Why was the California cancer unit risk used?
The California Health Assessment of Diesel Exhaust is one of the most comprehensive documents on health effects of diesel to date. California was able to establish a single unit risk factor for lung cancer attributable to diesel particulate matter (soot) of 3 X 10-4 (3 in 10,000). A single unit risk factor makes it easier to convey risks to the public. EPA has stated that diesel PM is a likely carcinogen, but chose to express the risk of diesel in a possible range of 10-3 to 10-5 (1 in 1,000 to 1 in 100,000) in its 2002 Diesel Health Assessment. California’s unit risk falls within the range of risk established by EPA. Whether California’s or EPA’s estimate of possible cancer risk, based on current air concentrations of diesel PM, the majority of the population in the U.S. are exposed to unacceptable cancer risks from diesel PM.
