhaust comes from non-road diesel equipment, such as bulldozers, portable generators, forklifts, and tractors. Current emission standards for these engines are comparable to the controls on cars as far back as the late 1960s. Cleaner fuel and modern pollution controls alone could slash emissions from these engines by over 90 percent.

EPA and the White House are developing a plan to reduce emissions from non-road diesel engines and fuel. These standards should be equivalent to the truck standards and implemented in the same time frame. In addition to reducing the cancer risk from diesel soot, a recent report by state and local air quality officials estimates that such standards could prevent more than 8,500 premature deaths and 180,000 asthma attacks each year and could save $67 billion in health care costs annually.

•Adopt a strong mobile source air toxics rule to reduce other toxic emissions from cars, trucks, and non-road engines. While reducing filthy soot from new diesel engines is crucial to reduce the public health risk from air toxics, additional measures are needed to reduce toxic emissions from cars, trucks, non-road engines, and their fuels. The good news is that major reductions in these emissions can be achieved simply from a wider application of existing technology. After nearly a decade of foot dragging, EPA should fulfill its Clean Air Act mandate to control toxic emissions from mobile sources and their fuels by adopting regulations to require cleaner fuels at the pump, expand the use of modern emission controls on old diesel trucks and non-road gasoline engines, and increase the number of intrinsically clean, advanced technology vehicles, such as hybrid-electric cars, on the roads.

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