Adsorption of Phosphate, Arsenate, Methanearsonate, and Cacodylate by Lake and Stream Sediments: Comparisons with Soils

Abstract

AbstractThe adsorption of phosphate, arsenate, MSMA (sodium methanearsonate) and cacodylic acid (hydroxydimethylarsine oxide) by 14 sediments from streams and lakes of the Mississippi River alluvial flood plain was measured using a phosphate fixation test and also dilate (1 g/100 mL) sediment‐water slurries at 50 and 500 µg/L P or As. The fixation experiment results were similar to a previous study with soils from the same geographic area in that sorption of the four species were similar and correlated with clay and extractable Fe and Al content. In contrast with the soils results, phosphate was more strongly adsorbed than the arsenicals because the sediments were richer in Fe and Al oxides than soils of the same clay content and the phosphate sorption index was most dependent on sediment Fe and Al content. Conversely, the arsenicals were most correlated with clay or Fe content. Arsenical fixation also exhibited some sediment‐pH dependence indicative of binding with Ca. In the dilute slurry experiments, the high‐clay sediments were extremely adsorptive of all the species and yielded equilibrium P concentration (EPC) values from 0.07 to 0.3 µg/L P. Cacodylate adsorption was dependent on sediment pH. Those sediments with high clay content had a very large unfilled capacity to adsorb phosphate or arsenate, and would act as sinks for P or As inputs into their associated lakes or streams.