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Fate and Speciation of Gasoline-Derived Lead in Organic Horizons of the Northeastern USA

^a Dep. of Earth Sciences, Dartmouth College, HB 6105 Fairchild Hall, Hanover, NH 03755
^b Environmental Studies Program, Dartmouth College, HB 6182 Steele Hall, Hanover, NH 03755
^c Yale School of Forestry and Environmental Studies, 370 Prospect St., New Haven, CT 06511

View larger version (21K): [in a new window]   Fig. 1. Locations sampled in 1980, 1990, and early 2000 in the northeastern regional forest floor survey.

View larger version (12K): [in a new window]   Fig. 2. The fractional amount of Pb loss calculated over the study period is significantly correlated with the thickness (cm) of the forest floor at each site. A logarithmic fit to these data give r2 = 0.65.

View larger version (105K): [in a new window]   Fig. 3. Micro-focused SXRF map of an Oe/Oa horizon collected from Whiteface Mtn. Units are in total counts of Pb collected over a 2 s interval.

View larger version (18K): [in a new window]   Fig. 4. Micro-focused XRF data collected for Ca, Pb, and Fe on transects from X to X' and Y to Y' on Fig. 3. Fe data are shown 5% scaled.

View larger version (19K): [in a new window]   Fig. 5. An example X-ray diffraction tracing obtained using micro-focused XRD on Pb-enriched soil grains identified in Fig. 3. Since substantial diffraction peaks are not evident, crystalline Pb minerals not likely to be significant in the O horizon.

View larger version (24K): [in a new window]   Fig. 6. Pb LIII radial distribution functions (left) derived from XAS experiments given for two Oa samples collected from the coniferous zone at Camels Hump Mountain. Theoretical shell fitting was done using an oxygen and an iron shell in FEFF 7.02. On the right, Fourier-filtered data from the backtransformed spectrum over R + = 2.9 to 4.1 Å are given; these data are used to derive the Pb-Fe coordination numbers and interatomic distances that we report in the text.