Six containers filled with thousands of litres of toxic diesel sludge have been dumped on the side of the road near Dunleer in Co Louth.
Two of the containers leaked sludge across the former main Dublin to Belfast road.
The road was closed for a time this morning for the clean-up operation.
The toxic sludge is a by-product produced when dye is illegally removed from agricultural diesel, which is then sold as more expensive road fuel.
Louth County Council has spent €820,000 this year cleaning up the sludge abandoned on roadsides around the county.
Last year, the local authority spent €1m on removing material, but it is expected the figure will be much higher this year.
