Metal(loid) Concentrations in Coastal (Sotalia guianensis) and Oceanic (Pseudorca crassidens) Odontocete Cetaceans Stranded Along the Northeastern Brazilian Equatorial Margin

Cetaceans face multiple threats, and pollution has become a major concern for their conservation worldwide. This study assessed metal(loid) concentrations in the tissues of two odontocete species with coastal and oceanic habits, namely Guiana dolphin (Sotalia guianensis; n = 11) and the false killer whale (Pseudorca crassidens; n = 8), respectively, stranded along the northeastern Brazilian equatorial margin. Silver (Ag), copper (Cu), cadmium (Cd), mercury (Hg), and selenium (Se) were determined in samples of liver, muscle, and kidney, expressed as mean ± standard deviation (SD), in µg g⁻¹ wet weight. In P. crassidens, Hg was detected in all individuals, with hepatic concentrations (794.1 ± 556.9 µg g⁻¹) higher than those in muscle (30.2 ± 16.7 µg g⁻¹); females exhibited higher levels than males in both tissues. In S. guianensis, mean Hg levels were also higher in the liver (1.6 ± 2.4 µg g⁻¹) compared to muscle (0.4 ± 0.4 µg g⁻¹), with the highest concentration detected in the kidney (3.1 µg g⁻¹). Detectable Cd concentrations occurred only in one juvenile (0.3 µg g⁻¹, liver). For Cu, Ag, and Se, values varied between species and tissues. The observed differences between species, as well as among sexes, age classes, and tissues, suggest that physiological factors, diet, and exposure time influence metal accumulation. These findings highlight the importance of considering the role of coastal versus oceanic habitat use, trophic ecology, and life history in the bioaccumulation of metal(loid)s since some of these factors were not assessed (i.e., trophic ecology).