Competitive Desorption Research Articles

Unraveling the Coupled Dynamics between DOM Transformation and Arsenic Mobilization in Aquifer Systems during Microbial Sulfate Reduction: Evidence from Sediment Incubation Experiment

Geogenic arsenic (As)-rich groundwater poses a significant environmental challenge worldwide, yet our understanding of the interplay between dissolved organic matter (DOM) transformation and arsenic mobilization during microbial sulfate reduction remains limited. This study involved microcosm experiments using As-rich aquifer sediments from the Singe Tsangpo River basin (STR) and Jianghan Plain (JHP), respectively. The findings revealed that microbial sulfate reduction remarkably increased arsenic mobilization in both STR and JHP sediments compared to that in unamended sediments. Moreover, the mobilization of As during microbial sulfate reduction coincided with increases in the fluorescence intensity of two humic-like substances, C2 and C3 (R = 0.87/0.87 and R = 0.73/0.66 in the STR and JHP sediments, respectively; p < 0.05), suggesting competitive desorption between DOM and As during incubation. Moreover, the transformations in the DOM molecular characteristics showed significant increases in CHOS molecular and low-O/C-value molecular intensities corresponding to the enhancement of microbial sulfate reduction and the possible occurrence of methanogenesis processes, which suggests a substantial bioproduction contribution to DOM components that is conducive to As mobilization during the microbial sulfate reduction. The present results thus provide new insights into the co-evolution between As mobilization and DOM transformations in alluvial aquifer systems under strong microbial sulfate reduction conditions.

Lack of P limitation on litter decomposition: a case study from long-term addition of phosphorus and nitrogen in three subtropical forests in southern China

ABSTRACT Contrary to the widely accepted belief that elevated soil respiration after phosphorus (P) fertilization indicates P limitations for soil microorganisms in (sub)tropical forests, our previous studies have proposed that the elevated respiration results from the abiotically elevated availability of carbon (C), originating from competitive desorption from sorption sites on the surface of soil particles following P fertilization. In this study, we tested the impact of P fertilization (150 kg NaH2PO4-P ha−1 yr−1) on the decomposition of tea bags (Lipton Rooibos and Green teas) in three types of subtropical forests (primary, secondary, and planted forests) at the Dinghushan Biosphere Reserve, where previous findings reported increased soil respiration following P fertilization. If the traditional view holds true, early-stage litter decomposition should be stimulated by P fertilization, similar to the observed stimulation in soil respiration. Conversely, if this is not the case, it strongly reinforces our new hypothesis. Tea bags were employed to serve a twofold purpose: to assess the effects of P fertilization on litter decomposition within the soil, rather than on the soil surface, and to concentrate on the decomposition of early-stage litter. Our results demonstrated that P fertilization did not accelerate the decomposition of tea bags, indicating the exclusive enhancement of soil respiration without simultaneous stimulation of litter decomposition. This contradicts expectations if P were limiting microbial activity, reinforcing our hypothesis. In conclusion, our study reaffirmed the hypothesis that microbial activity in tropical forest soils is not primarily limited by P availability.

Repeated Aqueous Film-Forming Foams Applications: Impacts on Polyfluoroalkyl Substances Retention in Saturated Soil.

Historical practices at firefighter-training areas involved repeated aqueous film-forming foams (AFFFs) applications, resulting in source zones characterized by high concentrations of perfluoroalkyl and polyfluoroalkyl substances (PFAS). Repeated applications of AFFF composed of 14 anionic and 23 zwitterionic perfluoroalkyl substances (PFAS) were conducted on a single one-dimensional saturated soil column to quantify PFAS retention. An electrofluorination-based (3M) Milspec AFFF, which was above the mixture's critical micelle concentration (CMC), was at application strength (3%, v/v). Retention and retardation of PFAS mass increased with each successive AFFF addition, although the PFAS concentration profiles for subsequent applications differed from the initial. Greater degree of mass retention and retardation correlated with longer PFAS carbon-fluorine chain length and charged-headgroup type and as a function of AFFF application number. Anionic PFAS were increasingly retained with each subsequent AFFF application, while zwitterionic PFAS exhibited an alternating pattern of sorption and desorption. Surfactant-surfactant adsorption and competition during repeat AFFF applications that are at concentrations above the CMC resulted in adsorbed PFAS from the first application, changing the nature of the soil surface with preferential sorption of anionic PFAS and release of zwitterionic PFAS due to competitive elution. Applying a polyparameter quantitative structure-property relationship developed to describe sorption of AFFF-derived PFAS to uncontaminated, saturated soil was attempted for our experimental conditions. The model had been derived for data where AFFF is below the apparent CMC and our experimental conditions that included the presence of mixed micelles (aggregates consisting of different kinds of surfactants that exhibit characteristics properties different from micelles composed of a single surfactant) resulted in overall PFAS mass retained by an average of 27.3% ± 2.7% (standard error) above the predicted values. The correlation was significantly improved by adding a "micelle parameter" to account for cases where the applied AFFF was above the apparent CMC. Our results highlight the importance of interactions between the AFFF components that can only be investigated by employing complex PFAS mixtures at concentrations present in actual AFFF at application strength, which are above their apparent CMC. In firefighter-training areas (AFFF source zones), competitive desorption of PFAS may result in downgradient PFAS retention when desorbed PFAS become resorbed to uncontaminated soil.

Consequences of sea level rise for high metal(loid) loads in the Ría of Huelva estuary sediments

Ría of Huelva, located in southwestern Spain, is a highly metal(loid)-contaminated estuary system where sediments are exceeding action limits in an increasing order for Cd, Zn, Pb, Cu, and As. With a predicted sea level rise over the next 50 years, the estuary will be subject to flooding with brackish water or seawater. To evaluate the risk of metal(loid) mobilization under future climate scenarios, different locations along the estuary were sampled at different depths. Samples were flooded with river water, brackish water, and seawater under different short- and long-term laboratory setups. Potential metal(loid) mobilization showed that water quality standards for As, Pb, Zn, Ni, Cu, and Cd could be exceeded upon seawater flooding. However, metal(loid) mobilization was not predictable solely based on sediment loads. The driving factors for cation and anion mobility were identified to be mainly pH under low salinity and competitive desorption under high salinity conditions. Further drivers such as wave movement or labile C input in C-limited systems were found to enhance metal(loid) mobilization. Long-term flooding of intact sediment cores revealed that sea level rise will have different effects on the estuary system depending on duration of flooding. Short-term flooding in the near future will first affect alkaline sediments and enhance currently low cation mobilization, while anion mobilization due to reductive Fe dissolution will remain high. Once acidic sediments further inland are flooded with seawater, highest contaminant mobilization can be expected as high salinity will further enhance already high cation mobilization under acidic pH. Long-term flooding with seawater will neutralize the sediment pH and limit cation mobilization compared to acidic pH. However, the contaminant load stored in the estuary is so high that, extrapolating data obtained, mobilization could last for >1000 years, e.g. for As, Pb, and Al.

Key drivers regulating arsenic enrichment in shallow groundwater of the Pearl River Delta: Comprehensive analyses of iron, competitive anions, and dissolved organic matter

Arsenic (As) contamination in groundwater is a global environmental geochemical problem that threatens over 100 million people around the world. Although groundwater As enrichment has been demonstrated to result from some major complex processes, including competitive desorption by anions and reductive release of As from iron (Fe) oxyhydroxides due to microbial respiration of dissolved organic matter (DOM), knowledge of the detailed interactions among these processes and their respective contributions is still limited. In this study, we aimed to elucidate the key variables that regulate the evolution of dissolved As in shallow groundwater from a typical As-contaminated region of the Pearl River Delta (PRD) after comprehensive statistical analysis of hydrogeochemical characteristics. The results showed that the highest concentration of As in the groundwater samples (n = 77) was 57 μg/L, with 9% of samples exceeding the drinking water standard. In comparison with other regions with geogenic As contamination in groundwater, the relatively low As concentration range is primarily controlled by the well-oxygenated environment, which also contributed to the dominance of As(V) (19.5–100.0%, median of 100.0%). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested that the presence of As in groundwater may be impacted by the reduction process of Fe/Mn oxyhydroxides and by competitive anions. Further analysis using structural equation modeling (SEM) indicated that the increased concentration of As(V) in the shallow groundwater was primarily induced by the competitive roles of phosphate and silicate, explaining 65.2% and 31.5% of total As(V), respectively. In contrast, the presence of As(III) was strongly explained by DOM (23.8%, 12.4%, and 5.7% from microbial humic-like, terrestrial humic-like, and protein-like components, respectively) and Fe (31.8%), followed by competitive desorption (26.3%), revealing the dominant contribution from DOM-facilitated Fe reduction to As(III) enrichment. Our study empirically demonstrated that decreasing the concentrations of phosphate and reactive organic matter can effectively alleviate As contamination in groundwater.

A critical review of arsenic occurrence, fate and transport in natural and modified groundwater systems in The Netherlands

Arsenic is a common trace element in groundwater and its fate and transport are controlled by combination of (i) natural processes, including redox conditions, salinity and pH, (ii) sedimentary and geochemical environment, and (iii) anthropogenic influences such as groundwater extraction, managed aquifer recharge (MAR), Aquifer Thermal Energy Storage (ATES), and pollution. We investigated the relative influence of these processes by presenting 10 cases from The Netherlands. Our review showed that the primary controlling factor for arsenic mobility in natural coastal dune systems is the redox state of groundwater, with concentrations between 2 and 10 μg/L. Strongly reduced greensands (containing glauconite and, more importantly, associated minerals) exhibited elevated As concentrations, with concentrations up to 40 μg/L. Groundwater systems modified by MAR or those that are influenced by nitrate pollution (NP) showed elevated As concentrations (20–110 μg/L), as a result of either pyrite oxidation (MAR, NP) or reductive dissolution of iron(hydr)oxides (MAR). Increasing temperature at ATES systems may cause mobilization of As at temperatures beyond 25 °C. The highest As concentrations were observed at sites where muddy sediments were recently deposited in surface water bodies (200–820 μg/L), for example in dammed Rhine River tributaries and sand pit lakes south of the city of Amsterdam. The reduction of arsenate to arsenite and competitive desorption during intrusion of polluted water also form important As mobilizing processes. The data for the Netherlands show that high CH4 and NH4 concentrations may form a risk indicator of elevated As levels in some fresh groundwater systems.

Transport and transformation of arsenic in coastal aquifer at the scenario of seawater intrusion followed by managed aquifer recharge

Release of contaminants from aquifers at the coastal area is of increasing concern, but remains unclear due to the complex groundwater dynamics and hydrochemistry. Specifically, frequently occurring seawater intrusion and the subsequent engineering measures of managed aquifer recharge (MAR) could alter the groundwater regime, which might affect the fate and behaviors of contaminants. In this work, we investigated the transport and transformation of arsenic (As) in the coastal aquifer at the scenario of seawater intrusion followed by the injection-based MAR process. Results showed that seawater intrusion induced 10.3% more release of aqueous As in aquifers, which was attributed to the competitive desorption as a result of elevated anion concentration and pH, and the reduction of As(V) to As(III) due to the reduced redox potential and enriched As-reducing bacteria. Furthermore, seawater intrusion inhibited the recrystallization of iron (hydr)oxides and instead facilitated its conversion to iron sulfide with lower affinity to As. The subsequent MAR introduced oxygenated recharge water into aquifers and increased the redox potential, leading to the dissolution of iron sulfide followed by formation of amorphous iron (hydr)oxides. However, the competitive desorption of As with rich HCO3− under increased pH dominated continuous increase in the aquifer aqueous As during MAR process. A constructed numerical model for describing As transport based on the experimental data showed that As transported along the interface between seawater and freshwater, and MAR enhanced the release of As and expanded the spread range of As. Our findings reveal that both seawater intrusion and subsequent MAR could cause the release, transport, and transformation of As, which provides new insight on the understanding of geochemical process of As in coastal aquifers.

Distribution, dynamic and influence factors of groundwater arsenic in the Manas River Basin in Xinjiang, P.R.China

High arsenic (As) groundwater in Xinjiang is mainly found in deep aquifers in the Manas River Basin (MRB) and the Kuitun River Basin (KRB) in the southern Junggar Basin. Groundwater samples (n = 21; including two phreatic water samples and 19 deep confined groundwater samples), were collected along hydrogeological profiles (north-south and west-east) in a high As groundwater area in the MRB in 2021. Inorganic As species, DOC and DIC were determined. As (V) was the major inorganic As species in 95% of the groundwater samples. High As groundwater was mostly found in reducing/sub-oxidizing and alkaline environments. Along the south-north groundwater flow path, a significant positive correlation was found between groundwater As, phosphate and carbonate, suggesting that competitive desorption may have been an important arsenic mobilizing process. Further, a significant negative correlation between groundwater As and the sulfate/chloride ratio and between DOC and the sulfate/chloride were observed - this suggests that sulfate reduction mediated by microorganisms may also have been an important mobilizing process. The lack of correlation between groundwater As and DOC suggests that the composition of organic matter as well as its concentration may have been an important controlling factor in arsenic mobilization.

Mechanistic insight into the release behavior of arsenic (As) based on its geochemical fractions in the contaminated soils around lead/zinc (Pb/Zn) smelters

Arsenic (As) was known as human carcinogen . It was therefore of great importance to better understanding the release behavior of arsenic in soils for managing and controlling the potential risks of smelter contaminated sites. The present work evaluated arsenic bioavailability and bioaccessibility, in combination with geochemical fractionation and valence analysis by X–ray photoelectron spectroscopy (XPS), and also investigated the release patterns of bioavailable and bioaccessible arsenic in soils. The present results showed that there was a significant variation in the bioavailable and bioaccessible fractions of arsenic, due to the great difference in soil properties, extractants types, and in vitro assays . Moreover, it was found that KH 2 PO 4 presented the relatively higher arsenic bioavailability with wide range of 9.89–25.5 %, which might better predict the arsenic bioavailability in soils than the other extractants. In addition, the relatively higher arsenic bioaccesibility was found in Solubility Bioaccessibility Research Consortium (SBRC) assay, ranging from 5.50 to 67.4 % for gastric phase (GP) and 3.85–18.8 % for gastrointestinal phase (GIP), respectively. In addition, the time–dependent release of bioavailable arsenic was controlled by the competitive desorption between phosphate and As (V) ions, while the time–dependent release of bioaccessible arsenic was dominated by the stable complexation of organic ligands and the strong affinity of Al, Mn and Fe–(hydr) oxides. According to the study results, a new insight into the arsenic behavior was provided to more scientifically evaluate its contamination risks. • The updated knowledge was provided for arsenic geochemical behavior in smelter soils. • KH 2 PO 4 was identified as the best extractant to assess the arsenic bioavailability. • SBRC showed the relatively higher arsenic bioaccessibility than PBET and IVG. • Arsenic desorption reaction was better explained by the pseudo second order model.

Inhalation Bioaccessibility of Polycyclic Aromatic Hydrocarbons in PM2.5 under Various Lung Environments: Implications for Air Pollution Control during Coronavirus Disease-19 Outbreak.

Global spread of coronavirus disease-19 (COVID-19) is placing an unprecedented pressure on the environment and health. In this study, a new perspective is proposed to assess the inhalation bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 for people with various lung health conditions. In vitro bioaccessibility (IVBA) was measured using modified epithelial lung fluids simulating the extracellular environment of patients with severe and mild lung inflammation. The average PAH IVBA in PM2.5 of 24.5 ± 4.52% under healthy conditions increased (p = 0.06) to 28.6 ± 3.17% and significantly (p < 0.05) to 32.3 ± 5.32% under mild and severe lung inflammation conditions. A mechanistic study showed that lung inflammation decreased the critical micelle concentrations of main pulmonary surfactants (i.e., from 67.8 (for dipalmitoyl phosphatidylcholine) and 53.3 mg/L (for bovine serum albumin) to 44.5 mg/L) and promoted the formation of micelles, which enhanced the solubilization and competitive desorption of PAHs from PM2.5 in the lung fluids. In addition, risk assessment considering different IVBA values suggested that PAH contamination levels in PM2.5, which were safe for healthy people, may not be acceptable for patients with lung inflammation. Because of the large number of COVID-19 infections, and the fact that some survivors of COVID-19 were observed to still show symptoms of interstitial lung inflammation, the finding here can provide important implications for both the scientific community and policy makers in addressing health risk and air pollution control during the COVID-19 outbreak.

The occurrence of geogenic fluoride in shallow aquifers of Kenya Rift Valley and its implications in groundwater management

Widespread concerns about high-fluoride groundwater and their health risks have been raised worldwide. Weathering of volcanic minerals is regarded as a principal source of groundwater fluoride in regions with volcanic bedrocks. However, how does the volcanic minerals control fluoride occurrence, if it induces other hydrogeochemical processes participating in and how this relates to human health still remain unclear. This study takes Kenya Rift Valley, which has volcanic geological formations, as an example to delineate the occurrence and origins of high-fluoride shallow groundwater with analysis of hydrochemistry, graphical and multivariate statistical methods. Over 40% of shallow groundwater (F-: up to 23.5 mg/L) show elevated fluoride values over the WHO standards of 1.5 mg/L. High fluoride groundwater are generally Na-rich and Ca-poor with high pH and HCO3¯ concentrations. Hydrogeochemical and principal component analysis indicate that weathering of hyper-alkaline volcanic rocks could release accumulated fluoride in melts and volatile fractions, as well as in clay minerals. Alkaline condition and high HCO3- contents lead to the competitive desorption of F- from clay minerals and Fe-hydroxides into groundwater. Clay minerals also provide abundant exchange sites where cation exchange happens and promotes the release of F- from the sediments by controlling the dissolution/precipitation of calcite and fluorite. Health risk assessment results show that chronic health risks by groundwater geogenic fluoride ingestion are identified to various individuals, with highest threats in children. Finally, a conceptual model has been developed to demonstrate the formations of high geogenic fluoride groundwater in regions with volcanic bedrocks and its relation with human health.

Study on the Adsorption Effect of Renewable Biochar Based on Energy Gain

This paper provides sufficient evidence on how the crop-residual-derived charcoal could effectively restore the soil polluted by the heavy metal. In this paper, straw char at three temperatures of 300°C, 500°C, and 700°C, labeled as RS300, RS500, and RS700, was prepared by low temperature pyrolysis technique using straw as raw material, and the competitive adsorption desorption of Pb2+, Cd2+, Cu2+, and Zn2+ in acidic solution and the mechanism were investigated by static adsorption experiments. Since the crop-residual-derived charcoal could effectively restore the nutritional structure of the soil, which contributes to preventing the decrease in grain yield, and it is also a kind of renewable environment-friendly resource by itself, which could be used in control the pollution of heavy metal ions, it is expected that the crop-residual-derived charcoal will be a new adsorption material that could be used to control the heavy metal pollution in the future; the adsorption effect of biochar as new adsorption material on heavy metal ions has a distinct advantage over traditional adsorbent materials, and biochar is a renewable energy source, which is cheap and better for recycling resources.

Mobilization of arsenic from coal fly ash in the presence of dissolved organic matter

In this study, we examined the influence of dissolved organic matter (humic and fulvic acids) on arsenic (As) mobilization from two Class F coal fly ashes under oxic and anoxic conditions. Batch leaching experiments were conducted to examine As leaching behavior and changes in As aqueous and solid phase speciation after exposure to humic and fulvic acids for up to 4 weeks (ash/buffer ratio = 0.01 g/mL). Under oxic conditions, mobilized As concentrations increased compared to the organic-free controls and were positively correlated with percent aliphatic carbon and oxygen/carbon ratio of the humic and fulvic acids, suggesting both non-specific hydrophobic association of the organic matter with the surface of the fly ash particles and competitive desorption between negatively charged organic functional groups and As anions adsorbed to mineral surfaces. Under anoxic conditions, organic matter enhanced the reductive dissolution of As-bearing iron oxides such as hematite, resulting in increased As mobilization. X-ray absorption spectroscopy indicated that the majority of As in the leached and unleached fly ash was As(V) (≥90%), with As(V)-ferrihydrite precipitation occurring under all leaching conditions tested. Our results demonstrated that humic and fulvic acids are capable of mobilizing As from fly ash under both oxic and anoxic conditions, though redox appeared to be a larger driver of As mobilization compared to dissolved organic matter (DOM). DOM is a parameter which should be considered in risk assessment strategies for fly ash that is exposed to water (e.g., subsurface infiltration) or released to aquatic systems.

Investigation of competitive adsorption and desorption of heavy metals from aqueous solution using raw rock: Characterization kinetic, isotherm, and thermodynamic

Heavy metals are the most dangerous inorganic pollutants Due to their bioaccumulation and their nonbiodegradability, for this, several studies have focused on the recovery of these metals from water using different techniques. In this context, our study consists of evaluating an efficient and eco-friendly pathway of competitive recovery of heavy metals (Cd, Cr and As) from aqueous solutions by adsorption using raw rock. This adsorbent was characterized before and after the adsorption process by several techniques. The multi-metals adsorption process in the batch mode was undertaken to evaluate the effect of adsorbent mass, contact time, pH, Temperature, and initial heavy metals concentration. The kinetic data were analyzed using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic models. According to the modeling of the experimental results, the adsorption kinetics of heavy metals were adapted to the pseudo-second-order model. The adsorption isotherms were evaluated by the Langmuir and Freundlich isotherm models. The experimental isotherm data of heavy metals were better fitted with the Langmuir model rather than Freundlich isotherm models. The maximum experimental adsorption capacities (Qmax) predicted by the Langmuir model are 15.23 mg/g for Cd (II), 17.54 mg/g for Cr (VI) and 16.36 mg/g for As (III). The values of thermodynamic parameters revealed that the heavy metals adsorption was exothermic, favorable, and spontaneous in nature. The desorption process of heavy metals showed that this raw rock had excellent recycling capacity. Based on the results, these untreated clays can be used as inexpensive and environmentally friendly adsorbents to treat water contaminated by heavy metals.

Biodegradation of bisphenol compounds in the surface water of Taihu Lake and the effect of humic acids

Bisphenol analogues (BPs) pollution in the aquatic environment is increasingly a worldwide concern. There is an urgent need to understand the fate of BPs in the aquatic environment. In this study, we studied the biodegradation of eight BPs in Taihu Lake and discussed the effect of humic acid (HA), which was extracted from Taihu Lake sediment, on the disappearance of BPs. Under aerobic conditions, bisphenol AF (BPAF) and bisphenol S (BPS) were recalcitrant to biodegradation in the lake water. The half-lives for bisphenol F (BPF), bisphenol A (BPA), bisphenol B (BPB), bisphenol E (BPE), bisphenol Z (BPZ), and bisphenol M (BPM) ranged from 34 to 75 days in the Taihu Lake water collected in October 2018 and 12–72 days in that collected in May 2019. The biodegradation of BPs in summer was significantly higher than that in autumn. The presence of HA promoted the disappearance of BPs from Taihu Lake water by adsorbing and binding BPs. The disappearance rate of BPs accelerated with increasing concentrations of HA. However, the presence of HA decreased the biodegradation of BPs. When the concentration of HA was 10 mg/L, the single-adsorption capacities for BPS, BPA, BPB, BPM and BPAF were 3.18–10.33 mg/g in the Taihu Lake water with little desorption. BP adsorption and desorption in the BP mixtures were different from that in the single BPs. Competitive desorption occurred among the mixtures. The results of this study are the first to indicate the biodegradation of eight BPs in natural lake water and the possible effect of HA on the fate of BPs in the environment.

Characterization and role of derived dissolved organic matter on arsenic mobilization in alluvial aquifers of Punjab, Pakistan

Biogeochemical mobilization of arsenic in groundwater depends on the presence of dissolved organic matter (DOM) that likely promotes the As release, i.e., reductive dissolution, complexation, competition, and electron shuttling. We investigated the role of DOM in As release, along with its complete characterization, in the Indus plain of Pakistan, one of the worst arsenic impacted zones in the South Asian region. In total, 60 groundwater and 15 soil samples, collected at six sites from north to south within the flood plain of the Ravi River, Lahore, Pakistan were investigated. Arsenic concentration ranged from 9.61 μg/L to 386 μg/L in the groundwater samples (high As observed in areas close to the river). Dissolved organic carbon (DOC) in 29 groundwater samples ranged between 0 and 10.1 mg-C/L. A moderately positive correlation of As with DOC and Fe in the northern part of the study area suggest the reductive dissolution of FeOOH associated with dissolved organic matter (DOM). The reductive dissolution plays an essential role for As enrichment in the area evidenced by the lower concentrations of SO42−, NO3−, and PO34−and a non-correlative pattern with As. In contrast, a positive correlation of As with PO34−, DOC, and HCO3− in the southern part indicate competitive desorption behind the As release. Fluorescence excitation-emission matrix intensity data of DOM indicate the maximum presence of humic-like substances in the northern part that gradually shifts to aromatic, fulvic and protein type towards the southern part. Specific ultraviolet absorbance and fluorescence index display aromatic and terrestrial (allochthonous) sources of DOM near the riverbank and mixed (both allochthonous and autochthonous) source away from the river. The positive correlations of As with DOC and fluorescence intensity also attest that DOM played a vital role in the As mobilization in groundwater of the study area.

Dissolved organic matter controls of arsenic bioavailability to bacteria

The presence of arsenic in irrigation and drinking waters is a threat to worldwide human health. Dissolved organic matter (DOM) is a ubiquitous and photoreactive sorbent of arsenic, capable of both suppressing and enhancing its mobility. Microbes can control the mobilization of mineral-bound arsenic, through redox processes thought to occur intracellularly. The role that DOM plays on the bioavailability of arsenic to microbes is often invoked but remains untested experimentally. Here, using a whole-cell biosensor, we tested the role of DOM on As(III) and As(V) bioavailability. Using cation amendments, we explored the nature of As-DOM interactions. We found As bioavailability to be dependent on [As]/[DOM] ratio and on the strength of As binding to DOM which varied as a function of time. We further tested the role of DOM on As(III) photooxidation and showed that As(III) photooxidation rate is limited by the strength of its interactions with DOM and sensitive to ionic competitive desorption. Our study demonstrates the dynamic control that photoreactive DOM poses on the bioavailability and reactivity of As in the environment and highlights the kinetic controls that DOM can possibly exert on As toxicity at various levels in foodwebs.

Desorption Kinetics of Heavy Metals (Lead, Zinc, and Nickel) Coexisted with Phenanthrene from a Natural High Buffering Soil

This work aims to investigate the competitive time-dependent desorption rate of heavy metals (lead, zinc, nickel) coexisting with phenanthrene from natural high buffering soil. Two non-ionic surfactants (Tween 80 and Brij 35) combined with disodium ethylene diamine tetraacetate salt (Na2-EDTA) were utilized as the reagents. The contaminants’ time-dependent desorption data was fitted with five kinetic models including parabolic diffusion, Elovich, fractional power function, pseudo-first and -second-order equations. The best removal of contaminants obtained by the mixture of Tween 80/EDTA; desorbing 93% of lead (Pb). The competitive desorption of nickel (Ni) and zinc (Zn) is affected by the stability of Metal-EDTA complexes. Moreover, phenanthrene removal in the soil studied was slow and laborious. The desorption kinetics are well described by parabolic diffusion (for phenanthrene) and pseudo-second-order (for heavy metals of interest). In the soil-surfactant-water system, soil structure changes were negligible; however, Tween 80 influenced the development of crystal faces of CaCO3 during the process.

Occurrence and distribution of high arsenic in sediments and groundwater of the Claromecó fluvial basin, southern Pampean plain (Argentina)

Occurrences of high arsenic (As) in sediments and groundwaters were investigated in the Claromecó fluvial basin, southern Pampean plain, Argentina. This investigation includes sedimentology, mineralogy, and hydrogeochemistry of the Neogene and Quaternary aquifers to determine possible sources and transport mechanisms for As in the Claromecó basin. Characterization of the sediments revealed homogeneous mineralogy in both Neogene highlands and Quaternary floodplains with abundant plagioclase, volcanic glass shards (VGS), K-feldspar, quartz, clay minerals and minor concentrations of clinopyroxenes, orthopyroxenes, hornblende, epidote, Fe-(oxy)hydroxides and fluorapatite. The sedimentary As concentrations ranged between 2.8 and 31 mg kg−1 in both aquifers. The average total dissolved As (dissolved AsT) concentrations was 47.2 ± 30.8 μg L−1 (15.3–110 μg L−1) in groundwater in Neogene aquifer (GW1), while it was 97.1 ± 30.6 μg L−1 (45–144 μg L−1) in Quaternary floodplain aquifer (GW2), with all samples exceeding WHO's guideline for dissolved AsT in safe drinking water of 10 μg L−1. Some GW1 (33%) and all GW2 samples contained high levels of fluoride (F−) ranging from 0.6 to 2.6 mg L−1 (1.37 ± 0.59 mg L−1) in GW1 and 2 to 5 mg L−1 (3.2 ± 0.9 mg L−1) in GW2 which also exceeded WHO's guideline for F− in safe drinking water of 1.5 mg L−1. Elevated concentrations of Na+, Cl− and SO42− in the Quaternary flood plain groundwater (GW2) could indicated some degree of sea water mixing as well as some contribution from inland processes (e.g. high evapotranspiration rates, long residence time and soil-water interactions). Dissolution of As bearing VGS or Fe-(oxy)hydroxides, alkaline desorption or competitive desorption with HCO3– from Fe-(oxy)hydroxides appear to be dominating processes of As mobilization, while desorption from fluorapatite elevate dissolved F− levels. This study provides valuable insights on As mobilization processes in Neogene and near coast Quaternary floodplain aquifer.

Removal of Chromium from a Contaminated Soil Using Oxalic Acid, Citric Acid, and Hydrochloric Acid: Dynamics, Mechanisms, and Concomitant Removal of Non-Targeted Metals.

Soil leaching is an effective remediation technique using agents to leach the target pollutants from the soil. However, the dynamics and mechanisms for leaching of Cr and other non-pollutant metals from Cr-contaminated soils are not yet well understood. Here, column leaching experiments were conducted to determine the effect of hydrochloric acid (HCl), citric acid (CA), and oxalic acid (OX) on the leaching of Cr, as well as of Ca, Mg, Fe, and Mn, from a soil contaminated by a Cr slag heap. Acid leaching decreased soil pH and enhanced the mobility of all the surveyed metals. Leaching dynamics varied with both metals and acids. OX had the highest removal rates for Cr, Fe, Mn, and Mg, but had the poorest ability to leach Ca. HCl leached the largest amount of Ca, while CA leached similar amounts of Mg and Mn to OX, and similar amounts of Fe and Cr to HCl. Cr in the leachates was correlated with Ca, Mg, Fe, and Mn. Cr mainly interacted with soil mineral components and showed a punctate distribution in soil particles. The X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) analyses showed soil mineralogical and morphological properties were differently altered after leaching by different acids. Complexation of Cr(III), competitive desorption, and reduction of Cr(VI) make significant contribution to Cr leaching by organic acids. In conclusion, OX can be applied in leaching remediation of Cr-contaminated soil, but the concomitant removal of other non-targeted metals should be taken into account because of the loss of soil minerals and fertility.