A CHEMICAL time bomb could lie ticking beside some of the region's rivers, an academic has warned.

Farmers and environmental campaigners have joined a university team studying the pollution effects of last autumn's floods in North Yorkshire in calling for urgent research into the health implications of lead deposited on riverside pastures.

Research has uncovered high levels of the metal, which has been linked with brain damage in children, on rich grazing land next to the River Swale, which runs from the Yorkshire Dales and feeds through to the Vale of York and beyond.

Findings by the University of Wales, Aberystwyth, team show that last year's floods - the worst for a century - dislodged contaminated riverside soil deposited during lead mining eras in the Dales and North Pennines in the 19th Century.

The poisoned soil was then dumped down-river on fields grazed by cattle and sheep.

Professor Mark Macklin, who led the team, said more than three quarters of the sediment samples taken along a 110km stretch of the Swale exceeded guidelines for lead levels permitted in grazing land, sometimes as much as ten times the maximum level.

And while the research has focused so far on the North Yorkshire river, Prof Macklin - who moved to Wales after years at Newcastle and Leeds universities, and is an expert on the industrial legacy of our region's rivers - said most watercourses fed from the lead mining areas, including the Tees and Tyne, were likely to be similarly affected.

He said that more work would need to be done to establish any risk to livestock or humans feeding off the produce of contaminated sites.

But he added: "Flood plains do represent a chemical time bomb - we've known that for some time.

"We can assume that some of those metals brought down as a consequence of the autumn flooding will get into the crops, and if the animals are grazing on affected areas they are likely to be affected too.

"It really is a long-term problem, and in the most extreme cases the land should not be used.

"If these were brownfield sites in the centre of a city, development would not be allowed to take place or, if it did, the metal would have to be removed or covered up."

Prof Macklin said plants which resist pollutants should be sown in the most polluted fields.

His team has developed a computer model to forecast the dispersal of contaminants in sediment.

But initial findings from this model make potentially grim reading for North Yorkshire, with evidence that flooding in Swaledale and the Vale of York will continue to dump contaminants on farmland for the next 60 years.

He said that Bob Pailor, the Dales area environment protection manager with the Environment Agency, had already contacted him about the issue.

Further research will be eagerly awaited by farmers and environmentalists fearing the potential effects of yet another health scare.

Rodney Kettlewell, a former National Farmers' Union county president who farms near Bedale, was concerned but sceptical.

"It would be another blow to us and, like foot-and-mouth, another nail in farming's coffin," he said.

"It's something they must test for, but where do you stop - at the sea?"

Pete Bowler, national campaigns officer with pressure group Waterwatch, said the emerging legacy of lead mining could be one of several pollution dangers waiting to emerge.

Referring to riverside farmers, he said: "Here we have an industry that has been battered from all directions, and here is yet another threat.

"Who would they turn to for compensation, for goodness sake? The lead mines have long since closed?