Assets securing public deposits shall be delivered to a custodian for the benefit of all public bodies whose funds are secured by the assets from time to time. A banking institution may act as custodian unless disapproved for this purpose by the Comptroller of the Currency in the case of a national bank or by the Department of Banking in the case of a State banking institution. The depository may make changes and substitutions in, additions to and withdrawals from the pool of assets delivered to a custodian, subject to the duty of the depository at all times to maintain the total amount of assets pledged at least in the amount required for all public deposits secured thereby. If the custodian is the trust department of a depository bank it shall have the responsibility to determine the validity of a pledge, the amount of assets required to be pledged and the eligibility or adequacy of the assets pledged and shall use reasonable care in the custody and preservation of the assets in its possession. Except where an agreement among the public body, the depository and the custodian with respect to the handling and disposition of pledged assets which are not pooled with other such assets provides otherwise, in the event of insolvency of a depository, the custodian may surrender the assets in its possession to the receiver or other successor in interest of the depository.