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