Abstract
NaOH is often used as an extractant for the fractionation of sediment-bound phosphates. Besides orthophosphate, a certain quantity of phosphate which is called ‘non-reactive NaOH-extractable phosphate’ is also extracted. In recent literature it has been suggested that this fraction consists of bacterial polyphosphates and might be responsible for the phosphate release from aquatic sediments under anoxic conditions.In a previous publication we have already shown that NaOH is not an accurate extractant as both the concentration of NaOH and the duration of the extraction have an influence on the quantity of phosphate extracted, due to the hydrolysis of organic phosphates.In this article we show that cold NaOH does not only extract iron-bound phosphate but phytate phosphate as well. Non-reactive phosphate in this extract was not related to the presence of polyphosphate, but mainly to phytate and humic phosphates. As it has been shown that phytate may disappear from sediments when they become anoxic, we suggest that phytate mineralization may be an important mechanism for anoxic phosphate release from sediments.