The routes and kinetics of trichloroacetic acid uptake and elimination in Sitka spruce (Picea sitchensis) saplings via atmospheric deposition pathways

A major flux of trichloroacetic acid (TCA) to forests is via wet deposition, but the transfer of TCA into tree foliage may occur by an above- or below-ground pathway. To investigate the routes and kinetics of TCA uptake, two groups of 10 Sitka spruce saplings (with an equivalent number of controls) were exposed to a single application of 200 μg TCA in solution, either to the soil only, or sprayed as a mist to the foliage only. The needle foliage was subsequently analysed regularly for TCA for 3 months during the growing season. Significant uptake into current year (C) needles was observed from both routes just a few days after application, providing direct evidence of an above-ground uptake route. Uptake of TCA was also observed in the previous year needle class (C+1). Kinetic modelling of the data indicated that the half-life for within-needle elimination (during the growing season) was ∼50±30 days. Most of the applied TCA appeared to be degraded before uptake, either in the soil, or externally on the sapling foliage.