Why is lead harmful to humans and wildlife?
Lead is a naturally occurring metal in the environment, but when ingested it can be highly toxic. Lead manifests its toxicity in multiple organ systems. It can cause anemia by altering red blood cell formation and inhibiting oxygen uptake, and it can affect the nervous system by impairing nerve signal transmission. Lead exposure can result in kidney damage and suppress the immune system, increasing susceptibility to disease. It can also negatively impact reproduction and is suspected to be a carcinogen. Children are particularly susceptible to lead poisoning.
Lead poisoning has been well-documented in many bird and mammal species. Some bird species can die after ingesting just one lead pellet. Fish, amphibians and reptiles have also been reported to experience toxicity to lead, although fewer studies have examined these animal groups (Rattner et al. 2008).
What are the sources of lead in the environment?
The most prevalent source of unregulated lead in the environment is spent ammunition that is discharged onto the landscape. The density of spent shot in a particular area is positively correlated with hunting intensity. The Environmental Protection Agency estimates that roughly 72,600 metric tons of lead shot and bullets are deposited in the U.S. environment each year at outdoor shooting ranges (US EPA 2001). Lost lead-based fishing tackle can pose a toxicological threat to waterbirds.
Regulations developed over the last 50 years have minimized the impact of many sources of lead in the environment, including leaded gasoline, lead-based paint, solder and batteries. Mining and smelting activities can also introduce lead into the environment, although in the U.S. these activities are highly regulated.
How are wild birds exposed to lead?
Scavenging and predatory birds are highly susceptible to lead poisoning when they consume lead shot or fragmented lead bullets in hunter-killed carcasses or discarded gut piles. Some ground feeding species (e.g. mourning doves, wild turkey, and pheasants) may consume lead pellets inadvertently as they forage for seeds. Waterfowl (ducks, geese, swans) may consume lead pellets / fishing tackle that settle to the bottom of lakes and ponds, which the birds mistake for grit that they consume to aid in grinding food. However, a 1991 nationwide ban on the use of lead shot for waterfowl hunting in the United States has dramatically curtailed impacts to waterfowl.
Which bird species are most affected?
Currently, raptors, vultures, crows and ravens are the species most impacted by lead shot, as they will often scavenge from hunter-killed carcasses and gut piles. The species most dramatically impacted by poisoning from lead-based ammunition is the highly endangered California Condor. Studies indicate lead poisoning is the key limiting factor preventing this species from achieving a full recovery (Finkelstein et al. 2012).
Worldwide, nearly 60 terrestrial bird species have been documented as having exposure to lead from ammunition sources, including upland game birds, owls, pigeons, doves, cranes, raptors, vultures, and songbirds (Fisher et al. 2006). Prior to the United States’ 1991 ban on lead shot for waterfowl hunting, up to 3 percent of all waterfowl in North America (i.e. millions of birds) were estimated to have died annually due to lead poisoning (Lahner and Franson 2009).
Is there a solution?
Non toxic, non lead ammunition has become increasingly available and price comparable to lead ammunition, with many manufacturers producing a variety of calibers and weights. Nonlead ammunition also has excellent ballistic qualities, is highly lethal, and does not fragment. Much work is being done to raise awareness about the availability of non-lead ammunition, to build confidence in these alternatives, and to improve market visibility and labeling of nontoxic alternatives. Visit the Hunting with Nonlead Ammunition website for more information: http://www.huntingwithnonlead.org/. Ammunition exchange programs are helping to encourage use of nonlead ammunition, but even in these areas, lead poisoning continues to occur.
Voluntary and Regulatory Lead Bans
Voluntary bans on lead ammunition have shown promise in some areas. In 2003, the Arizona Department of Fish and Game instituted a voluntary ban on lead ammunition and polling in the area has indicated up to 80 percent hunter compliance. These efforts have led to a decrease in condor lead exposure (Arizona Fish and Game 2007), but even with this level of hunter compliance, condors are still dying from lead poisoning in this region.
Nearly half of all states have nontoxic shot regulations for some or all hunting species that extend beyond those required by the 1991 U.S. federal law prohibiting the use of lead shot for waterfowl hunting. Most recently, the state of California passed a law that will ban the sale of lead ammunition across the state by 2019.
In areas where lead ammunition has been banned, lead levels have been shown to be significantly reduced from pre-ban levels for a number of affected species. Several studies have documented much lower rates of lead poisoning after the U.S. ban on lead-based ammunition for waterfowl hunting went into effect in 1991 (e.g. Anderson et al. 2000, Samuel and Bowers 2000) – the ban likely saved millions of ducks from death by lead poisoning.Lead exposure in both Golden Eagles and Turkey Vultures declined significantly following the 2008 ban in California on the use of lead ammunition for most hunting activities in the range of the California Condor (Kelly et al. 2011).
What is Portland Audubon doing about lead?
Portland Audubon is working to raise awareness about the impact of lead on birds and is currently focused on supporting voluntary, educational avenues for reducing wild animals’ exposure to lead in Oregon.
To learn more about lead poisoning at a local level, staff members in our Wildlife Care Center have also been using a lead-testing machine since January 2013 to assess lead levels in scavenging birds (raptors, owls, crows) in the Portland area. We are comparing our data set to others in the region to better understand lead toxicity levels in birds in the region.
What nonlead ammunition options are available to hunters?
Hunters have widely touted nonlead types of ammunition – particularly bullets made of copper – as the bullets have excellent ballistic qualities, in addition to being safe for the environment because they rarely fragment. Nonlead ammunition is widely accessible and becoming increasingly affordable. Premium lead hunting bullets actually cost about the same and sometimes more than nonlead bullets. Visit the Hunting with Non-lead Ammunition website for more information.
Does eating lead-shot game animals increase lead levels in people?
Recent studies suggest that incidental ingestion of lead in game meat may pose more of a health risk to humans than previously believed. Lead shot can fragment into tiny pieces and spread out into tissue from the entry point much further than previously known, even if the main shot pieces exit the animal (Tsuji et al. 2009, Hunt et al. 2009, Pain et al. 2010). As a consequence, the amount of lead in lead-shot animals can often exceed levels thought to be suitable for human consumption (Pain et al. 2010). A number of studies have reported elevated lead levels in humans that rely on lead-shot meat for subsistence (Johansen et al. 2004, Johansen et al. 2006, Tsuji et al. 2008). More recently, there is evidence that lead levels in people who eat recreationally caught lead-shot game can be elevated as well (Iqbal et al. 2009). These findings are important, particularly with respect to children. Children can be particularly sensitive to lead poisoning and even very low levels of lead can cause permanent cognitive damage (Lanphaer et al. 2005).
Anderson, W.L., S.P. Havera, and B.W. Zercher. 2000. Ingestion of lead and non-toxic shotgun pellets by ducks in the Mississippi flyway. Journal of Wildlife Management 64: 848-857.
Arizona Game and Fish Department. 2007. Condors and lead. www.azgfd.gov/w_c/california_condor_lead.shtml
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