The release of $4m (£2.5m) promised by Nigeria's president seven months ago to clean up villages contaminated by lead has been welcomed by campaigners.
US-based Human Rights Watch said the funds would help 1,500 children in urgent need of life-saving medical treatment in northern Zamfara state.
A BBC reporter says there has been a concerted online and media campaign to get the pledged funds released.
In 2009, it became clear that hundreds of children had died of lead exposure.
They were poisoned by dust released by gold miners breaking open rocks near their homes.
Children suffer more from lead poisoning because their size makes them more vulnerable to its effects.
In total, 460 children died and a further 4,000 were contaminated.
The medical charity, Medecins Sans Frontieres (MSF), has said the situation in Zamfara is one of the worst cases, if not the worst case, of lead poisoning worldwide.
The BBC's Bashir Abdullahi in Abuja says the bureaucratic nature of Nigeria's political system led to the funding delay.
The money was originally promised by the government in 2011 and President Goodluck Jonathan ordered its release last May.
But it was only made available following editorials in national newspapers, pressure from MSF and a Facebook campaign by the Nigerian Youth Climate Action Network and Human Rights Watch, our correspondent adds.
'Play without risk'
MSF's Ivan Gayton told the BBC the money had arrived just in time as the clean-up process would take five months and it was important for it to be completed before the start of the rainy season.
Large amounts of sand can by moved by the rain water, meaning clean-water supplies can be re-contaminated if the clean-up process is not finished.
Decontamination teams will start work next week when MSF staff will also begin screening children. Treatment will follow shortly after that.
"As long as the remediation is successful, as long as they not ingesting large amounts of lead, then we can flush the lead out of the blood," Mr Gayton said.
The problem first came to light when the price of gold almost doubled, with about seven villages in a large area of Zamfara being affected.
"President Jonathan's decision to release the clean-up funds could be life-saving for countless children," Jane Cohen, health researcher at Human Rights Watch, said in a statement.
"After years of living in contaminated homes, children will now be able to live and play without risking their lives."
The authorities have told people in Zamfara to stop mining.
But Mr Gayton said it would be better to improve mining standards and teach people about the health risks.