Low Molecular Weight Organic Substances Research Articles

Enhancing the Phytoextraction of Cd, Cu, Pb, and Zn by Portulaca oleracea in a Heavily Contaminated Soil Using Low Molecular Weight Organic Substances: Is Phytoremediation Viable?

AbstractPhytoremediation can be accelerated if contaminated soils are amended with releasing agents. We tested four such materials, citric acid (CA), EDTA, oxalic acid (OA), and tartaric acid (TA) at two doses, 20 and 40 mmol kg−1, amended in a pot experiment to a heavily contaminated soil cultivated with purslane (Portulaca oleracea). We found that Cd extracted with DTPA remained unchanged in all treatments compared to the control except for the treatment of added EDTA at 40 mmol kg−1 (“EDTA-40”). Similar was the case with Cu, Pb, and Zn. As a consequence, Cd in the aboveground plant material increased significantly from 1.21 (control) to 3.84 at EDTA-40 and 3.55 at EDTA-20 (mg kg−1). Similar was the case with all other metals, with Pb exhibiting an impressive fivefold increase to 280.35 mg kg−1 at EDTA-40 from the control. We conclude that EDTA was the most successful releasing agent among those tested, especially for Pb and Zn. However, we come to the conclusion that, based on calculations of the required time to meaningfully reduce soil metals contents, phytoremediation is not a practical option for extremely metal-elevated soils. These findings should be verified under field conditions.

The diversity of genes for the synthesis of opines and their products in representatives of various taxa

Opines are low molecular weight organic substances that occur in marine invertebrates, bacteria, some plants and fungi. Such an unusual range of organisms suggests the importance of studying and systematizing knowledge about the functions of these compounds and the genetic control of their metabolism. In recent years, new data have emerged on plants containing genes for the synthesis of opines as a result of horizontal gene transfer from agrobacteria. This review is devoted to systematization of information about opine synthase genes, their products and functions of the latter.

Genome analysis of the candidate phylum MBNT15 bacterium from a boreal peatland predicted its respiratory versatility and dissimilatory iron metabolism.

Uncultured bacteria of the candidate phylum MBNT15, distantly related to Desulfobacterota, have been identified in a broad range of mostly organic-rich aquatic environments. We assembled a near-complete genome of a member of MBNT15 from a boreal peatland metagenome and used genomic data to analyze the metabolic pathways of this bacterium and its ecological role. This bacterium, designated SHF-111, was predicted to be rod shaped, it lacks flagellar machinery but twitching motility is encoded. Genome-based phylogenetic analysis supported the phylum-level classification of the MBNT15 lineage. Genome annotation and metabolic reconstruction revealed the presence of the Embden–Meyerhof, Entner–Doudoroff and pentose phosphate pathways, as well as the complete tricarboxylic acid (TCA) cycle, and suggested a facultatively anaerobic chemoheterotrophic lifestyle with the ability to ferment peptides, amino acids, fatty acids and simple sugars, and completely oxidize these substrates through aerobic and anaerobic respiration. The SHF-111 genome encodes multiple multiheme c-type cytochromes that probably enable dissimilatory iron reduction. Consistently, the relative abundance of MBNT15 in peatlands positively correlated with iron concentration. Apparently, in the wetland ecosystem, MBNT15 representatives play the role of scavengers, carrying out the complete mineralization of low molecular weight organic substances formed as a result of microbial degradation of complex polymeric substrates. Comparative genome analysis of the MBNT15 phylum revealed that vast majority of its members are capable of aerobic respiration and dissimilatory iron reduction and some species also can reduce sulfur and nitrogen compounds, but not sulfate. Based on phylogenetic and genomic analyses, the novel bacterium is proposed to be classified as Candidatus Deferrimicrobium borealis, within a candidate phylum Deferrimicrobiota.

Control of disinfection byproducts in drinking water treatment plants: Insight into activated carbon filter

The removal efficiencies of disinfection byproducts formation potentials (DBPFPs) and generated DBPs under pre-chlorination condition (pre-generated DBPs) during different drinking water treatment trains in eight full-scale drinking water treatment plants (WTPs) were investigated through field and laboratory studies. Haloacetic acids (HAAs) and haloacetonitriles (HANs) were identified to be two representative DBPs based on cytotoxicity and genotoxicity assessments. The performances of advanced treatment train for HAAs and HANs were better than that of conventional treatment train. However, the efficacy of ozone - biological activated carbon (O3-BAC) was affected by its service time and position in the water treatment process. In addition, the consumption of free chlorine by activated carbon in old granular activated carbon (GAC) filter was higher than that in new one under pre-chlorination condition, resulting in the increase of HAAs and HANs in the GAC filter effluent. This demonstrated that the organic matter adsorbed on older activated carbon generated more HAAs and HANs during pre-chlorination, which inhibited the adsorption of pre-generated DBPs. The ability of GAC/O3-BAC to remove HAAs and HANs was consistent with that of protein-like and low molecular weight organic substances, which could predict the performance of GAC and O3-BAC in treating DBPs.

MEMBRANES FUNCTIONALIZED WITH 1d, 2d and 3d CARBON MATERIALS

Modification of polymer and ceramic mem­branes by modern one-, two- and three- di­men­sional carbon nanomaterials (carbon nano­tubes, fullerenes and their derivatives, oxi­dized and reduced graphene) is consi­dered. It is shown that carbon materials can be incorporated into membrane matrices both as independent components and as a part of multicomponent modifier. The main methods of modification are the addition of modifiers to the polymer solution with subsequent making of polymer membranes, incorporation of nanoparticles of carbon nanomaterials into the pristine membranes, deposition on the outer membrane surface, formation of nanoparticles directly in the pores of the ceramic matrix. Composite membranes containing carbon nanoparticles are used for pervaporation, gas separation, baromembrane processes and low-temperature fuel cells. The addition of carbon nanomaterials to polymers provides better mechanical strength of the membranes. Hydrophilic carbon modifiers increase the resistance of membranes to fouling by organic substan­ces and biofouling, improves their separation ability. Ion-exchange membranes modified with fullerenol and oxidized graphene maintain high proton conductivity at elevated temperatures and low humidity. Сarbon additives increase membrane productivity in baromembrane processes. This effect is especially evident for materials modified with nanotubes: their smooth surface ensures fast liquid transport. These carbon nanomaterials are characterized by antibacterial activity. Composites consisting of nanotubes and an ion-exchange biopolymer, and composites with oxidized graphene and inorganic ion exchanger, give to membranes selectivity to inorganic ions. Ceramic membranes modified with carbon nanoparticles that were formed in the pores of matrices by carbonization of synthetic polymers and polysaccharides have the same properties. Besides, these composites reject organic dyes too. The separating ability of composite membranes ocuures due to both dimensional and charge effects. Carbon or composite nano­particles block the pores of the membranes. The pores formed by the modifier prevent pene­tration of large particles of organic substances, for example, protein macromolecules. The charge effect is realized due to the functional groups of the modifier. For membranes modified with fullerenols, the retaining of low molecular weight organic substances occurs due to adsorption. Fullerene-modified gas sepa­ration and pervaporation membranes show increased permeability and selectivity.

Одержання дорожніх нафтових бітумів методом хімічного модифікування нафтових залишків.

PRODUCTION OF ROAD OIL BITUMENS BY THE METHOD OF CHEMICAL MODIFICATION OF OIL RESIDUES © V.М. Gunka, PhD in technical sciences, Yu.V. Prysiazhnyi, PhD in technical sciences, Yu.Ya. Demchuk, PhD in technical sciences, Yu.M. Hrynchuk, PhD in technical sciences, Yu.V. Sidun, PhD in technical sciences, M.M. Bratychak, Doctor of Chemical Sciences (Lviv Polytechnic Naional University, 12 Stepan Bandera Str., 79013, Lviv, Ukraine) The article is devoted to obtaining road oil bitumen from oil residues by modifying them with relatively cheap low molecular weight organic substances. The proposed method relates to a chemical modification, which, in case of its industrial implementation, will allow avoiding the use of expensive physical modifiers. A 37 % aqueous solution of formaldehyde was used as low molecular weight organic substances (modifier / chemical reagent of the process) for chemical modification of tar; concentrated sulfuric acid (H2SO4) was used as a catalyst for the chemical modification of tar. As a feedstock for chemical modification, we used an oil residue - tar, selected at PJSC “Ukrtatnafta” (Kremenchug, Ukraine). The chemical modification with formaldehyde was carried out in hermetic stationary containers capable of operating under excess pressure. The photographs of the equipment are given. Since the ultimate goal of the work was to obtain road oil bitumen, then, analyzing the results of experimental studies, we focused on the quality characteristics of this particular product. At the same time, the most important quality indicators were determined, namely: the depth of needle penetration, softening temperature, ductility (extensibility), adhesion to glass (adhesion to glass), Fraas brittle temperature, penetration index. For tar, the following characteristics such as density, flash point in an open crucible, and a boiling point were additionally determined. As a result of the experiments, the fundamental possibility of obtaining road oil bitumen by the method of chemical modification of tar with formaldehyde was established. It was revealed that the process factors (formaldehyde content in the reaction mixture, catalyst content in the reaction mixture, temperature and duration) have a significant effect on the quality of the resulting product. Changing their values allows you to adjust the values of the quality characteristics of the resulting bitumen. Keywords: binders, bitumen, oil residue, modification. Corresponding author V.М. Gunka, e-mail: volodymyr.m.hunka@lpnu.ua

Study on the Mechanism and Kinetics of Waste Polypropylene Cracking Oxidation over the Mn2O3/HY Catalyst by TG–MS and In Situ FTIR

The low temperature and high efficiency cracking oxidation of organic solid waste over the bifunctional catalyst with both acidity and oxidizing property is an environmentally attractive technology. In this study, the reaction mechanism and kinetics behavior of waste polypropylene (PP) during catalytic cracking oxidation processes were investigated utilizing thermo-gravimetry (TG), differential scanning calorimetry, TG–mass spectrometric, and in situ Fourier transform infrared (in situ FTIR) spectroscopy. PP was cracked into low-molecular weight organic substances (ester, ketone, etc.) over acid sites, which were further oxidized to CO2 and H2O over oxygen vacancy in the Mn2O3/HY catalyst. The kinetics of catalytic cracking oxidation of pure PP and PP over different model catalysts was analyzed by Gauss-Peak function and the distributed activation energy model (DAEM). The catalytic oxygenation apparent activation energy (E) values of pure PP and PP over Mn2O3, HY, and Mn2O3/HY catalysts were 130–190 kJ/mol, 200–618, 108–228, and 41–99 kJ/mol, respectively. DAEM expressed appropriately the various changing trends of E in the reaction process. This theoretical basis of the catalytic cracking oxidation process of polymers would provide a reference for the design and optimization of the reactor and application upgrade of engineering.

Highly sensitive determination of mercury by improved liquid cathode glow discharge with the addition of chemical modifiers

The sample introduction system of early miniaturized liquid cathode glow discharge (LCGD) was improved, and then LCGD was used as an excitation source of atomic emission spectrometry (AES) for the detection of mercury in water samples. The effects of chemical modifiers, such as ionic surfactants and low molecular weight organic substances, on emission intensities of Hg were investigated. The results showed that the addition of 4% methanol and 0.15% hexadecyltrimethylammonium bromide (CTAB) can enhance the net intensity of Hg about 15.5-fold and 7.7-fold, and the sensitivity (S) of Hg about 15.2-fold and 5.6-fold, respectively. Adding chemical modifiers markedly reduce the interferences from Fe3+, Co2+, Cl−, Br−, and I− ions. The limit of detection (LOD) is reduced from 0.35 mg L−1 for no chemical modifier to 0.03 mg L−1 for 4% methanol and 0.05 mg L−1 for 0.15% CTAB. The relative standard deviation (RSD) of Hg with adding 4% methanol, 0.15% CTAB and no chemical modifier is 2.38%, 1.17% and 3.00%, respectively, and the power consumption is below 75 W. All results indicated that the determination of Hg using improved LCGD with the addition of chemical modifiers has high sensitivity, low LOD, well precision and low power consumption. Water samples containing high mercury (10–20 mg L−1) and low mercury (0.2–5 mg L−1) can be determined by improved LCGD-AES with no chemical modifier and 4% methanol, respectively. Adding 4% methanol significantly reduces the matrix effects from real water samples. The measurement results of spiked samples using LCGD-AES are largely consistent with the spiked value. In addition, the recoveries of Hg are ranged from 95.7% to 114.8%, suggesting that the measurement results of Hg by LCGD-AES are accurate and reliable. Overall, the improved LCGD-AES with adding chemical modifiers is a promising technique for on-site and real-time monitoring of Hg in water samples because of its portability, lower cost and speed.

Evaluation of Dissolved Organic Matter Removal Characteristics in GAC Adsorption Process in Drinking Water Treatment Process using LC-OCD-OND

Objectives:In this study, we used liquid chromatograph-organic carbon detector-organic nitrogen detector (LC-OCD-OND) to evaluate adsorption and breakthrough characteristics of NOM fractions (biopolymers (BP), humic substances (HS), building blocks (BB) and low molecular weight organic substances (LMW-O)) according to the various characteristics of the different materials of granular activated carbons (GACs).Methods:Breakthrough characteristics, adsorption capacity and partition coefficients were evaluated by NOM fractions (BP, HS, BB, and LMW-O) using a lab-scale GAC adsorption column filled with coal-, coconut- and wood-based GAC. The GAC column test was operated with 10 minutes empty bed contact time (EBCT). The pore characteristics of each GAC were evaluated using an automated gas sorption analyzer (Autosorb iQ3, Quantachrome, USA) and the concentrations of NOM fractions in the influent and effluent were analyzed using chromatography LC-OCD-OND (Model 8, DOC-Labor, Germany).Results and Discussion:NOM adsorption capacity was evaluated for different materials of laboratory scale GAC adsorption column test. To study the adsorption behavior of individual NOM fractions according to the operation time, NOM was fractionated into BP, HS, BB and LMW-O by LC-OCD-OND, and the individual NOM fractions were quantified. Higher MW like BP was not adsorbed to GAC, in contrast, HS, BB, and LMW-O were well removed during the initial operation period, the concentrations in the effluent gradually increased as increase the operation period until reaching to the pseudo steady-state. Poor removal of BP in GAC adsorption may be a result of blocking the pores with large MW BP and hinder the access to the pores. However, in the case of HS, BB, and LMW-O, as the molecular size decreased, these organic matters easily access to the pores inside of GAC. It was confirmed through the partition coefficient that the adsorption capacity of these NOM fractions increased in proportion to the MW. In addition, in order to achieve a high NOM removal efficiency in the GAC adsorption process, not only the specific surface area, pore volume, and pore width of the GAC must be large, but also the pH<sub>zpc</sub> must be higher than the neutral pH level.Conclusions:In order to achieve a high NOM removal efficiency in the GAC adsorption process, not only the specific surface area, pore volume, and pore width of the GAC must be large, but also the pH<sub>zpc</sub> must be higher than the neutral pH level. In addition, in the NOM fractions, BP were not adsorbed to GAC, while the adsorption capacity of the remaining NOM fractions increased as the MW of the NOM fractions decreased. LMW-O was the most adsorbed, followed by BB, HS and BP. BP and HS play an important role in the membrane fouling that are introduced a lot into domestic and foreign water treatment plants. This study showed that the BP was not removed by the adsorption mechanism of the GAC process. In addition, HS was adsorbed and removed at the beginning of the operation, but the adsorption capacity of HS decreased rapidly as the operation period increased compared to other NOM fractions. Therefore, the GAC adsorption process is not expected to be an effective pre-treatment technology for reducing membrane foulants. Previous studies showed that the yields of DBPs (µmol･DBP/µmol･C) in the high MW humic and low MW non-humic fractions are similar. Therefore, it is suggested that the GAC adsorption process is more effective for DBP precursor control in water containing a larger percentage of LMW NOM.

MODIFICATION OF HUMIC SUBSTANCES FOR DEVELOPMENT OF MATERIALS FOR ENVIRONMENTAL TECHNOLOGIES

Humic substances are high molecular weight refractory polycationites formed during decay of living organic matter and through biosynthesis of low molecular weight organic substances (metabolites or decay products of living organisms). Presence of many functional groups in the structure of humic substances determines their ability to interact with metal ions forming stable complexes and influencing metal ion speciation in the environment and mobility, behaviour and speciation forms in the environment. Presently humic substances are a product of industrial scale and quantities in amounts of hundreds of tons are produced. The aim of this study is to analyse derivatization possibilities of humic substances. To achieve this aim derivatization of humic substances using acylation (at first introduction of acetylgroups, but also changing length acyl chains are considered) are used. Also alkylation is used. Mild oxidation can help to obtain modified products with reduced molecular weight. Another approach includes introduction of new functional groups and structures. To achieve this aim, conjugates with short peptides, amines and sugar derivatives using coupling with water-soluble carbodiimides are obtained. As basic characteristics elemental analysis as well as functional analysis have been used, supported with Fourier transform infrared (FTIR), 13C nuclear magnetic resonance spectrometry and other methods. Derivatives of humic substances containing sulpho, amino, and hydroxylgroups and thiolgroups were synthesized and their properties were analyzed in respect to their their elemental composition; functional group content changes in spectral characteristics. The derivatives of humic substances showed significant differences in the number and in ability to interact with the metal ions, which were reflected in their complexation properties towards metal ions. FTIR spectra gave evidence of the presence of metal ions, strongly bound and protected in inner sphere complexes. The obtained derivatives of humic substances can be used for remediation of environment contaminated with heavy metal ions.

Composition, Spatial Distribution Characteristics and Source Analysis of Chromophoric Dissolved Organic Matter in the Lanzhou Reach of the Yellow River

Chromophoric dissolved organic matter (CDOM) in riverine systems can be affected by environmental conditions and land-use, and can thus provide important information regarding anthropogenic activities in surrounding landscapes. It can modify the optical properties of waters and affect the balance and availability of dissolved nutrients and metals in water bodies. However, the characteristics of CDOM in the Lanzhou reach of the Yellow River have not yet been reported. In this study, the optical properties of water samples collected at 32 locations during April 2017 across the Lanzhou reach of the Yellow River were examined using UV-VIS and excitation-emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC), to determine CDOM compositional changes, spatial distribution characteristics, and sources. Cluster analysis was used to categorize samples into groups of similar pollution levels within a study area. Results showed that CDOM was primarily comprised of low molecular weight organic substances with aromatic structure belonging to complex "protein-like-humic-like" substances, and dominated by protein-like substances (organism sources). Two humic-like components (C1, C4), one tryptophan-like component (C2), and one non-humic-like component (C3) were identified by PARAFAC. Tryptophan-like substances were predominant in the components of CDOM, accounting for 51.06% of average total fluorescence intensity. Humic-like materials and non-humic-like substances accounted for 36.74% and 12.20%, respectively. Weak correlations were observed between protein-like substances and humic-like substances, indicating different sources of these components. The distribution of total fluorescence intensity showed a distinct spatial pattern; trends in fluorescence intensity were weak-strong-weak along an upstream to downstream continuum, mainly affected by changes in the content of protein-like substances. The spatial variation of the CDOM in the Lanzhou reach of the Yellow River can therefore be assessed based on protein-like materials dynamics. Public spaces along rivers offer opportunities for community gatherings and recreational activities. However, high-intensity anthropogenic activities strongly influence CDOM concentration and composition in this area in different ways; sources include increased residential/commercial wastewater, catering, water recreation facilities pollution, shipping, and a small amount of industrial discharge. In addition, it was concluded that endogenetic pollution may become the main source of internal loading in the Lanzhou reach of the Yellow River, implying that stronger endogenetic pollution control is needed to alleviate CDOM pollution and improve water quality.

Behaviour of carbon-14 containing low molecular weight organic compounds in contaminated groundwater under aerobic conditions

Short chain carbon-14 (14C) containing organic compounds can be formed by abiotic oxidation of carbides and impurities within nuclear fuel cladding. During fuel reprocessing and subsequent waste storage there is potential for these organic compounds to enter shallow subsurface environments due to accidental discharges. Currently there is little data on the persistence of these compounds in such environments. Four 14C-labelled compounds (acetate; formate; formaldehyde and methanol) were added to aerobic microcosm experiments that contained glacial outwash sediments and groundwater simulant representative of the Sellafield nuclear reprocessing site, UK. Two concentrations of each electron donor were used, low concentration (10−5 M) to replicate predicted concentrations from an accidental release and high concentration (10−2 M) to study the impact of the individual electron donor on the indigenous microbial community in the sediment. In the low concentration system only ∼5% of initial 14C remained in solution at the end of experiments in contact with atmosphere (250–350 h). The production of 14CO2(g) (measured after 48 h) suggests microbially mediated breakdown is the primary removal mechanism for these organic compounds, although methanol loss may have been partially by volatilisation. Highest retention of 14C by the solid fractions was found in the acetate experiment, with 12% being associated with the inorganic fraction, suggesting modest precipitation as solid carbonate. In the high concentration systems only ∼5% of initial 14C remains in solution at the end of the experiments for acetate, formate and methanol. In the formaldehyde experiment only limited loss from solution was observed (76% remained in solution). The microbial populations of unaltered sediment and those in the low concentration experiments were broadly similar, with highly diverse bacterial phyla present. Under high concentrations of the organic compounds the abundance of common operational taxonomic units was reduced by 66% and the community structure was dominated by Proteobacteria (particularly Betaproteobacteria) signifying a shift in community structure in response to the electron donor available. The results of this study suggest that many bacterial phyla that are ubiquitous in near surface soils are able to utilise a range of 14C-containing low molecular weight organic substances very rapidly, and thus such substances are unlikely to persist in aerobic shallow subsurface environments.

Construction of Viable Soil Defined Media Using Quantitative Metabolomics Analysis of Soil Metabolites.

Exometabolomics enables analysis of metabolite utilization of low molecular weight organic substances by soil bacteria. Environmentally-based defined media are needed to examine ecologically relevant patterns of substrate utilization. Here, we describe an approach for the construction of defined media using untargeted characterization of water soluble soil microbial metabolites from a saprolite soil collected from the Oak Ridge Field Research Center (ORFRC). To broadly characterize metabolites, both liquid chromatography mass spectrometry (LC/MS) and gas chromatography mass spectrometry (GC/MS) were used. With this approach, 96 metabolites were identified, including amino acids, amino acid derivatives, sugars, sugar alcohols, mono- and di-carboxylic acids, nucleobases, and nucleosides. From this pool of metabolites, 25 were quantified. Molecular weight cut-off filtration determined the fraction of carbon accounted for by the quantified metabolites and revealed that these soil metabolites have an uneven quantitative distribution (e.g., trehalose accounted for 9.9% of the <1 kDa fraction). This quantitative information was used to formulate two soil defined media (SDM), one containing 23 metabolites (SDM1) and one containing 46 (SDM2). To evaluate the viability of the SDM, we examined the growth of 30 phylogenetically diverse soil bacterial isolates from the ORFRC field site. The simpler SDM1 supported the growth of 13 isolates while the more complex SDM2 supported 15 isolates. To investigate SDM1 substrate preferences, one isolate, Pseudomonas corrugata strain FW300-N2E2 was selected for a time-series exometabolomics analysis. Interestingly, it was found that this organism preferred lower-abundance substrates such as guanine, glycine, proline and arginine and glucose and did not utilize the more abundant substrates maltose, mannitol, trehalose and uridine. These results demonstrate the viability and utility of using exometabolomics to construct a tractable environmentally relevant media. We anticipate that this approach can be expanded to other environments to enhance isolation and characterization of diverse microbial communities.

Effects of biotic and abiotic factors on soil organic matter mineralization: Experiments and structural modeling analysis

Soil organic matter (SOM) mineralization is affected by various abiotic and biotic factors, as well as the input of exogenous organic substances. Our previous studies have shown that SOM mineralization in flooded rice paddies is lower than that in adjacent upland soils in subtropical agro-ecosystems. However, the main factors contributing to the differences in SOM mineralization remain unclear. To compare the effects of biotic and abiotic factors on SOM mineralization between upland and paddy soils, we incubated upland and paddy (flooded) soils with three low molecular weight organic substances (LMWOS, i.e., glucose, acetic acid, or oxalic acid) for 30 days under field conditions. Generally, the average CO2 efflux from upland soil was higher than that in paddy soil with the same LMWOS addition. The total content of phospholipid fatty acids (PLFAs) in paddy soil was 2–5 times higher than that of upland soil, irrespective of the LMWOS added. Redundancy analyses indicated that microbial community composition was influenced mainly by the low redox potential (Eh) and dissolved organic carbon in paddy soil. Structural equation modeling revealed that, among abiotic factors, temperature exerted indirect effects on SOM mineralization by influencing biotic factors in both soils; Eh has a positive and direct effect on SOM mineralization in paddy soil. In terms of biotic factors, SOM mineralization in upland soil was mainly regulated by the quantity of bacteria. In paddy soil, SOM mineralization was largely influenced by the ratio of fungal to bacterial PLFAs and peroxidase activity.

Weaker priming and mineralisation of low molecular weight organic substances in paddy than in upland soil

Although soil organic matter (SOM) and microbial biomass pools in flooded paddy soils are generally larger than they are in upland soils, the processes (i.e., slower mineralisation, other types of C stabilization, and a negative priming effect) underlying higher SOM stocks in paddy soil are unclear. To elucidate these processes, three 13C labelled low molecular weight organic substances (13C-LMWOS) (i.e., glucose, acetic acid, and oxalic acid) were incubated in upland and paddy soils under simulated field conditions. Within 30 days of incubation, acetic acid exhibited the highest mineralisation in both soils. The amount of mineralisation of glucose in upland soil was higher than that of oxalic acid (p < 0.05), whereas the opposite was observed for paddy soil. Mineralisation of all three LMWOS was lower in paddy soil than that in upland soil (p < 0.05), illustrating that the molecular structure of the LMWOS as well as soil management determined the mineralisation rate. The priming effect evoked by oxalic acid and glucose was lower in paddy than in upland soil (p < 0.05). Therefore, the generally weaker mineralisation and priming effect of LMWOS observed in paddy soil contributed to higher carbon accumulation than they did in upland soil. Priming effect was positively correlated with fungal abundance, which was lower in paddy soil than in upland soil. Thus, slow organic C turnover in paddy soil is partly attributed to the suppression of fungal activity by flooding.

Mixing behavior and photobleaching of chromophoric dissolved organic matter in the Changjiang River estuary and the adjacent East China Sea

The distribution and chemical properties of chromophoric dissolved organic matter (CDOM) in the Changjiang River estuary and the adjacent ECS were determined in February and July 2014. CDOM concentration (aCDOM(355)) decreased along the salinity gradient, indicating that terrestrial input significantly influenced CDOM in the study area. The runoff from the Changjiang River with smaller spectral slope ratios (SR) dominated SR variability in our study area in July, and the photodegradation of allochthonous CDOM increased SR in the open sea in February. CDOM excitation/emission matrix spectra subjected to parallel factor analysis identified four components: terrestrial humic-like component (C1), autochthonous protein-like components (C2 and C4), and terrestrial tryptophan-like component (C3). C1 and C3 showed a conservative mixing behavior, whereas C2 and C4 were appeared to be influenced by chlorophyll-a (Chl-a). Our sunlight exposure experiment showed that aCDOM(355) (42% at station C1 and 16% at station A6-8) decreased and SR (27% at station C1 and 9.2% at station A6-8) increased. These findings suggested that CDOM molecules were photochemically degraded from high-molecular weight dissolved organic matter (DOM) into low-molecular weight organic substances. The fluorescence intensities of terrestrially derived C1 and C3 decreased with prolonged illumination in samples from both sites. However, autochthonous C2 and C4 moderately increased after they were exposed to sunlight. Results of this study demonstrated that terrestrially derived DOM was more susceptible to irradiation than autochthonous DOM.

Microbial uptake and utilization of low molecular weight organic substrates in soil depend on carbon oxidation state

The fate of low molecular weight organic substances (LMWOSs) in soil is regulated by microbial uptake. However, C oxidation state, the number of C atoms and –COOH groups in the LMWOS can affect their microbial utilization. Thus, the aim of this study was to reveal the effects of substance chemical properties on initial uptake and utilization of sugars, carboxylic and amino acids by microorganisms. Soil solution, spiked with 14C-labelled glucose, fructose, malate, succinate, formate, alanine or glycine, was added to the soil and 14C was traced in the soil solution, CO2, cytosol, and soil organic carbon (SOC) over 24 h. The half-life time of all LMWOS in the soil solution varied between 0.6 min (formic acid) and 5.0 min (sugars), indicating its dependence on C oxidation state of the substances. The half-life time of 14C in the fast mineralized pool in microorganisms, ranged between 30 (malic acid) and 80 (glycine) min and was independent on either C oxidation state, the number of C atoms, or number of –COOH groups. This suggests that intercellular metabolic pathways are more important for LMWOS transformation in soil than their basic chemical properties. The portion of mineralized LMWOS increased with their C oxidation state (20% for sugars vs. 90% for formic acid) corresponding to the decrease of C incorporated into the cytosol and SOC pools. Concluding, the physicochemical properties of the common LMWOS allow predicting their microbial uptake from soil solution and subsequent partitioning of C within microbial biomass.

“Non-metabolizable” glucose analogue shines new light on priming mechanisms: Triggering of microbial metabolism

Priming of soil organic matter decomposition has attracted much research interest, yet a conclusive mechanistic explanation of the phenomenon remains elusive. One proposal is that low molecular weight organic substances might “trigger” an acceleration of microbial metabolism. For the first time, we applied a glucose analogue to soil to demonstrate triggering of microbial metabolism, and to estimate its relative contribution to priming. “Non-metabolizable” glucose analogues have been widely used in pure culture studies to mimic glucose, but never in soil biochemistry. We hypothesized that analogue molecules will elicit a metabolic response in microorganisms despite limited catabolism, and thereby confirm the proposed triggering.The effect of 14C-labeled 3-O-methyl-d-glucose (OMG) – a common “non-metabolizable” glucose analogue – on soil organic matter mineralization was compared to that of 14C-labeled d-glucose. OMG was mineralized, but its mineralization was initially impeded and substantially delayed, relative to glucose. OMG caused brief but strong priming in the first 24 h, increasing unlabeled CO2 efflux by 173%, 89% and 36% above control for additions of 0.49, 2.4 and 4.9 μmol OMG g−1 soil, respectively. In contrast, glucose caused low or negative priming on the first day. On the first day after OMG addition, a negative correlation between priming and OMG mineralization indicated that triggering is a valid mechanism of microbial activation during a famine-feast transition, but is short-lived.Glucose mineralization peaked on the second day for medium and high additions, coinciding with peaks in positive priming. Maximum substrate mineralization also coincided with peaks in priming for medium and high OMG levels, but these occurred 9 and 11 days after addition, respectively. This revealed non-triggering priming mechanisms, which contributed most to priming and were closely coupled to substrate mineralization. By separating energy- and substrate-dependent metabolic processes from triggering processes, the glucose analogue 3-O-methyl-d-glucose enabled triggering to be demonstrated, but triggering by glucose occurs without contributing greatly to priming.

Characteristics and sources analysis of riverine chromophoric dissolved organic matter in Liaohe River, China

Chromophoric dissolved organic matter (CDOM) in riverine systems can be affected by environmental conditions and land-use, and thus could provide important information regarding human activities in surrounding landscapes. The optical properties of water samples collected at 42 locations across the Liaohe River (LHR, China) watershed were examined using UV-Vis and fluorescence spectroscopy to determine CDOM characteristics, composition and sources. Total nitrogen (TN) and total phosphorus (TP) concentrations at all sampling sites exceeded the GB3838-2002 (national quality standards for surface waters, China) standard for Class V waters of 2.0 mg N/L and 0.4 mg P/L respectively, while trophic state index (TSIM) indicated that all the sites investigated were mesotrophic, 64% of which were eutrophic at the same time. Redundancy analysis showed that total suspended matter (TSM), dissolved organic carbon (DOC), and turbidity had a strong correlation with CDOM, while the other parameters (Chl a, TN, TP and TSIM) exhibited weak correlations with CDOM absorption. High spectral slope values and low SUVA254 (the specific UV absorption) values indicated that CDOM in the LHR was primarily comprised of low molecular weight organic substances. Analysis of excitation-emission matrices contour plots showed that CDOM in water samples collected from upstream locations exhibited fulvic-acid-like characteristics whereas protein-like substances were most likely predominant in samples collected in estuarine areas and downstream from large cities. These patterns were interpreted as indicative of water pollution from urban and industrial activities in several downstream sections of the LHR watershed.

Evaluation of flow injection-solution cathode glow discharge-atomic emission spectrometry for the determination of major elements in brines

A new method for the determination of major metal elements in high salinity brines was developed by solution cathode glow discharge (SCGD) with flow injection analysis (FIA). The matrix interferences of major cations and anions in brines have been evaluated. It was found that high concentration of Na+ and K+ could interfere each other, K+ at a concentration of 400mgL−1 enhanced the signal intensity of Na+ more than 20%. The effect of the anions was observed and it was noted that the signal intensity of both Ca2+ and Mg2+ were suppressed significantly when the SO42− reached 100mgL−1. It was demonstrated that some low molecular weight organic substances such as formic acid, glycerol and ascorbic acid could eliminate interference of SO42− even with volume percentages of 0.5%. Under the optimized condition, the proposed FIA-SCGD can determine K, Na, Ca and Mg with the limits of detection of 0.49 (K), 0.14 (Na), 11 (Ca) and 5.5 (Mg) ngmL−1. The proposed method has been successfully applied to the analysis of 5 salt lake samples and compared with those obtained with inductively coupled plasma atomic emission spectrometry (ICP-AES). The advantages of small size, low energy consumption, good stability and repeatability indicated that the SCGD is promising for the determination of major ions in brine samples.