THE people of St Kilda, forced by poverty and bureaucratic intransigence to abandon their unique way of life in 1930 but seen as an idyllic society living in harmony with nature, had probably been polluting their environment for centuries.

Scientists from Aberdeen University have discovered high levels of heavy metals and other toxins in the soils of Hirta, the only inhabitable island in the group and the one on which St Kildans practised their subsistence agriculture.

The research may prompt a revision of the public perception of St Kilda supporting a society of hardy Utopians, winning a living from being at one with nature in the harshest of physical conditions.

Professor Andrew Meharg, of the university's plant and soil science department, believes that in the absence of any other obvious explanation, the hazardous concentrations of lead, zinc, cadmium, and arsenic probably came from the remains of millions of seabirds which formed the islanders' staple diet, possibly for millenniums.

Radio-carbon dating of one settlement in Village Glen indicates 3850 BC as the earliest settlement on Hirta.

St Kildans probably never numbered more than 200 at their peak, in the eighteenth century, and when evacuated in 1930, on board SS Dunara Castle, only 36 returned to the mainland.

They had existed on the islands, the rim of an extinct volcano, because of the seabird colonies - the gannet, the fulmar, and the puffin, in particular - which in previous centuries were vast.

The archipelago extended to no more than 2000 acres and yet they are still home to 400,000 breeding pairs of 15 species of seabird.

In the 1800s, said Darren Kindleysides, marine policy officer for RSPB Scotland, the puffins alone numbered an estimated three million.

St Kildans killed more puffins than all other species put together - 89,000 in one year alone - ate the flesh, made candles from the fat, and quilts from feathers.

What remained was thrown in the midden - a pit beside each house - in which valuable cattle dung and ashes from the house fires were carefully stored. In spring, the resultant fertiliser was dug into the impoverished soil to force on the staples of barley and potatoes.

Mr Kindleysides said: ''Seabirds prefer to eat sand eels, particularly at breeding time, because they are rich in oily fat. But we now know that the natural trace elements in the seas, such as those found in the soils of Hirta, concentrate in fish fats.

''In recent times, because of our industrial pollution, this has become more serious. A whale which famously washed ashore on a Belgian beach in 1994 was declared toxic waste because of the concentrations of PCBs and dioxins in its tissue. It is perfectly feasible that bio-accumulation of toxins in the seabirds caused the soil contamination.''

Professor Meharg said: ''The island community on the remote St Kilda archipelago, which has often been viewed as a Utopian society, given their closeness to the environment and local self-government, polluted the farmland of St Kilda with a range of potentially toxic elements, such as lead, zinc, cadmium, and arsenic.

''This contamination will change the perception of the St Kildans living in harmony with their environment.''

Robin Turner, senior archaeologist for the islands' owners, the National Trust for Scotland, professing amazement at the results of the research, said: ''Up to now, we thought of St Kilda as an idyllic society living in blissful harmony with nature. The demise of the community is always blamed on external pressures, firstly from the landlord, then from visitors, and latterly from the increased expectations of the population.

''Now we can see that the islanders were unwittingly poisoning the soil on which they relied, and perhaps themselves too. This makes the story even more interesting for us today. The message is that not only do we need to live in harmony with our environment, but we need to be very sure that any apparently sensible changes we make don't have unexpected side effects.''

Professor Meharg, who has secured funding from the Leverhulme Trust to continue the investigation on St Kilda, pointed out that people in cities and other large conurbations lived with similarly contaminated soils as the result of industrialisation.