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1. INTRODUCTION
Lead poisoning in waterbirds
through the ingestion of spent lead shot is a serious environmental
problem. Large-scale die-offs of waterbirds drew the attention
to the issue already in the 1950s and 1960s, but it took
several decades until the issue was first internationally
addressed. Even today, the issue is still far from being
widely acknowledged.
Cartridges for hunting waterfowl each contain around 30
grammes of lead. A hunter fires an average of 3-6 cartridges
for every bagged bird. Only a few pellets actually hit the
bird; the rest fall to the ground or into the water. Thus,
thousands of tonnes of lead are annually deposited in wetlands
around the world. In France, for example, the annual deposition
is estimated to be as high as 6250 tonnes per year, and
in Spain it is around 5000 tonnes per year. As a rule of
thumb, the annual lead deposition per hunter is somewhere
between four and five kilograms.
“Lead shot has been found
in gizzards of a large number of species. Mud samples have
shown that lead pellet densities are locally very high.”
(Nicola Baccetti, National Wildlife Institute
(infS), Bologna, Italy)
Waterbirds deliberately pick the pellets up from the bottom
and swallow them, mistaking them for food items or grit,
which is retained in the gizzard to facilitate the grinding
of the food. Lead is a highly poisonous metal, causing severe
anaemia and affecting the nervous and circulatory systems,
liver and kidneys. Birds that ingest ten or more lead pellets
will die of acute lead poisoning within a few days. If a
smaller number (two to ten) is ingested, birds will gradually
start to show signs of chronic lead poisoning, such as drooping
wings, green and watery faeces, weight loss and atypical
behaviour. This influences their ability to forage and to
escape from predators. These victims usually die within
two to three weeks. If a bird swallows only one pellet,
it usually survives, although its immune system and fertility
are likely to be affected. Also, even low concentrations
of lead have a negative impact on energy storage, which
affects the ability to prepare for migration.
“Lead is an extremely toxic
substance. Millions of waterbirds are estimated to die of
lead poisoning each year.” (Baz Hughes, Head of
Threatened Species at the Wildfowl and Wetlands Trust)
Already in the 1950s, scientists
in North America estimated the yearly number of victims
in their continent alone to be 1.5 to 4 million. Recent
surveys in Europe and North America showed that as many
as 40% of all waterbirds ingest at least one lead pellet
during a single season of exposure.
In addition, secondary lead poisoning can occur when predators
or scavengers consume affected waterbirds. Research conducted
in various countries (e.g. USA, Germany, Austria, France)
during the past five to ten years showed that secondary
poisoning, particularly of Bald Eagles (Haliaeetus leucocephalus)
and White-tailed Eagles (Haliaeetus albicilla), is a significant
source of mortality. In Europe, for example, it is responsible
for ca. 25% of post-fledging mortality in White-tailed Eagles.
Lead poisoning in waterbirds can also form a considerable
health risk to humans. On average, 15% of all waterbirds
have lead levels in their flesh well above the generally
accepted health norm for human consumption.
(Reference: Beintema, N.H.
2001. Lead Poisoning
in Waterbirds. International Update Report 2000.)
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