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IMAGINE a soldier in battle in the Middle East. An artillery shell lands
nearby with a surprisingly small explosion. The soldier has forgotten to
put on a gas mask and, within half a minute, feels the first signs of nerve
gas: sudden sweating, an urge to vomit, and a cramped feeling in the chest.
What is happening, and what can the soldier do?

There are four nerve agents; tabun, sarin, soman and VX. They kill by
blocking the action of a crucial enzyme called acetylcholin-esterase. This
enzyme breaks down and removes acetylcholine, which transmits nerve signals
to a variety of muscles, such as those controlling breathing and the digestive
system. If nerve agents prevent the enzyme from breaking down acetylcholine
after it causes a synapse to fire, the muscles will be continually stimulated,
causing convulsions, paralysis and death.

Upon feeling the first symptoms of nerve gas, American soldiers are
taught to pull out one of the three Mark I chemical antidote kits that they
carry, and slap it against the side of their thighs. If a soldier is already
unconscious, fellow soldiers are instructed to inject their fallen comrade
with all three of his or her Mark I kits.

Each kit contains two syringes that automatically inject the soldier
with 2 milligrams of atropine citrate and 600 milligrams of an oxime, pralidoxime
chloride. Atropine works by shutting down nerve receptors that are being
overstimulated by an excess of acetylcholine, effectively sedating the muscles.
Too much atropine can be dangerous, however, because it interferes with
normal sweating and breathing. Oximes break the bond between nerve gas and
acetylcholin-esterase, freeing the enzyme to do its work.

Tests with mice, guinea pigs and rhesus monkeys indicate that atropine
and oximes should work. There is much uncertainty, however, as researchers
cannot expose humans to nerve gas in controlled experiments, and no Mark
I kit has ever been used in combat. Researchers at the US Army Medical Research
Institute of Chemical Defense in Maryland were gratified to hear that atropine
helped Iranian victims of nerve gas during their war against Iraq. According
to Lloyd Roberts, a spokesman for the institute, the Iranian forces ‘were
quite desperate’ to receive supplies of atropine.

New antidotes to nerve gas

The institute has developed a drug, pyridostigmine, to boost the effectiveness
of the injections. Before soldiers encounter nerve gases, they would take
the drug in tablets every eight hours. Pyridostigmine inhibits the action
of the same enzyme as nerve gas, but less severely; it binds to acetylcholin-esterase
to save the enzyme from a deadlier bond with nerve gas. Later, the drug
releases the enzyme unharmed.

Army researchers are also working on a true vaccine to nerve gases,
says Roberts. One technique would use genetic engineering to produce an
artificial enzyme similar to acetylcholin-esterase that would mimic the
ability of the natural enzyme to bind to nerve agents. If large amounts
of these ‘scavenger’ enzymes, or monoclonal antibodies, were circulating
in the bloodstream, they would mop up the nerve gas before it got to the
body’s nervous system.

The nerve agents that Iraq has, tabun and sarin, both evaporate rapidly
and so must be inhaled to be effective. If a soldier is wearing a gas mask,
spraying the agents on a soldier’s clothes or skin would not do much damage
because the chemicals would evaporate before the skin absorbed them. One
advantage of these agents for the attacker is that troops can occupy an
area only a few hours after attacking it with poison. Alternatively, armies
can use VX, which is like oil, and evaporates 1000 times less rapidly than
water. This deadly nerve agent leaves an area contaminated for days.

Around 90 per cent of Iraq’s chemical weapons stockpile is mustard gas,
which is easier to manufacture than nerve agents. Mustard damages the DNA
within a cell, setting off a futile and self-destructive attempt by the
cell to repair the damage with a variety of enzymes, which cause the cell
to rupture. If soldiers touch mustard gas, they may not know about it for
a day or more, until their skin breaks out in painful, burn-like blisters.
For warning, soldiers carry strips of paper soaked in chemically treated
dyes. The dyes react to the poisons, turning the paper red if it has touched
mustard, green for VX and yellow for sarin and tabun.

Mustard’s deadly burns

If inhaled, mustard gas is often fatal. There are no antidotes. Injuries
are treated like burns; victims must be flushed with water as quickly as
possible. Mustard gas does not break down quickly; in cool, sheltered areas,
it can remain toxic for weeks. In areas contaminated with mustard gas, which
does not evaporate as quickly as sarin or soman does, armies should move
on. The gas must be washed off equipment with hot water and bleach. The
US Army has developed an alternative flushing agent, known as Decontaminant
Solution 2, or DS2, but tests show that this also corrodes and destroys
as it cleans (This Week, 28 July).

A soldier’s first line of defence is a protective suit, but soldiers
are generally reluctant to put these on. The suit used by US troops has
been redesigned to allow air to pass through it, making it more comfortable
in hot weather, but by most accounts, it is still awkward and hot. If there
is danger of an eventual chemical attack, soldiers would wear the suits,
but without the gloves, boots and gas masks. Chemical detectors set up around
the base would provide some warning of attack.

Iranian soldiers often had gas masks, but their beards made it more
difficult to ‘get a good seal between the mask and face’, says Roberts.
They also lacked protective clothing, leaving them vulnerable to mustard
gas.

The American suit has an outer layer of water-repellant cotton and nylon,
and an inner layer of foam and nylon that has been impregnated with charcoal.
The outer layer is supposed to repel liquid chemicals, and any poisonous
vapours that get through are absorbed by the second layer. The full suit
weighs about 5.5 kilograms.

The Army recently added a diaphragm to its mask that amplifies the voice
of the person inside. This followed the results of an experiment in 1987
that showed that only 64 per cent of the words spoken by people wearing
masks were understood.

American forces practise at the US Army’s National Training Center in
the Mojave Desert, California. These exercises typically include a segment
in which the troops are expected to fight in protective suits. Wearing the
full suit in the desert was ‘unbelievably horrible’, recalls one tank driver.

For American troops in Saudi Arabia, the chemical threat will be from
the air. Iraq relied on aircraft to drop bombs full of mustard and nerve
gas on Iranian troops and Kurdish civilians. US forces will try to shoot
down military aircraft before they can drop bombs. Artillery would have
to be within 20 or 30 kilometres of the target.

Iraq has Soviet-built missiles with a range of 500 kilometres, but none
has been used to deliver chemical weapons. According to Gordon Burck of
the Federation of American ¿ìè¶ÌÊÓƵs, long-range ballistic missiles are
not the most efficient way to deliver chemicals. A missile would carry a
large quantity of chemical agent, but would have difficulty spreading the
chemical over a wide area because of the speed it travels at. Releasing
the chemical at a high altitude would waste it, and a powerful explosion
at a lower altitude could destroy the agent, says Burck. Bombs that glide
slowly to earth or cruise missiles that travel slowly would be better at
spreading chemicals over a large area.

According to Matthew Meselson of Harvard University, who has studied
the military uses of chemicals for the US Arms Control and Disarmament Agency,
chemical weapons are generally ineffective against a prepared military force.
The combination of gas masks and protective clothing offers adequate protection.
In a closely-fought battle, even the side that fired the chemical weapons
would have to wear protective gear, since the gas could easily blow back.
Civilians without protective clothing are the most likely victims of chemical
warfare.

A more serious threat to the American troops in the Middle East could
be the biological weapons that some analysts think Iraq has been developing
for at least two-and-a-half years. Weapons capable of spreading typhoid,
cholera and anthrax are among those believed to be under development in
laboratories south of Baghdad, near the village of Salman Pak. They would
be about 160 times as deadly by weight as chemical agents, and American
troops are ill-equipped to deal with them.

American defence experts, however, are uncertain of the current military
capability of Iraq’s biological weapon programme. Production plants and
weapons are smaller and less conspicuous than those for chemical agents.
Anthrax bacteria spores must be delivered as wind-borne particles (aerosols)
so that they can be inhaled, but the experts say that Iraq does not have
the equipment needed to deliver them in this form by air. It is easy to
contaminate the food or water supply with typhoid or cholera bacteria, but
this would not affect American troops who have their own supplies.

Limited military usefulness

The US Army is trying to develop new vaccines using recombinant DNA
technology to fend off the threats of biological weapons. But, for the moment,
its soldiers must make do with ‘the immunisations that troops normally receive
when deployed’, says an army spokesman. These would include typhoid and
cholera vaccinations for the Middle East, but not an anthrax vaccination.

With the anthrax vaccine currently available, a soldier would receive
a series of shots and would develop short-lasting immunity only after several
weeks. The vaccine would cause unpleasant side effects, and is not practical
for rapid troop deployment. ‘Anthrax immunisation is not standard policy,’
says Anna Johnson-Winegar, a scientist at the Military Disease Hazard Office
at the US Army Medical Research and Development Command in Maryland.

A new vaccine, which is being tested in animals, would be faster acting
than the present vaccine, and require only one injection, says Johnson-Winegar.
Other vaccines, against Q fever, smallpox, a viral disease called chikungunya,
Rift Valley fever virus, junin virus and a family of encephalitis viruses,
are also being developed.

Accelerating developments in biotechnology have led some American analysts
to fear that rogue scientists may be creating exotic and deadly organisms
against which there is no defence. A new Genetic Engineering and Biotechnology
Research Centre was recently opened in Jadiriyah-Baghdad. But Raymond Zilinskas,
a scientist at the Centre for Public Issues in Biotechnology at the University
of Maryland, doubts that Iraq has the know-how in biotechnology ‘to surprise
the US army with some genetically engineered novel organism’. Iraq is more
likely to use chemical weapons than biological ones, he says.

Rachel Nowak is a science reporter with BioWorld