Bidirectional transfer of halogenated flame retardants between the gastrointestinal tract and ingested plastics in urban-adapted ring-billed gulls.

The hypothesis that plastics can transfer chemical pollutants to organisms after ingestion has been supported by several lab and field studies. However, models indicate that this transfer could be bidirectional and that whether chemicals move from plastics to the animal or vice versa, depends on several factors, including the relative concentrations of chemicals in both the animal and the plastics ingested. To explore this phenomenon in the field, we examined the relative concentrations of several halogenated flame retardants (HFRs) in a population of urban-dwelling ring-billed gulls (Larus delawarensis) and the plastics in their gastrointestinal (GI) tracts. We predicted the direction of transfer for HFRs between these birds and their ingested plastics using assumptions based on equilibrium theory. Because we were also interested in the sources of ingested plastics in this population, we investigated the relationships between time spent in different foraging habitats (determined using GPS-based telemetry) and the amounts and morphologies of plastics in their GI tracts. Results suggest that for this highly HFR-exposed population of ring-billed gulls, chemical transfer between plastics and bird is bidirectional, with a dominance of transfer from bird to ingested plastics. We also observed a relationship whereby birds that ingested no or low amounts of plastics were most closely associated with the use of residential habitats. Overall, we conclude that whether ingested plastics is a source or sink of chemicals to organisms is a complex and context-dependent phenomenon, and likely varies based on parameters such as exposure level and feeding ecology.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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