About 140 million people, mainly in developing
countries, are being poisoned by arsenic in their drinking water,
Speaking at the Royal Geographical Society (RGS)
annual meeting in London, scientists said this will lead to higher
rates of cancer in the future.
South and East Asia account for more than half
of the known cases globally.
Eating large amounts of rice grown in affected
areas could also be a health risk, scientists said.
"It's a global problem, present in 70 countries,
probably more," said Peter Ravenscroft, a research associate
in geography with Cambridge University.
"If you work on drinking water standards used
in Europe and North America, then you see that about 140 million
people around the world are above those levels and at risk."
Arsenic consumption leads to higher rates of
some cancers, including tumours of the lung, bladder and skin,
and other lung conditions. Some of these effects show up decades
after the first exposure.
"In the long term, one in every 10 people with high concentrations
of arsenic in their water will die from it," observed Allan Smith
from the University of California at Berkeley.
"This is the highest known increase in mortality
from any environmental exposure."
The international response, he said, is not
what the scale of the problem merits.
"I don't know of one government agency which
has given this the priority it deserves," he commented.
The first signs that arsenic-contaminated water
might be a major health issue emerged in the 1980s, with the
documentation of poisoned communities in Bangladesh and the
Indian state of West Bengal.
In order to avoid drinking surface water, which can be contaminated
with bacteria causing diarrhoea and other diseases, aid agencies
had been promoting the digging of wells, not suspecting that well
water would emerge with elevated levels of arsenic.
The metal is present naturally in soil, and
leaches into groundwater, with bacteria thought to play a role.
Since then, large-scale contamination has been
found in other Asian countries such as China, Cambodia and Vietnam,
in South America and Africa.
It is less of a problem in North America and
Europe where most water is provided by utilities. However, some
private wells in the UK may not be tested and could present
a problem, Mr Ravenscroft said.
Once the threat has been identified, there
are remedies, such as as digging deeper wells, purification,
and identifying safe surface water supplies.
As a matter of priority, scientists at the
RGS meeting said, governments should test all wells in order
to assess the threat to communities.
"Africa, for example, is probably affected
less than other continents, but so little is known that we would
recommend widespread testing," said Peter Ravenscroft.
His Cambridge team has developed computer models
aimed at predicting which regions might have the highest risks,
taking into account factors such as geology and climate.
"We have assessments of the Ganges and Brahmaputra river basins,
for example, and then we look for similar basins elsewhere.
"There are similar areas in Indonesia and the
Philippines, and very little evidence of tests; yet where there
has been some testing, in (the Indonesian province of) Aceh
for example, signs of arsenic turned up."
Asian countries use water for agriculture as
well as drinking, and this too can be a source of arsenic poisoning.
Rice is usually grown in paddy fields, often
flooded with water from the same wells. Arsenic is drawn up
into the grains which are used for food.
Andrew Meharg from Aberdeen University has
shown that arsenic transfers from soil to rice about 10 times
more efficiently than to other grain crops.
This is clearly a problem in countries such
as Bangladesh where rice is the staple food, and Professor Meharg
believes it could be an issue even in the UK among communities
which eat rice frequently.
"The average (British) person eats about 10g
to 16g of rice per day, but members of the UK Bangladeshi community
for example might eat 300g per day," he said.
The UK's Food Standards Agency is currently
assessing whether this level of consumption carries any risk.