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Hormesis associated with a low dose of methylmercury injected into mallard eggs
Gary H Heinz1, David J Hoffman, Jon D Klimstra
1United States Geological Survey, Patuxent Wildlife Research Center, BARC-East, Building 308, 10300 Baltimore Avenue, Beltsville, MD 20705, USA. gheinz@usgs.gov
Abstract:
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).
Insights
Methylmercury exposure in mallard eggs showed a hormetic effect, with low doses enhancing hatching success. Higher methylmercury concentrations, however, proved detrimental to avian reproduction.
Area of Science:
- Environmental Toxicology
- Avian Reproduction
- Developmental Toxicology
Background:
- Methylmercury is a potent neurotoxin impacting wildlife.
- Understanding dose-response relationships is crucial for ecological risk assessment.
- Hormesis, a beneficial effect at low doses, is increasingly recognized in toxicology.
Purpose of the Study:
- To investigate the effects of methylmercury chloride on mallard egg hatching success.
- To determine if methylmercury exhibits hormesis in avian embryos.
- To evaluate the potential for low-dose methylmercury to represent a no-observed adverse effect level (NOAEL).
Main Methods:
- Mallard eggs were injected with methylmercury chloride at varying concentrations (0 to 6.4 μg/g).
- Hatching success rates were recorded for each treatment group.
- Statistical analysis was performed to compare hatching success among doses and controls.
Main Results:
- The lowest dose (0.05 μg/g) significantly increased hatching success (93.3%) compared to controls (72.6%).
- Hatching success progressively decreased with increasing methylmercury concentrations.
- This pattern suggests a hormetic response to methylmercury in mallard eggs.
Conclusions:
- Low-dose methylmercury exposure may stimulate avian egg hatching success, a phenomenon known as hormesis.
- Higher methylmercury doses are detrimental to mallard embryo development and hatching.
- The observed low-dose effect could have implications for establishing regulatory guidelines and no-observed adverse effect levels (NOAELs).
