Lead Toxicity in Mute Swans

DISCUSSION
Blood lead levels as a measure of exposure to lead have been used
by many workers.
Ohi et al., (1974) and Hutton (1980) for example
identified birds exposed to lead in urban and rural sites. In addition
to anthropogenically produced lead from organo-lead emissions, lead
pellets from shooting and angling weights also pose a hazard to
wildfowl.
Experiments based on the dosing of captive birds with lead
have been carried out with a view to understanding the high and
variable blood lead levels in birds (Anders et al., 1982).
results have then been extrapolated to the field situation.
These
In the
present study, some of the variation in blood lead in caged birds was
due to changes in haemoglobin concentration during the diel cycle (Fig.
2). Since the variation of haematocrit was considerable and in view of
the large reference range for haematocrit reported by O'Halloran et
al., (b) (in press), all blood lead values were corrected for
haemoglobin.
This reduced the variation (Fig. 2) and the reduction was
not exclusive to caged birds, but was also evident in two birds sampled
in the field at six hour intervals.
The correction of lead levels for haemoglobin becomes more
important in chronically exposed animals (Peter et al., 1978) and this
~ ~
can clearly be seen from specimen C (Table 1). When the blood level is
expressed per litre of blood, on day 147 the concentration appears less
than that of day 84, however in the corrected value the reverse is
true.
This is due to anaemia as a result of lead poisoning, since the
proportion of red blood cells (which contains most of the lead) was low
and as a consequence the amount of lead in the sample was low (Table 1,
specimem C).
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