The
relatively low uptake efficiency (as measured by CF) of U in freshwater
macrophytes, and other freshwater biota (e.g. mean CF=9 for fish
CF=~6–11 for an insect (Chironomus
tentans) CF=~ 5–50 for H. azteca
(Alves, 2009)), may be due to its low bioavailability in freshwater
(where DOCb1 mg L−1) at circumneutral pH (~5% UO2
2+ at pH 6, reducing
to b0.001% UO2
2+ at pH 8), due to strong complexation of U to
carbonate (e.g., UO2CO3), and its propensity to form polymeric hydroxyl
complexes (e.g., (UO2)3(OH)5
+) with increasing dissolved U
concentration