A post-mortem test on a woman who drank water during the Camelford water poisoning incident has found abnormally high levels of aluminium in her brain.
A toxic chemical was tipped into the wrong tank at the Lowermoor works
It is the strongest evidence yet of a possible link between the poisoning and a disease similar to Alzheimer's.
Water in the Cornish town was contaminated with 20 tonnes of aluminium sulphate in 1988.
Hundreds of people said they became ill after the toxic chemical was put into the wrong tank at a treatment works.
West Somerset Coroner Michael Rose released the post-mortem examination results on Thursday.
He asked leading neuropathologist Prof Margaret Esiri to examine the woman's brain and spinal cord following her death in Musgrove Park Hospital, Taunton, in February last year.
The woman was living in Camelford at the time of the incident.
It was discovered that she died from beta amyloid angiopathy, a form of cerebrovascular disease usually associated with Alzheimer's disease, which could be connected to an abnormally high level of aluminium in her brain.
Mr Rose said: "Further research will be needed before the significance of the elevated brain aluminium concentration in this case can be clarified.
"A scientific report on the case has been submitted for publication. The inquest will stand adjourned until the completion of further research."
In the 17 years since the disaster at Lowermoor Treatment Works, local people have complained of a range of health issues ranging from brain damage and memory loss to joint problems.
Campaigners said the findings supported their claims, but criticised the authorities' failure to carry out any targeted post mortem examinations on water poisoning victims until now.
Lib Dem peer Lord Tyler, until this year the MP for North Cornwall, said the "scandalous cover-up" of the incident was gradually unravelling.
"Inevitably, this investigation will be too late for some victims, and has been thwarted by inadequate medical records and lax monitoring of the 20,000 people, including many children, whose health may have been affected," he said.
"But better late than never. The accident itself was a real disaster, but the subsequent cover-up was a scandal.
"The coroner's conclusions today add substantially to the weight of evidence and provide a devastating example of past failures.
"However, at long last there is a real chance that justice will be seen to be done, and realistic compensation considered."
Denis Cronin, the director of public health at the North and East Cornwall Primary Care Trust, said while he welcomed the new information, people should not be alarmed by the results of a single post mortem examination.
In 1991, the then South West Water Authority was convicted at Exeter Crown Court of supplying water likely to endanger public health and fined £10,000, with £25,000 costs.
Three years later 148 people won an out-of-court settlement totalling £400,000.
A draft independent report into the incident, the third to be carried out, said in January it was unlikely that the chemicals involved in the incident would have caused any delayed or persistent health effects.
No conclusive link was found between the incident and the chronic symptoms and diseases.
A final report is expected early in the new year.