Section 8. The department shall take all proper measures to obtain from Boston, without expense to the commonwealth, a conveyance of all the present right, title and interest of said city in and to Apple Island, and the flats appurtenant thereto, and in and to any other flats and rights of said city on the easterly side of East Boston, which the department deems are required for the development contemplated by section four, and said Boston may make such conveyance, and in furtherance of the development of the port make conveyance to the department or others, but only for maritime or commercial improvement, of any shore lands owned by it elsewhere, acquired either by purchase or taking.