Concentrations of monosaccharides in humic substances in the early stages of humification.

Deteriorated liquid packaging board (LPB) and biowaste compost are matrices, mainly consisting of cellulose, in the early stages of humification. Degradative studies on these matrices allow an examination of the role of carbohydrates in the synthesis of humic substances. Samples of different age were collected and divided by extraction into hot water extract (HWE), bitumen, humic acid (HA), fulvic acid (FA) and humin or residual fibre fractions. The following monosaccharides were identified in these fractions: L-arabinose, D-ribose, D-xylose, L-fucose, D-mannose, D-fructose, D-galactose, D-glucose, L-rhamnose and xylitol. The main component in all fractions was glucose. The concentrations of monosaccharides in humic acids (HAs) of LPB ranged from 67 to 503 mg/g of organic matter, and the concentrations in HAs of compost from 52 to 101 mg/g. As a general trend, the concentrations of monosaccharides decreased during LPB degradation and composting in all fractions. At the same time the relative amounts of D-xylose, D-mannose and D-galactose increased in HAs of compost samples.     

Long-term effect of sewage sludge application on soil humic acids

Sewage sludges are used in agriculture because they act as a fertilizer. Long-term studies are needed to evaluate the effect of sewage sludge on soil properties by paying particular attention to the soil organic matter. Soil plots were amended for 10 years with 1Mg dry matter ha(-1)year(-1) of sewage sludge. Chemical parameters such as total organic carbon (TOC), N, C/N ratio and CEC were determined when this period ended. Moreover, TOC was fractionated into humified and non-humified fractions. Humic acids (HA) were isolated and studied by elemental analysis, DRIFT, (1)H NMR and CPMAS 13C NMR spectroscopies. At the end of the tests, compared to the control soil, the sludge-amended soil did not exhibit change in total organic C and related humified fractions. However, the HA composition of the soil treated with sludge had developed an HA composition closer to that of the HA-sludge as a result of the enrichment of recalcitrant fractions contained in the sludge.     

Negative effects of humic acid addition on phytoremediation of pyrene-contaminated sediments by mangrove seedlings

Vegetated (with Kandelia candel seedlings) and non-vegetated mangrove microcosms were employed to remove pyrene from contaminated sediments, and the effects of adding 6.7% humic acid (HA) on such removal were investigated. At the end of 6-month treatment, residual pyrene concentrations in surface sediments (0-2 cm) of the contaminated microcosms reduced from an initial 5.82 to 0.63 microg g(-1) dw, and the reduction was less in HA amended microcosms with the residual pyrene concentration remained at 3.12 microg g(-1) dw. The pyrene removal percentages in microcosms with HA amendment were 29% for surface aerobic sediments and 41% for bottom (anaerobic) sediments, while the respective removal percentages in microcosms without HA amendment were 89% (surface sediments) and 53% (bottom sediments). Microcosms planted with K. candel seedlings had a significantly higher pyrene removal when compared to the non-vegetated ones, and the average removal percentages were 70.9% and 61.4%, respectively. However, when humic acid was added, no significant difference was found between vegetated and non-vegetated microcosms in pyrene removal, both had less than 40% removal, probably because plant growth in humic acid amended contaminated microcosms, in terms of total biomass, was reduced by 50%. Roots of K. candel could accumulate pyrene from contaminated microcosms, and pyrene concentrations in roots harvested from microcosms with and without humic acid addition were 6.01 and 3.46 microg g(-1) dw, respectively. These results suggest that the addition of HA to contaminated sediments decreased the mangrove microcosm's ability to remove pyrene as pyrene was more tightly bound to the organic matter and plant growth was reduced.     

Bioavailability and degradation of phenanthrene in compost amended soils

Bioavailability in soil of organic xenobiotics such as phenanthrene is limited by mechanisms of diffusion of the xenobiotics within soil micropores and organic matter. The agricultural utilization of compost may reduce the risk connected to organic xenobiotic contamination by means of: (i) a reduction of the bioavailable fraction through an increased adsorption and (ii) an enhanced degradation of the remaining bioavailable fraction through an inoculum of degrading microorganisms. Aim of this work is to test this hypothesis by assessing the effects of compost amendment on the bioavailability and degradation of phenanthrene in soil. Experiments were carried out in both sterilized and non-sterilized conditions, and chemical and microbiological analyses were carried out in order to determine the extent of degradation and bioavailability and to monitor the evolution of the soil micro flora in time. Bioavailability was assessed in sterilized microcosms, in order to assess the physical effects of compost on aging processes without the influence of microbial degradation. Results showed that bioavailability is significantly reduced in soils amended with compost, although no differences were found at the 2 doses of compost studied. In non-sterilized soils the amount of phenanthrene degraded was always higher in the amended soils than in the non-amended one. Microbiological analyses confirmed the presence of a higher number of phenanthrene degraders in the amended soils and in samples of compost alone. These results suggest that compost induces the degradation in soils of easily degradable compounds such as phenanthrene, when the proper bacteria are in the compost; more resistant xenobiotics may instead be trapped by the compost organic matter, thus becoming less available.     

Effects of long-term soil amendment with sewage sludges on soil humic acid thermal and molecular properties

Sewage sludges are frequently used as soil amendments due to their high contents of organic matter and nutrients, particularly N and P. However, their effects upon the chemistry of soil humic acids, one of the main components of the soil organic matter, need to be more deeply studied in order to understand the relation between organic matter structure and beneficial soil properties. Two sewage sludges subjected to different types of pre-treatment (composted and thermally dried) with very different chemical compositions were applied for three consecutive years to an agricultural soil under long-term field study. Thermal analysis (TG–DTG–DTA) and solid-state ¹³C NMR spectroscopy were used to compare molecular and structural properties of humic acids isolated from sewage sludges, and to determine changes in amended soils. Thermally dried sewage sludge humic acids showed an important presence of alkyl and O/N-alkyl compounds (70%) while composted sludge humic acids comprised 50% aromatic and carbonyl carbon. In spite of important differences in the initial chemical and thermal properties of the two types of sewage sludges, the chemical and thermal properties of the soil humic acids were quite similar to one another after 3 years of amendment. Long-term application of both sewage sludges resulted in 80–90% enrichment in alkyl carbon and organic nitrogen contents of the soil humic acid fraction.     

Effects of long-term soil amendment with sewage sludges on soil humic acid thermal and molecular properties

Sewage sludges are frequently used as soil amendments due to their high contents of organic matter and nutrients, particularly N and P. However, their effects upon the chemistry of soil humic acids, one of the main components of the soil organic matter, need to be more deeply studied in order to understand the relation between organic matter structure and beneficial soil properties. Two sewage sludges subjected to different types of pre-treatment (composted and thermally dried) with very different chemical compositions were applied for three consecutive years to an agricultural soil under long-term field study. Thermal analysis (TG–DTG–DTA) and solid-state ¹³C NMR spectroscopy were used to compare molecular and structural properties of humic acids isolated from sewage sludges, and to determine changes in amended soils. Thermally dried sewage sludge humic acids showed an important presence of alkyl and O/N-alkyl compounds (70%) while composted sludge humic acids comprised 50% aromatic and carbonyl carbon. In spite of important differences in the initial chemical and thermal properties of the two types of sewage sludges, the chemical and thermal properties of the soil humic acids were quite similar to one another after 3 years of amendment. Long-term application of both sewage sludges resulted in 80–90% enrichment in alkyl carbon and organic nitrogen contents of the soil humic acid fraction.     

Accumulation and fractionation of copper, iron, manganese, and zinc in calcareous soils amended with composts.

Amending soils with compost may lead to accumulation of metals and their fractions at various concentrations in the soil profile. The objectives of this study were to determine 1) the accumulation of Cu, Fe, Mn, and Zn with depth and 2) the distribution of water soluble, exchangeable, carbonate, Fe-Mn oxides, organic and residual forms of each metal in soils amended with MSW compost, co-compost, biosolids compost and inorganic fertilizer (as control). Total concentrations of Cu, Fe, Mn and Zn were concentrated in the 0-22 cm soil layer and scant in the rock layer. These metals were in the decreasing order of Fe > Mn > Zn > or = Cu. Copper, Fe, and Zn were predominantly in the residual form followed by fractions associated with Fe-Mn oxides, carbonate, organic, exchangeable and water soluble in all treatments except MSW compost amended soil where the organic fraction was higher than the carbonate fraction. In fertilizer, co-compost and biosolids compost treated soils Mn concentrated mainly in the Fe-Mn oxides form followed by residual, carbonate, and organic forms whereas, in MSW compost treated soil the same pattern occurred except that Mn organic fraction was higher than that in the carbonate form. The MSW compost has a greater potential to be used as a soil amendment to supply plants with Cu, Mn and Zn than other treatments in calcareous soils of south Florida.     

Potential availability of heavy metals to phytoextraction from contaminated soils induced by exogenous humic substances

Effective phytoremediation of soils contaminated by heavy metals depends on their availability to plant uptake that, in turn, may be influenced by either the existing soil humus or an exogenous humic matter. We amended an organic and a mineral soil with an exogenous humic acid (HA) in order to enhance the soil organic carbon (SOC) content by 1% and 2%. The treated soils were further enriched with heavy metals (Cu, Pb, Cd, Zn, Ni) to a concentration of 0, 10, 20, and 40 microg/g for each metal and allowed to age at room temperature for 1 and 2 months. After each period, they were extracted for readily soluble and exchangeable (2.5% acetic acid), plant-available (DTPA, Diethylentriaminepentaacetic acid), and occluded (1 N HNO(3)) metal species. Addition of HA generally reduced the extractability of the soluble and exchangeable forms of metals. This effect was directly related to the amount of added HA and increased with ageing time. Conversely, the potentially plant-available metals extracted with DTPA were generally larger with increasing additions of exogenous HA solutions. This was attributed to the formation of metal-humic complexes, which ensured a temporary bioavailability of metals and prevented their rapid transformation into insoluble species. Extractions with 1 N HNO(3) further indicated that the added metals were present in complexes with HA. The observed effects appeared to also depend on the amount of native SOC and its structural changes with ageing. The results suggest that soil amendments with exogenous humic matter may accelerate the phytoremediation of heavy metals from contaminated soil, while concomitantly prevent their environmental mobility.     

Effect of microbial activity, soil water content and added copper on the temporal distribution patterns of HCB and DDT among different soil organic matter fractions

Temporal changes in the distribution of exogenous HCB and DDT among different soil organic matter fractions were studied under sterile and non-sterile conditions, different soil water contents, and different concentrations of added Cu(2+). The residence time was 311days. Soil organic matter was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions by a methyl isobutyl ketone (MIBK) method. Results revealed that there is a mass transfer tendency of DDT and HCB from FA, HA and BHA to IR and lipid fractions with increasing residence time. Microbial activity accelerated the mass transfer, while the addition of Cu(2+) slowed it down. The HCB and DDT transfer rate decreased as the soil moisture increased from 1.9% to 60%, but increased when soil moisture increased further to 90%. A two-compartment first order kinetic model was used to describe the mass transfer from FA, HA and BHA.     

Immobilization of pentachlorophenol in soil using carbonaceous material amendments

In this study, three pentachlorophenol (PCP) laboratory-spiked and one field-contaminated soil were amended with 2.0% char, humic acid (HA) and peat, respectively. The amended soils were aged for either 7 or 250 days. After amendment, CaCl₂ extractability of PCP was significantly decreased. Desorption kinetics indicated that the proposed amendment could lead to a strong binding and slow desorption of PCP in soils. Amendment with char reduced the bioaccumulation factor (BAF) of PCP most significantly for earthworms (Eisenia fetida) in all soils studied. The results of both physicochemical and biological tests suggested that amendment reduced PCP bioavailability quickly and enduringly, implying that carbonaceous material amendment, especially char amendment, was a potentially attractive in situ remediation method for sequestration of PCP in contaminated soil.     

Temporal change in the distribution patterns of hexachlorobenzene and dichlorodiphenyltrichloroethane among various soil organic matter fractions

Residence time-dependent distribution patterns of hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane (DDT) among different soil organic matter fractions of three Chinese soils were investigated. Soil organic matter (SOM) was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions using methyl isobutyl ketone (MIBK) method. Results revealed that as the residence time prolonged, the amounts of HCB and DDT in the FA, HA and BHA fractions decreased, while those in the lipid and IR fractions increased. One- and two-compartment first order, and one- and two-parameter pore-diffusion kinetic models were used to describe the mobility of HCB and DDT from the FA, HA and BHA fractions. The results suggest that excellent agreements were achieved between the experimental data and fits to the two-compartment first order kinetic model (R2>0.97). The transfer rates of HCB and DDT followed the order FA>HA>BHA.     

Phytoavailability and fractionation of copper, manganese, and zinc in soil following application of two composts to four crops

Two experiments were conducted to evaluate the effect of compost addition to soil on fractionation and bioavailability of Cu, Mn, and Zn to four crops. Soils growing Swiss chard (Beta vulgaris var. cicla L.) and basil (Ocimum basilicum L.) were amended (by volume) with 0, 20, 40, and 60% Source-Separated Municipal Solid Waste (SS-MSW) compost, and dill (Anethum graveolens L.) and peppermint (Mentha X piperita L.) were amended with 0, 20, 40, and 60% of high-Cu manure compost (by volume). The SS-MSW compost applications increased the concentration of Cu and Zn in all fractions, increased Mn in acid extractable (ACID), iron and manganese oxides (FeMnOX), and organic matter (OM) fractions, but decreased slightly exchangeable-Mn. Addition of 60% high-Cu manure compost to the soil increased Cu EXCH, ACID, FeMnOX, and OM fractions, but decreased EXCH-Mn, and did not change EXCH-Zn. Addition of both composts to soil reduced bioavailability and transfer factors for Cu and Zn. Our results suggest that mature SS-MSW and manure composts with excess Cu and Zn could be safely used as soil conditioners for agricultural crops.     

Compost amendment of Cu-Zn minespoil reduces toxic bioavailable heavy metal concentrations and promotes establishment and biomass production of Bromus carinatus (Hook and Arn.)

A series of lab and greenhouse studies were undertaken to understand how Cu and Zn toxicity influences Bromus carinatus (Hook and Arn.) growth, to what degree an organic amendment (yard waste compost) may reduce Cu and Zn bioavailability in Cu-Zn minespoil and promote plant growth in combination with fertilizer, and how the vertical distribution of compost in the minespoil influences rooting depth. Root Cu and Zn toxicity thresholds were determined to be 1 mgL(-1) and 10 mgL(-1) in solution, respectively. The compost amendment had exceptionally high Cu and Zn binding capacities (0.17 and 0.08 g metal g C(-1), for Cu and Zn, respectively) that were attributed to high compost humic and fulvic acid concentrations. Maximum plant biomass was achieved when minespoil was amended with compost and fertilizer in combination. Fertilizer alone had no effect on plant growth. Mixing compost into the minespoil was essential to promote adequate rooting depth.     

Pyrethrins and piperonyl butoxide adsorption to soil organic matter

The adsorption and mobility of pyrethrins (Pys), the major insecticidal components obtained from the pyrethrum daisy Tanacetum cinerariifolium, and piperonyl butoxide (PBO), a pyrethrum synergist, were determined in soil using batch-equilibrium and reverse-phase thin-layer chromatographic techniques. Two soil management practices were used, soil mixed with yard waste compost (COM) at 50 t acre(-1) on dry weight basis and no-mulch (NM) bare soil. Adsorption isotherm experiments were carried out using known concentrations of Pys (Py-I and Py-II) and PBO mixed with known amounts of COM or NM soil at constant temperature and pressure until equilibrium was attained. Pys and PBO in soil extracts were purified and concentrated using solid-phase extraction cartridges containing C18-octadecyl bonded silica. Pys and PBO residues were quantified using a high-performance liquid chromatograph equipped with a UV detector. Adsorption studies showed that compost amended soil adsorbed more Pys and PBO than native (NM) soil. Py-I adsorption was greater than Py-II and PBO. Adsorption of Pys and PBO to humic and fulvic acids was also studied by reverse-phase thin layer chromatography (RPTLC). Results indicated that humic acid, a significant component of organic matter, reduced Pys and PBO mobility. Pys and PBO mobility decreased as the concentration of humic acid in the mobile phase increased.     

Influence of dissolved humic substances on the leaching of MCPA in a soil column experiment

The influence of dissolved humic substances on the transport of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in a sandy soil with a low organic carbon content was studied in a column experiment. Soil columns were eluted with aqueous solutions containing different fractions of humic substances. More than 70% of the applied compound was found in the leachate in all sandy soil experiments, but distinct differences were obtained depending on the composition of the eluent. The addition of both humic and fulvic acids to the eluent affected the leaching behaviour of MCPA. While the presence of humic acids increased and accelerated the movement of MCPA in the investigated sandy soil, fulvic acids caused the opposite effect: increased retention was observed relative to the control. We concluded that a possible carrier transport or retention strongly depends on the composition of the dissolved organic matter. Thus, changes in the composition of dissolved organic matter may affect MCPA movement into deeper soil layers.     

Changes in soil organic matter chemical properties after organic amendments

Organic inputs are used to improve soil physical and chemical properties, but the corresponding changes in soil organic matter (SOM) chemical properties are not well known. In this study, we compared some characteristics of the SOM of a soil receiving either no organic inputs, or two different amendments during 15 years (straw or conifer compost). Quantities of organic carbon and C/N values were determined on particle size fractions after physical soil fractionation to localize changes due to amendments. Contents in reactive functional groups, acid-base properties and copper binding affinities were determined by titration experiments for the soluble fraction of SOM: the fulvic acid fraction (FA). Data of FA extracted from the bulk soil were compared to data of FA extracted from the <20 microm size fraction with the help of either a discrete or a continuous model (fit of data with FITEQL or NICA, respectively). Copper binding characteristics of FA extracted from the <20 microm size fraction did not change significantly after organic inputs, while those of FA extracted from the bulk organic-amended soils were found different from the ones with no amendment. Minor effects observed in the finer soil fractions were ascribed to their low turn-over of organic carbon and/or to a greater homogeneity in the nature of the organic carbon entering these fractions. Our results show major chemical changes in coarser soil organic fractions after organic amendments.     

Carbon deposition in soil rhizosphere following amendments with compost and its soluble fractions, as evaluated by combined soil-plant rhizobox and reporter gene systems

We determined the organic carbon released by roots of maize plants (Zea mays L.) when grown in soils amended with compost and its soluble fractions. In rhizobox systems, soil and roots are separated from the soil of a lower compartment by a nylon membrane. Treatments are applied to the upper compartment, while in the lower compartment luminescent biosensors measure the bioavailable organic carbon released by roots (rhizodeposition). The rhizobox-plants systems were amended with a compost (COM), its water extract (TEA), the hydrophobic (HoDOM) and hydrophilic (HiDOM) fractions of the dissolved organic matter (DOM) extracted from the compost. After root development, the lower untreated compartments were sampled and sliced into thin layers. The bioavailable organic carbon in each layer was assessed with the lux-marked biosensor Pseudomonas fluorescens 10586 pUCD607, and compared with total organic carbon (TOC) analyses. The TOC values ranged between 8.4 and 9.6 g kg(-1) and did not show any significant differences between bulk and rhizosphere soil samples in any treatment. Conversely, the biosensor detected significant differences in available C compounds for rhizosphere soils amended with various organic materials. Concentrations of available organic compounds in the first 2 mm of soil rhizosphere were 1.69 (control), 1.09 (COM), 2.87 (HiDOM), 4.73 (HoDOM) and 2.14 (TEA)micromol Cg(-1) soil g(-1) roots. The applied rhizobox-biosensor integrated method was successful in detecting and quantifying effects of organic amendments on organic carbon released by maize plant roots. This approach may become important in assessing the carbon cycle in agricultural soils and soil-atmosphere compartments.     

INFLUENCE OF SOIL ORGANIC MATTER ON THE LEACHING OF POLYCYCLIC AROMATIC HYDROCARBONS IN SOIL

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Aside from total organic carbon, the ratio among the different organic matter fractions [dissolved organic matter, fulvic acid (FA), humic acid (HA) and humin] can also affect the mobility of these hydrocarbons in soils. In this study the effect of the whole organic carbon pool has been compared with that of HA and FA on the translocation of four PAHs (biphenyl, fluorene, phenanthrene and pyrene) in soil columns. Oxidized and untreated soil columns with and without HA or FA, were prepared, spilled with hydrocarbons and leached with a 0.01 M CaCl₂ solution. The influence of HA and FA on PAH translocation was investigated through determinations of the PAH contents and total organic carbon (TOC) in the layers of the columns. All molecules were moved vertically by the percolating solutions, their concentrations decreasing with depths. The non-oxidized soil tended to retain more PAHs (96%) than the oxidized one (60%), confirming that organic matter plays an important role in controlling PAH leaching. The whole organic matter pool reduced the translocation of pollutants downward the profile. The addition of HA enhanced this behaviour, by increasing the PAH retention in the top layers (7.55 mg and 4.00 mg in the top two layers, respectively) while FA increased their mobility (only 2.30 and 2.90 mg of PAHs were found in the top layers) and favoured leaching. In fact, in the presence of HA alone, the higher amounts of PAHs retained at the surface and the good correlation (r²=0.936) between TOC and hydrocarbon distribution can be attributed to a parallel distribution of PAHs and HA, while in the presence of FA, the higher mobility of PAHs can be attributed to the high mobility of the humic material, as expected by its extensive hydrophilic characteristics.     

Influence of soil organic matter on the leaching of polycyclic aromatic hydrocarbons in soil

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Aside from total organic carbon, the ratio among the different organic matter fractions [dissolved organic matter, fulvic acid (FA), humic acid (HA) and humin] can also affect the mobility of these hydrocarbons in soils. In this study the effect of the whole organic carbon pool has been compared with that of HA and FA on the translocation of four PAHs (biphenyl, fluorene, phenanthrene and pyrene) in soil columns. Oxidized and untreated soil columns with and without HA or FA, were prepared, spilled with hydrocarbons and leached with a 0.01 M CaCl2 solution. The influence of HA and FA on PAH translocation was investigated through determinations of the PAH contents and total organic carbon (TOC) in the layers of the columns. All molecules were moved vertically by the percolating solutions, their concentrations decreasing with depths. The nonoxidized soil tended to retain more PAHs (96%) than the oxidized one (60%), confirming that organic matter plays an important role in controlling PAH leaching. The whole organic matter pool reduced the translocation of pollutants downward the profile. The addition of HA enhanced this behaviour by increasing the PAH retention in the top layers (7.55 mg and 4.00 mg in the top two layers, respectively) while FA increased their mobility (only 2.30 and 2.90 mg of PAHs were found in the top layers) and favoured leaching. In fact, in the presence of HA alone, the higher amounts of PAHs retained at the surface and the good correlation (r2=0.936) between TOC and hydrocarbon distribution can be attributed to a parallel distribution of PAHs and HA, while in the presence of FA, the higher mobility of PAHs can be attributed to the high mobility of the humic material, as expected by its extensive hydrophilic characteristics.     

Binding of polycyclic aromatic hydrocarbons by humic acids formed during composting

Binding of two model polycyclic aromatic hydrocarbons (PAHs), phenanthrene and pyrene, by humic acids (HAs) isolated from an organic substrate at different stages of composting and a soil was investigated using a batch fluorescence quenching method and the modified Freundlich model. With respect to soil HA, the organic substrate HA fractions were characterized by larger binding affinities for both phenanthrene and pyrene. Further, isotherm deviation from linearity was larger for soil HA than for organic substrate HAs, indicating a larger heterogeneity of binding sites in the former. The composting process decreased the binding affinity and increased the heterogeneity of binding sites of HAs. The changes undergone by the HA fraction during composting may be expected to contribute to facilitate microbial accessibility to PAHs. The results obtained also suggest that bioremediation of PAH-contaminated soils with matured compost, rather than with fresh organic amendments, may result in faster and more effective cleanup.