Emerging Evidence of Pancreatic Metal Accumulation and Subcellular Metal Partitioning in Threatened Elasmobranchs from the Southeastern Coast of Brazil.

Elasmobranchs play crucial ecological roles and exhibit high biological diversity, yet their physiology, especially regarding contaminant regulation, remains poorly understood. In this sense, the pancreas, a vital organ for digestion and hormonal balance, is still severely understudied in ecotoxicological assessments concerning this group This study investigated, for the first time, total and subcellular concentrations of metals and metalloids by inductively coupled plasma mass spectrometry (ICP-MS) in the pancreatic tissue of five threatened elasmobranch species along the coast of Rio de Janeiro, Brazil. Species-specific bioaccumulation patterns were observed: Narcine brasiliensis exhibited the highest contamination, accumulating six elements, while Dasyatis hypostigma showed high Pb, Rb, Se and Ti levels. Zapteryx brevirostris exhibited the highest concentrations of Hg and V, while Atlantoraja castelnaui and Squatina guggenheim displayed high levels of Mn and Co, respectively. Subcellular analyses revealed that, in most species, metal concentrations associated with detoxification proteins (e.g., metallothioneins) were lower than total concentrations, suggesting either limited detoxification capacity, such as insufficient synthesis or metallothionein binding, or saturation of detoxification sites, implying maximum metal-binding capacity. Molar ratio assessments indicated potential protective interactions involving essential elements like Cu, Fe, Mn, and Zn, although these defenses do not always seem to be sufficient. Additionally, statistically significant associations such as Zn-As and Fe-Ti, among others, highlight potential competitive or antagonistic interactions affecting metal bioavailability. These findings suggest that the pancreas may be more vulnerable to metal toxicity than previously assumed. Overall, this study provides novel insights into metal handling in elasmobranchs and highlights the importance of including subcellular metal partitioning in future environmental exposure and physiological risk assessments in marine predators.