A method is presented for removing heavy metal anions from a fluid or gas medium containing metal anions. The method includes providing an adsorbent having deposited therein at least one oxygen-containing compound of at least one metal selected from the group consisting of iron, copper, and aluminum; and contacting a portion of the medium with the adsorbent. The oxygen-containing compound may be incorporated into the carbon by impregnation or dispersion of a suitable precursor of such a compound. The precursor may be further treated to yield the oxygen-containing compound. Such adsorbents are particularly useful for removing arsenic and/or selenium from the environment and may be used in treating drinking water sources.