Sequential extraction procedures for the determination of phosphorus forms in sediment

This article summarizes the main extraction methods for sedimentary phosphorus (P) determination. With sequential chemical extractions, P is supposed to be selectively removed from different compounds in the sediments. Extraction schemes using strong acids and alkaline solutions have been tested on different sediments and found not to extract well-defined fractions. In addition, several systematic errors in these schemes have been detected. Thus, these schemes have been modified and simplified accordingly. The Standards Measurements and Testing Program of the European Commission (SMT) method is a popular modification of these extraction schemes, as it is simple to handle, allows laboratories to achieve reproducible results and could provide a useful tool for routine use by water managers. The SEDEX (sequential extraction method) method, another popular modification, is widely applied in biogeochemical research as it can separate authigenic carbonate fluorapatite from fluorapatite. Other chemical extractions using chelating compounds have attempted to extract P bound with iron and calcium in sediments without disturbing clay-bound or organic P, the purpose being to determine the algal-available non-apatite, apatite and organic fractions of sediment P. All extraction procedures still yield operationally defined fractions and cannot be used for identification of discrete P compounds. Future modifications of the extraction scheme should aim to achieve better extraction efficiency and selectivity, simple handling techniques and methods that can prevent the extracted P from being re-adsorbed onto Fe(OOH) and CaCO3.