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Lead Studies

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Lead bullet through gelLead bullet gel radiograph

An overwhelming number of studies have accumulated over the last 120 years examining the risk to humans from various lead exposure pathways. These results have definitively shown that ingestion or inhalation of lead dust and particles in sufficient quantity causes very harmful impacts to human physiology, especially nervous system function. Studies assessing the effects of lead exposure to wildlife have gained increased emphasis since 1950, while during the last 5 years, awareness of the potential for lead exposure to both wildlife and humans from inadvertent ingestion of lead bullet fragments has gained recognition by hunters, wildlife researchers, public health officials, and veterinarians. Further studies are currently underway to better understand the potential for health risks.

Selected SCIENTIFIC PUBLICATIONS with summaries:

Turkey Vulture Lead Dosing Study

Turkey Vultures were fed lead shot to determine their physiological response. Two separate groups of three birds each were continually fed two different doses of lead. Of the three birds fed a small dose (3 pellets) one was euthanized after 170 days due to coordination problems, no appetite and general weakness. All three of the high dosed birds (10 pellets) died. Two after 143 and 148 days and the third was euthanized at day 183. All of the birds showed internal signs of lead poisoning.

Bald Eagle Lead Dosing Study

Five Bald Eagles were given five different doses of lead shot. The birds were fed doses ranging from 10 pellets to 156 (10, 20, 30, 80, and 156 pellets given) and all five birds died (on days 20, 12, 10,133, and 125 respectively). The birds that died on day 133 was euthanized because it was blind from lead ingestion.

Andean Condor Lead Dosing Study

Four Andean Condors were given doses of lead shot ranging from 7.3-8.5mm in diameter: roughly the size of #0 Buck shot pellet. Two birds were fed two pellets each feeding and two were fed six pellets each feeding. One of the low dosed birds was found dead on day 46 and the other survived to the end of the study but was euthanized after researchers determined the bird’s survival was unlikely and further suffering was unnecessary. The high dosed birds died on days 41 and 39. One bird was found dead and the other was euthanized due to lethargy, weight loss, and loss of coordination.
Using Lead Isotope Analysis to Document Time Sequences of Lead Poisoning in California Condors-
This study used isotopic lead signatures to determine the time sequences of lead poisoning in California Condors. Researchers analyzed the growing feathers from free-flying condors in California to establish a bird’s lead exposure history. Researchers were able to monitor lead exposure in California Condors that otherwise might have been missed during biannual blood testing. This study was also able to link a case of a pig shot with lead ammunition to condor lead poisoning using isotopic readings.

Patterns of Mortality in Free-ranging California Condors

This study takes a look at all of the California condor deaths from 1992 through December 2009. A total of 135 condors died; 98 were recovered and sent in for necropsy. Out of the 98 recovered Condors, 76 cases were able to confirm definitive causes of death, 53 were anthropogenic. Trash ingestion was the most important mortality factor in nestlings with 8 out of 11 deaths. Lead toxicosis was the most important factor in juvenile and adult mortality;   13 out of 50 juveniles and 10 out of 15 adults died from lead toxicosis. Of those 23 birds that died from lead poisoning 9 birds had lead metal fragments in their digestive tracts.

Lead Exposure in Free-Flying Turkey Vultures Is Associated with Big Game Hunting in California

This study found that the range of blood lead levels of Turkey Vultures is correlated to the intensity of deer and pig hunting in an area. In areas where hunting pressure is low the turkey vultures showed low blood lead level. The study showed that areas with higher hunting pressure resulted in higher blood lead levels in turkey vultures.

Lead Exposure in Bald Eagles from Big Game Hunting, the Continental Implications and Successful Mitigation Efforts

Researchers studied bald eagles around Grand Teton National Park and the National Elk Refuge for lead poisoning. They looked to see if lead exposure in bald eagles increased during the fall hunting season for elk and bison. They found that during the hunting season lead exposure increased in scavenging avian wildlife and exposure was very limited during the rest of the year. By partnering with local hunters to increase use of non-lead ammunition they were able to decrease lead exposure levels in the bald eagle population, even while hunter success increased.

The Persistent Problem of Lead Poisoning in Birds from Ammunition and Fishing Tackle

Scientists review research on the different pathways avian species are exposed to lead poisoning. Their main findings suggests most of the pathways can be traced back to hunting ammunition and fishing with lead weights. They highlight some of the important needs for future research to help guide policy, and potential mitigation methods that can help conserve wild birds.


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