Lead Toxicity in Mute Swans

one lead weight and it's blood lead increased dramatically.
This
cygnet was later found dead with three lead weights in it's gizzard.
Thus, while a great deal of variation occurs in blood lead values in
swans, on ingestion of a lead weight or pellet, a dramatic increase in
concentration occurs.
Acute lead poisoning resulting from the ingestion of lead pellets
has resulted in the deaths of 41 per cent of Mute swans found dead at
Cork Lough [O'Halloran et al., (a) in press)]. Most of the lead
poisoned birds died in winter and spring.
This pattern of mortality
coincides with the time of high median blood lead levels recorded here
(Fig. 3).
This is in contrast to the findings of Birkhead (1983) for
Mute swans on the River Thames.
There, the median blood lead level was
highest in July, August and September, which coincided with the peak
coarse-angling season.
The peak angling period at Cork Lough is the
same as on the Thames and the cause of increased lead levels at Cork
Lough is due to ingestion of lead weights as shown by radiology
[O'Halloran et al., (a) in press)]. A number of factors may be
responsible for the different pattern of blood lead levels at Cork
Lough; firstly, as mentioned earlier, the number of birds present is
greater in winter, secondly, poor natural feeding may force the birds
to forage more and thus ingest lead weights·; and thirdly, because of
the poor diet in winter, when the birds feed almost exclusively on
bread, their susceptibilty to absorption of lead is greater. Morton et
al., (1985) has shown that after a human has eaten, only 3 per cent of
lead administered is absorbed by the small intestine, but this
increases to 60 per cent when the human has fasted.
Trost (1981) also
noted a different pattern of lead absorbtion in ducks exposed to lead
on different experimental diets and grit types.
At Cork Lough, the
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