CHEMICAL weapons leave behind some distinctive fingerprints at the scene of the crime. As deadly as they are, most such weapons are also relatively easy to detect. Think of a spoonful of sugar, spilled over a square yard of ground. If the sugar were a nerve agent, it would be enough to kill an average adult.
Now think of a cube of sugar, split into a million parts. Then divide each of those million parts into a million more. Scientists, using modern techniques, can detect a particle of nerve agent that small.
The distinctive chemical ``signature'' of many chemical weapons could play an important role in verifying compliance with a chemical weapons treaty. Each time chemical agents are manufactured - and, more important, each time they are used - they leave behind traces that are to a chemist what fingerprints are to a detective.
If and when a treaty outlaws the manufacture, stockpiling, and use of chemical weapons, there will be little room for disagreement over whether a specific chemical compound is weapons-grade material - and therefore covered by the treaty. Even a minuscule sample of a suspect chemical, in the hands of a specialist, can yield evidence of a treaty violation.
That's why Marjatta Rautio describes herself as a ``political chemist.''
SHE is coordinator of the Finnish Project on the Verification of Chemical Disarmament, headquartered here in Helsinki.
And Professor Rautio knows that her work is as much diplomacy as it is chemistry.
Because of the work of this unique research project, the world already has a detailed data base on how to identify a wide variety of chemical weapons with a remarkable degree of precision.
Finland is a neutral nation. It has no chemical weapons, and is not a member of the Conference on Disarmament in Geneva, the 40-nation group trying to hammer out a treaty banning chemical warfare.
Still, that has not prevented Finland from making a singular contribution to chemical disarmament. The verification project has churned out a comprehensive series of volumes detailing the makeup of known chemical warfare agents and the laboratory procedures to identify them.
The project has also created a computer data base of the chemical characteristics of warfare agents, so that researchers around the world can tap into a standardized reference library of data.
The project is a joint effort of the Finnish Ministry of Foreign Affairs and the University of Helsinki. Some private companies have also supplied equipment and computer time.
Moreover, many of the chemical researchers involved in the project are volunteers. Only seven of the 35 staff members are paid by the government; the rest donate their time in hopes that their work will promote chemical disarmament.
``The binding glue is the satisfaction people get from the results. And that's pretty good compensation - better than [a] salary,'' says the project director, Prof. Jorma Miettinen.
High-tech tracking techniques
SOME of the work has been pioneering. Researchers have perfected techniques for analyzing gas-mask filters, soil, plant materials, and chemical mixtures for the presence of warfare agents. The suspect chemicals are then tested in a variety of equipment, such as gas chromatographs and mass spectrometers. Resulting graphs show distinctive peaks and valleys that are compared with a data base of known warfare agents.
Mobile sampling laboratories can perform these sophisticated analyses in the field.
``We can get identification in 30 minutes,'' project coordinator Rautio says. ``It's quite a good fingerprint of the material.''
Some of the field tests are on the order of a search for a needle in a haystack.
For example, researchers released about 10 pounds of a nontoxic agent, which simulates the nerve agent Sarin, in the air over the center of Finland. Special sensors were able to detect the substance 200 kilometers (125 miles) away.
In another test, researchers placed only 10 milligrams - about one-fourth of a drop - of the nerve agents sarin and soman on a patch of ground outdoors on a day in late April. When they collected air samples above it, they found that the presence of soman could still be detected after 11 days, and sarin after seven days.
These tests have the benefit of reassuring diplomats that the illegal use of chemical weapons can, in fact, be detected. And they allow engineers to make detection devices more accurate.
But the Helsinki Verification Project has found that even state-of-the-art monitoring techniques have limits. For one thing, it's clear that remote-sensing devices, by themselves, cannot reliably verify that a specific plant is not producing chemical weapons.
``Detecting production requires verification on the spot,'' Professor Miettinen says; ``in other words, a visit.''
Moreover, Ms. Rautio says, it's clear that a plant can switch back and forth between producing commercial chemicals and warfare agents with relative ease - in some cases, within 24 hours.
``We can analyze all the samples,'' she says. But to find every facility that's capable of making such chemicals depends upon inspection and verification mechanisms. ``To say we can discover all hidden stockpiles - well, we can never say that.''
And, she adds, so-called ``novel agents'' - exotic chemicals such as snake venom - cannot be precisely identified with present-day techniques.
Still, Miettinen sees the possibility of a treaty that would have a feasible verification procedure: ``Modern science can provide all the necessary techniques, if the treaty is politically sound and allows us to do it.''
``It is quite feasible to ban chemical warfare,'' he concludes.