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

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?

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

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

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

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

Royal tern and least tern colony

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

Egg structure

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

Survival of mallard and white ibis embryos

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

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

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