Influence of the Chemical Form of Mercury on its Adsorption and Ability to Leach Through Soils

The adsorption of Hg by two soils, differing in chemical and physical characteristics, indicated that both organic Hg compounds (methyl mercuric chloride [MMC] and phenyl mercuric acetate [PMA]) and inorganic compounds (mercuric chloride [HgCl2]) followed the linear form of the Langmuir adsorption isotherm. The highest adsorption maxima for all Hg compounds were found for the soils which had the higher organic matter content and clay content. Adsorption maxima increased in the order MMC < PMA < HgCl2. A two‐rate effluent leaching experiment was conducted utilizing undisturbed soil cores of the same two soils and the same three Hg compounds (labeled with 203Hg) which were applied uniformly to the top 0–10 cm of each column. In contrast to the movement of other cations in the effluent and soil, even at the higher irrigation rate, none of the applied Hg was found to move below the 10‐ to 20‐cm soil layer. More MMC than HgCl2or PMA were found in the 10‐ to 20‐cm layer; however, the differences were small. The lack of movement of Hg and the high adsorption maxima was a consequence of the strong binding between Hg compounds and soil. The inability of weak chemical extractants (CaCl2, NH4OAc, DTPA, EDTA) to remove significant quantities of Hg confirmed this hyphothesis. Seven to 31% of the applied Hg was lost from the columns during the experiment presumably by volatilization.