A BBC Wildlife documentary screened last Sunday has been accused of fabricating evidence to enhance viewing figures. Bill Durodié investigates whether the programme, part of the 'Warnings from the Wild' eco-gloom series, had a point or whether it was all a load of codswallop.

Salmon has been getting the BBC into hot water, but not Peter Salmon, the former Controller of BBC1, rather the programme 'The Price of Salmon', screened by BBC2 on Sunday evening. The high-profile documentary suggested that wild salmon may be becoming extinct, and was the subject of a radio debate on the 'Today' programme earlier in the week. It has spawned a rash of newspaper articles with titles such as 'Salmon Poison Alert' and 'King of Fish Contaminated by Chemicals', but also attracted condemnation for scaremongering from the recently established Food Standards Agency (FSA).

In essence Julian Pettifer, the programme's writer and presenter, claimed that farmed salmon are leading to the depletion of natural stocks as well as potentially damaging our health. To press the message home the 'beauty', 'power', 'grace' and 'endurance' of salmon, were contrasted to an 'intensive' 'industry' run by 'multinationals' and 'politicians' who have failed to learn the lessons of 'GM' or 'BSE'. Never mind that unlike cattle, salmon are natural carnivores, or that salmon returned to the River Thames in 1974 after a break of almost 150 years - in the effort to convince, everything was thrown into the pot. When they were not spreading sea-lice or being victims of 'stress', farmed salmon were disturbing natural habitats or even escaping, the latter appearing to be a bizarre metaphor for the dangers of racial interbreeding.

If this were not enough to convince, we were informed that these salmon now contain high levels of potentially dangerous pollutants. Being screened less than a fortnight after Christmas, this cannot have reassured the millions who will have enjoyed a welcome alternative to turkey over the festive season. Indeed, partly due to the spate of scare stories surrounding meat from farm animals, salmon has become one of our more popular dishes over the last decade and the industry as a whole has become the world's fastest growing food sector. Accusations of toxicity would not just harm producers concentrated in the Highlands and Islands of Scotland, Norway and Canada, but further erode consumer confidence in general as well as social trust in scientists and politicians in particular.

There may be many reasons why numbers of wild salmon appear to be in decline, such as problems relating to their freshwater habitats, rising seal populations in the absence of culls, or the fishing of their natural prey to feed the farmed variety, but these were not explored. As each apocalyptic scenario raised was quietly debunked - regulation and monitoring of parasites was working in Norway, impacts upon wild habitats are inevitable in all animal husbandry but the world's seas are pretty big and there is a necessary learning process - new and supposedly greater ones were raised in their stead. Infectious Salmon Anaemia (ISA) may have been contained, but there will be 'new diseases' that remained unspecified. Never mind the evidence, 'those who feel the case has already been made', were suffering from palpable outrage.

Reflecting a growing trend amongst contemporary panics, much of the research cited remains unpublished and hence unverifiable. Sponsored by the David Suzuki Foundation, a Canadian environmentalist group keen on religious metaphors and which has such scientific luminaries as Anita Roddick and Sting upon its Board of Directors, it admits to being based on 'a small sample size'. In the case of an independent study by Miriam Jacobs, a part-time lecturer studying for a PhD at the University of Surrey, which is cited as corroborating evidence, this consisted of tests on a total of 12 fish.

The researchers claimed to have discovered that farmed salmon, which now constitute some 98% of those we consume, contain levels of 'toxic' chemicals up to ten times greater than the levels found amongst their wild cousins. It was held that these pollutants originate from the concentrated protein pellets fed to the salmon. The pellets. made in part from fish the salmon would usually eat, were also purported to have high levels of such chemicals, although why this should be is far from evident and intriguingly these levels were less than in the salmon themselves. Specifically the chemicals 'causing concern' are polychlorinated biphenyls (PCBs), dioxins and other organochlorine compounds.

Tests on laboratory animals at very high doses suggest that these chemicals disrupt the nervous and immune systems as well as impairing development and possibly affecting fertility. But there is a vast gulf between potential and reality. Even in the worst instances, such as the explosion at a chemical plant in Seveso, Italy in 1976, nobody has ever been exposed to such doses for prolonged periods. The most potent dioxin, 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD), shot to public prominence as a result of the Seveso accident yet, the only abnormal finding detected to date amongst those exposed has been a form of acne. Nevertheless, in order to attract research funding its impact was overstated and it became known as 'the most toxic man-made chemical known'.

It is worth reminding ourselves that the first rule of toxicology is that all chemicals produce an effect, but it is the dose that makes the poison. The fact that a substance contains a toxin does not make it poisonous, otherwise all food, which invariably contains salt, a know toxin at high doses, would have to be banned. Nevertheless, resorting to the lowest common denominator of many such debates the programme repeated the cry; 'What about the children?', made famous in irony by the classic Simpsons cartoon episode; 'Much Abu about nothing'. A cursory look at the programme's message board on the BBC web-site after the event shows that this is where the greatest impact was felt.

Great import was attached to the recent downward revisions of tolerable daily intake (TDI) doses for such pollutants by the World Health Organisation (WHO) and the European Commission (EC). But, rather than using this as an example of how simply moving the goal posts can create a health scare, the programme-makers chose instead to berate UK government policy as reflected by the FSA's supposed reluctance to follow suit. In fact environmental levels of PCBs, now banned but once widely used as liquid coolants, lubricants and insulators on industrial equipment, and TCDD and other dioxins, products of many combustion processes including burning wood, have fallen steadily over the last twenty years.

Dietary intake of these in 1982 invariably exceeded the new TDI by up to ten times. The good news is that only the worst measured levels today marginally exceed this dose, and as an average this would have to be consistently repeated to breach the new recommendations. In other words you would be sick of salmon well before being made sick by it, although your mental health could be questioned if that was all you ate. If there remains a problem for children then presumably there is a whole cohort from the early 80s that are irreparably damaged and who can now serve as a source for much further experimentation.

Understanding that, unlike Billy the Fish, or the frenzied imaginations of the producers, man does not live by salmon alone, the FSA continue to adhere to the notion that in a proper risk analysis of the situation, the benefits vastly outweigh the risks. Eating fish is considered to be good for health and forms part of a balanced diet having a beneficial impact upon coronary problems and arthritis. Little wonder that Eskimos and the Japanese suffer less from these modern blights than all other cultures.

It is also worth indicating that the concerns that led to the WHO slashing exposure limits by 90% centred primarily upon these substances' purported actions as endocrine disrupting chemicals (EDCs), rather than their high-dose carcinogenicity, which has been disputed by the US National Academy of Science. EDCs are known by the media as 'gender-benders' and are chemicals that are held to affect our hormonal balance. Many of these are natural and found in food at doses millions of times greater than those to which we are exposed by synthetic compounds. Their action upon humans is widely disputed, as recognised by the EC in their own study, published last year, which showed no evidence for such effects. Nonetheless, they then followed the new WHO guidelines.

Meanwhile, the argument that modern intensive farming methods are to blame, smacks of an arrogant 'let them eat cake' attitude increasingly emanating from certain quarters. These people have simply transposed their instinctive hatred of the masses onto mass consumption. The fact that we can now all afford to eat salmon, thereby enhancing the overall health of the populace, is rejected for a presumed preference for 'natural' produce. Never mind that even connoisseurs consider wild salmon to be excessively salty and tougher than the farmed variety.

Miriam Jacobs, who undertook her research with the US Environmental Protection Agency (EPA), has since indicated that her findings have been misinterpreted and has requested an apology from the BBC, whilst the FSA are considering writing a formal letter of complaint. The evident nervousness and defensiveness of their officials on the programme however, is the real 'cause for concern'. This is unlikely to help its beleaguered chairman, Sir John Krebs, who has been previously accused of 'still giving advice like a scientist instead of a consumer health watchdog'. It seems you can set up new 'independent' bodies in the age of consumer risk but God forbid that they become too independent.

Bill Durodié is a research fellow with the European Science and Environment Forum and may be contacted for comment at w.j.durodie@lse.ac.uk