Recipient Organization
STATE UNIV OF NEW YORK
(N/A)
SYRACUSE,NY 13210
Performing Department
Forest & Natural Resources Management
Non Technical Summary
Mercury, a neurotoxic pollutant, has increased greatly in the environment due to emissions fromanthropogenic activities such as coal combustion and gold mining (Krabbenhoft and Sunderland 2013).Mercmy has been studied extensively in aquatic ecosystems, but is less well described in forests, althoughforests are important receptors, and biological Hg hotspots largely occur in forest regions (Evers et al.2007, 2011). The accumulation of Hg in vegetation is important to predicting the fate of Hg in terrestrialecosystems and in the aquatic systems downstream from them (Grigal 2002). Since wood is the largestbiomass pool in forests, it is likely the largest Hg pool. In a Douglas-fir stand in Washington, the woodcontained 0.5 g Hg ha-' compared to 0.3 g Hg ha-' in foliage, even though the concentrations of Hg infoliage were 24 times higher than in wood (Obrist et al. 2012).One reason that Hg in wood is rarely measured is that concentrations are low and analyticalmethods have not been optimized to detect them. For example, the Hg content of alder wood was belowdetection in a comparison of hardwoods and softwoods in Washington State (Obrist et al. 2012), and theconcentrations of maple species (red maple, sugar maple, and silver maple) were often below detection ina study in Ontario (Siwik et al. 2010). In a comparison of 13 forested sites across the United States, only 4had Hg concentrations in bole wood that were above the detection limit (Obrist et al. 2011).Where it has been measured, the concentrations of Hg in the boles of softwoods appear to behigher than those in hardwood species, which are more often below detection (Obrist et al. 2011 ). Forfoliage and leaf litter, which are more often measured than wood, conifers have been reported to havehigher Hg concentrations than hardwoods. In a study in Ontario, pine needles had Hg concentrationstwice as high as birch leaves (Hall and Louis 2004). At Acadia in Maine, litter Hg concentrations were nearly twice as high in the softwood than the hardwood site (Sheehan et al. 2006). Older red pine needlesin Minnesota had higher concentrations than younger needles, presumably due to their longer exposure(Fleck et al. 1999). If conifers differ from hardwoods in their rate of Hg accumulation in biomass, thisdifference will be important to understanding Hg retention in ecosystems and in determining whetherthere is cause for concern in biofuel burning and processing from different forest types (Siwik et al.2010).The mechanism for Hg accumulation in tree boles is a matter of dispute. Some claim that thesource of Hg in wood is translocation from the foliage (Fleck et al. 1999, Grigal 2003) because rootuptake is thought to be minimal in field settings (Grigal 2002). Uptake of Hg into plant tissues fromsolution (Bishop et al. 1998) and from soils (Frescholtz et al. 2003) has been demonstrated in thelaborat01y. Measuring nutrient uptake at the root surface using intact roots in the field is feasible for somenutrient elements (Yanai et al. 2009) but not for Hg, because loss from solution could be caused bysorption to the root surface, and thus might not be an indication of uptake and translocation. Mercury hasbeen measured in xlyem sap of pine and sprnce, and while the rate of Hg transport through the bole couldaccount for only~ 10% of that in litterfall (Bishop et al. 1998), transport through the bole in xylem sapsuggests that Hg moves from soil into the wood. Notably, the species studied by Bishop et al. (1998) wereconifers; we are not aware of any similar measurements in hardwoods.Measuring concentrations of Hg in wood as a function of wood age, in tree rings, could be ameans to settle the question of the atmospheric vs. soil origin of Hg in wood. Atmospheric Hgconcentrations have been declining since the early 1990s (Slemr et al. 2011); thus, if atmosphericdeposition to leaves is the source of Hg in wood, it should be lower in more recent years. Alternatively, if soil is the source of Hg to wood tissues, concentrations should be relatively stable or even increasing overtime, due to continued, albeit lessened, inputs to soils from throughfall and litterfall (Yu et al. in press).The results of this project will lower the barriers to further investigation of Hg cycling in forestecosystems and demonstrate the importance of including forest biomass as a Hg pool in understanding thefate of Hg in the environment. These are outcomes that will change the future of research on Hg in forestsworldwide and ultimately the management of the forest resource with regard to this important pollutant.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The purpose of this seed-grant project is to test and refine methods for the analysis of Hg in wood.
Project Methods
First, we will determine whether tissue Hg concentrations are above the analytical detection limit usingconventional dry combustion. If this method fails, we will use digestion, oxidation, purge and trap, anddesorption, which is much more sensitive (both methods are described below). We will also evaluate theeffect on Hg recovery of air-drying and oven-drying samples, compared to freeze-d1ying samples prior toanalysis, which is the standard procedure. Many archived wood samples could be appropriate for Hganalysis if these methods can be validated; few are freeze-dried.We have already collected disks from the boles of American beech (Fagus grandifolia Ehrh.),sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britton), at the HubbardBrook Experimental Forest in New Hampshire, and have begun testing them under the direction of MarioMontesdeoca, Laboratory Manager of the Center for Environmental Systems Engineering at SU. We willcollect samples of wood from red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea (L.) Mill),which will improve the utility of the results and their value in future requests for funding. Replicate samples from each of 5 species will be prepared by freeze-d1ying at -80° C, air-dryingat 20° C, and oven-d1ying at 65° C and 103-105° C. Prelimina1y tests on leaf material suggest that thedifference in Hg concentration due to sample diying can be explained by moisture content. If Hg is notlost in air- or oven-d1ying, this will greatly simplify sample preparation in future research efforts.Sample analysis for total Hg will use a Milestone DMA 80 or a Leco AMA 254 (method 7473,USEPA 1998), with a method detection limit (MDL) of0.2 μg kg- 1• Samples below detection using thatmethod (which may be improved by dosing) will be digested in nitric acid and hydrogen peroxide andanalyzed for total Hg using an automated oxidation, purge and trap, desorption, and cold-vapor atomicfluorescence spectrometry (method 1631, revision E, USEPA 2002), with an MDL of0.004 μg kg-1. Thismethod is thus 50 times more sensitive than the standard method which has failed to detect Hg in wood ofhardwood species in some previous studies (Siwik et al. 2010, Obrist et al. 2011).