Alex Caldicott, 11 years old, cups a handful of chirping primrose fluff. 'That's what a duckling should look like]' he says.

Through the living-room window, the incinerator stack of Rechem International, the chemical waste disposal company, rises above the trees at the edge of the field just beyond the garden. There is a sharp smell in the air, and a grinding noise.

Other than that, the Victorian stone farmhouse - down a rural lane, a kingfisher by the nearby stream - should be a child's paradise. Alex lives there with his parents and 15-year-old brother, Andrew, and in the surrounding land the family keeps two cats, three horses, a dog, 12 chickens and 27 ducks and ducklings.

Those ducklings have been one focus for Alex's anxiety. In the past few years some have hatched blind, others with limp, hanging necks. Poultry are sometimes born with disabilities. This year, after a University of East Anglia investigation - commissioned by the Welsh Office - of Rechem's site and the adjacent area, the Caldicotts were told not to eat or sell their ducks' eggs.

They were contaminated with 10 times the level of PCBs (polychlorinated biphenyls) as other eggs in the area, which the report thought was probably due to the ducks eating contaminated grass and soil.

Alex and Andrew have now been granted legal aid to sue Rechem International, claiming that emissions from the company's premises have increased their risk of developing illnesses, in particular cancer; damaged their quality of life, and put them in fear of future ill health. Rechem has always denied any charge of causing harm to health, and says it will defend vigorously any legal action of the kind described.

Environmental legal action based on seeking damages for fear of future harm is common in the United States but unusual, if not unprecedented, in this country. If the boys succeed, many others who live near industrial plants will be encouraged to take similar action.

The East Anglia report found levels of airborne PCBs at the Caldicott's home, Pontyfelin House in Pontypool, south Wales, to be 100 times higher than in a nearby rural area. Airborne dioxins were found to be 10 times higher than reported for UK urban areas.

Whether, or at what levels, PCBs or dioxins are damaging to humans is a controversial area. The exact effect of PCBs is unknown. Dioxins have been unequivocally linked to cancer in animals. Some studies have suggested that dioxins may also be linked with an increased incidence of certain human cancers, but some scientists say the evidence is inconclusive.

The East Anglia report concluded that, with the exception of the duck eggs, the increased exposure of humans to PCBs at Pontyfelin was small. On their own, the airborne dioxins would come to about half the World Health Organisation's estimated tolerable daily intake for an adult.

When the report was published David Hunt, then Welsh Secretary, said that the levels found did not pose a significant risk to the food chain or to public health. This was rebutted by Greenpeace, which says that Mr Hunt had no health studies of people in the area to support his claims. Michael Averill, the managing director of Rechem, says that a scientific study showed levels of PCBs in recycled stationery 10 times higher than anywhere around his site.

If the Caldicott boys' case reaches court, the scientific debate is likely to be lively and impassioned. In a separate case which opened in the High Court this week, Rechem has been accused by two farmers of negligence, nuisance and breach of duty in the operation of a former waste disposal plant in Stirlingshire. The farmers allege that hundreds of cattle died or had to be destroyed because of toxic emissions from the plant. Rechem denies the claims.

The Caldicotts' story began when they moved to Pontyfelin House six years ago, aged five and nine. Their father, Dr Ken Caldicott, a research chemist, was not worried by the closeness of the Rechem plant. Nor was their scientist mother, Shirley, a biology teacher. Both were locally born and, if anything, treated complaints about Rechem with cynicism.

''We thought other people were over-reacting,' says Dr Caldicott. 'Until we saw the smoke.'

Smoke of varying colours was seen coming from the stack, with the plume sometimes dipping to the ground. Dr and Mrs Caldicott rang various authorities, including Her Majesty's Inspectorate of Pollution, but say they received little response. Baffled, then irritated, and finally angry at the lack of response, they began to collect evidence - keeping a diary and taking photographs and videos.

Rechem says the incidents of smoke emission reported by the Caldicotts and campaigning groups were relatively few. They were investigated and, according to statements made in the Commons by a Welsh Office minister, presented no evidence of widespread contamination.

None of these statements has reassured the Caldicott family. 'Sometimes I'm frightened of going out,' says Alex. 'When we first experienced the smoke, my brother was playing cricket. A huge cloud came and covered us. I was seven. At first we said: 'It's smelling a bit.' There was smoke everywhere. We thought it was a fire. We ran into a hay barn, and then we ran to my mother.'

Exactly what was in the smoke, on this and other occasions, Mrs Caldicott is unsure of.

It was not the last panic. On 12 July 1991 Andrew, then 12, had just finished a training day with Army cadets. He came back to the house with three friends. 'We listened to music and then three loud bangs rattled the windows,' he says. 'There was loads of smoke coming out. We went outside. The fire alarm sounded like an air-raid siren. I thought: 'Oh My God, I'm going to die'. We thought the whole place would explode.'

They ran back into the house. Andrew picked up the video camera and filmed the scene outside. 'Then we tried to work out from our chemistry lessons what would be the best thing to do. Should we hit the deck? Then we thought it might be a heavy gas, so we shouldn't lie on the ground. So we ran upstairs and we hit the deck there instead.'

Meanwhile his mother had arrived, horrified to see the house engulfed by smoke. She sounded the car horn repeatedly and the boys ran out, holding their hands over their mouths and noses. They roared off. 'I didn't know the Astra could go that fast]' says Andrew admiringly.

The family was told that sodium sulphur cells at Rechem's plant had become wetted by rainwater and, accordingly, combusted. They did not suffer any burns or damage.

Andrew's schoolboy attempt at scientific analysis in the midst of panic is typical. Both the redheaded boys want to be scientists when they grow up. Their childhood has taken place against a background of scientific campaigning as their parents fought to find out what was happening at their home. Dr Caldicott, 43, says he has spent hours interpreting data from research commissioned by a local action group so that it could be understood. 'This business has been very costly in time,' he says.

Andrew says that in many ways he is sick of the whole subject. 'It doesn't affect my going outside,' he says. 'It's the invisible implications. I don't burst into tears over it. But it's not fair if I might become ill. Going to court doesn't worry me.'

Their mother does worry, about the way in which the issue has dominated their lives. 'If they make models for competitions,' she says, 'it's always models of Rechem. They draw the stack. Their teachers were worried that they were becoming obsessed. We're obsessive ourselves. Obviously they pick it up.'

Alex has written poems about Rechem:

I like the smell of flowers. I like the smell of nice food. I like ham.

I don't like the smell of cars. I don't like (worry is crossed out) carrying things. I don't like the smell of Rechem.

There is hope that the smell will improve. Rechem's licence was renewed, despite local protest, in July, and it has begun spending pounds 9m on improvements to the incinerator and stack at the plant. Rechem, which welcomed the conclusions of the report from the University of East Anglia that, with the exception of a 'localised area' which covers Pontyfelin House, the contamination near its site was not hazardous, says it has always been one of the most monitored and scrutinised plants in the country, and Her Majesty's Inspectorate of Pollution has said that the plant is now operating under the stricter conditions of the Environmental Protection Act.

Meanwhile, the Caldicotts ride their ponies in the shadow of the stack. A side-effect of the family's campaigning efforts is that their home is famous throughout Gwent for being contaminated. They doubt whether they could sell it. In any case, they say they do not wish to move. After the university report the family was advised that if they wanted reparation for the damage they allege has been caused, their only course was to sue the company privately.

'I said, you must be joking]' says Mrs Caldicott. 'It would cost an arm and a leg. I haven't pounds 100,000 to put up. But we have to try to fight.'

And so Andrew goes off to shut up the ducks, and Alex disappears to play with his computer, while the ducklings cheep quietly in their incubator at polluted Pontyfelin House.

(Photograph omitted)