Any municipality, or any board, commission, or other authority duly established by ordinance of any municipality, or the boards of trustees, respectively, of the firemen's relief and pension fund and the policemen's pension and relief fund of any such municipality, or the board of trustees of any retirement system created by the General Assembly of the State of Arkansas, may, in its discretion, invest any of its funds not immediately needed for its purposes, in bonds issued under the provisions of this chapter, and bonds issued under the provisions of this chapter shall be eligible to secure the deposit of public funds.