Mercury poisoning sufferer Jeremy Piven is buying a TriBeCa penthouse located, ironically, a few blocks away from sushi palace Nobu. Sources say the “Entourage” star has closed a deal on a 6,000-square-foot Hudson Street penthouse that once belonged to former Mets slugger Mike Piazza. The duplex, housed in the same building as Jon Stewart’s palatial pad, was listed by Prudential Douglas Elliman for $6.2 million. Piven’s new digs — bizarrely referred to in a listing as “muscular & voluminous!!” — has three baths and 1,800 square feet of outdoor space. Reps for Piven, who has been looking to buy a downtown pad for a while, didn’t get back to us.