Hormesis Associated with a Low Dose of Methylmercury Injected into Mallard Eggs
We injected mallard (Anas platyrhynchos) eggs with methylmercury chloride at doses of 0, 0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, and 6.4 μg mercury/g egg contents on a wet-weight basis. A case of hormesis seemed to occur because hatching success of eggs injected with 0.05 μg/g mercury (the lowest dose) was significantly greater (93.3%) than that of controls (72.6%), whereas hatching success decreased at progressively greater doses of mercury. Our finding of hormesis when a low dose of methylmercury was injected into eggs agrees with a similar observation in a study in which a group of female mallards was fed a low dietary concentration of methylmercury and hatching of their eggs was significantly better than that of controls. If methylmercury has a hormetic effect at low concentrations in avian eggs, these low concentrations may be important in a regulatory sense in that they may represent a no-observed adverse effect level (NOAEL).
KeywordsMercury Concentration Methylmercury Wild Bird Hatching Success Hormetic Effect
This research was funded by the CALFED Bay-Delta Program’s Ecosystem Restoration Program (grant no. ERP-02D-C12), with additional support from the United States Geological Survey Patuxent Wildlife Research Center. We thank Donna Podger and Carol Adkins of the California Bay-Delta Authority for help and project support. Steve Schwarzbach and Tom Suchanek provided much appreciated guidance and support during the development of the project, and Collin Eagles-Smith and Tom Maurer handled much of the work with reports and budget matters. We thank Kevin Brittingham, Michael Hammond, Michael Hoffman, and Dan Murray for help in conducting the laboratory parts of the study. Use of trade, product, or firm names does not imply endorsement by the United States Government.
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