A woman who drank water during a aluminium contamination incident in Camelford, Cornwall, in 1988 had traces of the metal in her brain, tests show.
A toxic chemical was tipped into the wrong tank at the Lowermoor works
A post-mortem examination was carried out on Irene Neal after she died in June 2007, suffering from Alzheimer's.
Results found Mrs Neal and another former Camelford resident Carole Cross, who died in 2004, both had high aluminium levels in their brains.
The post-mortem details were released by the West Somerset coroner's office.
Only two post-mortems have ever been carried out on people believed to have been affected by the incident.
Mrs Cross was referred to a neurologist in 2003 for repeated headaches, difficulties in finding words, doing simple sums and hallucinations.
A post-mortem examination of her brain revealed a rare form of Alzheimer's disease and very high levels of aluminium in the affected areas of her brain tissue.
At her inquest, West Somerset Coroner Michael Rose asked neuropathologists to examine the link between aluminium and brain diseases, which could take four years.
Mrs Neal died in a Devon care home aged 91, also suffering from the symptoms of Alzheimer's.
A joint inquest into their deaths is to be held at a later date.
No findings have yet been published about the incident when 20 tonnes of aluminium sulphate entered South West Water treatment works in Camelford.
Up to 20,000 people in and around the town were exposed to levels of aluminium 500 to 3,000 times the acceptable limit defined by the European Union.
A 2005 draft inquiry report said it was unlikely that the chemicals involved in the incident would have caused any persistent or delayed health effects but recommended further research.
An official inquiry concluded in May this year.
The report on whether exposure to chemicals resulted in ill-health was being reviewed by the Food Standards Agency's Committee on Toxicity and will then passed onto the Health and Environment ministers.
A Department of Health report into the incident is expected to be published before the end of the year.
Local representatives said they would be recommending future action to ensure people affected had been tested for ill-health and received on-going care.