Telomere length declines with mean blood lead concentration in an urban passerine

Lead (Pb) is a highly toxic and widespread environmental pollutant and can severely harm body tissues as well as DNA. Pb could potentially damage telomeres, whose length and shortening rate are linked with cellular senescence, physiological state, and mortality. Yet, studies investigating Pb and telomere dynamics in natural systems remain inconclusive. In this study, we used a free-living house sparrow (Passer domesticus) population in Broken Hill, Australia, chronically exposed to varying levels of environmental Pb, to assess the effects of Pb on telomere length and telomere rate of change. Using all data from adults and juveniles, we found that mean blood Pb concentration had a negative relationship with telomere lengths measured at capture sites, such that a standard deviation increase in the concentration of blood Pb was associated with an 8 % decrease in telomere length. In a series of robustness analyses we found that this negative relationship existed at both the individual and the site levels. Although not statistically significant, the relationship between telomere length and soil Pb also appeared to be consistent with that found for blood Pb. Our results demonstrated that while exposure to Pb damages telomeres in free-living house sparrows, the biological effect is relatively weak, and is only identified with a sample size of over 500 individuals. Nevertheless, our data reveal that in this urban setting in Australia, a human commensal bird is suffering from lead-induced damage to telomeres. Given the well-established relationship between telomere shortening and life-span, our study highlights a clear risk of Pb contamination on the biota of the urban area, including humans.