Low mobility of CuO and TiO nanoparticles in agricultural soils of contrasting texture and organic matter content.

The fate of nanoparticles (NPs) in soil under relevant environmental conditions is still poorly understood. In this study, the mobility of two metal-oxide nanoparticles (CuO and TiO) in contrasting agricultural soils was investigated in water-saturated soil columns. The transport of TiO and CuO-NPs were assessed in six soils with three different textures (from sand to clay) and two contrasted organic matter (OM) contents for each texture. TiO mobility was very low in all soils, regardless of texture and OM content. Mass recoveries were always less than 5%, probably in relation with the strong homo-aggregation of TiO-NPs observed in all soil solutions, with apparent sizes 3-6 times larger than their nominal size. This low mobility suggests that TiO-NPs present a low risk of direct groundwater contamination in contrasted surface soils. Although their retention was also generally high (more than 86%), CuO nanoparticles were found to be mobile in all soils. This is probably related to their smaller apparent size and low capacity of homo-aggregation of CuO-NPs in all soil solutions. No clear influence of neither soil texture or soil total organic matter content could be observed on CuO transport. However, this study shows that in contrasted agricultural soils, CuO-NPs transport is mainly controlled by the solutes dissolved in soil solution (DOC and PO species), rather than by the properties of the soil solid phase.