An ion-exchange model of lead-210 and lead uptake in a foliose lichen; application to quantitative monitoring of airborne lead fallout

Abstract

Lead, 210Pb and 210Po levels were determined in dated sequential growth of thalli of the foliose lichen Flavoparmelia baltimorensis from Great Falls and Plummers Island, Maryland. An ion-exchange model for uptake of Pb and 210Pb applied to these data is consistent with the experimentally measured Pb partition coefficient between water and lichen as well as the expected lead concentrations in rain. Lead-210/Polonium-210 activity ratios are significantly elevated in very young growth (<3 years old), as expected from model calculations. Retrospective Pb fallouts are computed which reflect the drop in gasoline lead emissions in the period sampled (1973–1986). With experimental determination of partition coefficients this methodology is a basis for retrospective quantitative monitoring of other airborne heavy metals using foliose lichens.