Louisville, Kentucky, has some of the worst air in the country. Given the city is a transit hub, tens of thousands of planes, trucks, and trains pass through the city each year, not to mention all the cars. Louisville is also an industrial center where chemicals are manufactured. Heart disease, strokes, asthma and other conditions caused by excessive pollution are found at very high levels. Last year, the city received a failing grade from the American Lung Association in its annual report.
In order to see if trees can help combat the negative health impacts of the city’s deadly air pollution, University of Louisville Medical Center, the Nature Conservancy, Hyphae Design Laboratory and other organizations are coming together in the Green Heart project, the first clinical trial where “nature is the pharmaceutical.”
According to the Nature Conservancy, “this ambitious effort will conduct a first-of-its-kind medical study by planting trees in strategic locations across a cluster of Louisville neighborhoods and observing precisely how they impact residents’ health.” The study is financed by the National Institutes of Health and Louisville-based philanthropies.
Dr. Aruni Bhatnagar at the University of Louisville Medical Center and his colleagues, who essentially created the field of “environmental cardiology,” are doing a controlled experiment to test the impact of nature, as if it was a drug, on a neighborhood scale.
The challenge is “a neighborhood is not a laboratory, where variables are easily controlled. And this project would be far beyond the scale of prior research that identified connections between neighborhood greenness and health.”
Bhatnagar said: “there has never been a rigorous scientific study that quantified the health effects of urban greening. This will be the first attempt to understand, is nature a viable, replicable therapy?”
This past October, the project has its official launch, with a community workshop and the start of baseline data collection. “Temperatures, particulate matter levels, volatile organic compounds in the air will all be tracked by a network of more than 50 passive air monitors as well as more elaborate monitoring arrays mounted on towers and even an electric car.”
Starting next fall, some 8,000 trees, shrubs, and other plants will be planted in South Louisville, according to a map devised by the Nature Conservancy, based in data on where likely impacts will the greatest benefit. As has been noted, trees catch small particulate matter in their leaves, reducing nearby air pollution by a third in some cases; and, if planted near highways, they can act as a buffer, reducing pollution by up to 60 percent.
The Green Heart project is now recruiting 700 neighborhood residents to “participate in several rounds of medical tests, tracking the residual evidence of air pollution in their blood and urine.”
The Nature Conservancy writes that “different chemical signals will be monitored, including the presence of cortisol and adrenaline that are produced when the body is under stress. Participants’ physiological reactions to air pollution will be studied over five years, because some compounds appear within hours of exposure while others take months or years to emerge.” Residents are essentially “human environmental monitors,” said Ray Yeager, PhD, a researcher with the University of Louisville Medical Center lab.
At the end of the five year study, the researchers will have a set of data on residents’ health — looking at both before and after the trees were planted, and, for comparison’s sake, data from people who live nearby but didn’t get new trees. It will be interesting to see if five years is enough to test the benefits of trees — newly-planted, young trees would appear to have less capacity to catch particulate matter and serve as buffers than mature, fully-grown trees with broad canopies.
Unhealthy air is estimated to claim 4 million lives a year. If Dr. Bhatnagar and his colleagues discover medical benefits from the strategic tree placements, the results of this study could result in a new public health model that can help reduce urban pollution-related deaths. Yeager is confident: “what we learn in Louisville is going to affect people all over the world.”
If benefits are proven, the study could also positively affect Louisville, reducing health inequities. The Nature Conservancy refers to data showing that life expectancy in the “leafy suburbs” of the city is 13 years longer than in South and West Louisville neighborhoods with lower incomes and less access to nature, proving once again that “zip code is a reliable indicator of health.”
If the results show positive benefits from trees, the city government should first address inequities and partner with local community groups to build robust tree canopies in the neighborhoods that lack them. With solid data, the city could also further invest in the existing urban forest, which loses about 55,000 trees every year.