A
150-foot-high garbage dump in Colombia, South America, may have new
life as a public park. Researchers at the University of Illinois have
demonstrated that bacteria found in the dump can be used to neutralize
the contaminants in the soil.
Jerry
Sims, a U of I associate professor of crop sciences and
USDA-Agricultural Research Service research leader and Andres Gomez, a
graduate student from Medellín, Colombia, have been working on a
landfill called “El Morro” in the Moravia Hill neighborhood of Medellín,
which served as the city dump from 1972 to 1984. In that period,
thousands of people came to the city from the rural areas to escape
diverse social problems. There was no housing or employment for them, so
they made a living picking up trash from this dump and built their
homes upon it.
“There
are some frightening pictures of this site on the Internet,” said Sims.
“At one point, close to 50,000 people lived there. They grew vegetables
on the contaminated soil and hand-pumped drinking water out of the
garbage hill.”
In
recent years, the Colombian government decided to relocate the people
to different neighborhoods with better conditions. Then they decided to
see if it was possible to clean up the area and turn it into a park.
Unfortunately, the most reliable solution—digging up the garbage and
treating it—is not economically feasible in Colombia.
Another problem was that there were no records of exactly what was in the dump.
“Apparently,
hydrocarbon compounds were one of the main sources of contamination,”
said Gomez. “Phenyls, chlorinated biphenyls, and all kinds of compounds
that are sometimes very difficult to clean up.”
Three
professors from The National University of Colombia in Medellin—Hernan
Martinez, Gloria Cadavid-Restrepo and Claudia Moreno—considered a
microbial ecology approach. They designed an experiment to determine
whether bioremediation, which uses biological agents such as bacteria or
plants to remove or neutralize contaminants, could be used to clean the
site.
Gomez,
who was working on his master’s thesis at the time, collaborated with
them. He was charged with finding out if there were microorganisms
living in the soil that could feed on the carbon in the most challenging
contaminants.
This
was not a trivial task. As Sims explained, “There are maybe 10,000
species of bacteria and a similar number of fungi in a gram of soil.”
Gomez’s
work was further complicated by the fact that the material in the hill
was loose and porous with air spaces and voids that resulted from dirt
being thrown over layers of garbage. Because of the unusual physical
structure and the contaminant levels, it was unclear if the indigenous
bacterial community would be as complex, and thus as effective at
bioremediation, as those normally found in soils.
Gomez
analyzed bacteria at different depths in the hill down to 30 meters. He
found microbial communities that appeared to have profiles typical of
bacteria involved in bioremediation. The communities seemed to contain a
robust set of many organisms that could be expected to weather
environmental insults or manipulations.
Gomez
then came to Sims’s lab at the U of I on a grant from the American
Society for Microbiology to perform stable isotope probing, a test to
link diversity and function that he was not able to do in Colombia.
Contaminants are labeled with a heavy isotope that serves as a tracer
that can be detected in the end products of biodegradation.
His
results confirmed that the bacterial communities had, in fact, been
carrying out bioremediation functions. In collaboration with assistant
professor of microbial ecology Tony Yannarell who assisted with the
microbial diversity analysis, he determined that the organisms involved
changed at every depth.
Based
on these results, the Colombian government decided to go ahead with the
bioremediation project using the indigenous organisms. One of the
professors who worked on the pilot study is looking at ways to provide
the microorganisms with extra nutrients to speed up the process. Another
project takes a phytoremediation approach, which uses plants to absorb
heavy metals.
Gomez
has gone back to his first love, animal microbiology. While he was at U
of I, he met animal sciences professor Bryan White and is now working
on a Ph.D. studying the microflora of primates.
The
study “Characterization of bacterial diversity at different depths in
the Moravia Hill landfill site at Medellín, Colombia” by Andres M.
Gomez, Anthony C. Yannarell, Gerald K. Sims, Gloria Cadavid-Resterpo and
Claudia X. Moreno Herrera was published in the Journal of Soil Biology
& Biochemistry, 2011.
Source: University of Illinois
