Scientists at the University of Strathclyde have detected significant levels of mercury at the bottom of the Union Canal close to the site of a former Nobel munitions factory near Falkirk where thousands of tonnes of waste containing the hazarous metal was dumped in the past.
Analysis by researchers revealed that concentrations of mercury in sediment in the stretch of the waterway nearest to the old military plant at Redding have dropped markedly down from 12,100 milligrammes per kilogramme (mg/kg) in 1992 – when the problem was first discovered – to 199 mg/kg in 2012.
However levels further away from the factory site in both directions were noticeably higher.
The greatest concentration of mercury, of 565 mg/kg, was found about two and a half miles west of the factory – and about three miles from the Falkirk Wheel – raising concern the chemical may still be leeching into the canal from “huge” areas of the surrounding land.
Dr Christine Davidson, environmental analytical chemist at Strathclyde, said: “The canal has been cleaned up but it seems that somehow the mercury is coming back in from somewhere… It could be that a huge area of soil still has some contamination… or there could be little hotspots. We would like to explore this further and find out if the sediment [which is contaminated] is moving.
“We would also like to find out which kind of mercury it is, because different forms have different levels of toxicity.”
Dr Richard Dixon, director of Friends of the Earth Scotland, said: “Most alarming is the suggestion that there is still a substantial pocket of mercury leeching into the water… soil sampling and testing of fish caught in the canal are needed to show exactly how big the problem is.”
Consuming contaminated fish can be fatal, while mercury poisoning has also been linked to birth defects and autism.
The Scottish Environment Protection Agency, which has continued to monitor water contamination, said samples “still exceeded” environmental quality standards, but mercury levels were on a downward trend.
Falkirk Council, which has responsibility for land contamination, said that after previous soil sampling met environmental standards it was “highly unlikely” that mercury was coming from the earth rather than the canal.