Geiger counter in every human revealed

[modsafety@GTNET.GOV.UK]

New Scientist reports:-

Geiger counter in every human revealed

19:00 28 May 03



http://www.newscientist.com/news/news.jsp?id=ns99993768



How much damage does cosmic radiation do to frequent flyers? Is depleted

uranium from shells causing cancers in former war zones such as Kosovo and

Iraq? The discovery that certain kinds of radiation leave a distinctive

pattern of damage in our cells could help answer these questions.



"If this works, we'll be able to take a measurement and see the lifetime

exposure in that person," says David Brenner of Columbia University in New

York. "Often there is no other reliable record of individual exposure." It

is this uncertainty about radiation exposure that makes it hard to pin down

the health risks.

"That they found this effect was there at all is significant," says Michael

Cornforth, a radiation biologist at the University of Texas Medical Branch

in Galveston. "But I was flabbergasted by how clear-cut it was."

Radiation is harmful because of its ionising effect, which can break DNA

chains. If the broken pieces are rejoined incorrectly, the resulting genetic

scrambling can harm cells or, far worse, set them on the road to cancer.

Some genetic damage is easy to spot, such as when parts of different

chromosomes are exchanged - known as interchromosomal changes. But because

mutagenic chemicals can also cause such exchanges, this is not a reliable

indicator of exposure to radiation.



Heavy particles

Researchers have long suspected that slow-moving, heavy particles such as

alpha particles and neutrons should leave a characteristic pattern of

damage. These kinds of radiation are known as "densely ionising" because

they wreak havoc within a short tunnel; "sparsely ionising" X-rays or gamma

rays spread their damage along a much longer path. Because the damage from

densely ionising radiation is so concentrated, it is far more likely to hit

one chromosome several times, triggering deletions or reordering of its DNA.

Detecting intrachromosomal changes like these has been extremely difficult

till now. But Brenner's team, together with a Russian group, took advantage

of new dyes to "paint" bands on chromosomes. Image analysis software

translates this into false-colour pictures (see graphic), making it easy to

spot any rearrangements.

The team used the technique to analyse chromosome 5 in thousands of blood

cells from 31 people who had worked at a secret nuclear weapons facility

near Ozyorsk in Russia. Though most of the workers were last exposed to

densely ionising radiation from plutonium over 10 years ago, the team found

a surprising amount of damage.



Nearly four per cent of blood cells in highly exposed workers had

rearrangements within chromosome 5. Extrapolating from this, Brenner thinks

that 62 per cent of these workers' blood cells have damage within at least

one chromosome.



Workers with moderate levels of exposure had a lower level of damage, while

those with no radiation exposure had none. Even workers at a nuclear reactor

exposed to high levels of sparsely ionising gamma rays and mutating

chemicals had very few intrachromosomal changes, though they had significant

interchromosomal damage.



There is still a lot of work to do before the technique can be widely

adopted. "We need to automate the technique," Brenner says. "Even in this

small study, it took us two years to look at all the cells."



Journal reference: The American Journal of Human Genetics (vol 72, p 1162)

Philip Cohen



Mr FWP Dawson Head Health Physics

Directorate of Defence Safety Environment and Fire Policy (D SEF Pol)

Ministry of Defence

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