Massive lead contamination due to illegal gold mining in Nigeria has led to 200 children dying and about 18,000 people being affected, the UN declared on Tuesday.
Five experts equipped with a mobile laboratory have arrived in the country to help health authorities pin down the extent of the contamination and tackle it, the UN's Organisation for the Coordination of Humanitarian Affairs said.
"From the latest figures we have, more than 200 children reportedly died from this poisoning," OCHA spokeswoman Elisabeth Byrs told journalists as the UN body warned of "acute massive lead poisoning."
Byrs told AFP that "an estimated 18,000 people were affected" in the villages around the gold mining area in northern Zamfara state, around Bukkuyum and Anka.
"It's a developing problem. Seven villages were affected but we don't know the full extent," she added.
"Proper sampling from the mobile laboratory is urgently needed to determine the scope and magnitude of the crisis and to assist in developing a rigorous response," according to an OCHA briefing note.
The poisoning was triggered by makeshift processing of lead-rich ore to extract gold, with crushed rock often taken into homes and communities, while the residue is discarded haphazardly in the soil.
Nigerian health authorities first noticed excess mortality in the area in March and brought in international help weeks later, but the extent of the poisoning and contamination appears to have grown.
The OCHA said soil also appeared to be heavily contaminated by mercury and copper, and was likely to need a massive clean up.
"The problem is that the rainy season will cause even greater contamination," Byrs said.
In June the US Centers for Disease Control and Prevention, which was called in by Nigeria to help, described the scope of the lead poisoning as unprecedented.
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 are the most vulnerable.