The authors rule out the suggestion that the symptoms could be due to anxiety - the explanation offered by an official investigation after the incident. They also note that the abnormalities are similar to those seen in kidney dialysis patients who suffered from a progressive dementia in the 1970s. The syndrome was tracked down to prolonged elevation of blood levels of aluminium which was not removed during dialysis.

The results lend support to the claims of an estimated 400 people who complained of dementia, memory loss and behavioural problems after the incident. To sceptics, however, they will be interpreted as a study of a self-selected group of individuals suffering normal age-related mental impairment which does not show any results specific to aluminium-related dementia.

Dr Altmann's findings appear to have spawned new legal claims against South West Water. One solicitor told the press that he will be claiming damages on behalf of three children, one unborn at the time of the incident. He also said he knew of other solicitors who may bring similar claims.

Unsupervised delivery
The Camelford incident began on Wednesday 6 July 1988 at the unmanned Lowermoor water treatment works which supplied a population of 20,000 with a soft, acidic surface water treated by coagulation and chlorination. The coagulation system involved dosing with lime to increase the pH and with aluminium sulphate.

The lime dosing system had been prone to failures and broke down twice on the day of the incident. This resulted in acidic, aluminium-rich water being put into supply - a failure which triggered the pH monitor at the works outlet and sent a signal to the control centre in Exeter. Both problems were rectified.

Unconnected to these failures, a tanker driver arrived at 16.30 with a load of 20 tons of aluminium sulphate solution. He had a key to the gate and instructions to call a neighbouring works for details of how to make the delivery. However, finding that the key fitted the lock and what he thought to be the correct storage tank, he proceeded without seeking assistance.

Instead of emptying the load into the storage tank, however, he pumped it into the contact tank - a post-chlorination unit after which the water went into supply. This was not surprising in view of the set-up of the plant at the time. To reach the correct tank, the solution should have been pumped through a narrow gap between a new tank and the building - a situation the Lawrence report recognised as a "serious hazard" and "the last place [the driver] would expect to be a receiving point for an important chemical."

The pH monitor was upstream of the contact tank, and the delivery error could not therefore be readily spotted by the control centre. Reports of unpleasant tasting, sticky water began to reach SWWA at about 21.00. Water quality managers assumed that the problem was due to the lime dosing pump and took no action. However, the operations controller had also heard of what he assumed to be a pH problem and decided to carry out a flushing operation.

Major fish kill
Exactly what was done that evening or for how long is not clear, but it was crucial in determining the amounts of aluminium put into supply. Still the most detailed account of the events at Lowermoor is a report commissioned by SWWA from Dr John Lawrence - a non-executive member of its own board. The report gives little information on the flushing procedure. But it is clear that sufficient aluminium was released into the rivers Allen and Camel to kill 60,000 fish.

The following day, the fish kill was linked to events at Lowermoor but its precise cause was not understood. It was resolved not to carry out further flushing except at points which emptied into the sea. The decision was questionable since there was clearly a problem with the supply, and preventing water pollution was in effect given priority above protection of human health.

The coastal flushing operation began on Thursday evening and lasted several days. Its impact on the higher inland parts of the supply area is not clear. The Lawrence report remarks that it would have taken "several days" to clear the system, "and in some extreme places possibly much longer."

Although customers were complaining about their water throughout this time, the SWWA was blithely assuring people that it was safe to drink.

The misdelivery of the aluminium sulphate was not discovered until the Friday morning. By then, customers had begun to complain of sickness, blue water from their copper plumbing and their hair turning green.

Even when the SWWA realised what had happened, there was no co-ordinated response and no public warning to avoid drinking the water. Although bowsers were sent out, the public were largely left to cope as best they could. It was only two weeks later that a small announcement revealed that the problem was due to aluminium sulphate.

Failure to follow up
It may seem surprising that a report from the SWWA itself, with terms of reference confined largely to the proximate causes of the incident, was taken as the final word on an affair of such gravity - and that no investigation was ordered by the Government.

The report gives no details of the SWWA's "ad hoc" monitoring effort after the incident. Later, the Authority simply admitted that the lowest pH it recorded was 3.7 and the highest aluminium concentration a massive 109,000 micrograms per litre. The range of pH recommended by the 1980 EC Directive on drinking water quality is 6.5-8.5, and the legal limit for aluminium is 200µg/l.

The Lawrence report calculated that the average aluminium concentration put into supply if the 20 tons of aluminium sulphate were completely mixed into the 300,000 gallons of water in the contact tank would have been 3,800,000µg/l. Levels this high were not measured, but in one sample the health authority found 620,000µg/l.

After the incident, at least 400 people reported health effects. The initial symptoms included joint and muscle pain, rashes, mouth ulcers and digestive disorders. Later reports also mentioned dementia, behavioural problems, memory loss and even premature death.

A report by the charity Environmental Assistance, prepared for the campaigning Camelford Action Group in 1997, casts doubt on the SWWA's monitoring figures and practices. It cites one example of an employee of the successor water company refusing to take samples of clearly contaminated water. It also cites press reports that high levels of aluminium were still being detected in the supply six years after the incident - although it is not clear whether these were due to remaining pockets of contamination or to continuing problems at the treatment works.

In addition to being supplied with acidic water containing high levels of aluminium, the population was exposed to a cocktail of other metals such as copper, zinc and lead as the acid solution dissolved metals and sediments in the mains. Copper and zinc levels of up to 9,000µg/l were recorded at customers' taps, while lead levels reached up to 350µg/l. Much higher figures were measured in hot water systems. In themselves these may have caused health effects which need to be considered in any attempt to evaluate chemical exposures during the incident.

The local health authority also responded in a low key. According to the Lawrence report, it was informed of the acidity and aluminium problems in the supply on 7 July. It was also alerted to aluminium levels of up to 40,000µg/l on 12 July. But no emergency response was triggered, and the authority appears to have believed that the incident passed with no significant health complaints.

Delayed official study
The view of the water industry and, to an extent, the medical establishment, has been that aluminium in drinking water is not toxic. This is a controversial opinion, but it was one promoted by the Lawrence report.

The report said that the only effects to be expected were "sensations of nausea and discomfort." It continued: "Aluminium salts are abundant in nature, universally present in food and, in the form of aluminium hydroxide which was the form present in the water in this incident, are widely used in medical preparations. There is relatively little uptake in the gastro-intestinal tract and any excess is readily excreted in the kidneys."

The response of the Department of Health (DoH) was delayed. Six months after the event, it commissioned a report from a group of health experts headed by Professor Dame Barbara Clayton - a physician and prominent member of the medical establishment.

Published a year after the incident, the group's report concluded that most symptoms had been "mild and short lived". Although acknowledging that increased absorption of aluminium may have occurred, it concluded that increases in body levels would have been "transient" and "all the known toxic effects of aluminium are associated with chronically elevated exposure."

The group concluded: "It is not possible to attribute the?health complaints to the toxic effects of the incident, except insofar as they are a consequence of sustained anxiety." It went on to blame the media for whipping up public concern.

The conclusions were greeted with disbelief and outrage in the Camelford area. But the issue refused to lie down. Scientists reported high levels of aluminium in the blood and bone of affected residents. Hospital discharge rates were well above average, and doctors confirmed reports of memory loss and other psychological problems. Concern was voiced in the press over nail and skin problems and potential effects on children.

An epidemiological study by the health authority found that residents supplied by the Lowermoor works were more likely to report excess joint pain than those served by a neighbouring works. Another study of congenital birth defects found an excess of cases of club foot.

However, both studies were later found to be flawed because the control area used was the neighbouring Bastreet supply zone. This also had a history of high aluminium levels in water, and had a derogation under the EC Directive on drinking water quality due to the "nature and structure of the ground," allowing supplies to contain up to 500µg/l of aluminium.

In October 1990, following a health authority conference in Truro which highlighted these health effects, the Clayton Committee was called upon to examine the new evidence. But its findings did not change.

Reporting in November 1991, it concluded that there was no "convincing evidence that harmful accumulation of aluminium has occurred nor that there is a greater prevalence of ill health in the exposed population." It attributed high aluminium levels found in blood to sample contamination, and concluded that symptoms such as joint pains, memory loss and fatigue were "common in all populations" and that their incidence in the locality was "not excessive".

Legal action by residents meant that the Committee did not have access to Dr Altmann's findings. However, the report did comment that "in the absence of adequate exposure data the cause of any abnormal results would remain a matter of surmise."

"Whitewash" charge
The report has been condemned by Environmental Assistance as a "whitewash". The Clayton Committee did not consider that the SWWA's measurements might underestimate exposure, be biased in favour of lower readings, or fail to represent isolated parts of the supply system. And it did not acknowledge that the incident may have been part of an on-going pattern of high aluminium levels in the water supply.

At the time of the incident, the Lowermoor works was probably incapable of complying consistently with the 200µg/l limit for aluminium. Its lime dosing system regularly broke down, jeopardising the flocculation process. The result would be to supply un-neutralised acid water enriched with aluminium.

Moreover, after the incident, when reducing aluminium levels became a priority, press reports revealed that Environment Secretary Michael Howard had been forced to admit that "significant operational and mechanical failures" at the works had caused continuing episodes of elevated aluminium levels in the supply.

Neither was the Lowermoor works unusual. In October 1989, the new water company, South West Water, made undertakings to improve 24 water treatment works in order to ensure that the aluminium limit was met by the end of 1994.

Many of those alleging long-term health effects from the incident complained of neurological problems such as memory loss and dementia. Evidence of aluminium's role in these effects was equivocal at the time and remains so today. But the Clayton Committee appears to have believed that health impacts were wholly implausible, and placed overriding emphasis on the orthodox views of the likely impact of aluminium on health.

Livestock deaths
The Committee also made little effort to reach its own conclusions about the health of those claiming to have been affected. According to a member of the Camelford Scientific Advisory Panel - established by residents to provide advice and gather evidence on the incident - the Committee flew down from London to interview just a dozen patients and several GPs. It returned to London the same evening unconvinced it had seen any health effects at all.

Another line of evidence that the Committee chose not to pursue was effects on local livestock. The Camelford Scientific Advisory Panel noted unusual mortalities at some farms where stock were watered with mains supplies. Some 1,300 hens died at one farm, and 40 Muscovy ducklings died at another. Lambs on another farm also died, and a piggery suffered a decline in fertility and increased post-natal mortality. Analyses of tissue samples showed elevated levels of aluminium, copper and iron in liver, kidney, bone and hair.

However, the Clayton Committee dismissed the findings as "at marked variance with the local Veterinary Investigation Centre which saw no noticeable increase in health problems" among farm animals. Although it conceded that aluminium levels were elevated in some tissues, this appears to have been given no weight in its conclusions.

Privatisation sensitivities
The choice of Professor Clayton to chair the inquiry was an interesting one. In January 1989, privatisation of the water authorities was only nine months away, and continuing publicity about the Camelford incident was drawing the City's attention to the industry's potential liabilities. What the Government needed was a safe pair of hands.

Professor Clayton had been a member of another controversial working party which advised the Department of Health in the late 1970s on the effects of exposure to another neurotoxic metal pollutant - lead in petrol. The group, chaired by Professor Patrick Lawther, produced a report which was the basis of the Government's last stand in defence of lead in petrol.

Lead emissions from vehicles had become a major public concern at the time because of mounting evidence from the US and Germany that low levels of lead exposure affected the intelligence and behaviour of children - and that petrol lead was a significant source of exposure.

Professor Clayton's own research had consistently failed to find ill-effects of lead exposure in children. She was also one of four scientists who displayed a lack of objectivity in 1974 after being asked by the Department of Health to prepare a critique of a key US study which had shown a relationship between lead and neuropsychological dysfunction in children. Their paper made serious criticisms - but it was eventually shown to be based, not on the full published work or data obtained directly from the researchers, but on a 250-word abstract.

Call for a public inquiry
In opposition, the Labour Party promised a public inquiry into the Camelford affair. Local campaigners and Environmental Assistance have now called for that promise to be honoured. Ministers have not ruled out an inquiry - but neither have they taken a decision on the matter in over two years.

The water industry, meanwhile, evidently still regards the affair as highly sensitive. In September 1998, Environmental Assistance and local campaigners organised a conference on the incident, and asked the industry's trade association, Water UK, to send a speaker as well as inviting water companies to send representatives.

On 27 August, Water UK said it would be happy to send a speaker. But something quickly changed its mind. By 4 September, it had discovered that it had no one "qualified to speak on the issue, and our member companies are unable to release anyone to attend." Only a couple of water companies were represented at the conference.

Likewise, the Cornwall and Isles of Scilly Health Authority refused to send a speaker - claiming that the programme was unbalanced, but missing the opportunity to correct the balance.

A dossier putting the case for an inquiry was submitted to Deputy Prime Minister John Prescott in 1997. North Cornwall Liberal Democrat MP Paul Tyler said after last year's conference that he had been assured that Ministers were examining the case. "They now accept that there has never been a proper, open examination of the accident itself, or - more important - of the failure of the Authority to inform residents adequately or even let them know that their supply was contaminated." Mr Tyler said last month that he was still hopeful there would be a "fresh look at these issues".

Further information from:
    1 Altmann, P et al 1999, British Medical Journal, Vol 319, pp 807-811.