Mercury in tree wood has been overlooked in ecosystem science, in part because concentrations are so low as to often be below detection limits of some analytical methods. We tested methods for the preparation and analysis of Hg in tree wood by analyzing samples of four species at the Hubbard Brook Experimental Forest, New Hampshire, USA, using thermal decomposition, catalytic conversion, amalgamation, and atomic absorption spectrophotometry (USEPA Method 7473). Samples that were freeze-dried or oven-dried at 65 ˚C were suitable for analysis of Hg, whereas oven-drying at 103 ˚C resulted in Hg losses, and air-drying resulted in Hg gains, presumably due to adsorption from the indoor atmosphere.
Mean (± SE) concentrations of Hg in wood were 1.7 ± 0.3 ng g-1 for American beech, 0.8 ± 0.3 ng g-1 for sugar maple, 1.9 ± 0.1 ng g-1 for red spruce and 1.3 ± 0.1 ng g-1 for balsam fir. Mean (± SE) concentrations of Hg in leaves were 22.7 ± 1.6 ng g-1 for American beech, 18.0 ± 1.5 ng g-1 for sugar maple, 19.5 ± 2.2 ng g-1 for red spruce, and 33.2 ± 3.4 ng g-1 for balsam fir. Based on these samples, we estimated the Hg content of wood in the reference watershed at Hubbard Brook (0.14 g ha-1) to be at least as large as the foliar Hg pool (0.07 g ha-1). Mercury in wood deserves more attention; we suggest that biomass burning may be an important source of Hg emissions to the atmosphere.