Patuxent Science Meeting 2006 Poster Abstract

Determining how avian embryos differ in their sensitivity to Methylmercury

Heinz GH, Hoffman DJ, Schoen KR, Klimstra JD

Environmental contamination by mercury is a serious problem in many parts of the United

States. Because methylmercury (MeHg), the most toxic form of mercury found in the

environment, biomagnifies in food chains, wildlife, especially fish-eating birds, are especially

vulnerable. Avian embryos are known to be the most sensitive life stage among birds to MeHg

poisoning, but limited research to date suggests that the embryos of different species of birds

may differ in their sensitivity to MeHg. No single approach is likely to answer the question of

how variable different avian species are in their sensitivity to mercury. Combinations of field,

controlled laboratory feeding, and hybrid field-lab studies (such as egg injection studies) will be

required to gain a good idea of how the embryos of various birds respond to MeHg exposure.

More field research is needed to study differences in embryo sensitivity under realistic natural

conditions, although these studies are complicated by the presence of other environmental

stressors. Laboratory breeding studies can control for other stressors, but the great cost and

time required to conduct captive breeding studies with wild birds is going to severely limit the

number of these studies undertaken. Most of what is known from the lab about toxic levels of

MeHg in bird eggs came from game farm species such as mallards (Anas platyrhynchos), ring-

necked pheasants (Phasianus colchicus), and chickens (Gallus gallus). How the sensitivity of

the embryos of the game farm species compares to the sensitivities of the embryos of wild birds

is unknown. Using a field-lab hybrid study in which various doses of methylmercury are injected

into the eggs of wild birds will complement data from field and controlled feeding studies.

Friday, September 22, 2006