Plastic in regurgitated pellets and mercury contamination of skua chicks on the Antarctic Peninsula

Plastic pollution represents a widespread threat to marine ecosystems. As top predators, seabirds are capable of ingesting substantial amounts of plastic waste, which can cause physical harm and may serve as a route for heavy metal contamination, with potential repercussions on physiology and body condition. This study investigates plastic in regurgitated pellets of brown skua Stercorarius antarcticus and south polar skua S. maccormicki chicks at Bahía Esperanza/Hope Bay, Antarctic Peninsula, and its association with blood total mercury (THg) concentrations, trophic ecology, anthropogenic activity and health markers. Regurgitated pellets ( n = 445) were collected from active nests during the chick-rearing period and the plastic content was analyzed (occurrence, size, color and polymer composition). Additionally, THg concentrations and stable isotopes of carbon ( δ ¹³C) and nitrogen ( δ ¹⁵N), which are proxies of foraging habitat and trophic level, respectively, were determined in the blood of fully fledged chicks ( n = 39). A total of 33 plastics were identified in pellets, with pink and polyvinyl chloride being the most common color (45.4%) and polymer (69.7%), respectively. A significant positive relationship was found between blood THg concentrations and the number of plastic in pellets and their surface area. Chicks with higher blood THg concentrations were fed with prey from terrestrial-coastal areas, rather than offshore/pelagic prey. Additionally, increased glutamic-oxaloacetic transaminase activity was associated with higher blood THg concentrations. Based on these findings, our hypothesis is that interaction with plastics may act as an alternative exposure route of Hg to seabirds.