Proposal may improve hazardous waste cleanup

Research leads to more precise method of analyzing coal tar and related pollutants



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," said Associate Professor of Civil and Environmental Engineering Catherine Peters.

Professor 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 under-estimate risks and has proposed a new approach that has attracted significant attention from environmental regulators.

Focusing on polycyclic aromatic hydrocarbons

Professor Peters' 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 cleanup 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," Professor Peters said, "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.

Accounting for all

"We need to account for the entire mixture, but in a more manageable way," Professor Peters said. 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, Professor Peters said.

Professor Peters' policy paper has generated more requests for reprints than any of her purely scientific work. The attention has been gratifying, she said, 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 policy makers is a very important place for scientists to be, but sometimes it's uncomfortable. There's something very comforting about the science."

Work at interface of science, technology

It's no coincidence that Professor 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 one of the more traditional engineering disciplines really defines how I look at all engineering problems," Professor Peters said.

After a two-year postdoctoral fellowship at the University of Michigan, she came to Princeton as an assistant professor in 1994; she received tenure in 1999.

In the coming years, Professor 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 said, 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.

Measuring microbes' response to pollution

Professor 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 speculated, 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 asked. 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 is 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 Professor 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."