EFFECTS OF DISSOLVED HUMIC SUBSTANCES ON THE SPECIATION OF IRON AND PHOSPHATE AT DIFFERENT PH AND IONIC-STRENGTH

The effects of dissolved humic substances (DHS) on the speciation of i ron and phosphate at different pH in waters of contrasting ionic stren gth and DHS content were studied by Sephadex gel filtration following incubation of filtered (0.2 mum) epilimnetic lake water samples to whi ch both (FeCl3.6H2O)-Fe-55 and (PO43-)-P-32 had been added. The simult aneous movement of Fe-55 and P-32 to fractions of greater apparent mol ecular size depended on the presence of DHS and diminished in response to decreasing pH. In the absence of significant quantities of DHS, mu ch of the added 55Fe precipitated from the incubation mixture or was r etained within the gel column. (PO43-)-P-32 added to clear water of hi gh ionic strength underwent minor transformations to large apparent mo lecular size, while the (PO43-)-P-32 recovered in eluates from experim ents with clear waters of low ionic strength was dependent on pH and d id not undergo transformation, the remainder being coprecipitated with 55Fe and retained within the gel column.