Acute Toxicity of Ingested Zinc Shot to Game-farm Mallards

Abstract

We conducted a 30-day acute toxicity test of zinc (Zn) shot using 6- to 8-month-old wild-type game-farm Mallards (Anas platyrhynchos), 40 of which (20 males and 20 females) were dosed with 6 No. 4 candidate shot pellets containing 98% Zn and 2% tin (Sn); the remaining 40 ducks were dosed with 6 No. 4 steel (Fe) shot and served as controls. The Zn shot resulted in high mortality, with a greater proportion of females dying than males. For the 30-day study, survival averaged 18 and 23 days for female and male Zn-dosed ducks, respectively; all Fe-dosed ducks survived to Day 30. Ataxia/paresis and other signs of intoxication were noted in a large portion of Zn-dosed ducks. For all ducks retaining 6 shot pellets, including those that survived < 30 days, shot retention, percent of the original shot weight dissolved, and dissolution rates were similar for Zn- and Fe-dosed ducks. For those ducks that retained 6 pellets and survived to Day 30, percent loss of the original shot weight and the dissolution rate were higher in Zn-dosed ducks. Mean body weight in Zn-dosed ducks decreased between Days and 15, and between Days 15 and 30 in Zn-dosed females. Zn-intoxicated ducks lost a considerable proportion of their body weight between dosing and death. The kidneys of Zn-dosed ducks as a group were heavier, and the pancreases, livers, and gizzards lighter, as compared with Fe-dosed ducks. The liver (males) and kidneys of Zn-dosed ducks that died as a result of Zn intoxication were heavier, whereas thegonads (females) and gizzards were lighter, as compared with those that survived. The liver, pancreas, and kidneys increased, whereas the gonads (males) and gizzards decreased, as a proportion of total body weight in Zn-dosed ducks that died prior to Day 30. Mean packed cell volume (PCV) decreased between Days and 15 and increased between Days 15 and 30 in male and female Zn-dosed ducks. PCV values changed little in Fe-dosed ducks over the course of the study; however, PCV decreased dramatically in Zn-intoxicated ducks. A variety of gross lesions was observed, most often associated with the gastrointestinal tract. Grossly, cecal lesions were the most consistent and dramatic changes observed. No macroscopic lesions were observed in the Fe-dosed ducks, and histologic lesions in this group were considered within normal limits for game-farm ducks. Histologic lesions observed in Zn-dosed Mallards most often included pancreatic apoptosis, splenic lymphoid depletion and/or lympholysis, necrohemorrhagic typhlitis, and necrosis of the epithelial cells of the renal tubules. We detected high concentrations of Zn, and alterations in levels of other elements, in the tissues of Zn-dosed ducks relative to Fe-dosed controls. Mean Zn concentrations were greater in Zn-dosed ducks for all tissues examined, and levels in the kidneys, livers, and pancreases of Zn-intoxicated Mallards were similar to levels associated with toxic effects reported in other studies. Mean tissue tin (Sn) concentrations were below the Method Detection Limit (MDL) in all cases; few individual Sn values were above MDLs. Changes in tissue element concentrations tended to be more dramatic in ducks that died as a result of Zn intoxication than in Zn-dosed ducks that survived the experiment. Gender differences in analyte concentrations were detected for some tissues. These results indicated that dosing of 6- to 8-month-old game-farm Mallards with 6 No. 4 shot comprised of 98% Zn and 2% Sn produced toxic effects under the test conditions.