Abstract
Lead poisoning from ingested anglers' lead weights was investigated by postmortem examination and blood lead analysis of mute swans Cygnus olor in the Thames area. The regional and seasonal patterns of poisoning were compared with the distribution of lead in the sediment and with the quantity of discarded anglers' lead weights. Background lead contamination partially accounted for elevated blood lead levels, but did not account for the overall pattern of lead poisoning. Lead poisoning was most common in areas where the largest number of lead weights were found, where it accounted for up to 94% of the local swan deaths. There was a direct relationship between the seasonal pattern of lead poisoning and the fishing season. The incidence dropped markedly during the ‘close season’ when no coarse angling is allowed. Large numbers of accumulated lead weights remained accessible to the swans during this period. It appears that swans mainly ingest the most recently used lead weights. On the basis of this finding, it is predicted that if lead weights were no longer used, there should be a measurable reduction in the incidence of lead poisoning during one season.
Published Version
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