Effect of liming on polycyclic aromatic hydrocarbons leaching from hydrocarbon-contaminated tectogenic industriosol.

Soil stabilization/solidification is commonly employed remediation method for contaminated soils. Until now, limited attention has been given to the application of quicklime in polycyclic aromatic hydrocarbons (PAHs) contaminated soil. We treated a tectogenic industriosol spiked with 50 mg kg-1 of four PAHs (12.5 mg kg-1 each of fluorene (FLU), phenanthrene (PHE), fluoranthene (FLT) and pyrene (PYR)) using three different liming agents at 1% (w:w): quicklime (CaO), hydrated lime (Ca(OH)2) and carbonate calcium (CaCO3). All treated samples were leached in water at a solid-liquid ratio of 10, with subsequent analysis of leached soil and leachates for PAHs content. Results revealed that the addition of liming agents led to a reduction in FLU and PHE concentrations in treated soil by 6.81 ± 2.47% and 28.88 ± 4.18%, respectively, compared to a not-treated sol. However, no significant impact was observed on the 4-cycles PAHs (FLT and PYR). The addition of liming agents also significantly decreased the amount of PAHs in the leachate, by 100% for FLU and PHE, and by 74.9 ± 17.5% and 72.3 ± 34.8%, for FLT and PYR, respectively, compared to not limed soil. Among the liming agents, quicklime was the most effective in reducing the amount of 4 cycles PAHs in the leachate. Various mechanisms, such as encapsulation, volatilization and oxidation could contribute to this observed reduction. Quicklime treatment at a concentration of 1% w:w in PAHs-contaminated soil emerges as a promising technique to effectively reduce PAHs concentration in soils and mitigate PAHs mobility through leaching. This study also sheds light on the possibility to limit CO2 emissions and resources exploitation to assure the remediation process, thereby enhancing its overall environmental sustainability.

Does anoxia promote the mobilization of P-bearing colloids from dam reservoir sediment?

In the context of a reservoir, the anoxia that develops in the bottom sediment induces the release of phosphorus (P) into the overlying water, thus supporting eutrophication. Most studies focusing on P dynamic in an aquatic environment fail to consider the "truly" dissolved and colloidal fractions, hence the colloidal P has gone largely unexplored. The aim of this study was to investigate the release of sedimentary P under oscillating aerobic, anoxic and aerobic conditions, in taking into account the colloidal (10 kDa-1 µm) and truly dissolved (< 10 kDa) fractions. Laboratory incubations of wet sediment originating from a dam reservoir were performed over 63 days, consisting of 25 days of aerobic conditioning (lasting 2 periods) and 38 days of anoxia. Results showed that oxic conditions induced a very limited release of phosphorus, both in truly dissolved and colloidal forms. In turn, the development of anoxic conditions caused a large release of P, mainly in the colloidal fraction, representing about 90 % of the total water-mobilizable P (PWM < 1 µm). The initial release of truly dissolved P during the anoxic stage gradually diminished over time, possibly due to the formation of secondary minerals or re-adsorption processes. Approximately half of the PWM released during anoxia persisted under subsequent oxic conditions and consisted solely of colloidal P. The dynamics of PWM were primarily influenced by two main factors: (i) the reductive dissolution of iron, which released both dissolved and colloidal P, and (ii) the release of indigenous organic matter, which impacted the stability of the released colloids through bridging mechanisms.

Effect of extraction methods on mobilizable colloids and associated phosphorus from reservoir sediment.

Mobilizable colloids from reservoir sediment contain nutrients and contaminants, thus may affect water quality once being released. A major obstacle to evaluate the quantity and quality of mobilizable colloids in natural system is the using of appropriate method for colloid extraction from sediment and their separation from dissolved and particulate phases. This work evaluates the role of different extraction methods (agitation, sonication at sediment pH, and sonication at alkaline pH) on the characteristics (mass, size, shape and composition) of water-mobilizable colloids from sediment of Champsanglard dam reservoir (France). Attention has been paid to phosphorus (P), an important element in controlling eutrophication. Recovered colloids were highly affected on both quantity and quality according to the different applied protocols. The less aggressive agitation liberated low-energy water-dispersible colloids without physical damage and with less modification in colloidal chemical composition and shape, whereas sonication released 10-20 times higher colloid quantity but in lower size, due to physically disruption of fragile sediment structure or aggregated/chained colloids. In contrast, alkaline pH intensified colloid release by fortified repulsive forces between colloids and dissolution of organic coat. Concerning phosphorus, competition with hydroxide ions for sorption site or dissolution of phosphate minerals in alkaline pH caused release of dissolved P to solution and decrease of P content in recovered colloids. A special care should be paid to method selection according to the aim of the study and when comparing data from experiments conducted with different colloid extraction methods.

Correction to: Sedimentary phosphorus accumulation and distribution in the continuum of three cascade dams (Creuse River, France).

The missing Electronic Supplementary Material in the original paper is included in this paper.

Sedimentary phosphorus accumulation and distribution in the continuum of three cascade dams (Creuse River, France).

Dam construction leads to both sediment discontinuities and the creation of internal phosphorus (P) loads in reservoirs capable of supporting eutrophication. Today, majority of large rivers are dammed and numerous of these infrastructures are constructed in cascade. However, few studies focus on the cumulative effect of the presence of dam on sediment P mobility and bioavailability in downstream reservoirs and rivers parts or throughout the continuum. The influence of three cascade dams has been studied herein on the sedimentary P distribution in surface bed sediments along a 17-km fluvial continuum of the Creuse River (Massif Central, France). The sediments (17 samples) were analyzed for their physical (grain size, specific surface area) and chemical (pH, contents of P, Fe, Al, Ca, Mn, organic matter (OM), and P fractionation) characteristics. Results indicated an amount of P 3 to 7 times higher in dam sediments (1.59 ± 0.51 mgP/g DW) than in free-flowing river sections (0.27 ± 0.11 mgP/g DW). Unexpectedly, sedimentary TP content did not decrease from the first to the third reservoir. The spatial variations of sediment characteristics between river and reservoirs were correlated with the retention of particles sized under 200 µm within the reservoirs. In reservoir sediment, P was mainly associated with the ascorbate fraction (P associated with the redox-sensitive Fe/Mn precipitates). Inside each dam reservoir, longitudinal variations of the sedimentary P distribution were mainly due to the increase of amorphous Fe precipitate content accumulated in fine sediments toward the dam, as characterized by a low Fe-Asc/P-Asc molar ratio. In the river sections, P distribution (mainly associated with HCl and ascorbate fractions) was not significantly influenced by cascade dams.

Phosphorus mobility in dam reservoir affected by redox oscillations: An experimental study.

The internal sedimentary phosphorus (P) load of aquatic systems is able to support eutrophication, especially in dam-reservoir systems where sedimentary P stock is high and where temporary anaerobic conditions occur. The aim of this study therefore is to examine the response of sedimentary P exposed to redox oscillations. Surface sediments collected in the Champsanglard dam-reservoir (on the Creuse River, France) were subjected to two aerobic phases (10 and 12 days) alternated with two anaerobic periods (21 and 27 days) through batch incubations. The studied sediment contained 77 ± 3 µmol/g DW of P, mainly associated with the ascorbate fraction (amorphous Fe/Mn oxyhydroxides). The used sediment was rich in organic matter (OM) (21% ± 1%) with primarily allochthone signature. Our results showed that redox oscillations enhance dissolved inorganic phosphorus release at sediment/water interface. During the first anaerobic stage, the P release was mainly controlled by the dissolution/precipitation of iron minerals. The more pronounced increase of P release during the second anaerobic stage (44%) was due to various mechanisms related to the change in quality of dissolved organic matter (DOM), namely a higher SUVA254 and humification indices. The release of more refractory DOM (rDOM) served to lower the microbial metabolism activity, possibly favored iron oxyhydroxide aggregation and thus limiting iron reduction. In addition, rDOM is able to compete for mineral P sorption sites, leading to a greater P release. In reservoir with predominant allochthone OM input, the release of more aromatic DOM therefore plays an important role in P mobility.

Weathering of historical copper slags in dynamic experimental system with rhizosphere-like organic acids.

This study was undertaken to simulate experimentally the weathering of slags disposed nearby soil rhizosphere. The aim of the research was to differentiate the effect of pH and organics on slags dissolution as well as to indicate weathering sequence of phase components. The studied slags are mainly composed of Fe (34.5 wt%) and Si (17.9 wt%) and contain up to 3761 mg kg-1 of Cu and 3628 mg kg-1 of Zn. The main identified phases are fayalite and glass, whereas sulfides and metallic Cu are volumetrically minor. A 30 days long slag weathering experiment was carried out with artificial root exudates (43.7 mM) and demineralized water at initial pH = 3.5 and pH = 6.7. The highest metal release (up to 10.9% of Zn and 4.6% of Cu) was observed in ARE solution at initial pH 3.5. Dissolution of sulfides and fayalite was mainly driven by pH. Artificial root exudates enhance glass dissolution as compared to demineralized water regardless of initially fixed pH. Based on this study following weathering sequences are delineated: i) under ARE 3.5 conditions: silicates > glass > sulfides, ii) under DW 3.5 conditions: sulfides > silicates > glass, iii) under near-neutral conditions: sulfides > glass > silicates.

Key role of the sorption process in alteration of metal and metalloid quantification by fouling development on DGT passive samplers.

The DGT technique (diffusive gradients in thin films) is widely used for passive sampling of labile trace metals and metalloids in natural waters. Although development of fouling on the protective membranes is frequently observed, its effect on DGT sampling has been barely investigated. This study evaluates the influence of fouling on sampling of trace cationic metals Cd(II), Cu(II), Ni(II) and Pb(II) and oxyanions As(V), Cr(VI), Sb(V) and Se(VI). Fouling was developed in situ on polycarbonate membranes in four diverse natural freshwater environments and sampling alteration was assessed in controlled laboratory experiments. Accumulation of oxyanions and Ni was unaltered in the presence of fouling whereas significant alteration occurred in sampling of Cd, Cu and Pb (at pH ∼5.4). Characterization of the fouled membranes highlighted the intervention of sorption phenomenon as sampling alteration was systematically observed alongside element sorption onto fouled membrane. A preliminary flowchart for identifying potentially biased quantifications linked to fouling development during in situ DGT deployment in natural waters is proposed.

Metal mobilization from metallurgical wastes by soil organic acids.

Three types of Cu-slags differing in chemical and mineralogical composition (historical, shaft furnace, and granulated slags) and a matte from a lead recovery process were studied with respect to their susceptibility to release Cu, Zn and Pb upon exposure to organic acids commonly encountered in soil environments. Leaching experiments (24-960 h) were conducted with: i) humic acid (20 mg/L) at pH t0 = 4.4, ii) fulvic acid (20 mg/L) at pH t0 = 4.4, iii) an artificial root exudates (ARE) (17.4 g/L) solution at pH t0 = 4.4, iv) ARE solution at pH t0 = 2.9 and v) ultrapure water (pH t0 = 5.6). The results demonstrated that the ARE contribute the most to the mobilization of metals from all the wastes analyzed, regardless of the initial pH of the solution. For example, up to 14%, 30%, 24% and 5% of Cu is released within 960 h from historical, shaft furnace, granulated slags and lead matte, respectively, when exposed to the artificial root exudates solution (pH 2.9). Humic and fulvic acids were found to have a higher impact on granulated and shaft furnace slags as compared to the ultrapure water control and increased the release of metals by a factor up to 37.5 (Pb) and 20.5 (Cu) for granulated and shaft furnace slags, respectively. Humic and fulvic acids amplified the mobilization of metals by a maximal factor of 13.6 (Pb) and 12.1 (Pb) for historical slag and lead matte, respectively. The studied organic compounds contributed to different release rates of metallic contaminants from individual metallurgical wastes under the conditions tested.

Effects of NO3 (-) and PO4 (3-) on the release of geogenic arsenic and antimony in agricultural wetland soil: a field and laboratory approach.

The dynamics of arsenic (As) and antimony (Sb) in wetland soil periodically submitted to agricultural pressure as well as the impact of soil enrichment with NO3 (-) (50 mg L(-1)) and PO4 (3-) (20 mg L(-1)) on As and Sb release were evaluated at both field and laboratory scales. The results showed that As and Sb exhibited different temporal behaviors, depending on the study scale. At field scale, As release (up to 93 µg L(-1)) occurred under Fe-reducing conditions, whereas Sb release was favored under oxidizing conditions (up to 5 µg L(-1)) and particularity when dissolved organic carbon (DOC) increased in soil pore water (up to 92.8 mg L(-1)). At laboratory scale, As and Sb release was much higher under reducing conditions (up to 138 and 1 µg L(-1), respectively) compared to oxic conditions (up to 6 and 0.5 µg L(-1), respectively) and was enhanced by NO3 (-) and PO4 (3-) addition (increased by a factor of 2.3 for As and 1.6 for Sb). The higher release of As and Sb in the enriched reduced soil compared to the non-enriched soil was probably induced by the combined effect of PO4 (3-) and HCO3 (-) which compete for the same binding sites of soil surfaces. Modeling results using Visual Minteq were in accordance with experimental results regarding As but failed in simulating the effects of PO4 (3-) and HCO3 (-) on Sb release.

Bio-dissolution of colloidal-size clay minerals entrapped in microporous silica gels.

Four colloidal-size fractions of strongly anisotropic particles of nontronite (NAu-2) having different ratios of basal to edge surfaces were incubated in the presence of heterotrophic soil bacteria to evaluate how changes in mineral surface reactivity influence microbial dissolution rate of minerals. To avoid any particle aggregation, which could change the reactive surface area available for dissolution, NAu-2 particles were immobilized in a biocompatible TEOS-derived silica matrix. The resulting hybrid silica gels support bacterial growth with NAu-2 as the sole source of Fe and Mg. Upon incubation of the hybrid material with bacteria, between 0.3% and 7.5% of the total Fe included in the mineral lattice was released with a concomitant pH decrease. For a given pH value, the amount of released Fe varied between strains and was two to twelve-fold higher than under abiotic conditions. This indicates that complexing agents produced by bacteria play an important role in the dissolution process. However, in contrast with proton-promoted NAu-2 dissolution (abiotic incubations) that was negatively correlated with particle size, bacterial-enhanced dissolution was constant for all size fractions used. We conclude that bio-dissolution of nontronite particles under acidic conditions seems to be controlled by bacterial metabolism rather than by the surface reactivity of mineral.

Dissolution of anisotropic colloidal mineral particles: evidence for basal surface reactivity of nontronite.

Anisotropic textural and crystallographic properties of phyllosilicate particles often influence the mineral weathering rate. The purpose of this study was to investigate how the changes in mineral surfaces (basal vs. edge) as a result of changes in crystal size control the dissolution of the mineral. Different nano-size fractions of Na-exchanged nontronites (NAu2 and NAu1) were immobilized in a silica gel and then incubated under acidic conditions using HNO(3) at 28 degrees C for 5 days. For each sample, the dissolution behavior was analyzed by measuring the amount of iron released from the mineral lattice. The results showed that for a given pH, a decrease in particle size significantly increased NAu2 and NAu1 dissolution. At pH 1.5, 7.2% of the total iron of the highest size sample of NAu2 was released in solution whereas this proportion increased up to 25% for the smallest size fraction. The percentage of total iron extracted from NAu1 at the same pH (1.5) was less important: 3.5% and 6.5% for higher and smaller size fractions, respectively. The observed increase in dissolution was not directly correlated to the increase in the amount of edge faces, suggesting that all mineral surfaces contributed to mineral dissolution. In the present case this may be related to the fact that 8% and 2% of total iron of NAu2 and NAu1, respectively, are located in the tetrahedral sheet. In conclusion, the basal surface of nontronites plays an important role in the weathering process.

Is trace metal release in wetland soils controlled by organic matter mobility or Fe-oxyhydroxides reduction?

Aerobic and anaerobic incubation experiments on a wetland soil samples were used to assess the respective roles of organic matter (OM) release, Fe-oxyhydroxides reduction and redox/speciation changes on trace metal mobility during soil reduction. Significant amounts of Cu, Cr, Co, Ni, Pb, U, Th and Rare Earth Elements (REE) were released during anaerobic incubation, and were accompanied by strong Fe(II) and dissolved organic matter (DOM) release. Aerobic incubation at pH 7 also resulted in significant trace metal and DOM release, suggesting that Fe-oxyhydroxide reduction is not the sole mechanism controlling trace metal mobility during soil reduction. Using these results and redox/speciation modeling, four types of trace metal behavior were identified: (i) metals bound to organic matter (OM) and released by DOM release (REE); (ii) metals bound to both OM and Fe-oxyhydroxides, and released by the combined effect of DOM release and Fe(III) reduction (Pb and Ni); (iii) metals bound solely to soil Fe-oxyhydroxides and released by its reductive dissolution (Co); and (iv) metals for which release mechanisms are unclear because their behavior upon reduction is affected by changes in redox state and/or solution speciation (Cu, Cr, U and Th). Even though the process of soil Fe-oxyhydroxide reduction is important in controlling metal mobility in wetland soils, the present study showed that the dominant mechanism for this process is OM release. Thus, OM should be systematically monitored in experimental studies dedicated to understand trace metal mobility in wetland soils. Due to the fact that the process of OM release is mainly controlled by pH variations, the pH is a more crucial parameter than Eh for metal mobility in wetland soils.