Lead Mobility within the Xylem of Red Spruce Seedlings: Implications for the Development of Pollution Histories

Development of Pb pollution histories using tree ring analyses has been troubled by possible mobility of Pb within stem xylem. In a 2yr study, we exposed red spruce (Pic.ea rubens Sarg.) seedlings to Pb during one growing season, with Pb excluded in either the pre­ vious or following growing season. Lead levels within xylem rings and bark were subsequently determined using atomic absorption analyses. Lead concentrations in tissues from exposed seedlings were significantly higher than controls, and significant Pb concentrations were found in xylem formed during periods of Pb exclusion. Routes of Pb movement are uncertain, but were mos t likely acropetal from temporary storage sites in the roots.