uses. This has led to a number of publications on the toxicological effects of nanoceria in ecological receptor species, but only limited information is available on possible environmental releases, concentrations in environmental media, or environmental transformations. Increasing material flows of nanoceria in many applications is likely to result in increasing releases to air, water and soils however; insufficient information was available to estimate aquatic exposures that would result in acute or chronic toxicity. The purpose of this review is to identify which areas are lacking in data to perform either regional or site specific ecological risk assessments. While estimates can be made for releases from use as a diesel fuel additive, and predicted toxicity is low in most terrestrial species tested to date, estimates for releases from other uses are difficult at this stage. We

The sonication process is commonly used for de-agglomerating and dispersing nanomaterials in aqueous based media, necessary to improve homogeneity and stability of the suspension. In this study, a systematic step-wise approach is carried out to identify optimal sonication conditions in order to achieve a stable dispersion. This approach has been adopted and shown to be suitable for several nanomaterials (cerium oxide, zinc oxide, and carbon nanotubes) dispersed in deionized (DI) water. However, with any change in either the nanomaterial type or dispersing medium, there needs to be optimization of the basic protocol by adjusting various factors such as sonication time, power, and sonicator type as well as temperature rise during the process. The approach records the dispersion process in detail. This is necessary to identify the time points as well as other above-mentioned conditions during the sonication process in which there may be undesirable changes, such as damage to the particle surface thus affecting surface properties. Our goal is to offer a harmonized approach that can control the quality of the final, produced dispersion. Such a guideline is instrumental in ensuring dispersion quality repeatability in the nanoscience community, particularly in the field of nanotoxicology.

Nanoparticle morphology is 8 expected to play a significant role in the 9 stability, aggregation behaviour and 10 ultimate fate of engineered nanomaterials 11 in natural aquatic environments. The 12 aggregation kinetics of ellipsoidal and 13 spherical titanium dioxide (TiO 2 ) 14 nanoparticles (NP) under different 15 surfactant loadings, pH values and ionic strengths are investigated in this study. The stability results 16 reveal that alteration of surface charge is the stability determining factor. Among five different 17 surfactants investigated, sodium citrate and Suwannee river fulvic acid (SRFA) were the most 18 effective stabilizers. It was observed that both types of NP were more stable in monovalent salts 19 (NaCl and NaNO 3 ) as compared with divalent salts (Ca(NO 3 ) 2 and CaCl 2 ). The aggregation of 20 spherical TiO 2 NP demonstrated a strong dependency on the ionic strength regardless of the presence 21 of mono or divalent salts; while the ellipsoids exhibited a lower dependency on the ionic strength but 22 is more stable . This work acts as a benchmark study towards understanding the fate of stabilized NP 23 in natural environments that are rich in Ca(CO 3 ) 2 , NaNO 3 , NaCl and CaCl 2 along with natural organic 24 matters. 25

This study compared results of nanoparticle number concentration measurements collected from 74 instruments hosted across 50 laboratories, providing users with useful discussion and reference data to assess and benchmark their measurement capability.