Inhibitory effect of active aluminum on arsenic solubility in anaerobic soils

Abstract

Understanding As dynamics in anaerobic soils is important for developing an effective strategy for reducing As in paddy rice grains. We aimed to clarify the soil properties controlling As solubility under anaerobic conditions. As solubility (as the percentage of dissolved As; As%) was evaluated after anaerobic incubation of 26 paddy soils with different chemical properties. Spearman’s rank correlation analyses showed a significant negative correlation between As% and some soil properties including oxalate-extractable Al (AlOX). After removing the effect of AlOX by partial correlation analysis, significant correlations between As% and most soil properties disappeared. In contrast, the correlation between As% and AlOX was not substantially different between the results from the zero-order correlation analyses and partial rank correlation analyses controlling for each soil property. Our results demonstrated that only AlOX (i.e., “active Al”) had a strong inhibitory effect on As solubility in the examined soils under anaerobic conditions. Although the role of Fe-bearing phases in controlling As mobility in paddy soils is already well-established, a potentially important contribution of active Al in limiting As dissolution in anoxic environments was implied in this study.