Gravity-driven transport of three engineered nanomaterials in unsaturated soils and their effects on soil pH and nutrient release

• Movement of metal oxide engineered nanomaterials through unsaturated topsoils is limited by nanoparticle aggregation.
• Nanomaterials alter the release and behavior of soil ions and consequently soil pH.
• Changes in soil pH are dependent on soil properties but independent of nanomaterial concentration.

The gravity-driven transport of TiO2, CeO2, and Cu(OH)2 engineered nanomaterials (ENMs) and their effects on soil pH and nutrient release were measured in three unsaturated soils. ENM transport was found to be highly limited in natural soils collected from farmland and grasslands, with the majority of particles being retained in the upper 0–3 cm of the soil profile, while greater transport depth was seen in a commercial potting soil. Physical straining appeared to be the primary mechanism of retention in natural soils as ENMs immediately formed micron-scale aggregates, which was exacerbated by coating particles with Suwannee River natural organic matter (NOM) which promote steric hindrance. Small changes in soil pH were observed in natural soils contaminated with ENMs that were largely independent of ENM type and concentration, but differed from controls. These changes may have been due to enhanced release of naturally present pH-altering ions (Mg2+, H+) in the soil via substitution processes. These results suggest ENMs introduced into soil will likely be highly retained near the source zone.

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