Distribution of biocides in Douglas-fir poles 42 months after application of groundline preservative systems
Morrell, J.; Forsyth, P.; Newbill, M.
Forest products journal 44(6): 24-26
Diffusion of four new external groundline preservative systems and two older pentachlorophenol-based systems was compared over 42 months in Douglas-fir posts in contact with soil. Preservative chemicals were detected up to 25 mm inward from the surface in nearly allsystems, although the levels varied widely. As expected, chemical levels were markedly lower in the inner zones than in the outer, reflecting the slow rate of diffusion from the surface. Also as expected, fluoride- and boron-based systems, which are water diffusible, migrated to the greatest depth; fluoride levels exceeded those of boron in all but three sampling times or locations. All four of the newly developed systems appear to be capable of diffusing into the wood for comparable distances and at levels similar to those found with older bandage systems. Further evaluations to determine when chemical loss necessitates reapplication are planned.