Lead Toxicity in Mute Swans

I
values were getierally found in the liver of lead · d .
poisone swans which
had ingested lead weights, though high levels were also found in the
kidney.
The significance of these findings is that, if only a single
tissue is taken for analysis, the lead status may not be clearly
determined.
Barry (1975) found raised pancreatic lead levels in humans
exposed to lead.
In the present study, pancreatic lead levels were
high and variable but lower than those of the kidney or liver (Tables
1-2). No pancreatic lead values have been recorded for birds.
O'Halloran et al., [(A) in press] found changes in circulating plasma
glucose levels in swans suffering from acute lead poisoning.
Whether
lead has a high affinity for pancreatic tissue and causes sub-lethal
effects is not known.
It is interesting to note that some birds that
died from reasons other than lead poisoning or collisions, had high
levels of lead in the pancreas (Table 2).
Lead may have a high
affinity for pancreatic tissues and the levels present may be
indicative of past exposure.
The way in which lead exerts its toxic effect on the nervous system
is poorly understood, but it may be mediated through primary vascular
damage (Christian and Tryphonas, 1971); direct action of lead on
neurons (Bouldin et al., 1975) or alterations in porphyrin metabolism
(Pentschew and Garro, 1966).
Hunter and Wobeser (1980) found
encephalopathy and nervous disorder in Mallard ducks exposed to lead in
an experimental situation. These pathological findings were found to
precede anaemia.
In the present study, levels of lead in the tissues
of swans which died from collisions were elevated (Table 2).
Some
tissue lead levels would be considered diagnostic of acute lead
poisoning yet the birds were a 1 ive. . No lead weights were found in the
birds which had had collisions, but they appear to have been exposed to
excess lead at some time in t h e past.
It is noteworthy that swans
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