The study, commissioned by the Nairobi-based UN Environment Programme (UNEP), found that half of 328 children tested had concentrations of lead in their blood exceeding the internationally accepted level.

Exposed to pollutants from heavy metals and toxic substances in soil, water and air, almost half the children tested were also suffering respiratory diseases, including chronic bronchitis and asthma, a UNEP statement said.

Nearly half of soil samples from the area had lead levels almost 10 times higher than unpolluted samples.

"The Dandora site may pose some special challenges for the city of Nairobi and Kenya as a nation. But it is also a mirror to the condition of rubbish sites across many parts of Africa and other urban centres of the developing world," said UNEP head Achim Steiner, exhorting city leaders to remedy the situation.

"Urgent action is needed to reduce the health and environment hazards so that children and adults can go about their daily lives without fear of being poisoned and without damage to nearby river systems."

SCHOOL

Dandora waste gets into Nairobi River, polluting water used by locals and by farmers further downstream, the report added.

At a school nearby, the dispensary has treated more than 27,000 people in the last three years for respiratory problems.

"We have been witnessing an alarming situation regarding Dandora children's health: asthma, anaemia and skin infections are by now endemic," said the report's main author and local biochemist Njoroge Kimani.

"Since waste dumping is unrestricted and unmanaged, people are also at risk from contracting blood-borne diseases such as hepatitis and HIV/AIDS."

The UNEP statement said a quarter of all diseases affecting mankind were attributable to environmental risks, with children especially vulnerable.

Some 4.7 million children under five die each year from environmentally related illnesses, it said, quoting World Health Organisation (WHO) figures. And 25 percent of deaths in developing countries are linked to environmental factors.

"The children of Dandora, Kenya, Africa and the world deserve better than this," Steiner said.

A priest working in slums around the dump said locals were pressing for the closure of Dandora, to be replaced by a proper waste-processing facility in another location. Both city authorities and private companies dump at the site.