Study Focuses On How Plants Help Toxic Pollutants Travel Around The World

August 05, 1997

BUFFALO, N.Y. -- The "grasshopper" nature of chemical transport in the environment will be the focus of tests to be conducted by a UB researcher to determine how plants contribute to the global distribution of toxic organic pollutants.

Keri C. Hornbuckle, Ph.D., assistant professor of civil engineering at UB, has received a prestigious grant from the National Science Foundation to study the effects of temperature, humidity and ultraviolet light on the transport through the atmosphere of persistent organic pollutants.

The project, which has been funded with a $200,000 award over four years by the NSF's Faculty Early Career Development program, will examine how chemicals such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons and pesticides, including DDT, travel around the world.

"My primary interest is how and why concentrations of persistent organic pollutants change as a function of weather conditions," Hornbuckle said.

From research she already has conducted, she added, it appears that concentrations of these chemicals -- probable endocrine disrupters that can cause reproductive harm -- are highest during the warmest part of the day and lowest during the coolest. Hornbuckle hopes her research will show how these chemicals adsorb and volatilize to plant surfaces, "similar to the condensation and evaporation of water," she said.

Testing will take place in a 600-cubic-meter facility located in Ashford, N.Y., south of Buffalo. Owned and maintained by Calspan SRL Corp., the environmental test chamber is one of the largest such facilities in the United States. According to Hornbuckle, retrofitting of the facility will begin this fall, followed by two years of testing.

Originally designed as a military ordnance test facility, the interior of the chamber measures 9 meters in diameter and 9 meters high -- as tall as a three-story building.

"It had been sitting empty for several years, and previously had been used for Department of Defense nerve-gas tests," Hornbuckle said. "We're going to put plants in the system, which has never been done before."

Most environmental test chambers are much smaller, about 5 cubic feet, according to Hornbuckle. Using a chamber of this size will allow her to conduct research in conditions that are very near to natural, with one fundamental difference -- the conditions can be controlled. In the field, the separate importance of temperature, relative humidity and solar radiation (ultraviolet light) are difficult to evaluate because all three factors vary simultaneously and often are dependent upon each other.

"In this, we can control most of the parameters. In a natural system, that gets mixed up. We can avoid some of that using this chamber," she said.

Although the cylindrical chamber is not thermostatically controlled, its ultraviolet lights and air-circulation and air-flow rates can be used to vary temperature. Its environment also can be controlled for humidity.

Before any plants are introduced into the environmental test chamber, the system will be "swept" with ambient -- natural -- air, which then will be tested to determine the amounts of chemicals that already exist in the environment.

"We'll close up the system and measure what's in there, then start varying the concentrations of chemicals in the chamber," Hornbuckle said. These initial tests are designed to see how the walls, which are coated with a Teflon-like material to provide a homogeneous surface, interact with the chemicals being introduced into the system.

The test chamber then will be populated with common house plants that are relatively inexpensive, can easily be replaced and have many individual leaves. The plants' leafiness is important to the research because bark and stems do not store chemicals.

The plants' soil will be covered with a Teflon-like material so no chemicals can be absorbed into the dirt. The number of leaves will be counted and a few will be picked off each plant and tested to determine existing chemical concentrations.

Persistent organic pollutant vapors will be added to the chamber, and the air will be tested for chemical levels by pulling it through ports located in the side of the chamber. Fans will pull the air through cores of polyurethane foam from which the chemicals will be extracted and analyzed by a spectrometer. Fiberglass filters will be used to ensure that no particles get into the foam.

Because the chemicals to be studied degrade so slowly and are believed to have such a negative impact on health, it is important that researchers have a better understanding of how chemicals are disbursed through the atmosphere, Hornbuckle said.

The interaction of persistent organic pollutants with plant surfaces is "very important in predicting how these chemicals travel," she noted.

Over the past 10-12 years, scientists have seen evidence that there is a "grasshopper effect" to the way chemicals travel. Chemicals "volatilize and deposit, volatilize and deposit" until they have spread worldwide, Hornbuckle said. Scientists need to be able to predict how and to where chemicals travel.

"It's not how fast the wind blows. It's how often the chemicals bounce on the surface of the earth," Hornbuckle said.

"In order to decide if we should be concerned whether other countries' outputs -- emissions -- are a problem, we must understand transmission."

It appears that emissions travel from warmer climates to cooler ones, Hornbuckle noted.

"If emissions are not controlled and are produced in warm parts of the globe, they're going to go up to cooler climates quickly. We need to be able to mathematically predict that much better than we are now."

She added that the Great Lakes region is "an important zone for emissions to settle."

While Hornbuckle's primary focus will be on chemicals that are persistent and do not change much, she said her research also may look at photolysis -- how chemicals change in ultraviolet light. She also hopes to combine lab studies with field studies, conducting simultaneous experiments outside the environment test chamber.

University at Buffalo

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