The moneys realized from the sale of bonds under the provisions of sections 644.501, 644.511, 644.516, 644.521, 644.526, 644.531, 644.541, 644.546, 644.551, 644.556, and 644.561 shall be paid into the state treasury to the credit of the water pollution control fund, and shall be appropriated by the general assembly for the purposes for which the bonds are hereinabove authorized to be issued and for the payment of all necessary expenses incidental thereto.