Lead Toxicity in Mute Swans

I
INTRODUCTION
The importance of lead shot from shotgun cartridges as a source of
environmental contamination has been widely investigated in North
America since first recognised in 1874 (Philips and Lincoln, 1930;
Jordan and Bellrose, 1951; Bellrose, 1959; Rosen and Bankowski, 1960;
Trainer and Hunt, 1965; Bagley et al., 1967).
The significance of this
source of contamination has also been investigated in Europe,
especially in England (see Olney, 1960; Thomas, 1975; Mudge, 1983).
Other countries in Europe where investigations have been carried out
include: Scotland (Owen, 1987), Italy (Del Bono, 1970), Sweden (Danell
and Anderson, 1975), Denmark (Clausen and Wolstrup, 1979), France
(Hovette, 1974), Switzerland (Bouvier and Horning, 1965), Federal
Republic of Germany (Borkenhagen, 1979), Norway (Holt et al., 1978) and
the Netherlands (Th.Smit pers. cornm.1986).
In many of the above
studies workers have simply looked at the prevalence of ingested
pellets in the gizzard which, though useful, is only presumptive
evidence of lead poisoning.
Quantitative chemical analyses of tissues
for lead is the only diagnostic test of lead poisoning in dead birds.
Lead is an ubiquitous element in the environment, principally from
the use of organo-lead additives in petrol.· Thus it is useful to
define the categories of lead exposure.
namely background and acute exposure.
Two categories are recognised,
Background exposure is a
function of organo-lead input and thus is variable but can be roughly
divided into two groups depending on traffic density, namely rural and
suburban/urban exposure (Johnson et al., 1982).
Exposure to high urban
background_ lead for considerable periods of time may lead to chronic
lead poisoning, this has recently been reported in Feral pigeons
- 56 -