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The European Food Safety Authority has published a guidance regarding risk assessment of nanomaterials in food and feed. Following these recommendations, an in vitro gastrointestinal digestion has been applied to study the biopersistence of TiO 2 and Ag NPs in standards, molluscs and surimi. TiO 2 NPs standards and TiO 2 NPs/ TiO 2 microparticles from E171 were not found to be degraded. Ag NPs proved to be more degradable than TiO 2 NPs, but the biopersistence rates were higher than 12%, which means that Ag NPs are also biopersistent. Findings for seafood are quite similar to those obtained for TiO 2 NPs and Ag NPs standards, although the calculation of the biopersistence rate proposed by the EFSA was not found to be straightforward for foodstuff (the use of the NPs concentration in the sample instead of the NPs concentration at initial time (sample mixed with the gastric solution before enzymatic hydrolysis) has been proposed., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

A procedure for the size characterization and quantification of titanium dioxide (TiO 2 ) nano- and microparticles by Asymmetric Flow Field-Flow Fractionation (AF4) coupled to Dynamic Light Scattering (DLS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is described. Different strategies for size characterization with size standards and the use of the DLS signal for the estimation of hydrodynamic diameters are evaluated. The procedure has been applied to the characterization of TiO 2 nanoparticles in photocatalytic products and crab sticks (surimis), where TiO 2 is present as E171 food additive. Sizes in the range of 50-90 nm and 160-170 nm were estimated in the different photocatalytic products by AF4-DLS, in good agreement with the sizes predicted by calibration versus SiO 2 and polystyrene standards. In surimis, sizes between 140 and 350 nm were estimated by AF4-DLS, similar to those reported in literature for E171 additive. These results were also compared to those obtained by single particle ICP-MS, which allowed the detection of a nano-sized fraction of TiO 2 present in the four surimis analyzed. Titanium contents in one of the photocatalytic products determined by AF4-ICP-MS was 16.86 ± 2.54 mg g -1 , whereas the alkaline extraction followed by AF4-ICP-MS allowed the determination of TiO 2 content in four surimis at concentration levels in the range of the μg g -1 (from 3.14 ± 0.10 to 14.55 ± 1.46 μg Ti g -1 ), with channel recoveries above 85% in all cases. The method has been validated by comparison with the Ti content determined by ICP-OES after microwaved assisted acid digestion of all the samples. The methodology proposed allows the complete quantification of the (nano)particulate forms of titanium in complex matrices together with their size characterization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A reliable sample pre-treatment based on enzymatic hydrolysis has been fully optimized and validated for TiO 2 NPs isolation and determination/characterization in surimi (crab sticks). Efficient extractions have been found when using a pancreatin/lipase mixture at pH 7.4 and 37 °C for 12 h under continuous stirring. The proposed sample pre-treatment procedure has been found not to change TiO 2 NPs size distribution, therefore guaranteeing TiO 2 NPs integrity. TiO 2 NPs determination (TiO 2 NPs concentration) and TiO 2 NPs characterization (size distribution) were assessed by single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS) working with dwell times in the microsecond range (high frequency of data acquisition). Method validation was performed for TiO 2 NPs concentrations and TiO 2 NPs sizes. Good repeatability (25% and 8% for TiO 2 NPs concentration and TiO 2 NPs most frequent size), and sensitivity (limit of detection of 5.28 × 10 5 NPs g -1 for TiO 2 NPs concentrations, and 31.3-37.1 nm for TiO 2 NPs size) were obtained. Accuracy, calculated through analytical recovery was adequate. Recoveries for TiO 2 NPs standards of 50 and 100 nm were 108 ± 5 and 105 ± 4%, respectively. The proposed methodology was applied to several surimi samples for assessing TiO 2 NPs concentrations and size distribution. Some surimi samples were found to contain TiO 2 NPs (concentrations from 1.40 × 10 7 to 1.19 × 10 9 NPs g -1 ). TiO 2 NPs size distributions were very different among the samples, and some of them showed wide size ranges (the most frequent size varied from 53.8 to 62.1 nm; whereas, the mean size values were within the 73.4-217.5 nm range)., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Applicability of single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS) using dwell times equal to or shorter than 100 μs has been tested for assessing titanium dioxide nanoparticles (TiO 2 NPs) in bivalve mollusks. TiO 2 NPs isolation from fresh mollusk tissues was achieved by ultrasound assisted enzymatic hydrolysis procedure using a pancreatin/lipase mixture. Optimum extraction conditions imply ultrasonication (60% amplitude) for 10 min, and 7.5 mL of a solution containing 3.0 g L -1 of pancreatin and lipase (pH 7.4). The developed method was found to be repeatable (repeatability of 17% for the over-all procedure, TiO 2 NPs concentration of 5.33 × 10 7  ± 8.89 × 10 6 , n = 11), showing a limit of detection of 5.28 × 10 6 NPs g -1 , and a limit of detection in size of 24.4-30.4 nm, based on the 3σ criteria, and on the 3σ/5 σ criteria, respectively. The analytical recovery within the 90-99% range (use of TiO 2 NPs standards of 50 nm at 7 and 14 μg L -1 as Ti). Several bivalve mollusks (clams, cockles, mussels, razor clams, oysters and variegated scallops) were analyzed for total titanium (ICP-MS after microwave assisted acid digestion), and for TiO 2 NPs by the proposed method. TiO 2 NPs concentrations were within the 2.36 × 10 7 -1.25 × 10 8 NPs g -1 range, and the most frequent sizes were from 50 to 70 nm., (Copyright © 2018 Elsevier B.V. All rights reserved.)