"We have to reduce the exposure of people to diesel exhaust"

Daniel Greenbaum , president and the chief executive officer of the US-based Health Effects Institute, has done pioneering work on the health effects of air pollution. During his recent visit to India, he spoke to Chandrachur Ghose on a wide range of issues concerning public health

Published: Monday 15 October 2001

Why was Health Effects Institute (HEI) established?
hei was founded in 1980 to conduct research on the health effects of air pollution and help policymakers to evolve strategies to tackle this problem. The us Environmental Protection Agency (usepa) and the worldwide motor vehicle industry fund us on the grounds that they can use the research to take decisions. Independent experts, who are top scientists, constitute the board of the organisation.

In the 1980s, the truck industry, for instance, was being regulated for the first time and they viewed the regulation process with suspicion. At the same time both the epa and the industry were frustrated because they had spent a lot of time debating over the health effects, but could not do much about the problems. So the heads of the automobile companies and the head of the epa took thisinitiative to establish hei .

What are the institutional mechanisms that help you to be unbiased in your research, despite getting 50 per cent funding from the industry?
To maintain our individuality we don't take or recommend specific policy positions or decisions. But we do try to communicate with all sides -- sponsors, environmental non-governmental organisations, government officials and others. We also have a standing research committee comprising experts from top institutions around the world, who devise strategies and select investigators from among international competitors.

There is growing concern over the combined effect of a mixture or combination of pollutants on human health, particularly in countries like India. What are your findings?
Our general priorities at the moment worldwide are air pollution mixtures. We have funded a lot of work on criteria pollutants, like particulate matter, sulphur dioxide, oxides of nitrogen, ozone and also air toxics. Now, we have moved a little bit beyond that. These pollutants remain important but we're trying to begin with a very difficult topic -- a mixture of air pollutants, especially in different settings to see whether the effects are additive or synergistic. A reassessment of the Harvard six cities study and the American Cancer Society study (which had found a correlation of particulate pollution with mortality) shows that taking other pollutants into account in the model did not effect the original findings much.

HEI has laid special importance on studying the health effects of diesel. How would you summarise the current status of scientific knowledge about the health effects?
In terms of cancer, there are over 30 studies worldwide of workers exposed to diesel exhaust that have found a relatively small but close association between exposure to diesel exhaust and increased risk of lung cancer. This has led a number of national and international agencies like World Health Organisation (who), usepa , International Agency for research on Cancer (iarc) and others to classify diesel exhaust as a "probable" human carcinogen.

In terms of non-cancer effects, the data has focused on two areas: First, diesel particles are a component of particulate matter in the environment, which have been associated in a number of studies with increased levels of premature mortality, respiratory and other hospitalisations, and incidence of diseases in children.

Second, a small number of preliminary studies in adults and children have suggested that diesel exhaust can significantly exacerbate a person's response to allergens in the environment. hei has launched a new set of intensive studies to examine the strength and nature of these effects. These studies clearly show that we need to reduce exposure of people to diesel exhaust.

What conclusion would you draw for Delhi where the particulate pollution level is among the highest in the world?
If we take studies done in the West and apply the results to Delhi, you would find an amazing number of people are dying prematurely due to air pollution. It is possible that's happening, but it would be very difficult to know if that's true. If the health effects at different levels of pollution increase linearly and higher levels just lead to more and more deaths and illnesses that would be a matter of concern. However, there are a number of air pollution studies which suggest that as you get to the higher levels, the corresponding health effects do not have the same proportion.People's bodies work in the same way in the us as in India. Despite these similarities, there are differences. People have different diets, life expectancies and face different diseases. Therefore, there could be different scale of effects -- it could be worse or it could be lower.

Do you think that the new aftertreatment systems for diesel engines being developed can curb the adverse health effects of diesel exhaust?
We have funded some research into this in the past. The trap technology changes very rapidly. It has got better over the years. There are, however, two issues we have to continuously watch out for. One of them is the regeneration process of the particulate trap, That is, burning and cleaning up of the trapped particles. Depending on the nature of regeneration there can be dramatic periodic explosions in emissions. This can have significant health effects.

The second issue is related to the technology that is used to regenerate the traps. Some use fuel additives to lower the regeneration temperature. For instance, cerium is in use in France now. When we use such technologies, we have to be careful about whether or not we are adding something new that might create new problems. We have just concluded a study on the use of cerium in diesel fuel with particulate traps. We found that though cerium might not have significant health effects, but if used in all traps, there would be an increase in the background levels of cerium in the soil and in the air. Though cerium is not very toxic, it is important to be careful.

We need to make sure that we do not go down the mtbe (methyl tertiary butyl ether) path of thinking that something is a perfect additive. mtbe as an oxygenate for petrol was good in some respects, but created new problems, like contaminating groundwater.

In many countries, gaseous fuels have come up as alternatives to conventional liquid petroleum fuels. What role will gaseous fuels play in future?
It is really impressive to see the degree to which Delhi is trying to take action against air pollution. Though Delhi is now leading the world in the converting its vehicles to a gaseous fuel like compressed natural gas (cng), there have been similar initiatives in many parts of the us and Europe, albeit on a much smaller scale. This is partly because of conflicting uses of cng . It's a bit difficult to imagine where all these things are going to go because it is linked with the energy policy -- as to where you want to use clean fuels.

Even as we reduce the emissions from motor vehicles, both particles and ozone pollution from other sources including coal-fired power plants remain. For example in the us , one of the challenges in moving to cng or a gas-based fuel for vehicles is that there is a competing and very strong pressure to put the cng into the power plants in place of coal to clean up the power sector, which is probably less controlled in the us than anything else. From the health point of view, a study on comparative estimate of emissions from different fuels and their health effects would be very helpful not only in India but for other places also.

What do you make of health studies done in India? And what are your suggestions for designing epidemiological studies in India, which has a great diversity in its population?
We haven't seen all the health effects studies but are familiar with just some of them. My sense is that there are only a handful of studies on air pollution and their impacts on human health.

But, there are challenges in doing such studies here, like getting access to datasets. You need to get some access to somewhat confidential personal health records. The air pollution data also need to be collected on a daily basis.

Experience in the us shows that air pollution does not go away after five years of action. It will continue to be an issue as India grows. You may also find problems in other sources you know about. Therefore, the building of a health database needs to be long-term investment.

You could get cooperating researchers working in hospitals in major cities to start building cohorts (sample groups of people with common traits) of people from among those who are coming into the hospital and also those who are not coming into the hospital and design the studies using same protocols and definition (for instance, what is a respiratory admission), using the same techniques of analysing the air pollution data. This will help to compare the rate of hospitalisation at certain levels of pollution in these cities, for instance. This will also give the opportunity to look into the question of threshold. For instance, you might notice more hospital admissions per unit of pollution in a city like Delhi with higher levels of pollution than with a city with lower levels, or even you might not.

What according to you are the important issues in the transition to CNG in Delhi?
We must find out how transition becomes smoother, how the technologies installed can become stronger and more durable. Then you can make natural gas a success. For those who have been trying to get these kind of fuels in lots of other places, it would be great to see this effort succeed dramatically. Obviously it still has some way to go. But at the same time it drives other technologies to become cleaner.

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