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Feat
of
Clay
rowing up near the McKenzie River in western Oregon, I often wandered to the water’s edge
to skip stones or run my fingers through the ripples and think. I valued the river both as a
refuge of tranquility and a means of exploration. From its banks, I watched great blue herons
fly, and fish grow and migrate. When I moved to the relative metropolis of Portland, I brought
with me a curiosity about the natural world, a delight in water, and a desire to preserve the environment.
I discovered an outlet for my curiosity in independent
science research projects, required at my school beginning in
sixth grade. Invariably, I chose to focus on biology. When I participated in an International Collaboration Project on wetlands
conservation in the summer after seventh grade, I discovered
the junction between microbiology and water science that I
would incorporate into all my subsequent research projects.
For my eighth-grade science project, I investigated the effects
of different stimulant compounds on the speed with which
bacteria break down environmental pollutants. I won one of
Paul Reynolds under Creative commons
G
by Laurie Rumker
I set out to identify a potential
problem with organoclay
that instead turned out
to be a possible strong
suit of the material.
seven discretionary prizes at the 2007 Discovery Channel Young
Scientist Challenge for my research, as well as for my performance in the competition challenges.
A Problem with the Solution?
I continued my research on bioremediation in ninth grade, but
found that going further with the stimulant research would
require me to work with a dangerous pollutant and to use
expensive gas-chromatography analyses. In tenth grade, my
teacher introduced me to organoclay, a manufactured claybased product used in water systems to contain contaminants
in underlying sediments. Organoclay was in use in Oregon’s
Willamette River, which cuts through the heart of downtown
Portland and is a hub of public activity. On the riverbank, at the
site of a wood-treatment company that operated from 1944 to
1991, creosote had leeched into the soil, flowed under the water,
and threatened to rise into the river. Large mats of organoclay
were incorporated into a 23-acre sand cap laid on the sediment
to prevent the pollutants from getting into the water. Placed
directly upon contaminated sediment this way, organoclay mats
contain pollutants while naturally occurring bacteria eliminate
the dangerous compounds, a process of biodegradation called
natural attenuation.
As I examined the chemical mechanism organoclay uses
to contain pollutants, I found a hole in the research that had
been conducted on organoclay prior to its use in the Willamette
River and at other sites around the world. Though many studies
highlighted the interactions between bacteria in the sediment
and the pollutants being contained, none addressed interactions between microorganisms and organoclay itself. Was it
possible that the organoclay could be biodegraded?
Premises and Puzzles
Because of my previous work with biodegradation by microorganisms, I recognized the similarity between straight-chain
hydrocarbon compounds, which are biodegraded by many
bacteria found in sediments, and surfactants—chemical compounds within organoclay that allow the material to contain
pollutants. If the organoclay surfactants were eliminated by
biodegradation, the pollutants could rise into the river.
Although it appeared that no one had examined this
before, the chemistry-based logic behind my research premise seemed reasonable. In an experiment, I added a surrogate
pollutant—a red dye less dangerous to work with than PCBs
or PAHs (such as creosote)—to organoclay. I then exposed the
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Jan/Feb 2011
Right: Laurie used diagrams to plan
her experiments. Left: To avoid
contamination, Laurie worked under
a biological fume hood.
organoclay to three strains of hydrocarbon-degrading bacteria that had been isolated from lake sediment. I submersed
the clay and bacteria in a carbon-limited nutrient solution,
which would force the bacteria to use the organoclay surfactant as a carbon (food) source. If the bacterial population
increased, I would know that the microorganisms were
biodegrading the organoclay.
But this was not the case. My spectrophotometric analyses
demonstrated full retention of the dye by the clay, no bacterial growth, and therefore no biodegradation. Skeptical that
the result was due to the bacteria’s inability to degrade the
surfactant, I conducted follow-up experiments to test other possible explanations: settling of crystallized dye during centrifugation, contamination of
the microbial inoculum with a strain incapable of degrading hydrocarbons,
and the death of bacterial cultures prior to inoculation. When none of those
appeared to have occurred, my conclusion became clear.
Contrary to my hypothesis, my project had evidenced no degradation.
I brought it to competition anyway, emphasizing the premise and thinking
that went into developing my hypothesis and experimental design. Much to
my amazement, I won second place in Environmental Management at ISEF
2009 and first place in Environmental/Earth and Space Sciences at the 2009
National Junior Science and Humanities Symposium.
A Change of Approach
I did not give up on the possibility of organoclay biodegradation. The potential consequences were too grave to dismiss the prospect after testing it from
only one angle. For my junior year research project, I decided to isolate the
specific part of the organoclay—the surfactant—that I thought would be
susceptible to biodegradation. However, isolating the surfactant from the clay
presented some challenges. The positively charged ions on the surfactants
that hold them to the clay, which has a slight negative charge, are themselves
toxic to bacteria. Once I determined a concentration of surfactant that didn’t
inhibit the growth of the bacteria, I modified the nutrient solution so the
surfactants were the only available carbon source. And voilá! Surfactant
biodegradation!
Why didn’t the biodegradation of the isolated surfactant translate to biodegradation of the surfactants within intact organoclay? After a follow-up study
incorporating both intact organoclay and isolated surfactant, I hypothesized
that the organoclay contained too high a concentration of surfactant for the
bacteria to tolerate. Thus, organoclay did not appear susceptible to biodegradation in the near term. However, over time, some surfactants dissociate from
organoclay and dissipate into the sediment at lower concentrations. As microorganisms in the surrounding sediment develop a tolerance to organoclay
surfactants through interaction with those dissociated surfactants, long-term
organoclay biodegradation does appear possible.
www.cty.jhu.edu/imagine
But I realized that long-term organoclay biodegradation could actually
have positive implications for the environment. If, after the contained pollutants had been eliminated by natural attenuation, the organoclay itself
was biodegraded, then only empty clay would be left where dangerous
compounds once posed a serious health hazard. That prompts a question I
need to address in further research: whether the pollutants or the organoclay
intended to contain them will be eliminated first.
Compared to the common solution of wholesale dredging removal,
organoclay appears to be a viable, less-invasive solution for dealing with
certain pollutants in sediment, and a possible option for remediating damage
in the Gulf following the recent devastating oil spill. However, it is important
to monitor the organoclay over time to ensure that pollutants don’t seep
through due to surfactant biodegradation.
A Matter of Perspective
I set out to identify a potential problem with organoclay that instead turned
out to be a possible strong suit of the material. While I had confirmed my
null-hypothesis my first year, my project was acknowledged for its premise,
rather than its result. Everything depended on perspective, something I try
to keep in mind in my research.
I also learned the value of skepticism. When I persisted and ultimately
did find degradation in my second year’s research, I won first place in
Environmental Management at ISEF 2010 and a $25,000 Davidson
Fellowship. Most importantly, though, I realized that we cannot take our
resources—nor the solutions engineered to protect them—for granted.
CTY alumna Laurie Rumker is a senior at Oregon
Episcopal School in Portland, OR. When she’s not doing
scientific research, Laurie enjoys playing for her school’s
varsity soccer and lacrosse teams, studying classical piano
and singing in choir and a cappella groups. She is also a
member of the Portland Leadership Team for Run for
Congo Women, which raises sponsorships for Women for
Women International.
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