Plastic-related chemicals associated with polymers and their effects on thyroid hormones in fledglings of Northern fulmars (Fulmarus glacialis) from Svalbard

Abstract

Northern fulmars (Fulmarus glacialis) are pelagic seabirds prone to ingest plastics. Upon ingestion, plastic particles can have both physical and chemical impacts, although these effects are poorly understood. This study investigated the occurrence of plastic-related chemicals (PRCs) in relation to the type of plastic polymers ingested, as well as their potential endocrine disrupting effects on thyroid hormones in fulmar fledglings from Kongsfjorden, Svalbard. To do so, liver concentrations of polybrominated diphenyl ethers (PBDE) and per- and polyfluorinated substances (PFAS, further classified into carboxylates (PFCA) and sulfonates (PFSA)) and plasma concentrations of total and free tri-iodothyronine and thyroxine (TT3, FT3, TT4. FTA, respectively) were measured. Plastic particles from the gastrointestinal tract were quantified, weighed and their polymer type identified using Fourier Transform Infrared spectroscopy (FTIR) in a previous study (Marhaug, 2024). Spearman correlation matrices were used to investigate the relationships between PRCs and plastic polymers, as well as between PRCs and thyroid hormones. As ∑PBDE, ∑PFCA and ∑PFSA showed no correlation with plastic mass or quantity, none of these PRCs appear to be reliable proxies for plastic ingestion. Likewise, none of the plastic polymers showed any significant patterns related to PRCs. However, polyurethane, polyamide and polyhydroxybutyrate (PHB) showed a tendency toward positive associations with several PRCs, suggesting these polymers may accumulate certain chemicals more readily. We recommend that further studies should take polymer type into account when evaluating the transfer of PRCs through plastic ingestion. Finally, while PBDE-209, ∑PBDE and 7:3 FTCA showed significant positive correlations with TT3 and TT3:FT3. While PFNA, PFDA, PFUnDA, PFDoDA and ∑PFCA showed significant negative correlations with TT4:FT4. These findings may indicate a thyroid disrupting effect of plastic-related chemicals.