WATER and sewage treatment has left a "potentially nasty" legacy of 26 toxic sludge lagoons scattered around Scotland, an investigation by the Sunday Herald has revealed.

Tens of thousands of cubic metres of sludge contaminated with aluminium and other pollutants are being stored at sites near Wigtown, Barrhead, Coatbridge, Falkirk, Cupar and Inverness, as well as across Argyll, Aberdeenshire, Sutherland, Orkney and elsewhere.

An investigation into the safety of the sludge lagoons has been launched by the Government company, Scottish Water, while environmentalists are demanding the sites be cleaned up.

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According to the Scottish Environment Protection Agency (Sepa), 18 of the sites are left over from when drinking water was treated with an aluminium compound to remove impurities. The resultant sludges have been contaminated with aluminium, which has been linked to breast cancer, Alzheimer's disease and other health problems.

"There is a possible risk of such aluminium leaching," Sepa said, though its "binding nature" meant it was likely to stay in the sludge.

"Many people will be shocked to learn of these potentially toxic lagoons dotted around Scotland," said Green MSP Alison Johnstone.

"They are an unfortunate legacy and it's vital Scottish Water and Sepa properly assess them and figure out what to do with them."

Johnstone called for assurances that sites posing the greatest risk would be safely cleaned up as soon as possible.

"These lagoons are proof that we need sustainable infrastructure systems to minimise our impact on the environment and prevent future generations being left to clear up the mess we leave behind," she said.

Dr Richard Dixon, the director of WWF Scotland, said: "Aluminium is not something we want leaching out because it represents a danger to human health and to wildlife. This is a large and potentially nasty legacy Scotland needs to deal with.

"The public needs to be assured these sites are currently in good condition, and that, at the least, there is a detailed plan to make sure they stay that way. But we need to look for permanent ways to remove this threat to the environment."

It is uncertain how much sludge is in the lagoons, but Sepa said that the one at Cupar in Fife could contain up to 2000 cubic metres.

"Almost all these sites are still within the curtilage of existing Scottish Water works and are being maintained and managed to some extent," said Sepa manager, Colin Anderson.

"To develop greater understanding, Scottish Water is commissioning an extensive study to assess these sites and any potential risks they pose. We will continue to work with Scottish Water to ensure remediation is undertaken where required."

Scottish Water said the lagoons dated back to when local authorities provided water and waste treatment. It had inherited them when it was formed in 2002.

"Our focus is always to ensure we manage the material in a sustainable way," stressed a Scottish Water spokesman. For the sewage sludge, this means recycling it to land to use its nutrients.

"It is not believed these sites present a particular risk," he said.

"We are delivering a project to undertake surveys to understand the extent and nature of them, and to confirm environmental issues.

"This will help determine the means to manage them in agreement with Sepa."