Unextractable Fraction Research Articles

Analysis of pectin-cellulose interaction in cell wall of lotus rhizome with assistance of ball-milling and galactosidase

The current study sought to depict the structural feature of polysaccharides extracted from Na2CO3 unextractable fraction (LUN) of lotus rhizome using galactosidase with assistance of ball milling. The extracted polysaccharides were a complex of cellulose microfibrils and the RG-I structural domain of pectin, and the top three monosaccharides were glucose, galactose and galactose uronic acid, which allowed to tune the properties of the enzyme-hydrolyzed polysaccharide from LUN after 15 and 45 min of ball milling. The data of XRD revealed that pectin has a masking effect on the diffraction peaks of cellulose components. The removing of the polysaccharides could increase the degree of crystallinity and the pectin-cellulose interaction mainly occured through the galactan side chain was speculated. Textural characterization by SEM exhibited a cross-linked rod-like structure, which is similar to the structure of cellulose microfibrils. The morphological analysis of AFM revealed that L15-P (enzyme-hydrolyzed polysaccharide from LUN after 15 min of ball milling) contained relatively ordered and uniform network structures. Overall, the present study provides an important insight into cell wall of lotus rhizome matrix polysaccharide.

Targeted pectin depletion enhances the potential of high-pressure homogenization to increase the network forming potential of tomato cell wall material

The current study addresses the influence of pectin depletion on the potential of high-pressure homogenization (HPH) to increase the network forming potential of the cell wall material (CWM) from tomato. Therefore, the microstructure, water binding capacity and viscoelastic properties of the alcohol-insoluble residue (AIR) and unextractable fractions (UFs) obtained after different levels and methods of pectin extraction were determined in suspension before and after functionalization by HPH. Before HPH, the AIR and the UFs obtained by solvent-based pectin extraction were all characterized by particles displaying cell-like morphology and the storage modulus (G′) of the respective suspensions was maximal at partial pectin depletion. The network forming potential of the CWM could only be increased by HPH when extensive disruption of the cell wall network was realized instead of mainly breakage. Even when higher pressure levels were applied (up to 80 MPa), preceding weakening of the cell wall network by pectin extraction was a prerequisite to favor efficient disruption of the CWM during HPH above deformation and breakage. Apart from the effect of partial pectin depletion as such on the cell wall strength, the impact of the extraction conditions (e.g., acid conditions at high temperature) weakening the residual cell wall seemed important. This had repercussions on the potential of HPH to functionalize the CWM. While the G’ decreased upon HPH (evaluated at 20 MPa) for non-pectin-depleted or partially pectin-depleted CWM generated by using mild extraction conditions, a clear increase was observed upon HPH of CWM which was partially or extensively pectin-depleted using harsher extraction conditions.

Microstructural and Texturizing Properties of Partially Pectin-Depleted Cell Wall Material: The Role of Botanical Origin and High-Pressure Homogenization.

In the current study, the texturizing properties of partially pectin-depleted cell wall material (CWM) of apple, carrot, onion and pumpkin, and the potential of functionalization by high-pressure homogenization (HPH) were addressed. This partially pectin-depleted CWM was obtained as the unextractable fraction after acid pectin extraction (AcUF) on the alcohol-insoluble residue. Chemical analysis was performed to gain insight into the polysaccharide composition of the AcUF. The microstructural and functional properties of the AcUF in suspension were studied before HPH and after HPH at 20 and 80 MPa. Before HPH, even after the pectin extraction, the particles showed a cell-like morphology and occurred separately in the apple, onion and pumpkin AcUF and in a clustered manner in the carrot AcUF. The extent of disruption by the HPH treatments at 20 and 80 MPa was dependent on the botanical origin. Only for the onion and pumpkin AcUF, the water binding capacity was increased by HPH. Before HPH, the texturizing potential of the AcUFs was greatly varying between the different matrices. Whereas HPH improved the texturizing potential of the pumpkin AcUF, no effect and even a decrease was observed for the onion AcUF and the apple and carrot AcUF, respectively.

The Structure and Composition of Extracted Pectin and Residual Cell Wall Material from Processing Tomato: The Role of a Stepwise Approach versus High-Pressure Homogenization-Facilitated Acid Extraction.

In literature, different pectin extraction methods exist. In this study, two approaches starting from the alcohol-insoluble residue (AIR) of processing tomato are performed in a parallel way to facilitate the comparison of pectin yield and the compositional and structural properties of the extracted pectin and residual cell wall material obtained. On the one hand, pectin is extracted stepwise using hot water, chelating agents and low-alkaline conditions targeting fractionation of the pectin population. On the other hand, an industrially relevant single-step nitric acid pectin extraction (pH 1.6) is performed. In addition to these conventional solvent pectin extractions, the role of high-pressure homogenization (HPH) as a physically disruptive treatment to facilitate further pectin extraction from the partially pectin-depleted fraction obtained after acid extraction is addressed. The impact of HPH on the pectin cell wall polysaccharide interactions was shown as almost two thirds of the residual pectin were extractable during the subsequent extractions. For both extraction approaches, pectin obtained further in the sequence was characterized by a higher molecular mass and a higher amount of rhamnogalacturonan I domains. The estimated hemicellulose and cellulose content increased from 56 mol% for the AIR to almost 90 mol% for the final unextractable fractions of both methods.

Molecular transformation of dissolved organic matter in refinery wastewater.

Dissolved organic matter (DOM) has an important impact on the water treatment and reuse of petroleum refinery wastewater. In order to improve the treatment efficiency, it is necessary to understand the chemical composition of the DOM in the treatment processes. In this paper, the molecular composition of DOM in wastewater samples from a representative refinery were characterized. The transformation of various compounds along the wastewater treatment processes was investigated. A total of 61 heteroatomic class species were detected from the DOM extracts, in which CHO (molecules composed of carbon, hydrogen, and oxygen atoms) and CHOS (CHO molecules that also contained sulfur) class species were the most abundant and account for 78.43% in relative mass peak abundance. The solid phase extraction DOM from the dichloromethane unextractable fraction exhibited a more complex molecular composition and contained more oxygen atoms than in the dichloromethane extract. During wastewater treatment processes, the chemical oxygen demand (COD) and ammonia-nitrogen were reduced by more than 90%. Volatile organic compounds (VOCs) accounted for about 30% of the total COD, in which benzene and toluene were dominant. After biochemical treatment, the VOCs were effectively removed but the molecular diversity of the DOM was increased and new compounds were generated. Sulfur-containing class species were more recalcitrant to biodegradation, so the origin and transformation of these compounds should be the subject of further research.

Identification and characterization of some putative genes involved in arabinoxylan biosynthesis in Plantago ovata.

Plantago ovata is an important source of Psyllium (Isabgol), which swells upon contact with water forming mucilaginous mass, largely composed of arabinoxylans. In this study, we analyzed the expression pattern of arabinoxylan biosynthetic pathway genes at different stages of seed development in P. ovata. Besides, arabinoxylans were quantified at different stages of seed development in water extractable and water unextractable fractions. The expression analysis revealed 5-8 fold increase in the levels of expression of some genes involved in arabinoxylan biosynthetic pathway such as UDP-arabinopyranose mutase, UDP-xylosyltransferase 2 and xylan glucuronosyltransferase at 15days after pollination stage in seed. The xylose and arabinose units were analyzed at different stages of seed development and also in water-soluble (cold water and hot water), alkali and ethanolic fractions. The concentration of xylose and arabinose units increased steadily after pollination. Overall, alkali extract had high concentration of xylose (0.70 ± 0.022mg/g) and arabinose units (0.10 ± 0.01mg/g) at 15days after pollination stage.

Variation of protein MWD parameters and their associations with free asparagine concentration and quality characteristics in hard red spring wheat

The lower free asparagine concentration (FAC) in wheat is better since it is a precursor to form carcinogenic acrylamide during baking. This research was performed to determine the variations of protein molecular weight distribution (MWD) parameters and the associations of protein MWD parameters with quality characteristics and FAC using eleven hard red spring (HRS) wheat genotypes grown at three locations in North Dakota. Among MWD parameters, the polymeric proteins of SDS unextractable fraction were found to be useful in screening HRS wheat genotypes for low FAC and improvement of bread-making quality characteristics. The ANOVA indicated that growing locations and genotypes significantly (P < 0.01) influenced variation of SDS unextractable polymeric protein parameters while effect of genotype by location interaction was non-significant (P > 0.05). The quantity of SDS unextractable polymeric proteins had significant and positive genotypic correlations (rg) with quality characteristics including mixograph pattern (rg = 0.87, P < 0.01) and bread loaf volume (rg = 0.86, P < 0.01). The ratio of SDS unextractable polymeric proteins to total protein had a negative correlation with FAC (rg = −0.92, P < 0.01). These results supported the conclusion that the genotypic variations were primarily associated with the significant (P < 0.05) correlations of SDS unextractable polymeric protein parameters with mixograph pattern, bread loaf volume, and FAC.

Variation and Correlation of Protein Molecular Weight Distribution and Semolina Quality Parameters for Durum Genotypes Grown in North Dakota

This research assessed variation of protein molecular weight distribution (MWD) parameters and their correlations with quality characteristics of semolina samples that were obtained from durum genotypes grown in North Dakota. Sodium dodecyl sulfate buffer extractable and unextractable proteins in semolina were analyzed for MWD by size‐exclusion HPLC with a microbore column. ANOVA indicated that quantitative variations of all the HPLC protein fractions were significantly (P &lt; 0.001) influenced by growing environments. The extractable and unextractable gluten proteins correlated differently with semolina gluten characteristics. Both gluten index and mixograph classification showed positive correlations (P &lt; 0.05) with unextractable polymeric proteins and negative correlations (P &lt; 0.05) with extractable gliadins and polymeric proteins. Quantitative variations of gluten proteins greatly influenced spaghetti cooking characteristics. Specifically, cooked spaghetti firmness (CSF) had high and positive simple linear correlations (P &lt; 0.001) with quantity of gluten proteins in both extractable and unextractable fractions. However, a qualitative MWD parameter, percentage of the extractable gliadins in total protein, had a negative genotypic correlation with CSF (r = –0.81, P &lt; 0.01), whereas percentage of the unextractable polymeric proteins had a positive genotypic correlation (r = 0.75, P &lt; 0.01). Those two MWD parameters also showed significant (P &lt; 0.05) variations for genotypes, indicating that they might be useful for screening durum genotypes for pasta cooking quality.

Feruloylation and structure of arabinoxylan in wheat endosperm cell walls from RNAi lines with suppression of genes responsible for backbone synthesis and decoration.

SummaryArabinoxylan (AX) is the major component of the cell walls of wheat grain (70% in starchy endosperm), is an important determinant of end‐use qualities affecting food processing, use for animal feed and distilling and is a major source of dietary fibre in the human diet. AX is a heterogeneous polysaccharide composed of fractions which can be sequentially extracted by water (WE‐AX), then xylanase action (XE‐AX) leaving an unextractable (XU‐AX) fraction. We determined arabinosylation and feruloylation of AX in these fractions in both wild‐type wheat and RNAi lines with decreased AX content (TaGT43_2 RNAi, TaGT47_2 RNAi) or decreased arabinose 3‐linked to mono‐substituted xylose (TaXAT1 RNAi). We show that these fractions are characterized by the degree of feruloylation of AX, <5, 5–7 and 13–19 mg bound ferulate (g−1 AX), and their content of diferulates (diFA), <0.3, 1–1.7 and 4–5 mg (g−1 AX), for the WE, XE and XU fractions, respectively, in all RNAi lines and their control lines. The amount of AX and its degree of arabinosylation and feruloylation were less affected by RNAi transgenes in the XE‐AX fraction than in the WE‐AX fraction and largely unaffected in the XU‐AX fraction. As the majority of diFA is associated with the XU‐AX fraction, there was only a small effect (TaGT43_2 RNAi, TaGT47_2 RNAi) or no effect (TaXAT1 RNAi) on total diFA content. Our results are compatible with a model where, to maintain cell wall function, diFA is maintained at stable levels when other AX properties are altered.

Evidence for different supramolecular arrangements in pasta from durum wheat (Triticum durum) and einkorn (Triticum monococcum) flours

The effects of the replacement of einkorn flour on pasta proteins aggregation were studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis and size exclusion high performance chromatography. Pasta was produced replacing durum wheat semolina with an increasing amount of einkorn flour (30, 50 and 100%). The polymeric protein structure of flours and related pasta and pasta mixture was determined by protein subunits composition and size of polymeric proteins. The unextractability of polymeric protein was related to the unextractable protein fraction and to the determination of –SH/-SS groups. Durum wheat semolina and einkorn flours increased their unextractable and polymeric fractions during pasta processing. The unexpected results derived from the areas of unextractable fractions and total and large unextractable polymeric fractions of 70/30 semolina/einkorn pasta mixture that were lower than those of 50/50 semolina/einkorn pasta mixture. Although the semolina flour contained more gluten proteins than einkorn flour, a higher aggregation was registered for 50/50 semolina/einkorn flour pasta. These results suggested that a different assessment of gluten network occurred in pasta mixture and it was regulated by a self-assembling machine influenced by nature of HMW-GS. The 50/50 semolina/einkorn pasta mixture determined a supramolecular structure in the developing of its network architecture.

Effect of flour polymeric proteins on dough thermal properties and breadmaking characteristics for hard red spring wheat genotypes

The aim of this research was to investigate the effect of variation of flour polymeric proteins on dough thermal properties for hard red spring (HRS) wheat genotypes grown in the U.S. state of North Dakota. Flour polymeric proteins were analyzed by size exclusion HPLC for sodium dodecyl sulfate (SDS) buffer extractable and unextractable fractions. Mixolab was employed to measure dough thermal property. The Mixolab torque profile was fitted to nonlinear equations, and envelope amplitude value was calculated by treating the torque profile as a wave. The dough tolerance to thermal weakening, as determined from the Mixolab parameters (including the constants of a nonlinear model and envelope torque amplitude values derived from the mixing torque profile during heating from 30 to 70 °C), was identified to have significant (P < 0.05) and positive correlations with flour bread loaf volume potential. Variations of high molecular weight polymeric proteins appeared to affect dough tolerance to thermal weakening and bread loaf volume for HRS wheat genotypes, and different associations with breadmaking characteristics were observed according to extractability in SDS buffer. Negative correlations with tolerance to thermal weakening and bread loaf volume were seen for SDS extractable polymeric proteins and positive correlations were observed for unextractable polymeric proteins.

Towards the understanding of end-use quality in intermediate wheatgrass (Thinopyrum intermedium): High-molecular-weight glutenin subunits, protein polymerization, and mixing characteristics

Intermediate wheatgrass (Thinopyrum intermedium; IWG), is a perennial crop that is well-known for providing good environmental services. As a perennial relative of wheat, IWG has good potential for development into a perennial grain crop. But the diversity and potential of the end-use quality of IWG grain are still unknown. Here, to understand the end-use quality of IWG, we investigated the variability among seed from 60 IWG genotypes in high-molecular-weight glutenin subunits (HMW-GS), protein polymerization, and mixing characteristics. IWG genotypes have high grain protein content, ranging from 16.4 to 23.6%. Of the total proteins, the percentage of polymeric proteins show a large range across IWG genotypes, varying from 9.2 to 25.1%. Many genotypes have limited amounts of polymeric proteins, but several genotypes have large amounts of polymeric proteins and promising mixing properties, comparable to common wheat, Triticum aestivum. The amount of protein polymers in the SDS buffer unextractable fraction are significantly correlated (r ≥ 0.76) with mixograph parameters. Furthermore, we observed that HMW-GS variants showed differential contribution to protein polymerization and mixograph parameters. But the composition of HMW-GS in IWG was contributed by both parents, which might bring challenges for the evaluation of grain quality of open-pollinated IWG genotypes.

Mechanism study of degradative solvent extraction of biomass

We have recently proposed a novel and effective degradative solvent extraction method to upgrade and convert various types of biomass feedstocks into high-grade carbonaceous materials under rather mild conditions. The feasibility of this method has been preliminarily proven in our previous work. However, the conversion mechanism of this process remains unknown. Hence, in this study the conversion process of the degradative solvent extraction of biomass was investigated in detail. A typical biomass (fir sawdust) was treated in 1-methylnaphthalene at 350°C with the residence time from 0 to 90min. Three solid products, which were the fraction soluble in the solvent at room temperature (termed Soluble), the fraction soluble in the solvent at treatment temperature but insoluble at room temperature (Deposit) and the unextractable fraction (Residue), were obtained. The products were then characterized by various analysis methods in detail. The oxygen, carbon and minerals in the raw biomass were mainly recovered as CO2/H2O, Deposit/Soluble, and Residue, respectively. With the residence time increasing from 0 to 45min, the soluble yields increased obviously but the deposit yields decreased significantly. The yield variations of the Solubles and Deposits obtained at residence time longer than 45min were not significant. The chemical structure and properties of Solubles were independent of the residence time, while those of Deposits varied obviously with residence time. According to the results, the conversion process of the degradative solvent extraction of biomass was proposed. The process can be divided into two stages. The first stage took place at heating up stage from 250 to 350°C and the beginning of the isothermal stage at 350°C. In this stage, the thermal extraction, deoxygenation and aromatization reactions of the raw biomass occurred significantly. The main product was Deposit. The oxygen was removed as CO2 and H2O. At the second stage, the Deposit was further deoxygenated and converted into Soluble. In this stage, the Deposit underwent complex reactions, such as the cleavages of oxygen containing cross-links and slight aromatization reactions. The oxygen was mainly removed as H2O at the second stage.

Evaluation of sequential solvent and thermal extraction followed by analytical pyrolysis for chemical characterization of carbonaceous particulate matter

A stepwise analytical protocol is presented for recognition of uncharacterized organic chemical entities comprising carbonaceous air particulate matter (PM). In this method, thermal treatment of PM samples starts with thermal extraction (TE) using temperatures below 300°C to evolve volatile high molecular weight (LMW) chemicals followed by pyrolysis (Py) of non-volatile high molecular weight (HMW) compounds to yield signature patterns of their decomposition products. Both volatile species and pyrolyzed products are characterized using gas chromatography (GC) with a mass spectrometric (MS) detection. The efficacy of sequential TE (at 200 and 300°C) and Py (at 400, 500, 600, 700, 800, 900 and 1000°C) was demonstrated on a defined mixture of LMW species and non-volatile polystyrene, a model HMW compound. When a solid matrix, in a form of silica or graphite particles, was introduced to this system, we determined that a solvent extraction (SE) applied prior to a sequential TE/Py-GC/MS sample analysis was an essential step to eliminate the analyte–matrix interactions, which hindered the efficient vaporization of LMW compounds from a solid matrix resulting in a poor TE/Py separation. This SE/TE/Py-GC/MS method was then successfully applied to PM samples representing real-world PM matrices to discover several novel features of PM composition. HMW species were observed in both water-soluble (extracts) and unextractable (solid residues after an exhaustive solvent extraction) fractions of wood smoke and urban PM. The species evolving upon pyrolysis were associated with the corresponding precursor polymers, such as oxidized fragments of lignin, polysaccharides and lipids, in wood smoke PM and non-volatile anthropogenic hydrocarbons in urban PM. The proposed sequential SE/TE/Py-GC/MS protocol is capable of revealing otherwise unobserved chemical components while providing useful information on their interactions within a complex and poorly characterized PM matrix. Signature SE/TE/Py profiles, i.e., PM “fingerprints,” provided by our approach may prove useful in source apportionment studies.

SORPTION-DESORPTION CHARACTERISTICS OF HEAVY METALS AND THEIR AVAILABILITY FROM THE SEDIMENT OF SEGARA ANAKAN ESTUARY

Estuarine sediments are increasingly recognized as both a carrier and a possible source of heavy metals in pollution of aquatic ecosystems. The bioavailability of heavy metal from sediments, however, is a long-standing impediment of questions in determining the metal effects in ecosystems. The fraction considered as available heavy metal are both the dissolved heavy metal and the exchangable cations. The main objective of this study is to understand the extent of heavy metal availability from sediments in estuarine ecosystem. It was found that the availability of heavy metals, i.e. copper, zinc, cadmium, and mercury in the estuarine ecosystem investigated, are governed by the relative strength of the electrostatic attraction of their complexation to the ligands present both in the sediment and the overlaying waters. Under simulated estuarine ecosystem, it was observed that Cu and Zn prefer to form organo-complex through ligand exchange, while Cd and Hg tend to form chloro-complex through electrostatic interaction. Therefore, the availability of Hg and Cd is higher in more saline overlaying water. On the contrary, the availability of Cu and Zn is lower in more saline overlaying waters, as indicated by their respective water-sediment distribution coefficient, KD. Similar behaviour of heavy metal was observed in natural field conditions of Segara Anakan estuary. Due to the higher salinity of the overlaying water, the availability of Cd and Hg in dry season was higher than in wet season, while Zn was more available in wet season due to the higher input of organic matters from the inland. The patterns of heavy metal release from the sediment are consistent to that obtained in experiments of the undisturbed simulation, where highest release was obtained for Cd. Surprisingly, it was found that even though Cd was not detected in the sediment, higher level of Cd in water medium was observed in dry season, and Cu seems to retain in the sediment in both dry and wet seasons. Compared to the unextractable fraction, the extractable was very low, therefore Geloina sp. was used as biomonitor for dissolved Cd and Hg, and Zn in sediment. Generally, the heavy metal concentration in Geloina sp. was higher in dry season than in wet season, but no Cu uptake was detected. Therefore, the establishment of limit values of heavy metals in sediment is highly recommended. Keywords: heavy metal, sorption-desorption, estuary, availability.

Association of Size‐Exclusion HPLC of Endosperm Proteins with Dough Mixing and Breadmaking Characteristics in a Recombinant Inbred Population of Hard Red Spring Wheat

ABSTRACTVariation of polymeric proteins affects wheat end‐use quality. This research investigated associations of polymeric proteins with dough mixing strength and breadmaking characteristics in a near‐homogenous population of 139 recombinant inbred lines (RILs) derived from a cross between two hard red spring wheat breeding lines. Flours from the RILs grown at three locations were analyzed for molecular weight (MW) distribution of SDS‐extractable and unextractable proteins using size‐exclusion HPLC protocol. Correlations were calculated between mixing and breadmaking properties and HPLC absorbance data obtained a 0.01‐min retention time interval to identify protein fractions that had a significant effect on the quality traits. Very high MW polymeric proteins in the unextractable fraction had more distinct and positive associations with dough mixing strength and bread loaf volume than did other polymeric protein fractions, whereas extractable polymeric had negative influence. Consequently, the ratio of unextractable very high MW polymeric proteins to extractable polymeric proteins had greater correlations with dough mixing parameters than other HPLC absorbance area data. Covariate‐effect biplots also visually validated positive effects of unextractable very high MW polymeric proteins and negative effects of extractable polymeric proteins on mixing properties and loaf volume across three growing locations.

Radiocarbon dating reveals different past managements of adjacent forest soils in the Campine region, Belgium

The soils of adjacent first generation monospecific stands of Scots pine ( Pinus sylvestris L.) and pedunculate oak ( Quercus robur L.) in the Campine region, Belgium, apparently developed under the same forming factors, were studied for carbon dynamics to disentangle eventual different past land uses. In fact, visual observations suggested that the soil under pine experienced substantial addition of organic matter and ploughing, such to be considered a plaggen, opposite to the soil under oak, which is inexplicably much poorer in C. In order to prove this hypothesis, the soil organic carbon was quantified by horizons and, both bulk soil organic matter (SOM) and the least mobile SOM fractions – the humic acid and the unextractable fractions – were radiocarbon dated. Surprising was the marked difference between the mean SOM age from the two stands. In fact, while under oak this age is a few years or decades, under pine it amounts to more than a millennium, so confirming the hypothesis of a confined C supply occurred mainly in the Middle Age, or later using partly humified matter. The mean residence time (MRT) of SOM in the organic layers matches almost perfectly with that estimated via a mass balance approach and, as expected, was much lower in the oaks than in the pines. The humic acid fraction, generally the most stable fraction of SOM, in terms of both mobility and degradability, reflects the behaviour of the bulk SOM, showing higher radiocarbon ages under pine. The findings of this work indicate that the large human-induced additions of organic material in the area now occupied by the pine stand, probably occurred in the Middle Age and it continues to strongly affect the present soil C pools and their dynamics. Any study dealing with budgets and dynamics of C in soil should avail itself of a careful reconstruction of the land uses and management history, in order to provide reliable conclusions about the real role of the current vegetation on soil carbon.

CHARACTERISTICS OF SOIL ORGANIC MATTER IN A LIMNIC HISTOSOL OF THE ALPINE MORAINIC SYSTEM

Histosols represent a large carbon reservoir and their preservation is important to limit the emission of CO2 and the related ecological consequences. In these soils, C storage is governed by waterlogging, bacterial activity, and type of vegetation from which soil organic matter (SOM) originated. In limnic peats, moreover, calcium could play some roles on SOM dynamics. The characteristics of organic fractions composing a Limnic Histosol subjected to intermittent periods of oxidation have been studied to understand the main factors influencing SOM dynamics and accumulation. Soil organic matter was constituted mainly by the unextractable fraction (88.0% of organic C). Dissolved organic matter was in low concentrations (1.30%), formed mainly by undecomposed labile material. Fulvic and humic acids (HAs) were highly humified and rich in O-containing groups, probably because of the periodic oxidizing conditions. Humic acids (concentration, 5.38%), further fractionated by dialysis in three fractions on a molecular weight basis, were constituted mainly by the heaviest fraction (greater than 50 kDa; concentration, 5.36%). Humin was composed of a hydrophobic fraction, derived probably from lipids and waxes, and of a hydrophilic fraction, with features closer to those of HA. Both fractions contained surprisingly large amounts of carboxyl and phenolic groups and trapped a large percentage of Ca, which is unextractable even after strong acid treatments. This suggests that humin was actually formed by smaller molecules that strongly interact with Ca through their polar groups, forming larger aggregates. The large percentage of unextractable organic material and the strong interaction with Ca could preserve SOM from microbial degradation and, hence, limit the mineralization even in the absence of water, preserving a C sink that is presently storing a large amount of C in both organic and carbonate forms.

A Model for the Effect of Rhizodeposition on the Fate of Phenanthrene in Aged Contaminated Soil

Microcosm data were used to develop a deterministic model to describe how rhizodeposition affects the fate of phenanthrene in aged contaminated soil. Microbial mineralization and soil sequestration of 14C-phenanthrene were compared in microcosms amended weekly with phenolic-rich mulberry root extracts versus unamended controls. Mineralization was higher in the amended soils simulating the rhizosphere (57.7 +/- 0.9%) than in controls simulating bulk (unplanted) soils (53.2 +/- 0.7%) after 201 days (p < 0.05). Humin was the main soil sink for the residual 14C-label. Whereas the total 14C-label associated with humin remained constant in biologically active soils (at about 30%), it increased up to 80% after 201 days in sterile controls. The initial phenanthrene extraction with n-butanol (commonly used to assess bioavailability) slightly underestimated the fraction thatwas mineralized (assessed by 14CO2 recovery). Changes in the unextractable fraction (determined by combustion in a biological oxidizer) suggested the presence of two soil sequestration domains: (1) irreversibly bound residue, and (2) an intermediate transition phase that is unextractable by solvents at a given point in time but could become bioavailable due to physicochemical or biological transformations of the binding matrix. The fate of phenanthrene was accurately modeled by considering the transfer of the 14C label between different soil compartments as first-order kinetic processes. Model simulations suggested that the system was approaching a stable end-point after 201 days of simulated rhizoremediation, and corroborated that microorganisms have a significant impact on the fate of phenanthrene in soil.

Biotransformation of dissolved and sediment‐bound fluoranthene in the polychaete, Capitella sp. I

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the marine environment and have physicochemical properties that make them likely to bioaccumulate. The main purpose of this study was to investigate fluoranthene (FLU) uptake, biotransformation and elimination in the deposit-feeding polychaete Capitella sp. I exposed via different routes. Individual worms were exposed to either dissolved FLU or to both dissolved and sediment-bound FLU. The 14C-FLU was used as a tracer to determine the amounts of unmetabolized FLU (parent), water-soluble (aqueous)- and water-insoluble (polar) FLU metabolites and FLU residues (unextractable fraction) in sediment, water, and worm tissue. Capitella was capable of accumulating and biotransforming FLU regardless of route of exposure, thus suggesting that biotransformation activity is not restricted to gut tissues. Although both feeding and nonfeeding worms were able to biotransform FLU extensively, feeding worms eliminated/transformed parent FLU faster than both aqueous and polar FLU metabolites after transfer to clean conditions, whereas nonfeeding worms barely excreted FLU in any form. The high biotransformation capability of Capitella sp. I. along with the dependency of elimination on exposure route, demonstrates the potential importance of these processes in controlling the fate and effects of PAH and possibly other organic toxicants in contaminated marine sediments.