Detection and quantification of heavy metals in blood and milk of Amazon river dolphin (Inia geoffrensis) (Cetartiodactyla: Iniidae) using wavelength-dispersive X-ray fluorescence spectrometry

River dolphins of the genus Inia are among the most endangered cetacean species in the world. However, information on the elemental constitution of the blood and milk of these species is still quite scarce. This study aims to evaluate the wavelength-dispersive X-ray fluorescence (WD-XRF) spectrometry to detect and quantify heavy metals in blood and milk samples of a free-ranging female Amazon river dolphin (Inia geoffrensis) from Central Amazon, Brazil. The WD-XRF method detected and quantified 14 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Cr, Mn, Fe, Zn, and Cu) in the samples analyzed, in which 13 elements were in the blood and 14 were in the milk. The WD-XRF method did not detect some heavy metals, including those already described for the Amazon river dolphin milk (e.g., mercury) detected by other analytical methods, such as atomic absorption spectrometry (AAS). However, it is possible that the samples analyzed may come from a non-contaminated individual. Therefore, the joint use of different analytical methods is recommended for future analyses. In addition, both blood and milk samples presented high concentrations of some metals, and the health risks of botos are discussed. This result demonstrates that the WD-XRF method is a viable analytical procedure for detecting certain elements and quantifying their concentrations in liquid biological samples of Amazonian cetaceans.

Automated summary

This study used wavelength-dispersive X-ray fluorescence (WD-XRF) spectrometry to detect and quantify heavy metals in blood and milk samples of a free-ranging female Amazon river dolphin. The WD-XRF method detected and quantified 14 elements, with 13 in the blood samples and 14 in the milk samples. Some heavy metals, like mercury, were not detected, suggesting the possibility of non-contaminated samples. It is recommended to use different analytical methods in future analyses and the high concentrations of certain metals in the samples raise health risks for the river dolphins.