Sulfur, e-Waste Contaminants and Sharks.

Marine apex predators face increasing contaminant exposure, yet non-lethal assessments remain rare. Here, we quantify essential, toxic, and technology-critical elements, including rare earth elements (REEs), in freeze-dried whole blood of two shark species (Carcharhinus obscurus and Carcharhinus plumbeus) sampled in the Eastern Mediterranean Sea. Using inductively coupled plasma mass spectrometry (ICP-MS), we describe multi-element concentration profiles and inter-individual variability in shark whole blood. Elemental profiles differed between species under the sampled demographic structure. Sulfur and lithium were detected at relatively high concentrations, while PAAS-normalized REE patterns were broadly similar between species, characterized by low normalized values for light and middle REEs and comparatively higher normalized values for the heaviest measured element. This study represents one of the few reports of REEs in shark blood and highlights whole-blood elemental profiling as a minimally invasive approach for contaminant surveillance in threatened marine predators. The data provide baseline information to support future monitoring and non-lethal ecotoxicological studies in vulnerable coastal ecosystems.