The element matrix of Amazon waters and its relationship with the mineral content of fishes (Determinations using Neutron Activation Analysis)

Abstract

Thirty water samples from different water types of the Central Amazon, the southern (Rondonia) and northern (Roraima) border areas, and the Andes foothills (Bolivia, Province Beni) were analysed using the technique of neutron activation analysis. Qualitative analyses were carried out for the following 22 elements and trace elements (Table 2): Au, Ba, Br, Ca, Ce, Co, Cr, Cs, Fe, Hf, Hg, La, Mg, Mn, Na, Pa, Rb, Sb, Sc, Sm, Yb and Zn. Of these, Ca, Mg, Ba, Na, Fe, and Mn (Table 3) were determined quantitatively. The qualitative analysis gave a surprisingly uniform picture in that 14 of the elements were present in all the water bodies sampled. Those not present in all waters were Au, Hf, Hg, Pa, Rb, Yb and, of particular importance in production biology and nutritional physiology, Ca and Mg. The quantitative analysis showed that the levels of the elements investigated decreased from the border areas and Andes foothills in the direction of the Central region; however, except for Ca and Mg, no elements are actually missing. The fact that Ca and Mg could not be detected at the sensitivity level of NAA in some water bodies which nevertheless had rich fish populations, prompted investigations into a postulated metabolic-physiological relationship between fish and water type. The fish genus investigated was Symphysodon (Cichlidae): S. d¡scus inhabits clear waters and S. aequifasciata inhabits white waters. The mineral content of the vertebrae of these two fish species differs clearly according to the limnochemistry of their respective habitats (Table 6)