TY - JOUR

T1 - Study of plant-air transfer of PCBs from an evergreen shrub: Implications for mechanisms and modeling

AU - Barber, J L

AU - Thomas, G O

AU - Kerstiens, Gerhard

AU - Jones, Kevin

PY - 2003/9/1

Y1 - 2003/9/1

N2 - The depuration of gas-phase polychlorinated biphenyls (PCBs) from a slow-growing evergreen shrub, Skimmia japonica Thunb., was studied to investigate the reversibility of uptake and the compartmentalization of PCB congeners within leaves with respect to air-plant exchange processes. Depuration of PCBs was monitored over periods of hours, days, and weeks. Equilibrium had not been attained between air and leaves during the uptake phase after many weeks. Depuration followed two-phase clearance kinetics, with phase 1 occurring over the order of hours and phase 2 continuing slowly over weeks. In phase 1, a substantial part (ca. 40%) of the PCB burden that the plants had accumulated over weeks was lost in 2-3 h. This observation is further evidence for the close dynamic coupling of air and vegetation compartments. In the second phase,very slow depuration over 28 d only removed a further similar to25% of the accumulated PCB burden. Depuration rates in phase 2 varied between compounds and were not influenced by growth dilution. Depuration rates for both phases were not correlated with K-0A, indicating that plant-air mass transfer coefficients were proportional to plant-air partition coefficients and, therefore, probably dominated by the plant-side resistance to diffusion. Photolysis and metabolism are unlikely to have influenced the rates of congener disappearance. Pathways into the leaf and possible storage locations within the plant are discussed with respect to the observed differences between uptake and clearance rates. Uptake and depuration are not mirror image processes, with a fraction of accumulated PCBs effectively stored in the leaves. This has important implications for terrestrial food chain transfer and global cycling with leaf concentrations remaining elevated long after a contamination event.

AB - The depuration of gas-phase polychlorinated biphenyls (PCBs) from a slow-growing evergreen shrub, Skimmia japonica Thunb., was studied to investigate the reversibility of uptake and the compartmentalization of PCB congeners within leaves with respect to air-plant exchange processes. Depuration of PCBs was monitored over periods of hours, days, and weeks. Equilibrium had not been attained between air and leaves during the uptake phase after many weeks. Depuration followed two-phase clearance kinetics, with phase 1 occurring over the order of hours and phase 2 continuing slowly over weeks. In phase 1, a substantial part (ca. 40%) of the PCB burden that the plants had accumulated over weeks was lost in 2-3 h. This observation is further evidence for the close dynamic coupling of air and vegetation compartments. In the second phase,very slow depuration over 28 d only removed a further similar to25% of the accumulated PCB burden. Depuration rates in phase 2 varied between compounds and were not influenced by growth dilution. Depuration rates for both phases were not correlated with K-0A, indicating that plant-air mass transfer coefficients were proportional to plant-air partition coefficients and, therefore, probably dominated by the plant-side resistance to diffusion. Photolysis and metabolism are unlikely to have influenced the rates of congener disappearance. Pathways into the leaf and possible storage locations within the plant are discussed with respect to the observed differences between uptake and clearance rates. Uptake and depuration are not mirror image processes, with a fraction of accumulated PCBs effectively stored in the leaves. This has important implications for terrestrial food chain transfer and global cycling with leaf concentrations remaining elevated long after a contamination event.

KW - SEMIVOLATILE ORGANIC-COMPOUNDS

KW - POLYCHLORINATED-BIPHENYLS

KW - PASTURE TRANSFER

KW - CHEMICAL VAPORS

KW - GAS-PHASE

KW - BIOCONCENTRATION

KW - FOLIAGE

KW - LEAVES

KW - GRASS

KW - PAHS

U2 - 10.1021/es0261326

DO - 10.1021/es0261326

M3 - Journal article

VL - 37

SP - 3838

EP - 3844

JO - Environmental Science and Technology

JF - Environmental Science and Technology

SN - 0013-936X

IS - 17

ER -