Gerald Meyer
Scientists looking for ways to clean up a common, persistent type of organic pollutant have developed an approach that not only restores the power of a naturally occurring pollution buster but also boosts it to levels of effectiveness that they can't currently explain.

"It's safe to say that we don't fully understand why this approach works so well, but we'll take it and develop it and figure out the details as we  go," said Gerald Meyer, professor of chemistry in the Krieger School of Arts and  Sciences at The Johns Hopkins University.

The targets of the new technique, developed by Sherine Obare, a  postdoctoral fellow in Meyer's lab, are organohalides, a class of compounds  used in pesticides, pharmaceuticals, and manufacturing.  They pose health  risks to humans and have been linked to environmental problems like ozone  depletion and climate change.

Obare's new approach combines an extremely thin film of titanium dioxide with a compound found in life known as hemin. After exposure to ultraviolet light, the hemin and titanium dioxide can break up organohalides at surprisingly high rates. 

Seventeen of the top 25 organic groundwater contaminants in urban areas are organohalides, according to a 1997 Environmental Protection Agency report.  Organohalides are a class of organic compounds that include a halogen, a group of elements comprised of bromine, fluorine, iodine and chlorine. The  compounds are very difficult to break down chemically. Some instances of  organohalides in the environment today, for example, can be traced back to  the dry cleaning industry of the 1920s and 1930s.

Meyer is director of the National Science Foundation-funded Collaborative  Research Activities in Environmental Molecular Sciences (CRAEMS) Center at Johns Hopkins, which is dedicated to finding ways to deal with the  environmental effects of organohalides. "These compounds play many  important and beneficial roles in the chemical and pharmaceutical  industries, so they're not going away soon, and it's important that we find  ways to minimize their environmental effects," he said.

According to Meyer, scientists have known for decades that hemes, a naturally occurring group of compounds that contain iron atoms, can break up organohalides. The most well-known heme is hemoglobin, a compound in red  blood cells that carries oxygen.

"There's a lot of speculation that hemes in proteins are what cells use to defend themselves from organohalides," Meyer explained.  "We can buy hemes  we don't have to extract them from protein or anything but when you remove them from their naturally occurring environment, you tend to oxidize them."

In their oxidized state, hemes are no longer useful for breaking down organohalides.  Hemes can be re-activated using chemical or electrochemical techniques, but Obare wanted to try using a practical, easily available energy source to power the re-activation: sunlight. She decided to try to take advantage of titanium dioxide's abilities as a photocatalyst, a substance that promotes chemical reactions in other nearby materials when exposed to light.

"I anchored hemin on porous thin films of nanocrystalline titanium dioxide, and when I exposed the system to light, the hemin was activated to a reduced state where it reacted rapidly with organohalides, producing much better results than I expected," Obare explained. "I've even been able to recycle and reactivate the thin films for further organohalide degradation."

Meyer noted that there's still a lot of development work to be done, not the least of which is figuring out exactly how the chemistry of the new system works. But he speculated that scientists might someday be able to insert a similar system in drinking water down a well, for example and 
power the removal of organohalides with sunlight.

Source: John Hopkins University

Our Toxic World: A Wake Up Call by Doris Rapp 
Environmental Medical Research Foundation, 2004

One of the truths about life in the developed world is that we live out our lives enveloped in a sea of chemicals, some of them benevolent to humans and others highly toxic. Man-made chemicals permeate the air we breathe, the water we drink, the foods we eat and almost everything we touch. There is no escaping them completely, but there are ways to reduce exposure, contain the polluters and protect ourselves and our families.

This book diligently documents the chemicals in our environment and the effects they have on our bodies, brains, behavior and sex. From avoiding problem foods and contaminated water to identifying mold and finding a chemically safe home, it also suggests steps that can be taken to avoid the most toxic hazards.