Assessment of Cd and Cr Bioavailability in Sediment of River Challawa, Nigeria

Sediment quality assessment are a scientific tools that synthesize information regarding the relationships between the sediment concentrations of heavy metals and any biological effects resulting from exposure to these heavy metals. A field study was conducted to determine the physico-chemical parameters and level of Cd and Cr bioavailability of the river sediment of Challawa. The study revealed that the physiochemical parameters of river Challawa such as pH and organic matter favours bioavailability of Cd and Cr. The distribution pattern of Cr chromium in different fractions was in the order; Residual > Carbonate bound > Fe-Mn oxide bound > Organic bound > Exchangeable in the study and control areas. Chromium was associated mainly (65 – 93.3%) with the residual fraction in all the samples and relatively small amount of chromium occur in the non-residual fractions. The Cd association with different sediment fraction followed the order: Residual bound > Exchangeable > Carbonate bound > Fe-Mn oxide bound > Organic bound. In the residual fractions, 26.68% was associated with exchangeable. Also, despite the high levels of Cr, the very low percentages of the metal in the non-residual fraction indicate their limited environmental mobility. Cd is associated more with exchangeable and carbonate fractions, an indication of potential bioavailability of the metals. The potential risk to river water contamination was highest downstream (Site C) for Cd based on the calculated contamination factor. Based on this study, Cd posed the highest risk to Challawa river water contamination.