BBC News, Chandigarh
Tests on children with cerebral palsy or mental disabilities in the Indian state of Punjab have revealed high levels of uranium.
A charity based in Faridkot city said chemical analyses of hair specimens collected from 149 children in its care showed "unexpected amounts" of toxins.
The children included in the study were all under 13, it said.
The result has baffled the authorities as there are no known sources of uranium in Punjab.
The chemical tests were conducted on the suggestion of Dr Carin Smit, a South African metal toxicologist associated with the UK-based non-governmental organisation Defeat Autism Now.
Samples of hair collected from the 149 children, then resident at the Faridkot-based charity, Baba Farid Centre for Special Children, were tested at Trace Mineral, a laboratory in Germany.
The results were startling, Prithpal Singh, head of Baba Farid, said.
"Around 80% of the samples, including those from children with cerebral palsy, revealed the presence of uranium in levels that the experts have described as pathological," Mr Singh said.
"We are informed that there is a fairly well established correlation between exposure to uranium and birth defects, renal damage and several forms of cancer.
"This could well be among the causes of the conditions afflicting our children."
The "unexpected" results have drawn Dr Smit and her colleague Vera Dirr back to Faridkot, where they have now collected urine samples from the children to get more specific evidence of uranium exposure.
No-one seems to have any idea as to the source of the uranium.
Some experts say the problem may be more widespread.
No-one apart from the children at the Faridkot centre has been examined for the presence of toxic metals.
Mr Singh said experts had clarified that the results did not imply any exposure to radioactivity.
Health officials in Punjab said they were unaware of the problem.
"This is not a health subject. We don't know how children are showing such high concentrations of uranium," Punjab health minister Lakshmi Kanta Chawla said.
"It is for the central government in Delhi to deal with the problem."