First record of trace elements in cetaceans stranded along the Asturias Coastline, Northwest Spain: One great diversity area of marine mammals

The concentrations of cadmium (Cd), lead (Pb), arsenic (As), selenium (Se) and mercury (Hg) in the kidney, liver, brain and muscle of 20 individuals of cetaceans, stranded along the Asturias coastline between 2018 and 2020, have been studied. Species studied include fin whale (Balaenoptera physalus), striped dolphin (Stenella coeruleoalba), common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), harbour porpoise (Phocoena phocoena) and pygmy sperm whale. (Kogia breviceps). All trace elements analyzed were detected in all cetacean families. The most detected compound was Se in the kidney (90 %), closely followed by Hg in muscle (85 %), while the least detected metal was Pb in the kidney (5 %). The highest concentrations of Se (66.00 mg/kg), Hg (44.00 mg/kg) and As (2.00 mg/kg) were detected in the liver, followed by Cd (53.00 mg/kg) in the kidney and Pb (0.37 mg/kg) in the brain. The family that presented the highest concentrations of toxic metals was Delphinidae, compared to the family Balaenopteridae, which is explained by the feeding and behavioural habits of odontocetes. The concentrations found are lower than those detected in other areas of Spain and the Atlantic Ocean and lower than those considered responsible for toxic effects in cetaceans. In addition, low levels of metal contamination (IMP) were found in most samples, although in two individuals we cannot exclude effects at the renal level due to metal accumulation. The overall effect of biologically relevant variables on metal concentrations was assessed by generalised linear modelling (GLM) analysis, with tissue being the most influential variable on metal concentrations. In addition, the Hg:Se molar ratio was lower than 1 in most samples analyzed, so the detoxifying action of Se against Hg is confirmed. As it represents the first record of trace element analysis in cetaceans of this area, our study supplies useful data for the development of conservation strategies in the Cantabrian Sea, as well as provides valuable information for future research.