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A large amount of lead gunshot, bullets, and fragments thereof,
is deposited in the environment annually and accumulates over
time. Much of this may be available for animals to ingest directly,
probably mistakenly for food, for grit, or inadvertently along
with soil or foodstuffs.
Gunshot densities in the environment tend to be highest in
areas of intense and/or regular hunting/shooting pressure. They
typically range from just a few to hundreds per square metre
(e.g. Mudge 1984, Spray and Milne 1988, Mellor and McCartney
1994 for the UK, and Mateo 2009 for Europe) but thousands
can be found per square metre in some situations. For example,
O’Halloran et al. (1988) reported gunshot density in the vicinity
of a clay pigeon shooting range in Lough Neagh, County Antrim,
of 2,400 gunshot/m2 in the upper 5 cm of shoreline in front of
the range and with gunshot being retrieved on the lake bed up
to 60 m from the shore.
Lead is a relatively stable metal under most conditions and
remains as pellets of gunshot for considerable periods of time.
It has been used in the UK for over two centuries and, indeed,
the potential for a “historical legacy” of gunshot remaining
available to wildlife is an important aspect of the epidemiology
of lead poisoning in wildlife. Complete decomposition of
particulate lead probably takes tens or hundreds of years under
most conditions (Scheuhammer and Norris 1996, Rooney et
al. 2007). Gunshot degradation is caused by a combination of
physical erosion/abrasion, which is accelerated in coarse and
gritty soils and/or those with marked levels of movement and
chemical activity.
Densities of lead gunshot in the soil tend to increase over time
if lead gunshot continues to be used. However, gunshot will
generally sink slowly through the soil and new soil accumulates
above the gunshot with rates of sinking affected by soil
density and other characteristics. Hartikainen and Kerko (2009)
found that on the coarse stony soil of a shooting range in
southern Finland, lead gunshot migrated downwards relative
to the surface at a rate of some 2-3 mm per year. Flint (1998)
found in various wetland types to which gunshot was added
experimentally that most gunshot was still within the top 4
cm of sediment three years after deposition. In the Camargue
marshes (southern France), assuming a constant settlement
rate, Tavecchia et al. (2001) estimated a half-life of gunshot in
the first 0-6 cm, thus available to waterfowl, for 46 years, with
complete settlement beyond this depth after 66 years. Flint and
Schamber (2010) found that 10 years after seeding experimental
plots on tundra wetlands with number 4 gunshot, about 10%
remained in the top 6 cm and >50% in the top 10 cm. These
authors predicted that it would probably require >25 years for
spent lead pellets to exceed depths at which waterfowl forage.
However, one would expect the proportion of pellets available
to feeding waterfowl to decrease with time over this period.
Lead gunshot may become less available when redistributed by
cultivation (e.g.Thomas et al. 2001), and some farming practices
could hypothetically make lead gunshot deposited decades ago
more available (Chrastny et al. 2010, Rooney and McLaren 2000,
Stansley et al. 1992, White Young Green Environmental 2006), as
can the lowering of water levels (Spray and Milne 1988).
While a historical legacy of deposited gunshot exists, there
is good evidence that the majority of gunshot ingested by
wildfowl is that most recently deposited. Anderson et al. (2000)
found that in the fifth and sixth years after a nationwide ban
on the use of lead gunshot for shooting waterfowl in the USA,
75.5% of 3,175 gunshot ingested by a sample of 15,147 mallard
on the Mississippi flyway were non-toxic.
LEAD AMMUNITION IN THE TISSUES OF GAME
SPECIES THAT CAN BE CONSUMED BY PREDATORS
AND SCAVENGERS (i.e. OF RELEVANCE TO
EXPOSURE ROUTE 2)
Of the tens of millions of animals shot in the UK each year using
lead ammunition, an unknown proportion of the carcasses is
not recovered and hence is potentially available to scavengers.
For many of the tens of thousands of red deer Cervus elaphus
shot per year, the viscera are discarded in the field and they, and
any remnants of lead ammunition within them, are potentially
available to scavengers. A further additional set of animals are
wounded by gunshot and bullets but survive and may carry
remnants of lead ammunition in their bodies. These animalsmay
be eaten by predators, perhaps selected as prey because of their
weakened condition, or die later and be eaten by scavengers.
The tissues of game animals killed using shotgun cartridges
usually contain some of the gunshot that struck the animal
and killed it. Pain et al. (2010) performed X-radiography on
121 entire carcasses of wild red grouse Lagopus lagopus, red-
legged partridge Alectoris rufa, pheasant Phasianus colchicus,
mallard, woodpigeon Columba palumbus and woodcock
Scolopax rusticola killed by shooting and obtained from retailers
and shoots in the UK (16 – 26 individuals per species). Eighty
seven percent of all birds examined had whole gunshot, large
Lead poisoning of wildlife in the UK