Lead Poisoning

Lead Poisoning

Risk Factor

Metallic lead is a highly toxic metal that when ingested, affects many organs and organ systems.
Wildlife are generally exposed to lead following ingestion of shot pellets, bullet fragments, or from consuming lead fishing jigs and sinkers.
Before laws were introduced in North America to restrict the use of lead in ammunition, annual losses of waterfowl to lead poisoning were up to 3 million birds.
Waterfowl and birds of prey are at greater risk of exposure to lead than are mammals and other species of birds because of feeding habits that involve ingesting lead shot as grit or consuming lead shot from the tissues of prey animals, respectively.
Lead poisoning has been mainly reported in birds but has also been documented in wild mammals that presumably have fed upon lead-contaminated prey.

Images

Click on a photo to enlarge.

Atrophy of breast muscles and lack of observable fat is commonplace in lead poisoned birds (at arrow).

Lead shot may be present within the gizzard of lead poisoned birds (at arrows).

Metallic lead is visible in the gizzard and shoulder of this lead poisoned bald eagle.

The feces of a lead poisoned bird are often bile-stained - bright green in colour. Wings may droop and birds may also appear listless.

Distribution and Seasonality

Lead exposure and poisoning has occurred throughout North America and may occur throughout the year.
Historically, higher rates of exposure and poisoning in birds occurs during the fall and winter coinciding with hunting seasons where large amounts of lead shot were used.

Mechanism of Action

In waterfowl, the highly muscular stomach grinds and erodes metallic lead which then is rapidly distributed through the circulatory system to other body tissues. Similar action occurs in birds of prey which have less muscular stomachs, but are more acidic than those of waterfowl.
Once absorbed within the body, lead can interfere with body functions that rely heavily upon the activity of calcium.
Lead interferes with the production of the oxygen carrying component of blood called hemoglobin, leading to a decreased ability of red blood cells to carry oxygen.
Lead has also been documented to damage and modify the function of kidneys, bone, nervous system, circulatory system and gastrointestinal tract.
If a sufficiently large number of metallic lead is ingested, death can be rapid (acute poisoning); or if a small amount of lead is ingested, death may occur after several weeks following chronic ill-health.

Signs and Symptoms

Meat Edible?

Game-bird hunters are aware that lead shot pellets are commonplace in tissues of shot birds and are deliberately avoided when the bird is consumed.
Most of the lead present in a lead poisoned bird is in organs such as liver and kidneys rather than in muscle tissue. Although there is no appreciable risks to human health from eating organ tissues from a lead-poisoned bird, it is not advisable to do so.
Dogs are at the same risk of exposure to metallic lead in hunter-killed game meat.

Risk Reduction

As of 1999, Canadian law prohibits the use of lead shot for hunting migratory birds such as ducks, geese, thick-billed murres, cranes, rails, gallinules and coots, and common snipe. Restrictions have also been made on the use of lead fishing sinkers and jigs. For a review of environmental effects of lead on wildlife in Canada, click here.
The ban on using lead shot for hunting migratory birds should decrease the annual losses; however, metallic lead remains in the environment for years, thus allowing lead deposited prior to the government bans to be available to feeding birds.
More recently, in the Fraser Valley of British Columbia and Northern Washington, trumpeter swans are dying from lead poisoning in large numbers. Intensive studies by the Canadian Wildlife Service and counterparts from Washington are now underway to address this problem. For more information, click here.

Samples for Diagnosis

Typically, lead levels in the liver and kidneys are used to determine the extent of exposure after death.
Whole birds should be submitted for analysis; however, the entire liver or kidney can be submitted alone. Liver or kidney samples should be wrapped in tin foil and submitted frozen.