The use of Pb/ 210Pb ratios in lake sediments for estimating atmospheric fallout of stable lead in South-Central Ontario, Canada

Abstract

The ratio of Pb concentrations (μg g −1) to excess 210Pb ( 210Pb exc) activities (dpm g −1) in the surface (0–1 cm) sediments of lake cores, together with a knowledge of atmospheric 210Pb fluxes, were used to estimate the atmospheric deposition of stable Pb in south-central Ontario, Canada. Between three and five cores were collected from each of 10 lakes, while in one lake (Red Chalk - Main Basin) a total of 25 cores were obtained. The average atmospheric 210Pb exc flux to the main basin of Red Chalk Lake was calculated to be 1.1 dpm cm −2 year −1, a value which compares favourably with literature estimates of 210Pb deposition for Ontario. The surface Pb/ 210Pb exc ratios for 61 cores ranged between 1.26 and 3.44 μg dpm −1(average 2.15 ± 0.45 μg dpm −1). Therefore, the predicted atmospheric Pb deposition was 14–38 mg m −2 year −1 (average 24 ± 5.0 mg m −2 year −1). This estimate of stable Pb fallout is similar to those measured by alternate methods and indicates that elemental ratios in lake sediments might be useful for predicting the behaviour of other contaminants in lakes.