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Bill Burton at (847) 491-3115 or e-mail [email protected]
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If you've ever tried and failed at keeping an aquarium at home, you may have done this experiment yourself: After the last fish died, you didn't bother cleaning out the tank for a while.
Before long, a green, slimy algae coated the gravel bottom and started climbing the walls. At this point, you probably grabbed the scrub brush and abandoned your study of ecological succession. But for environmental engineer Kimberly Gray, this is when things just begin to get interesting.
Down in the basement of the Technological Institute, an array of huge tanks gurgles and hums under grow lights. Gray, associate professor of civil engineering, is showing off an elaborate system she spent two years developing to model a reach of a shallow stream. With just a few inches of water and a wall-to-wall carpet of green algae, her six-foot-long tanks look far worse than the relatively pristine ecosystem thriving in your rec room. In fact, her algae aren't just ugly, they're toxic: she laces them with PCBs.
"We're simulating what happens to a chemical released into the environment," Gray says. "Where does it go, how does it change ecological structure?"
The contaminant she studies -- a notorious family of related compounds called polychlorinated biphenyls -- is one of particular concern.
"PCBs are very prevalent industrial compounds linked to all sorts of bad effects including birth defects and cancer," she says. "They quit producing them in the mid-1970s, but they're highly persistent and continue to leak from existing sources. They don't go away. We're trying to show that even natural processes of burial in sediments in rivers don't remove them."
Most researchers studying PCBs have looked at lakes, and how PCBs get into fish, Gray says. They haven't systematically worked their way up from the sediment, and they haven't looked at rivers. Gray's approach is to ask how PCBs get taken up by the algae -- which become an entry point to the food web and eventually to humans.
"We're trying to understand how PCBs get into the biological compartment and then work their way up a food web," Gray explains. "We go out in the field, we bring some of this stuff back, and we grow it. We inject it with PCBs and look at how much goes into the slimy stuff, how much stays in the water, how much goes into the sediment and how much into the air."
The highest concentration is in the algae, Gray says, because algae contain a lot of fat, and like most pollutants, PCBs are fat-soluble and don't like water. "We're trying to understand the link between the chemistry of this chemical and its biological effects -- and then assess what kind of feedback the biological effects have on the chemistry," she says.
The artificial stream, with its custom-designed, 500 gallon-per-minute pumps and heat exchangers, serves as an important intermediate-scale model of these chemical and biological processes, Gray says. "In the field, you can't control things enough to understand cause-and-effect relationships between a particular set of variables. And in the laboratory, just on the bench, you can't simulate conditions realistically enough to be able to truly study them," she says. "We do some work on the bench, and then we have these intermediate-scale experiments, and then we link those observations to what's going on in the field."
Now that Gray and two of her students, Ph.D. student Jill Kostel and McCormick freshman Nate Turner, have completed the preliminary studies that establish the artificial stream as a useful experimental system, they're setting out to make it more complicated. Among the variables they will be adding to the mix are temperature variation and grazing of the algae by snails.
"We're trying to couple this experiment to a site in Wisconsin, and we're going to take sediments contaminated with PCBs and metals from the site, and look at how these little critters come in and re-colonize and mobilize the pollutants out of the sediments," she explained. "In this case we will be looking at the combined effects of metal and organic pollutants."
Adding layers of complexity in this manner, rather than dissecting out individual things, is the essence of Gray's method. "I always couple things. My work is very integrative," she says. "Maybe it's a feminist approach."
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