ZAMAN GIRA, Nigeria (Reuters) - Ibrahim Bello says he can earn $23 in two hours extracting gold from the ground, more than he can make in two months from cultivating millet.
It is a princely sum in this mud-brick village in northwestern Nigeria, a region on the southern fringe of the Sahara where most people eke out a living as subsistence farmers and survive on as little as $2 a day.
Such is the economic draw of the "gold rush", with impoverished farmers digging up rocks by hand in open mines, that many are in denial about its devastating consequences.
At least 400 children have died from poisoning caused by illegal gold mining since March because the ore being unearthed around their villages contains high concentrations of lead, contaminating the air, soil and water.
International agencies including the United Nations, Medecins Sans Frontieres (MSF), the World Health Organisation and the U.S. Centers for Disease Control and Prevention (CDC) have been working for months to try to contain the pollution.
But heavy rains have spread the contamination and the reluctance of villagers to admit that their new-found source of wealth is to blame has hampered their work.
Aid agencies said in June at least six villages in Zamfara state had been affected and around 170 children, mostly under five, killed. More contaminated communities have been discovered since then and the infant death toll has more than doubled.
"The reluctance of communities to disclose lead-related illnesses or deaths, and where they conduct mining activities, is seriously hampering our efforts to identify communities at risk," said John Keith, a technical advisor with New York-based anti-pollution consultancy the Blacksmith Institute.
"In some cases it takes two weeks to convince a community to open up," said Keith, whose organisation specialises in cleaning up polluted sites around the world.
Residents fear that disclosing the problem will lead the government to clamp down on their mining, which often brings the contaminated ore into direct contact with children.
The men carry the ore back from the open mines for their wives to crush into a powder, using a hammer or stone. They then flush it with water to remove the sand and retain gold traces.
Close to them, in family compounds, children play barefoot, exposed to the contaminated water and inhaling the dust.
Symptoms of lead poisoning are particularly acute in children under five, damaging the nervous system and kidneys and causing convulsions which can quickly lead to death.
"I have never experienced something like this in my life. When it affected a child, you will see he will begin shaking and vibrating. Before daybreak the child could die," said Saminu Mohammed, a resident in Bagega, one of the affected villages.
Exposure to too much lead can cause irreparable damage to the nervous and reproductive systems and the kidneys. While adults can get sick, the risk is most acute in young children whose bodies are not fully developed.
Zamfara's poor rural communities are no strangers to illness, with regular outbreaks of cholera, meningitis and malaria. But few residents have received much formal education and science is often treated with scepticism.
"Communities deny such deaths or attribute them to spirits and other beliefs," the MSF coordinator in Zamfara, El Shafi'i Muhammad Ahmad, told Reuters.
It is not the first time Western medicine has clashed with deep religious and traditional beliefs in northern Nigeria.
Zamfara was one of three states to suspend a polio immunisation programme led by the World Health Organisation in 2003 because some Muslim leaders feared the oral vaccine was a Western plot to spread AIDS and cause infertility.
The lead poisoning outbreak initially went unreported, with the high infant mortality rate thought to have been caused by cerebral malaria, which can trigger similar symptoms such as convulsions in small children.
It was only when an MSF team testing for meningitis found high levels of heavy metal in the villagers' blood that the true cause was discovered.
Aid workers fear many children may not have been brought to hospital because the rainy season has impeded access to remote villages, only two of which have been decontaminated.
MSF has been treating hundreds of children at clinics set up in towns including Anka and Bukuyyum, but Zamfara state's health ministry has identified as many as 180 remote villages and communities where children may have been poisoned.
"I lost three children to this epidemic in the last ten days, this is the fourth," said Halima Garba, a mother of five carrying her sick daughter along a track to the main road, where she hoped to find a motorbike to take her to an MSF clinic.
"It seems like help is not coming to the village so I was left with no option," she said.
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Writing by Nick Tattersall