The Last Paper by Ron Hites. A Tale of Four Cities: Polychlorinated Biphenyls in America

Local, regional and taxonomic factors influencing PCB bioaccumulation between two colonial waterbirds: non-migratory facultative vs migratory obligate piscivores

Studies of legacy contaminants (e.g., PCBs) in wildlife typically focus on singular bioaccumulation mechanisms related to organism physiology, food web effects or environmental factors. However, several mechanisms may jointly determine chemical burdens of biomonitoring species making the interpretation of burdens a significant challenge. We used ecological tracers (carbon and nitrogen stable isotopes, fatty acids) to infer and compare major PCB bioaccumulation mechanisms in eggs of a non-migratory facultative piscivore and a migratory obligate piscivore - the herring gull (Larus argentatus) and the double-crested cormorant (Nannopterum auritum), respectively. We found stark differences between species in how PCBs accumulated at nine Laurentian Great Lakes sites from 2015 to 2018. Semi-precocial gulls accumulated 70 % more PCBs in their eggs compared to altricial cormorants, consistent with higher parental investment in lipid content. Site-specificity also varied, with nearly twofold more variation in per-lipid PCBs being site-linked in gulls (84 %) than in cormorants (47 %). Fatty acid and stable isotope profiles indicated gulls bioaccumulated more PCBs at more mesotrophic sites where they fed on aquatic over terrestrial resources. Cormorants, in contrast, bioaccumulated more PCBs in oligotrophic lakes where, potentially, mixotrophic food webs may lead to high bioconcentration. Higher bioaccumulation of PCBs occurred in cormorants during winters with earlier ice-in dates, raising possibilities of PCB subsidy from overwintering grounds or metabolic effects. The potential variety of life history, ecological and geographic influences on egg PCB burdens underscores the importance of accounting for these in biomonitoring species as tissue burdens may have complex origin.