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Lead Concentrations Within The Condor Skeleton: Advancing Biomarkers Of Lead Exposure History And Poisoning

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Lead (Pb) poisoning is a global problem among avian species, including the endangered California Condor (Gymnogyps californianus). Condors are highly monitored and frequently lead poisoned and may serve as a model species to investigate Pb exposure biomarkers. Bone Pb levels are a well-recognized biomarker of Pb exposure and related health effects in humans but have not been used widely in avian species. My overarching objective is to further establish biomarkers of lead exposure history and poisoning in avian species using bone Pb concentrations. In chapter 1, I investigated whether bone Pb differed between and within condor bones, depending on Pb exposure history between epiphyses, mostly composed of trabecular bone type, and diaphysis, mostly composed of compact bone type. In chapter 2, I determined if Pb levels in different bones can be used as biomarkers of recent and cumulative Pb exposure history and examined the effects of Pb exposure on bone mineral density and potential risk for bone fracture. In chapter 3, I used Pb stable isotopic composition to inform about Pb uptake into multiple bones and bone regions. My results showed that Pb concentrations were ~3-fold higher in epiphysis than diaphysis of tibiotarsus in condors that died of Pb toxicosis but less than 2-fold in condors that died of other causes. A discriminant analysis using bone Pb concentrations correctly classified 17 out of 18 birds as to whether they were Pb poisoned at the time of death, suggesting that bone Pb, particularly tibiotarsus epiphysis proximal, can be used as an additional piece of information to inform recent Pb exposure. Bone Pb levels, particularly in tibiotarsus diaphysis, were associated with time in the wild, consistent with prior studies in humans showing that bone Pb levels in long bones reflect long term cumulative Pb exposure. I also found a modest negative association between bone Pb and bone mineral contents in epiphyses of long bones, suggesting that bone Pb may be associated with a reduction in bone mineral. Finally, using stable lead isotopes, I found that there was ~10-fold difference in the rate of Pb incorporation between the tibiotarsus proximal epiphysis and diaphysis following a Pb exposure event. In conclusion, bone Pb levels in condors, and by extension other large avian species, appear to be a valuable biomarker of both recent acute and cumulative Pb exposure, and may help inform Pb poisoning status at the time of death.

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