Uranium Amazon River

Figure 4 Measurements of (A) uranium aetivity ratios, UARs ( U U) and U eoneentrations (B) aeross a salinity gradient off the Amazon River mouth (1996). UARs were determined by thermal ionization mass speetrometry (TIMS) at Calteeh (D. Poreelli) U eoneentrations by ICPMS...

Several studies have examined the partitioning of U on particles and colloids. Results from detailed sampling and particle separation in the Amazon estuary shows that most of the uranium at the Amazon River mouth is associated with particles (>0.4 im) and that >90% of the uranium in filtered water (<0.4 im) is transported in a colloidal phases (from a nominal molecular weight of 10 000 MW up to 0.4 im) (Swarzenski et al. 1995 Moore et al. 1996). Mixing diagrams for uranium in different size fractions in the Amazon estuary reveal that uranium in all size fractions clearly display both removal and substantial input during mixing. 

Figure 4 Measurements of (A) uranium activity ratios, 1.22 Amazon River A...

Mac Kee BA, Demastre DJ, Nittrouer CA (1987) Uranium geochemistry on the Amazon Shelf Evidence for uranium release from bottom sediments. Geochim Cosmochim Acta 51 2779-2786 Mangini A, Sormtag C, Bertsch G, Muller E (1979) Evidence for a higher natural uranium content in world rivers. Natrrre 278 337-339... 

Moore DG (1967) Amazon and Mississippi River concentrations of uranium, thorium, and radium isotopes. Earth Planet Sci Lett 2 231-234... 

Swarzenski, P.W., and McKee, B.A. (1998) Seasonal uranium distributions in the coastal waters off the Amazon and Mississippi Rivers. Estuaries 21, 379-390. 

The behavior of uranium varies considerably across samples studied. Palmer and Edmond (1993) have reported increasing trends of uranium concentration with river alkahnity in the Orinoco, Amazon and Ganga river basins, showing the importance of limestone and black shale dissolution for the control of uranium concentrations in river waters. The association of uranium and major soluble elements is also reported by Elbaz-Poulichet et al. (1999) for the upper Amazonian basins of Bohvia. However, under the organic-rich conditions of Scandinavian rivers (Porcelli et al., 1997) or African rivers (Viers et al., 1997), uranium concentrations can be decoupled from those of major elements, due to the existence of a colloidal fraction of uranium. 

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