A skip hire boss has been detained as part of an investigation into the illegal dumping of thousands of tons of building rubble on the outskirts of Belfast.
Asbestos and other toxic waste has also discovered on hills above the city.
It is understood a second man is wanted for questioning in connection with the inquiry, which involves the Northern Ireland Environment Agency (NIEA).
Thursday's arrest by police followed a series of inspections of land at Ballyutoag Road on the northern outskirts of the city. The NIEA has dealt with several complaints, some going back 10 years, of illegal dumping.
The landowner has also started a civil action in the High Court in a bid to get the rubble shifted.
His legal representative, Ernie Waterworth of the Belfast firm of solicitors McCartan Turkington Breen (MTB) said: "Hopefully this positive action will signal the beginning of the end of a long running issue.
"Our client has given the enforcement agencies every possible assistance."
The Department of Environment revealed the man had also been arrested for questioning about money laundering and criminal damage.
His skip hire business is based in Co Antrim.
A statement said: "The arrest forms part of one of the most significant investigations carried out to date by the NIEA's environmental crime unit."