High Ozone Increases Soil Perchlorate but Does Not Affect Foliar Perchlorate Content

摘要

Ozone (O-3) is implicated in the natural source inventory of ClO4-, a hydrophilic salt that migrates to groundwater and interferes with the uptake of iodide in mammals, including humans. Tropospheric O-3 is elevated in many urban and some rural areas in the United States and globally. We previously showed that controlled O-3 exposure at near-ambient concentrations (up to 114 nL L-1, 12-h mean) did not increase foliar ClO4-. Under laboratory conditions, O-3 has been shown to oxidize Cl-to ClO4-. Plant tissues contain Cl- and exhibit responses to O-3 invoking redox reactions. As higher levels of O-3 are associated with stratospheric incursion and with developing megacities, we have hypothesized that exposure of vegetation to such elevated O-3 may increase foliar ClO4-. This would contribute to ClO4- in environments without obvious point sources. At these high O-3 concentrations (up to 204 nL L-1, 12-h mean; 320 nL L-1 maximum), we demonstrated an increase in the ClO4- concentration in surface soil that was linearly related to the O-3 concentration. There was no relationship of foliar ClO4- with O-3 exposure or dose (stomatal uptake). Accumulation of ClO4- varied among species at low O-3, but this was not related to soil surface ClO4- or to foliar ClO4- concentrations following exposure to O-3. These data extend our previous conclusions to the highest levels of plausible O-3 exposure, that tropospheric O-3 contributes to environmental ClO4- through interaction with the soil but not through increased foliar ClO4-.