Diesel may be the most commercially viable fuel at present, but one that raises serious doubts on the future of urban health. Sundeep Salvi of Air Pollution Research Group, Southhampton, UK, talks to Sarita and Chandrachur Ghose on the magnitude of the problem
What is the latest information on adverse health effects of diesel exhaust?
Over 200 epidemiological studies conducted in different geographical locations of the world have shown a significant and consistent association between diesel emissions and increased deaths and cardio-respiratory illnesses such as heart attacks and strokes, allergies, asthma, bronchitis and respiratory tract infections. Short-term exposure to diesel exhaust has been shown to produce various damaging effects on the respiratory tract, while chronic high dose exposure has been linked to a significantly increased risk of developing lung cancers.
Is there a safe level of exposure to pollutants emitted by diesel vehicles?
In a test recently, we exposed healthy and mild asthmatic human volunteers in a specially designed exposure chamber to levels of diesel exhaust that are routinely found in cities like Delhi, Kolkata and Mumbai. We noted the changes that occurred in the lung tissue at the molecular and cellular level and found that a single one or two hour exposure to diesel exhaust produced a strong inflammatory response in the airways. This effect was similar to that produced during an acute bronchitis infection, as well as a mild systemic inflammatory response in the blood.
Researchers from the us have shown that a single instillation of diesel exhaust particles in the nose produces adverse effects on the nasal mucosa and increases the risk of developing allergies significantly. Therefore, even single short-term exposures to diesel exhaust have shown adverse effects, both on the human lung and nose. Moreover, adverse effects to particles in the ambient air have been observed at all levels, even those which are currently believed to be safe according to World Health Organisation (who) guidelines.
I, therefore, do not think that there is a safe level of exposure to pollutants from diesel.
Which diesel exhaust component is the most dangerous to human health?
Over 40 chemicals in diesel exhaust are considered toxic air contaminants responsible for adverse respiratory effects. Many components such as benzene, arsenic, dioxins and formaldehyde are known carcinogens, while toluene and dioxins are known reproductive toxicants. However, the organic fraction, which represents up to 60 per cent of the total mass of the particle seems to be responsible for the major toxic effects on cells that are present in the lung. Amongst these, the hydrocarbons (polyaromatic, aliphatic and nitroaromatic) seem to be the most likely candidates. Transition metals such as iron, nickel and vanadium that are generated during combustion of diesel fuel have also been regarded responsible for toxic effects, mainly due to generation of reactive oxygen species. However, more work still needs to be done in this area to identify if there are any other components that are responsible.
There is a growing trend of dieselisation of the automobile fleet in Europe and India. How do you view its effects on health?
In Europe, there are very strict legislative bodies that make sure that levels of pollutants emitted from motor vehicles are well within acceptable limits. Emission levels are regularly reviewed by the authorities. Vehicular checks are also carried out strictly. Moreover, public awareness on the adverse effects of pollutants from motor vehicles is high. Therefore, it is likely that levels of diesel exhaust pollutants are kept well within safety standards in forthcoming years. In India, on the other hand, there does not seem to be any effective legislative action on vehicles that churn out gallons of black smoke. Vehicles are poorly maintained and often the diesel fuel is mixed with kerosene which increases the levels of particles emitted. All these factors will certainly cause further increase in levels of diesel exhaust emissions.
Why does the diesel lobby insist on creating doubts over the carcinogenic effects of diesel on humans?
Clearly diesel engines are the most efficient power plants amongst all internal combustion engines. Banning diesel vehicles from coming on the roads will significantly affect the economy of any nation. When so much is at stake, creating doubts in the minds of people about the serious adverse effects of diesel exhaust is not difficult.
To what extent would reducing sulphur and aromatic content of diesel and using particulate traps affect the toxicity of diesel exhaust?
Attempts made to reduce particles from diesel exhaust with the help of particulate traps have been shown to increase emissions of nitrogen oxides. Although newer techniques are being developed to reduce both particulates as well as nitrogen oxides, these are expensive and their efficacy remains to be proven. A research carried out in Sweden recently has shown that reducing particulate matter levels by 50 per cent with the use of aftertreatment particulate traps did not significantly reduce adverse effects on human lungs. Bringing down levels of sulphur and aromatic content in diesel fuel can help to reduce toxic effects of diesel exhaust, although the degree of improvement needs to be further assessed.
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