Sunke, Nigeria (CNN) -- Standing at the local graveyard, Mohammed Abubakar cannot find the grave of the son he unwittingly poisoned. The grass has grown too high.
"He started convulsing and vomiting," Abubakar said. "Everywhere we went, we could not get medicine. And then, he died."
His son is among an estimated 400 children who have died and 30,000 others who have been poisoned in Zamfara state, northern Nigeria, since March in the world's worst recorded outbreak of lead poisoning.
"The situation is more extensive than anyone thought when this was first discovered last May," said John Keith, of the Blacksmith Institute, an international non-profit organization that investigates environmental hazards and is organizing the cleanup of the lead contamination.
"There are more villages involved, and the lead levels are higher, and the number of children impacted is higher than anyone first estimated," he added.
The remote mud-hut villages were contaminated after the international price of gold soared above $1,300 an ounce due to the global economic crisis.
Young men began to dig metal ore from nearby mines and process it in their homes in the search for gold. But they were unknowingly mining lead, and the dust from the processing contaminated their houses.
As children play in the dust around his water well, tests show Abubakar's home to be contaminated with 11,000 parts per million of lead. According to the U.S. Environmental Protection Agency, the safe level of lead is 400 parts per million.
"It's incredibly dangerous," said Casey Bartrem, a Blacksmith project coordinator testing the homes in the villages. "It's the reason we have to come in here and remove the soil."
As camels walk lazily through the village, men in protective overalls and facemasks methodically move from one mud-hut compound to another with shovels and wheelbarrows.
The cleanup operation is a relatively simple process of removing the top layer of soil and replacing it with new clean earth. In the dry heat, the kicked-up dust covers the workers with a layer of lead-contaminated soil, so each night their overalls are washed.
Four villages have been completed, while three are being processed, and seven more lacking funding.
But the real problem is the size and remoteness of the region.
"Transport is a very difficult challenge here. It takes a 4x4 to get here, to any of the villages, and those are hard to come by here," said Keith.
"If we can't get the workers here, we can't do the remediation. And of course we need to stay in budget and do this work fast."
The longer the lead stays in peoples' homes, the greater the risk of more poisoning and deaths -- especially for children.
International aid group Medecins Sans Frontiers (MSF) has set up two treatment centers to deal with the crisis.
"There are a significant number of villages affected, and in those villages up to 90 percent of the children are in immediate need for treatment," said Ellen Van der Velden, an emergency coordinator for MSF.
"Their [children's] bodies are smaller, so the same amount of lead in a smaller body gives you a higher concentration," she said, noting that they also "are the ones who spend the most time on the floor, sit and crawl on the floor, pick things up and put it in their mouth."
Lead levels in the human body above 10 micrograms are considered dangerous. But in blood tests in Zamfara state, MSF has found levels as high as 700 micrograms.
MSF is evacuating children from the worst-affected villages and providing chelation therapy --- which helps remove heavy metals from the body --- in the most urgent cases.
The state government has banned mining and has dismissed accusations that they have not done enough to deal with the crisis.
"There is rigorous public enlightenment, issues, advocacy and dialogue and contact with the communities, "said Abubakar Maru, Zamfara state's environmental commissioner. "And I'm sure people in Dareta and those other places are aware of the dangers."
As he meets with local government officials and village elders, Keith does not believe there are any "bad guys" in this crisis.
"This is a disaster that is born out of poverty and unawareness," he said, adding, "ignorance of the hazards of lead and what they were dealing with, not people who were trying to hurt their children.
"They were just trying to make a living. They thought they'd found a way to make a few extra dollars with the high price of gold. They didn't know."
But the concern is that, if the international price of gold remains high, all of Blacksmith's work may be in vain.
Abubakar has stopped processing ore in his home but needs the income he could get if he can find gold --- he has nine other children to care for.
"When the issue is resolved I am ready to continue gold mining," he said, "because it's the only way to make money."