A consignment of genetically modified corn containing an illegal strain was impounded yesterday by Department of Agriculture officials in Co Louth.
The shipment of livestock feed, which came in from the US, was seized at Greenore Port near Dundalk as it did not have the necessary documentation for entry into the EU.
After testing, the corn gluten feed was found to be contaminated with the banned Bt-10, a genetically modified strain of maize.
"We are satisfied that the testing arrangements and protocols that are in place worked very well," said a spokesman for the Department of Agriculture.
The matter is being investigated but officials have described the breach as an "inadvertent contamination" and the company in question has reportedly co-operated fully with the department.
"The matter will have to be examined," said the spokesman, who added that the feed would be unloaded, tested and then destroyed.
According to the European Commission the shipment was tested in the US and the positive results for Bt-10 were sent to Ireland so officials here could stop the cargo on arrival.
"The Irish authorities are taking necessary measures to ensure that the contaminated consignment does not enter the food chain," commission spokesman Philip Tod told a news conference in Brussels yesterday.
Last month the EU blocked imports of maize from the US unless shipments carried proof that they were free of Bt-10, which is not authorised for use either in Europe or the US.
The curb will be reviewed at the end of October but the EU's food safety chief said last month the conditional ban may be extended if more contaminated products were discovered.
US exporters send 3.5 million tonnes of corn gluten feed to Europe each year, a trade worth some €350 million.