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Harvard Public Health Review/Summer 2002

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Tools of the Trade

There's a right tool for every job, so the saying goes, but in certain areas of public health that tool may not be readily at hand or even exist at all. Consequently, researchers at the Harvard School of Public Health have had to be resourceful in coming up with novel ways to get the job done. By developing new tools for solving previously intractable problems, changing the way research is conceptualized, or expanding possibilities for investigation, they are adding to the arsenal of public health knowledge. Nowhere is this more true than in environmental health. From new methods for measuring exposures in the body to new devices for measuring hazards in the air, the environmental health innovations of School scientists are making our world a safer place to live and breathe.

For Wael Al-Delaimy, a researcher in the Department of Nutrition, it was just a matter of teaching an old technique new tricks. While still a doctoral candidate at the Wellington School of Medicine in New Zealand, Al- Delaimy knew that as early as the 1800s forensic scientists analyzed samples of human hair to detect toxins such as arsenic. He suspected that analyzing nicotine in hair samples could be a cheap and easy method for quantifying second- hand tobacco smoke, with myriad advantages over the techniques already in use.

Smoke wafting from the tip of a lit cigarette contains certain toxins in higher concentrations than the smoke inhaled directly by an active smoker, and evidence of health problems associated with secondhand smoke--from throat irritation to increased risk of lung cancer and ischemic heart disease--is mounting. "For children, the consequences of exposure to secondhand smoke start before they are even born and persist until adulthood," says Al-Delaimy. "Premature birth, low birth weight, sudden infant death syndrome, asthma, lower respiratory infections are just some of the observed consequences in young children." For the last couple of decades, scientists have tested urine samples for the biomarker cotinine, a metabolite of nicotine, to monitor levels of environmental tobacco smoke, or ETS. But the cotinine test only provides information about the previous three to five days of ETS exposure, and collecting urine samples from hundreds of young children is no easy task. Researchers also use questionnaires to gauge long-term levels of "passive smoking," or secondhand smoke exposure. Respondents, however, may not recall every moment spent in the presence of a smoker. Parents may downplay their smoking habits. And such surveys can't account for subtle factors, such as proximity, ventilation, and air flow that can influence nicotine dosage--the difference between a half hour with a smoker down the hall and a half hour with a smoker at the kitchen table.

Giving new meaning to a healthy head of hair, Al-Delaimy's sampling method overcomes many of these problems. After secondhand smoke is inhaled, nicotine circulates through the body via the bloodstream, and small quantities of the toxin are drawn up into shafts of hair. Each centimeter of hair represents over one month of growth and contains toxins from any exposures during that period of time. Easy to collect and store, the samples are ideal for large epidemiologic studies. While Al-Delaimy knew of a preexisting method to isolate nicotine from swatches of hair, the cost of the test was over one hundred dollars per sample--much too expensive from a public health standpoint.

So Al-Delaimy enlisted the help of Graeme Nigel Mahoney, a biochemist, to develop a less expensive, simpler assay, while he designed epidemiologic studies and collected hair samples. Their subjects were young patients at a local teaching hospital. "I became an expert barber," laughs Al-Delaimy. Hundreds of samples were clipped, and questionnaire data was collected on household smoking for each child or infant in the study. At first, Al-Delaimy optimistically estimated that the test would be perfected in just three months. Instead, it took three years of hard work in the lab before the reversed-phase HPLC method was fine-tuned. But the results were worth the wait. Mahoney and Al-Delaimy have shown that the new test is accurate, and it's since led to several groundbreaking studies.

In the spring of 2001, Al-Delaimy and colleagues published a paper showing that avoidance strategies--efforts by parents to minimize their child's exposure to secondhand smoke by smoking in a separate room or outdoors--were unsuccessful. Nicotine levels measured in hair clippings of children whose parents who reported making attempts to protect them from smoke were no lower than those of children whose parents did not make such efforts. "Our work shows that smoking cessation is really the best avoidance strategy," says Al-Delaimy. In another study that garnered national attention, Al-Delaimy and his team examined occupational exposure to secondhand smoke in a cohort of restaurant and bar workers, a population exposed to levels of ETS up to six times higher than that of office workers. The study demon- strated that non-smoking workers employed in smoking-permitted establishments receive doses of nicotine similar to those of active smokers. Both studies underscore the seriousness of ETS as a public health threat, and the latter was cited in the recent policy battle to ban smoking in all indoor workplaces across Massachusetts, including restaurants and bars. Al-Delaimy is now working on adapting the nicotine assay for use on the vast collection of toenail samples gathered in the Nurses' Health Study.

But secondhand smoke may not be the worst thing we're breathing--and finding the right tool to prove it has been a mission for Petros Koutrakis, professor of environmental sciences. Small particles, some as tiny as 1/100th the diameter of a single human hair, drift in ambient air. These particles may include sulfate and nitrate ions and trace metals released in combustion and incineration processes, as well as pollen, bacteria, and viruses. Epidemiologic observations have suggested that frequently occurring high concentrations of inhaled fine particles are responsible for serious pulmonary health effects in those exposed. But scientists in toxicology labs have had little success in replicating such results when exposing test subjects to concentrated artificial particles, which they had generated from pure compounds. Even the particles collected from ambient air, formed in the wild from a melange of toxic compounds, failed to produce significant health effects. It became apparent that the collection process, which removed particles from the air by filtration, and then re-suspended them, fundamentally altered their properties, even changed their size--producing particles quite unlike those found in ambient air.

Enter Koutrakis and his colleagues in the Department of Environmental Health and Engineering, who have developed an instrument to collect and concentrate particles--without transforming them in the process. "The cost of controlling particulate pollution is extremely high," says Koutrakis, "therefore, in order to justify stringent air quality standards, it is imperative that both epidemiologic and toxicological studies provide clear evidence of health effects. We hope that our research findings will enable policymakers to develop cost-effective control strategies to protect public health."

Although he has had a hand in several other innovations in exposure assessment, "the problem of keeping miniscule particles airborne while bringing them to high enough concentrations for conducting laboratory exposure tests was uniquely challenging," says Koutrakis, who labored for over three years at the task. Here's how his invention works. The ambient particle concentrator first removes larger particles from a sample of ambient air. The fine particles and gasses remaining in this sample are then accelerated through several long ultra-thin slits, in parallel, at a flow of several thousand liters per minute. As the air sample hurtles through the acceleration slits, fine particles accumulate in the collection slits below, while the bulk of air, now depleted of fine particles, is shunted off to the side. The process increases the fine particle concentration in the sample roughly three-fold and is repeated twice more at successively lower flows. The particles, ever airborne, are now about 30 times as concentrated as in ambient air and are delivered at a rate of 60 liters per minute. This flow is sufficient to test human or animal subjects. In a final stage, pollutant gasses, such as ammonia, ozone, and sulfur dioxide, can be siphoned off, while the sample is drawn into a built-in exposure chamber. The chamber is maintained at a small negative pressure, which has negligible impact on the test subjects.

In 1994, using the newly perfected ambient particle concentrator, Koutrakis and his team were able to produce, under controlled laboratory conditions, effects on lung and cardiac function similar to those associated with particles in epidemiologic studies. Ambient particle concentrators, constructed in the environmental science and engineering labs at the School, are now in used in Brazil, the Netherlands, Japan, Canada, and at four sites in the United States. The concentrators are mobile--they can be placed in trailers, and transported to sample air at sites of particular concern. Stratospheric chemists, studying minute levels of pollution in the rarified upper atmosphere, have even used the ambient particle concentrator in flight to concentrate stratospheric particles to masses sufficient for analysis.

With new additions to the public health toolkit, researchers like Al-Delaimy and Koutrakis are delivering hard data on heath hazards--the proof desperately needed to transform public health policy and practice. Whether the culprits are lodged in few strands of hair or drifting in the vast expanse of the stratosphere, researchers will invent the tools to track them down--and they'll broaden the possibilities for new inquiry while they're at it. Just give them a little time to work out the kinks.

Zannah Marsh

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