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).