Lead is a poisonous metal present in a variety of commercial products, and as a pollutant from industrial activities. Lead has become an environmental contaminant in many areas of the world, and in many habitat types both urban and rural. When ingested or inhaled, the body "mistakes" lead for calcium and other beneficial metals, and thus incorporates lead into nerve cells and other vital tissues. Results in humans and wildlife include neural degeneration, modification of kidney structure and bone, inhibition of blood formation and nerve transmission, and numerous other harmful manifestations (Eisler 1988). Death may occur acutely, or the individual may emaciate as a result of digestive paralysis (Locke and Thomas 1996). Clinical symptoms associated with blood lead concentrations exceeding one part per million may include depression, lethargy, vomiting, diarrhea, nonregenerative anemia, anorexia, blindness, and seizures (Locke and Thomas 1996, Kramer and Redig 1997). Accumulating evidence of the effects of sublethal exposure points to permanent adverse effects upon cognitive function in human children with histories of blood levels averaging 0.1 parts per million - a level formerly considered benign (Canfield et al. 2003).

Scientific evidence of the effects of lead on human health has brought forth large scale restrictions on its use in the United States, including the prohibition of lead in gasoline and paint. Responses on behalf of wildlife have been less forthcoming, but Bald Eagle consumption of contaminated ducks and geese contributed to the 1991 ban on lead shot for waterfowl hunting in the United States (United States Department of the Interior 1986). Other countries have instituted similar measures. Evidence of lead exposure in arctic subsistence hunters who continue to use lead shot (Dewailly et al. 2001, Johansen et al. 2003) suggests that the ban in behalf of eagles may have benefited humans as well.

Lead ammunition is still used in America for purposes other than waterfowl harvest, and the extent to which lead is secondarily ingested by wildlife and humans has been the subject of some recent investigations. Mourning doves, for example, confuse shotgun pellets for grit and grain around hunted stock ponds and accordingly die in large numbers (Schulz et al. 2002). Harmata and Restani (1995) found lead in the blood of 97% of 37 Bald Eagles and 85% of 86 Golden Eagles captured as spring migrants in Montana during 1985-1993; they implicated lead bullet fragments in ground squirrel carcasses as one source. Pattee et al. (1990) reported that among 162 free-ranging Golden Eagles captured during 1985-86 in southern California, 36% had been exposed to lead. Six of nine dead eagles in Japan died of lead poisoning, and five had lead bullet fragments in their stomachs (Iwata et al. 2000). Lead ingestion was a principal cause of recorded death in wild California Condors prior to the mid-1980s when the population was brought into captivity (Wiemeyer et al. 1988).

Field studies by The Peregrine Fund from 2000 to the present show that ingestion of lead rifle bullet fragments and shotgun pellets from animal remains is likely the only significant obstacle to the establishment of the California Condor in the wilds of Arizona and Utah. Evidence includes (1) high rates of lead exposure and required treatment, (2) the presence of lead fragments or shot in radiographs of condors and their food, and (3) temporal and spatial associations of condors with the remains of gun-killed animals (Parish et al. in press, Hunt et al. 2006, Hunt et al. in press). During the 2006 hunting season, 90 percent of 57 free-ranging condors showed evidence of lead exposure, and four died of it, including a proven breeder almost 12 years old. This represents an 11% mortality rate for birds five years old or older, a meaningful consideration given the high sensitivity of condor populations to mortality within the older age categories. The additional unknown proportion of condors that would have died without treatment renders doubtful the survival of the species in the wild without continuing, intensive management.

Close monitoring of condors by radio tracking and blood testing, together with ancillary studies of lead prevalence in gun-killed deer and other animals, have produced new insights regarding the pervasive nature of lead contamination in scavenger food webs. One must now consider, on a global scale, the scope of sickness, death, and demographic impact inflicted upon a myriad of species by a contaminant now so easily substituted with less toxic alternatives. The invention of highly efficacious non-lead bullets and pellets during recent decades parallels the discovery of lead’s widespread impact on wildlife (and coincides with additional studies documenting lead's effects on humans), and it is evident that conditions now favor large scale mitigation.

An important step in understanding this problem is the gathering together of relevant knowledge and scientific progress on these important topics. Nowhere would such an assembly of facts and interpretation be more fruitful than in the proceedings of a conference of world experts. The Peregrine Fund therefore proposes to bring them together in May of 2008, and to publish the proceedings and resolutions soon thereafter.

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