Physical Effects on Soil Structure of Iron-Based Remediation Practices Used in As Contaminated Soils

Uptake of solubilized As in rice is a crucial issue due to reducing conditions typical of traditionally cultivated paddy soils. Iron grit soil amendment is one of the most used soil remediation practices in many countries to immobilize As in soils. Physical consequences on soil structure of this soil remediation practice are very rarely investigated, especially in shrink-swell soils, where wetting-drying cycles can trigger significant structure changes. Paddy fields are generally subjected to many cycles of alternate flooding and drying which can induce changes in soil structure strongly influencing water and solute transport. Unpredicted changes in soil hydrological behavior can in turn affect plant growth and effectiveness of the remediation practice.In order to identify and directly quantify the physical effects of the iron grit addition on soil pore system, a laboratory experiment was carried out by adding iron grit to two soils with high shrinkage-swelling potential, using repacked soil samples undergone to several wetting-drying cycles. Soil micromorphology and pore image analysis were combined using procedures providing results well correlated with some soil hydrological properties.A porosity increase was observed in both soils, and the used methodological approach allowed to observe different pore geometries in the two soils, probably due to their different plasticity.The obtained results showed overall the high potential of soil micromorphology and pore image analysis in order to evaluate the physical effects on soil structure of a soil remediation practice suitable for paddy soils.