Lead shot and sinkers: Weighty implications for fish and wildlife health

Lead is a metal with no known beneficial role in biological systems, and its use in gasoline, paint, pesticides, and solder in food cans has nearly been eliminated. Although lead shot was banned for waterfowl hunting in 1991, its use in ammunition for upland hunting, shooting sports, and in fishing tackle remains common.

While noting that more information is needed on some aspects of the impact of lead on wildlife, the authors said that numerous studies already documented adverse effects to wildlife, especially waterbirds and scavenging species, like hawks and eagles. 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.

Frequently used upland hunting fields may have as much as 400,000 shot per acre. Individual shooting ranges may receive as much as 1.5 to 23 tons of lead shot and bullets annually, and outdoor shooting ranges overall may use more than 80,000 tons of lead shot and bullets each year. Although precise estimates are not available for lead fishing tackle in the environment, about 4,382 tons of lead fishing sinkers are sold each year in the United States.

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, emphasized USGS contaminants experts Drs. Barnett Rattner and Chris Franson. The two scientists are lead authors of The Wildlife Society (TWS) technical report and co-authors with five other experts of a recent Fisheries 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. 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.

Although lead from spent ammunition and lost fishing tackle is not readily released into aquatic and terrestrial systems, under some environmental conditions it can 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. 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.

Research on lead poisoning related to spent ammunition and lost fishing tackle has been focused on bird species, with at least two studies indicating that the ban on the use of lead shot for hunting waterfowl in North America has been successful in reducing lead exposure in waterfowl, the report said. The authors found that upland game -- such as doves and quail -- and scavenging birds -- such as vultures and eagles -- continue to be exposed to lead shot, putting some populations (condors in particular) at risk of lead poisoning.

Some states have limited the use of lead shot in upland areas to minimize such effects, and others are considering such restrictions. 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.

The authors of the report concluded that a better understanding of the toxicity and amount of lead poisoning in reptiles and aquatic birds related to fishing tackle is needed, as well as more information on the hazards of spent ammunition and mobilized lead at or near shooting ranges. In addition, the authors suggested that a more detailed knowledge of how lead shot and fishing tackle specifically affect wildlife here and in other countries is essential, as well as studies that evaluate the effects on wildlife health and ecosystems of regulations restricting the amount of lead ammunition and lead fishing tackle.

Source: United States Geological Survey