A FIRM has been fined £600 for releasing illegally high concentrations of cyanide into a sewerage system.

Harvey Plating, of Yarm Road Industrial Estate, Darlington, was prosecuted by Northumbrian Water at Bishop Auckland Magistrates' Court yesterday, for releasing cyanide and zinc into drains above the legal limit.

On January 29, a scientific inspector employed by the water authority took samples of effluent, which were found to have 85mg of cyanide per litre and 110mg of zinc per litre.

Paul Kelly, for Northumbrian Water, said the legal amount of cyanide is 2mg per litre, because higher concentrations could result in hydrogen cyanide being released into the sewerage system.

Only 3mg of zinc per litre is allowed to be released into drains.

Mr Kelly said it is also important that levels of the metals were kept low because sewerage treatment works were not designed to get rid of them.

Company director Paul Fletcher, representing Harvey Plating, said: "We sincerely apologise for this incident. There is no excuse.

"It was an isolated incident that was rectified immediately. As a company policy, we try not to use these metals."

The company was fined £600 and ordered to pay £200 costs.