An estimated 3,000 litres of diesel sludge were found dumped in north Co Louth this week.
Three containers of the toxic oil-laundering waste were discovered on a slip road at Carrickarnon close to the main Dublin-Belfast road late on Wednesday night.
The sludge is generated after green dye is removed from agricultural diesel, which is then sold as road diesel in a multi-million-euro cross-Border racket.
Two of the containers were on fire and had to be dealt with by the Dundalk fire service. North Co Louth has in recent years become the main dumping ground for the cross-Border gangs involved in fuel-laundering.
The sludge poses a pollution threat. Last year the cost to the taxpayer of cleaning up 90 sludge finds in the county amounted to almost €1 million as specialist contractors have to be called in to remove the material, most of which is sent to Germany for safe disposal.
The four local authorities in Louth, Meath, Cavan and Monaghan, which have to deal with the waste, are currently evaluating tenders from expert contractors who will be appointed in the coming months to deal with finds of oil-laundering residue.