Chlorinated hydrocarbons and mercury in sediments, red‐winged blackbirds (Agelaius phoeniceus) and tree swallows (Tachycineta bicolor) from wetlands in the Great Lakes–St. Lawrence River Basin

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Abstract
In 1991, we collected red‐winged blackbird (Agelaius phoeniceus) eggs and tree swallow (Tachycineta bicolor) eggs and nestlings, and sediment samples from 12 wetland sites in the Great Lakes and St. Lawrence River basin. We analyzed for chlorinated hydrocarbons and total mercury and found that biota contained contaminant concentrations which were one to two orders of magnitude above those in sediments. Maximum concentrations (wet weight) of contaminants were found in Akwesasne, St. Lawrence River (PCBs = 18,558.8 ng/g in red‐winged blackbird eggs, oxychlordane = 58.8 ng/g and mirex = 40.1 ng/g in tree swallow eggs); Mud Creek, Lake Erie (total mercury = 0.079 μg/g;p,p′‐DDE = 4,376.2 ng/g in tree swallow eggs); and Cootes Paradise (211.4 ng/g dieldrin and 115.6 ng/g heptachlor epoxide in tree swallow nestlings). Despite the migratory habits of red‐winged blackbirds and tree swallows, agreement among biota and sediment in geographic variation of contaminant concentrations supports the use of these animals as biomonitors of persistent chemicals. Although chlorinated hydrocarbon concentrations in red‐winged blackbird eggs were significantly correlated with sediment contamination, the local nature of the tree swallow chick diet suggests that nestlings would be the best indicator of local contaminant trends.

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