Organo-mineral Complexes Research Articles

Comparative evaluation of the mineralogical composition of Sphagnum peat and their corresponding humic acids, and implications for understanding past dust depositions

With 6.5 m of peat accumulated during the past ca. 15,000 years, Etang de la Gruère (EGr) represents the longest continuous record of atmospheric dust deposition in northern hemisphere. This paper presents a comparative study of the mineralogical composition of Sphagnum peat samples and their corresponding humic acids (HA) from a peat core collected at EGr bog. The purpose of this study was to better understand the dominant process responsible for the amount and distribution of mineral matter in ombrotrophic (i.e., rain-fed) peat. Specifically, the goal was to separate the relative importance of the changing rates of atmospheric mineral dust deposition (during the past two millennia) from the mineralization of organic matter (OM), for the distribution of the ash fraction of the peat profile.The results suggest that variations in ash content at EGr are mainly the result of an increase in the rate of supply of dust particles and cannot be attributed simply, or exclusively, to differences in the degree of OM decay: evidence is provided by both acid insoluble ash (AIA) profiles and the correlations among lithogenic elements (Al, Si, Ti, Y, and Zr), total ash content and AIA. Moreover, our findings suggest that part of the AIA occurring in peat extremely is stable, and is unaffected by the extreme chemical conditions used to extract the HA fraction: this may be partly due to the inherent stability of quartz and “heavy minerals” such as zircon and rutile, but organic coatings developed on mineral surfaces during peat diagenesis, or the formation of some other kind of organo-mineral complex, might also play a role. Consequently, testimonies of past dust depositions can be observed also into the recalcitrant HA fraction of the peat.

Sustainable sorption strategies for removing Cr3+ from tannery process wastewater

Two different strategies for the removal of trivalent chromium (Cr3+) from contaminated water are reported. The first one is based on the sorption process on an organo-mineral complex, named LDH–HP, obtained in turn by sorption of polymerin, the humic acid-like fraction occurring in olive oil mill wastewater, on a layered double hydroxide (LDH) of magnesium and aluminium with carbonate in the interlayer. This sorption process is preliminary developed on simulated wastewater (SW) as theoretical model and successively applied on tannery process wastewaters (TPWs) natively containing Cr3+. The removal of Cr3+ from TPW is lower than that observed for SW, because of the large compositional variability of TPW. The second one is based on the direct production of a LDH of magnesium and chromium (Cr3+), using as starting material TPW, naming LDH–TPW the complex produced. This process allows the complete removal of Cr3+ from TPW and also the abatement of chemical oxygen demand, indicating to be a very promising purification process for an industrial application.

Sequential chemical extractions of the mineral-associated soil organic matter: An integrated approach for the fractionation of organo-mineral complexes

Long-term stabilisation of soil organic matter (SOM) largely depends on its interaction with the active mineral components of soils. SOM may become associated with the mineral active surfaces through a wide variety of linkages, with different strength. Thus, fractionation procedures capable of assessing the strength through which mineral-associated SOM is stabilised can be very useful. This paper presents a soil organo-mineral fractionation method (henceforth, SOF) that essentially resumes the work of classical pedologists, who aimed to quantify the different modes through which organic compounds are bound to the mineral matrix using sequential extractions with chemical reagents (0.1 M sodium tetraborate, 0.1 M sodium pyrophosphate, 0.1 M sodium hydroxide, 0.1 M sodium hydroxide after sodium dithionite pretreatment, and 0.1 M sodium hydroxide after hydrofluoric acid pretreatment). We added a previous extraction with 0.5 M potassium sulfate to remove soluble organic compounds, and a weak acid attack with 0.33 M sulfuric acid to destroy possible SOM-occluding carbonate films, which are often assumed to contribute to SOM stability in calcareous soils. The proposed sequence is applied only to the organo-mineral complexes (<20 μm), after the removal of the particulate organic matter (POM) by ultrasonic dispersion and wet sieving.We tested the SOF method on four contrasting soils: two Haplic Calcisols (under crop and forest) and two Humic Cambisols (under forest and pasture), with organic C (OC) contents ranging from 1.8 to 3.4% and pH from 3.9 to 8.0. Our results showed that the mineral-associated SOM represents the largest SOM fraction (67–72% of the total organic C content), and that a substantial part of it is weakly associated with the mineral matrix, as it can be extracted by sodium tetraborate or sodium pyrophosphate. While the sodium tetraborate extract was the main fraction in acid soils, the sodium pyrophosphate extract was the main fraction in calcareous soils, thus highlighting the role of Ca in SOM stability. In contrast, our results suggest a small role of carbonate precipitation in the stabilisation of SOM < 20 μm. The sodium hydroxide extractions after both the sodium dithionite and HF treatments released little SOM in the studied soils, but the remaining (insoluble) residue accounted for 15–30% of total OC, and deserves further study. The SOF method can be a valuable tool for splitting mineral-associated SOM into different fractions regarding their proneness for extraction, and its thoroughness may prove most useful for comparative studies about SOM stabilisation.

Storage and stability of organic carbon in soils as related to depth, occlusion within aggregates, and attachment to minerals

Abstract. Conceptual models suggest that stability of organic carbon (OC) in soil depends on the source of plant litter, occlusion within aggregates, incorporation in organo-mineral complexes, and location within the soil profile. Density fractionation is a useful tool to study the relevance of OC stabilization in aggregates and in association with minerals, but it has rarely been applied to full soil profiles. We aim to determine factors shaping the depth profiles of physically unprotected and mineral associated OC and test their relevance for OC stability across a range of European soils that vary in vegetation, soil types, parent material, and land use. At each of the 12 study sites, 10 soil cores were sampled to 60 cm depth and subjected to density separation. Bulk soil samples and density fractions (free light fractions – fLF, occluded light fractions – oLF, heavy fractions – HF) were analysed for OC, total nitrogen (TN), δ14C, and Δ14C. Bulk samples were also incubated to determine CO2 evolution per g OC in the samples (specific mineralization rates) as an indicator for OC stability. Depth profiles of OC in the light fraction (LF-OC) matched those of roots for undisturbed grassland and forest sites, suggesting that roots are shaping the depth distribution of LF-OC. Organic C in the HF declined less with soil depth than LF-OC and roots, especially at grassland sites. The decrease in Δ14C (increase in age) of HF-OC with soil depth was related to soil pH as well as to dissolved OC fluxes. This indicates that dissolved OC translocation contributes to the formation of subsoil HF-OC and shapes the Δ14C profiles. The LF at three sites were rather depleted in 14C, indicating the presence of fossil material such as coal and lignite, probably inherited from the parent material. At the other sites, modern Δ14C signatures and positive correlations between specific mineralization rates and fLF-OC indicate the fLF is a potentially available energy and nutrient source for subsurface microorganisms throughout the profile. Declining specific mineralization rates with soil depth confirm greater stability of OC in subsoils across sites. The overall importance of OC stabilization by binding to minerals was demonstrated by declining specific mineralization rates with increasing contributions of HF-OC to bulk soil OC, and the low Δ14C values of HF-OC. The stability of HF-OC was greater in subsoils than in topsoils; nevertheless, a portion of HF-OC was active throughout the profile. While quantitatively less important than OC in the HF, consistent older ages of oLF-OC than fLF-OC suggest that occlusion of LF-OC in aggregates also contributes to OC stability in subsoils. Overall, our results indicate that association with minerals is the most important factor in stabilization of OC in soils, irrespective of vegetation, soil type, and land use.

Characterisation of organic matter from organo-mineral complexes in an Andosol from Reunion Island

Organo-mineral complexes play a major role in the stabilisation of organic matter (OM) within soils, but only few data are presently available about the nature of the OM bound to mineral phases. In this study, we aimed at determining the nature of the OM present in various organo-mineral complexes in a tropical soil (Andosol). Organo-mineral complexes were isolated thanks to densimetric separation techniques. The mineral phases of organo-mineral complexes were identified using XRD, and OM was analysed by Py–GC–MS after carbon enrichment obtained through 5% hydrofluoric acid hydrolysis.We thus studied OM bound to poorly crystallised aluminosilicates (PC-AlSi), gibbsite and iron oxides, as well as free-OM (<1.9gcm−3 fraction), which represents OM that is not bound to mineral phases. In the organo-mineral complexes of the studied Andosol, lipids were mainly present with PC-AlSi while polysaccharides and proteins/amino acids were the main organic compounds associated with gibbsite. Lignin compounds were found in high quantities in free-OM but were not found in organo-mineral complexes. Only few organic compounds were bound to iron oxides. Furthermore, proteins/amino acids and lipids were also observed in all organo-mineral complexes, but polysaccharides were not. The present results show that mineral phase type influences not only the proportion but also the nature of the organic compounds present in organo-mineral complexes. This study provides new information about the nature of the OM bound to mineral phases, and will thus contribute to improving models of organo-mineral complexes in order to better understand OM stabilisation in soils.

Long-term incubations of size and density separated soil fractions to inform soil organic carbon decay dynamics

Soil organic matter in coarse-textured soils is more vulnerable to environmental disturbances due to reduced potential for soil organic carbon (SOC) stabilization in aggregates or organo-mineral complexes. In sandy loam soils from the Rio Grande Plains region of southern Texas, woody encroachment has resulted in the rapid accrual of root and leaf tissues derived from trees and shrubs into poorly physically protected (macroaggregate >250 μm) and non-mineral associated (free light fraction <1.0 g cm−3) soil fractions. To determine the impact of changing plant input chemistry on potential degradability of accumulating SOC fractions, we measured the quantity and isotopic composition of respired CO2 from year-long incubations of the macroaggregate and free light soil fractions along a grassland to woodland successional chronosequence. During incubation of both fractions, the proportion of SOC respired from older woody stand soils (∼40–90 yrs) relative to recently established woody stands (<40 yrs) and remnant grassland soils decreased. We interpreted this decrease with woody stand age to result from a change to plant input chemistry with more lignin and aliphatic structures combined with a progressive shift to more non-hydrolyzable, poorly accessible forms of soil organic nitrogen, resulting in a system with slower short-term decay dynamics. The δ13C values of respired CO2 from all landscape elements indicated a selective release of older grassland-derived SOC in the first month of the macroaggregate incubation, possibly due to the disruption and rapid microbial utilization of grassland SOC after the soil fractionation process. Due to the sensitivity of these rapidly-cycling soil fractions to environmental disturbance and their capacity to influence longer-term SOC dynamics, understanding their decay dynamics is essential for understanding mechanisms of SOC stabilization. This is especially important in coarse-textured soils where large SOC stocks may be present in physical fractions that are relatively unprotected from decomposition.

Sorption kinetics of ofloxacin in soils and mineral particles

The environmental behavior of antibiotics is not well known and the precise environmental risk assessment is not practical. This study investigated the sorption kinetics of ofloxacin, a widely used antibiotics, on soil particles with different organic carbon contents as well as soil components (a humic acid, ferric oxide and kaolinite). Two-compartment sorption kinetics were mathematically recognized (except ferric oxide because of its very fast sorption). The apparent sorption rate and the contribution of fast sorption compartment decreased with the increased organic carbon content with the exception of humic acid, suggesting that the slow sorption sites were partially located in organo-mineral complex. The OFL concentration-dependent sorption kinetics suggested that the slow sorption compartment was not controlled by diffusion process as indicated by slower sorption at higher OFL loading. The difference between OFL sorption kinetics and those of hydrophobic organic contaminants was discussed and possible mechanism of OFL two-compartment sorption was proposed.

Physical, chemical, and biochemical mechanisms of soil organic matter stabilization under conservation tillage systems: A central role for microbes and microbial by-products in C sequestration

Conservation tillage practices that entail no or reduced soil disturbance are known to help preserve or accumulate soil organic matter (OM). However, the underlying mechanisms especially at the molecular level are not well understood. In this study soil samples from 25-year-old experimental plots continuously cropped with barley (Hordeum vulgare L.) under no-tillage (NT) and chisel tillage (CT) were subjected to a new physical fractionation method to isolate dissolved OM, mineral-free particulate OM located outside aggregates (physically and chemically unprotected), OM occluded within both macroaggregates and microaggregates (weakly and strongly protected by physical mechanisms, respectively), and OM in intimate association with minerals (protected by chemical mechanisms). The whole soils and OM fractions were analyzed for organic C and N content and by modern nuclear magnetic resonance (NMR) techniques. The soil under NT stored 16% more organic C and 5% more N than the soil under CT. Compared to CT, NT increased free organic C content by 7%, intra-macroaggregate organic C content by 20%, intra-microaggregate organic C content by 63%, and mineral-associated organic C content by 16% and decreased dissolved organic C content by 11%. The mineral-associated OM pool accounted for 65% of the difference in total organic C content between NT and CT, whereas the intra-microaggregate OM only explained 18%, intra-macroaggregate OM 14%, and free OM 11%. The NMR experiments revealed that the free and intra-aggregate OM fractions were dominated by crop-derived materials at different stages of decomposition, whereas the mineral-associated OM pool was predominately of microbial origin. Overall, our results indicate that microbes and microbial by-products associated with mineral surfaces and likely physically protected by entrapment within very small microaggregates constitute the most important pool of OM stabilization and C sequestration in soils under NT. Most probably the slower macroaggregate turnover in NT relative to CT boosts not only the formation of microaggregates and thereby the physical protection of crop-derived particulate OM, but more importantly the interaction between mineral particles and microbial material that results in the formation of very stable organo-mineral complexes.

Erratum to ‘Are organo-mineral complexes and allophane content determinant factors for the carbon level in Chilean volcanic soils?’ [CATENA 92C (2012) 106–112

Erratum to ‘Are organo-mineral complexes and allophane content determinant factors for the carbon level in Chilean volcanic soils?’ [CATENA 92C (2012) 106–112

Soil organic carbon and total nitrogen in intensively managed arable soils

The conversion from cereal fields to vegetable production in the last three decades represents a significant shift in land use in China. Here, we studied the effects of conversion form cereal fields to vegetable production in north China on soil organic carbon (SOC) and total nitrogen (TN) in both bulk soil and soil aggregates. We used two approaches: (1) measurements of paired soil samples from wheat (Triticum aestivum L.) – maize (Zea mays L.) fields and adjacent greenhouses vegetable fields in three vegetable production areas representing various management intensities in terms of C and N inputs and frequency of tillage; (2) fractionating soil to distinguish intra-aggregate particulate organic matter (iPOM) and organo-mineral complexes (silt+clay). Our results indicated that converting cereal fields to greenhouse vegetable production with intermediate and high management intensity led to increases in SOC and TN and decreases in C:N ratios in the top soil. The accumulation rates of C and N in the surface soil (0–30cm) were estimated to be 1.37MgCha−1yr−1 and 0.21MgNha−1yr−1 over an average period of 8 years after cereal fields to greenhouse vegetable production conversion. At the soil aggregate level, only the coarse (>250μm) and fine (53–250μm) iPOM fraction contributed to the increases in soil C (e.g., 49% and 51% of total C increases, respectively), while the coarse and fine iPOM, and silt+clay fraction accounted for 22%, 30% and 48%, respectively, of total N increases. This illustrates how the addition of readily available C (manure) and N (manure and inorganic N) leads to a temporary stabilization of C in relatively labile SOM fractions, but to a preferential stabilization of N in organo-mineral SOM fractions. In conclusion, the conversion to highly intensive vegetable systems in China leads to marked differences in C and N stabilization dynamics.

Activity of antioxidant enzymes and processes of free radical oxidation in experimental hypothyroidism and correction of thyroid shifts with iodized polysaccharide complexes

Aim. To determine the activity of antioxidant enzymes in rat liver tissue on the background of thiamazole hypothyroidism, and also after its correction with iodine-containing organo-mineral complexes. Methods. Studies were conducted on rats, which were divided into four groups: the first group - the control, in animals of the second, third and fourth groups hypothyroidism was induced by daily intragastric administration of thiamazole at a dose 2.5 mg per 100 g body weight for the duration of 3 weeks. Beginning from the 22-day of the experiment the animals of the fourth group for the duration of a month received a biologically active additive in a dose that provides the daily requirement of iodine in rats, while the animals of the third group were on the standard diet of the vivarium. The activity of superoxide dismutase and glutathione peroxidase was determined using a set of reagents «RANSOD Randox» manufactured by «Laboratories Ltd.», the catalase activity was determined by the method of M.A. Korolyuk. Results. Experimental hypothyroidism in rats was characterized by a decrease in the concentrations of free thyroxine, an increase in the content of total triiodothyronine and thyroid-stimulating hormone. In animals treated with tiamazol, the superoxide dismutase activity was 85.6% of the activity level of the control animals, glutathione activity - 77.3% of the level of intact animals. The catalase activity in hypothyroidism decreased significantly - down to 40% of the control level (p ≤0.001). In the liver homogenate of rats, treated for 1 month with «iodine biopolymer» after hypothyroidism induction, the superoxide dismutase activity almost reached the control values and accounted for 95.5% of the activity of intact animals. The activity of glutathione peroxidase and catalase, was even slightly higher than the control values, reaching 115.6 and 112.7% of levels of activity in the control group, respectively (p ≤0,05). At the same time in the animals, which were on a standard diet, the activity of the studied enzymes remained below the control values, with the catalase activity - significantly lower (49.9% of the control, p ≤0,001). Conclusion. The introduction of an iodine-containing biologically active compound on the background of hypothyroidism made it possible to restore the activity of thyroid-dependant antioxidant enzymes, to normalize the functional state of the pituitary-thyroid system and to inhibit the processes of lipid peroxidation in the liver the of animals.

Are organo-mineral complexes and allophane content determinant factors for the carbon level in Chilean volcanic soils?

The existing information on soil carbon (C) stabilisation in allophanic soils is conflicting because active Al3+ and sesquioxides (i.e., the oxides/hydroxides of Al and Fe) as a stabilising agent of soil C are emphasised in opposition to allophane and imogolite type materials. Two hypotheses were tested in this study: 1) Al (and Fe) complexed with soil C and allophane content are the key variables to explain the soil C level in Chilean allophanic soils, and 2) the existing metal–SOM complex and short-range ordered aluminosilicate minerals in allophanic soils mainly result from soil pH variation and competition between Al (and Fe) for SOM and allophane formation. This study established the relationship among different soil properties such Al-, Fe-complexes and allophane content on soil C levels in Chilean volcanic soils as well as the effect of soil pH on metal–OM complexes. A total of 45 soil samples from 15 soil pedons were sampled at 0–0.1, 0.1–0.2 and 0–2–0.4 m. The soil samples were analysed for the content of soil organic C, allophane, clay, silt and Na- pyrophosphate extraction (Alp, Fep, Cp) and soil pH (water). We examined the relationship between the soil C content and soil properties using simple and multiple linear regressions. The silt and clay contents explained little, while the allophane, soil pH and Alp explained most of the soil C variation. We found an inverse relationship between soil pH and Alp (and Fep), indicating that the soil pH was significantly correlated with Alp and Fep, while the allophane content was positively related with soil pH. The results also showed a higher atomic ratio (Al + Fe)p:Cp in deep (0.2–0.4 m) horizons; the opposite was true in the top soil horizon (0–0.1 m), supporting the idea that SOM in deep soils is saturated with Al and Fe, leaving extra metal to react with silica for allophane formation.

耕作方式对紫色水稻土轻组有机碳的影响

Physical fractionation of soil organic carbon(SOC) has been useful in distinguishing specific carbon pools that are responsive to management and identifying the physical control of organic matter.Density fractionation allows the separation of SOC fractions from different locations in the soil and degree of association with mineral particles.The free light fraction carbon(F-LFC) includes loose organic particles in the soil and particulate organic carbon adhering to the exterior of secondary organomineral complexes,which is chemically very close to litter and has generally a very fast decomposition rate.The occluded light fraction carbon(O-LFC) is the fraction of uncomplexed organic matter that is trapped and physically protected within secondary complexes(intra-aggregate organic carbon).This fraction shows a more advanced degree of decomposition and a slower turnover.The heavy fraction carbon(HFC) is composed mainly of highly decomposed materialand has a very slow decomposition rate.Changes in these different fractions,especially in the low-density fractions,may be more sensitive to management-induced impacts on soil than the total SOC or the complicated heavy fraction organic carbon.However,there are few direct data quantifying these two light fractions and their contributions to total SOC storage as related to changes in tillage practices. The impact of tillage on SOC fractions has been of great interest in recent years.The tillage experiment was located at the farm of Southwest University(30°26′N,106°26′E) in Chongqing since 1990.In this paper four tillage treatments including conventional tillage with rice only system(DP),conventional tillage with rotation of rice and rape system(SH),no-till and ridge culture with rotation of rice and rape system(LM),and ridge culture with rotation of rice and rape system(LF) were selected as research objectives to measure the contents of different soil carbon fractions.Soil sampling at the depths of 0—10,10—20,20—30,30—40,40—50 and 50—60 cm was performed with a soil drill after the rape harvest in the spring of 2009. Results indicated that most carbon(69.6%—92.7%) was held in the HF,carbon dynamics in the whole soil were controlled by the behavior of this fraction.The proportion of F-LF carbon to the total SOC was 5.03%—26.43%.O-LF contained the least amount of organic carbon(1.37%—4.93%) of total SOC.In the four tillage soils the greatest contents of F-LFC,O-LFC and HFC were found in the 0—10cm depth.In the whole soil layer(0—60cm),the order of F-LFC contents was LM(4.36g/kg) DP(2.11g/kg) LF(1.74 g/kg) SH(1.46 g/kg),and the corresponding proportions of F-LFC to total SOC were 17.12,14.00,12.17 and 11.29%,respectively.The order of O-LFC contents was LM(0.82 g/kg) DP(0.51 g/kg) LF(0.36 g/kg) SH(0.34 g/kg),and the corresponding proportions were 3.36,3.45,3.00 and 2.71%,respectively.Compared with the other tillage systems,LM treatment significantly increased the contents and proportions of the two light fraction carbons which suggested LM could improve the soil quality in a purple paddy soil in Southwest China.Additionally,the data analysis showed that F-LFC was the most sensitive pool of organic carbon to detect changes in SOC due to soil tillage.

Location and stability of a recombinant ovine prion protein in synthetic humic-like mineral complexes

Location and stability of a recombinant prion protein (recPrP) and its interaction with humic-like complexes were investigated by low-temperature ashing (LTA), thermal gravimetric (TG), and scanning electron microscopy (SEM) analyses. Humic-like complexes were obtained by abiotic polymerization of catechol, one of the possible precursors of soil humic matter, through the catalysis of birnessite, a manganese oxide common in soil environment. The recPrP was immobilized in organomineral complexes via sorption or entrapment. Complexes were treated by LTA, allowing the controlled removal of organic matter layer by layer, from the external to the internal side, with minimal disturbance of mineral constituents. Thermal gravimetric and SEM analyses were performed on specimens before and after LTA treatment. Entrapped recPrP, compared with sorbed, resulted less easily accessible to LTA treatment and showed a higher thermal stability by TGA analyses. On the basis of these findings, we hypothesize that the processes leading to newly formed organic complexes can enhance prion stability in soil and thus influence the environmental diffusion of infectivity.

Application of δ&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C and δ&amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N isotopic signatures of organic matter fractions sequentially separated from adjacent arable and forest soils to identify carbon stabilization mechanisms

Abstract. Identifying the chemical mechanisms behind soil carbon bound in organo-mineral complexes is necessary to determine the degree to which soil organic carbon is stabilized belowground. Analysis of δ13C and δ15N isotopic signatures of stabilized OM fractions along with soil mineral characteristics may yield important information about OM-mineral associations and their processing history. We anlayzed the δ13C and δ15N isotopic signatures from two organic matter (OM) fractions along with soil mineral proxies to identify the likely binding mechanisms involved. We analyzed OM fractions hypothesized to contain carbon stabilized through organo-mineral complexes: (1) OM separated chemically with sodium pyrophosphate (OM(PY)) and (2) OM occluded in micro-structures found in the chemical extraction residue (OM(ER)). Because the OM fractions were separated from five different soils with paired forest and arable land use histories, we could address the impact of land use change on carbon binding and processing mechanisms. We used partial least squares regression to analyze patterns in the isotopic signature of OM with established mineral and chemical proxies indicative for certain binding mechanisms. We found different mechanisms predominate in each land use type. For arable soils, the formation of OM(PY)-Ca-mineral associations was identified as an important OM binding mechanism. Therefore, we hypothesize an increased stabilization of microbial processed OM(PY) through Ca2+ interactions. In general, we found the forest soils to contain on average 10% more stabilized carbon relative to total carbon stocks, than the agricultural counter part. In forest soils, we found a positive relationship between isotopic signatures of OM(PY) and the ratio of soil organic carbon content to soil surface area (SOC/SSA). This indicates that the OM(PY) fractions of forest soils represent layers of slower exchange not directly attached to mineral surfaces. From the isotopic composition of the OM(ER) fraction, we conclude that the OM in this fraction from both land use types have undergone a different pathway to stabilization that does not involve microbial processing, which may include OM which is highly protected within soil micro-structures.

Detoxification of olive mill wastewaters by zinc–aluminium layered double hydroxides

Disposal of olive mill waste waters (OMWW) represents a serious problem due to its elevated toxicity and pollution risk for environmental and aquatic bodies, which is mainly related to its polyphenol content. The use of layered double hydroxides (LDHs) or anionic clays for OMWW detoxification may represent an effective remediation process. In the current study, OMWW was treated with cold methanol to obtain a dark humic acid-like precipitate made of high molecular weight organic compounds named polymerin and a supernatant made of low molecular weight organics named OMWW-S. After precipitation with methanol, phenol content decreased from 2.14 g L −1 to 0.80 and 1.20 g L −1, in polymerin and OMWW-S, respectively. The chemical oxygen demand of OMWW-S decreased by about 30% with respect to raw OMWW, from 62.2 to 40.2 g L −1. A phenolic concentrate, named OMWW-E was also obtained by ethyl acetate extraction of OMWW-S at pH 2.0. LDHs of zinc and aluminium (LDH) were obtained at room temperature and after calcination at 450 °C (LDH-450). An organo-mineral complex of LDH with polymerin (LDH-Pol) was also synthesised. Phenols from OMWW-E were sorbed preferentially on three matrices according to the following order: LDH-450 > LDH > LDH-Pol, with percent sorption of up to 73% for LDH-450. Repeated cycles of sorption of OMWW-S onto LDH-450 decreased phenol concentration by about 90%. Use of remediated water in a phytotoxicity bioassay revealed scant inhibition of germination and coleoptile elongation rate in tomato seeds and seedlings. Thus, OMWW-S after sorption onto LDH-450 could represent a low cost source of irrigation water for arid soil of the Mediterranean region.

The removal of colloidal lead during estuarine mixing: seasonal variations and importance of iron oxides and humic substances

In the present study, seven colloidal fractions of lead (Pb) were analysed along the mixing zone of the Penzé estuary over the Year 2009, with the aim to provide some insight into the mechanism that removes the metal from the &lt;0.45-µm fraction. According to our results, Pb was generally found as large colloids (&gt;300 kDa) and was removed in the salinity range 0–10 from all of the size fractions where it was significantly found. Because the colloidal fractionation of Pb was strongly linked to that of iron (Fe) and humic substances (HS), the removal of Pb in the mixing area must occur under flocculation of organomineral complexes. A key period corresponding to the first strong autumnal precipitations was also revealed in the present work. At this time of the year, the mobilisation of Pb (and Fe) from catchment soils is enhanced by the mobilisation of HS and the metal is associated with smaller colloids (30–300 kDa).

Evaluation of potentially labile soil organic carbon and nitrogen fractionation procedures

Abstract Particulate organic matter (POM) and light fraction (LF) organic matter are potentially labile (active) fractions of soil organic matter (SOM) that have been shown to be indicators of short-term changes in soil management practices (e.g. tillage, manure and fertilizer applications, and crop rotation). These two fractions consist mainly of partially decomposed plant residues, microbial residues, seeds, and spores forming organo-mineral complexes with soil mineral particles; however, they cannot be used as synonyms because of their different chemical composition and structure. Particulate-OM is recovered by size-based procedures while LF is generally recovered in two distinct fractions [free-LF (FLF) and occluded-LF (OLF)] using density-based solutions in conjunction with soil-aggregate disruption. Solutions used in these density-based separations have most commonly varied in density from 1.6 to 2.0 g cm −3 . Sodium iodide (NaI) and sodium polytungstate (SPT) are the chemicals most often used to prepare the density solutions in LF recovery but comparisons of the effectiveness of two solutions have not been conducted. The objectives of this research were: (1) compare the efficiency of similar density solutions of NaI and SPT in recovering FLF; and (2) compare POM, FLF, and OLF as possible sensitive indices of short-term soil changes due to tillage management. Soil samples were collected at 0–15 cm depth from a cropping system experiment conducted on a silt loam Ultisol. Plots selected for sampling had received either reduced till (RT) or no-till (NT), and cropping was continuous corn silage for a period of 3 years prior to sampling. Solutions of NaI and SPT at densities of 1.6 and 1.8 g cm −3 were used to recover FLF, and OLF was recovered with SPT solution at a density of 2.0 g cm −3 from the soil pellet remaining after FLF recovery with SPT 1.6 g cm −3 . The average total soil organic carbon (SOC) content of these samples was of 12.7 g kg −1 , and carbon-POM (C-POM), carbon-FLF (C-FLF), and carbon-OLF (C-OLF) represented 22.4, 5.5, and 5.2% of it, respectively. In general, C-FLF and nitrogen-FLF (N-FLF) contents recovered did not differ significantly between chemical solutions (NaI or SPT) adjusted to the same density (1.6 or 1.8 g cm −3 ). Increasing the density within a specific solution (NaI or SPT) resulted in significantly higher C-FLF and N-FLF recovery. For instance, C-FLF recovery averaged 637 and 954 mg kg −1 at 1.6 and 1.8 g cm −3 , respectively. For both chemicals increasing density from 1.6 to 1.8 g cm −3 reduced the variability in recovering C-FLF and N-FLF with coefficient of variation values decreasing from a range of 14.9–19.1% for densities of 1.6 g cm −3 to 6.7–10.4% when densities increased to 1.8 g cm −3 . In the present work, POM and OLF were more sensitive than FLF to changes in tillage management, with significantly greater amounts of the sensitive fractions in RT samples. A better sensitivity of FLF would be expected if treatments dealing with residue input (e.g. crop rotation and cover crop) were evaluated.

Influence of Long-Term Localized Fertilizer Applications on Soil Organo-Mineral Complexes in a Sheltered Vegetable Field

Organo-mineral interactions are considered to play a relevant role in organic matter (OM) protection against biodegradation in regard to soil developed under sheltered vegetable conditions. However, little is known about the effect of fertilizer applications on the composition of organo-mineral interactions. A long-term (16 years) fertilizer experiment was carried out in a sheltered vegetable field at Shenyang Agricultural University, Shenyang, China, in order to study the effects of different fertilizer applications on organo-mineral complexes. It was found that a long-term application of a combination of organic plus chemical fertilizers induced a higher concentration of OM than applying chemical fertilizers alone, and loosely bound humic (LB-H) slightly increased with application of a combination of organic and chemical fertilizers. No significant influence on firmly bound humic (FB-H) was found among the chemical fertilizer treatments, whereas the application of organic fertilizer slightly decreased the content of FB-H compared to chemical fertilizer treatments. More tightly bound humic (TB-H) was observed in organic fertilizer treatments than in chemical fertilizer treatments, and its highest concentration (11.53 g kg−1) was in the treatment of organic fertilizer plus nitrogen (N)-phosphorus (P)-potassium (K) chemical fertilizers. The ratio of LB-H/TB-H tended to decrease after a long-term application of organic fertilizer, being the lowest (1.10) in the treatment of organic fertilizer plus P-K chemical fertilizer.

Competitive sorption of copper(II), chromium(III) and lead(II) on ferrihydrite and two organomineral complexes

The competitive sorption of Cu, Cr and Pb on a ferrihydrite and two synthetic organomineral complexes, obtained by coprecipitating iron with different quantities of oxalate and tartrate were studied. Greater amounts (μmol/m 2) of heavy metals were sorbed onto the organomineral complexes than ferrihydrite, the higher the carbon content in the samples the greater the sorption of heavy metals. Lead was sorbed much more and more tightly than Cr and Cu on the sorbents. In binary systems, the sorption and the inhibitive efficiency of one metal (M1) to the other (M2) were affected by the nature of the metal, initial M2/M1 molar ratio, addition sequence of M1 and M2, and residence time. Lead showed a much greater capacity to inhibit the sorption of the other two metals, whereas the opposite was true for Cu. In ternary systems, when equimolar amounts of each metal were added, the sorbents were covered with more than 50% by Pb alone. However, even in the presence of large excess of Pb and Cr, considerable extent of Cu sorption still occurred regardless of sorbent types, indicating that some sorption sites on each sorbent had a high affinity for Cu. The results of this study would contribute to further our current understanding on the mobility of multi heavy metals in soils and related environments.