Lead has long been known to be damaging to biology. It's previous use in gasoline, paint, pesticides, and solder in food cans has nearly been eliminated. Lead shot was banned for waterfowl hunting in 1991, but its use in ammunition for upland hunting, shooting sports, and in fishing tackle remains common.
Numerous previous studies have documented adverse effects to wildlife, especially waterbirds and scavenging species, like hawks and eagles, the researchers say. Lead exposure from ingested lead shot, bullets, and fishing sinkers also has been reported in reptiles, and studies near shooting ranges have shown evidence of lead poisoning in small mammals.
The USGS released images of a young eagle with lead shot inside it and the stomach of a pelican loaded with fishing gear.
Outdoor shooting ranges overall are thought to use more than 80,000 tons of lead shot and bullets each year, according to the report. Precise estimates are not available for lead fishing tackle in the environment, but about 4,382 tons of lead fishing sinkers are sold each year in the United States. Frequently used upland hunting fields were found to have as much as 400,000 shot per acre.
The most significant hazard to wildlife is through direct ingestion of spent lead shot and bullets, lost fishing sinkers and tackle, and related fragments, or through consumption of wounded or dead prey containing lead shot, bullets or fragments, said U.S. Geological Survey contaminants experts Barnett Rattner and Chris Franson. The two scientists are lead authors of a new Wildlife Society technical report and co-authors with five other experts of a recent Fisheries department article on the same subject.
"Science is replete with evidence that ingestion of spent ammunition and fishing tackle can kill birds," Rattner said. "The magnitude of poisoning in some species such as waterfowl, eagles, California condors, swans and loons, is daunting. For this reason, on July 1, 2008, the state of California put restrictions on the use of lead ammunition in parts of the range of the endangered California condor because the element poses such a threat to this endangered species."
Lead poisoning causes behavioral, physiological, and biochemical effects, and often death. The rate of mortality is high enough to affect the populations of some wildlife species, the scientists conclude. Although fish ingest sinkers, jigs, and hooks, mortality in fish seems to be related to injury, blood loss, exposure to air and exhaustion rather than the lead toxicity that affects warm-blooded species.
Lead can also slowly dissolve and enter groundwater, making it potentially hazardous for plants, animals, and perhaps even people if it enters water bodies or is taken up in plant roots, the study points out. For example, said Rattner, dissolved lead can result in lead contamination in groundwater near some shooting ranges and at heavily hunted sites, particularly those hunted year after year.
Some states have limited the use of lead shot in upland areas to minimize such effects, and others are considering such restrictions, according to a USGS statement. Environmentally safe alternatives to lead shot and sinkers exist and are available in North America and elsewhere, but use of these alternatives is not widespread, according to the report.
- Ten Species Success Stories
- Gallery: Birds of Prey
- 101 Amazing Earth Facts