Leading scientists called for a fresh inquiry into the effect of Britain's worst large-scale water poisoning yesterday after providing the first evidence to suggest it caused the death of a woman from an extremely rare form of Alzheimer's.

Research published yesterday suggests Carole Cross's neurological illness and subsequent death could have been brought on by the 1988 Camelford incident, in which 20 tonnes of highly toxic aluminium sulphate was added to drinking water at a treatment works by mistake.

Up to 20,000 people were exposed to concentrations of aluminium up to 3,000 times the legal limit but, despite three inquiries, there has been no systematic monitoring of residents.

Now Chris Exley, the lead author of research published in the Journal of Neurology, Neurosurgery and Psychiatry, and Professor Daniel Perl, an authority on Alzheimer's and aluminium, are calling for the Camelford residents to be monitored after finding that Mrs Cross had more than 20 times the normal level of aluminium in her brain. She also suffered from a rare type of Alzheimer's, sporadic early onset beta amyloid angiopathy, which would not be expected in someone with no genetic predisposition to it.

"This may be a one-off, although it is highly unlikely, " said Dr Exley, reader in bioinorganic chemistry at Keele University. "We need to set up a monitoring programme of the people so we can put their minds at rest."

The scientist, who conducted the research with Professor Margaret Esiri of Radcliffe Infirmary, Oxford, added: "There has to be an element of risk [to other residents] before we discover this. This can't be explained away easily."

Mrs Cross and her husband, Doug, were living in the small north Cornwall town in July 1988 when a driver tipped the aluminium sulphate into the wrong tank at the water treatment works at Lowermoor, on the edge of Bodmin Moor. She tried to avoid drinking the water but realised she had been exposed when she took a bath which turned blue when she added soap to it. "Like a lot of people in Camelford, she refused to talk of it. She found it too traumatic," Mr Cross said yesterday.

In May 2003, at the age of 58, she was referred to a neurologist for headaches, difficulties in finding words and doing sums, and hallucinations. Her condition worsened and she died in April 2004.

An inquest into her death was adjourned in December last year, after the West Somerset coroner, Michael Rose - persuaded by Mr Cross, who refused to accept that she had died of an unknown neurological condition - called in the scientists to examine her brain.

The findings show Mrs Cross - who had no family history of Alzheimer's - had up to 23 micrograms of aluminium per gram of brain in parts of her brain compared with the normal concentration of two micrograms. Aluminium, which is a neurotoxin, has previously been associated with an increased risk of developing Alzheimer's. Dr Exley told the Guardian that Mrs Cross may have reached her toxic threshold for aluminium at 58. "There is nothing in her lifestyle to suggest abnormal exposure other than a period of weeks and months in 1988, when she was exposed to high levels of aluminium."

Mr Cross, an environmental scientist and member of the sub-group of the Commons committee on toxicity set up to look at the effects of the incident, said the findings sent out a "frightening message to people living in Camelford today".

"There is a cover-up going on. I know of up to 20 deaths that can't really be explained. We have been demanding testing for 18 years. It is absolutely essential."