Asthma and Diesel Soot"There's a man who lives a life of danger, Acute exposures, such as running an engine in a closed space, are known causes of asthma attacks. But what about chronic lower level exposure, like riding in a car? Could asthma-causing immune system changes develop over a long period of time as a result of air quality in cars? Note: this article is not intended as scientific analysis or medical advice. Its purpose is to alert readers to an unsuspected asthma and allergy causing hazard. We take driving for granted, doing it from cradle to grave, often feeling more threatened by our TV imagery than the real risk we are taking. Those of us with a predisposition to allergies and asthma need to look carefully for asthma causation. I remember coming over the pass into the Los Angeles basin for the first time. The year was 1967. It seemed like there was a forest fire, the sky was black. Emissions controls imposed over the years have made the visibility and color better, but that improvement is in some ways a deception. Coarse particulate matter in the air has declined during those years, but levels of invisible fine particulate matter (less than 2.5 micron size), are still health threatening. One source of fine particles is vehicle exhaust. It is impossible for asthmatics to avoid exposure to these inflammation causing fumes. Diesel engines move over three million commercial vehicles in America. Many of these motors are decades old, accumulating as many as a quarter million miles annually. Maintenance is often delayed until a failure occurs. Top end overhauls, which include rebuilt injector nozzles, are easiest to forgo. But scarred and unclean injectors waste fuel, which pours out unburned, a gray-white color instead of the usual black. Asthma Cocktail: Shaken, not StirredThe toxic, sooty cocktail from truck stacks is a well-known health hazard. Multiple studies have associated diesel emissions with tumor genesis. Particulate matter, commonly referred to as soot, is made up of small carbon particles covered with many types of toxic molecules. Fine particles act as carriers of these carcinogenic compounds into the body. Ultrafine particles, less than .1 micron in diameter, make up over 80% of soot (by numbers, not weight). These are lung penetrators, able to slip through the network of hairs and natural filters in the airways. Experts disagree on whether the carbon core or the molecules stuck to it are the real causes, but regardless of the actual mechanism, these particles are dangerous to everyone, especially those with asthma. Ultrafines cause inflammation and scarring of the small sacks in the lungs (alveoli). Such a particle with Mercury or Cadmium on its surface will provoke immune cells to abandon the search for viral or bacterial invaders, attacking the toxin carrier instead.
Particulates and AsthmaFine particulate, known to be an asthma trigger, may also cause immune system changes which worsen or induce asthma. Studies find a relationship between asthma attacks and proximity to major roadways. The closer to a major highway, the more serious the asthma. It appears that diesel exhaust can cause allergic sensitization. Sulphur dioxide and Nitrogen dioxide gasses can directly instigate the inflammatory response. However it is particulate matter which invades tissues that really reorganizes the immune response, predisposing the person to asthma. Evidence suggests that chronic exposure to truck exhaust particles at low concentrations causes increased expression of cytokines, chemokines, and production of IgE antibodies. These mediators of inflammation are the essence of allergy and asthma. Add oxidant stress in airway tissues, and you have a precursor state to asthma. Fine particulate can even cause an increased response to normal allergens, increasing IgG mediated long term asthmatic and allergic reactions. These changes take place over time, so it's never too lateto evaluate the environment in your car cabin. Fumes build up in tunnels or on construction sites where unregulated off-road diesels work. Truck engines are not designed for prolonged idling, and much unburned vapor permeates the areas near truck stops. EPA recently adopted strong air borne emissions standards fornewly manufactured diesel engines. This reduced demand for new trucks, with many overhauls of existing fleets. It will be at least 2030 before emissions are reduced. Since moving to Houston, I try to drive only when traffic is light, like first thing |
