Fig. 4. The As(III) adsorption edges on ferrihydrite (Fe₅OH₈·4H₂O) in the presence and absence of dissolved organic carbon (DOC): humic acid (peat), Suwannee River fulvic acid, and citric acid. Ferrihydrite suspension concentration = 1.00 g L^-1, As(III) = 1.0 mM, DOC = 1.0 mM C, background electrolyte = 0.01 M NaNO₃.