Microwave-enhanced thermal removal of organochlorine pesticide (chlordecone) from contaminated soils.

Soil contamination with chlordecone, an organochlorine pesticide, is causing serious health problems, affecting crop production and local livestock valorization in the French West Indies. In-situ chemical reduction (ISCR) processes for soil remediation have shown promise but need improvement in terms of time, cost and effective treatment, particularly for andosol soil types. Our study shows that a 10-min microwave treatment significantly reduces chlordecone concentrations (50-90%) in contaminated andosol and nitisol soils. Dry andosol soils show the highest removal yields and reach a higher final temperature (350 °C). Microwave treatment is in all cases more effective or at least as effective as 60 min of conventional heating at a target temperature of 200 °C. The thermal response of andosol and nitisol to microwave exposure is different, as the former is likely to undergo thermal runaway, reaching high temperatures in a short time, resulting in highly efficient thermal removal of chlordecone. These results encourage further scale-up, particularly for the treatment of andosol soils due to their strong microwave response.

Relating mercury occurrence in soil gases at establishments hosting children to historical mercury-using activities in Paris, France.

Volatile pollutants from former industrial sites can degrade the buildings' indoor air quality that were built after the industrial activities. Since 2010, environmental assessments have been conducted in French establishments hosting sensitive populations identified as being on or near potentially contaminated former industrial sites. These projects are based on historical studies traditionally carried out as part of managing contaminated sites, to determine which substances should be analyzed. They pinpoint former activities likely to have stored or used pollutants. We show that the historical information collected is not effective in targeting sites with increased probability of mercury being present in soil gases. Environmental history has demonstrated the existence of large-scale artisanal contamination, both prior to and concomitant with the industrial era. Classic historical studies would not take into account artisanal activities, which are less documented than industrial activities. We carried out additional research for three schools located in three different Parisian districts. Although information on activities which could have emitted mercury was relatively imprecise (in terms of location, type and duration of activities) and uncertainties exist about the completeness of the archival documents available, our investigations identified several mercury-using activities that had not been identified during the classic historical study. However, we have shown that the number of activities identified does not provide information on how mercury has affected soil gas. Consequently, although a more extensive historical research improves knowledge about the presence of potential mercury-using activities, our study shows that a systematic analysis of mercury as part of the assessment of establishments hosting sensitive populations remains relevant. This approach should be applied to other cities around the world.

Degradation of tetrachloroethylene by zero valent iron nanoparticles in the presence of a natural groundwater bacterial biofilm in a sandy porous media.

Biofilms are naturally present in aquifers and can interact with zero valent iron nanoparticles (nZVI) used as remediation agents in contaminated groundwater; thereby they may alter nZVI reactivity towards targeted contaminants in porous media. Laboratory scale experiments using columns filled with sand (50 cm long and 5.2 cm in diameter) were performed to investigate the impact of natural biofilms on nZVI reactivity towards tetrachloroethylene (PCE) in conditions simulating an unconsolidated sandy aquifer. Solutions containing PCE were injected through the sand columns in the presence or absence of biofilm and nZVI. Concentrations in PCE and its metabolites were monitored during 45 days in dissolved and gas phases. PCE concentrations decreased at the column outlets due both to its reductive dechlorination by nZVI (~30% of injected PCE) and its sorption or deposition (as PCE-DNAPL) on sand (~35% of injected PCE). No significant differences in PCE concentrations were found in presence or absence of biofilm. However, biofilm presence affected the nature of PCE metabolites. A higher release of ethene in the column containing biofilm was observed, whereas ethane was dominant in the absence of biofilm. Microbes consumed H2 released by the corrosion of nZVI limiting the hydrogenation of ethene to ethane. The consequences of biofilm development in porous media should be taken into account when considering treatment with nZVI, as it may affect the nature of produced metabolites.

Sources and behavior of perchlorate in a shallow Chalk aquifer under military (World War I) and agricultural influences.

Perchlorate (ClO4ö) has been detected at concentrations of concern for human health on a large scale in groundwater used for drinking water supplies in NE France. Two sources are suspected: a military source related to World War I (WWI) and an agricultural source related to past use of Chilean nitrate fertilizers. The sources and behavior of ClO4ö have been studied in groundwater and rivers near the Reims city, by monitoring monthly the major ions and ClO4- concentrations for two years (2017-2019), and by measuring the isotopic composition of ClO4ö and NO3ö in water samples. ClO4ö was detected throughout the study area with high concentrations (> 4 µg⋅L-1) detected mainly downgradient of the Champagne Mounts, where large quantities of ammunition were used, stored and destroyed during and after WWI. A WWI military origin of ClO4- is inferred from isotopic analysis and groundwater ages. Different tendencies of ClO4- variation are observed and interpreted by a combination of ClO4- concentrations, aquifer functioning and historical investigations, revealing major sources of ClO4- (e.g., unexploded ordnance, ammunition destruction sites) and its transfer mechanisms in the aquifer. Finally, we show that concentrations of ClO4ö in groundwater seems unlikely to decrease in the short- to medium-term.

Laboratory study on the mobility of chlordecone and seven of its transformation products formed by chemical reduction in nitisol lysimeters of a banana plantation in Martinique (French Caribbean).

The contamination by chlordecone (CLD) of soils and water in the French Caribbean (FC) has major environmental and human health impacts. In Situ Chemical Reduction (ISCR) is a promising method to degrade CLD but it generates transformation products (TPs). Here, the fate and transport of CLD and its TPs have been studied using three lysimeters, 65-70 cm-long and 20 cm in diameter, collected from a CLD contaminated nitisol in the FC. A simulated ISCR remediation process (Sim-ISCR) was applied to the top 15 cm layer. An equivalent of 9.8 years of effective rainfall was simulated during the 451 days of the experiments. CLD and seven TPs were analyzed in soils, soil pore waters and outflow waters of the lysimeters before and after the Sim-ISCR. CLD concentration in the soil pore waters increases with depth. In the Sim-ISCR treated layer, the CLD contamination was lowered by 41 to 47% in the soil and by 48 to 73% in the soil pore water. In the lysimeters outflow, however, the CLD concentration was lowered by only 13 to 25%, the flux of CLD from the untreated 50-55 cm of the profile concealing much of the beneficial impact of treating the top 15 cm. Remediating by ISCR the topsoil only will therefore not be sufficient for preventing further CLD contamination of the underlying groundwater. Sim-ISCR generated 5-hydroCLD in soils and waters and, to a much lesser extent, a trihydroCLD, a tetrahydroCLD, a pentahydroCLD and a heptahydroCLD. 5-hydroCLD is more mobile than CLD, but it still interacts strongly with the soil. The 5-hydroCLD values measured in the outflow were up to a factor of 4.4 lower than in the treated soil pore waters, indicating some natural attenuation.

Transport of chlordecone and two of its derivatives through a saturated nitisol column (Martinique, France).

Soils, surface and groundwater in Martinique (French West Indies) are contaminated by chlordecone (CLD), a highly persistent organochlorine pesticide. In Situ Chemical Reduction (ISCR) using zero valent iron has been tested as a remediation technique to lower CLD levels in soils but it produces derivatives whose fate in environment may differ from the parent molecule. Here, the transfer of CLD and two of its main derivatives resulting from ISCR, CLD5aH and a CLD-3Cl, have been investigated in untreated and treated nitisol from a banana plantation using column experiments (20 cm long and 2.5 cm in diameter) under saturated conditions. The circulation of CaCl2 10-2M solution, simulating the ionic strength of soil water, in untreated nitisol results in CLD concentrations in solutions that remain for decades above the threshold limit for drinking water. ISCR treatment lowers the CLD concentration by ~50% in soil and by a factor 3 in waters but they remain above the threshold values. CLD derivatives, CLD5aH and a CLD-3Cl and, to a lesser extent, a CLD-2Cl and a CLD-5Cl, are found in waters after treatment. Dechlorination increases the mobility of the derivatives with respect to the parent molecule, which is likely to induce their transfer to deeper soil layers than those treated by ISCR: CLD-3Cl is more mobile than CLD5aH which is more mobile than CLD. When the water is in contact with the contaminated soil, a period of fast desorption kinetic of CLD and its derivatives, followed by a period of slow kinetics are found. This attests the high risk for water contamination and the potential influence of rainfall events on the concentrations likely to be encountered in soil waters or in waters accumulated on the soil surface.

Shift in Natural Groundwater Bacterial Community Structure Due to Zero-Valent Iron Nanoparticles (nZVI).

Toxic and persistent contaminants in groundwater are technologically difficult to remediate. Remediation techniques using nanoparticles (NPs) such as nZVI (Zero-Valent Iron) are applicable as in situ reduction or oxidation agents and give promising results for groundwater treatment. However, these NP may also represent an additional contamination in groundwater. The aims of this study are to assess the impact of nZVI on the nitrate-reducing potential, the abundance and the structure of a planktonic nitrate-reducing bacterial community sampled in groundwater from a multicontaminated site. An active nitrate-reducing bacterial community was obtained from groundwater samples, and inoculated into batch reactors containing a carbon substrate, nitrate and a range of nZVI concentrations (from 0 to 70.1 mg Fe.L-1). Physical (pH, redox potential), chemical ( NO 3 - concentrations) and biological (DNA, RNA) parameters were monitored during 1 week, as well as nZVI size distribution and mortality of bacteria. Nitrate-reducing activity was temporally stopped in the presence of nZVI at concentrations higher than 30 mg L-1, and bacterial molecular parameters all decreased before resuming to initial values 48 h after nZVI addition. Bacterial community composition was also modified in all cultures exposed to nZVI as shown by CE-SSCP fingerprints. Surprisingly, it appeared overall that bacteria viability was lower for lower nZVI concentrations. This is possibly due to the presence of larger, less reactive NP aggregates for higher nZVI concentrations, which inhibit bacterial activity but could limit cell mortality. After 1 week, the bacterial cultures were transplanted into fresh media without nZVI, to assess their resilience in terms of activity. A lag-phase, corresponding to an adaptation phase of the community, was observed during this step before nitrate reduction reiterated, demonstrating the community's resilience. The induction by nZVI of modifications in the bacterial community composition and thus in its metabolic potentials, if also occurring on site, could affect groundwater functioning on the long term following nZVI application. Further work dedicated to the study of nZVI impact on bacterial community directly on site is needed to assess a potential impact on groundwater functioning following nZVI application.

Worldwide occurrence and origin of perchlorate ion in waters: A review.

Perchlorate (ClO4-) is a persistent water soluble oxyanion of growing environmental interest. Perchlorate contamination can be a health concern due to its ability to disrupt the use of iodine by the thyroid gland and the production of metabolic hormones. Its widespread presence in surface water and groundwater makes the aquatic environment a potential source of perchlorate exposure. However, the amount of published data on perchlorate origins and water contamination worldwide remains spatially limited. Here, we present an overview of research on perchlorate origins and occurrences in water, and the methodology to distinguish the different perchlorate sources based on isotope analysis. All published ranges of isotopic content in perchlorate from different sources are presented, including naturally occurring and man-made perchlorate source types, as well as the effects of isotope fractionation that accompanies biodegradation processes. An example of a case study in France is presented to emphasize the need for further research on this topic.

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.

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.

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.

Do natural biofilm impact nZVI mobility and interactions with porous media? A column study.

Nanoparticles (NP) used as remediation agents for groundwater treatment may interact with biofilms naturally present, altering NP mobility and/or reactivity and thereby NP effectiveness. The influence of the presence of a multi species biofilm on the mobility of two types of zero-valent iron NP (nZVI; NANOFER 25S and optimized NANOFER STAR, NanoIron s.r.o. (Czech Republic)) was tested in laboratory experiments with columns mimicking aquifer conditions. Biofilms were grown in columns filled with sand in nitrate reducing conditions using groundwater from an industrial site as inoculum. After two months growth, they were composed of several bacterial species, dominated by Pseudomonas stutzeri. Biofilm strongly affected the physical characteristics of the sand, decreasing total porosity from ~30% to ~15%, and creating preferential pathways with high flow velocities. nZVI suspensions were injected into the columns at a seepage velocity of 10mday-1. Presence of biofilm did not impact the concentrations of Fe at the column outlet nor the amount of total Fe retained in the sand, as attested by the measurement of magnetic susceptibility. However, it had a significant impact on NP size sorting as well as on total Fe distribution along the column. This suggests nZVI-biofilm interactions that were confirmed by microscopic observations using SEM/STEM coupled with energy-dispersive X-ray spectroscopy. Our study shows that biofilm modifies the water flow velocity in the porous media, favoring the transport of large aggregates and decreased NP mobility due to physical and chemical interactions.

Cryo-Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM)-in-SEM for Bio- and Organo-Mineral Interface Characterization in the Environment.

Understanding biofilm interactions with surrounding substratum and pollutants/particles can benefit from the application of existing microscopy tools. Using the example of biofilm interactions with zero-valent iron nanoparticles (nZVI), this study aims to apply various approaches in biofilm preparation and labeling for fluorescent or electron microscopy and energy dispersive X-ray spectrometry (EDS) microanalysis for accurate observations. According to the targeted microscopy method, biofilms were sampled as flocs or attached biofilm, submitted to labeling using 4',6-diamidino-2-phenylindol, lectins PNA and ConA coupled to fluorescent dye or gold nanoparticles, and prepared for observation (fixation, cross-section, freezing, ultramicrotomy). Fluorescent microscopy revealed that nZVI were embedded in the biofilm structure as aggregates but the resolution was insufficient to observe individual nZVI. Cryo-scanning electron microscopy (SEM) observations showed nZVI aggregates close to bacteria, but it was not possible to confirm direct interactions between nZVI and cell membranes. Scanning transmission electron microscopy in the SEM (STEM-in-SEM) showed that nZVI aggregates could enter the biofilm to a depth of 7-11 µm. Bacteria were surrounded by a ring of extracellular polymeric substances (EPS) preventing direct nZVI/membrane interactions. STEM/EDS mapping revealed a co-localization of nZVI aggregates with lectins suggesting a potential role of EPS in nZVI embedding. Thus, the combination of divergent microscopy approaches is a good approach to better understand and characterize biofilm/metal interactions.

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.

An innovative application of stable isotopes (δ2H and δ18O) for tracing pollutant plumes in groundwater.

The identification of the sources of contaminants present in groundwater at industrial sites is primordial to address environmental and industrial issues. However, available tools are often inadequate or expensive. Here, we present the data of stable isotopes (δ18O and δ2H) of the water molecule at an industrial site where electrochemistry plant occurs impacting the groundwater quality. High ClO3 and ClO4 contents and 2H enrichment have been measured in groundwater. Recharge of aquifer relates to infiltration of rainwater and by subsurface inflow. On-site, industrial products are generated by electrolysis. We show that the electrolysis process leads to a large 2H enrichment (+425‰) in solutions. In the absence of hydrothermal water input containing H2S, we demonstrate that the relationship between δ18O and δ2H can be easily used in a way to trace the origin of the ClO3 and ClO4 in groundwater. Isotopes evidenced first a leakage from end-product storage tanks or during the production process itself. Then, an accumulation and release of ClO3 and ClO4 from soil is demonstrated. Our study successfully shows that stable isotopes are a powerful and low cost tool for tracing pollutant plumes in an industrial context using electrolysis process.

Evidence for TiO2 nanoparticle transfer in a hard-rock aquifer.

Water flow and TiO2 nanoparticle (NP) transfer in a fractured hard-rock aquifer were studied in a tracer test experiment at a pilot site in Brittany, France. Results from the Br tracer test show that the schist aquifer can be represented by a two-layer medium comprising i) fractures with low longitudinal dispersivity in which water and solute transport is relatively fast, and ii) a network of small fissures with high longitudinal dispersivity in which transport is slower. Although a large amount of NPs was retained within the aquifer, a significant TiO2 concentration was measured in a well 15m downstream of the NP injection well, clearly confirming the potential for TiO2 NPs to be transported in groundwater. The Ti concentration profile in the downstream well was modelled using a two-layer medium approach. The delay used for the TiO2 NPs simulation compared to the Br concentration profiles in the downstream well indicate that the aggregated TiO2 NPs interacted with the rock. Unlike Br, NPs do not penetrate the entire pore network during transfer because of electrostatic interactions between NP aggregates and the rock and also to the aggregate size and the hydrodynamic conditions, especially where the porosity is very low; NPs with a weak negative charge can be attached onto the rock surface, and more particularly onto the positively charged iron oxyhydroxides coating the main pathways due to natural denitrification. Nevertheless, TiO2 NPs are mobile and transfer within fracture and fissure media. Any modification of the aquifer's chemical conditions is likely to impact the groundwater pH and, the nitrate content and the denitrification process, and thus affect NP aggregation and attachment.

Screening of French groundwater for regulated and emerging contaminants.

Nationwide screening of 411 emerging contaminants and other regulated compounds, including parent molecules and transformation products (TPs) having various uses and origins, was done at 494 groundwater sites throughout France during two sampling campaigns in the Spring and the Fall of 2011. One hundred and eighty substances (44% of the targeted compounds) were quantified in at least one sampling point. These included pharmaceuticals, industrial products, pesticides, their transformation products and other emerging compounds. Fifty-five compounds were quantified in more than 1% of the samples. Both regulated and emerging compounds were found. Among the unregulated compounds, acetaminophen, carbamazepine, perfluorinated compounds, dioxins/furans, tolyltriazole, bisphenol A, triazine transformation products, and caffeine were quantified in more than 10% of the samples analyzed. Concentrations exceeding the threshold of toxicological concern of 0.1 µg/L were found for tolyltriazole, bisphenol A and some of the triazine transformation products (DEDIA). These new results should help the water resource managers and environmental regulators develop sound policies regarding the occurrence and distribution of regulated and emerging contaminants in groundwater.

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

Engineered 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.

Multi-bioindicators to assess soil microbial activity in the context of an artificial groundwater recharge with treated wastewater: a large-scale pilot experiment.

In the context of artificial groundwater recharge, a reactive soil column at pilot-scale (4.5 m depth and 3 m in diameter) fed by treated wastewater was designed to evaluate soil filtration ability. Here, as a part of this project, the impact of treated wastewater filtration on soil bacterial communities and the soil's biological ability for wastewater treatment as well as the relevance of the use of multi-bioindicators were studied as a function of depth and time. Biomass; bacterial 16S rRNA gene diversity fingerprints; potential nitrifying, denitrifying, and sulfate-reducing activities; and functional gene (amo, nir, nar, and dsr) detection were analyzed to highlight the real and potential microbial activity and diversity within the soil column. These bioindicators show that topsoil (0 to 20 cm depth) was the more active and the more impacted by treated wastewater filtration. Nitrification was the main activity in the pilot. No sulfate-reducing activity or dsr genes were detected during the first 6 months of wastewater application. Denitrification was also absent, but genes of denitrifying bacteria were detected, suggesting that the denitrifying process may occur rapidly if adequate chemical conditions are favored within the soil column. Results also underline that a dry period (20 days without any wastewater supply) significantly impacted soil bacterial diversity, leading to a decrease of enzyme activities and biomass. Finally, our work shows that treated wastewater filtration leads to a modification of the bacterial genetic and functional structures in topsoil.

Influence of surface conductivity on the apparent zeta potential of TiO2 nanoparticles: application to the modeling of their aggregation kinetics.

Titanium dioxide nanoparticles (TiO2 NPs) are extensively used in consumer products. The release of these NPs into aquatic environments raises the question of their possible risks to the environment and human health. The magnitude of the threat may depend on whether TiO2 NPs are aggregated or dispersed. Currently, limited information is available on this subject. A new approach based on DLVO theory is proposed to describe aggregation kinetics of TiO2 NPs in aqueous dispersions. It has the advantage of using zeta potentials directly calculated by an electrostatic surface complexation model whose parameters are calibrated by ab initio calculations, crystallographic studies, potentiometric titration and electrophoretic mobility experiments. Indeed, the conversion of electrophoretic mobility measurements into zeta potentials is very complex for metal oxide nanoparticles. This is due to their very high surface electrical conductivity associated with the electromigration of counter and co-ions in their electrical double layer. Our model has only three adjustable parameters (the minimum separation distance between NPs, the Hamaker constant, and the effective interaction radius of the particle), and predicts very well the stability ratios of TiO2 NPs measured at different pH values and over a broad range of ionic strengths (KCl aqueous solution). We found an effective interaction radius that is significantly smaller than the radius of the aggregate and corresponds to the radius of surface crystallites or small clusters of surface crystallites formed during synthesis of primary particles. Our results confirm that DLVO theory is relevant to predict aggregation kinetics of TiO2 NPs if the double layer interaction energy is estimated accurately.