ASSESSING LEAD BIOAVAILABILITY AND UPTAKE IN FORESTS AND THEIR SOILS ACROSS NEW ENGLAND, HINTS AT MODERN AND HISTORICAL LEAD CYCLING

Lead in a toxic metal that has been widely dispersed across New England from industrial, commercial, and municipal processes. One of the largest emissions of lead occurred from the addition of tetra-ethyl lead to gasoline, which was phased out from the Clean Air Act of 1970 and Amendments of 1977 and 1990. However, the pollutant lead exists in the forests of New England with the potential to leach into ground and surface waters or remain enriched in surface soils from biological cycling by trees. We conducted a spatial gradient of 48 sites from Connecticut and Rhode Island up to central Vermont and New Hampshire to assess the bioavailability and its uptake by trees. At each site we collected forest floor samples and mineral soil samples (0-10cm, 10-20cm, 20-30cm, 30-40cm, 40-50cm) and four upper canopy hardwood tree leaf samples. Pseudototal soil digests yielded decreasing Pb concentrations with depths and an average Pb concentration of 37 mg/kg across the 48 sites. However, several sites had forest floor and surface mineral soil horizons with >100 mg/kg. Across all soil horizons, exchangeability of Pb was < 3% demonstrating high sorption of Pb to soil materials. Foliar concentrations were comparable across sugar maples, red maples, oaks, American beech, and birches at less than 0.3 mg/kg, suggesting either similar uptake rates or exposure to modern atmospheric Pb sources. Similar patterns demonstrate either modern or historical impacts on Pb in soils and foliage.