Brain concentrations of flame retardants and trace elements related to habitat use and brain measures in an urban-adapted gull

Exposure to environmental contaminants, such as halogenated flame retardants (HFRs) and trace elements, has been associated with a several health effects, including neurotoxicity. However, information on contaminant concentrations in brain and factors influencing their accumulation and exposure-related effects are limited in wild birds. We quantified 45 HFRs and 16 trace elements in brain of ring-billed gulls ( Larus delawarensis ) breeding in a highly urbanized environment and related their concentrations to foraging habitat use and a range of coarse and fine-scale neuroanatomical measures. Ten polybrominated diphenyl ethers (PBDEs), hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), and anti -dechlorane plus ( anti -DP) were detected in over 80 % of brain samples, as well as cobalt, nickel, copper, selenium, silver, cadmium, lead, and mercury. For certain compounds or elements, brain concentrations correlated with foraging habitat use, for example, PBDEs and lead increased with the proportion of time gulls spent foraging in waste management facilities. Additionally, we found correlations between brain contaminant concentrations and certain brain measures. For example, the number of immature neurons in the nucleus pretectalis principalis (Pt), a region in the visual system in birds, correlated negatively with brain concentrations of PBDEs and lead. Our results showed that urban-adapted ring-billed gulls accumulate a wide range of HFRs and trace elements in brain, and that some of these contaminants might be associated with variations in selected neural measures. Although the present correlative study cannot establish causality, these findings highlight potential toxicity pathways in the avian brain that warrant mechanistic investigation under controlled conditions. • We showed that HFRs and trace elements pass the blood-brain barrier in gull brain • Brain PBDE and lead levels increased with time gulls spent foraging in landfills • Brain levels of anti -DP increased with time gulls spent foraging in urban areas • Pt volume and cell numbers decreased with brain levels of copper, lead, and PBDEs • Hippocampal volume and cell numbers increased with brain levels of cadmium