ARTICLE pubs.acs.org/est
Solubility and Batch Retention of CeO2 Nanoparticles in Soils Geert Cornelis,*,† Brooke Ryan,† Mike J. McLaughlin,†,‡ Jason K. Kirby,‡ Douglas Beak,#,‡ and David Chittleborough§ †
School of Agriculture, Food and Wine, University of Adelaide, SA 5005 Adelaide, Australia CSIRO Land and Water, Centre for Environmental Contaminants Research, Advanced Materials Transformational Capability Platform, PMB 2, SA 5064 Glen Osmond, Australia § School of Earth and Environmental Sciences, University of Adelaide, SA 5005 Adelaide, Australia ‡
bS Supporting Information ABSTRACT: 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 CeIII and CeIV 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 kg1) relative to Kd values of dissolved CeIII and CeIV (median Kd = 3763 and 1808 L kg1, 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.
’ INTRODUCTION Cerium oxide (CeO2) nanoparticles (CeO2 NPs) are used in many new applications that take advantage of the high oxygen storage and the UV absorbing capacity of CeO2 NPs and the low redox potential of the CeIV/CeIII redox couple.1 CeO2 NPs are used particularly in the automotive industry as catalysts reducing the particulate outputs of diesel engines,2 but are also found in a variety of consumer, pharmaceutical, and agricultural products.3 The increased production of CeO2 NPs has raised a number of concerns because similarly to other manufactured nanoparticles there are many uncertainties regarding the exposure, fate, and effects of CeO2 NPs on organisms in the environment.4 The natural environment may be exposed to CeO2 NPs from exhaust catalysts after deposition on soils, when they are collected with road runoff,5 or by industrial wastewaters that contain CeO2 NPs.6 Very fine (
