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of meat uncontaminated by elevated levels of lead to the UK and
foreign public, and compliance with any food safety standards
that might apply now or in future.
Lead poisoning is in many ways
a ‘hidden disease’; how can we
address that barrier effectively?
Whilst large-scale mortality events from lead poisoning do
occasionally occur (e.g. as reported in O’Connell 2008) this is
the exception rather than the rule. Lead-poisoning mortality is
usually inconspicuous, often resulting in frequent and largely
invisible lossesof small numbersof birds that remainundetected.
Moribund birds often become increasingly reclusive and dead
birds may be scavenged before being detected (e.g. Pain 1991).
This is why lead poisoning of birds is referred to as an ‘invisible
disease’. Unlike cases of diseases such as botulism, where large
numbers of birds often die in one place, few people find those
scattered individuals that have died from lead poisoning.
However, it is estimated that in the UK, as many as 50,000-
100,000 wildfowl and larger numbers of terrestrial birds may die
from lead poisoning each year (Pain et al. 2015).
The rarity of shooters observing sick lead poisoned birds
is a frequently cited reason for underestimating the extent
of the problem. Addressing this barrier will require good
communication regarding the nature and likely extent of
the problem by all stakeholder groups, not least by shooting
interests. The use of visual footage of lead poisoned birds from
animal recovery centres may also help to illustrate the reality
and welfare impacts of the disease.
Is ingested lead shot poisonous
to all animals?
Lead is poisonous to all animals, irrespective of the source.
Ingested lead from ammunition is particularly a problem for
birds. The amount of ingested lead that will produce similar
signs of toxicity may differ among individual birds, as well as
species. The absorption of dissolved lead into the blood can be
influenced heavily by different factors. Thus a diet rich in animal
protein and calcium interferes with the absorption of lead in
the blood (Snoeijs et al. 2005, Scheuhammer 1996). A diet low
in protein and calcium, but high in starch and fibre (such as in
winter), may not moderate the absorption of lead from shot.
Also, if the dietary items are large and hard, they will require
much grinding with grit, and this, simultaneously, increases the
physical breakdown and dissolution of gunshot. Consequently,
the toxic effects of lead shot ingestion may vary according
to the seasonal diet of individuals, and also by species, as in
herbivorous and carnivorous waterfowl (USFWS 1997).
The physical condition of an animal also influences it
susceptibility to lead toxicosis. Animals that are stressed or
starving, with few body reserves, are more likely to show signs
of lead poisoning than animals in robust health with the same
amount of ingested lead shot.
The size of lead shot may also influence the dissolution in the
avian gizzard. Large lead shot are retained longer in the gizzard
and are progressively broken down until they are so small
that they pass through the sphincter into the intestine. Small
diameter lead shot may pass through without much abrasion
and ultimately exit the body in the faeces. Thus the amount of
lead absorbed into the body may be different even though the
same total weight of lead shot was ingested.
Some birdsmay ingest only one or two lead shot at the same time.
This level of leadmay ormay not be fatal, dependingupon a range
of factors such as those described above.When not fatal, ingestion
of small numbers of shot could result in sub-clinical signs of lead
poisoning which, if more lead shot were ingested, could result in
chronic poisoning or acute and possibly fatal poisoning.
Are any of the substitute shot
types also toxic?
During the Symposium discussion session, panellists were
asked whether any of the substitutes were also toxic. Lead shot
substitutes made from iron, tungsten, bismuth and tin were
developed first in the USA, and are now used internationally. In
the USA and Canada any substitute for lead shot must undergo
mandatory experimental testing to receive approval under
federal law. To be approved, a candidate shot must first undergo
laboratory toxicity testing as ingested shot in mallard ducks
Anas platyrhynchos over two generations. This involves testing
for metal accumulations, harmful effects on all of the major
organ systems of the body, and any effects on all aspects of
reproduction, including the ability of hatched birds to thrive. In
addition, it must be shown that the shot in stipulated very high
densities has no adverse effects on aquatic and terrestrial plants
and animals, and the quality of soil and waters (USFWS 1997). It
must also be shown that the proposed substitute would not have
Key questions and responses regarding transition to use of lead-free ammunition