No Commissioner shall have any pecuniary interest in any contract, employment, leases, purchase or sale made under the provisions of this Act, and any such transaction made in which any Commissioner has a pecuniary interest shall be void ab initio; provided, however, that any property required for the purposes of this Act in which a Commissioner has a pecuniary interest may be acquired but only by gift or condemnation.
(`77 Code, § 15.05)