Proposal may improve hazardous waste cleanup
By Steven Schultz
Before World War II, towns and cities all
through the country had plants that made gas from
coal, fueling the industrial economy and ensuring
decades of environmental hazards.
The byproduct of these coal gas plants was coal
tar, a complex mixture of chemicals that seeps
through the ground and pools onto the bedrock,
where it may or may not foul the water supply for
many years.
"The standard disposal procedure for coal tar
was simply to dump it out back," says Associate
Professor of Civil and Environmental Engineering
Catherine Peters.
Peters has devoted the last six years to
studying coal tar and related pollutants and has
developed an improved approach to assessing and
cleaning up such hazardous waste sites. Based on
research into the chemical properties of these
materials, she has shown that previous assessment
methods can either over or underestimate risks and
has proposed a new approach that has attracted
significant attention from environmental
regulators.
Aromatic hydrocarbons
Peters's work focuses on polycyclic aromatic
hydrocarbons, which are found in creosote, diesel
fuel and other petroleum-derived materials as well
as in coal tar.
A dilemma for people trying to clean up these
messes is that the contaminant is far from
homogenous; it usually contains a wide range of
chemicals that pose different risks and require
different cleanup strategies. Some chemicals, for
example, are very carcinogenic, while others are
less so but much more likely to spread and come in
contact with people.
"A lot of work has been done understanding
individual pollutants," says Peters, "but not when
they exist as very complex chemical mixtures --
which is often the case."
A standard approach for cleanups has been to
focus on removing just one or two chemicals --
those judged to be the most toxic or most mobile --
out of the hundreds of compounds present. Another
has been simply to reduce the overall level of
aromatic hydrocarbons, regardless of what they are.
Neither approach assures that risks to humans and
the local ecology have been minimized, and
sometimes such methods overstate the risks.
"We need to account for the entire mixture, but
in a more manageable way," says Peters. Her
solution is based on years of her own research into
the nature of these chemicals, which revealed that
they could be divided into groups with similar
characteristics. In a 1999 paper published in
Environmental Science and Technology, she
proposed a new policy that involves dividing the
chemicals into classes, depending on a range of
factors from their solubility in water to their
carcinogenic risk.
The categories allow regulators to view the
risks in a more nuanced way, while avoiding the
impractical task of analyzing each chemical. By
looking at the relative contribution of a
manageable number of categories, regulators could
design a more effective -- and possibly more
economical cleanup plan, says Peters.
No coincidence
Peters' policy paper has generated more requests
for reprints than any of her purely scientific
work. The attention has been gratifying, she says,
but also a little awkward because she is often
asked to give opinions about questions she has not
thoroughly investigated. "Talking to the public and
to policymakers is a very important place for
scientists to be, but sometimes it's uncomfortable.
There's something very comforting about the
science."
It's no coincidence that Peters' work has come
to the interface of science and policy. Her 1992
PhD from Carnegie Mellon University is a joint
degree that met the requirements of two
departments: civil engineering and an
interdisciplinary department called engineering and
public policy.
"I think that having studied public policy in
conjunction with more one of the traditional
engineering disciplines really defines how I look
at all engineering problems," says Peters.
After a two-year postdoctoral fellowship at the
University of Michigan, she came to Princeton as an
assistant professor in 1994; she received tenure
this year.
Creation of biosensors
In the coming years, Peters hopes to nudge
public policy a little further by taking an even
more inclusive view of the risks posed by hazardous
waste sites. Environmental protection, she says,
has traditionally focused on minimizing the direct
impact that pollutants have on human health.
Relatively little attention has been devoted to
assessing the overall impact on the ecosystem, from
microbes to plants to animals.
Peters hopes to measure ecological impacts with
the help of microorganisms. The way microbes
respond to pollution in their environment might be
a good indicator of changes in general ecosystem
health, she speculates, adding that some of the
biochemical stress responses in microorganisms are
similar to those in humans.
"Do certain pollutants evoke measurable stress
responses, and what type of responses do they
evoke?" she asks. To find out, she plans to use
tools of modern molecular biology, to create
"biosensors" that detect chemical or behavioral
changes within the microbe communities. The
prevalence of certain microbial genes or proteins
might tell scientists how the ecosystem in faring
and give clues about how to approach cleanup
efforts. Biosensors also might report more relevant
or detailed information about the quantity and
identity of pollutants in a particular
location.
As with Peters' earlier work, her goal is to
drive the policy ideas with the force of rigorous
research.
"It's one thing to say pollution is having an
effect, but if you can come up with a firm
quantitative understanding of the impact -- an
understanding that does not narrowly focus on human
health -- that gives us a better place to stand
when we talk about the effect of the environment on
the ecosystem."
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