LEAD POISONING IN MUTE SWANS (<i>CYGNUS OLOR</i>) IN IRELAND: RECENT CHANGES

Abstract

Studies over two decades have shown a marked trend towards a decrease in blood lead levels in the mute swan (Cygnus olor) in parts of Ireland. However, this study shows that a small percentage of some populations of mute swans in Co. Cork still have significantly elevated lead levels, causing some potentially sublethal effects to the health status of the swans. Overall, at both urban and rural sites the median blood lead levels in adults and cygnets of both sexes were below a threshold level of 1.21mmol l (1 , which is indicative of elevated lead. However, 27% of the population at Cork Lough had elevated lead levels, with the highest blood lead level being 27.66mmol l (1 , indicating that acute poisoning is still a problem in some individuals. Mute swans from rural sites generally showed no variation, and median blood lead levels were generally low. Lead levels reached a peak in October 2004 and again during the spring months of 2005. Swans may be more susceptible to lead poisoning during spring, as it follows the winter months when natural food is scarce and lead is easily absorbed across the gut after ingestion. Autumn peaks may be explained by an increase in fishing activity over the summer months. A positive association was found between elevated lead levels and packed cell volume*an indicator of health status. Overall, a decline in acute lead poisoning at urban and rural sites is apparent from this study. However, due to its continued and persistent use in the environment, lead still poses a threat at a sublethal level.

Hematological parameters in relation to age, sex and biochemical values for mute swans (Cygnus olor)

“…Mute swans are particular sensitive to lead exposure and may serve as sentinel species for toxicological contaminations in the environment (Degernes 2008 ). The studies have found many route of exposure to lead in this species (Perrins et al 2003 ; Bowen and Petrie 2006 ; Degernes 2008 ; O’Connell et al 2009 ; Turner and Hambling 2012 ). Lead toxicosis induced significant changes in the values of commonly measured hematologic parameters in waterfowl (Katavolos et al 2007 ).…”

“…Hematology may show hemolytic anemia (mild to moderate) with Heinz bodies, poikilocytosis, polychromasia. The increased serum uric acid concentrations, LDH and total protein could be observed (O’Halloran et al 1988 ; Campbell and Ellis 2007 ; Katavolos et al 2007 ; Degernes 2008 ; O’Connell et al 2009 ).…”

“…The blood examination in mute swans is more often performed, because of importance in clinical diagnosis. Measurement of hematological and biochemical parameters is used for the birds health status assessment, monitoring of the condition, facilitate diagnosis of disease, inflammations, intoxications subclinical processes (Driver 1981 ; Ritchie et al 1994 ; Olsen et al 2002 ; Cousquer and Patterson-Kane 2006 ; Artacho et al 2007a ; Katavolos et al 2007 ; Clark et al 2009 ; O’Connell et al 2009 ).…”

Use of grit supplements by waterbirds: an experimental assessment of strategies to reduce lead poisoning

“…One year after the supplementation, a decrease in Pb shot ingestion from 39.4% to 8.3% was observed in tufted ducks (Aythya fuligula) but not in common teal (Anas crecca) or mallards (Anas platyrhynchos; Hoffmann 1960). More recently, grit supplementation helped reduce mortality by Pb poisoning due to the ingestion of Pb weights in mute swans (Cypus olor) at Cork Lough (Ireland; O'Halloran et al 2002;O'Connell et al 2009). Experiments with captive mallards showed that grit availability reduced both Pb shot ingestion (Mateo and Guitart 2000) and the effects of Pb poisoning (Godin 1967;Longcore et al 1974).…”

“…In this case, 40 tonnes of sandstone <10 mm was first spread in 1986, and 50 tonnes was added annually from 1997 to 2000 (O'Halloran et al 2002). Later in the same area, 150 tonnes of grit was supplemented from 2001to 2005(O'Connell et al 2009). After grit supplementation, declines in the median blood lead level and in the proportion of swans suffering from acute lead poisoning were observed (O'Halloran et al 2002;O'Connell et al 2009).…”