Concentrations of 60 elements in the soil solution as related to the soil acidity

Little is known about solubility and soil solution concentrations of most e lements occurring in the solid phase of soils. This study reports changes i n solution concentrations of 60 mineral elements following CaCO3 addition t o a moderately acid semi-natural soil, and possible mechanisms accounting f or the differing solubility patterns as related to soil acidity are discuss ed. Soil solutions were obtained by high-speed centrifuging and ultrafiltra tion (0.2 mum) of samples at 60% water-holding capacity of the A horizon of a Cambisol developed from a shale-gneiss moraine and supplied with CaCO3 a t 20 rates to yield a soil solution pH range of 5.2-7.8. Concentrations of elements were determined in the solutions by ICP-AES or (for most elements) ICP-MS. Several distinct patterns of soil solution concentrations as a fun ction of soil solution pH were demonstrated. Positively related to pH and C aCO3 supply were soil solution concentrations of As, Br, Mo, S, Sb, Se, U, and W, and to a lesser degree, Co, Cr, Hg, Mg, and Sr. Inversely related to pH were concentrations of Al, B, Ba, Bi, Cs, Ce, Eu, Ga, Ge, Fe, Li, K, Rb , Na, Th, and Ti; less distinctly inversely rated were Dy, Er, Gd, Hf, La, Lu, Mn, Nd, Pr, Sm, Sc, Si, Tl, Tm, and Yb. 'U-shaped' relationships to pH were demonstrated for the concentrations of Ag, Cd, Nb, Ni, P, V, and Zr. T here were no or irregular relations between pH and concentrations of Be, Cu , Ho, Pb, Ta, and Tb. Differences between elements in their soil solution c oncentrations as related to total (HNO3-digestible) concentrations and the solubility of organic C were also treated. Increasing the pH of a soil by a dding CaCO3 changes the solubility of most mineral elements substantially, the several distinct patterns observed being governed by, for example, ioni c properties and charge, affinity for organic compounds, and pH-dependent f ormation and solubility of complexes.