Lead Poisoning

This fact sheet was created on 1/27/21.

Cause

Lead has no known beneficial biological function and is toxic to animals and humans when high enough concentrations are absorbed. Waterfowl and other birds are particularly susceptible to lead poisoning because they often consume shotgun pellets, bullet fragments, and fishing tackle made of lead while feeding. The lead is broken down in the gizzard or stomach (depending on the species) and absorbed into other tissues. Lead toxicity has been recognized in humans and domestic animals for at least 2,500 years, and it was first reported in waterfowl in the United States in 1874 in Texas.

Significance

Lead poisoning has resulted in major die-offs in waterfowl and many other species of birds. The impact on upland birds and their predators is not clear, but new studies are being initiated to determine their susceptibility. Bald eagles and California condors are species of particular concern. Lead toxicity that does not result in death can suppress the immune system and lead to death by infection with other disease agents like bacteria and fungi (such as Aspergillosis).

Species Affected

Lead poisoning has been reported in every major species of waterfowl in the United States, but it is most common in ducks, geese, swans, and loons. It also occurs with less frequency in upland game birds such as mourning doves, wild turkeys, pheasants, and quail. Eagles are the most commonly affected of the land birds though other raptors can also experience lead poisoning. Any animal, humans included, can suffer from lead poisoning following ingestion of hazardous amounts of lead, but this toxicity is much more common in birds than in other wildlife.

Distribution

Lead poisoning occurs throughout North America. It has also been reported in migratory birds throughout Europe, Japan, Russia, and Australia. Birds can experience lead toxicity at any time of year, but losses are more common after a period of accumulating lead from the environment. For example, swans, geese, and puddle ducks experience their highest mortality in January and February while deaths due to lead poisoning in diving ducks are more commonly reported in the spring.

Transmission

Ingestion of lead pellets or projectile fragments are the most common source of lead poisoning for wild birds. Less commonly, birds can experience toxicity following the consumption of other lead objects such as fishing sinkers, lead bullets or their fragments, mine waste, and paint chips. Rarely trauma by a lead projectile that results in significant tissue damage can lead to exposure. In wetland environments, lead pellets can remain available for ingestion by waterfowl for 25 years or more. Raptors suffer from lead poisoning as a result of feeding on prey containing lead. The acidic environment of the gizzard or stomach causes the objects to erode, and the lead is absorbed into the blood stream and transported to tissues throughout the body. Birds may also be indirectly exposed to lead through ingestion of soil, water or other organisms, such as earthworms, that are contaminated with lead. Lead is not commonly absorbed from pellets or bullet fragments lodged in the body.

Clinical Signs

Lead toxicity is a chronic disease and over time can cause damage to different body systems, resulting in wide range of clinical signs. Clinical signs vary with the species and the amount of lead absorbed. Waterfowl suffering from lead poisoning usually exhibit loss of appetite, lethargy, and greenish diarrhea that stains the feathers around the vent. They will also experience progressive muscle weakness, which first causes weak flight, then an inability to fly, followed by inability to walk, coma, and death. Affected birds often hold their wings in a "roof shaped" position, followed by wing droop. These chronically affected birds will also exhibit progressive weight loss and will become emaciated. In affected Canada geese, the neck may appear bent during flight, and the head is often swollen. Raptors experiencing lead poisoning usually show nonspecific signs including generalized weakness, depression, and weight loss. They may also exhibit neurological signs and labored breathing. Sudden death without other clinical signs can occur in any bird that ingests large quantities of lead.

At necropsy, waterfowl will often have food or sand impacted within the esophagus and stomach, while raptors usually have an empty stomach. The gall bladder may be engorged with bile, and the normally yellow gizzard lining may be green from bile staining. Lead pellets may or may not be found in the stomach.

Diagnosis

Demonstration of lead in the stomach at necropsy or using X-rays can be helpful but is not diagnostic for lead poisoning. Post-mortem diagnosis is reached by measuring lead levels within the liver or kidney though these values must be interpreted with caution. Blood lead levels can also be used for ante-mortem diagnosis of lead poisoning and to monitor progress if treatment has been attempted.

Treatment

Demonstration of lead in the stomach at necropsy or using X-rays can be helpful but is not diagnostic for lead poisoning. Post-mortem diagnosis is reached by measuring lead levels within the liver or kidney though these values must be interpreted with caution. Blood lead levels can also be used for ante-mortem diagnosis of lead poisoning and to monitor progress if treatment has been attempted.

Management

The use of lead shot for hunting waterfowl has been banned in the United States since 1991, and this has resulted in a decrease in lead poisoning in waterfowl. Government agencies are considering banning the use of lead fishing sinkers and other fishing tackle as well as lead projectiles of all sorts in upland and big game hunting because these practices continue to make lead available in the environment. A variety of non-toxic alternatives to lead are available for use in hunting, shooting sports and fishing. When outbreaks of lead poisoning occur, sick and dead birds must be removed promptly to prevent scavengers from becoming secondarily poisoned as well. Wildlife managers must also attempt to prevent birds from using the contaminated area.

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