A man has been arrested as part of the investigation into illegal tipping of waste at a site near the River Cherwell in Oxfordshire, the Environment Agency said.
The dumping of a 150-metre long mountain of waste in a field alongside the A34 in Kidlington, raising risks of pollution into the nearby river, provoked widespread outrage.
The Environment Agency, which was first alerted to the illegal waste dump in July, said co-operation between officers from its major investigation team and the South East Regional Organised Crime Unit has led to the arrest of a 39-year-old man from the Guildford area.