リン循環の解明に向けたリン酸酸素安定同位体比分析法の発展とその適用

抄録

Phosphorus is an essential element for all living organisms and important resource for human society hence, understanding phosphorus cycling is crucial. Although phosphorus possesses only one stable isotope, it exists in the environment as phosphate (PO₄), and its oxygen isotope ratio (δ¹⁸O_PO4) can be used as a tracer. The use of δ¹⁸O_PO4 has been increasing since the 2000s, contributing toward better understanding of the biogeochemical processes of phosphorus. However, the use of δ¹⁸O_PO4 has been limited owing to methodological difficulties involved in its sampling and pretreatment. In current studies, δ¹⁸O_PO4 values are analyzed by converting the PO₄ in a sample to silver phosphate (Ag₃PO₄). The removal of impurities from samples (purification) to produce pure Ag₃PO₄ is essential for accurate δ¹⁸O_PO4 measurements. The conventional purification methods can be classified into two main categories, both of which comprise a combination of PO₄ precipitation formation and resin treatment. Recently, a solid-phase extraction method has been developed as a new purification method that uses zirconium, which causes specific adsorption with PO₄. Zirconium has also been applied to passive sampling. This review presents the basic principles of δ¹⁸O_PO4 and its applications, focusing on the description of the analytical methods.