BIOENERGETICS-BASED MODEL FOR ACCUMULATION OF POLYCHLORINATED-BIPHENYLS BY NESTLING TREE SWALLOWS, TACHYCINETA BICOLOR

A bioenergetics-based model was developed to simulate the accumulation of polychlorinated biphenyls by nestling tree swallows (Tachycineta b icolor). The model was largely parameterized using published informati on for passerine birds and accurately describes the observed growth of nestling swallows. The model was evaluated by comparing predicted con centrations of selected congeners with those measured in 15 d-old nest lings collected from two sites within the Saginaw River watershed. Res idue concentrations in nestlings were calculated as the sum of compoun d inherited in the egg and that assimilated from the diet, consisting principally of emergent aquatic insects. Model predictions were in goo d agreement with those measured in nestlings collected from a relative ly uncontaminated site but consistently over-estimated concentrations in birds from an area of known sediment contamination. The cause of th is discrepancy is unknown, but did not appear to be related to metabol ic biotransformation of individual congeners. Instead, it is suggested that dietary composition may have varied between sites. Alternatively , food consumption by nestling birds may have been overestimated. The results of this study indicate that caution must be used when interpre ting residue information from nestling swallows, which have been propo sed for use as sentinels of local sediment contamination.