Evidence that Soil Properties and Organic Coating Drive the Phytoavailability of Cerium Oxide Nanoparticles

Abstract

The ISO-standardized RHIZOtest is used here for the first time to decipher how plant species, soil properties, and physical-chemical properties of the nanoparticles and their transformation regulate the phytoavailability of nanoparticles. Two plants, tomato and fescue, were exposed to two soils with contrasted properties: a sandy soil poor in organic matter and a clay soil rich in organic matter, both contaminated with 1, 15, and 50 mg·kg of dissolved Ce(SO), bare and citrate-coated CeO nanoparticles. All the results demonstrate that two antagonistic soil properties controlled Ce uptake. The clay fraction enhanced the retention of the CeO nanoparticles and hence reduced Ce uptake, whereas the organic matter content enhanced Ce uptake. Moreover, in the soil poor in organic matter, the organic citrate coating significantly enhanced the phytoavailability of the cerium by forming smaller aggregates thereby facilitating the transport of nanoparticles to the roots. By getting rid of the dissimilarities between the root systems of the different plants and the normalizing the surfaces exposed to nanoparticles, the RHIZOtest demonstrated that the species of plant did not drive the phytoavailability, and provided evidence for soil-plant transfers at concentrations lower than those usually cited in the literature and closer to predicted environmental concentrations.

Cerium Oxide Nanoparticles Affect Heavy Metals Uptake by Pea in a Divergent Way than Their Ionic and Bulk Counterparts

“…In the conclusion, they suggested that model plants should be subjected to tests with NPs of standardized concentrations and sizes. This approach is of particular relevance when risk assessment is to be concerned (Layet et al 2017; Núñez and de la Rosa-Alvarez 2018).…”

Phytoavailability of silver at predicted environmental concentrations: does the initial ionic or nanoparticulate form matter?

“…The sensitivity of the RHIZOtest has already been highlighted with CeO 2 NMs. 16 Antagonist clay and carbonate effects on Ag phytoavailability at 100× PEC Fig. 4 shows that for a given modality, Ag fluxes always increased in the order clay < loam with high OM content < sandy loam < loam with high carbonate content (Ag fluxes being significantly lower in the clay soil than in the loam soil with high carbonate content).…”

“…The experimental procedure is detailed elsewhere. 16,24 The RHIZOtest is a two-step procedure. The plant seedlings were first grown (preculture period) for 14 days in hydroponics in a cylinder closed at the bottom with a 30 μm polyamide mesh to promote the development of a dense, planar root mat.…”

“…The interactions between NMs and mineral phases, natural organic matter, and microbiota 15 have to be taken into account when studying Ag phytoavailability and phytotoxicity in the soil. 16,17 Dimkpa et al (2013) 18 exposed wheat to Ag NMs in a sand matrix (0.5-2.5 mg kg −1 ) and observed a dosedependent reduction in growth. Pradas del Real et al (2016) 19 spread Ag NM-amended sludge (18 and 400 mg kg −1 ) on soil and detected Ag in the rhizosphere of wheat and rape, as nanosized Ag 2 S, Ag-S species and mixed metallic sulfides with Zn and Cu.…”

“…Recently, the RHIZOtest was shown to be a useful tool to analyze the phytoavailability of CeO 2 NMs at concentrations close to PEC in fescue and tomato. 16 Here, we selected two concentrations lower than the ones already published in studies dealing with the phytoavailability of Ag NMs in soils i.e. close to Ag PEC in soils (0.0015 mg kg −1 ) and 100 times higher than PEC (0.15 mg kg −1 ).…”