STRONG coffee and plenty of it may reduce the risk of heavy-metal poisoning
in cities where drinking water contains high levels of these contaminants. An
international team of scientists has found that while coffee is filtering, the
coffee grounds mop up as much as 90 per cent of the copper and lead dissolved in
the water.
Many cities in the developing world have high levels of toxic metals as
soluble metal ions in their drinking water. Copper and lead enter the water as
it runs through pipes and storage tanks or makes contact with lead solder.
Mike McLaughlin of CSIRO Land and Water in Adelaide wondered if ground coffee
might remove heavy metals. Because dissolved heavy metal ions are positively
charged, and coffee contains uncharged and negatively charged molecules, the
metal ions might be taken out of solution by binding to negatively charged
molecules in the coffee grounds.
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To test this idea, McLaughlin and his colleagues used water spiked with
different levels of copper and lead to brew coffee by the water-drip method.
When they measured the concentrations of metal ions in the resulting coffee they
found that between 78 and 90 per cent of the copper and lead had been removed.
鈥淭he deeper the bed of coffee in the drip-maker, the more effective the removal
of heavy metals,鈥� says McLaughlin.
He adds that the process probably also removes other heavy metals such as
mercury, cadmium and zinc, though this hasn鈥檛 been tested. 鈥淚t is also possible
tea bags and tea leaves may work in the same way,鈥� he suggests.
The findings could mean that the risk of lead and copper poisoning in cities
where people drink a lot of coffee is lower than expected. 鈥淒aily human exposure
to heavy metals in many cities round the world may have been greatly
overestimated,鈥� says McLaughlin.
John Bisby, a consultant in environmental and occupational medicine in
Melbourne, says the work may be helpful in assessing risk. But he stresses that
drinking more coffee is not a practical way to combat water contamination.
鈥淐offee is not the solution,鈥� he says. 鈥淵ou can鈥檛 drink all your water as coffee
or you will have other side effects that are a lot worse than lead. The answer
is to get water safe at source.鈥�