Partitioning of inorganic orthophosphate in soil‐water systems∗

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Abstract
The fate of phosphorus in terrestrial ecosystems is of concern because it has been identified as a major contributor to eutrophication of surface water supplies. In order to ascertain the impact of inorganic phosphate on water quality, the chemical speciation, concentration, bio‐availability, and distribution in the soil‐water system are prerequisites. Environmental regulations and land disposal of organic wastes also require quantifying the partitioning of inorganic phosphate between solid and solution phases in soil‐water systems. In order to develop a partition coefficient or a partition function, several aspects of the solution chemistry of inorganic phosphate were reviewed. Several sorption mechanisms and mathematical models have been used to describe equilibrium sorption and the time‐dependent phosphate removal from solution. The most frequently applied equilibrium model was the Langmuir equation in the single‐surface form. Because of the amount of Langmuir data available, Langmuir parameters were compiled for the purpose of obtaining a partition coefficient and for correlating Langmuir parameters with selected soil chemical properties. A lack of uniformity was noted in experimental methods used for determining soil properties and phosphate sorption parameters. Correlation of sorption parameters with soil chemical properties indicated that “active”; iron and aluminum species are involved in phosphate sorption. The “active”; species appear to be quantified best by oxalate extractants.