The Coastguard have given up its search for the source of the substance which killed hundreds of seabirds off the Dorset coast.
The Maritime and Coastguard Agency (MCA) launched an investigation to find the source of a chemical which contaminated birds off the south coast of England.
Tests on a sample of the substance identified it as polyisobutene, which is commonly carried on ships across the world.
An MCA spokesperson said: "Despite further tests, we have been unable to identify specific components of the product that may have helped us find the source.
"We did not receive any reports of pollution within the English Channel area at the time when the birds were coming ashore, but a MCA counter pollution surveillance aircraft surveyed the English Channel. No pollution was detected.
"As such, we have concluded that it is highly unlikely we will be able to link the pollution to any specific vessel. Unless we receive any new information, our investigation is now closed."
Yesterday, it was announced that hundreds of birds rescued from the contamination will soon be released back into the wild.