Effects of reduced lead deposition on Pied flycatcher (Ficedula hypoleuca) : tracing exposure routes using stable lead Isotopes

• To what extent the lead burden of birds living in strongly contaminated ecosystems is responding to decreased atmospheric lead deposition is not well known. In this study, we measured lead concentrations and stable lead isotope ratios (206Pb/207Pb and 208Pb/207Pb) in liver and feces from pied flycatcher nestlings (Ficedula hypoleuca) along a 90 km pollution gradient from the Rönnskär smelter in northern Sweden. Changes in lead concentration in the birds from 1984 to 2006 were used for assessing the recovery of the environment following reduced lead emissions at the smelter. The 206Pb/207Pb and 208Pb/207Pb ratios were used to identify lead sources to the birds. Lead concentrations in liver and feces have decreased since the 1980s, typically by 9−15% (liver) and 18−40% (feces) as a result of a 98% emission reduction. This relatively weak recovery is explained by a transfer of old lead contaminants accumulated in soil to the birds via their prey, which was evident by a 206Pb/207Pb ratio in liver tissue (1.15 ± 0.01) that overlapped with the ratio in ants (1.16 ± 0.01) and organic soil horizon (1.17 ± 0.01) rather than the current atmospheric lead pollution (1.11 ± 0.01). Our findings suggest that insectivorous birds living around smelters may remain contaminated decades after ceased emissions.

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