27 



kidneys in 2 months, and approximately 99% 

 was lost in 6 months (Borg et al. 1969). 

 Ospreys apparently have a similar loss rate of 

 mercury (Johnels et al. 1968). 



When methyl mercury dicyandiamide was 

 fed to mallard ducks at a concentration of 

 3 ppm mercury (dry weight), mercury accumu- 

 lated in the eggs to an average of 7.2 and 

 5.5 ppm in 2 successive years (Heinz and 

 Locke 1976). Mercury in the eggs caused brain 

 lesions in ducklings. Lesions included demye- 

 lination, neuron degeneration, necrosis, and 

 hemorrhage in the meninges overlying the 

 cerebellum. Brains of dead ducklings con- 

 tained an average of 6.2 and 5.2 ppm mercury 

 in the 2 successive years. 



Upon necropsy, ring-necked pheasants that 

 were killed after receiving 4.2 ppm mercury 

 (dry weight) in their diet for 350 days ap- 

 peared normal, but those that received 

 greater concentrations (12.5, 37.4, or 

 112 ppm, dry weight) died during the experi- 

 ment and showed variable amounts of subcu- 

 taneous edema and decreasing amounts of 

 subcutaneous and abdominal adipose tissue 

 as survival time on the treated diet increased 

 (Spann et al. 1972). Birds that died on the 

 higher dosages showed signs of neurological 

 disturbance, including ataxia and torticollis, 

 before death. 



Lead poisoning has long been recognized as 

 a serious problem for waterfowl (Wetmore 

 1919; Jordan and Bellrose 1951; Bellrose 

 1959). Histopathological changes occur in the 

 kidneys of mallards as a result of lead shot in- 

 gestion (Locke et al. 1966, 1967). In addition, 

 significant changes in activity of three en- 

 zymes often used to assess hepatic damage 

 occurred in mallard ducks following oral ad- 

 ministration of lead shot (Rozman et al. 1974). 



The ingestion of one number 4 lead shot by 

 each of 80 pen-reared mallards that were fed 

 whole-kernel corn caused 19% mortality 

 within an average of 20 days (Longcore et al. 

 1974a). Coating or alloying lead with other 

 metals only delayed mortality among dosed 

 ducks. Disintegrate lead shot with water- 

 soluble binder and lead-containing biochemi- 

 cal additives were as toxic to mallards as com- 

 mercial lead shot. 



Lead levels in brains, tibiae, and breast 

 muscle of mallard ducks that died and in 

 tibiae of those that were sacrificed increased 

 significantly from dosage with one number 4 

 lead shot (about 1.4 g) until death (Longcore 



et al. 1974b). In mallard ducks, lead levels ex- 

 ceeding 3 ppm in the brain, 6 to 20 ppm in the 

 kidney or liver, or 10 ppm in clotted blood 

 from the heart indicated acute exposure to 

 lead. 



One month after dosage, mean lead levels in 

 mallards given one number 4 all-lead shot 

 were about twice those in tissues of mallards 

 given one number 4 lead-iron shot that con- 

 tained about 50% lead (Finley et al. 1976a). 

 Necropsy of sacrificed ducks failed to reveal 

 any of the tissue lesions usually associated 

 with lead poisoning in waterfowl. Lead in the 

 blood of ducks dosed with all-lead shot aver- 

 aged 0.64 ppm, and 0.28 ppm in ducks given 

 lead-iron shot. Lead residues in livers and 

 kidneys of females given all-lead shot were 

 significantly higher than in males. In both 

 dosed groups, lead levels in wingbones of the 

 females were about 10 times those in males, 

 and were significantly correlated with the 

 number of eggs laid after dosage. It appeared 

 that after the laying hens ingested sublethal 

 amounts of lead shot, high lead deposition in 

 the bone occurred as a result of mobilization 

 of calcium from the bone during eggshell for- 

 mation. Lead levels in contents and shells of 

 eggs laid by hens dosed with all-lead shot were 

 about twice those in eggs laid by hens dosed 

 with lead-iron shot. Lead levels in eggshells 

 best reflected levels of lead in the blood. 



The inverse correlation between delta- 

 aminolevulinic acid dehydratase (ALAD) ac- 

 tivity and blood lead concentrations was 

 highly significant in canvasback ducks from 

 the Chesapeake Bay (Dieter et al. 1976). 

 ALAD is an important enzyme in hemoglobin 

 synthesis. The activity of this enzyme in the 

 blood provides a sensitive and precise esti- 

 mate of lead contamination in waterfowl. In 

 mallards, lead concentrations in blood were 

 strongly correlated with erythrocyte ALAD 

 activity, suggesting that biochemical re- 

 sponse to two types of lead shot (one all-lead, 

 the other containing 50% lead) depends upon 

 the quantity of lead present (Finley et al. 

 1976b). 



Reproduction 



Mercury levels (3.5 to 1 1 ppm) in the eggs of 

 Swedish white-tailed eagles that failed to 

 hatch indicate that the decline in reproduction 

 of this species could be attributed to mercury 

 poisoning (Borg et al. 1969). A corresponding 



