The Effects of Diesel Exhaust Emissions On Cyclists

 

 

Robert W. Derlet, MD

Professor of Medicine

University of California, Davis

 

 

Cyclists who ride on our streets and highways are exposed to diesel exhaust emissions.  Over the past several years there has been an increase in the number of diesel vehicles in California including a disproportionate number of diesel lightweight pickup trucks.  Exhaust emissions from diesel engines are highly toxic.  Several scientific studies have reported that on an equal horsepower basis, diesel exhaust is 100 times more toxic than that from automobiles.1  For example, a 200-horsepower lightweight pickup truck is 200 times more toxic than that of a new mid-sized 100 horsepower car sold in California.  The toxic effects of diesel engines are magnified even further when one considers large trucks with engines in the 400-600 horsepower range.

 

In contrast to gasoline engines, many of the toxic particles emitted by diesels are particulate (PM2.5 and PM10), that tend to be found in the greatest concentration within the immediate vicinity of the street or highway.2  This is in contrast to some other air pollution gases comprised of small molecules.  For example, ozone is usually distributed over a wide area after its formation from nitrate oxides and oxygen.  The concentration of ozone adjacent to a street or highway is similar to that of a forest or open green field one or two miles away.  Therefore, the cyclist who rides on roadways frequented by diesel engines has a higher health risk from the exposure to the particulate matter, than a cyclist along the American River parkway even though ozone concentrations on the bike trail are similar to roadways.  Other toxic substances emitted by diesels in disproportionately higher concentrations include nitric oxides (Nox), sulfur compounds and smaller organic molecules. Recently, more attention has been focused on the hundreds of different types of organic molecules created from the high 20:1 compression ratios standard in diesel engines.  Many of the molecules are highly toxic.  Summarized below are some of the health risks associated with diesel exhaust.

 

A.        Short Term Medical Effects of Diesel Air Pollution

The effects on the human body can be considered as developing short-term, or long term.  Short-term exposure can result in the following:

1.   Decreased quality of life:  Most cyclists deplore having black diesel exhaust sprayed into their faces as they pump up a hill or wait at a traffic light.  Cycling through noxious exhaust fumes in itself detracts from the enjoyment of cycling.

2.   Exacerbation of asthma:  Several medical studies have shown that patients with underlying asthma or other respiratory problems have increased symptoms as a result of diesel exhaust.3  Diesel exhaust particles combine with normal atmospheric allergenic molecules to make those allergens more toxic. In medical terms diesel acts as an “adjunct.”

3.   Infections:  Medical studies have shown the deleterious effect of diesel air pollution on macrophages the cells providing first line of immune defense in the lung.4  Macrophages that have been exposed to the same concentrations of diesel toxins inhaled by humans have the ability to fight bacterial infections severely restricted.  This results in increased rates of bronchitis , pneumonia, and airborne viruses such as the flu and common cold.

4.   Difficulty breathing:  Even if a cyclist does not have asthma, they may notice difficulty breathing when cycling through high concentrations of diesel exhaust.  Toxins in the exhaust interfere with air exchange by causing inflammation of lung tissue.5

5.   Direct effects on the heart:  Increased heart attacks:  Medical studies have demonstrated that acute high levels of air diesel pollution increase the number of patients sustaining acute myocardial infarction.6  

B.         Long Term Exposure

Long term exposure over many months or years results in many serious effects of a person’s health.  These include:

1.   Cancer:  Diesel air pollution causes cancer.7,8  Very small particles (PM2.5) are loaded with carcinogens and are absorbed into the body through the lungs.  It is clear that the lung is the most susceptible organ facing the front line of air pollution.  However, numerous other cancers including breast, bowel, brain, pancreatitis, and leukemia may be associated with cancer.  The toxic materials such as volatile organic compounds and nitrites may circulate throughout the body.

2.   Inhibited growth of lung tissue in children: A recent study in The New England Journal of Medicine compared the growth and development of lungs over a 10 year period in polluted vs. non polluted areas.9  Of the substances measured in the low growth group, most were emitted by diesel engines.

3.   Destruction of lung tissue:  Destruction of lung tissue over the years leads to emphysema, restricting physical activity and ultimately leading to death.  Many substances contribute to lung tissue destruction.  Ozone is formed from nitrate oxides, which diesel engines emit in disproportionately higher amounts compared to catalytic converter equipped gasoline engines.  In addition to ozone, many of the hydrocarbon molecules emitted by diesels destroy lung tissue. 

4.   Heart disease:  Atherosclerosis is accelerated from the chemicals emitted from diesel engines.10  Atherosclerosis of the coronary arteries results in heart attacks, and in some cases death.

5.   Hypertension:  Increase of blood pressure has been reported in persons residing in high pollution areas when other factors are accounted for.1  A recent study reported an increase between infant mortality and particulate air pollution in the Europe.

6.   Effects on brain cells:  Animal models have shown a negative effect on brain cells and neurofunction from diesel particulate matter.10  Volatile hydrocarbons are rapidly absorbed into the central nervous system.  Effects on learning abilities in children are of great concern. Coordination, memory and judgment may be effected.  Residents in highly polluted areas have brain inflammation that leads to degeneration of brain cells.10

7.   Early deaths:  An association between diesel air pollution and premature mortality has been well established.1  Above and beyond the mortality caused by diesel induced cancers and lung disease.11

8.   Birth defects:  More than a dozen studies in the United States, Brazil, Europe, Mexico, and South Korea have linked diesel to low birth weight, premature births, still births, and infant deaths.12  A recent study at UCLA found that pregnant women examined between 1987 and 1993 were three times more likely to have children with birth defects than those who lived in non-diesel polluted areas.  This was despite the fact that virtually the entire time of the study, the L.A. area met federal standards.

 

Measuring the Toxicity of Polluted Air:  The AQI

The Air Quality Index (AQI) is reported daily through the news media.  An AQI is calculated from each of the many toxic chemicals in the air, including ozone, nitrate oxides, PM2.5, carbon monoxide, or sulfates.  Technically, the actual AQI reported should be derived from the chemical with the highest AQI.  Unfortunately, not all compounds are easily monitored, and news media usually reports only the ozone AQI.  For example, on a winter day in Sacramento the ozone level may be so low as to calculate an AQI of say 35.  However, the PM2.5 the same day may be in such high concentration as to equate an AQI of 150. Yet the AQI will still be reported as 35, and people may have a false sense that the air is not polluted.

 

Conclusions:  Cyclists should avoid streets and highways that have high volumes of diesel powered vehicles.  Alternative routes on less polluted roadways will benefit the health of cyclist. Advocating for bike pathways away from streets provides even greater benefit.

 

 

REFERENCES

1.         Sydbom A, Blomberg A, Parnia S, Stenfors N, Sandstrom T, Dahlen SE.  Health effects of diesel exhaust emissions.  Eur Respir J 2001, 17(4):733-46.

2.         Kagawa J.  Health effects of diesel exhaust emissions –a mixture of air pollutants of worldwide concern.  Toxicology 2002, 181-182:349-53.

3.         Proietti L, Spicuzza L, Polosa R.  Urban air pollution at the crossroads of the allergic pandemic.  Ann Ital Med Int. 2003, 18(2):64-72.

4.         Harrod KS, Jaramillo RJ, Berger JA, Gigliotti AP, Seilkop SK, Reed MD.  Inhaled diesel engine emissions reduce bacterial clearance and exacerbate lung disease to pseudomonas aeruginosa infection in vivo.  Toxicol Sci 2004, October 13 (Epub ahead of print).

5.         Holgate ST, Sandstrom T, Frew AJ, Stenfors N, Nordenhall C, Salvi S, Bloomberg A, Helleday R, Soderberg M.  Health effects of acute exposure to air pollution.  Part I:  Healthy and asthmatic subjects exposed to diesel exhaust.  Res Rep Health Eff Inst. 2003, 112:1-30; discussion 51-67.

6.         Peters A, von Klot S, Heier M, Trentinaglia I, Hormann A, Wichmann HE, Lowel H; Cooperative Health Research in the Region of Augsburg Study Group.  Exposure to traffic and the onset of myocardial infarction.  N Engl J Med 2004, 351(17):1721-30.

7.         Lee WJ, Baris D, Jarvholm B, Silverman DT, Bergdahl IA, Blair A.  Multiple myeloma and diesel and other occupational exposures in Swedish construction workers.  Int J Cancer 2003, 107(1):134-8.

8.         Jarvholm B, Silverman D.  Lung cancer in heavy equipment operators and truck drivers with diesel exhaust exposure in the construction industry.  Occup Environ Med 2003, 60(7):516-20.

9.         The effect of air pollution on lung development from 10 to 18 years of age.  N Engl J Med 2004 351(11):1057-67.

10.       Calderon-Garciduenas L, Reed W, Maronpot R, Henriquez-Roldan C, Delgado-Chavez, Calderon-Garciduenas A, Dragustinovis I, Franco-Lira M, Aragon-Flores M, Solt A, Altenburg M, Torres-Jardon R, Swenberg J.  Brain inflammation and Alzheimer’s-like pathology in individuals exposed to severe air pollution.  Toxicol Pathol 2004, 32(6):650-8.

11.       Peters A, Pope CA.  Cardiopulmonary mortality and air pollution.  Lancet 2002, 360:1184-1185.

12.       Urban air pollution linked to birth defects.  J Environ Health 2002, 65(2):47-48.