Lead in the Environment
Where can lead be found in the environment?
Lead is a naturally occurring metal found in the earth's crust. Lead can be found many places, much because of human activity through burning fossil fuels, mining, and manufacturing. Water can be contaminated with lead from mines, waste dumps, and industrial plants. House paint and gasoline were once manufactured with lead. Fishing sinkers and jigs are often made from lead. Most firearms ammunition contain lead including pellets, shot, slugs, round balls, and bullets.
Assorted lead fishing tackle
By the mid-1990s, lead had been removed from the manufacturing process in many products in the U.S., including paint and gasoline.
How does lead poison?
Lead is a potentially deadly toxin that damages internal organs of the body and can impact all animals, including humans. For both birds and people, lead must be eaten (ingested) or lead particles or fumes inhaled to elevate lead levels to cause poisoning. Examples of how people can ingest lead include eating paint chips, inhaling paint fumes and paint dust, eating wildlife harvested with lead shot or lead slugs. Stomach acid breaks down lead and then lead is absorbed into the blood stream. Fine particles and fumes that are inhaled are absorbed into the bloodstream through the lungs.
Lead shot shells, 22s, and round balls
Primary lead exposure in animals is caused by the animal eating lead directly, mistaking it for food or grit. Secondary lead exposure in animals comes from the animal eating another animal that contains lead. This prey animal either swallowed lead or has lead shot/slug embedded in it.
Click here to learn more about SOAR's efforts to rehabilitate birds with lead exposure.
What are the effects of lead poisoning?
Lead mimics calcium in an animal's body, it impacts nervous tissue and is stored in bone. Blood lead levels (BLL) are measured in micrograms per deciliter. At a BLL below 10 micrograms per deciliter (10 µg/dL), this lead can cross the placenta and can be found in breast milk.
Young children and pregnant women absorb more lead than do adult males. In children, even a small amount of lead can cause learning delays, decreased intelligence, shortened attention span, and very high lead levels may cause brain damage or even death. Lead exposure in children may also result in expression of antisocial behaviors.
Very low lead levels increase an adult males’ risk of stroke and heart attack and can decrease sperm count.
Later in life, lead can re-emerge from bone tissue causing high blood pressure, kidney failure, and Parkinson’s Disease.
High BLL in birds (from loons, doves, cranes, swans, to vultures, eagles, crows, and other scavenging birds) impacts the nervous and circulatory systems and the kidneys. The weakened bird has trouble flying, hunting/feeding, is much more susceptible to infection, and often starves. In female birds with low BLL, reproduction is impacted.
Click here to read more about the lead and eagles research SOAR has done.
What are the exposure thresholds for humans and wildlife?
The current blood lead level which defines lead poisoning in children under the age of six is 5 micrograms of lead per deciliter of blood or more (≥5 µg/dL). A blood lead level of 5 or greater in a child is a trigger for continued monitoring by healthcare providers. This level changed in May 2012 upon recommendation from the the Advisory Committee on Childhood Lead Poisoning Prevention from 10 to 5 µg/dL. This panel also recommended that CDC look at lowering this target level every four years. Many consider that there are no safe levels of lead in the body.
There are no established exposure levels for wildlife as it is different for each species. In clinical trials, 200 milligrams of lead (one #4 size piece of shot) was found to be the lethal dose for a bald eagle.
Bluer Shade of Blue
Chad Elliot, a Coon Rapids, Iowa musician wrote a song to highlight the tragic affects of lead hunting ammunition on the bald eagle. SOAR volunteer, "PharmerDave," put a video to Chad's music.
A bit more about lead poisoning...
The bald eagle admitted on 13 December 2011 that had been caught in a leg-hold trap also had elevated blood lead levels (BLL) of 9.6 µg/dL. She coughed up a pellet (accumulated undigested material, in the case of eagles primarily hair) shortly after initial exam at SOAR. This pellet was x-rayed for lead fragments. The bright white flecks are lead fragments that were not dissolved and absorbed into her blood stream.
The leg-hold traps were set near a deer carcass. Had she not been caught in the trap and found, it is likely she would've continued to eat off this deer carcass and ingest more lead.
A 1997 University of Minnesota Raptor Center retrospective study concluded that spent lead ammunition is an important source of lead exposure for bald eagles. TRC also undertook a subsequent retrospective study to test the hypothesis that lead fragments in carcasses and gutpiles of white-tailed deer represents an important source of lead exposure lead in bald eagles. Read this research paper published in Spring 2012.
Since 2004, SOAR has been compiling statewide eagle data that now includes over 180 eagles. All of these eagles had either a BLL taken or the lead level was determined post-mortem via liver biopsy. Over half of these eagles had abnormal lead levels in blood, liver, or bone. This is a much higher percentage than the random types of injuries, seen in other species.
In a 2008 paper presented at the Peregrine Fund's Spent Ammunition Conference, SOAR Executive Director Kay Neumann noted, "...more random events seem to occur at a much lower percentage of the total number of eagles admitted. Gunshot wounds, for example, were recorded in ten of the 82 [those in the database up to the submission of the paper] eagles in this database (12.2%). The data does not indicate that the increasing number of bald eagles being admitted by Iowa wildlife rehabilitators is simply a function of the increasing numbers of eagles in wild populations. If this were the case, it would be expected that a variety of causes would be seen for admittance (miscellaneous trauma, fractures, starvation, disease, etc.), at percentages relative to that seen for gunshot wounds. This has been the case for other species."
For instance, the Cooper's hawk (see photo at right) population has rebounded from DDT exposure and have also increased numbers by discovering a new niche -- Cooper's hawks are now nesting in town. As would be expected, a higher population means that more birds will be seen by rehabilitators. In the last 4-5 years, there has been an increase in Cooper's hawks being admitted to rehabilitators across the country with a random assortment of injuries, not just one.
As reported in the 14 December 2011 issue of the North Iowa Times, "Dr. Julie Ponder of the Raptor Center at the University of Minnesota sees about 100 eagles per year. The Raptor Center is one of the premiere raptor treatment and research facilities in the country. All receive blood testing for lead, as well as an x-ray. She said that 95 percent of the birds show some lead exposure, and 25-30 percent have lead poisoning. That’s a pretty significant number."
Lead poisoning affects eagles more than other raptors. Thousands of bald eagles winter in Iowa -- estimates of up to one-fifth of the lower 48 states' eagle population -- congregate near open water along the big rivers and reservoirs in the state. Other scavengers like turkey vultures have migrated south. Hawks tend to hunt more than scavenge and an eagle will chase off hawks feeding on a carcass.
Iowa has deer hunting seasons for hunters from September (for youth hunts) through January (extended doe season). The extended hunting seasons mean an increased opportunity for deer carcasses to be available at a time when thousands of eagles are in Iowa.
"This is a problem that we can solve," Dr. Laura Johnson, a veterinarian and a licensed wildlife rehabilitator at Tender Care Animal Hospital in Prairie du Chien, Wisconsin, said in an interview with the North Iowa Times. "We want people to know that they can change the kind of ammunition they use," she added.
For more information about lead, visit:
- Environmental Protection Agency
- Centers for Disease Control
- Department of Health and Human Services, Agency for Toxic Substances and Disease Registry
Articles about the impacts of lead:
- Neurotoxicity and aggressiveness triggered by low-level lead in children: a review (135 KB PDF)
- Whole-Body Lifetime Occupational Lead Exposure and Risk of Parkinson’s Disease (506 KB PDF)
- Home page