Lead Exposure of Obligate Avian Scavengers in Eastern North America

Abstract

Lead is a toxic element within the body of living organisms. Lead poisoning cases still occur in both humans and wildlife on a regular basis in the United States. Although the harmful effects of lead within the body are well known, such as decreased IQ in children, increased renal dysfunction, hypertension, anemia, and other morbid and mortal consequences in humans and wildlife, lead continues to be used in anthropogenic activities today. Through the use of lead in ammunition and fishing sinkers, and its presence in coal-fired power plant and other industrial emissions, lead is dispersed throughout modern human and natural systems. Due to the persistence of anthropogenic lead-use, it is necessary to understand the pervasiveness of this toxin in both modern ecosystems and throughout the body of individuals. To understand the degree to which wildlife populations are chronically exposed, we quantified lead levels within American black vultures (Coragyps atratus) and turkey vultures (Cathartes aura); two species that are useful as environmental sentinels in eastern North America. Individuals of both vulture species are known to be more resistant to the effects of lead toxicity than are many other animals. This resistance allows vultures to accumulate and harbor lead for a longer period of time than more sensitive species, thus providing us with a lifetime lead exposure history. In our study, chronic lead exposure was quantified from femur lead concentrations of 98 black vultures and 10 turkey vultures and compared to lead concentrations of liver tissues sampled from the same individuals. We found that the extent to which vultures are exposed suggests that anthropogenic lead permeates eastern North American ecosystems to a previously unrecognized degree. Discovery of an epidemic of chronic lead exposure in such widespread and common species and the failure of soft-tissue sampling to diagnose this pattern has dramatic implications for understanding modern wildlife and human health concerns. Bone sampling, however, is difficult to replicate in living individuals. Although bone provides information regarding the depth and breadth of lead exposure, blood is most commonly sampled in live individuals. This is because phlebotomy is one of the most minimally invasive sampling techniques currently available, which makes it attractive despite the fact that blood and other soft tissues (liver, kidney) are indicative of only recent exposure to lead. However, if an individual's blood (collected by phlebotomy) or muscle (collected by biopsy) lead levels could be statistically linked to the amount of lead found within its bone, it would permit use of less invasive sampling techniques to reveal total body lead burden. Therefore, to determine if soft tissue lead concentrations have a quantifiable relationship with femur lead concentrations, we collected and analyzed multiple tissues (femur, liver, kidney, breast muscle, and thigh muscle) from the 108 black and turkey vultures mentioned above. We found that although all soft tissues we...