THE HAZARDS OF DIESEL EXHAUST

The Port of Houston Authority’s plans for the Bayport Terminal Complex raise several serious environmental concerns. The Bayport Terminal Complex is a 1,050 acre major marine terminal project slated to open in July, 2001. The complex will be located five miles south of the existing Barbours Cut Terminal, immediately south of Shoreacres and completely surrounding El Jardin del Mar on two sides. The dual container and cruise terminals are expected to receive 7,060 trucks per day, adding to the air and noise pollution from the port and to traffic congestion as well. The most threatening impact of the surge of traffic from these trucks is their diesel fuel emissions.

Most heavy-duty equipment is powered by diesel fuel instead of cleaner burning gas because diesel engines are more durable and energy efficient. Diesel fuel, sometimes referred to as oil distillate No. 2, comes from crude oil, but is a heavier fraction than gasoline. The two produces different emissions when burned; diesel engines can emit up to 100 times more particulate matter (PM) than comparable gasoline engines [2]. The exhaust from diesel engines is a complex mixture of vapors and fine particles. Unburned fuel and lubricant components, products of incomplete combustion, engine wear, or trace contamination of the fuel and lubricant oil all contribute to such pollutants in the exhaust as carbon monoxide (CO), nitrogen oxides (NO_x), oxides of sulfur (SO_x), volatile organic compounds (VOC), particulate matter (PM), aldehydes, ketones, sulfates, cyanides, phenols, metals and ammonia.

Diesel exhaust, the ubiquitous black smoke that can be seen streaming out of large trucks, has recently been getting a lot of attention. The Natural Resources Defense Council (NRDC) launched a Dump Dirty Diesels Campaign with the ad slogan in 1996: "Standing behind this bus could be more dangerous than standing in front of it." After eight years of research, the California air resources board (CARB) finally declared the soot, or particulate matter, from diesel exhaust to be a cancer causing pollutant. CARB also identified forty chemicals found in diesel exhaust as toxic air pollutants. The U.S. Environmental Protection Agency (EPA) is currently conducting its own study of the health impacts of diesel exhaust. They have already introduced new regulations reducing allowable emissions from heavy duty trucks and buses. The new standards, however, will not be applied until 2004 and only to 2004 and later model vehicles.

Diesel exhaust can cause a number of health impacts, which are listed in Table 1. The exhaust contains some known carcinogens and hazardous materials. Arsenic, benzene and nickel, are known carcinogens among many other suspected carcinogenic components of diesel exhaust. The exhaust contains 38 other components that are hazardous pollutants listed by the EPA. (compared to the 40 recently identified by the CARB) including suspected carcinogens benzo[a]pyrene, 1,3-butadiene, and formaldehyde. The exhaust itself is listed as a probable carcinogen by the EPA, NIOSH (National Institute for Occupational Safety & Health), and IARC (International Agency for Research on Cancer).

There is plenty of evidence from studies with rats and mice that diesel exhaust is carcinogenic. However, it is listed only as a "probable carcinogen" because the ubiquitous nature of diesel exhaust makes human carcinogenicity extremely difficult to prove. Diesel exhaust is very strongly linked with lung cancer, especially for people who are occupationally exposed. Higher incidences of bladder cancer from occupational exposure to diesel exhaust have also been suggested but are still not proven. In addition to concerns over cancer, diesel exhaust has also been identified as a mutagen. Biochemical changes are induced or intensified in cells by mutagens, radiation being a famous example.

Table 1: Possible Health Effects of Diesel Exhaust

The EPA and Harvard School of Public Health as well as other experts in public health estimate that particulates in the air are responsible for at least 60,000 premature deaths in the U.S. each year [1]. Researchers believe majority of the health risk from diesel exhaust is caused by PM, which can carry many harmful organics and metals. The PM averages 0.1 to 0.25 microns (1 x 10 ^-6 meters), with 75 percent of particles less than 1 micron. This is a size range easily inhaled, resulting in possible lung cancer or non-cancerous lung damage. The particulate matter also, like other forms of air pollution, has the greatest impact on children, asthmatics, and the elderly.

Non-cancer toxicity from chronic exposure to diesel exhaust causes such respiratory ailments as airway restrictions, reduced pulmonary function, and immunological and allergenic reactions. This is much like the effect of smoking cigarettes, however, the inhalation of diesel exhaust is involuntary. Acute exposure can cause tissue irritation and permanent respiratory damage. Exposure and sickness from diesel exhaust is usually hard to pinpoint, since affected people can exhibit cold-like symptoms of headache, runny eyes and nose, nausea, and asthma-like responses. Exposure usually occurs directly through breathing exhaust, though particles can deposit on skin as well. Once inside the body, the pollutants are absorbed through tissue to the bloodstream and eventually are excreted as other toxins in the body are.

In addition to the health effects discussed above, most of the pollutants from diesel exhaust are regulated by federal air standards called NAAQS (National Ambient Air Quality Standards). The standards were set up by the 1970 Clean Air Act to protect public health and welfare. Today, NAAQS put limits on the concentration in the air of CO, NO₂, SO₂, PM, Hydrocarbons excluding methane, Ozone, and lead. When areas, such as Houston-Galveston for example, exceed these concentrations of air pollutants, they are said to be non-attainment areas and the state must create a plan (SIP -state implementation plan) to reduce pollutant concentrations below the NAAQS.

Air emissions of diesel exhaust are more than just another air pollution issue. Diesel exhaust can deposit onto water, soil, and vegetation, contaminating anything it comes into contact with. It contributes to global warming because it contains the greenhouse gases methane and carbon dioxide and fine carbonaceous PM. Diesel exhaust also contributes to acid deposition because it contains nitric and sulfuric acids and other substances which can be transformed to acidic PM in the atmosphere. The NO_x portion of diesel emissions also contributes to ozone (O₃) formation and eutrophication of coastal waters (spurring algae to bloom to such an extent that the algae blocks sunlight from aquatic life beneath the surface). The contribution of NO_x to the formation of ozone is significant in the Houston-Galveston area because it is a non-attainment area for ozone air pollution standards. Ozone in the troposphere (caused by pollution), as opposed to stratospheric ozone (the good ozone) has been known to exacerbate asthmatics and increase hospital admissions on high ozone concentration days.

Exhaust emissions come from mobile sources, stationary area sources (oil & gas production and industrial), and stationary point sources including industrial, electric utilities, and commercial-institutional sources. From mobile sources, heavy duty engines emit 60 percent of NO_x, 17 percent of hydrocarbons, and close to 90 percent of total particulate emissions [3]. The following Figures 1 -3 show the sources of NO_x, VOCs, and CO in the Houston-Galveston area in 1993. From these figures, it is apparent that mobiles sources in this area contribute to a significant amount of the total NO_x and CO pollution, 31 and 57 percent respectively.

Figure 1 - 3: 1993 NO_x, VOC, and CO emissions in the Houston-Galveston area

Though diesel emissions in Texas have not been studied extensively, California has analyzed its own diesel exhaust problem extensively. In 1990, approximately 3.3 billion gallons of diesel fuel were burned in internal combustion engines in California, producing almost 58,000 tons of highly respirable diesel exhaust. Motor vehicles emit ~ 70% of diesel exhaust particular matter (PM) in California in 1990. A study in Vienna, Austria showed that diesel exhaust comprised 12 - 33 % of total PM in the air. Knowing this, one can easily ponder whether it’s safer to stand in front of a truck or behind it. Diesel exhaust is a serious threat to public health.

[1] NRDC’s Dump Dirty Diesels Campaign: The Facts on Fumes in New York City, 5/96.

[2] Williams, Paul T., G. E.. Andrews, and Keith D. Bartle, 1987, The Role of Lubricating Oil in Diesel Particulate and Particulate PAH Emissions, Society of Automotive Engineers, Inc.

[3] Regulators, Engine Makers Agree on Plan to Begin Reducing Diesel Emissions in 2004, Environment Reporter, 1995, p. 565.

[4] Volkswagen, 1989, Unregulated Motor Vehicle Exhaust Gas components, Volkswagen AG, Research and Development (Physico-Chemical Metrology), Project Coordinator: Dr. K.-H. Lies, 3180 Wolfsburg 1, F. R. Germany.