Maruti Sadashiv Ghavte (28) from Solapur district was detained when a pesticide bottle was found on him when he was entering Mantralaya this evening, police said.
Ghavte said he wanted to construct an access road to his land but the owner of the adjoining plot was refusing to cooperate, said a police officer.
He had come to Mantralaya to seek redress for this issue, he told police.
Marine Drive police in south Mumbai are conducting further probe.
Patil was seeking due compensation for his land, acquired for a project.