A critical review on synergistic toxicity: Plastics as “Trojan-Horses” for mercury biomagnification in polar avian predators

Long-range transport of mercury (Hg) pollution and bioaccumulating microplastics (MPs) is a severe issue, and polar environments are continuously changing. To critically discuss the hypothesis of the “Trojan-Horse,” in which MPs might be carriers of increased Hg bioavailability and/or biomagnification in the polar bird food web. It integrates information on MP contamination in Arctic and Antarctic environments, the transport of Hg via Arctic and Antarctic food chains, and the interactions between MP and Hg toxicity. Laboratory studies have shown that UV-aged MPs can significantly increase Hg bioaccumulation (up to 1.61-fold), oxidative stress, neurotoxicity, and multigenerational reproductive toxicity. Polar seabirds have also been reported to have a high MPs ingestion frequency (FO: 15-93%) and biomagnification of Hg (2.3-8.6). Field studies have provided evidence of a link between MP ingestion and an increase in the Hg burden, which is somewhat contradictory to laboratory studies. Nanoplastics (NPs) may be an underestimated vector because of their high surface area-to-volume ratio and membrane-penetrating ability. Foraging/hunting ecology, foraging level, and migration result in varying vulnerabilities among albatrosses, petrels, fulmars, skua, and penguins. Some of the key gaps are limited in-field validation, seasonal plastic and Hg transfer processes, variable co-contaminant monitoring, and a lack of predictive models of plastic-Hg trophic interactions.