Plastic ingestion and plastic-related chemicals in northern fulmars (Fulmarus glacialis): Exploration of histopathological and endocrine alterations.

Northern fulmars (Fulmarus glacialis) are pelagic seabirds prone to ingesting plastics. Ingestion of plastic particles can have both physical and chemical impacts, although these effects are poorly understood. This study investigated scar tissue formation and thyroid disruption in relation to plastic ingestion. Abundance of ingested plastic types and polymers, and liver concentrations of plastic-related chemicals (PRCs; including plastic additives, production aids and adsorbed environmental contaminants) were determined. A total of 14 (N = 15, 93.3%) of the fledglings exceeded the EcoQO threshold (containing more than 0.1g of plastic). None of the quantified PRCs appeared to be reliable proxies for plastic ingestion. Only the plastic type "Industrial" (i.e., pellets/"nurdles", distinct from plastic derived from industry-specific activities, such as fisheries) showed a significant positive correlation with per-/poly-fluoroalkyl substances (PFAS) in liver. Regardless of plastic exposure, some PFAS compounds showed significant negative correlations with the ratio between total and free thyroxine (TT4:FT4), while other PFAS and some polybrominated diphenyl ethers (PBDEs) showed significant positive correlations with total 3-triiodothyronine (TT3) and the ratio between total and free T3 (TT3:FT3). Most histological observations of scar tissue were classified as "moderate" and no correlation was observed between collagen prevalence (or scar tissue severity) and plastic ingestion. However, some PBDEs and PFAS showed positive correlations with collagen prevalence. Finally, thyroid hormones tended to be negatively correlated with collagen prevalence. Together with uptake from prey as an important exposure pathway for PRCs, uptake from plastic is a probable additional route. In conclusion, we hypothesise that the presence of PRCs, potentially originating from industrial plastic, may induce a thyroid-disrupting effect. However, as total plastic mass was not correlated with PRCs, other exposure routes, are likely important for the contaminant burden in the majority of the fulmar fledglings. The impact of plastic ingestion on collagen prevalence remains unclear.