Although there are various types of particulate matter such as smoke from fires that can damage the lungs, diesel particulate matter is of primary concern since it is so widespread. Diesel exhaust is emitted from a broad range of diesel engines; the on-road diesel engines of trucks, buses and cars and the off-road diesel engines that include tractors, bulldozers, locomotives, marine vessels and heavy duty equipment. Diesel particulate matter is part of a complex mixture that makes up diesel exhaust, which consists of gas and particles. The gas component comprises many of the urban hazardous air pollutants, such as acetaldehyde, acrolein, benzene, 1,3-butadiene, formaldehyde and polycyclic aromatic hydrocarbons.
The particle component includes many different types of particles that can be classified by size and composition. The size of diesel particulates that are of greatest health concern are those that fall into the categories of fine and ultra fine. These fine and ultra fine particles may be composed of elemental carbon with adsorbed compounds such as organic matter, sulfates, nitrates, metals and other trace elements.
The most common means of exposure is breathing air that contains diesel particulate matter. The fine and ultra fine particles are respirable which means that they can avoid many of the human respiratory system defense mechanisms and enter deeply into the lung.
How Can Diesel Particulate Matter Affect My Health?
Diesel exhaust causes health effects from both short term (acute) exposure and long term (chronic) exposure, such as repeated occupational exposures. The type and severity of health effects depends upon several factors including the amount of chemical one is exposed to and the length of time exposed. Individuals react differently to different levels of exposure; there is limited information on exposure to just diesel particulate matter but there is enough evidence to indicate that inhalation exposure to diesel exhaust causes acute and chronic health effects.
Acute exposure to diesel exhaust may cause irritation to the eyes, nose, throat and lungs, and some neurological effects such as lightheadedness. Acute exposure may also elicit a cough or nausea as well as exacerbate asthma. Chronic exposure in experimental animal inhalation studies have shown a range of dose-dependent lung inflammation and cellular changes in the lung and there are also diesel exhaust immunological effects. Based upon human and animal studies, there is considerable evidence that diesel exhaust is a likely carcinogen.
At What Levels Should I Be Concerned?
EPA's National Scale Assessment uses several types of health hazard information to provide a quantitative "threshold of concern" or a health benchmark concentration at which it is expected that no adverse health effects occur at exposures to that level. Health effects information on carcinogenic, short- and long-term noncarcinogenic end points are used to establish selective protective health levels to compare to the modeled exposures levels.
Unfortunately the exposure response data in human studies are considered too uncertain to develop a carcinogenic unit risk for EPA's use. There is a 'Reference Concentration' that is used as a health benchmark protective of chronic noncarcinogenic health effects but it is for diesel exhaust and not specifically set for diesel particulate matter which is what was modeled in NATA. The RFC for diesel exhaust, which includes diesel particulate matter, is 5mcg/m3. This value is similar to the National Ambient Air Quality Standard established for fine particulate matter which is 15mcg/m3.
Long-term effects of particulate air pollution on the incidence of bronchitis, emphysema and asthma have been documented. There is an unexpectedly high COPD mortality found in small agricultural communities, which may be in part due to occupational dust exposure. The authors felt that prevention of COPD should start in childhood, with emphasis on infection prevention and the control of indoor pollution. [Environmental Factors and Chronic Obstructive Pulmonary Disease, European Respiratory Review, 1992;2:9; pp.144-148]