MERCURY AND PLANTS IN CONTAMINATED SOILS - 1 - UPTAKE, PARTITIONING, AND EMISSION TO THE ATMOSPHERE

The uptake, distribution, and subsequent emission of mercury to the at mosphere 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 differen t ecological and physiological attributes. Transfer coefficients for m ercury in the soil-plant system were calculated. Plant-to-atmosphere e missions of mercury were determined using a controlled environment gas exchange system and ranged from 10 to 93 ng/m(2)/h in the light; emis sions in the dark were an order of magnitude less. Transfer coefficien ts for mercury within the soil-plant system increased acropetally (roo t-to-leaf axis) by orders of magnitude. Estimated mercury emissions fr om plants in the Carson River Drainage Basin of Nevada over the growin g season (0.5 mg/m(2)) add to the previously reported soil mercury emi ssions (8.5 mg/m(2)), resulting in total landscape emissions of 9 mg/m (2). For L. latifolium, 70% of the mercury taken up by the roots durin g the growing season was emitted to the atmosphere. For every one mole cule of mercury retained in foliage of L. latifolium, 12 molecules of mercury were emitted. Within this arid ecosystem, mercury emissions ar e a dominant pathway of the mercury cycle. Plants function as conduits for the interfacial transport of mercury from the geosphere to the at mosphere, and this role is undervalued in models of the behavior of me rcury in terrestrial ecosystems and in the atmosphere on a global scal e.