Geochemical maps of soils in Japan have been created by using 3,222 soil samples collected from a depth of 0 to 20 cm at each site. Fifty-three elements have been analyzed to reveal the abundance and spatial distribution of elements in soils of whole Japan to know the transportation mechanism of element on the surface layer. Chemical compositions in soils are considered to differ from those in stream sediments because they reflect the result of complex interactions among factors such as the origin of the soil, depositional environment, climate system, and diagenetic and weathering effects. Nevertheless, spatial distribution patterns of elements in soil fundamentally resemble those in stream sediments, which are basically controlled by underlying geology. Comparing median elemental concentrations of soils and stream sediments, soils are systematically depleted in Na, Mg, Al, K, Ca, Rb, Sr, and Ba due to their dissolution during chemical weathering process; highly concentrated in P, Cu, Cd, Sb, Hg, Pb, and Bi due to mainly anthropogenic activities. However, we find difference between chemical compositions of andosols and lowland soils in Kanto region, which are caused by differences of chemical compositions in their origins and those of weathering process to elements between soil types.

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.