There is a paucity of information on the environmental fate of cerium oxide nanoparticles (CeO2 NPs) for terrestrial systems that may be exposed to CeO2 NPs by the application of biosolids derived from wastewater treatment systems. Using ultrafiltration (UF), dissolution, and nonequilibrium retention (Kr) values of citrate-coated (8 nm diameter) CeO2 NPs and partitioning (Kd) values of dissolved Ce(III) and Ce(IV) were obtained in suspensions of 16 soils with a diversity of physicochemical properties. Dissolution of CeO2 NPs studied in solutions was only significant at pH 4 and was less than 3.1%, whereas no dissolved Ce was detected in soils spiked with CeO2 NPs. Kr values of CeO2 NP were low (median Kr=9.6 L kg(-1)) relative to Kd values of dissolved CeIII and CeIV (median Kd=3763 and 1808 L kg(-1), respectively), suggesting low CeO2 NP retention in soils. Surface adsorption of phosphate to CeO2 NP caused a negative zeta potential, which may explain the negative correlation of log Kr values with dissolved phosphate concentrations and the significant reduction of Kr values upon addition of phosphate to soils. The positive correlation of Kr values with clay content suggested heterocoagulation of CeO2 NPs with natural colloids in soils. Co-addition of CeO2 NPs with biosolids, on the other hand, did not affect retention.

Soils are likely to be increasingly exposed to nanoparticles due to growing consumer use of nanoparticles. This has necessitated an investigation into the fate and bioavailability of nanoparticles in natural soils. However, the effect of soil properties on these processes are unknown. To find the dominant properties that determine AgNP retention in natural soils, nonequilibrium retention (Kr) values of polyvinylpyrrolidone (PVP) coated silver nanoparticles (AgNP) were obtained in suspensions of 16 soils having a wide range of physical and chemical properties. The AgNP dissolution was investigated using ultrafiltration, but could only be detected in six soils, possibly due to strong partitioning of dissolved Ag (median Kd 1791 L kg−1); a process that increased predominantly with the organic matter content of the soils. When corrected for partitioning, dissolution of AgNP was higher (median 26% of total Ag added as AgNP) in these six soils compared to dissolution in artificial soil solutions. The homocoagulation kinetics of AgNP as a function of increasing NaClO4 concentrations were studied at pH 4 and pH 8, showing that homocoagulation of AgNP is unlikely in the studied soil suspensions. Moreover, Kr values (median value 589 L kg−1) only correlated with the soil granulometric clay content and not with parameters that increase the homocoagulation rate, a correlation that suggests that negatively charged AgNP were adsorbed preferentially at positively charged surface sites of clay‐sized minerals. Adsorption of negatively charged engineered nanoparticles by Fe and Al oxides and mineral clay edges may thus be an important fate‐determining reaction in soils, and possibly also in aquatic systems.

Environmental context. Soils are the environmental compartment likely to be exposed most to manufactured nanoparticles, but there is no method available at present to assess their retention, which determines potential mobility and bioavailability. Optimisation and application of a method to determine retention values for silver (Ag) and cerium oxide (CeO 2 ) manufactured nanoparticles in soils found in many cases that they differed from the partitioning of their bulk and soluble counterparts. Wider application of this method can assist in comparing the risk of many different manufactured nanoparticles with other contaminants in soil systems and model their relationship to soil properties.Abstract. Methods to study the retention of manufactured nanoparticles (MNP) are lacking for soils that are likely to be increasingly exposed to MNP. In this study we present, for the first time

The solubility of Zn in Zn fertilizers plays an important role in the agronomic effectiveness of the fertilizer. On the basis of thermodynamics, zinc oxide (ZnO) nanoparticles (NPs) should dissolve faster and to a greater extent than bulk ZnO particles (equivalent spherical diameter >100 nm). These novel solubility features of ZnO NPs might be exploited to improve the efficiency of Zn fertilizers. In this study, we compared the Zn solubility and dissolution kinetics of ZnO nanoparticles and bulk ZnO particles coated onto two selected granular macronutrient fertilizers, urea and monoammonium phosphate (MAP). The main Zn species on coated MAP and urea granules were zinc ammonium phosphate and ZnO, respectively. Coated MAP granules showed greater Zn solubility and faster dissolution rates in sand columns compared to coated urea granules, which may be related to pH differences in the solution surrounding the fertilizer granules. The kinetics of Zn dissolution was not affected by the size of the ZnO particles applied for coating of either fertilizer type, possibly because solubility was controlled by formation of the same compounds irrespective of the size of the original ZnO particles used for coating.

The risk posed from incidental ingestion to humans of arsenic-contaminated soil may depend on sorption of arsenate (As(V)) to oxide surfaces in soil. Arsenate sorbed to ferrihydrite, a model soil mineral, was used to simulate possible effects on ingestion of soil contaminated with As-(V) sorbed to Fe oxide surfaces. Arsenate sorbed to ferrihydrite was placed in a simulated gastrointestinal tract (in vitro) to ascertain the bioaccessibility of As(V) and changes in As(V) surface speciation caused by the gastrointestinal system. The speciation of As was determined using extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES). The As(V) adsorption maximum was found to be 93 mmol kg(-1). The bioaccessible As(V) ranged from 0 to 5%, and surface speciation was determined to be binuclear bidentate with no changes in speciation observed post in vitro. Arsenate concentration in the intestine was not constant and varied from 0.001 to 0.53 mM for the 177 mmol kg(-1) As(V) treated sample. These results suggest that the bioaccessibility of As(V) is related to the As(V) concentration, the As(V) adsorption maximum, and that multiple measurements of dissolved As(V) in the intestinal phase may be needed to calculate the bioaccessibility of As(V) adsorbed to ferrihydrite.