Pollutant Lead Mobility in Forest Soils of the Northeastern United States Evaluated with a 40-Year Resampling Study

Abstract Lead (Pb) is a toxic metal that was dispersed by humans worldwide largely through Pb gasoline combustion. Regional scale long-term datasets detecting changes and processes governing pollutant Pb pools are exceedingly rare. Here, we evaluated changes in forest floor (Oie + Oa) Pb from 1980–2021, differences in mineral soil Pb with depth (0–10, 10–20, 20 -30, and 30–50 cm), and variations in foliar and litterfall Pb at seventeen sites across the northeastern US. Forest floor Pb concentrations and pools have further decreased by 65 to 87% with forest floor Pb concentration response time ( TrespC ) of 35 years. The correlation between TrespC with the soil organic matter, site latitude, and site longitude highlights that colder sites have slower forest floor turnover that in turn promotes Pb retention. Forest floor Pb desorption was greatest for circumneutral organic ligands and mineral soil partition coefficient (Kd) varied among subregions and decreased with depth. Overall mineral soil Pb concentrations were 14.3 ± 2.2 mg kg −1 and mineral soil amounts (top 50 cm) were 27 ± 2.2 kg ha −1 . Seven forest floor Oa horizons still exceed ecological screening levels for impacting wildlife. Foliar Pb concentrations did not vary among genera nor correlated with soil concentrations. Estimated Pb litterfall fluxes (1 to 4 g ha −1 yr −1 ) were < 1% of the current forest floor pool, highlighting uptake discrimination against Pb. Our study highlights the power of sustained long-term repeated decadal measurements of legacy Pb to quantify changes and variation at a regional scale.