Although the use of iron oxide nanoparticles (IONPs) has high potential in remediation and agricu... more Although the use of iron oxide nanoparticles (IONPs) has high potential in remediation and agriculture, a major hindrance to their use includes the risk of contamination of soil and water resources with underexplored effects of IONPs on biota. The fate, phytotoxicity and remediation potential of IONPs are investigated with soil column experiments using 7 nm-sized magnetite (Fe 3 O 4 ) nanoparticles (magnNPs) and sunflower (Helianthus annuus). Control soil, magnNP-containing soil (10 g magnNPs per kg soil), copper-polluted soil (500 mg Cu per kg soil) and copper-polluted soil containing magnNPs (10 g magnNPs per kg soil and 500 mg Cu per kg soil) support sunflower growth for 57 and 95 days. In magnNP-exposed plants, the occurrence of magnNPs does not affect the growth of the vegetative aerial parts and photosynthetic efficiency. Decreased lipid peroxidation indicates an enhanced antioxidant enzymatic response of magnNP-exposed plants. In plants grown in Cu-and magnNP-Cu-soils, the physiological and biochemical impacts of excess copper are clearly identified, resulting in growth retardation, decreased pigment contents and photosynthetic efficiency, and increased lipid peroxidation and peroxidase (POD) activities. Based on magnetic susceptibility, a higher amount of magnNPs is detected after 57 days in the roots of magnNP-exposed plants (1400 mg kg À1 ) than in the roots of magnNP-Cu-exposed plants (920 mg kg À1 ). In the latter, magnNP internalization is likely hampered because of the plants' physiological responses to Cu toxicity. At the working Cu and magnNP concentrations, magnNPs neither decrease Cu accumulation in the plant tissues nor alleviate the overall growth retardation of sunflowers and certain phytotoxic effects induced by excess Cu. However, this study highlights several positive environmental aspects relative to magnNP use, including the harmless effects of magnNPs on sunflowers (1% magnNPs in soil) and the ability of magnNPs to influence Cu mobility in the soil (which could be even more pronounced at lower Cu concentration).
Oxygen and strontium isotopic composition of sedimentary pore fluids obtained by drilling at the ... more Oxygen and strontium isotopic composition of sedimentary pore fluids obtained by drilling at the Chile Triple Junction have been used to obtain information on the diagenesis and transport mechanisms of fluids. Samples were collected from three sites located on an east-west transect of the pre-collision zone (Sites 859, 860, and 861) and from Site 863 located at the base of the trench slope at the point where the Chile Ridge is being subducted. Closer to the toe of the wedge (Sites 859 and 860), non-steady state depth profiles were obtained, whereas linear chemical and isotopic profiles at the upper trench slope (Site 861) are indicative of diffusion of solutes at this site. The nature of fluids from the sites located in the transect prior to ridge subduction is quite different from that observed after ridge subduction (Site 863). Even though in all cases oxygen and strontium isotopic fingerprint indicates alteration of volcanogenic sequences to form authigenic clay mineral, the reactions that modified the chemical composition at Sites 859, 860, and 861 occurred at low temperatures, while high temperature reactions are responsible for the isotopic composition of the fluids at Site 863. At this later site, the 18 O of pore fluids show values as high as 0.7‰ SMOW and a 87 Sr/ 8 °Sr ratio as low as 0.706 in the interval from 400 to 500 mbsf, a sediment section characterized by the presence of a cementation front and steep chemical gradients in the pore fluids. These data suggest that the basal fluids (>400 mbsf) at this site are likely to have been influenced by the hydrothermal reactions occurring at high temperatures.
Potentiometric acid-base titration curves collected on humic (nano)particles as a 16 function of ... more Potentiometric acid-base titration curves collected on humic (nano)particles as a 16 function of pH and salt concentration reflect the electrostatics of the particles and the amount 17 of chemical charges (Q) they carry. In turn, interpretation of titration data helps quantifying 18 their reactivity towards metals provided that both intrinsic chemical and non-specific 19 electrostatic contributions to proton binding are correctly unraveled. Establishing a titration 20 curve requires several steps, i.e. blank subtraction, relative curve positioning with respect to 21 electrolyte concentration, and absolute curve positioning achieved by estimation of particle 22 charge Q 0 at low pH. Failure in establishing properly each step may lead to misevaluation of 23 nanoparticle charging behavior. Here, we report (i) a simple procedure to measure and position 24 titration curves for humic substances (HS) versus salt concentration, and (ii) an original 25 approach for absolute curve positioning upon exploitation of proton affinity spectra. The latter 26 do not depend on Q 0 and they thus constrain titration data analysis using Soft Poisson 27 Boltzmann-based Titration (SPBT) formalism for nanoparticles in the thick electric double 28 layer regime. We illustrate the benefits of our approach by analyzing titration measurements 29 for a large range of humic nanoparticles and by comparing the outcome with results from 30 literature. Synopsis. This article provides a simple and accurate approach to determine the acid-base 33 properties and electrostatic features of humic nanoparticles.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The behaviour of nanoparticles in aqueous solution resulting from a complex balancing between pH,... more The behaviour of nanoparticles in aqueous solution resulting from a complex balancing between pH, surficial and intrinsic properties of nanoparticles.
Colloids have been recognized as key vectors of pollutants in aqueous environment. Amongst them, ... more Colloids have been recognized as key vectors of pollutants in aqueous environment. Amongst them, those formed by iron (Fe) and organic matter (OM) are of major importance due to their ubiquity in the surface environment and strong affinity for metals. In the recent years, Fe stable isotopes have been increasingly used to elucidate the sources and biogeochemical cycling of Fe in Earth's surface environments. In this study, we aim to elucidate (i) the possible Fe isotopic signature resulting from the Fe/OM colloid formation and (ii) the mechanisms involved in the development of such isotopic signature. For this purpose, Fe-OM associations were synthesized through binding and titration experiments. Various pH levels were used in order to study the isotope behavior of Fe occurring as free species at pH 1, as Fe-OM complexes at pH 2 and as mixed Fe-oxyhydroxide/OM nanoaggregates or particles at pH 6.5. Organic matter-free, Fe-free and OM membrane-deposition experiments were also performed. These suspensions were (ultra)filtered at 0.2 µm, 30 kDa and 5 kDa to evidence the possible Fe isotope fractionation between fractions. This protocol allowed also testing the potential of (ultra)filtration techniques to generate isotope fractionation. The results provided evidence that abiotic Fe precipitation, (ultra)filtration techniques and OM deposition were not able to produce significant Fe isotope fractionation under the experimental conditions. However, at circum-neutral pH, the Fe-OM binding and titration experiments displayed a significant enrichment of heavy Fe isotopes in the < 30 kDa fractions relative to the total Fe pool δ 56 Fe = 0.35 ± 0.05‰ and 0.26 ± 0.05‰ (95% confidence interval, 2σ and relative to international standard IRMM-14), respectively. Mass balance and error propagation calculation showed Fe isotope fractionation in binding and titration experiments between the > 30 kDa and < 30 kDa fractions for -0.35 ± 0.05‰ and -0.27 ± 0.05‰, respectively. This Fe isotope fractionation could be due to the complexation of Fe by OM in the < 30 kDa fractions. At pH 2, the OM-free experiment, the < 30 kDa fraction showed Fe isotope ratio δ 56 Fe = 0.75 ± 0.03‰ with an enrichment in heavy Fe isotopes of δ 56 Fe' = 0.14 ± 0.04‰ relative the total Fe pool (δ 56 Fe' is δ 56 Fe value which was corrected by δ 56 Fe of total fraction). This enrichment in heavy Fe isotopes induced an isotopic fractionation factor of -0.87 ± 0.26‰ between the > 30 kDa and < 30 kDa fractions produced by the complexation between the heavy Fe isotopes and OH -ligands in the < 30 kDa fraction. Natural Fe-OM associations were further investigated through oxidation experiments of a reduced wetland soil solution. The oxidized soil solution was (ultra)filtered at 5 µm, 3 µm, 0.2 µm, 30 kDa and 5 kDa. The highest δ 56 Fe was obtained in the smallest size fraction, i.e. < 5 kDa fraction, yielding a negative isotopic fractionation Δ 56 Fe >5kDa -<5kDa = -0.23 ± 0.08‰ suggesting that Fe heavy isotopes are preferentially bound to small humic OM molecules in the form of Fe monomers or small clusters. This study highlights the importance of organic matter for metals' isotopic systems.
The venting at the northern Peru convergent margin, unlike at other margins, has produced large b... more The venting at the northern Peru convergent margin, unlike at other margins, has produced large barite deposits, which have not been observed outside the vents. The 87 Srf6Sr isotopic ratios of the fluids are more radiogenic than seawater. To explain these elevated values, we propose either the influence of a fluid characterized by a more radiogenic signature originating from the continent, or a reaction between seawater and the underlying continental metamorphic basement. The presence of this nonlocal radiogenic component is marked more strongly on the 87 Sr/" 6 Sr ratios measured in the barite deposits. We assume that the fluid sampled at the venting site and the fluid responsible for the barite deposit sampled at the same site originated from the same source, i.e., the Paleozoic metamorphic basement of the Andean continental margin.
Although the use of iron oxide nanoparticles (IONPs) has high potential in remediation and agricu... more Although the use of iron oxide nanoparticles (IONPs) has high potential in remediation and agriculture, a major hindrance to their use includes the risk of contamination of soil and water resources with underexplored effects of IONPs on biota. The fate, phytotoxicity and remediation potential of IONPs are investigated with soil column experiments using 7 nm-sized magnetite (Fe 3 O 4 ) nanoparticles (magnNPs) and sunflower (Helianthus annuus). Control soil, magnNP-containing soil (10 g magnNPs per kg soil), copper-polluted soil (500 mg Cu per kg soil) and copper-polluted soil containing magnNPs (10 g magnNPs per kg soil and 500 mg Cu per kg soil) support sunflower growth for 57 and 95 days. In magnNP-exposed plants, the occurrence of magnNPs does not affect the growth of the vegetative aerial parts and photosynthetic efficiency. Decreased lipid peroxidation indicates an enhanced antioxidant enzymatic response of magnNP-exposed plants. In plants grown in Cu-and magnNP-Cu-soils, the physiological and biochemical impacts of excess copper are clearly identified, resulting in growth retardation, decreased pigment contents and photosynthetic efficiency, and increased lipid peroxidation and peroxidase (POD) activities. Based on magnetic susceptibility, a higher amount of magnNPs is detected after 57 days in the roots of magnNP-exposed plants (1400 mg kg À1 ) than in the roots of magnNP-Cu-exposed plants (920 mg kg À1 ). In the latter, magnNP internalization is likely hampered because of the plants' physiological responses to Cu toxicity. At the working Cu and magnNP concentrations, magnNPs neither decrease Cu accumulation in the plant tissues nor alleviate the overall growth retardation of sunflowers and certain phytotoxic effects induced by excess Cu. However, this study highlights several positive environmental aspects relative to magnNP use, including the harmless effects of magnNPs on sunflowers (1% magnNPs in soil) and the ability of magnNPs to influence Cu mobility in the soil (which could be even more pronounced at lower Cu concentration).
Oxygen and strontium isotopic composition of sedimentary pore fluids obtained by drilling at the ... more Oxygen and strontium isotopic composition of sedimentary pore fluids obtained by drilling at the Chile Triple Junction have been used to obtain information on the diagenesis and transport mechanisms of fluids. Samples were collected from three sites located on an east-west transect of the pre-collision zone (Sites 859, 860, and 861) and from Site 863 located at the base of the trench slope at the point where the Chile Ridge is being subducted. Closer to the toe of the wedge (Sites 859 and 860), non-steady state depth profiles were obtained, whereas linear chemical and isotopic profiles at the upper trench slope (Site 861) are indicative of diffusion of solutes at this site. The nature of fluids from the sites located in the transect prior to ridge subduction is quite different from that observed after ridge subduction (Site 863). Even though in all cases oxygen and strontium isotopic fingerprint indicates alteration of volcanogenic sequences to form authigenic clay mineral, the reactions that modified the chemical composition at Sites 859, 860, and 861 occurred at low temperatures, while high temperature reactions are responsible for the isotopic composition of the fluids at Site 863. At this later site, the 18 O of pore fluids show values as high as 0.7‰ SMOW and a 87 Sr/ 8 °Sr ratio as low as 0.706 in the interval from 400 to 500 mbsf, a sediment section characterized by the presence of a cementation front and steep chemical gradients in the pore fluids. These data suggest that the basal fluids (>400 mbsf) at this site are likely to have been influenced by the hydrothermal reactions occurring at high temperatures.
Potentiometric acid-base titration curves collected on humic (nano)particles as a 16 function of ... more Potentiometric acid-base titration curves collected on humic (nano)particles as a 16 function of pH and salt concentration reflect the electrostatics of the particles and the amount 17 of chemical charges (Q) they carry. In turn, interpretation of titration data helps quantifying 18 their reactivity towards metals provided that both intrinsic chemical and non-specific 19 electrostatic contributions to proton binding are correctly unraveled. Establishing a titration 20 curve requires several steps, i.e. blank subtraction, relative curve positioning with respect to 21 electrolyte concentration, and absolute curve positioning achieved by estimation of particle 22 charge Q 0 at low pH. Failure in establishing properly each step may lead to misevaluation of 23 nanoparticle charging behavior. Here, we report (i) a simple procedure to measure and position 24 titration curves for humic substances (HS) versus salt concentration, and (ii) an original 25 approach for absolute curve positioning upon exploitation of proton affinity spectra. The latter 26 do not depend on Q 0 and they thus constrain titration data analysis using Soft Poisson 27 Boltzmann-based Titration (SPBT) formalism for nanoparticles in the thick electric double 28 layer regime. We illustrate the benefits of our approach by analyzing titration measurements 29 for a large range of humic nanoparticles and by comparing the outcome with results from 30 literature. Synopsis. This article provides a simple and accurate approach to determine the acid-base 33 properties and electrostatic features of humic nanoparticles.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The behaviour of nanoparticles in aqueous solution resulting from a complex balancing between pH,... more The behaviour of nanoparticles in aqueous solution resulting from a complex balancing between pH, surficial and intrinsic properties of nanoparticles.
Colloids have been recognized as key vectors of pollutants in aqueous environment. Amongst them, ... more Colloids have been recognized as key vectors of pollutants in aqueous environment. Amongst them, those formed by iron (Fe) and organic matter (OM) are of major importance due to their ubiquity in the surface environment and strong affinity for metals. In the recent years, Fe stable isotopes have been increasingly used to elucidate the sources and biogeochemical cycling of Fe in Earth's surface environments. In this study, we aim to elucidate (i) the possible Fe isotopic signature resulting from the Fe/OM colloid formation and (ii) the mechanisms involved in the development of such isotopic signature. For this purpose, Fe-OM associations were synthesized through binding and titration experiments. Various pH levels were used in order to study the isotope behavior of Fe occurring as free species at pH 1, as Fe-OM complexes at pH 2 and as mixed Fe-oxyhydroxide/OM nanoaggregates or particles at pH 6.5. Organic matter-free, Fe-free and OM membrane-deposition experiments were also performed. These suspensions were (ultra)filtered at 0.2 µm, 30 kDa and 5 kDa to evidence the possible Fe isotope fractionation between fractions. This protocol allowed also testing the potential of (ultra)filtration techniques to generate isotope fractionation. The results provided evidence that abiotic Fe precipitation, (ultra)filtration techniques and OM deposition were not able to produce significant Fe isotope fractionation under the experimental conditions. However, at circum-neutral pH, the Fe-OM binding and titration experiments displayed a significant enrichment of heavy Fe isotopes in the < 30 kDa fractions relative to the total Fe pool δ 56 Fe = 0.35 ± 0.05‰ and 0.26 ± 0.05‰ (95% confidence interval, 2σ and relative to international standard IRMM-14), respectively. Mass balance and error propagation calculation showed Fe isotope fractionation in binding and titration experiments between the > 30 kDa and < 30 kDa fractions for -0.35 ± 0.05‰ and -0.27 ± 0.05‰, respectively. This Fe isotope fractionation could be due to the complexation of Fe by OM in the < 30 kDa fractions. At pH 2, the OM-free experiment, the < 30 kDa fraction showed Fe isotope ratio δ 56 Fe = 0.75 ± 0.03‰ with an enrichment in heavy Fe isotopes of δ 56 Fe' = 0.14 ± 0.04‰ relative the total Fe pool (δ 56 Fe' is δ 56 Fe value which was corrected by δ 56 Fe of total fraction). This enrichment in heavy Fe isotopes induced an isotopic fractionation factor of -0.87 ± 0.26‰ between the > 30 kDa and < 30 kDa fractions produced by the complexation between the heavy Fe isotopes and OH -ligands in the < 30 kDa fraction. Natural Fe-OM associations were further investigated through oxidation experiments of a reduced wetland soil solution. The oxidized soil solution was (ultra)filtered at 5 µm, 3 µm, 0.2 µm, 30 kDa and 5 kDa. The highest δ 56 Fe was obtained in the smallest size fraction, i.e. < 5 kDa fraction, yielding a negative isotopic fractionation Δ 56 Fe >5kDa -<5kDa = -0.23 ± 0.08‰ suggesting that Fe heavy isotopes are preferentially bound to small humic OM molecules in the form of Fe monomers or small clusters. This study highlights the importance of organic matter for metals' isotopic systems.
The venting at the northern Peru convergent margin, unlike at other margins, has produced large b... more The venting at the northern Peru convergent margin, unlike at other margins, has produced large barite deposits, which have not been observed outside the vents. The 87 Srf6Sr isotopic ratios of the fluids are more radiogenic than seawater. To explain these elevated values, we propose either the influence of a fluid characterized by a more radiogenic signature originating from the continent, or a reaction between seawater and the underlying continental metamorphic basement. The presence of this nonlocal radiogenic component is marked more strongly on the 87 Sr/" 6 Sr ratios measured in the barite deposits. We assume that the fluid sampled at the venting site and the fluid responsible for the barite deposit sampled at the same site originated from the same source, i.e., the Paleozoic metamorphic basement of the Andean continental margin.
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