UV filter occurrence in beach water of the Mediterranean coast - A field survey over 2 years in Palavas-les-Flots, France.

OBJECTIVE: A 2-year sampling campaign was realized on French Mediterranean beach (Palavas-les-Flots Hérault) in order to measure the concentration of UV filters released from the sunscreen used by bathers. Multiple factors suspected of playing determining roles in the UV filter pattern in water were explored, such as the seasonal and daily time evolutions, or the vertical and horizontal distributions, and they were regarded through the UV filter characteristics. METHODS: The beach was monitored during periods of high and low tourist attendance, typically before, during and after the summer peak. The beachgoers attendance was counted. Bathing water was sampled distinctly from the bulk column and from the top surface layer, testing different sampling tools. Sediments and mussels were also sampled and analysed as potential UV filter sinks. Three organic UV filters (octocrylene OCR, avobenzone BMDBM and octyl methoxycinnamate OMC) and one mineral (titanium dioxide TiO2 ) were studied here as representatives of the current cosmetic market. RESULTS: Summer peak attendance on the beach was confirmed associated with peak levels of UV filter concentration in the bathing water, even more pronounced during a heat wave period. This relation was also observed at day scale with an afternoon peak, suggesting a rapid evolution of the UV filter pattern in water. Contrasted fates were measured between the four studied UV filters, that could be mainly explained by their respective characteristics, i.e. particulate or dissolved, hydrophilic or lipophilic, lifetime. Generally, this resulted in a concentration ranking TiO2 > OCR > OMC > BMDBM, ranging from 0.5 to 500 µg/L. The most lipophilic and recalcitrant OCR was found most vertically differentiated and over concentrated in the top surface layer of water. Finally, a large horizontal heterogeneity was also observed in the UV filter concentration pattern, raising the need for sample replicates that cover a significant area. CONCLUSION: This work fulfils some knowledge gaps on the issue of UV filter release in coastal environments, not only by providing original field data and methodological recommendations but also importantly in the comparison made of organic and mineral UV filters, which are often considered separately and rarely evaluated at the same time.

OBJECTIF: Une campagne d'échantillonnage de deux ans a eu lieu sur une plage de la Méditerranée en France (Palavas-les-Flots dans l'Hérault) afin de mesurer la concentration de filtres UV libérés par la protection solaire utilisé par les baigneurs. Plusieurs facteurs suspectés de jouer des rôles déterminants dans le modèle de filtre UV dans l'eau ont été étudiés, comme les évolutions saisonnières et quotidiennes, ou les distributions verticales et horizontales, et ils ont été examinés à travers les caractéristiques du filtre UV. MÉTHODES: La plage a été surveillée pendant les périodes de fréquentation touristique élevée et faible, généralement avant, pendant et après le pic estival. La présence des baigneurs a été comptabilisée. L'eau de baignade a été prélevée distinctement de la colonne principale et de la couche superficielle supérieure, en testant différents outils de prélèvement d'échantillons. Des sédiments et des moules ont également été prélevés et analysés comme réservoirs de filtre UV potentiels. En l'occurrence, trois filtres UV organiques (octocrylène OCR, avobenzone BMDBM et octyl méthoxycinnamate OMC) et un minéral (dioxyde de titane TiO2 ) ont été étudiés comme représentants du marché cosmétique actuel. RÉSULTATS: Les pics estivaux de présence de baigneurs sur la plage ont été confirmés comme étant associés à des pics de concentration du filtre UV dans l'eau de baignade, encore plus prononcés pendant une période de vague de chaleur. Cette relation a également été observée à l'échelle d'une journée, avec un pic l'après-midi, suggérant une évolution rapide du profil de filtre UV dans l'eau. Les effets de contraste ont été mesurés entre les quatre filtres UV étudiés, ce qui pourrait s'expliquer principalement par leurs caractéristiques respectives, c'est-à-dire particulaires ou dissous, hydrophiles ou lipophiles, tout au long de la vie. En général, cela a donné lieu à un classement de la concentration : TiO2 > OCR > OMC > BMDBM, comprise entre 0,5 et 500 ug/L. Il est apparu que c'est l'OCR le plus lipophile et le plus récalcitrant qui est le plus différencié verticalement et sur-concentré dans la couche supérieure de l'eau. Enfin, on a observé une grande hétérogénéité horizontale dans le profil de concentration du filtre UV, ce qui a nécessité des réplicats d'échantillons couvrant une zone significative. CONCLUSION: Ce travail comble certaines lacunes en matière de connaissances sur la libération des filtres UV dans les environnements côtiers, non seulement en fournissant des données originales sur le terrain et des recommandations méthodologiques, mais également en comparant des filtres UV organiques et minéraux, qui sont souvent pris en compte séparément et rarement évalués en même temps.

Influence of TiO2 nanocomposite UV filter surface chemistry and their interactions with organic UV filters on uptake and toxicity toward cultured fish gill cells.

Aquatic environments have been found to be contaminated with a variety of inorganic and organic UV filters. This includes novel nano-sized titanium dioxide (TiO2) composite particles, which have been increasingly developed and incorporated into commercial sunscreens in recent years. So far, relatively little is known about the effects of this novel class of UV filters on aquatic life. Therefore, this study aimed to determine and compare the toxicity of three such nanoparticulate TiO2 UV filters with different surface coatings, namely Eusolex® T-Avo (SiO2-coated), T-Lite™ SF (Al(OH)3/PDMS-coated), and Eusolex® T-S (Al2O3/stearic acid-coated) either alone, or in the presence of selected organic UV filters (octinoxate, avobenzone, octocrylene), toward fish using RTgill-W1 cell cultures as an in vitro experimental model. Besides standard exposure protocols, alternative approaches (i.e., exposure to water accommodated fractions (WAFs), hanging-drop exposure) were explored to account for nanoparticle (NP)-specific fate in the medium and obtain additional/complementary information on their toxicity in different conditions. The AlamarBlue, CFDA-AM and Neutral Red Retention (NR) assays were used to measure effects on different cellular endpoints. Transmission electron microscopy (TEM) was used to examine NP uptake. Our results showed that none of the TiO2 NP UV filters were cytotoxic at the concentrations tested (0.1-10 µg/mL; 24 h) but there were differences in their uptake by the cells. Thus, only the hydrophilic T-AVO was detected inside cells, but the hydrophobic T-Lite SF and T-S were not. In addition, our results show that the presence of NPs (or the used dispersant) tended to decrease organic UV filter toxicity. The level of combination effect depended on both NP-type (surface chemistry) and concentration, suggesting that the reduced toxicity resulted from reduced availability of the organic UV filters due to their adsorption to the NP surface. Thus, mixtures of TiO2 NP UV filters and organic UV filters may have a different toxicological profile compared to the single substances, but probably do not pose an increased hazard.

A network perspective reveals decreasing material diversity in studies on nanoparticle interactions with dissolved organic matter.

Dissolved organic matter (DOM) strongly influences the properties and fate of engineered nanoparticles (ENPs) in aquatic environments. There is an extensive body of experiments on interactions between DOM and ENPs and also larger particles. [We denote particles on the nano- and micrometer scale as particulate matter (PM).] However, the experimental results are very heterogeneous, and a general mechanistic understanding of DOM-PM interactions is still missing. In this situation, recent reviews have called to expand the range of DOM and ENPs studied. Therefore, our work focuses on the diversity of the DOM and PM types investigated. Because the experimental results reported in the literature are highly disparate and difficult to structure, a new format of organizing, visualizing, and interpreting the results is needed. To this end, we perform a network analysis of 951 experimental results on DOM-PM interactions, which enabled us to analyze and quantify the diversity of the materials investigated. The diversity of the DOM-PM combinations studied has mostly been decreasing over the last 25 y, which is driven by an increasing focus on several frequently investigated materials, such as DOM isolated from fresh water, DOM in whole-water samples, and TiO2 and silver PM. Furthermore, there is an underrepresentation of studies into the effect of particle coating on PM-DOM interactions. Finally, it is of great importance that the properties of DOM used in experiments with PM, in particular the molecular weight and the content of aromatic and aliphatic carbon, are reported more comprehensively and systematically.

Heteroaggregation of titanium dioxide nanoparticles with natural clay colloids.

To better understand and predict the fate of engineered nanoparticles in the water column, we assessed the heteroaggregation of TiO2 nanoparticles with a smectite clay as analogues for natural colloids. Heteroaggregation was evaluated as a function of water salinity (10(-3) and 10(-1) M NaCl), pH (5 and 8), and selected nanoparticle concentration (0-4 mg/L). Time-resolved laser diffraction was used, coupled to an aggregation model, to identify the key mechanisms and variables that drive the heteroaggregation of the nanoparticles with colloids. Our data show that, at a relevant concentration, nanoparticle behavior is mainly driven by heteroaggregation with colloids, while homoaggregation remains negligible. The affinity of TiO2 nanoparticles for clay is driven by electrostatic interactions. Opposite surface charges and/or high ionic strength favored the formation of primary heteroaggregates via the attachment of nanoparticles to the clay. The initial shape and dispersion state of the clay as well as the nanoparticle/clay concentration ratio also affected the nature of the heteroaggregation mechanism. With dispersed clay platelets (10(-3) M NaCl), secondary heteroaggregation driven by bridging nanoparticles occurred at a nanoparticle/clay number ratio of greater than 0.5. In 10(-1) M NaCl, the clay was preaggregated into larger and more spherical units. This favored secondary heteroaggregation at lower nanoparticle concentration that correlated to the nanoparticle/clay surface area ratio. In this latter case, a nanoparticle to clay sticking efficiency could be determined.

Heteroaggregation of titanium dioxide nanoparticles with model natural colloids under environmentally relevant conditions.

The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and fate of ENPs. Attachment efficiencies for heteroaggregation, α hetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining α hetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 µm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in α hetero values close to 1. At pH 8, where all particles are negatively charged, α hetero was strongly affected by the solution conditions, with α hetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation.

Aged TiO2-based nanocomposite used in sunscreens produces singlet oxygen under long-wave UV and sensitizes Escherichia coli to cadmium.

TiO2-based nanocomposite (NC) are widely used as invisible UV protectant in cosmetics. These nanomaterials (NMs) end in the environment as altered materials. We have investigated the properties of T-Lite SF, a TiO2-NC used as sunscreen, after weathering in water and under light. We have examined the formation of ROS and their consequences on cell physiology of Escherichia coli. Our results show that aged-T-Lite SF produced singlet oxygen under low intensity long wave UV and formed hydroxyl radicals at high intensity. Despite the production of these ROS, T-Lite SF had neither effect on the viability of E. coli nor on mutant impaired in oxidative stress, did not induce mutagenesis and did not impair the integrity of membrane lipids, thus seemed safe to bacteria. However, when pre-exposed to T-Lite SF under low intensity UV, cells turned out to be more sensitive to cadmium, a priority pollutant widely disseminated in soil and surface waters. This effect was not a Trojan horse: sensitization of cells was dependent on the formation of singlet oxygen. These results provide a basis for caution, especially on NMs that have no straight environmental toxicity. It is crucial to anticipate indirect and combined effects of environmental pollutants and NMs.

Adsorption of anti-inflammatory and analgesic drugs traces in water on clay minerals.

The aim of this study was to assess the adsorption of four non-steroidal anti-inflammatory drugs (NSAIDs), namely Paracetamol (PRC), Diclofenac (DIC), Ibuprofen (IBU), and Ketoprofen (KET), using both batch and continuous experiments with clay. Various analytical techniques, including XRD, FTIR, SEM coupled to EDX, and Zeta potential, were employed to characterize both raw and calcined clay. XRD and FTIR analyses confirmed the kaolinite nature of the clay. SEM data revealed a lamellar structure formed in the clay after calcination at 550 °C. Adsorption tests were conducted to determine the optimal adsorption conditions. Batch kinetics of adsorption demonstrated rapid adsorption of all four NSAIDs, with the highest adsorption occurring at pH 4 (DIC, IBU, and KET) and pH 6 for PRC, using a concentration of 20 mg L-1 of calcined clay. Additionally, the pseudo-second-order model provided the best fit for all NSAIDs adsorption processes. Maximum adsorption capacities, as determined by the Langmuir model, were 80 mg g-1 for PRC, 238 mg -1g for DIC, 138 mg g-1 for IBU, and 245 mg g-1 for KET. In fixed bed column studies, three dynamic models (Thomas, Adams-Bohart, and Yoon-Nelson) were utilized to describe the breakthrough curves, with linear regression used to identify key characteristics for process design. The fixed bed column adsorption study revealed that DIC exhibited the highest removal efficiency at 98%, while KET, IBU, and PRC were more persistent, with removal efficiencies of 77.1%, 76.7%, and 67.1%, respectively. The Thomas model was deemed appropriate for describing the breakthrough curve. These findings offer valuable insights into the interactions between clay and pharmaceuticals with varying physicochemical properties. They also provide information on the adsorption models, saturation, and adsorption capacities of various pharmaceuticals on natural clays, which can be crucial for further research and environmental remediation efforts.

Sunscreen use during recreational activities on a French Atlantic beach: release of UV filters at sea and influence of air temperature.

Organic UV filters are emerging contaminants in personal care products such as sunscreens. The toxicity of numerous of these UV filter compounds has been demonstrated in several marine taxa. However, whilst the biological impact has already been largely demonstrated, the anthropogenic drivers leading to UV filter contamination still need to be identified. In this work, a survey was conducted on a site of the French Atlantic Coast (i) to describe beachgoers' behaviours (sunscreen use and beach frequentation), (ii) provide an estimation of the UV filters released at sea and (iii) highlight the effect of air temperature on these behaviours and on the release of UV filters. In parallel with these estimations of the UV filters released at sea, in situ chemical measurements were performed. By comparing the results of both approaches, this interdisciplinary work provides an insight of how the observations of beachgoers' behaviour modulations and attendance level fluctuations could be used to prevent UV filter contaminations and ultimately manage the ecotoxicological risk.

Avoidance behaviour and toxicological impact of sunscreens in the teleost Chelon auratus.

There is increasing evidence that sunscreen, more specifically the organic ultra-violet filters (O-UVFs), are toxic for aquatic organisms. In the present study, we simulated an environmental sunscreen exposure on the teleost fish, Chelon auratus. The first objective was to assess their spatial avoidance of environmental concentrations of sunscreen products (i.e. a few µg.L-1 of O-UVFs). Our results showed that the fish did not avoid the contaminated area. Therefore, the second objective was to evaluate the toxicological impacts of such pollutants after 35 days exposure to concentrations of a few µg.L-1 of O-UVFs. At the individual level, O-UVFs increased the hepatosomatic index which could suggest pathological alterations of the liver or the initiation of the detoxification processes. At the cellular level, a significant increase of malondialdehyde was measured in the muscle of fish exposed to O-UVFs which suggests a failure of antioxidant defences and/or an excess of reactive oxygen species.

Transport of nanoparticulate TiO2 UV-filters through a saturated sand column at environmentally relevant concentrations.

The fate of sunscreen residues released during bathing activities around recreational areas is an emerging concern regarding the potential ecotoxicity of some of their ingredients, including nanoparticulate TiO2 UV-filters. To assess the extent of contamination in the natural medium, sand-packed column experiments were carried out with bare TiO2 engineered nanoparticles (ENPs) and two commercial nano-TiO2 UV-filters coated with either SiO2 (hydrophilic) or a combination of Al2O3 and simethicone (amphiphilic). The high sensitivity of (single particle)ICPMS online monitoring of the breakthrough curves made it possible to inject the ENPs at trace levels (2-100 µg L-1) in eluents composed of 10-3 and 10-2 M NaCl and pHs of 5.7 and 7.8. The deposition of all ENPs in the sand increased with the ionic strength and decreased with the pH of the carrier. Both bare and SiO2-coated ENPs showed a clear control by the electrostatic interactions between the particles and the quartz grains surfaces, in partial agreement with classical DLVO theory. Unexpectedly high rates of transfer were observed with the amphiphilic UV-filter, which could be explained by the addition of a contribution to the DLVO model to account for the steric repulsion between the sand collector and the polysiloxane surface layer of this ENP. These results demonstrate the major role played by the coating of UV-filters regarding their fate in porous media like soils, sediments and aquifers.

Release and fate of nanoparticulate TiO2 UV filters from sunscreen: Effects of particle coating and formulation type.

Nanoparticulate mineral UV filters, such as titanium dioxide (TiO2) nanocomposites, are being increasingly used in sunscreens as an alternative to organic UV filters. However, there is still a lack of understanding regarding their fate and behavior in aquatic environments and potential environmental impacts after being released from a bather's skin during recreational activities. In this work, we assessed the release, fate, and transformation of two commercial nanocomposite TiO2 UV filters, one hydrophobic and one hydrophilic, in ultrapure water and simulated fresh- and seawater. The hydrophobic TiO2 nanocomposite, T-SA, was coated with a primary Al2O3 photopassivation layer and a secondary stearic acid layer, while the hydrophilic TiO2 nanocomposite, T-SiO2, was coated with a single SiO2 photopassivation layer. The influence of the sunscreen formulation was examined by dispersing the TiO2 nanocomposites in their typical continuous phase (i.e., oil for T-SA and water for T-SiO2) before introduction into the aqueous system. After 48 h of aqueous aging and 48 h of settling, 88-99% of the hydrophobic T-SA remained floating on top of the water column in all aqueous systems. On the other hand, 100% of the hydrophilic T-SiO2 settled out of the water column in the fresh- and seawaters. With respect to the photopassivation coatings, no loss of the T-SA Al2O3 layer was detected after aqueous aging, but 99-100% dissolution of the SiO2 layer on the T-SiO2 nanocomposite was observed after 48 h in the fresh- and seawaters. This dissolution left behind T-SiO2 by-products exhibiting a photocatalytic activity similar to that of bare rutile TiO2. Overall, the results demonstrated that the TiO2 surface coating and sunscreen formulation type drive environmental behavior and fate and that loss of the passivation layer can result in potentially harmful, photoactive by-products. These insights will help guide regulations and assist manufacturers in developing more environmentally safe sunscreens.

Silica-clay nanocomposites for the removal of antibiotics in the water usage cycle.

The increasingly frequent detection of resistant organic micropollutants in waters calls for better treatment of these molecules that are recognized to be dangerous for human health and the environment. As an alternative to conventional adsorbent material such as activated carbon, silica-clay nanocomposites were synthesized for the removal of pharmaceuticals in contaminated water. Their efficiency with respect to carbamazepine, ciprofloxacin, danofloxacin, doxycycline, and sulfamethoxazole was assessed in model water and real groundwater spiked with the five contaminants. Results showed that the efficacy of contaminant removal depends on the chemical properties of the micropollutants. Among the adsorbents tested, the nanocomposite made of 95% clay and 5% SiO2 NPs was the most efficient and was easily recovered from solution after treatment compared with pure clay, for example. The composite is thus a good candidate in terms of operating costs and environmental sustainability for the removal of organic contaminants.

Aqueous aging of a silica coated TiO2 UV filter used in sunscreens: investigations at the molecular scale with dynamic nuclear polarization NMR.

Short-term, aqueous aging of a commercial nanocomposite TiO2 UV filter with a protective SiO2 shell was examined in abiotic simulated fresh- and seawater. Under these conditions, the SiO2 layer was quantitatively removed (∼88-98%) within 96 hours, as determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). While these bulk ICP-AES analyses suggested almost identical SiO2 shell degradation after aging in fresh- and seawater, surface sensitive 29Si dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (SSNMR), with signal enhancements of 5-10× compared to standard SSNMR, was able to distinguish differences in the aged nanocomposites at the molecular level. DNP-SSNMR revealed that the attachment of the silica layer to the underlying TiO2 core rested on substantial Si-O-Ti bond formation, bonds which were preserved after freshwater aging, yet barely present after aging in seawater. The removal of the protective SiO2 layer is due to ionic strength accelerated dissolution, which could present significant consequences to aqueous environments when the photoactive TiO2 core becomes exposed. This work demonstrates the importance of characterizing aged nanocomposites not only on the bulk scale, but also on the molecular level by employing surface sensitive techniques, such as DNP-NMR. Molecular level details on surface transformation and elemental speciation will be crucial for improving the environmental safety of nanocomposites.

Safety Evaluation of TiO2 Nanoparticle-Based Sunscreen UV Filters on the Development and the Immunological State of the Sea Urchin Paracentrotus lividus.

Sunscreens are emulsions of water and oil that contain filters capable of protecting against the detrimental effects of ultraviolet radiation (UV). The widespread use of cosmetic products based on nanoparticulate UV filters has increased concerns regarding their safety and compatibility with both the environment and human health. In the present work, we evaluated the effects of titanium dioxide nanoparticle (TiO2 NP)-based UV filters with three different surface coatings on the development and immunity of the sea urchin, Paracentrotus lividus. A wide range of NP concentrations was analyzed, corresponding to different levels of dilution starting from the original cosmetic dispersion. Variations in surface coating, concentration, particle shape, and pre-dispersant medium (i.e., water or oil) influenced the embryonic development without producing a relevant developmental impairment. The most common embryonic abnormalities were related to the skeletal growth and the presence of a few cells, which were presumably involved in the particle uptake. Adult P. lividus immune cells exposed to silica-coated TiO2 NP-based filters showed a broad metabolic plasticity based on the biosynthesis of metabolites that mediate inflammation, phagocytosis, and antioxidant response. The results presented here highlight the biosafety of the TiO2 NP-based UV filters toward sea urchin, and the importance of developing safer-by-design sunscreens.

Assessing UV filter inputs into beach waters during recreational activity: A field study of three French Mediterranean beaches from consumer survey to water analysis.

In order to assess the release of UV filters from the sunscreen used by beachgoers into seawater within the bathing zone, a field campaign was carried out during the summer of 2017 at three beaches in Marseille, along the French Mediterranean coast. A social survey analyzed beachgoer attendance, the quantities and types of suncare products used and the bathing frequencies, while the bathing water was analyzed spatially and temporally so as to quantify both mineral and organic UV filters directly released and recovered. During the peak recreational time at the three beaches, both mineral and organic UV filters were detected in higher concentrations in the bathing area than offshore. In general, higher concentrations were recovered in the water top surface layer than in the water column, giving respectively 100-900 and 20-50 µg/L for TiO2, 10-15 and 1-3 µg/L for ZnO, 40-420 and 30-150 ng/L for octocrylene, and 10-15 and 10-350 ng/L for avobenzone. More than 75% of the 471 interviewees reported bathing every time they go to the beach, with 68% using a suncare product 2.6 times on average. From these data we estimated that an average mass of 52 kg/day or 1.4 t/month of suncare products are possibly released into bathing water for a beach attended by 3000 people daily. The mass ratio of UV filters in such products typically ranges from 0.03 to 0.1, allowing us to propose theoretical maximum concentrations in the beach water. Our recovery of measured UV filter concentrations in seawater compared to the theoretical concentrations revealed two distinct scenarios for the mineral and organic filters. While up to 49% of the mineral filters used by beachgoers may be released into the seawater, the organic filters were minimally recovered in the environment, most likely due to internalization through the skin barrier or partial photodegradation.

Nanoparticle stability in lake water shaped by natural organic matter properties and presence of particulate matter.

Predicting nanoparticle (NP) fate in the environment continues to remain a challenge, especially for natural surface water systems, where NPs can hetero-aggregate with natural organic and mineral suspended matter. Here we present the interactions and aggregation behavior of TiO2 NPs with natural organic matter (NOM) in a natural lake water. NP fate in a synthetic water of the same pH and ionic composition was also tested in the presence and absence of NOM analogs to gain insight into the different stabilizing effects of each NOM type. Several complementary analytical techniques were utilized to assess lake NOM composition, including pyrolysis-gas chromatography-mass spectrometry, gel permeation chromatography, the polarity rapid-assessment method, and Nanoparticle Tracking Analysis. In the natural lake water, the TiO2 NPs preferentially interacted with mostly anionic NOM of high and medium molecular weight (~1200-1450 and 400-520 Da). Specifically, strong interactions with proteins and polyhydroxy aromatics were observed. NP fate and stability were determined in both raw lake water containing mineral particulate matter and total NOM (NOMtot) and filtered lake water containing only NOM <0.8 µm (NOM<0.8), with different aggregation profiles observed over time. Additionally, three times the number of TiO2 NPs remained in suspension when only NOM<0.8 was present compared to the unfiltered water containing mineral particulate matter and NOMtot. These results demonstrate the contrasting NP fates in the aquatic environment according to the presence of NOMtot vs. NOM<0.8 and further suggest that the use of pure NOM analogs may not accurately represent NP interactions and fate in the natural system.

The influence of past research on the design of experiments with dissolved organic matter and engineered nanoparticles.

To assess the environmental fate of engineered nanoparticles (ENPs), it is essential to understand their interactions with dissolved organic matter (DOM). The highly complex nature of the interactions between DOM and ENPs and other particulate matter (PM) requires investigating a wide range of material types under different conditions. However, despite repeated calls for an increased diversity of the DOM and PM studied, researchers increasingly focus on certain subsets of DOM and PM. Considering the discrepancy between the calls for more diversity and the research actually carried out, we hypothesize that materials that were studied more often are more visible in the scientific literature and therefore are more likely to be studied again. To investigate the plausibility of this hypothesis, we developed an agent-based model simulating the material choice in the experiments studying the interaction between DOM and PM between 1990 and 2015. The model reproduces the temporal trends in the choice of materials as well as the main properties of a network that displays the DOM and PM types investigated experimentally. The results, which support the hypothesis of a positive reinforcing material choice, help to explain why calls to increase the diversity of the materials studied are repeatedly made and why recent criticism states that the selection of materials is unbalanced.

Natural attenuation of TiO2 nanoparticles in a fractured hard-rock.

Successive transport experiments of TiO2 nanoparticles (NP) suspension through fractured hard-rock column were done in laboratory. A low ionic strength (IS) water (0.8-1.3 10-3 M) at pH ∼4.5 was used, corresponding to the chemical composition of groundwater where the rock was collected (Naizin, France). The surface charge of TiO2 NP was positive while that of rock was negative favoring NP deposition. SEM/EDX reveals that NP were retained on a broad distribution of mineral collectors along the preferential flow pathways (i.e., fractures). However, a non-negligible amount of NP (∼10%) was transferred through the rock. Divalent cation (Ca2+) was responsible for the reduction of the negative charge of the rock and thus contributed to limit the NP deposition as attested by DLVO model. Blocking of rock surfaces by NP favored NP transfer while the ripening process and the size exclusion of aggregates decreased NP mobility. Decrease of water flow favored the exchange of solutes from the immobile to the mobile water in the porous medium, which in turn favored the aggregation of the NP and led to their natural attenuation. The result evidences how slight modifications of the environmental conditions can strongly influence the fate of NP in groundwater.

Non-linear release dynamics for a CeO2 nanomaterial embedded in a protective wood stain, due to matrix photo-degradation.

The release of CeO2-bearing residues during the weathering of an acrylic stain enriched with CeO2 nanomaterial designed for wood protection (Nanobyk brand additive) was studied under two different scenarios: (i) a standard 12-weeks weathering protocol in climate chamber, that combined condensation, water spraying and UV-visible irradiation and (ii) an alternative accelerated 2-weeks leaching batch assay relying on the same weathering factors (water and UV), but with a higher intensity of radiation and immersion phases. Similar Ce released amounts were evidenced for both scenarios following two phases: one related to the removal of loosely bound material with a relatively limited release, and the other resulting from the degradation of the stain, where major release occurred. A non-linear evolution of the release with the UV dose was evidenced for the second phase. No stabilization of Ce emissions was reached at the end of the experiments. The two weathering tests led to different estimates of long-term Ce releases, and different degradations of the stain. Finally, the photo-degradations of the nanocomposite, the pure acrylic stains and the Nanobyk additive were compared. The incorporation of Nanobyk into the acrylic matrix significantly modified the response of the acrylic stain to weathering.

Fullerol cluster formation in aqueous solutions: implications for environmental release.

Here we report on the characteristics of fullerol in aqueous systems and examine those conditions that affect the physical state of fullerol in water. When dispersed in water fullerol forms polydisperse suspensions characterized by both small ( approximately 100 nm) and large associations (>500 nm). These clusters are charged with a point of zero net proton charge (PZNPC) of approximately pH 3. Though the size of fullerol clusters may be manipulated through changes in solution chemistry, principally pH, cluster formation cannot be entirely prevented through these means alone. The fullerol cluster structure is amorphous as revealed by X-ray diffraction analysis, which is in contrast to clusters of C(60) formed through dissolution in toluene and then introduced into water through sonication (SONnC(60)). The SONnC(60) clusters are crystalline with a structure similar to that of unreacted C(60) crystals.