Relation of lead exposure to sediment ingestion in mute swans on the Chesapeake Bay, USA

Abstract

Although wildlife risk assessments are generally based on the accumulation of environmental contaminants through food chains, wildlife may also ingest contaminants incidentally with sediment. Forty-two mute swans (Cygnus olor) were collected from unpolluted portions of central Chesapeake Bay, Maryland, USA, in spring 1995, and their intestinal digesta were analyzed for 13 metals (aluminum [Al], boron, barium, cadmium, copper [Cu], iron, magnesium, manganese, nickel, lead [Pb], strontium, vanadium, and zinc) and for acid-insoluble ash, a marker of sediment. Swan livers and sediment samples also were analyzed for the same metals. Group method of data handling demonstrated that the digesta Al, which is associated with clays, was the best predictor of digesta Pb. Adding concentrations of other metals as predictors did not improve the accuracy of the estimates of Pb concentrations from Al concentrations. The r 2 of the equation relating the log of digesta Pb to the log of digesta Al was 0.86, whereas the r 2 of the equation relating the log of digesta Pb to the log of digesta acid-insoluble ash was 0.50. Accounting for the sediment ingested was critical to determining the exposure of mute swans to Pb, as well as to some of the other metals, and sediment ingestion should be considered in ecotoxicological risk assessments of waterfowl. The mean of 7.4% acid-insoluble ash in the digesta corresponded to an estimated 3.2% sediment in the diet. The Pb concentrations in the digesta were two to three times the concentration that would have been predicted from sediment Pb concentrations; presumably, the swans had ingested clays high in Pb that had settled on the vegetation. The swans were probably not exposed to high Cu concentrations but nevertheless had hepatic Cu concentrations that would be considered very high if found in other species.

Monitoring of Pb Exposure in Waterfowl Ten Years after a Mine Spill through the Use of Noninvasive Sampling

“…Among the three sites studied here, geese feces from the Cerro de los Ánsares showed the highest mean Pb concentration (5.2 µg/g), and this was also higher than previously described for the same area (2.5 µg/g; [24]). However, overall, Pb concentrations in geese feces recorded here were within the range reported for waterfowl feces in uncontaminated areas (such as National Wildlife Refuges) in the USA, i.e., 10 µg/g d.w. [21], [25], [43], [44]. Also, fecal Pb levels detected here were within the range described in feces from hunted mallards (without Pb shot in their gizzards) from the Ebro Delta, Spain [32].…”

Sediment Ingestion Rates in Waterfowl (Anatidae) and Their Use in Environmental Risk Assessment

“…Tundra and mute swans eat mainly vegetation supplemented with some animal matter. In agreement with previous work on swans in Chesapeake Bay, we estimate the average digestibility of swan diets as 50% (Beyer, Day, et al 1998). Common goldeneyes (Bucephala clangula) eat mainly insects, mollusks, and crustaceans and a little vegetation (Eadie et al 1995).…”

Lesser White-fronted (Anser erythropus) and Greater White-fronted (A. albifrons) Geese wintering in Greek wetlands are not threatened by Pb through shot ingestion

“…2). Such a relationship has also been found in wood ducks (Beyer et al, 1997), mute swans (Beyer et al, 1998b), various dabbling ducks (Beyer et al, 1999), mallards (Martinez-Haro et al, 2010, coots (Fulica atra) (Martinez-Haro et al, 2011), greylag geese and purple gallinules (Porphyrio porphyrio) (Martinez-Haro et al, 2013). Since Al is a proxy of ingested soil or sediment in feces, the close co-variation between the two metals provides a sound indication that most of the Pb ingested by the studied geese originates from the soil, rather than from other sources such as food items or shot (Beyer et al, 1999).…”

“…Owen (1976) found a higher proportion of clover stolons and roots in the diet of GWfG in Britain when the ground was wet in relation to leaves of grasses and forbs, which would presumably increase soil ingestion. Sediment ingestion rates were estimated between 3% and 5% in mute swans typically feeding on submerged aquatic vegetation (Beyer et al, 1998b(Beyer et al, , 2008, between 9% and 15% in tundra swans (Cygnus columbianus) whose diet consists mainly of mollusks but also winter cereals (Beyer et al, 1998a(Beyer et al, , 2008 and 9% in Canada geese (Branta canadensis) from the same area (Beyer et al, 2000). Soil ingestion rates in the range of 6%-14% were calculated for greylag geese in the Guadalquivir Marshes (southwestern Spain) (Mateo et al, 2006).…”