Rare earth elements in a tropical marine food web: multi-species insights from oceanic and coastal islands in the Southwest Atlantic

Rare earth elements (REEs) are increasingly recognized as emerging contaminants, yet field data remain scarce for tropical marine ecosystems and for seabird matrices beyond feathers. Here, we present a multi-matrix assessment of REEs across a tropical oceanic–coastal gradient in the South Atlantic, including, to our knowledge, the first measurements of REEs in seabird blood and eggs. We analyzed 311 samples including brown booby ( Sula leucogaster) blood, feathers and eggs, fish muscle and liver, and crab muscle from a remote oceanic archipelago (SPSPA) and a nearshore coastal archipelago (Santana). ΣREE differed among matrices, with feathers generally showing higher median values than blood and eggs, underscoring matrix-specific integration of exposure. Spatial patterns in seabirds were also matrix- and age-dependent: blood ΣREE did not show a consistent site contrast, feather differences between sites were largely restricted to juveniles, and eggs showed higher ΣREE at Santana, indicating that maternal transfer provides a clear pathway for expressing site-specific exposure signals. In fishes, interspecific differences were detected at SPSPA in both liver and muscle, whereas no among-species difference was detected for muscle at Santana; liver often exceeded muscle, consistent with tissue-dependent accumulation. A screening-level dietary assessment indicated negligible carcinogenic risk from ΣREE exposure via edible fish muscle under adult and child scenarios, with intake distributions far below the provisional tolerable daily intake and zero exceedance probability. Overall, these results expand baseline REE knowledge for tropical marine food webs and highlight seabird eggs as a sensitive matrix for spatial comparisons. • Dietary screening showed <3% TDI and zero exceedance in adult/child scenarios • Crabs show higher ΣREE levels than pelagic and demersal fish • SPSPA brown bobbies juveniles had higher feather ΣREE than adults and Santana juveniles • Egg ΣREE was higher at coastal island than the oceanic • First report of REEs in seabird blood and eggs in a tropical marine system