Dissolved Organic Matter Solutions Research Articles

Fate and behaviour of the UV filter 3-methylbutyl-(2E)-3-(4-methoxyphenyl)-acrylate (IMC) in aqueous solution

The disinfection-induced and photo-induced degradation of the UV filter 3-methylbutyl-(2E)-3-(4-methoxyphenyl)-acrylate (IMC) is investigated. High performance liquid chromatography was used to follow the degradation reactions, determine kinetic features and also the influence of external variables on degradation [pH; temperature; chlorine concentration; dissolved organic matter (DOM) concentration]. Liquid chromatography preceded by solid-phase extraction, was used for the determination of by-products. IMC was found to rapidly and substantially degrade in aqueous solution, when in exposure to active chlorine, displaying a pseudo second-order degradation rate constant of 0.042±0.001Lmol−1s−1, and a half-life period of 23.8±0.6s. Contact with aqueous active chlorine proved to yield merely the dichlorinated form of IMC, as the prominent disinfection by-product. The assessment of influence of external variables on degradation, was insured by a Box-Behnken experimental design formulation approach, with factorial analysis. In this regard, data shows that temperature plays a decisive factor in the reaction rate, without DOM in solution, leading to decreasing degradation rates as the temperature increases. With DOM in solution, pH and DOM proved to be the most influential variables on IMC degradation. Regarding the photo-degradation study, results have shown that IMC remained quite stable in aqueous solution when exposed to artificial solar radiation, with a rate constant of 0.00073±0.00002min−1 and a half-life period of 938.5±31.1min. This work addresses yet another filter that has never been studied, and hopes to provide clarification on its environmental fate and behaviour when in the aqueous environmental compartments.

Catalytic role of iron in the formation of silver nanoparticles in photo-irradiated Ag+-dissolved organic matter solution

Photo-reduction of Ag+ to silver nanoparticle (AgNPs) by dissolved organic matter (DOM) is a possible source of naturally occurring AgNPs. However, how this photo-reduction process is influenced by ubiquitous metal ions is still not well understood. In addition, in previous studies, the formation of AgNPs in DOM solution was usually monitored by UV-Vis spectroscopy, and there is still lack of quantitative analysis for the formed AgNPs. In the present study, the role of Fe2+/Fe3+ at environmental concentration level on this photochemical process was investigated, and the enhanced formation of AgNPs by Fe2+/Fe3+ was probed and quantified by using UV-Vis spectroscopy, transmission electron microscopy, and liquid chromatography-inductively coupled plasma mass spectrometry. It was demonstrated that while Fe3+ can oxidize AgNPs to release Ag+, Fe2+ can reduce Ag+ into AgNPs. However, the DOM-induced reduction of Fe3+ makes iron an effective electron shuttle between DOM and Ag+, and both Fe2+ and Fe3+ enhanced AgNP formation. The impacts of environmentally relevant factors, including DOM concentration and solution pH, on this process were studied comprehensively, which showed that the catalytic role of iron was more significant at higher DOM concentration and lower pH. This iron-enhanced formation of AgNPs in photo-irradiated Ag+-DOM solution have great environmental implications on the formation of natural AgNPs and the transformation of engineered AgNPs in acidic surface water with high iron content.

Quantitative relationships between the adsorptivity of carbonaceous materials in soil for Pb(II) and soil organic matter content

Strong adsorptivity of manufactured carbonaceous materials (MCMs) mediates the behavior of heavy metals in soil. Laboratory-reported adsorptivity of MCMs often deviates from their actual abilities in soil, because soil organic matter (SOM) can change the adsorptive abilities of MCMs by coating dissolved organic matter (DOM) on the surface of the MCMs. It was considered that the influence of SOM on the adsorptivity of MCMs in soil follows a sequential pathway of SOM releasing DOM in soil solution and subsequent DOM binding onto MCMs, thereby altering MCM surface acidity and hence changing MCM adsorptivity for heavy metals. In this study, we first extracted DOM from ten topsoils collected over a broad region of China with a wide range of SOM. The DOM solutions were then used to load DOM onto four MCMs including activated carbon (AC), multiwalled carbon nanotube (MWCNT), and two biochars (BC400 and BC700), respectively, obtaining a total of 44 MCM-DOM complex samples with known amounts of bound DOM. These MCM-DOM complex samples were then determined for their surface acidities and adsorptive abilities for Pb(II). We found that there were significant correlations between DOM concentration and SOM content, between DOM binding onto MCMs and DOM concentration, between surface acidity of MCM-DOM complexes and DOM binding onto MCMs, as well as between Pb(II) adsorption on MCM-DOM complexes and surface acidity of MCM-DOM complexes. With understanding of these individual linear correlations, linear relationships between the Pb(II) adsorption and SOM content were established by combining individual correlations and by directly plotting the former against the latter. These relationships may be used to accurately predict the adsorptive abilities of MCMs for heavy metals in soils via simply determining SOM.

Changes in fluorescent dissolved organic matter upon interaction with anionic surfactant as revealed by EEM-PARAFAC and two dimensional correlation spectroscopy

Surfactants are present in significant amounts in both domestic and industrial wastewater, which may interact with dissolved organic matter (DOM). The present study investigated the interactions of sodium dodecyl sulfate (SDS) with three different DOM solutions, including bovine serum albumin (BSA), humic acid (HA), and the mixture of the two (BSA-HA), based on two advanced spectroscopic tools: excitation emission matrix (EEM) combined with parallel factor analysis (EEM-PARAFAC) and two dimensional correlation spectroscopy (2D-COS). The responses of two protein-like components to the addition of SDS differed depending the presence and the absence of HA. A decreasing and an increasing trend was observed for tryptophan-like (C1) and tyrosine-like (C2) components, respectively, in the BSA solution, while the BSA-HA mixture exhibited increasing fluorescence trends for both protein-like components. The conflicting results suggest that HA plays a secondary role in the protein-SDS interactions. No interaction between the SDS and humic-like component was found. 2D-COS combined with fluorescence spectra demonstrated that the protein-SDS interaction occurred on the order of C2 > C1 for the BSA solution but C1 > C2 for the BSA-HA mixture. Analyses of Scatchard plots confirmed the sequential order interpreted from 2D-COS, showing consistent trends in the binding constants. However, the presence of HA affected the protein-SDS interactions in different manners for C1 and C2, enhancing and reducing the binding constants, respectively. Circular dichroism spectra confirmed the occurrence of conformational changes in BSA with SDS. EEM-PARAFAC and 2D-COS successfully explained different interactions of surfactant with protein-like components in the presence of HA.

Spectroscopic characterization of dissolved organic matter derived from different biochars and their polycylic aromatic hydrocarbons (PAHs) binding affinity

In recent years, biochar has received a great attention due to its high application in different sectors of environment. The feasibility of biochar applications is depended on its physical and chemical properties and biochar-derived dissolved organic matter (DOM) characteristics. This study was conducted to investigate the spectroscopic characteristics of biochar-derived DOM and its binding capacity of hydrophobic organic chemicals (HOCs). DOM solutions were isolated from five different biochars prepared through pyrolysis and analyzed for dissolved organic carbon (DOC) contents. The optical analysis with UV–visible absorption and excitation-emission matrix (EEM) fluorescence spectroscopes and DOC water distribution coefficient (KDOC) were calculated in the presence of PAHs and DOM. The DOC contents and the estimated aromaticity (SUVA254) were different for selected biochars. The DOM derived from soybean straw biochar (SBBC) showed the highest DOC contents followed by rice straw biochar (RSBC). The SBBC and RSBC peak position in the fluorescence excitation/emission matrix at longer wavelength corresponded to the peak position of other three biochars indicating that SBBC and RSBC had relatively higher degree of humification. This was well correlated with the observed KDOC values, suggesting that the KDOC value's dominant factor was the degree of biochar-derived DOM humification. The results of this study indicate that the optical analysis may provide valuable information regarding the characteristics of biochar-derived DOM and its application as environmental amendments for minimization of toxic organic compounds.

Simple, quantitative method for low molecular weight dissolved organic matter extracted from natural waters based upon high performance counter-current chromatography

A simple, high-performance counter-current chromatography method with sequential UV absorbance (254 nm) and evaporative light scattering detection (ELSD) was developed for the quantification of pre-extracted low molecular weight dissolved organic matter (DOM) extracted from natural waters. The method requires solid-phase extraction (SPE) extraction of only small volumes of water samples, here using poly(styrenedivinylbenzene)-based extraction cartridges (Varian PPL). The extracted and concentrated DOM was quantified using reversed-phase high-performance counter-current chromatography (HPCCC), with a water/methanol (5:5) mobile phase and hexane/ethyl acetate (3:7) stationary phase. The critical chromatographic parameters were optimised, applying a revolution speed of 1900 rpm and a flow-rate of 1 mL min−1. Under these conditions, 50 μL of extracted DOM solution could be injected and quantified using calibration against a reference natural dissolved material (Suwannee River), based upon UV absorbance at 254 nm and ELSD detection. Both detection methods provided excellent linearity (R2 > 0.995) for DOM across the concentration ranges of interest, with limits of detection of 4 μg ml−1 and 7 μg ml−1 for ELSD and UV absorbance, respectively. The method was validated for peak area precision (<5%), and accuracy and recovery based upon spiking seawater samples prior to extraction, together with DOM solutions post-extraction (>95% recovery). The developed method was applied to the determination of the concentration of DOM in seawater, based upon initial sample volumes as small as 20 mL.

Aluminum-induced changes in properties and fouling propensity of DOM solutions revealed by UV–vis absorbance spectral parameters

The integration of pre-coagulation with ultrafiltration (UF) is expected to not only reduce membrane fouling but also improve natural organic matter (NOM) removal. However, it is difficult to determine the proper coagulant dosage for different water qualities. The objective of this study was to probe the potential of UV–vis spectroscopic analysis to reveal the coagulant-induced changes in the fouling potentials of dissolved organic matter (DOM) and to determine the optimal coagulant dosage. The Zeta potentials (ZPs) and average particle size of the four DOM solutions (Aldrich humic acid (AHA), AHA-sodium alginate (SA), AHA-bovine serum albumin (BSA) and AHA-dextran (DEX)) coagulated with aluminum chloride (AlCl3) were measured. Results showed that increasing the aluminum coagulant dosage induced the aggregation of DOM. Meanwhile, the addition of aluminum coagulant resulted in an increase in DSlope325-375 (the slope of the log-transformed absorbance spectra from 325 to 375 nm) and a decrease in S275-295 (the slope of the log-transformed absorption coefficient from 275 to 295 nm) and SR (the ratio of Slope275-295 and Slope350-400). The variations of these spectral parameters (i.e., DSlope325-375, S275-295 and SR) correlated well with the aluminum-caused changes in ZPs and average particle size. This implies that spectral parameters have the potential to indicate DOM aggregation. In addition, good correlations of spectral parameters and membrane fouling behaviors (i.e., unified membrane fouling index (UMFI)) suggest that the changes in DSlope325-375, S275-295 and SR were indicative of the aluminum-caused alterations of fouling potentials of all DOM solutions. Interestingly, the optimal dosage of aluminum (40 μM for AHA, AHA-BSA, and AHA-DEX) was obtained based on the relation between spectral parameters and fouling behaviors. Overall, the spectroscopic analysis, particularly for the utilization of spectral parameters, provided a convenient approach for the exploration of combined coagulation and UF systems for DOM removal.

DOM fractionated from pig waste affecting the solubility of PAHs along with non-ionic surfactant

Studies on the intensification of water solubility for polycyclic aromatic hydrocarbons (PAHs) including phenanthrene and pyrene using individual surfactant and dissolved organic matter (DOM) fractionated from pig wastewater or mixed surfactant–DOM solutions were conducted. Excess surfactant dosages producing critical micelle concentration (CMC) dramatically enhance the solubility of phenanthrene and pyrene in the contaminated soil. The synergetic effect from non-ionic surfactants such as polyoxyethylene sorbitan fatty acid ester, and Tween 80, and DOM on the solubility of PAHs was also evaluated using batch experiments. The current study shows that the solubility of PAHs is respectively increased with an increase in the concentrations of Tween 80 or DOM, especially in the dosage of CMC or high hydrophobic property of DOM. Furthermore, an increase in the solubility of PAHs strengthened by the coexistence of Tween 80 and DOM was strongly affected by the concentration of Tween 80. It proves that the selection of optimal surfactant dosage is the key factor while the way is possibly applied into the remediation technologies in the on-site soil region with pollution.

Environmental pH and ionic strength influence the electron-transfer capacity of dissolved organic matter

Dissolved organic matter (DOM) plays an important role in the cycling of elements and the transformation of pollutants in the environment due to its electron-transfer capacity (ETC), but ETC may be affected by environmental factors such as pH and ionic strength. This study was aimed to reveal the effects of pH and ionic strength on the ETC of DOM and the possible mechanisms. DOM was prepared into solutions with various pH values (4, 6, 7, 8, and 10) and ionic strength (0.001, 0.01, 0.1, and 0.5 mol/L KCl). ETC of DOM including electron-accepting capacity (EAC) and electron-donating capacity (EDC) was determined with chronoamperometry. Spectroscopic and chromatographic properties of DOM were evaluated to obtain related structural information to explore the possible mechanisms for the ETC changes. Both the EAC and EDC of DOM increased consistently with increasing pH from 4 to 10. EAC and EDC increased with increasing ionic strength, peaked at 0.1 mol/L KCl, and then decreased. Gel permeation chromatogram displayed different molecular size distribution for the DOM in solution with different pH and ionic strength. Environmental pH and ionic strength influence the ETC of DOM by altering the conformation of DOM molecules.

Diffusive gradients in thin films for predicting methylmercury bioavailability in freshwaters after photodegradation

Determination of the dissolved-bioavailable fraction of methylmercury (MeHg) and its degradation pathways in freshwaters deserve attention, to further our understanding of the potential risk and toxicity of MeHg. Since the photodegradation of MeHg is the most important known abiotic process able to demethylate MeHg, this study investigated the role of sunlight on MeHg bioavailability in freshwater environments. Experiments to calculate photodegradation rate constants of MeHg in different types of freshwater in combination with experiments to distinguish the labile fraction of MeHg after being exposed to sunlight were performed. The ability of diffusive gradients in thin films based on polyacrylamide (P-DGT) to assess DGT-labile MeHg during photodegradation was successfully tested. First order photodegradation rate constants (kpd) of bioavailable MeHg determined in five different types of waters with different amount of dissolved organic matter (DOM), were in the range 0.073–0.254h−1, confirming previous findings that once there is DOM in solution, which would favour the photodegradation process, the kpd is mainly affected by light attenuation. Simulated sunlight seems not to alter the lability of MeHg, although photodegradation processes may decrease the concentrations of MeHg, contributing to reduce the amount of bioavailable MeHg (i.e. MeHg uptake by DGT). However, the quality of DOM, rather than the quantity, plays an important role in the bioavailability of MeHg in freshwater.

PAHs Sorption and Desorption on Soil Influenced by Pine Needle Litter-Derived Dissolved Organic Matter

Study of the relationship between plant litter-derived dissolved organic matter (DOM) and organic pollutant transport in soil is important for understanding the role of forest litter carbon cycling in influencing pollutant behaviour and fate in forest soil. With the aim of providing insight into the capacity of plant litter-derived DOM to influence sorption and desorption of selected polycyclic aromatic hydrocarbons (PAHs) on soil, batch experiments were carried out with application of a sorption-desorption model incorporating DOM effects. Freshly fallen pine (Pinus elliottii) needles were used as the source of organic matter. Input of the pine needle litter-derived DOM was found to significantly decrease desorption hysteresis as well as soil adsorption capacity of phenanthrene (PHE) and fluoranthene (FLA). Addition of 1 728 mg L−1 dissolved organic carbon (DOC) lowered the organic carbon-normalized sorption distribution coefficient of PHE from 7 776 to 2 541 L kg−1 C and of FLA from 11 503 to 4 368 L kg−1 C. Decreases of the apparent sorption-desorption distribution coefficients of PHE and FLA with increased DOC concentration indicated that DOM favored desorption of PAHs from soil. Increases in the fraction of apparently dissolved PAHs were attributable to the dissolved PAH-DOM complexes, accounting for the dissolved proportions of 39% to 69% for PHE and 26% to 72% for FLA in the sorption and desorption processes as the concentration of the added DOM solution rose from 0 to 1 728 mg L−1. Our results suggest that pine needle litter-derived DOM can have a substantial effect of inhibiting PAHs sorption and promoting PAHs desorption, thus leading to enhanced leaching in soil, which should be taken into account in risk assessment of PAHs accumulated in forest soil.

Fractionation of Dissolved Organic Matter by (Oxy)Hydroxide‐Coated Sands: Competitive Sorbate Displacement during Reactive Transport

Sorptive retention of dissolved organic matter (DOM) at soil particle surfaces controls C flux through the critical zone. Prior studies have shown that pristine Al‐ and Fe‐(oxy)hydroxide surfaces are especially reactive toward DOM sorptive stabilization. However, the impact of progressive and/or preexisting organic surface coatings on further surficial uptake and exchange during repeated DOM infusion episodes remains unclear. In this study, DOM solutions were extracted from organic horizons in grassland (G) and mixed conifer forest (F) vegetation types in the Jemez River Basin Critical Zone Observatory. Extracted DOM solutions were used to sequentially irrigate columns packed with either quartz sand (Qtz), Al‐hydroxide‐coated quartz sand (Al‐Qtz), or Fe‐hydroxide‐coated quartz sand (Fe‐Qtz). Use of distinct DOM sources enabled investigation of how sorption, fractionation, and exchange ensued during reactive transport through mineral media progressively coated with sorbate organic matter (SOM). During initial irrigation of fresh mineral media with G‐DOM, the magnitude of DOM sorption (per unit sorbent mass) followed the trend: Al‐Qtz ≥ Fe‐Qtz &gt; Qtz. Effluent solutions showed diminished molar absorptivity and humification index (HIX) values, indicating preferential uptake of high‐molar‐mass aromatic constituents. Introduction of F‐DOM to G‐SOM‐coated surfaces revealed competitive desorption of G‐SOM from the organo–mineral interface. During F‐DOM irrigation, high HIX values were observed in effluent solutions, indicating remobilization of G‐SOM by displacement. According to spectroscopic analyses, the displaced G‐SOM consisted of aromatic phenolic acids with high excitation–emission “fingerprints” characteristic of fulvic‐ and humic‐acid‐like compounds, providing evidence for kinetic DOM exchange reactions.

Normal-phase high-performance counter-current chromatography for the fractionation of dissolved organic matter from a freshwater source

Normal-phase high-performance counter-current chromatography (HPCCC) is used to obtain a preliminary fractionation of components in dissolved organic matter (DOM) from a freshwater source. The HPCCC solvent system involved a normal-phase approach with water/methanol (1:1) as the lower stationary phase and hexane/ethyl acetate (1:1) as the upper mobile phase. The critical experiment parameters were optimised: revolution speed 1800 rpm and flow rate 0.15 mL/min. Under these conditions 50 μL of a 0.50 mg/mL DOM solution was loaded. The detection wavelength was monitored at 330 nm in order to isolate the main portion of DOM, which includes substances such as carboxyl-rich alicyclic molecules. By optimising this system it was possible to isolate materials that, according to GC-MS, can be related to molecules with an analogous structural background. Where fraction analysis was not suitable for GC-MS, RP-HPLC with UV absorbance detection was used, showing unique chromatograms for each fraction at both 210 and 330 nm.

Soil organic matter stability in organo-mineral complexes as a function of increasing C loading

Soil carbon (C) saturation behavior predicts that soil C storage efficiency observed under field conditions decreases as a soil approaches C saturation. This may be due to a decline in soil organic matter (SOM) stability as the result of changes in the type, strength or turnover time of organo-mineral interactions with increasing organic C input. The goal of this study was to test whether the stability of organic matter bound to soil minerals decreases as organo-mineral complexes approach C saturation with increasing C loading. A series of batch sorption experiments with natural dissolved organic matter (DOM) and soil mineral components was conducted to obtain organo-mineral complexes with a range of organic C loadings. The relative stability of C in these organo-mineral complexes was subsequently assessed using evolved CO2 gas analysis during thermal analyses and laboratory incubations. Results indicated that differences in dissolved organic C before and after sorption overestimated the amount of sorbed C when compared to differences in solid-phase C concentrations. Values of C/N, δ13C, and δ15N of the organo-mineral complexes were significantly smaller or more negative than initial soil samples or the stock DOM solution, consistent with the concept of molecular fractionation by sorption to minerals and suggesting that the composition of the organic matter in the organo-mineral complexes may have changed as the amount of sorbed organic matter increased. Observations that organic C loadings at maximum sorption did not substantially exceed 1 mg C m−2 and linear rather than asymptotic relations between sorbed C and initial DOM concentrations suggest that organo-mineral complexes may not have reached C saturation under the conditions in the batch sorption experiments of this study. The temperature at which half of the CO2 evolved during thermal analysis (i.e., CO2-T50) increased with increasing C loading, suggesting the sorbed C required greater energy input for combustion. Results of the laboratory incubations to determine relative biological stability of sorbed C were not consistent with the initial hypothesis. The size of potentially mineralizable C pool relative to the total sorbed C decreased with increasing C loading, even though this pool was being degraded more rapidly. Overall, the results did not support the hypothesis that SOM stability decreases with increasing C loading. In spite of generating a wide range of C loadings substantially greater than previous studies, the conditions of the DOM sorption experiments conducted in this study appeared unable to generate organo-mineral complexes exhibiting C saturation behavior. We speculate that measurable decreases in SOM stability may occur only once the threshold of C saturation is reached.

Production of Photo-oxidants by Dissolved Organic Matter During UV Water Treatment

Dissolved organic matter (DOM) irradiated by sunlight generates photo-oxidants that can accelerate organic contaminant degradation in surface waters. However, the significance of this process to contaminant removal during engineered UV water treatment has not been demonstrated, partly due to a lack of suitable methods in the deep UV range. This work expands methods previously established to detect (1)O2, HO•, H2O2, and DOM triplet states ((3)DOM*) at solar wavelengths to irradiation at 254 nm, typical of UV water treatment. For transient intermediates, the methods include a photostable probe combined with selective scavengers. Quantum yields for (1)O2, (3)DOM* and H2O2 were in the same range as for solar-driven reactions but were an order of magnitude higher for HO•, which other experiments indicate is due to H2O2 reduction. With the quantum yields, the degradation of metoxuron was successfully predicted in a DOM solution irradiated at 254 nm. Further modeling showed that the contribution of DOM sensitization to organic contaminant removal during UV treatment should be significant only at high UV fluence, characteristic of advanced oxidation processes. Of the reactive species studied, (3)DOM* is predicted to have the greatest general influence on UV degradation of contaminants.

Direct Photodegradation of Androstenedione and Testosterone in Natural Sunlight: Inhibition by Dissolved Organic Matter and Reduction of Endocrine Disrupting Potential

In surface waters, two of the most commonly observed androgenic steroid hormones are androstenedione (AD) and testosterone (T). This study compares the photodegradation of dilute (<10 μg L(-1)) aqueous solutions of AD and T in natural sunlight, and evaluates the endocrine-disrupting potential of the resulting solutions. This study also examines the effect of dissolved organic matter (DOM) on AD photodegradation. During spring and summer at Henderson, NV, USA (latitude 36.04°N), AD and T underwent direct photodegradation, with half-lives ranging from 3.7 to 10.8 h. In three model DOM solutions, AD's half-life increased by 11% to 35%. Using screening factors to eliminate DOM's inner filter effect, quantum yield calculations suggested that light screening was primarily responsible for AD's increased half-life, and that physical quenching further inhibited AD's photodegradation in two out of three DOM solutions. In vitro androgenic activity of the AD and T solutions decreased approximately as fast as AD and T were removed, suggesting that solar photodegradation reduces the risk of endocrine disruption in surface waters impacted by AD or T, subject to continuing inputs. Reduced in vitro androgenic activity appears to be related to steroid ring cleavage and the formation of highly oxidized photoproducts.

Effect of Dissolved Organic Matter Source and Character on Microbial Hg Methylation in Hg–S–DOM Solutions

Dissolved organic matter (DOM) is a key component of fate and transport models for most metals, including mercury (Hg). Utilizing a suite of diverse DOM isolates, we demonstrated that DOM character, in addition to concentration, influences inorganic Hg (Hg(II)i) bioavailability to Hg-methylating bacteria. Using a model Hg-methylating bacterium, Desulfovibrio desulfuricans ND132, we evaluated Hg-DOM-sulfide bioavailability in washed-cell assays at environmentally relevant Hg/DOM ratios (∼1-8 ng Hg/mg C) and sulfide concentrations (1-1000 μM). All tested DOM isolates significantly enhanced Hg methylation above DOM-free controls (from ∼2 to >20-fold for 20 mg C/L DOM solutions), but high molecular weight/highly aromatic DOM isolates and/or those with high sulfur content were particularly effective at enhancing Hg methylation. Because these experiments were conducted under conditions of predicted supersaturation with respect to metacinnabar (β-HgS(s)), we attribute the DOM-dependent enhancement of Hg(II)i bioavailability to steric and specific chemical (e.g., DOM thiols) inhibition of β-HgS(s) growth and aggregation by DOM. Experiments examining the role of DOM across a wide sulfide gradient revealed that DOM only enhances Hg methylation under fairly low sulfide conditions (≲30 μM), conditions that favor HgS nanoparticle/cluster formation relative to dissolved HgS species.

Reclamation of copper-contaminated soil using EDTA or citric acid coupled with dissolved organic matter solution extracted from distillery sludge

Soil washing using a strong chelating agent is a common practice for restoring contaminated soils, but significant soil fertility degradation and high operation costs are the major disadvantages. Washing soil with a dissolved organic matter (DOM) solution has been identified as a method that can moderate the loss of nutrients in the soil and enhance metal removal. The DOM solutions were extracted from waste sludge obtained from a local whisky distillery. Single chelating washing and chelate-DOM washing were carried out using ethylenediaminetetraacetic acid (EDTA), citric acid, and DOM solutions to remediate highly Cu-contaminated soil. Two-phase washing using 0.34 M citric acid and then 1500 mg L−1 DOM solution (pH 8.5) was found to be most favorable for the soil. With this treatment, 91% Cu was removed from the topsoil; the organic matter, cation exchange capacity, plant-available nitrogen, and available phosphate content increased by 28.1%, 103%, 17.7%, and 422%, respectively.

Reclamation of cadmium-contaminated soil using dissolved organic matter solution originating from wine-processing waste sludge

Soil washing using an acid solution is a common practice for removing heavy metals from contaminated soil in Taiwan. However, serious loss of nutrients from soil is a major drawback of the washing. Distillery sludge can be used to prepare a dissolved organic matter (DOM) solution by extracting its organic constituents with alkaline solutions. This study employed DOM solutions to remediate Cd-contaminated soil (with concentrations up to 21.5mgkg−1) and determine the factors affecting removal of Cd, such as pH, initial concentration of DOM solution, temperature, and washing frequency. When washing with pH 3.0 and 1250mgL−1 DOM solution, about 80% and 81% of Cd were removed from the topsoil at 27°C and subsoil at 40°C, respectively. To summarize the changes in fertility during DOM washing with various pH solutions: the increase in organic matter content ranged from 7.7% to 23.7%; cation exchange capacity (CEC) ranged from 4.6% to 13.9%; available ammonium (NNH4) content ranged from 39.4% to 2175%; and available phosphorus content ranged from 34.5% to 182%. Exchangeable K, Ca, and Mg remained in the topsoil after DOM washing, with concentrations of 1.1, 2.4, and 1.5 times higher than those treated with HCl solution at the same pH, respectively.

Impacts of Sampling Dissolved Organic Matter with Passive Capillary Wicks Versus Aqueous Soil Extraction

Quantitative characterization of dissolved organic matter (DOM) in soil and vadose zone solution is needed to interpret mechanisms of nutrient and C cycling as well as bio‐weathering processes. Passive capillary wick samplers (PCaps) are useful for soil solution sampling because they can provide measures of water and associated DOM‐constituent flux in the unsaturated zone, however potential impacts of the wick material on DOM chemical properties has not been investigated yet. We therefore conducted experiments where aqueous soil extracts were transported along PCap fiberglass wicks in flow‐through experiments. Results indicated limited dissolved organic carbon (DOC) sorption and DOM fractionation, and related parameters (total dissolved nitrogen [TDN], DOM fluorescence components) also remained largely unaffected. We note that this experiment does not account for the extent to which soil hydrologic processes may be affected by PCap field installations. However, given that the wicks did not fractionate significantly DOM, we compared field‐based PCap DOM solution collected in situ with laboratory‐based aqueous soil extraction (ASE) of DOM from the same soils to assess differences in DOM quality. Spectroscopic analysis of DOM in ASE solutions showed lower O‐H stretch/carboxlyate band intensity ratios, more pronounced aliphatic C‐H stretching (Fourier Transform Infrared analysis), higher specific ultraviolet‐absorbance (SUVA254) values as well as greater abundance of fluorescence components in the region attributed to fulvic acids. We conclude that difference in molecular properties of DOM derived from laboratory ASE vs. PCap field collection of the same soils is attributable to differential disturbance effects of the two methods of soil solution collection.