International audience | Sulfidation is a major transformation product for manufactured silver nanoparticles (Ag-MNPs) in the wastewater treatment process. We studied the dissolution, uptake, and toxicity of Ag-MNP and sulfidized Ag-MNPs (sAg-MNPs) to a model soil organism, Caenorhabditis elegans. Our results show that reproduction was the most sensitive endpoint tested for both Ag-MNPs and sAg-MNPs. We also demonstrate that sulfidation not only decreases solubility of Ag-MNP, but also reduces the bioavailability of intact sAg-MNP. The relative contribution of released Ag+ compared to intact particles to toxicity was concentration dependent. At lower total Ag concentration, a greater proportion of the toxicity could be explained by dissolved Ag, whereas at higher total Ag concentration, the toxicity appeared to be dominated by particle specific effects. 2014 Elsevier Ltd. All rights reserved.

International audience | Wastewater Treatment Plants (WWTPs) are a key pathway by which nanoparticles (NPs) enter the environment following release from NP-enabled products. This work considers the fate and exposure of CeO2 NPs in WWTPs in a two-step process of heteroaggregation with bacteria followed by the subsequent reduction of Ce(IV) to Ce(III). Measurements of NP association with solids in sludge were combined with experimental estimates of reduction rate constants for CeO2 NPs in Monte Carlo simulations to predict the concentrations and speciation of Ce in WWTP effluents and biosolids. Experiments indicated preferential accumulation of CeO2 NPs in biosolids where reductive transformation would occur. Surface functionalization was observed to impact both the distribution coefficient and the rates of transformation. The relative affinity of CeO2 NPs for bacterial suspensions in sludge appears to explain differences in the observed rates of Ce reduction for the two types of CeO2 NPs studied. (C) 2015 Elsevier Ltd. All rights reserved.

Tris(2-chloroethyl) phosphate (TCEP) is a widely found emerging pollutant due to its heavy usage as a flame retardant. It is chemically stable and is very difficult to removal from water. The goal of this study was to explore whether iron monosulfide (FeS) can be used for reductive transformation of TCEP as FeS can react with a variety of halogenated organic contaminants. We used batch reactor systems to quantify the transformation reactions in the absence and presence of cetyltrimethylammonium bromide (CTAB, a common surfactant in aquatic environments). The results showed that, in the presence of CTAB (100 mg L⁻¹), FeS exhibited much greater reactivity towards TCEP as 93% of initial TCEP had been transformed within 14 d of reaction. In the absence of CTAB, it required 710 d of reaction to achieve 97.3% reduction of initial TCEP. The enhancement of CTAB on TCEP transformation rate could be due to the facts that CTAB could stabilize FeS suspension against aggregation, protect FeS from rapid oxidation, and increase surface adsorption of TCEP on FeS. XPS analysis showed that both Fe(II) and S(-II) species on the FeS surface were involved in the reductive transformation of TCEP. Analysis of transformation products revealed that TCEP was reductively transformed into bis(2-chloroethyl) phosphate (BCEP), Cl⁻ and C₂H₄. These findings showed that FeS may play an important role in the reductive transformation of TCEP when TCEP coexisting with CTAB in aquatic environments.

The abundance of silver nanoparticles (AgNPs) in consumer products has led to their environmental release and therefore to concern about their impact on human health. The ingestion of AgNP-contaminated soil from urban sites is an important exposure pathway, especially for children. Given the limited information on oral bioaccessibility of soil Ag, we used a physiologically based extraction test (PBET) to evaluate the bioaccessibility of AgNPs and AgNO₃ from soil digestion. The AgNPs underwent several biochemical transformations, including their simultaneous dissolution and agglomeration in gastric fluid followed by the disintegration in the intestinal fluid of the agglomerates into NPs containing silver and chlorine. Therefore, Ag-containing soil exposed the intestine to nanoparticulate Ag in forms that were structurally different from the original forms. The bioaccessibility of AgNPs (0.5 ± 0.05%–10.9 ± 0.7%) was significantly lower than that of AgNO₃ (4.7 ± 0.6%–14.4 ± 0.1%), as a result of the lower adsorption of nanoparticles to soil residues during the digestive process. For the soils tested, the bioaccessibility of AgNPs increased with decreasing clay contents and lower pH. By identifying the soil properties that control AgNP bioaccessibility, a more efficient and accurate screening can be performed of soil types that pose the greatest health risk associated with AgNP exposure.

AgCl and Ag2S prevalently exist in the environment as minerals and/or the chlorination and sulfidation products of ionic silver and elemental silver nanoparticles (AgNPs). In this work, we investigated the chemical transformation of AgCl and Ag2S under simulated sunlight (in water) and incineration (in sludge and simulated municipal solid waste, SMSW). In the presence of natural organic matter, AgCl in river water was observed to be transformed into AgNPs under simulated sunlight, while photo-reduction of Ag2S could not take place under the same experimental conditions. During the course of incineration, pure Ag2S was transformed into elemental silver while AgCl remained stable; however, both Ag2S in sludge and AgCl in SMSW can be transformed to elemental silver under incineration, evident by the results of X-ray absorption spectroscopy and scanning electron microscopy measurements. Incineration temperature played an important role in the transformation of Ag2S and AgCl into elemental silver. These results suggest that chemical transformations of Ag2S and AgCl into elemental silver could be a possible source of naturally occurring or unintentionally produced AgNPs, affecting the fate, transport, bioavailability and toxicity of silver. Therefore, it is necessary to include the contributions of this transformation process when assessing the risk of ionic silver/AgNPs and the utilization and management of incineration residues.

Tetrabromobisphenol A (TBBPA) is the brominated flame retardant with the highest production volume and its bioaccumulation in environment has caused both human health and environmental concerns, however the fate and metabolism of TBBPA in plants is unknown. We studied the fate, metabolites, and transformation of 14C-labeled TBBPA in rice cell suspension culture. During the incubation for 14 days, TBBPA degradation occurred continuously in the culture, accompanied by formation of one anisolic metabolite [2,6-dibromo-4-(2-(2-hydroxy)-propyl)-anisole] (DBHPA) (50% of the degraded TBBPA) and cellular debris-bound residues (46.4%) as well as mineralization (3.6%). The cells continuously accumulated TBBPA in the cytoplasm, while a small amount of DBHPA (2.1% of the initially applied TBBPA) was detectable inside the cells only at the end of incubation. The majority of the accumulated residues in the cells was attributed to the cellular debris-bound residues, accounting for 70–79% of the accumulation after the first incubation day. About 5.4% of the accumulation was associated with cell organelles, which contributed 7.5% to the cellular debris-bound residues. Based on the fate and metabolism of TBBPA in the rice cell suspension culture, a type II ipso-substitution pathway was proposed to describe the initial step for TBBPA degradation in the culture and balance the fate of TBBPA in the cells. To the best of our knowledge, our study provides for the first time the insights into the fate and metabolism of TBBPA in plants and points out the potential role of type II ipso-hydroxylation substitution in degradation of alkylphenols in plants. Further studies are required to reveal the mechanisms for the bound-residue formation (e.g., binding of residues to specific cell wall components), nature of the binding, and toxicological effects of the bound residues and DBHPA.

The fraction of trans-chlordane (TC) in chlordane was used to indicate racemic degradation while the enantiomer fractions (EFs) indicated enantioselective depletion. In 44 soils of the Central Tibetan Plateau, the fractions of TC ranged from 0.368 to 0.411. The EFs ranged from 0.174 to 0.696 for TC and from 0.483 to 0.672 for cis-chlordane (CC). (−) enantiomer excess (ee) was found to be 80.0% in the soils for TC and (+) ee was 86.5% for CC. The fraction of TC changed with the clay content while the EFs changed with the soil organic carbon. Meanwhile, the fractions of TC and the EFs were determined for the surficial sediments in Yamzhog Yumco Lake, which were compared with those in the soils at its catchment area. The composition and chiral signature of chlordane did not vary between soils and sediments. Our results will help to elucidate the transformation of chlordane in soils and in surficial transport.

Triclinic birnessite (TB), a typical layered Mn oxide which is abundant naturally occurring minerals with a vital impact on the transformation of arsenite (As(III)) by adsorption and oxidation. As one of the most common critical metalloids, ammonium ion (NH₄⁺) universally coexists with birnessite in marine, sediments or groundwater where are contaminated with As(III). In this study, we investigated the impacts of NH₄⁺ on TB towards the transformation of As(III). Compared with the original TB (40.1%), the As(III) removal efficiencies of three different concentration (0.5 M, 1 M and 2 M) NH₄⁺ impressed triclinic birnessite (TB-0.5 N, TB-1N and TB-2N) are increased rapidly in the order of: TB-2N (80.4%) > TB-1N (75.8%) > TB-0.5 N (71.5%). In addition, TB-2N exhibited the highest initial oxidation rate of 0.0031 min⁻¹ which exceeds twice as much as this of TB (0.0014 min⁻¹). And TB-2N could reach the max oxidation efficiency when the As concentration is 0.08 mM. Due to two different mechanisms of As(III) oxidation on birnessites under acidic and alkaline conditions, TB-2N showed a higher removal efficiency than TB at pH 3.0, 5.0, 7.0 and 9.0. Hence, there are two main reasons for the advanced As(III) oxidation capacity of TB-2N. One is the improvement of the average oxidation state of Mn, the other is the increase of oxygen vacancy with the coexistence of NH₄⁺. Moreover, the larger specific surface area of TB-2N also contribute to enhancing As(III) oxidation capacity. This study holds a fundamental understanding of the behavior of triclinic birnessite which is coexisted with ammonium ion towards the transformation of As(III) in the environment.

Rice growing in flooded paddy soil often accumulates considerable levels of inorganic and organic arsenic (As) species, which may cause toxicity to plants and/or pose a risk to human health. The bioavailability and toxicity of As in soil depends on its chemical species, which undergo multiple transformations driven primarily by soil microbes. However, the role of endophytes inside rice roots in As species transformation remains largely unknown. We quantified the abundances of microbial functional genes involved in As transformation in the endosphere and rhizosphere of rice roots growing in three paddy soils in a pot experiment. We also isolated 46 different bacterial endophytes and tested their abilities to transform various As species. The absolute abundances of the arsenate reductase gene arsC and the dissimilatory arsenate reductase gene arrA in the endosphere were comparable to those in the rhizosphere, whereas the absolute abundances of the arsenite methylation gene arsM and arsenite oxidation gene aioA in the endosphere were lower. After normalization based on the bacterial 16S rRNA gene, all four As transformation genes showed higher relative abundances in the endosphere than in the rhizosphere. Consistent with the functional gene data, all of the 30 aerobic endophytic isolates were able to reduce arsenate, but only 3 strains could oxidize arsenite. Among the 16 anaerobic endophytic isolates, 4 strains belonging to Desulfovibrio, Terrisporobacter or Clostridium could methylate arsenite and/or methylarsenite. Six strains of aerobic endophytes could demethylate methylarsenite, among which three strains also could reduce and demethylate methylarsenate. None of the isolates could demethylate dimethylarsenate. These results suggest that diverse endophytes living inside rice roots could participate in As species transformation and affect As accumulation and species distribution in rice plants.

During their lifecycle, many engineered nanoparticles (ENPs) undergo significant transformations that may modify their toxicity, behaviour, and fate in the environment. Therefore, understanding the possible environmentally relevant transformations that ENPs may undergo as a result of their surroundings is becoming increasingly important. This work considers industrially produced ceria (CeO2) and focuses on a particle library consisting of seven zirconium-doped variants (Ce1-xZrxO2) where the Zr doping range is x = 0–1. The study assesses their potential transformation in the presence of environmentally relevant concentrations of phosphate. These ENPs have an important role in the operation of automotive catalysts and therefore may end up in the environment where transformations can take place. Samples were exposed to pH adjusted (c. 5.5) solutions made up of either 1 mM or 5 mM each of KH2PO4, citric acid and ascorbic acid and the transformed particles were characterised by means of DLS – size and zeta potential, UV/VIS, TEM, FT-IR, EDX and XRD. Exposure to the phosphate solutions resulted in chemical and physical changes in all ceria-containing samples to cerium phosphate (with the monazite structure). The transformations were dependent on time, ceria concentration in the particles (Ce:Zr ratio) and phosphate to ceria ratio. The presence of Zr within the doped samples did not inhibit these transformations, yet the pure end member ZrO2 ENPs showed no conversion to phosphate. The quite dramatic changes in size, structure and composition observed raise important questions regarding the relevant form of the materials to investigate in ecotoxicity tests, and for regulations based on one or more dimensions in the nanoscale.