Technique reveals chlorinated hydrocarbons

Jan. 17, 2002 at 2:24 PM
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PRINCETON, N.J., Jan. 17 (UPI) -- An X-ray bombardment technique, used for the first time to detect chlorinated hydrocarbons in plant and soil samples, shows the natural substances routinely form in decaying plant material but appear to be non-toxic at the levels at which they occur.

There is great concern about man-made chlorinated hydrocarbons, such as many pesticides.

Chlorine that normally occurs in plant material, in the form of a salt such as sodium chloride, used almost universally as table salt, provides the chlorine for the reaction.

The study used very high energy X-rays to bombard a soil or plant sample and then passed the rays that were deflected through a spectroscope. The presence of different chemical substances gave different readings.

The research was done by Satish Myneni, an environmental chemist working at Princeton University in Princeton, N.J., and at Lawrence Berkeley National Laboratory in Berkeley, Calif.

Previous work showed relatively small concentrations of chlorinated hydrocarbons in plant material. Myneni's work shows chlorinated hydrocarbons occur at a much higher level than was known.

The X-ray analysis application Myneni pioneered will allow much more extensive analysis of soil samples for chlorinated hydrocarbons because the technique does not require elaborate sample preparation, some of which can affect experimental outcomes.

Identifying compounds in soil or plant material is very difficult because of the extreme complexity of the material.

"When we're doing an experiment in the lab, we can identify chlorinated compounds pretty easily; it's a piece of cake," Myneni told United Press Interntaional. "We can use gas chromatography methods and things like that. But the problem is when you are bringing a leaf sample or a soil sample or any of the natural samples, the heterogeneity is so high it is very difficult to detect them."

While the x-ray approach has been used before, this is the first time published work reports the technique has been used to analyze chlorinated hydrocarbons in soil and plant samples.

"What this study shows is that we have to think about this a lot more because organochlorines are extremely reactive and they are there in all the soil and all the top soils all over the place that means they may be doing a lot of interesting reactions that we don't know about," Myneni said.

The results are published in the journal Science and avaiable on the Web site.

One expert on chlorine's use and hazards, Joe Thornton, told UPI that Myneni's work was very interesting scientifically but added, "I don't think it has much bearing at all on what we know about the hazards of industrially produced organochlorines and what we need to do about them."

"The fact that some chlorinated hydrocarbons are produced in the soil doesn't have any impact on our judgment about the impacts on health and the environment of worldwide pollution by dioxins and PCBs, pesticides and other organochlorines and the need to find and implement alternatives to those hazardous substances," he said.

Thornton teaches biology at Columbia University in New York City and is the author of "Pandora's Poison: Chlorine, Health and a New Environmental Strategy," (MIT Press).

While a number of experts acknowledged the novel quality of the work and regarded it as very valuable, they also questioned the quantitative aspect of the results Myneni obtained.

Donald Macalady, professor of geochemistry at Colorado School of Mines in Golden, told UPI: "The exciting part of that paper is the application of that technique to the new materials and the fact that it enables you to look at chlorine in a variety of different organic materials. Where I part company a little bit with (Myneni) is I think he made an attempt to make some quantitative statements that I don't think were justified.

"I'm not trying to say this (work) isn't remarkable. It is remarkable and I think it's a wonderful application," Macalady told UPI, but added he wondered if it would be possible to refine the technique to get more quantitative results.

Myneni said he has found levels of chlorinated hydrocarbons in decayed plant matter in the range of about 50 milligrams per kilogram of soil sample. According to Macalady: "No one has ever found anything anywhere near that high. If that were true that would be rather amazing."

Macalady wondered if some of the sites chosen were remote enough to be free of airborne contamination. Macalady said it could be a problem if people use Myneni's work to say, "'So, you found trace organic chlorine, that doesn't necessarily mean it's anthropogenic (man-made).

Professor William Casey, a geochemist at the University of California in Davis told UPI: "This is not a brand new result, but his very elegant method is a real advance."

Casey, in a commentary accompanying the article, said "it remains unclear whether the organic molecules are really progressively chlorinated during humification (weathering)."

Casey thinks the entire result is dependent upon the ratios of chloride ion to chlorinated hydrocarbons that show up in Myneni's results and does not show absolute amounts of chlorinated hydrocarbons.

But Myneni told UPI the criticism of his work -- that it is impossible to quantify his results -- is incorrect. He said the techniques he used do give quantitative results which leave little doubt the inorganic chlorine is converting to chlorinated hydrocarbons.

(Reported by Joe Grossman in Santa Cruz, Calif.)

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