Lead poisoning has killed more than 400 children under the age of five as a result of contamination from illegal gold extraction in northern Nigeria, an international aid agency said on Tuesday.
The children died over the last six months in several villages in Zamfara state, where lead-rich run-off from illegal gold mining has entered the soil and water supply, said Medecines Sans Frontieres (Doctors Without Borders - MSF).
"Based on the record of fatalities from lead poisoning, more than 400 children have died in the last six months," said El-Shafii Muhammad Ahmad, MSF project director in Zamfara.
"But we in MSF believe the figure is much more than that," he told AFP by telephone.
Preliminary findings by UN experts on the contamination in Zamfara state, which were released on Tuesday, said that "growing amounts of children are dying from lead poisoning."
Elisabeth Byrs, a spokeswoman for the UN office for the Coordination of Humanitarian Affairs, told AFP in Geneva that more than 3,000 children lived in seven affected villages in an area of high-intensity wildcat gold mining.
Byrs said many parents were afraid to come forward when their children fell ill, or mistook symptoms including convulsions with malaria.
"The pollution is far from over in these areas, we have looked at five villages," Byrs told journalists following the release of a joint OCHA-United Nations Environmental Programme (UNEP) report into the poisoning.
Women and children often participated in the makeshift processing of lead-rich ore to extract the gold, and crushed rock often ended up being taken into homes, MSF said. Residue was discarded haphazardly in the open, exposing children to inhalation or ingestion of contaminants.
"The lead pollution and intoxication crisis in Zamfara State is far from over. In fact, we have only seen the tip of iceberg," the UN report said.
However, the Nigerian government's chief epidemiologist disputed the MSF figures.
"The MSF figure on the death toll is not true," said Henry Akpan, who declined to provide a government toll, adding that there had not been "any new deaths in the past weeks".
"We now have good treatment for children, pregnant women and those affected," he said.
But MSF's Ahmad said even the 400 deaths "is an under-estimation because many lead-related deaths are never reported and in many cases, these communities attribute them to other factors or deny them altogether."
Local communities mainly concealed or denied the fatalities and illnesses from lead poisoning for fear that authorities will ban their mining activities, he added.
Illicit gold mining is more lucrative than agriculture for the impoverished farming communities.
The UN report, which follows a fact-finding visit to the region, said lead poisoning was spreading in mining communities in northwestern Zamfara.
"The list of polluted villages continues to grow," it said, adding that there were signs of resumed mining activities in Dareta, one of two villages decontaminated by a US-based environmental firm.
The study focused on ground water pollution in the affected areas of the state and found "highly fluctuating" concentrations of lead in samples after a survey of five of the villages.
Contamination levels of up to 10 times above maximum standards were recorded in water wells in two villages.
"The concentrations of lead in ponds and rivers are often not meeting the drinking water standards for lead," the report added.
Symptoms of lead poisoning normally build up over long periods as the heavy metal accumulates in the human body, producing abdominal pain, nervous disorders affecting growth and ultimately leading to kidney failure.
Children, especially fast growing under five year-olds, are most at risk.