A large amount of hydrochloric acid was discharged onto Greenabella marsh on Teesside from a factory belonging to Tioxide, an ICI subsidiary, which makes titanium dioxide, an ingredient of cosmetics. The marsh is part of the Tees and Hartlepool Foreshore and Wetlands Site of Special Scientific Interest, a network of pools, marsh and mudflats in the Tees estuary, a major wintering place for wading birds.
Greenabella marsh is an important haven for birds such as the curlew, redshank, teal and shelduck. It was feared the local invertebrate life, the shrimps, molluscs and worms on which the birds feed, could become contaminated with the acid and put the birds themselves at severe risk.
The acid is believed to have leaked into a stormwater drain and so out onto the marshland, which Tioxide owns.
The company itself discovered the leak and alerted the Environment Agency, whose officers spent yesterday supervising the pumping of seawater onto the marsh, which by last night was successfully diluting the spill.
The work will go on over the weekend until the water acidity level returns to normal.
Steve Hardy of the Environment Agency said it was one of the worst incidents he had attended. "The water was as acidic as you can get," he said.
Yesterday afternoon the first signs of dead invertebrates were seen but no dead birds had been found.