Risks to Birds in the Lake Calumet Region from Contaminated Emergent Aquatic Insects

The highly industrialized Grand Calumet River basin includes an extensive wetlands complex that has been severely degraded through heavy industrial activity, sewage and industrial discharges, landfills, and hazardous waste storage/disposal. Sediments and other environmental media in this area are contaminated with heavy metals and organic compounds. Our objective was to empirically quantify risks to insectivorous birds in the Lake Calumet wetlands region from contaminated sediments via ingestion of aquatic insects using tree swallows (Tachycineta bicolor) as a model organism. To accomplish this objective, we completed the following tasks: (1) assessed organic contaminant transfer (polychlorinated biphenyls [PCBs], organochlorine pesticides, polybrominated diphenylethers [PBDEs]) from an aquatic ecosystem (sediment and benthic macroinvertebrates) to a terrestrial food chain (tree swallows feeding on emergent aquatic insects), (2) quantified elemental contaminants in these locales and biota, (3) evaluated ecological effects these contaminants may have on tree swallows, comparing mercury loads and nesting ecology data at different sites as a case study, and (4) assessed the value of stable isotope data in determining how food chain length and food source (aquatic versus terrestrial, location of origin) affects contaminant loads in tree swallows nesting at Lake Calumet wetlands. With the exception of timing of nest initiation and other variables that are dependent on nest initiation timing (e.g., clutch size, and nestling mass), we observed no differences among sites in tree swallow nesting ecology endpoints. A variety of inorganic and organic contaminants were accumulated by nestlings via their insect diets, but concentrations of nearly all the contaminants were at the lower end of ranges in the literature. The exception to this trend was dichlorodiphenyldichloroethylene (DDE) concentrations in eggs and nestlings at Big Marsh which were among the higher reported values. To our knowledge, this paper is the first report of PBDEs concentrations in tree swallow nestlings. Our stable isotope analysis suggested a terrestrial origin for many of the contaminants as has been suggested by others.