Atmospheric Emission and Plant Uptake of Mercury from Agricultural Soils near the Almadén Mercury Mine

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Abstract
Surface soils collected near the Almadén, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCO3 or NH4OAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 µg/g) and mine site soils (1 km; total Hg = 97 µg/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high‐density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while aerial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (∼0.13 and 0.33 µg/m2 per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.

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