Fractional phosphate composition in sediments from a tropical river (Catatumbo River, Venezuela)

The distribution of phosphate species in the Catatumbo River, Venezuela, wa s studied using a sequential extraction scheme. Extraction was performed us ing 1.0 M NH4Cl, 0.1 M Na2S2O4-NaHCO3, 1.0 M NaOH and 0.5 M HCl. Total phos phate was in the range between 121 and 581 mug g(-1) D.W. About 64% of the total phosphate is inorganic and present the following composition: 1% NH4C l-P, 10% BD-P, 20% NaOH-P, 33% HCl-P; while org-P is 36%. The main form of P in sediment from the Catatumbo River is calcium bound-P, like apatite. Th e metal concentrations present in sediment are in the following order: Fe > Al > Ca > Mg > Mn. Relationships between P and Fe, Al and Ca were found. C luster analysis showed that speciation is not dependent on the inorganic ma trix of the sediments. Analysing the influence of NaOH concentration and du ration of the extraction invalidated the use of NaOH as extracting agent in P-speciation.