Uptake of two chlorinated chemicals in conifer needles: reversibility and compartmental analysis

The distribution of pentachlorophenol and 2,4-dichlorophenoxyacetic acid in conifer needles was studied following uptake from aqueous solutions for up to 21 h. Desorption kinetics revealed two compartments (C₁ j and C₂ ) in which organics were sorbed reversibly and one compartment (C_s ) from which organics could not be desorbed. Reversible sorption proceeded very rapidly (less than 1 h for equilibration) and was made up of sorption to the surfaces of cuticular waxes and sorption in waxes and cutin. C₃ appears to be identical with the apoplast and the symplast of needles. Penetration into C₃ proceeded slowly and remained steady up to 21 h (longer periods not tried). The distribution of organics between the three compartments varied with time of loading and depended on plant species and properties of solutes. Data are discussed in relation to methods of exposure monitoring.