SCIENTISTS have identified the mystery substance responsible for killing hundreds of seabirds off the Dorset coast.

The ‘colourless, odourless, sticky’ substance is a form of polyisobutene, scientists at the University of Plymouth have discovered.

The university’s Professor Steve RowlandRowland led the research, based on a detailed examination of a guillemot, and said the substance was used as an additive in lubricating oils.

He said the substance was not known to be toxic but could act as an irritant, which might be why it had caused injuries to the birds’ legs.

He added: “It depends on exactly which manufacturer’s substance we are dealing with.

“Some websites I have looked at have safety sheets which say to avoid contact with the skin, and one or two said it can act as an irritant, which explains what happened to the birds’ legs.”

But despite the findings, investigators are no closer to finding the source of the contamination.

The Maritime and Coastguard Agency (MCA) confirmed yesterday that searches using satellite technology and counter pollution and surveillance aircraft had returned no results.

The agency has searched the area between Dover and the Isles of Scilly but no pollution has been detected.

The findings have been reported to the MCA and ProfessorRowland Rowland is hopeful that it will be used to aid the search for the source, though he admitted it ‘might be quite difficult’.

It is believed to be only the second reported incident of this substance being dispersed into the sea.

He added: “I do not think it will biodegrade but it may be that it will disperse and hopefully it will break up.

“The number of birds coming in over the last few days is much less than last week, which does reflect that.

“I think birds suffer most because they come into contact with anything floating about on the surface of the water, and it gets in their feathers.

“Other wildlife, like fish, are just able to swim away, so hopefully nothing else will be badly impacted.”

More than 300 birds were found washed up on beaches along the south coast, with the majority concentrated around Portland and Chesil Beach.

Those left alive but unable to fend for themselves were taken to the RSPCA centre at West Hatch, which is based near Taunton.