"It is clear... that waste sugar solution... originating on the Wyeth Medica site in Newbridge, County Kildare... was wrongly labelled as 'green list' waste and shipped under this classification to Bioland, the firm at the centre of the investigation into pig feed contamination," it said.

Feed tainted with MPA, which scientists believe can cause infertility in humans, has been uncovered at thousands of farms across Europe, particularly in the Netherlands, Belgium and Germany.

Under European Union rules waste exports are classified as "green", "amber", or "red". Only the latter two classifications require the notification of relevant national authorities.

The agency said it had not been notified Wyeth was exporting waste containing MPA through Dublin-based waste brokerage service Cara Environmental Technology Ltd.

"This would appear to be in breach of (Wyeth's) Integrated Pollution Control licence," said the agency.

In a statement Wyeth said it would continue to co-operate with the investigation.

"As soon as Wyeth Medica Ireland was contacted by the Department of Agriculture it immediately ceased sending waste to Bioland through Cara," it said.

A Cara spokesman said the company was co-operating fully with the investigation and had "followed the letter of the law" regarding the shipments.

Last week Ireland said was halting shipments from Wyeth and launching an investigation after identifying the plant, southwest of Dublin, as the source of the contamination.