1. Gary H. Heinz and David J. Hoffman USGS Patuxent Wildlife Research Center Beltsville, MD 20705 Threshold levels of mercury in bird eggs: what we know and don’t know

2. Exposure of adults can be high The mother deposits mercury in her eggs Avian embryos are very sensitive to mercury Protecting avian embryos will protect other wildlife (and probably human health) Why study mercury in bird eggs?

3. We know the toxic thresholds of mercury in the eggs of some lab species (ducks, chickens, pheasants) What we know

4. We don’t know the toxic thresholds of mercury in the eggs of wild birds What we don’t know

5. We can study the effects of mercury on birds in the field We can breed wild birds in captivity and feed them mercury Other approaches How we can find out what we don’t know

6. Collect the eggs of wild birds Inject the eggs with doses of methylmercury Determine how sensitive each species is Egg injections as another approach

7. Royal tern and least tern colony

8. Pelican, gull, cormorant, tern, egret, and swallow eggs

9. Egg structure

10. Hg injection. Egg drilling prior to injection. Sealing injection site. Placing eggs in incubator.

11. Survival of mallard and white ibis embryos

12. Embryotoxic thresholds in mallard eggs and diet Harmful concentrations of mercury in eggs (ppm, wet-weight) Mercury in diet of adults that produces 0.8 – 1.0 ppm mercury in eggs (ppm, wet-weight) 0.8 – 1.0 ~ 0.1

13. Country/State/Agency Harmful concentrations of mercury in diet (ppm, wet- weight) U.S. EPA and FDA 1.0 Michigan0.5 Sweden1.0 Italy0.7 Canada0.5 Brazil0.5 Australia0.5 Japan0.4 Dietary thresholds in humans

14. 0.4 vs. 0.1 (ppm Hg in diet, wet-weight) Human vs. Wildlife Health