Influence of air-drying on adsorption and oxidation of phenolic acids in Andosols and non-Andosols

Phenolic acids in soils playa variety of important roles in the environment. Several studies have been conducted on the reaction of phenolic acids in soils. Air-dried soils, however, were used in these reports, and reactions of phenolic acids in field-moist soils may differ. In this study, the influence of air-drying of soils on the adsorption and abiotic oxidation of 3 phenolic acids showing different levels of oxidizability (in the order of ferulic acid>vanillic acid≫p-hydroxybenzoic acid) was investigated, using 16 samples of field-moist and air-dried soils. Residue levels in the aqueous phases of ferulic acid (RFA) and vanillic acid (RVA) significantly increased when phenolic acids were added to air-dried nonAndosols, while the changes were negligible in Andosols. No significant difference due to air-drying was found in the residues of p-hydroxybenzoic acid (RHA). Abiotic soil oxidative activity, determined by the amounts of Cr(VI) derived from Cr(III), significantly decreased by air-drying in both non-Andosols and Andosols. It was also observed that the relationship between the abiotic oxidative activity and RV A level was linear in non-Andosols, suggesting the validity of the Cr(III) oxidation method to evaluate the abiotic soil oxidative activity for phenolic acids. Consequently, the increases of RFA and RV A levels in air-dried nonAndosols can be attributed to the decrease in the abiotic oxidative activity, while the adsorptive capacity for phenolic acids was not significantly influenced. It is considered that adsorption is prevalent in Andosols with relatively little influence of air-drying, compared with non-Andosols.