Environmental groups in Cork have expressed anger at the disclosure that 250,000 litres of caustic soda leaked into Cork Harbour while a ship was being unloaded at Ringaskiddy almost three weeks ago.

They are demanding an explanation from the Environmental Protection Agency (EPA), which was informed of the incident but decided at the time not to make a public statement about it.

Late on 2 July a cargo of caustic soda was being unloaded from a ship into storage tanks at the ADM plant at Ringaskiddy in Cork Harbour. The company manufactures citric acid for soft drinks and caustic soda is one of the ingredients.

The ship was docked at a jetty and the caustic soda, which is corrosive, was being pumped to storage tanks in the ADM plant through a flexible hose.

During the unloading more than 250 tonnes of the chemical, or a quarter of a million litres, escaped through an open valve in the pipeline into Cork Harbour.

The leak was discovered within half an hour and ADM's site emergency plan was put into operation.

Environmental groups in Cork only discovered the incident yesterday.

The EPA, which was informed of the incident by the company, says that while it was serious, there was no risk to human health and the impact on marine life was localised and short-lived.