EFFECT OF ORGANIC CONSTITUENTS AND COMPLEXED METAL IONS ON AGGREGATE STABILITY OF SOME EAST ANGLIAN SOILS

Paired soils of high and low organic matter content from the East Anglian silts were used to determine the role of different organic constituents and complexed metal ions in relation to aggregate stability. Although leaching with periodate and borate caused some loss of stability for most of the soils, the changes were much less than those due to extraction of the soils with pyrophosphate or acetylacetone which were more effective in removing organic materials complexed with iron and aluminium. Amounts of iron and aluminium extracted were not well correlated with changes in stability. The results indicate that in these soils polysaccharides are less important to aggregate stability than organic matter bonded to the clay particles through association with aluminium or iron.     

IRON AND ALUMINIUM AS CEMENTING SUBSTANCES OF SOIL AGGREGATES

A method is described for extracting fractions of soil iron and aluminium without removing organic matter. The extraction is by acetylacetone in a non–polar solvent and is virtually complete in zoo h. Similar amounts of iron and aluminium are extracted by acetylacetone in either benzene or water, but organic matter is extracted in detectable amounts only by acetylacetone in water. Extraction in aqueous solution after acetylacetone in benzene removes only organic matter, with no appreciable release of iron and aluminium. Metals extracted by acetylacetone in benzene are therefore considered to be bonded to that part of the organic matter which is extracted by acetylacetone. Water alone does not extract significant amounts of organic matter after removal of iron and aluminium by acetylacetone in benzene. The refolding of the hydrophilic surface units of the organic matter, caused by non–polar solvents, may hinder the extraction by water.     

Influence of organic matter on phosphate adsorption by aluminium and iron oxides in sandy soils

The phosphate adsorption capacity (P_max) of samples from various horizons of five Danish podzolized soils were investigated before and after organic matter removal. Removal of organic matter had no direct influence on P_max suggesting that organic matter did not compete with phosphate for adsorption sites. In the soils investigated aluminium and iron oxides were the main phosphate adsorbents. Thus, more than 96% of the variation in P_max could be accounted for by poorly crystalline aluminium and iron oxides (extractable by oxalate) and by well-crystallized iron oxides (taken as the difference between dithionite-citrate-bicarbonate-extractable iron and oxalate-extractable iron). Organic matter affected phosphate adsorption indirectly by inhibiting aluminium oxide crystallization. The resulting poorly crystalline oxides had high P_max. In contrast, the influence of organic matter on the crystallinity of the iron oxides, and therefore on their capacity to adsorb phosphate, seemed limited.     

STRUCTURAL FEATURES OF AGGREGATES IN SOME EAST ANGLIAN SILT SOILS

Samples from field plots of silty soils in East Anglia, which were high and low in organic matter, were subjected to mild ultrasonic vibration. In soils high in organic matter particles in the 2–20 μm or 20–50 μMm size range contained most humified organic matter, whereas in soils low in organic matter, most was present in the clay sized fraction. Scanning electron micrographs of the ultrasonically separated particles showed that those from the high organic matter soils had more extensive surface coatings. Clean fragments were left after peroxide and calgon dispersion treatment.     

Effect of peroxidation on soil electrochemical properties

Treatment with hydrogen peroxide to destroy the organic matter shifts the surface charge towards positive values. This is in agreement with the suggestion that per oxidation produces artefacts in the soil residues, since metals released from organic matter precipitate as hydroxide coating and produce positively charged surfaces. In the presence of 0.1 M sodium pyrophosphate, treatment with hydrogen peroxide always shifts the surface charge towards negative values, notwithstanding the removal of the electronegative organic components. It is suggested that the bulk of electropositive iron and aluminium oxides in soil are associated with the organic matter and removed by the treatment, so that permanent negative charges of clay minerals dominate in soil residue.     

Tea Plantation–Induced Activation of Soil Heavy Metals

Abstract

The accumulation of heavy metals in tea leaves is of concern because of its impact on tea quality. This study characterized long‐term changes of soil properties and heavy‐metal fractions in tea gardens and their effect on the uptake of metals from soils by the plants. Soil and tea leaf samples were collected from five plantations with a history of 2–70 years in Jinghua, Zhejiang Province, southeast China. The six chemical fractions (water‐soluble, exchangeable, carbonate‐bound, organic‐matterbound, oxide‐bound, and residual forms) of cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), manganese (Mn), lead (Pb), and zinc (Zn) in the soils were characterized. Dissolved organic‐matter accumulation in the soils and effects of low‐molecular‐weight organic acids on solubility of soil heavy metals were also tested. Long‐term tea plantation use resulted in accumulation of dissolved organic matter, decrease of soil pH, and elevation of water‐soluble and exchangeable metal fractions, thereby increasing metal contents in leaves. The influence was more significant when soil pH was less than 4.4. The results indicated that both acidification and accumulation of dissolved organic matter induced by tea plantations were also important causes of increased accumulation of the metals in the tea leaves. This was particularly true for the soils polluted with low concentration of heavy metals, because availability of the metals in these soils was mainly controlled by pH and dissolved organic matter.     

Effect of different management strategies on soil quality of citrus orchards in Southern Italy

Twenty‐six soil samples were collected from 13 paired orchards (organically vs. conventionally managed) homogeneous for age, rootstock and cultivars, belonging to the Eastern Sicily Organic Citrus farm Network. The soil quality was evaluated by chemical and biochemical indicators. The total organic C, humification parameters and isoelectric focusing of extracted organic matter were measured to quantify the size of relevant soil C pools. In addition, C turnover was evaluated by determining microbial C mineralization, C microbial biomass and by calculating the mineralization and metabolic quotient (qCO₂). The results obtained demonstrated that organic citrus soils were characterized by a general increase in all the organic matter pools, which means a greater C supply for soil metabolic processes. This observed trend did not directly influence the organic matter turnover, indicating that the organic approach could act as a soil C‐sink. The soil microflora of organically managed soils showed an improved efficiency in use of energy and organic resources, corresponding to an increased ability of soils under organic management to sustain biological productivity in the long term.     

Methods for remediation of metal‐contaminated soils: Preliminary results

Abstract

Contamination of soils by heavy metals is one of the environmental problems that the scientific community faces today. Such soils are difficult to treat because the heavy metals cannot be destroyed. Moreover, they are usually bonded with other contaminants, in particular organic ones. The presence of these organic pollutants can make the removal of metals from soils substantially more complicated. One way of coping with the problem which has been studied in recent years is the use of fixing agents which make the heavy metals unavailable to the plants, or prevent their leaching towards the groundwater. Inorganic fixing agents in particular have been tested and found to be suitable, but some organic ones can also be used, at least as temporary fixing materials. This paper gives preliminary results on remediation techniques using compost and Trichoderma viride Pers.: Fr. as heavy metal fixing agents.     

The influence of soil clay constituents on surface free energy of clay fractions

Measurements were made of the contact angle for glycerol, di-iodomethane and cis-decalin drops settled on the surface of pellets prepared from sodium forms of clay fractions of soils before and after successive removal of organic matter, iron and aluminium. On the basis of contact angles thus measured and a modified Young equation, the dispersive and non-dispersive components of the surface free energy of the clay fractions were calculated. It was found that the non-dispersive component decreased linearly with an increase in organic matter content, and with Fe and Al in the clay fractions of the soils studied. However, the dispersive component was not dependent on organic matter content, but decreased with increasing content of Fe and Al in the clay fractions studied.     

Forms of aluminium in some acid permanent grassland soils

The more labile forms of aluminium in a range of soils from areas of permanent grassland were determined with a number of selective extractants. The amounts of exchangeable A1 extracted with molar KCl were dependent upon pH, while the amounts exchangeable with 0.3 M LaCl³, although much greater, were not well correlated with pH. There were good correlations between soil organic C content and A1 extracted by (i) 0.5 M EDTA and (ii) 0.1 M potassium pyrophosphate. Pyrophosphate extracted greater amounts than any of the other extractants (sodium citrate/dithionite, ammonium oxalate (dark), acid oxalate (UV radiation), as well as those already mentioned). It was concluded that much of the extractable A1 in soils was associated with organic matter. Addition of lime to one of the soils reduced the amount of A1 extracted by all reagents except dithionite and acid oxalate solutions. There were considerable differences between soils in their release of A1 to continuous leaching with 0.01 M CaCl². Despite these differences between the soils in organically bound extractable Al, the differences in the amounts and patterns of release of A1 with CaCl² did not appear to be related to organic matter contents, nor to the other determined properties.     

铵、钾同时存在时, 土壤对铵的优先吸附

The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studied. The results showed that the water stability of soil aggregates declined with increasing size, especially for the low organic matter soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of soil aggregates. Removal of organic matter markedly disintegrated the large water-stable aggregates (> 2.0 mm) and increased the small ones (< 0.25-0.5mm) to some extent, whereas removal of free iron(aluminium) oxides considerably destroyed aggregates of all sizes, especially the < 0.25-0.5 mm classes. The contents of organic matter in water-stable aggregates increased with aggregate sizes. It is concluded from this study that small water-stable aggregates (< 0.25-0.5 mm) were chiefly cemented by Fe and Al oxides whilst the large ones (> 2.0 mm) were mainly glued up by organic matter. Both free oxides and organic matter contribute to the formation and water stability of aggregates in red soils.     

Chemical pools of cadmium, nickel and zinc in polluted soils and some preliminary indications of their availability to plants

This study was conducted to determine the chemical distribution and plant availability of Cd, Zn and Ni in eight metal-polluted soils in southern Ontario, Canada. There were altogether 30 different soil samples because two of the soils had received various sewage sludge treatments. The soils were sequentially extracted with 1 m ammonium acetate to remove soluble plus exchangeable metals, with 0.125 m Cu(II) acetate to remove complexed metals, and with 1 m HNO₃ to dissolve chemisorbed or occluded metals and precipitates such as oxides and carbonates. Expressed as a percentage of the metal so extracted, exchangeable Cd and Zn and Ni; complexed Cd and Zn>Ni and Ni>Zn>Cd in the acid-soluble pool. With a few exceptions (soils with high organic matter content or low pH) at least 50 per cent of the extracted metal was in the acid-soluble pool. The percentage of metal complexed was significantly correlated with organic matter content. The percentage of metal in the acid-soluble fraction was significantly correlated with soil pH. Preliminary findings based on the results with two soils suggested that for Cd and Zn plant availability was correlated with the concentrations of exchangeable, complexed or acid-soluble pools of Cd and Zn.     

Distribution of Trace Elements in Soils from the Sudbury Smelting Area (Ontario,Canada)

The sequential extraction procedure proposed by the European Commission Measurement and Testing Programme, combined with Scanning Electron Microscopy and Energy Dispersive X-ray Analysis(SEM/EDS), was applied to identify and quantify the chemical andmineralogical forms of Cu, Ni, Fe, Mn, Zn, Pb, Cr and Cd presentin the topsoil from a mining and smelting area near Sudbury (Ontario, Canada). The possible mobility of the chemical forms was also assessed. The metal fractions: (1) soluble and exchangeable, (2) occluded in manganese oxides and in easily reducible iron oxides, (3) organically bound and in form of sulphides, (4) residual mainly present in the mineral lattice structures were separated. Cu and Ni were the major metallic contaminants, occurring in soils in broad ranges of concentrations: Cu 11–1890 and Ni 23–2150 mg kg^-1. Cu was uniformly distributed among allthe extracted fractions. Ni was found associated mainly withthe residual forms, accounting for 17–92%, with an averageof 64%, of the total Ni present in the soils. Fe, Mn, Zn,Pb, Cr and Cd, while occurring in most analysed samples innormal soil concentrations, were primarily held in theresidual mineral fraction (on average >50%). The solubleand exchangeable forms made a small contribution (≤8.1%)to the total content of metals extracted. At least 14% ofthe total Cd, Mn and Pb was mobilised from the reducibleforms. The oxidizable fraction assumed mean values higher than10% only for Pb and Zn. Statistical treatment of the experimental data showed significant correlations between totalmetal content of the soils, some soil properties such as pH value, clay and organic matter content, and metal concentrationsin the various fractions. SEM/EDS analysis showed Fe in form ofoxides and sulphides in soils and Cu, Ni, Mn, Zn and Cr in association with iron oxides. Numerous black carbonaceous particles and precipitates of aluminium fluoride salts, observedin the solid residue left after `total’ digestion, were found tocontain Fe, Ni and Cr.     

A 13C-NMR study of the interactions of soil organic matter with aluminium and allophane in podzols

The stabilization of organic matter in soil by interaction with aluminium (Al) or allophane is important in maintaining soil quality, and in retarding the decomposition of soil organic matter. Complexation of Al by soil organic matter may also ameliorate Al toxicity. Here we use ¹³C-NMR spectroscopy to assess the interaction of soil organic matter with both Al and allophane in two poorly drained podzols containing only trace amounts of iron. The ¹³C-NMR spectrum of the subsoil of the allophane-rich One Tree Point podzol shows an intense peak at 179 p.p.m., assigned to carbon in carboxylic acids. This peak shifts to 177 p.p.m. after removal of allophane (11% of the soil mass) by treatment with HF. We infer that the carboxyl groups in the organic matter are bonded to structural Al on the surface of allophane spherules. In the non-allophanic Te Kopuru podzol, on the other hand, the organic matter apparently interacts with Al ions in the soil solution. This soil also has more aromatic carbon and fewer carbons in carboxyl and carbohydrate structures than the allophanic sample. There is an indication that allophane stabilizes carbohydrate groups as well as carboxyl groups.     

Effect of soil components on the adsorption of heavy metals under technogenic contamination

The adsorption of copper, zinc, and lead by two urban soils with different degrees of contamination was studied. Changes in the sorption capacity of the soils and the binding strength of the metals with the soil were determined after the removal of organic matter and iron minerals with a potassium pyrophosphate solution and Tamm’s reagent. The selectivity of these solutions for the dissolution of soil components was estimated.     

Leaching of Metals in Coastal Technosols Triggered by Saline Solutions and Labile Organic Matter Removal

This study aims to understand the influence of salinity and labile organic matter removal on the fate and behavior of metals in coastal technosols. Two technosol cores were collected near the Lebanese shore. The cores were sectioned into layers; each layer was characterized for pH, salinity, electric conductivity, labile and total organic matter, grain size, and total and oxalate-extractable metals. Consequently, two saline solutions were used in desorption experiments to understand the role of ionic strength and labile organic matter on metal release. The results showed that the technosol layers were highly heterogeneous; most layers were enriched with Fe, Zn, Pb, and Cu. The mineralogical investigations showed that the metals, notably Fe, were not present as crystalline minerals, rather big percentages of the metals were found in amorphous or poorly crystalline phases. Desorption experiment showed that Mg release was dependent on salinity and organic matter in both technosols, while Pb release was dependent on both factors only in one. Additionally, Zn and Cu were associated to organic matter, and their release was conditioned by the removal of labile organic matter; iron was primarily found as amorphous or poorly crystalline phases, and salinity had a major role in its release. The role of ionic strength and labile organic matter removal on the behavior of metals in technosols was demonstrated. Finally, understanding metal dynamics between the solid and liquid compartments in technosols, especially where salt deposition occurs, is important to reduce unwanted metal leaching to groundwater or seawater and transfer to biota.     

THE COVARIANCE OF PHOSPHATE SORPTION WITH OTHER SOIL PROPERTIES IN SOME BRITISH AND TROPICAL SOILS

Phosphate sorption capacity estimated by Piper's (1942) ‘anion exchange capacity’ and Bache and Williams's (1971) phosphate sorption index were correlated with soil pH, clay, organic matter, ‘free iron oxides’ and ‘extractable aluminium’ (McLean et al., 1958) for topsoil and subsoil samples from twenty tropical and twenty British acidic soil profiles. These two groups of soils did not differ significantly in phosphate sorption. Extractable aluminium and free iron oxide were well correlated with phosphate sorption, free iron oxide being superior to aluminium in freely drained British soils but not in poorly drained ones. Organic matter content correlated well with phosphate sorption for the poorly drained British soils, and for the tropical soils when sorption capacitywas measured using a high phosphate concentration.     

Soil organic matter chemistry in allophanic soils: a pyrolysis-GC/MS study of a Costa Rican Andosol catena

Soil organic matter (SOM) in allophanic soils is supposed to accumulate due to protection caused by binding to allophane, aluminium and iron. We investigated a catena of allophanic and non‐allophanic soils in Costa Rica to determine the effect of such binding mechanisms on SOM chemistry. These soils contain no contribution of black carbon. Molecular characterization of litter, extractable and dispersed organic matter was done by Curie‐point pyrolysis‐GC/MS. The molecular chemistry of the organic fractions indicates a strong decomposition of plant‐derived organic matter and a strong contribution of microbial sugars and N‐compounds to SOM. Both the decomposition of plant‐derived SOM – including that of relatively recalcitrant compounds – and the relative contribution of microbial SOM were greater in allophanic samples than in non‐allophanic ones. This suggests that chemical protection does not act on primary OM, although it may influence the accumulation of secondary OM in these soils. The effect of allophane on SOM contents in such perhumid soils is probably through incorporation of decomposition products and microbial SOM in very fine aggregates that – in a perhumid environment – remain saturated with water during much of the year. Greater concentrations of aliphatics are found in allophanic residues, but there is no evidence of any specific mineral‐organic binding. The results do not support the existing theory of chemical protection of plant‐derived components through binding to allophane, iron and aluminium.     

Laboratory studies of crust development in Irish and Iraqi soils II. Effects of some physico-chemical constituents on crust strength and seedling emergence

The influence of soil constituents including sand, silt, clay, organic substances, aluminium and iron on crust development and seedling emergence was investigated in a selection of 30 soils. After treatment with simulated rain, soil crust strength as measured by penetration resistance to an upward-moving probe tended to decrease with increasing total organic carbon content, but the relationship was not a simple one. Consideration of other factors showed that in some soils (soils of 1.5–2% total organic carbon), alkali-exractable carbon and clay contents had the greatest influence on penetration resistance values whereas in other soils (2.4–3% total organic carbon), coarse sand, fine sand, EDTA-extractable aluminium and humic acid carbon were highly correlated with penetration resistance. In a group of soils with around 4% total organic carbon, oxalate-extractable aluminium appeared to exert a dominant influence. There was a good correlation between humic acid carbon and penetration resistance after rain treatment in soils containing less than 40% sand. A similar relationship was also noted with EDTA-extractable iron.Combination of all factors in a multiple regression analysis accounted for a considerable proportion of the variation in penetration resistance of soils with and without simulated rain application and in seedling emergence of barley. Organic carbon, and the humic acid fraction in particular, were most important in determining crust strength for all soils as a group.A significant correlation between plastic limit moisture and the logarithm of penetration resistance is explained partially, at least, by the relationships that exist between organic carbon alone, clay alone and a combination of both, with variation in moisture.     

土壤铁矿物的生物-非生物转化过程及其界面重金属反应机制的研究进展

铁矿物作为土壤的重要组成成分,一般可通过吸附、络合和共沉淀等方式影响重金属的生物有效性和毒性.此外,土壤中有机物的存在会影响铁矿物的转化,导致转化产物的结构和表面特性发生改变,进一步影响重金属的环境行为.本文从铁矿物、有机质和重金属等要素入手,综述了反应pH、温度、亚铁和微生物等因素影响下土壤铁矿物非生物和生物转化过程...