Mercury and plants in contaminated soils: 1. Uptake, partitioning, and emission to the atmosphere

The uptake, distribution, and subsequent emission of mercury to the atmosphere were investigated in five plant species (Lepidium latifolium [L.], Artemisia douglasiana [Bess in Hook], Caulanthus sp. [S. Watson], Fragaria vesca [L.], and Eucalyptus globulus [Labill]) with different ecological and physiological attributes. Transfer coefficients for mercury in the soil‐plant system were calculated. Plant‐to‐atmosphere emissions of mercury were determined using a controlled environment gas‐exchange system and ranged from 10 to 93 ng/m2/h in the light; emissions in the dark were an order of magnitude less. Transfer coefficients for mercury within the soil‐plant system increased acropetally (root‐to‐leaf axis) by orders of magnitude. Estimated mercury emissions from plants in the Carson River Drainage Basin of Nevada over the growing season (0.5 mg/m2) add to the previously reported soil mercury emissions (8.5 mg/m2), resulting in total landscape emissions of 9 mg/m2. For L. latifolium, 70% of the mercury taken up by the roots during the growing season was emitted to the atmosphere. For every one molecule of mercury retained in foliage of L. latifolium, 12 molecules of mercury were emitted. Within this arid ecosystem, mercury emissions are a dominant pathway of the mercury cycle. Plants function as conduits for the interfacial transport of mercury from the geosphere to the atmosphere, and this role is undervalued in models of the behavior of mercury in terrestrial ecosystems and in the atmosphere on a global scale.