People who eat watercress from geothermal-fed areas may risk arsenic poisoning, scientists say.
HortResearch scientist Brent Robinson said yesterday that a survey of aquatic plants from geothermal regions around Taupo and Rotorua, and from the Waikato River, had shown that they accumulate concentrations of up to 3000 parts per million ofarsenic.
High arsenic levels have been blamed for some types of cancer.
Dr Robinson said the survey had health implications for New Zealanders who ate watercress from streams fed with geothermal water.
The discovery was "an extraordinary find and quite disturbing, as people eat watercress", he said.
Watercress from uncontaminated streams with no geothermal water flowing into them was probably safe.
But the find has positive implications for countries that have problems with arsenic-contaminated water, Dr Robinson said.
"We would like to find out how these aquatic plants accumulate arsenic, and whether they could be used to remove arsenic from drinking water," he said.
"This may be a low-cost means of improving public health in countries like Bangladesh and West Bengal in India, where there are high levels of arsenic in the water that can result in widespread poisoning."
Arsenic has been detected in the drinking water of up to half of Bangladesh's population of 120 million and the Indian state of West Bengal, where it leaches into wells from underground rock.
Some parts of Bangladesh and West Bengal have arsenic levels 100 times higher than the World Health Organisation's recommended limit.
Many villagers have black blotches on their skin and fingernails caused by arsenic poisoning.
In New Zealand, arsenic has also been recorded as a significant problem at an estimated 10,000 former sheep-dip sites and in sawdust and wood shavings at former timber treatment sites.
