A meta-analysis of nanomaterial and nanoplastic fate in small column experiments and implications for fate in soils

A long list of possible processes may simultaneously control retention of engineered nanomaterials (NMs) and nanoplastics (NPs) in soils, but there is little insight in which of these processes dominates and under which circumstances. Though not easily transferable to field situations, repacked saturated column tests compose the richest available dataset to explore for overall trends in the behaviour of NMs and NPs in soils. Global attachment efficiencies (α_global) were calculated uniformly from metadata of 624 column experiments and correlated against metadata using partial least squares and linear regression analysis. α_global values appeared to some extent operationally defined as they correlate with the experimental column flow rate and in some cases with the particle concentration used in the feedstock. Particle aggregation occurred more as the feedstock concentration increased, but this only had a limited effect on subsequent column retention. In homogeneous sandy media, attachment of particles obeyed well-known trends indicative of non-favourable electrostatic interactions, whereas interactions in non-sandy media were dominated by favourable attractions to positively charged sites on clay edges and/or oxides as well as hydrophobic interactions with soil organic matter. The results may help to prioritize further research such as the currently unclear role of hydrophobic interactions in the fate of particles in porous media and identify the most important transport processes in more complex field situations.