Lead Toxicity in Mute Swans

developed and (c) information on blood lead levels in other species is
readily available.
FRBCP is routinely used in screening for lead
exposure in birds. Protoporphyrin IX is a precursor of haemoglobin, the
concentration of which is known to increase in lead poisoning (Van Den
Bergh, 1933; Lamola et al., 1975).
Though there is a correlation
between blood lead and FRBCP, these two parameters reflect different
types of exposure.
Blood lead gives an indication of exposure of up to
60 days in humans (Moore, 1986) and is estimated to be 20 days in birds
(Anders et al., 1982).
FRBCP gives a measure of metabolic damage caused
by lead at erythropoiesis, thus any damage caused by lead at this stage
can be assessed over the life span of the red blood cell. The life span
of avian red blood cells is short (£.35-40 days) (Hodges, 1977) and not
£.120 days as in humans (Dacie and Lewis, 1975; Eccleston, 1977).
The level of blood lead and FRBCP reported in birds following lead
exposure is very variable and much of the available data is from
experimental studies on captive birds (see Lumeij, 1985).
This raises,
in particular, two questions about the methods for determining lead
exposure in birds.
Is the large variation in blood lead levels
explained in any way by the variation in haemoglobin or haematocrit?
And how representative are values obtained during dosing experiments to
the field situation?
Blood lead must be considered in the context of its distribution in
the blood cells. In humans, 80% of lead is bound to haemoglobin in the
erythrocytes (Ong and Lee, 1980) and this appears to be true also in
birds (Anders et al., 1982).
Blood lead values should therefore, be
corrected for haematocrit or haemoglobin (Chamberlain, 1985; Landsdowne
and Yule, J986).
FRBCP is, to an even greater extent than lead,
associated predominantly with erythrocytes,' therefore the whole blood
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