Fate of TiO2 nanoparticles in the aquatic environment in the presence of anthropogenic compounds

International audienceThe increasing production and use of nanoparticles (NP) in consumer products inevitably lead to ENP emissions into the environment. The physicochemical properties of NP depend on various parameters (e.g. pH, cations, IS). In natural waters, the stability of NP can vary as a function of a sum of these parameters and occurs by one of the numerous scenarios. In particular, the presence of anthropogenic organic molecules (AOM) can change the NP fate. Also, the presence of NP may affect the organic pollutants (fate and toxicity). The main objective of the work was to study the aggregation of TiO2 NP (pure hydrophilic 100 % rutile and pure hydrophilic 100 % anatase, 5−30 nm) in the presence of the most frequently occur and representative pesticides (glyphosate, AMPA, 2.4D) in natural waters considering lab experiments under relevant aqueous conditions (pH, ionic strength, presence and concentrations of mono- and bivalent cations). The presence of pesticides affected TiO2 NP homoaggregation in solutions (IS=10-3M - 10-2M) with pH values below the NP point of zero charge (PZC) for the anatase NPs (pH=6.5) and with pH values above the NP PZC for the rutile NP (pH=4.5). No changes in NP aggregation were observed in very low (IS=10-4M) or very high (IS= 10-1M) ionic strength solutions. The presence of the pesticides caused a significant modification of the NP surface charge (zeta potential) over a large range of salt concentrations (IS=10-4M - 10-1M). Compared to mono-valent cations (Na+), bi-valent cations (Ca2+) favor an increase in zeta potential of NP (anatase and rutile) at pH 8. There is no significant difference between at pH 5. Finally, these results demonstrated that, among the studied AOMs, glyphosate (with 4 pKa-s from 0.8 to 11) affects NP aggregation/stabilization in a wider range of physicochemical conditions. Overall, these results will aid in the evaluation of potential environmental risks posed by engineered NP in the aquatic environments exposed to pesticide load

The role of pesticides in aggregation ofTiO 2 nanoparticles in aquatic environments

International audienceThe fate and behavior of engineered nanoparticles (NPs) released in aquatic environments will be influenced by the water chemistry, as well as the pesticide load due to the potential for NP interaction with anthropogenic organic molecules (AOMs). As such, surface charge and aggregation of pure hydrophilic 100 % rutile and pure hydrophilic 100 % anatase titanium dioxide nanoparticles (TiO2 NPs, 5−30 nm) were evaluated in a modeled water solution in the presence of three common AOMs, glyphosate, aminomethylphosphonic acid (AMPA), and 2.4-D. The surface charge and size distribution were assessed over time as a function of various factors including surface chemistry of the NPs and AOMs, presence of mono- and bi-valent cations, pH, and ionic strength of the aqueous solution. The presence of AOMs (5 µg/L) affected TiO2 NP (5 mg/L) homoaggregation in solutions (IS=10-3M - 10-2M) with pH values below the NP point of zero charge (PZC) for the anatase NPs (pH=6.5) and with pH values above the NP PZC for the rutile NPs (pH=4.5). No changes in NP aggregation were observed in very low (IS=10-4M) or very high (IS= 10-1M) ionic strength solutions. Passing through the PZC resulted in irreversible aggregation of the NPs, even in the presence of AOMs. The presence of the pesticides also caused a significant modification of the NP surface charge (zeta potential) over a large range of salt concentrations (IS=10-4M - 10-1M). Compared to mono-valent cations, bi-valent cations (Ca2+) favored NP aggregation and an increase in zeta potential. Finally, these results demonstrated that, among the studied AOMs, glyphosate (with 4 pKa-s from 0.8 to 11) affects NP aggregation/stabilization in a wider range of physicochemical conditions. Overall, these results will aid in the evaluation of potential environmental risks posed by engineered NPs in the aquatic environments exposed to pesticide load

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

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

International audienceDissolved 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

Insights into natural organic matter and pesticide characterisation and distribution in the Rhone River

International audienceThorough characterisation of natural organic matter (NOM) in natural surface waters remains vital for evaluating pollutant dynamics and interactions with NOM under realistic environmental conditions. Here, we present the characterisation of NOM and pesticide compositions for nine sampling sites over the length of the Rhone River, also evaluating the advantages and limitations of different analytical techniques to determine how they complement one another. Together with dissolved and particulate organic carbon analyses, the dissolved organic matter (DOM, <0.8 mu m) or NOM (unfiltered organic matter) was characterised with gel permeation chromatography, the polarity rapid-assessment method, excitation-emission matrix fluorescence, and pyrolysis-gas chromatography-mass spectrometry to evaluate both composition and distribution. An additional objective was the determination of the NOM degradation state (i.e. constantly produced autochthonous or weakly degraded allochthonous species), an important factor in assessing potential NOM-pollutant interactions. The NOM compositions (i.e. proteins, polyhydroxy aromatics, polysaccharides, amino sugars) and proportions were similar between sites, but variations were observed in the relative proportions of autochthonous and allochthonous material from north to south. Anionic proteins and polyhydroxy aromatics in a molecular weight range of similar to 1000-1200 Da comprised the majority of the DOM. As a pollutant case study, five pesticides (glyphosate, metalochlor, chlortoluron, isoproturon, propyzamide) and some of their metabolites (aminomethylphosphonic acid, metolachlor ethanesulfonic acid and metolachlor oxanilic acid) were measured. Several exhibited trends with the NOM, particulate organic carbon and suspended particulate matter distributions in the Rhone waters, suggesting a significant influence on pesticide fate and transport in the river

The role of pesticides in stabilization of TiO2 nanoparticles in aquatic environments

International audienceThe influence of pesticides (glyphosate, aminomethylphosphonic acid (AMPA) and 2.4-D) on the surface charge and aggregation of pure TiO2 nanoparticles (NP; 5-30 nm; anatase and rutile) have been investigated in modeled water solutions. The dependence of the surface charge and the size distribution at upon the various factors (including surface chemistry of NP and pesticides, presence of mono- (Na+) and bi-valent (Ca2+) cations, pH value, and ionic strength (IS) of an aqueous solution) has been studied. The presence of glyphosate (5µg/L) affects rutile TiO2 NP (5 mg/L) stabilization in NaCl solution of IS=10-4M - 10-3M (>CCC) and in CaCl2 solution of IS =10-4M (>CCC) with pH=5 near the pH point of zero charge (PZC) (pHPZC=4.5). With adding of the glyphosate no changes in NP aggregation were observed in very high (IS= 10-1M) ionic strength solutions for rutile NP and in all studied conditions for anatase NP. No significant changes in NP aggregation were observed in the presence of AMPA and 2.4-D. Compared to mono-valent cations, bi-valent cations favored an increase in zeta potential at pH8 and no changes at pH5. These results show new evidences of the role of pesticides on the NP mobility in aquatic environments

Addressing the complexity of water chemistry in environmental fate modeling for engineered nanoparticles

International audienceEngineered nanoparticle (ENP) fate models developed to date — aimed at predicting ENP concentration in the aqueous environment — have limited applicability because they employ constant environmental conditions along the modeled system or a highly specific environmental representation; both approaches do not show the effects of spatial and/or temporal variability. To address this conceptual gap, we developed a novel modeling strategy that: 1) incorporates spatial variability in environmental conditions in an existing ENP fate model; and 2) analyzes the effect of a wide range of randomly sampled environmental conditions (representing variations in water chemistry). This approach was employed to investigate the transport of nano-TiO2 in the Lower Rhône River (France) under numerous sets of environmental conditions. The predicted spatial concentration profiles of nano-TiO2 were then grouped according to their similarity by using cluster analysis. The analysis resulted in a small number of clusters representing groups of spatial concentration profiles. All clusters show nano-TiO2 accumulation in the sediment layer, supporting results from previous studies. Analysis of the characteristic features of each cluster demonstrated a strong association between the water conditions in regions close to the ENP emission source and the cluster membership of the corresponding spatial concentration profiles. In particular, water compositions favoring heteroaggregation between the ENPs and suspended particulate matter resulted in clusters of low variability. These conditions are, therefore, reliable predictors of the eventual fate of the modeled ENPs. The conclusions from this study are also valid for ENP fate in other large river systems. Our results, therefore, shift the focus of future modeling and experimental research of ENP environmental fate to the water characteristic in regions near the expected ENP emission sources. Under conditions favoring heteroaggregation in these regions, the fate of the ENPs can be readily predicted

Investigations into titanium dioxide nanoparticle and pesticide interactions in aqueous environments

International audienceThe influence of three pesticides (glyphosate, aminomethylphosphonic acid (AMPA) and 2,4-dichlorophenoxyacetic acid (2,4-D)) on the colloidal fate of TiO2 nanoparticles (NPs; anatase and rutile) has been investigated under aqueous conditions of variable chemical composition (Na+ or Ca2+), ionic strength (IS, 10(-4) -10(-1) M), and pH (5 or 8). Sorption and degradation of these pesticides in the presence of the NPs were evaluated. In the absence of the pesticides, increasing IS, the presence of the divalent cation Ca2+ and a pH value close to the NP isoelectric point favored NP homoaggregation as expected. However, at low IS (<= 10(-2) M in NaCl; <= 10(-3) M in CaCl2), in the presence of a few mu g L-1 of glyphosate and rutile in the mg L-1 range, NP homoaggregation was prevented, despite the pH = 5 close to the NP isoelectric point (4.0-4.2). The phosphonate group of the pesticide drove glyphosate adsorption onto the NP, while the carboxylic group was responsible for the electrostatic stabilization of the NP. The stabilizing effect of glyphosate on NP aggregation however appears to be temporary. Furthermore, TiO2 NPs also adsorbed AMPA and promoted degradation of glyphosate to AMPA. These results highlight new evidence of NP-pesticide interactions and the differences in their fate and potential co-migration behavior in aquatic environments

Heteroaggregation of titanium dioxide nanoparticles with suspended particulate and natural organic matter analogues

International audienceThe fate of engineered nanoparticles (ENPs) in natural aqueous environments is influenced by ENP dispersion/transport and aggregation/deposition related to environmental factors as well as those intrinsic to the nanoparticles themselves. For example, at environmentally relevant concentrations (μg/L), TiO2 ENPs likely have a higher probability of interacting with suspended particulate matter (SPM) and natural organic matter (NOM) present at mg/L to g/L concentrations in natural surface waters, rather than with themselves. With both high specific surface area and reactivity, the SPM and NOM may act as TiO2 ENP carriers in the water column, strongly affecting their fate and transport via the heteroaggregation process. Herein, previously identified and characterized SPM and NOM compositions of the Rhone River, a major European river, were used to guide the selection of relevant analogues for mechanistic evaluation of TiO2 ENP fate in surface waters. The TiO2 ENPs (μg/L) were first spiked into synthetic riverine waters containing one of the main SPM analogues (e.g., quartz, calcite, chlorite, feldspar, muscovite). With rapid heteroaggregation and subsequent sedimentation, the TiO2 ENPs demonstrated a significant affinity for several of the SPM analogues, especially quartz and calcite. In addition to determining the ENP/SPM heteroaggregation kinetics and attachment efficiencies, the influence of NOM on the TiO2 ENP fate and behaviour was also assessed. Four common families of NOM analogues (i.e., proteins, polyhydroxy aromatics, polysaccharides, and amino sugars) were added to the SPM-containing synthetic waters to evaluate the role of NOM on the TiO2 ENP compartmentalization. The protein (bovine serum albumin) and polyhydroxy aromatic (Suwannee River humic acid) analogues, followed by the amino sugar (N-acetyl-D-glucosamine) had the strongest stabilising effects on the system, while enhanced aggregation was observed in the presence of the polysaccharide (YAS 34). Together, these mechanistic data, coupled to a river-scale fate model, will aid in ranking potential TiO2 ENP fate scenarios and assessing their risk within natural aqueous environments. This work was funded by the French National Research Agency and the Swiss FOEN as NANOHETER under the frame of SIINN. http://nanoheter.cerege.f