The hidden threat in your salmon

It looks pretty inviting there on the plate, with a slice of lemon and some brown buttered bread. It's Atlantic smoked salmon, the traditional luxury food that, more than any other, is now available to everyone, at not much more than the price of ham. Thanks to modern production techniques.

Look a little closer at that slice of salmon as it glistens so seductively in front of you. Is the colour a bit lurid? More like bubble gum than the traditional nicotine-tinged blush? Well that's because farm salmon - and 99 per cent of the salmon eaten in Britain is farmed - is made pink by being fed a dye called axanthin, also used in sun-tan pills, carcinogenic if used in excess. One popular brand of the chemical is called NatuRose - but there's little natural about dyeing the fish. Left to itself, farmed salmon would be the colour of cheddar cheese.

That's modern production techniques for you. It's all about pleasing the consumer. But what about the flavour of the smoked salmon - does it have that tartan-wrapped, old-smokehouse taste that the packet promises - or is it something a bit more chemistry lab? The closest some cheap smoked salmon comes to the traditional kiln of smoking oak chips is a vat of spray-on flavour known as Liquid Smoke.

There's worse. The succulent flesh may be tainted with antibiotics and growth enhancers; it certainly contains the residues of the pesticides the fish farmers use to control disease - infectious anaemia, necrosis and sea lice among them - in the packed cages in which farmed salmon pass their short lives. Battery chickens live no worse - a wild salmon is a great adventurer of a fish, crossing oceans during its four-year life. Farmed salmon, which reach maturity in 18 months, damage themselves as they try to leap from the pens that can contain 20 kilos of fish per cubic metre.

But this isn't just a tale to upset animal-lovers. Salmon eaters should worry too. New research shows that farmed salmon carry a possibly lethal load of polychlorinated biphenyls (PCBs) and dioxins, by-products of industrial chemical processes that have found their way into the sea. The pollutants show up in wild salmon, but the concentrations are generally higher in the farmed fish, perhaps because of the concentrated fish meal used as feed. According to some research, salmon alone may account for 60 per cent of the residual toxins in the fatty tissue of human beings.

"Eat just one 125g portion of farmed salmon and you could put yourself well over the EU food committee's proposed level for the weekly tolerable intake of dioxins and PCBs," says Dr Paul Johnston, environmental toxicologist at Exeter University, who has been leading a study of farmed fish and fish oils for Greenpeace. These pollutants are known to cause problems in the nervous system and immune systems - they are particularly dangerous to brain development in children, and are passed on through a mother's milk.

So - is salmon this year's beef? Are we watching the dawn of yet another food disaster, this time in a "healthy" food that we're all being advised to eat more of? "Absolutely not," says Brian Simpson, director of the salmon industry association, Scottish Quality Salmon. "Levels of the chemicals are generally decreasing and we as an industry are making certain the fish products we use are monitored very carefully. There's no cause for concern."

There are some disturbing parallels with the BSE story. Extraordinary growth in the industry during the Nineties - the UK produced 125,000 tonnes of farmed salmon last year, 18 times more than it did 15 years ago - brought on a frightening price crash, as supermarkets competed to bring the former luxury food to everyone. With Norway, Europe's biggest producer, undercutting prices, British fish farmers cut corners.

The feeding of the waste from dead salmon to their children in the cages has, thankfully, been outlawed, but "aquaculture" has some equally dubious practices. One of these is the (illegal) use of pesticides designed to kill parasites on sheep or cattle - these get tipped wholesale into the fish farms - a cheap solution to the fish farmer with tight margins, but the toxins get into the fish flesh and add to the lethal build-up in humans.

Mr Simpson says that his industry, just 20 years old, has grown up and is far less reliant on "medicines" than it used to be. "Organically produced" salmon is beginning to appear - at a price - on the market. But some observers ask why salmon is allowed to be sold with levels of contaminants present that would not be tolerated in other foodstuffs. In 1999 the Government's Food Stan-dard's Agency produced a report admitting that British fish eaters could be consuming dioxins above levels recommended by the World Health Organisation, but no action has been taken.