Five people have been arrested as part of a cross-border investigation into the contamination scare in the pork industry which cost pig producers an estimated 120 million euro.
Four men were detained north of the border in Co Tyrone and Co Armagh by detectives belonging to the Police Service of Northern Ireland and a man in his 50s was arrested by gardai in Co Monaghan in connection with the investigation.
At the time of the alert, just before Christmas 2008, shelves across Europe had to be cleared of pork produced in Ireland after traces of dioxins were found in oil used in the making of feed to pigs and cattle.
The four men held in Northern Ireland are being questioned on suspicion of fraud by false representation - moving oil without proper authorisation.
The oil was allegedly supplied to producers in Ireland, who lost an estimated 120 million euro.
Members of the Garda National Bureau of Criminal Investigation, which launched the initial investigation, are liaising with police colleagues north of the border.
The man in his 50s is being held at Monaghan garda station under Section 4 of the Criminal Justice Act. He can be questioned for up to 24 hours.
Three of the four men arrested in Northern Ireland are from the Dungannon and Coalisland areas of east Tyrone. The fourth was detained in Blackwatertown, Co Armagh. They are aged 43, 29, 27 and 25 and it is understood some of them are related.
A High Court judge ordered a Northern Ireland company to pay 38.7 million euro damages to a Co Wexford company arising from the animal feed contamination. Mr Justice Peter Kelly ruled that Millstream Recycling Ltd was entitled to the damages against O'Neill Fuels Ltd, of Coalisland, Co Tyrone, which had denied supplying any fuel containing dioxins.
The 2008 recall was ordered after pig meat on a number of farms was found to have had between 80 and 200 times more dioxins than the recognised safety limit. Dioxins such as polychlorinated biphenyls (PCBs) were detected in the biscuit feed meal for pigs and cattle.