Orinoco River sediments

The dissolved concentrations of zinc in the Yangtze, Amazon, and Orinoco rivers have been shown to strongly decrease with pH, between 5 and 8.5 (Shiller and Boyle, 1985). This decrease is similar to that obtained in an experiment in which the pH of unfiltered Mississippi River water was adjusted to various pH values, and to isotherms of zinc adsorption on various natural and synthetic metal oxides surfaces (Figure 23). According to Shiller and Boyle (1985), alkaline rivers have less dissolved zinc because they are more suspended sediment-rich that acidic rivers. values between adsorbed (acid-leachable) zinc and dissolved zinc approach 10 for the Mississippi, which indicates that the Mississippi transports 10 times more adsorbed zinc than dissolved zinc. 

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