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TECHNICAL REPORTS

Heavy Metals in the Environment

Dendrochemical Record of Historical Lead Contamination Sources, Wells G&H Superfund Site, Woburn, Massachusetts

^a Dep. of Earth Sciences, Boston Univ., Boston, MA 02215
^b Geosciences Dep., Wellesley College, Wellesley, MA 02481
^c Dep. of Environmental, Earth and Ocean Sciences, Univ. of Massachusetts Boston, Boston, MA 02125

^* Corresponding author (kurtz{at}bu.edu).

Received for publication September 13, 2006. Laser-ablation inductively coupled-plasma mass-spectrometry analysis of red oak (Quercus rubra) from a well documented heavy metal contaminated United States Environmental Protection Agency superfund site in Woburn, Massachusetts reveals decade-long trends in Pb contaminant sources. Lead isotope ratios (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) in tree rings plot along a linear trend bracketed by several local and regional contamination sources. Statistically significant interannual variations in ²⁰⁷Pb/²⁰⁶Pb suggest that atmospheric Pb is rapidly incorporated into wood, with minimal mobility subsequent to deposition in annual growth rings. We interpret the decadal trends in our record as a changing mixture of local pollution sources and gasoline-derived Pb. Between 1940 and 1970, Pb was predominantly derived from remobilization of local industrial Pb sources. An abrupt shift in ²⁰⁷Pb/²⁰⁶Pb may indicate that local Pb sources were overwhelmed by gasoline-derived Pb during the peak of leaded gasoline emissions in the late 1960s and early 1970s.

Abbreviations: LA-ICP–MS, laser ablation inductively coupled plasma mass spectrometry • SRM, standard reference material • USGS, United States Geological Survey