Al Oxyhydroxides Research Articles

XANES spectroscopy proofs pH‐dependent P sorption partitioning to Fe oxyhydroxides versus montmorillonite in acidic soils

AbstractBackgroundFe and Al oxyhydroxides are well‐known phosphorus (P)‐retaining minerals in soils. Little information is available regarding the relevance of clay minerals for the sorption of P in mixed oxyhydroxide–clay mineral systems and pH effects on P sorption partitioning.Aims and MethodsWe wanted to investigate pH effects on P sorption partitioning between Fe oxyhydroxides and high‐activity clay minerals in mixed‐mineral systems. We quantified the relative contribution of ferrihydrite or goethite versus Al‐saturated montmorillonite (Al‐MT) to the retention of orthophosphate (oPO4) and inositol hexakisphosphate (IHP) at different pH values (3–6). We combined the analysis of P solution concentration changes with the quantification of P bound to Fe(III) versus Al in the Fe oxyhydroxide/Al‐MT mixtures by X‐ray absorption near‐edge structure (XANES) spectroscopy.ResultsOrthophosphate was preferentially retained by ferrihydrite, compared to Al‐MT at pH 3–6. The opposite was observed for goethite at low P solution concentrations. The contribution of Al‐MT versus Fe oxyhydroxides to oPO4 retention increased with pH. This is attributed to a speciation change of clay‐adsorbed Al from monomeric Al3+ to polynuclear Al hydroxy species. IHP was predominantly retained by Al‐MT rather than ferrihydrite at pH 3–6, probably by the formation of adsorbed and surface‐precipitated Al phytate complexes.ConclusionsSynchrotron‐based XANES spectroscopy allows for quantifying P adsorbed to co‐existing pedogenic Fe(III) oxyhydroxides versus Al‐MT in mixed‐mineral systems. Soil P retention partitioning to these minerals depends on (1) dominating P form (oPO4, IHP), (2) relative abundance of high‐activity clay minerals, short‐range ordered and crystalline Fe oxyhydroxides, and (3) solution pH.

Potential for high-grade recovery of rare earth elements and cobalt from acid mine drainage via adsorption to precipitated manganese (IV) oxides

High demand for rare earth elements (REEs) has increased interest in their recovery from unconventional sources, such as acid mine drainage (AMD). AMD contains elevated concentrations of Mn, Fe, and Al, which precipitate as (oxy)hydroxide minerals as pH is raised. These precipitates can remove cations including REEs and Co from solution via sorption and/or coprecipitation. In this study we developed a method to recover these critical minerals by sorption to MnO2, precipitated by oxidation of in situ Mn (II) with added KMnO4 at acidic pH. MnO2 solids were prepared with varying concentrations of KMnO4, SO42−, and Cl−, to elucidate the effects of excess KMnO4, SO42− concentration, and ionic strength on adsorption. When using a stoichiometric ratio of Mn (II) and KMnO4, 100% removal of REEs and Co occurred at approximately pH 3.5, nearly 2 pH units lower than was observed by sorption to Fe and Al hydroxysulfates. When using excess KMnO4 nearly 100% removal of REEs and Co was accomplished at approximately pH 2, although SO42− was found to inhibit REE sorption. From these results, we developed a two-stage process for recovery of REEs from AMD; a preliminary pH adjustment to remove Fe and Al hydroxy-sulfates, followed by adding KMnO4, precipitating MnO2, enabling recovery of REEs and Co. We tested this process in a representative synthetic AMD, achieving a grade of 6.16 mg REEs per g of solid, which is 65 % of the maximum possible grade based on solution composition. Fractionation of REEs was observed, with light REEs (LREEs) preferentially sorbed to MnO2 relative to both medium REEs (MREEs) and heavy REEs (HREEs). In contrast, preferential sorption of HREEs was observed for sorption to Fe and Al oxyhydroxides at all pH ranges. These results suggest the mechanisms of REE sorption differ among the solids and warrant further study.

Soil Abandonment as a Trigger for Changes in Zn Fractionation in Afforested Former Vineyard Acidic Soils

Zinc is an essential element for plant nutrition, but it may cause toxicity depending on its bioavailability and potential transformation in soil. In vineyard soils, high concentrations of Zn are usually found, mainly due to agricultural practices. However, a great abandonment of vineyards has recently occurred, leading to changes in the total and bioavailable Zn concentrations, as well as Zn fractionation. We analyzed Zn concentrations (total, ZnT, and bioavailable, ZnED) and fractionation in the soil of three paired sites (PM, PT, and AR) up to depths of 50 cm in active and adjacent abandoned vineyards that were already transformed into forests. The ZnT averaged at 210 mg kg−1 among all studied vineyards. The results showed changes in the vertical pattern ZnT concentrations after vineyard abandonment at the PM and PT sites, while at the AR site, no great variation occurred. The ZnED (mean values = 7 mg kg−1) decreased after abandonment at PM and AR in the uppermost surface layers, while it increased in the top 10 cm at the PT site, reaching up to 60 mg kg−1. Regarding Zn fractionation in active vineyards, the residual fraction (ZnR) was the most abundant, followed by Zn bound to crystalline Fe and Al oxy-hydroxides (ZnC) and Zn bound to soil organic matter (ZnOM). After abandonment, the ZnR slightly increased and the ZnC slightly decreased at the PM and AR sites at all depths, while the ZnOM showed a noticeable variation in the uppermost 10 cm of the PT site. These results suggest that the soil organic matter that is provided during afforestation may play an important role in Zn fractionation and mobilization, depending on its humification degree and chemical stability. Zn mobilization could result in a positive nutrient supply for plants, but caution must be taken, since an excess of Zn could cause toxicity in long-term abandoned vineyards.

PH: A core node of interaction networks among soil organo-mineral fractions

Mineral-associated organic matter (MAOM) is the largest soil organic carbon (OC) pool with the longest turnover. MAOM is expected to have relatively little sensitivity to climate change due to mineral protection, but its persistence involves several organo-mineral fractions. The uncertainty in the response of specific organo-mineral fractions to climate change hampers the reliability of predictions of MAOM preservation in the future. Here, we applied a sequential chemical fractionation method integrated with network analysis to investigate MAOM stabilization mechanisms across five alpine ecosystems: alpine desert, alpine steppe, alpine meadow, alpine wetland, and alpine forest. Hierarchical cluster analysis revealed grouping of seven extractable OM fractions in MAOM into three OM clusters: a cluster with weak bondings consisting of water-soluble OM (WSOM) and weakly adsorbed fractions (2.1–21.3% of total OC); a cluster with metal-bound complexes comprising Ca-OM complexes and Fe/Al-OM complexes (3.8–12.2% of total OC); and a cluster with strong bonding composed of Al oxyhydroxides, carbonates and Fe oxyhydroxides (12.2–33.5% of total OC). The relative percentages of OM from soils of the five ecosystems in the three clusters exhibited distinct pH dependence patterns. With the increase in pH, the cluster with weak bondings decreased, and that with strong bondings increased, while the one with metal-bound complexes showed a maximum at weakly acidic pH. Organo-mineral fractions and metal cations in MAOM constructed a complex network with pH as the central node. Results suggest that precipitation does not only alter vegetation type and microbial biomass but also regulate soil pH, which is balanced by specific metal cations, thus resulting in particular pH preference of specific OM clusters. These findings demonstrate that soil pH plays a central role in unveiling MAOM dynamics and can serve as a good predictor of soil organo-mineral fractions across alpine ecosystems.

Occurrence forms and environmental characteristics of phosphorus in water column and sediment of urban waterbodies replenished by reclaimed water

To illustrate the evolution process, environmental feature and phytoremediation effect of phosphorus (P) in waterbodies with long-term replenishment by reclaimed water (RW), an urban waterbody using RW as the sole supply was selected as a case study. The concentration and distribution of soluble reactive phosphate (SRP), dissolved organic P (DOP) and particulate P (PP) in water column, as well as organic P (OP), inorganic P (IP), exchangeable P (Ex-P), BD-P (redox-sensitive P), NaOH-P (P bound to Fe and Al oxyhydroxides) and HCl-P (P bound to Ca) in sediment were investigated. Results showed that the seasonal average concentrations of total phosphorus (TPw) in water column ranged from 0.048 to 0.130 mg∙L−1, with the highest in summer and the lowest in winter. P in water column was predominantly present in dissolved state, with the similar proportions of SRP and DOP. SRP decreased apparently in midstream, where the phytoremediation was applied extensively. PP content obviously increased in non-phytoremediation area in downstream, due to visitor activity and sediment resuspension. Total phosphorus (TPs) in sediments was between 352.9 and 1331.3 mg∙kg−1, with average 365.7 mg∙kg−1 of IP and 382.8 mg∙kg−1 of OP. Among IP, HCl-P had the highest proportion, followed by BD-P, NaOH-P and Ex-P. OP was significantly higher in phytoremediation areas than that in non-phytoremediation areas. Coverage of aquatic plants was positively correlated with TP, OP, BAP, while it was negatively correlated with BD-P. Hydrophyte stabilized and conserved active P in sediment and prevented release of active P. Moreover, hydrophyte increased NaOH-P and OP contents in sediment through regulating the abundance of phosphorus-solubilizing bacteria (PSB), such as Lentzea and Rhizobium. Four sources were identified through two multivariate statistical models. RW and runoff were the dominant sources of P accounting for 52.09 %, which mainly contributed to P in sediment especially IP.

Quantifying soil properties relevant to soil organic carbon biogeochemical cycles by infrared spectroscopy: The importance of compositional data analysis

Oxyhydroxides, soil texture and soil organic carbon (SOC) fractions are key parameters determining organic carbon cycling in soils. Standard laboratory methods to determine these soil properties are, however, time–consuming and expensive. Visible near infrared (Vis–NIR) and mid infrared (MIR) spectroscopy have been recognized as a promising alternative, but previous studies have not explicitly considered the above–mentioned soil properties as compositional data. The fractional components in compositional data are interrelated but their sum should be unity – these features should be represented in the spectral modeling process to minimize the prediction bias. In this study, two unique datasets were used to test these premises. The first one consisted of 655 samples collected from agricultural terraces and lynchets across Europe, which were scanned to acquire MIR spectra, while in the second one 4516 samples from private gardens across Flanders, Belgium were used to acquire Vis–NIR spectra. Memory–based learning models were optimized using both raw data (conventional method) and transformed data of soil properties by additive log–ratio (alr), centered log–ratio (clr), and isometric log–ratio (ilr) transformation methods. Results showed that the log–ratio transformation methods produced predictions as accurate as the conventional method, whilst also added two significant benefits: (1) they ensured the predicted fractions added up to 100% and (2) they reduced the number of samples with extreme prediction errors. We found that for 11 out of 18 investigated soil properties, the three log–ratio transformation methods provided similar model performance, whilst ilr outperformed clr for the prediction of silt and sand content of garden soils, for coarse particulate SOC (>250 µm) and microaggregate–associated SOC (250–53 µm) of terrace soils. For the remaining three properties (Al oxyhydroxides) alr outperformed ilr. Fair to excellent predictive models (RPD from 1.4 to 4.3; R2 from 0.50 to 0.95) were achieved for soil oxyhydroxides (Fe, Al, Mn) and soil texture from MIR spectra. Our approach also enabled accurate predictions of silt and sand content of garden soils using Vis–NIR spectra (RPD = 1.9; R2 = 0.72), although accuracy for clay was lower (RPD = 1.3; R2 = 0.49). This study demonstrates that combining soil infrared spectroscopy with a compositional data analysis is a promising technique that enables cost-effective and reliable quantification of soil properties relevant to SOC stability, thus offering a practical opportunity to assess the role of SOC in global C cycling.

Role of soil minerals on organic phosphorus availability and phosphorus uptake by plants

Organic phosphorus (OP) represents a significant fraction of the total P pool in soils. With the increasing use of organic resources to substitute mineral P fertilizers and the need to recover P from the soil, it is pivotal to gain insight into the interactions between various OP forms and soil minerals and their consequences on P availability. Here, we aim at elucidating the extent to which OP compounds adsorbed onto major soil minerals may be available to plants. Ryegrass (Lolium multiflorum) plants were grown in RHIZOtest devices in the presence of OP including myo-inositol hexakisphosphate (IHP), glycerophosphate (GLY), and glucose-6-phosphate (G6P) and inorganic P (IP) compounds that were previously adsorbed onto Fe and Al oxyhydroxides (goethite and gibbsite, respectively) and clay minerals (montmorillonite and kaolinite). Phosphorus availability and P uptake were then determined through rhizosphere and plant characterization. Irrespective of the type of mineral, ryegrass was able to take up about 3–18 % of adsorbed OP compounds. The magnitude of availability and uptake depended on the OP compounds and the type of soil minerals. The potential availability of OP adsorbed by different minerals was strongly mediated by mineral-OP interaction types and properties. The P uptake increased in the following order: kaolinite-OP ≪ gibbsite-OP ≤ goethite OP ≪ montmorillonite-OP. Phosphorus uptake from adsorbed OP compounds showed contrasting patterns compared to adsorbed IP and depended more on available P concentration in the rhizosphere rather than on the binding strength of OPs to the mineral surface.

Physico-chemical properties of aluminum adjuvants in vaccines: Implications for toxicological evaluation

Aluminum salts have been used as adjuvants in human vaccines since 1932. The most used adjuvants are Al oxyhydroxide (AlOOH) and Al hydroxyphosphate (AlOHPO4). Al adjuvants have different physico-chemical properties. The differences in these properties are not well documented and not considered by the Food and Drug Administration (FDA), though they can largely influence biological effects of the adjuvants which are particulate components. In this study, different physico-chemical properties including the shape, size and charge of particles have been evaluated under different conditions in three Al adjuvants containing-vaccines and two corresponding commercial adjuvants suspensions. The results showed that the two Al adjuvants have different shapes, sizes and charges but both form aggregates. In addition, a clear effect of dilution on the size of the aggregates was observed. Moreover, different sizes of Al particles were measured for both Al oxyhydroxide adjuvant alone or in the vaccine, at identical concentrations, displaying the impact of adsorbed proteins on the size of aggregates in the case of the vaccine. Taken together, this paper suggests the importance to evaluate, before any biological and especially toxicological impact study, the whole physico-chemical properties of Al particle without restricting to the sole evaluation of the injected concentration. Furthermore, any modification of these mentioned parameters during manipulation, before animal or cell exposure, should be considered. In a more global way, the fixed “safe dose” of Al adjuvants should be specific for each type of Al adjuvant independently or for a mix of the two compounds, due to their different properties.

Influence of chemical and mineralogical soil properties on the adsorption of sulfamethoxazole and diclofenac in Mediterranean soils

BackgroundThe irrigation with treated wastewaters can be a way for the introduction of organic contaminants in soils. However, their adsorption onto soils can allow a control of their bioavailability and leaching. The adsorption is influenced by properties of contaminants (water solubility, chemical structure) and soils (organic matter content, pH, mineralogy). This study aimed to investigate the effect of mineralogical composition, organic matter content and others parameters of soils on the adsorption of sulfamethoxazole (SMX) and diclofenac (DCF), two contaminants of emerging concerns (CECs), in real cases (Altamura, Sibari and Noci soils).ResultsThe isotherms data showed that the adsorption of the two CECs closely matched the Freundlich model, even if the DCF could also fit the linear one. The only exception was the adsorption of SMX on the soil of Sibari, for which Langmuir's model fitted better. In all cases, the Kd values were the highest for Altamura soil according mainly to its content of organic carbon. Positive correlations were found between Kd value of DCF and the soil organic carbon and Al oxyhydroxides content, suggesting their roles in its adsorption, while SMX showed only a slight positive correlation with the soil organic carbon content. Finally, between the two CECs studied, DCF was more adsorbed than SMX also because of the lower water solubility of the former.ConclusionsThe good interaction between DCF and soil organic carbon suggests the organic amendment of soils before the application of treated watewaters. The low adsorption of SMX onto soils suggests greater leaching of this compound which is, therefore, potentially more dangerous than DCF. For this reason, the application of a filtration system with appropriate adsorbent materials before the application of wastewater to soils should be expected.Graphical

Challenges and opportunities for drinking water treatment residuals (DWTRs) in metal-rich areas: an integrated approach.

The physicochemistry and production rate of drinking water treatment residuals (DWTRs) depends on the raw water composition and the plant operational parameters. DWTRs usually contain Fe and/or Al oxyhydroxides, sand, clay, organic matter, and other compounds such as metal(oids), which are relevant in mining countries. This work proposes a simple approach to identify DWTRs reuse opportunities and threats, relevant for public policies in countries with diverse geochemical conditions. Raw water pollution indexes and compositions of DWTRs were estimated for Chile as a model case. About 23% of the raw drinking water sources had moderate or seriously contamination from high turbidity and metal(loid) pollution If the untapped reactivity of clean DWRTs was used to treat resources water in the same water company, the 73 and 64% of these companies would be able to treat water sources with As and Cu above the drinking water regulations, respectively. Integrating plant operational data and the hydrochemical characteristics of raw waters allows the prediction of DWTRs production, chemical composition, and reactivity, which is necessary to identify challenges and opportunities for DWTRs management.

Phosphorus adsorption capacity in sandy textured soils with built fertility

The specific adsorption of phosphorus in minerals from the clay fraction of the soil, such as Fe and Al oxyhydroxides, is responsible for the decrease in the availability of this element for plants. In Brazil, this condition is studied substantially in medium to very clayey textured soils, whose adsorption activity is expressive. The aim of this study was to evaluate the maximum phosphorus adsorption capacity (CMAP) in sandy-textured soils with fertility built in the Cerrado biome. Areas with representative soils were selected in the cities Luís Eduardo Magalhães (LEM / BA) and Guaraí (TO), with the following vegetation cover: a) LEM: natural vegetation and cotton; b) Guaraí: natural vegetation and soybean. Soil samples were collected in the 0-20 cm and 60-80 cm layers, in which chemical and physical analyzes were performed periodically, as well as analyzes related to phosphorus adsorption such as Prem and CMAP and PESN. Prem contents are higher in the 0-20 cm layer for the LEM region. The CMAP is not very expressive in the soils of the two studied regions, with the Guaraí soils having higher relative adsorption potential due to the higher values of the CMAP/clay ratio.

The role of iron in the rare earth elements and uranium scavenging by Fe–Al-precipitates in acid mine drainage

The scavenging of soluble metals by iron (Fe) and aluminium (Al) oxyhydroxides is a natural process that occurs in acid mine drainage (AMD). This phenomenon is relevant to the immobilization, transport, and recovery of important natural resources such as rare earth elements (REE) and uranium (U). Furthermore, understanding the players and the reactions that govern the scavenging of REE and U by Fe and Al oxyhydroxides in aqueous systems is fundamental for natural and engineering sciences and for environmental management. In this scenario, the current work investigated the role of iron in the co-precipitation of REE and U when treating effluents by pH neutralization in an AMD system located in Brazil. The research employed water sampling, co-precipitation batch experiments, sequential extraction, X-ray diffraction and 57Fe Mössbauer spectroscopy. The results revealed that the presence and the amount of Fe in the initial solution can influence the REE removal efficiency positively. The effect of the addition of Fe over the REE removal efficiency was irrelevant when the pH of the AMD was raised to values equal to 7–8. The scavenging of U was not influenced by the addition of Fe to the AMD. The sequential extraction results showed that precipitates containing higher amounts of Fe tend to be less labile. The 57Fe Mössbauer spectra revealed that the REE can occupy iron sites in the structure of the amorphous precipitates. The findings of the current study can be extrapolated to other AMD systems and contribute to the development of novel REE recovery and hydrometallurgical techniques.

The Catalytic Effect of the Heterotrophic Bacterium Virgibacillus marismortui on Basaltic Rock Dissolution Under Excess Nutrient Conditions

Biotic and abiotic batch experiments were performed in the presence of excess nutrients (N and P) and basaltic rocks in the medium under various conditions (NA, non-agitated; A, agitated). Changes in solution chemistry were monitored to characterize the influence of aerobic heterotrophic bacteria (Virgibacillus marismortui) on the dissolution rates and mechanisms of two basaltic rocks collected from King George (BAn; basaltic andesine) and Deception Island (BD, basalt), Antarctica. The presence of bacteria in the medium accelerated dissolution of basaltic rocks by a factor of 1.5 to 3 depending on both the rock composition and experimental conditions. The calculated linear element release rates in the biotic experiments (B, biotic) are enhanced in comparison with abiotic systems (A, abiotic) in the order: BD-B-NA > BD-B-A > BAn-B-NA. Unlike the abiotic reference experiments (BD-A-NA; BD-A-A, BAn-A-NA) with pH shifts of less than 0.5 units an accelerated release of Si, Ca, Mg, Fe and Al coincided with an increase in protein concentrations and a marked decrease in pH in the biotic experiments. As indicated by solution acidity, element release, trends of the reactive fluids and surface chemistry of the reacted rock samples, the catalytic effect of bacteria on mineral dissolution reactions was predominantly acidification due to bacterial metabolism. The major catalytic effect of acidification on mineral dissolution was likely suppressed by ammonification, resulting in a pH increase in the reactive fluid. The absence of secondary phases (e.g. Fe and Al oxyhydroxides) on the surface of biotically reacted rock particles and the presence of divalent cations (i.e. Ca and Mg) on the cell surfaces further show the role of the bacteria and associated organic ligands for metal-complexation reactions during basalt dissolution. This study shows that aerobic heterotrophic bacteria may play a critical role for acidity driven silicate dissolution in environments rich in nitrogenated organic compounds and may even influence the amount of Ca and Mg being released from Ca and Mg rich silicates to environments.

Experimental study of epidote dissolution rates from pH 2 to 11 and temperatures from 25 to 200 °C

The dissolution rates of Green Monster Mine epidote at temperatures of 25, 100 and 200 °C, and over the pH range 2–11, were determined from far-from equilibrium experiments performed in both batch and mixed-flow reactors. Epidote dissolution rates based on silicon release decrease with increasing pH to pH ∼ 8, then increase in response to further pH increases. The apparent relative metal release rates from epidote at chemical steady-state were found to vary with pH and temperature, in part due to secondary phase formation. At 100 and 200 °C, Al is preferentially released relative to Si at alkaline pH, but preferentially retained by the solid at 2 < pH < 8. This behaviour is interpreted to stem from the precipitation and re-dissolution of Al oxy-hydroxides such as boehmite, diaspore, and gibbsite, as observed in solids recovered after the experiments. Calcium tends to be preferentially released compared to Si and Al at acidic and near to neutral pH. Iron was found to be retained in the solid phase due to the prompt formation of secondary Fe minerals. Nevertheless, neither the dissolution of 20 wt% of the initial epidote mass nor the formation of secondary phases on the epidote surface substantially changed epidote dissolution rates. As epidote (i) is almost three times more Ca-rich than a typical basaltic glass, (ii) preferentially releases Ca at pH typical of CO2-charged water injections, and (iii) exhibits increasing dissolution rates as pH increases at alkaline conditions, it seems likely that the presence of epidote in altered basalts may be beneficial for the formation of calcite and other Ca-carbonates during mineral carbonation efforts. In addition, the relatively rapid rates of epidote dissolution at acidic conditions suggest that epidote has a significant role in the weathering of altered mafic rocks.

Transformations in aluminum oxyhydroxide under powerful short-pulse microwave radiation

Modification of a material based on Al oxyhydroxide (boehmite/γ-Al2O3) with metal Al fragments (nanoparticles, clusters) has been achieved by the treatment of the material under powerful short-pulse microwave radiation (pulse duration 20 ns, pulse repetition 25 Hz, power density 8 kW/cm2, frequency 2.85 GHz, amplitude of the electric strength component ~2.5·106 V/m). The Al oxyhydroxide was precipitated from a mixture of AlCl3 with ammonia solution and heated at 250 °C for 4 hours. The prepared sample was of predominant amorphous structure, the overall water content (adsorbed, bound, structured) amounted to 15 wt.% in average. The microwave irradiation of the samples (1-3 min) resulted in formation of Al fragments smaller than 100 nm within the solid matrix. Formation of metal Al in the irradiated samples was detected by means of thermal analysis, X-ray diffraction, and transmission electron microscopy. The average content of Al in irradiated samples amounted to ~1.5 wt.%. A rational explanation of the observed metallization effect has been suggested.

Importance of Al/Fe oxyhydroxide coating and ionic strength in perfluorooctanoic acid (PFOA) transport in saturated porous media

Understanding subsurface transport of per- and polyfluoroalkyl substances (PFASs) is of critical importance for the benign use and risk management of PFASs. As one of the most commonly found PFASs, perfluorooctanoic acid (PFOA) is used as a representative PFAS and water-saturated column experiments were conducted to investigate the effect of Al/Fe oxyhydroxide coating and ionic strength on its transport at an environmentally relevant PFOA concentration (6.8 μg L−1). Our results showed a clear increase in PFOA retardation in Al/Fe oxyhydroxide coated sand (retardation factor: Al: 1.87–5.58, Fe: 1.28–4.05) than those in uncoated sand (1.00–1.05), due to the stronger electrostatic attraction between anionic PFOA and Al/Fe oxyhydroxide coated sand surface. Notably, Al oxyhydroxide have a more profound effect on PFOA retention and retardation than Fe oxyhydroxide. Besides, higher ionic strength significantly inhabited PFOA retention and retardation in positively charged sand, and the considerable retention of PFOA (∼90%) in deionized water than those in 1.5 mM and 30.0 mM NaCl (<10%) clearly proves the role of competitive adsorption of Cl− on PFOA transport in positively charged sand. In contrast, higher ionic strength (0 mM–30 mM NaCl) slightly increased PFOA retardation in negatively charged sand, illustrating the dominance of electrostatic interaction. Our findings advance current knowledge to understand PFOA transport in natural media with different surface charge property under environmental PFOA concentrations.

Water chemistry and water quality pollution indices of heavy metals: a case study of Chahnimeh Water Reservoirs, Southeast of Iran

Chahnimeh reservoirs are the main drinking water sources for the big cities of Sistan and Baluchestan Province (Zabol, Zahak and Zahedan) and their water quality of may have a great influence on public health. Therefore, the aims of this study are to assess hydrogeochemical characteristics, and heavy metal(loid)s pollution in four Chahnimeh reservoirs using water quality pollution indices and principal component analysis. The concentrations of Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, U, and Zn in 84 water samples were measured for two periods. Hydrogeochemical analyses, Piper and Gibbs diagrams, show a change in the water type from Na–HCO3 and Na–SO4 to Na–Cl, and a bit tendency of water–rock interaction to evaporation, from September 2017 to April 2018. Based on the heavy metal pollution index, heavy metal evaluation index, and contamination index, water quality of Chahnimeh reservoirs is decreased in order: reservoirs 2 > 3 > 4 > 1. The result of statistical analysis reveals that Mo content is affected by a geogenic origin, while Se and U indicate a quasi-independent behavior within the groups reflecting contribution of both geogenic and anthropogenic sources. HCO3 plays a significant role in distribution of Se and U. Also, Fe, Mn and Al oxy-hydroxides can control concentrations of Cu, Pb and Ni. Overall the obtained results indicated that the variation of water quality in the study area was related to climatic conditions, high evaporation, water–rock interaction, different land uses, drying Hamoun Lakes and anthropogenic effects in the Hirmand watershed. The current study reveals that the use of integrated methods such as statistical methods and heavy metal pollution indices to determine the water quality is very suitable.

Soil Phosphorus Bioavailability and Recycling Increased with Stand Age in Chinese Fir Plantations

Phosphorus (P) is a limiting nutrient for plant growth in most forest ecosystems. In response to P deficiency, plants alter root exudates (organic acids, phosphatases, and protons) to increase P bioavailability in soils. However, little is known about how bioavailable P pools (soluble-P, exchangeable-P, hydrolysable-P, and ligand-P extracted by CaCl2, citric acid, enzyme mixture, and HCl solution, respectively) change with stand age, especially for plantation forests. We selected a chronosequence of second-generation Chinese fir [Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae] plantations with increasing age including 3, 8–11, 16, 20, 25, 29, and 32 years. We measured total P and four bioavailable P pools in organic (O) and mineral horizons, and rhizosphere soil, as well as root exudates in the rhizosphere, litter biomass on the forest floor, and annual P uptake. Soluble-P, exchangeable-P, and ligand-P in the O horizon increased with stand age due to litter accumulation. Exchangeable-P and ligand-P in mineral soil decreased with stand age because of the increasing annual P uptake that depleted inorganic P. Exchangeable-P and ligand-P in the rhizosphere increased with stand age because the decrease in pH and citric acid concentration led to phosphate being more strongly bound to Fe and Al oxyhydroxides. Consequently, the trees’ ability for P mobilization decreased with stand age, but the P recycling within the tree increased. Continuous mineralization of hydrolysable-P by acid phosphatase replenished inorganic P pools, especially in solution. The progressive incorporation of P in the biological cycle with increasing tree age indicates that extending rotation periods might be an appropriate measure to increase P supply.

Farmyard manure improves phosphorus use efficiency in weathered P deficient soil

Crop production is limited by low soil fertility in sub-Saharan Africa (SSA), particularly by P deficiency due to strong fixation by Fe and Al oxyhydroxides. Organic amendments are known to increase P availability in fertilizer and in such soils by different mechanisms. This study investigated the effect of adding farmyard manure (FYM) versus mineral triple super phosphate (TSP) fertilizer on P availability in different cropping systems. Field experiments were conducted in three succeeding summer seasons to compare two different upland cropping systems: a Bambara (Vigna subterranea)–rice rotation and a rice–rice system on a highly P deficient Ferralsol. Nine treatments including sole TSP at 0, 10, 20, 30 kg P ha−1 year−1, and sole FYM at 0, 10, 20, 30 kg P ha−1 year−1 (i.e. 100% FYM substitution), and combined FYM and TSP (FYM + TSP) at 20, 30 kg P ha−1 year−1 (i.e. 50% and 67% FYM substitution, respectively) were applied. Results showed that FYM treatments increased Bambara and rice grain yields compared to TSP treatment alone particularly in year three. Phosphorus uptake efficiency was higher in FYM treatments combined or not with TSP in year three of the experiment. The notable response to FYM was associated with increased agronomic efficiency resulting from additional C originating from the FYM with a low initial soil C content, (around 2%), and the effect of liming that reduced soil P sorption thereby improving P availability from FYM. Partial (67%) substitution of TSP by FYM increased grain yields of Bambara by 1.67 Mg ha−1 and of rice by 1.01 Mg ha−1 compared to TSP alone in year three at the highest P rate (30 kg P ha−1). The effect of FYM could be linked to inputs of C and nutrients from added FYM and to the indirect effect on soil physico–chemical properties including soil pH, soil moisture, soil biological activity, low P capacity sorption. This study confirms that application of FYM can help minimize rates of TSP applied in smallholder farms in SSA.

Investigation on the control of phosphate leaching by sorption and colloidal transport: Column studies and multi-surface complexation modelling

Surface complexation modelling (SCM) is a powerful tool to estimate speciation and fate of solutes in soil, provided sufficient model validation. This study aims to describe phosphate (PO4) leaching with SCM. The leachate phosphorus concentrations ([P]) of 120 unsaturated columns of contrasting agricultural soils were measured and modelled. Leachate [P] ranged 0.7–240 μM. Leachate [P] increased as the ratio of P to iron and aluminium (PAl+Fe) in acid oxalate soil extracts increased and as leachate Fe and Al concentrations ([Al + Fe]) increased. SCM was used to describe PO4 sorption to ferrihydrite (CD-MUSIC model). This yielded adequate description of leachate [P] (RMSElog10 = 0.39), but only when reactive PO4 was described from isotopically exchangeable PO4, when organic matter was included as the main competing adsorbate and when mobile colloidal ferrihydrite was included. The model reveals that colloidal PO4 transport enhanced leachate PO4 concentrations up to a factor 50 at small soil P content and small calcium (Ca2+) concentration in solution, as a large Ca2+ concentration enhances colloidal stability. This modelling approach explained that long-term application of organic fertilisers with higher Ca content reduced P leaching, likely due to the effect of Ca2+ on colloidal stability. A two-parameter empirical Langmuir model, based on soil Fe and Al oxyhydroxides, fitted data better than any SCM, suggesting that the empirical model might be advocated for application at large scale. This study revealed the power of SCM to better understand colloidal transport of P in soil.