Arsenic has an Accomplice?
Research reveals the toxin that contaminates wells may get
assistance from a newly discovered microbe
They live a dark, unassuming existence,
going about their quiet, microscopic lives in underground waterways. But
now University of Maine researchers are questioning whether the
lifestyle of these microbes is inadvertently poisoning our groundwater,
contaminating it with elevated amounts of arsenic.
In the laboratory, UMaine environmental engineer Jean MacRae and a team
of researchers have isolated a previously unknown species of bacteria.
Given the right conditions, the microbes can speed up the normally slow
chemical processes that release arsenic from bedrock into groundwater.
If confirmed through additional research in the field, MacRae's findings
could contribute to our knowledge about how arsenic gets into Maine's
groundwater.
The possible breakthrough comes none too soon. Arsenic is a naturally
occurring chemical element in rock and soil — the 20th most common in
the Earth's crust. Bedrock is one of the most significant sources of
arsenic in water, as demonstrated in research by UMaine scientist Andrew
Reeve and other geologists. In addition, arsenic contamination can come
from manufactured products such as treated wood and pesticides.
Knowing how arsenic seeps out of Maine's bedrock and into wells could
help landowners keep it out of the water, MacRae says, and could aid in
reducing a long-term health threat.
At high levels in drinking water, arsenic can kill quickly; at lower
levels, it can cause cancer of the skin, bladder, kidney, lung and
liver, and it can affect blood circulation. Even at very low levels, new
evidence suggests that arsenic can affect reproduction and contribute to
diabetes.
MacRae's interest in the toxin stems from her awareness of just how
severe the problem can be. In Bangladesh, millions of people suffer from
health problems caused by drinking arsenic-laced water. According to the
World Health Organization, more than 200,000 people could die of
arsenic-related cancers in Bangladesh.
In Maine, arsenic levels in some wells are similar to those found in
South Asia, but the problem is far less widespread. Nevertheless, the
State Drinking Water Program estimates that 10 percent of homes with
private wells have unsafe levels of arsenic in their water. Instead of
being evenly spread out across Maine, these homes tend to occur in
clusters, such as the Bayside community in Northport, and along Green
and Branch lakes near Ellsworth.
"Arsenic levels are high in parts of Maine, and they are hard to explain
in terms of the geology," says MacRae, who this year was awarded a
National Science Foundation Career Award in support of her research.
"One home may have a high level, while a neighboring home is low. That
made me think that we have either a patchy situation where the geology
is affecting (the levels), or we've got different cultural practices and
land uses that make it a problem in one area and not in another."
While the bulk of arsenic research has focused on geology, the role of
bacteria has remained largely unexplored. "Everywhere we look there's an
important role for microorganisms in cycling (elements) in the
environment. I think the likelihood of microbial involvement in cycling
(arsenic) in the subsurface is great. Chemical reactions in the
environment happen slowly, but you can get things to speed up if you add
some microbial action," says MacRae, who combines her engineering
expertise with a master's degree in microbiology.
With a grant from the U.S. Geological Survey through UMaine's Senator
George J. Mitchell Center for Watershed and Environmental Research,
MacRae and Kevin McCaffery, a master's student, collected water samples
in 2001 from two wells with high arsenic levels, one in Bayside and the
other near Ellsworth.
In the lab, they isolated some bacteria that could have an effect on
arsenic compounds in the water, transforming a less toxic form into a
more toxic, mobile form. The next step is to prove bacteria are making
this transformation in the environment.
This year, MacRae received a $375,000 five-year grant from the National
Science Foundation to continue her research on bacteria and arsenic.
Working with her will be engineering graduate students Ingrid Lavine and
Erin McCormick. They will work respectively on refining techniques to
identify the presence of arsenic-transforming bacteria and to determine
what factors affect the rate of leaching. MacRae also is planning to
involve public school students and teachers in using the subject for
meeting Maine's Learning Results goals in the classroom.
In addition to contributing knowledge about how arsenic gets into
groundwater, MacRae may be breaking new ground in microbiology. When she
and McCaffery took a closer look at the identity of the Northport
bacteria species, they found that it was not described in the scientific
literature. The species they found is new to science.
Geochemists and microbiologists are increasingly teaming up to consider
the role that microbes play in the environment. For MacRae, such
collaborations offer the potential for solutions to environmental
problems. "I got interested in environmental engineering because it was
closer to finding a solution that would happen in my lifetime," she
says.
"Once you get a sense of how things are actually working in the
environment, then you have more angles on how to fix a problem. If we
find that these organisms are responsible for speeding up the release of
arsenic from bedrock or from the groundwater environment, then we can
start looking at land-use factors, such as septic field maintenance or
the addition of manure to fields," she adds. Under some circumstances,
such activities could promote the growth of bacteria underground and
make a small arsenic problem worse.
by Nick Houtman
November-December, 2002
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