Speciation of phytate ion in aqueous solution. Sequestering ability toward mercury(II) cation in NaClaq at different ionic strengths

As a contribution to understanding the speciation of mercury in the environment and to the study of the sequestering ability of phytate (Phy) toward heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 degrees C by potentiometry, ISE-H+ glass electrode) of its interactions with mercury(II) cation in NaCl aqueous solutions at different ionic strengths (I = 0.15 and 1.0 mol L(-1)), in the pH range 2.5 < or = pH < or = 9.5 and considering metal-to-ligand ratios of 1:1 < or = Hg/Phy < or = 4:1. The formation of 11 HgiHjPhy(12-2i-j)(- species with i = 1 and 0 < or = j < or = 7 and i = 2 and 0 < or = j < or = 2 was observed. Their complex formation constant values proved to be fairly dependent on ionic strength. The speciation of phytic acid and mercury(II) is also dependent on the metal-to-ligand ratio; the dependence of the stability of phytate-mercury(II) species on the phytate protonation step was modeled, and an empirical predictive relationship was proposed. From the results obtained, phytate has very good sequestering ability toward Hg2+, even in the presence of considerable excesses of chloride ion, that is, another ligand strongly interacting with mercury; this supports future studies both on the use of plants that naturally synthesize it for phytoremediation purposes and on its direct application in remediation techniques.     

Influence of herbicide structure,clay acidity,and humic acid coating on acetanilide herbicide adsorption on homoionic clays

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite was studied by coupling batch equilibration and FT-IR analysis. Adsorption decreased in the order metolachlor > acetochlor > alachlor > propachlor on Ca(2+)- or Mg(2+)-saturated clays and in the order metolachlor > alachlor > acetachlor > propachlor on Al(3+)- or Fe(3+)-saturated clays. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in bonding. For the same herbicide, adsorption of alachlor, acetachlor, and metolachlor on clay followed the order Ca(2+) approximately Mg(2+) < Al(3+) < or = Fe(3+), which coincided with the increasing acidity of homoionic clays. Adsorption of propachlor, however, showed an opposite dependence, suggesting a different governing interaction. In clay and humic acid mixtures, herbicide adsorption was less than that expected from independent additive adsorption by the individual constituents, and the deviation was dependent on the clay-to-humic acid ratio, with the greatest deviation consistently occurring at a 60:40 clay-to-humic acid ratio.     

Phytase and acid phosphatase activities in plant feedstuffs

A total of 183 samples representing 24 feedstuffs were analyzed for total phosphorus, phytate phosphorus content, phytase (Phy), and acid phosphatase (AcPh) activities with the objective to predict the capacity to hydrolyze phytic acid and to contribute to formulating environmentally adequate diets for monogastric animals. Of the cereals and cereal byproducts analyzed, only rye (5147 U kg(-)(1); 21 955 U g(-)(1)), wheat (1637 U kg(-)(1); 10 252 U g(-)(1)), rye bran (7339 U kg(-)(1); 56 722 U g(-)(1)), and wheat bran (4624 U kg(-)(1); 14 106 U g(-)(1)) were rich in Phy and AcPh activities. Legume seeds and oilseeds contained negligible Phy activity and a moderate amount of AcPh activity, except for kidney bean (33 433 U g(-)(1)) and full-fat linseed meal (13 263 U g(-)(1)). On the other hand, a significant linear regression between phytate phosphorus (y) and total phosphorus (x) was observed in cereal byproducts (R(2) = 0. 95; y = 0.8458x - 0.0367; P < 0.001) and oil seeds (R(2) = 0.95; y = 0.945x - 0.20; P < 0.001). Phy and AcPh were positively correlated with respect to phytate phosphorus in cereals, cereal byproducts, and other byproducts and negatively correlated in legume seeds and oilseeds. Except for cereals, the highest correlation between enzyme activities and phytate phosphorus was found for phytase. It is not possible to predict Phy and AcPh activities from phytate phosphorus content by linear and quadratic regressions. Finally, only highly significant and positive correlation was found between Phy and AcPh activities for cereals, cereal byproducts, and oilseeds.     

Interactive effects of aluminum and chromium stresses on the uptake of nutrients and the metals in barley

Aluminum (Al) and chromium (Cr) stresses often occur simultaneously in agricultural soils, and pose a great damage to crop growth, yield formation and product safety. In the current study, the influence of combined Al and Cr stresses on plant biomass, metal and nutrient contents was determined in comparison with that of Al or Cr stress alone. A hydroponic experiment was conducted to investigate the effect of pH, Al and Cr in the medium solution on the uptake of mineral elements as well as Al and Cr in the two barley genotypes differing in Al tolerance. Aluminum sensitive genotype Shang 70-119 had significantly higher Cr and Al contents in plants than Al-tolerant genotype Gebeina. Barley roots had much higher Al and Cr contents than above-ground plant parts. Chromium contents were much higher in the solution with pH 4.0 than in that with pH 6.5. Aluminum stress reduced phosphorus (P), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), manganese (Mn), zinc (Zn) and boron (B) contents in roots and restrained potassium (K) and iron (Fe) from being translocated into shoots and leaves. Chromium stress resulted in reduced P, K, Mg, S, Fe, Zn and Mn contents in roots at pH 6.5 and P, K, Ca, Mg, S, Zn and Mn contents at pH 4.0. Translocation of all nutrients from roots to upper parts of plants was inhibited except Ca in pH 6.5 with Cr addition. Lower contents of all nutrients were observed at pH 4.0 as compared to pH 6.5. Combined stress of Cr and Al, on the whole, caused further reduction in mineral content in all plant parts of the two barley genotypes as compared to Al or Cr stress alone. Moreover, the reduction was more pronounced in Al sensitive genotype Shang 70-119.     

Computer simulation of the interactions of glyphosate with metal ions in phloem

Essential nutrients such as trace metal ions, amino acids, and sugars are transported in the phloem from leaves to other parts of the plant. The major chelating agents in phloem include nicotianamine, histidine, cysteine, glutamic acid, and citrate. A computer model for the speciation of metal ions in phloem has been used to assess the degree to which the widely used herbicide glyphosate binds to Fe(3+), Fe(2+), Cu(2+), Zn(2+), Mn(2+), Ca(2+), and Mg(2+) in this fluid over the pH range of 8 to 6.5. The calculations show that glyphosate is largely unable to compete effectively with the biological chelating agents in phloem. At a typical phloem pH of 8, 1.5 mM glyphosate binds 8.4% of the total Fe(3+), 3.4% of the total Mn(2+), and 2.3% of the total Mg(2+) but has almost no effect on the speciation of Ca(2+), Cu(2+), Zn(2+), and Fe(2+). As the pH decreases to 6.5, there are some major shifts of the metal ions among the biological chelators, but only modest increases in glyphosate binding to 6% for Fe(2+) and 2% for Zn(2+). The calculations also indicate that over 90% of the glyphosate in phloem is not bound to any metal ion and that none of the metal-glyphosate complexes exceed their solubility limits.     

Theoretical speciation of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) in agronomic conditions

The presence of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) as the second largest component in commercial EDDHA iron chelates has recently been demonstrated. Here is reported the speciation of o,p-EDDHA by the application of a novel methodology through the determination of the complexing capacity, protonation, and Ca(2+), Mg(2+), Cu(2+), and Fe(3+) stability constants. The pM values and species distribution in solution, hydroponic, and soil conditions were obtained. Due to the para position of one phenol group in o,p-EDDHA, the protonation constants and Ca and Mg stability constants have different values from those of o,o-EDDHA and p,p-EDDHA regioisomers. o,p-EDDHA/Fe(3+) stability constants are higher than those of EDTA/Fe(3+) but lower than those of o,o-EDDHA/Fe(3+). The sequence obtained for pFe is o,o-EDDHA/Fe(3+) >/= o,p-EDDHA/Fe(3+) > EDTA/Fe(3+). o,p-EDDHA/Fe(3+) can be used as an iron chelate in hydroponic conditions. Also, it can be used in soils with limited Cu availability.     

氮、磷、钾肥与酚对漂洗水稻土硅、铝、铁的活化效应

本研究以四川盆地西缘茶区漂洗水稻土为供试土壤,采用浸提试验探讨尿素（N）、磷酸二氢钙（P）、硫酸钾（K）和邻苯二酚（Phy）对其硅、铝、铁的活化效应（以浸提液硅、铝、铁的浓度表征）,结果表明: 1）各种处理浸提液均以硅的浓度最大,铝次之,铁最小,即活化效应为硅＞铝＞铁; 2）浸提液硅的浓度为NPK+Phy＞NPK P＞Phy＞K CK N处理,说明磷肥通过磷酸根的配位吸附对其活化产生最重要的影响,同时酚类物质也通过弱酸作用促进其活化; 3）浸提液铝的浓度为NPK+Phy＞Phy＞P NPK K N CK处理,说明酚类物质通过与游离铝形成可溶性络合物而对其活化起突出作用,同时磷肥中的钙离子和钾肥中的钾离子也能将强酸性供试土壤中大量交换性铝离子交换而活化; 4）浸提液铁的浓度为NPK+Phy＞Phy＞K P NPK CK N处理,说明酚类物质通过络合溶铁、还原溶铁等作用对其活化做出重大贡献,同时钾肥中的钾离子和磷肥中的钙离子也将土壤胶体吸附的亚铁离子交换而活化; 5）尿素对漂洗水稻土硅、铝、铁均无显著活化效应。综上所述,磷、钾肥和酚类物质是漂洗水稻土中硅、铝、铁活化的重要影响因素。     

Aluminum and iron(III) species in the soil solution including organic complexes with citrate and humic substances

The solubility of Al and Fe in soil is of relevance for their toxicity and availability, respectively, to plant roots. Humic substances as the main part of stable soil organic matter and citrate which is often excreted by P deficient plants are strong complexants of Al and Fe(III). Therefore, equations were developed to calculate the Al and Fe(III) species distribution in the soil solution in the presence of humic substances and citrate as organic ligands. Calculations in the pH range 4.0–7.0 showed that at higher pH humic-Al complexes were the most important species whereas AlOH-citrate^? dominated between pH 4.0 and 5.4. Free monomeric Al and AlSO₄⁺ were of minor relevance. Iron(III) species calculations showed that humic-Fe complexes were the main species in the pH range 4.0–7.0. But if mugineic acid, a Fe complexing phytosiderophore released into the rhizosphere by graminaceous plant species, was present in the soil solution (10^?6 M), Fe-mugineic acid complexes accounted for most of the Fe in solution. Fe-citrate^? was relevant at lower pH but contributed little to Fe(III) species at pH > 6.0. The results demonstrate the strong importance of the considered organic ligands for Fe and Al in the soil solution.     

Studies on Adsorption Characteristics of Al-Free and Al-Substituted Goethite for Heavy Metal Ion Cr(VI)

In the present paper, α-FeOOH and α-Fe(Al)OOH were prepared, and the adsorption of Cr(VI) on the two samples was investigated. The influence of pH, initial concentration, and some anions such as SO₄ ^2?, H₂PO₄ ^?, C₂O₄ ^2?, CO₃ ^2?, and SiO₃ ^2? on the adsorption of Cr(VI) on α-FeOOH and α-Fe(Al)OOH was studied by batch techniques. The results show that the adsorption capacity of Cr(VI) on α-Fe(Al)OOH increases with the introduction of aluminum, but decreases with the increase of pH. The adsorption irreversibility of Cr(VI) on α-Fe(Al)OOH is much higher than that on pure α-FeOOH. The adsorbed Cr(VI) species mainly exists in the form of *Fe(wk)-OHCrO₄ ^2? on the surface of the samples. With the presence of SiO₃ ^2?, CO₃ ^2?, C₂O₄ ^2?, SO₄ ^2?, and H₂PO₄ ^?, the binding of Cr(VI) is inhibited by different degree. The inhibition of those anions is larger in the pure goethite than that in the Al-substituted goethite system. After Al was introduced into α-FeOOH, Cr(VI) ions are preferentially adsorbed on Al sites rather than Fe sites on α-Fe(Al)OOH.     

Phytate Quantification using HPIC in the Presence of Iron and Aluminum

Phytate is an organic form of P that is difficult to analyze in complex matrices. To test if high concentrations of aluminum (Al) and iron (Fe) hinder accurate quantification of phytate in dairy manure and broiler litter when measured by high-performance ion chromatography (HPIC), researchers spiked dairy manure and broiler litter samples with Al, Fe, and phytate. Samples were alkaline extracted, acidified, and filtered, and then phytate spike recovery was analyzed with HPIC. High concentrations of Fe did not hinder phytate recovery in manure or litter samples. While phytate recovery was complete at typical manure and litter Al concentrations, high concentrations of Al inhibited phytate recovery in litter samples and in some manure samples. Overall, alkaline extraction of dairy manure and broiler litter and analysis with HPIC proved to be relatively accurate, fast, and cheap within normal Al and Fe ranges, compared to the commonly used nuclear magnetic resonance (NMR) method.     

Effect of natural organic soil solutes on weathering rates of soil minerals

The rate at which minerals in the soil weather is affected by pH and concentration of organic solutes (DOC). The rates of release of Al, Ca, Fe, K, Mg, Na, P and Si from a mineral soil sample to solutions of natural organic solutes and HCI (control) were determined at pH 3 and 4 for up to 17 weeks. Soil solutions were collected by centrifuging materials of O horizons from various soil types under four tree species (spruce, birch, oak, beech) and passed through a cation-exchange resin to yield H⁺-saturated organic solutes. The acceleration of the elements' release by the organic solutes was shown directly by the relative ligand effect (RLE), that is, the release rate in the organic solute solution divided by the release rate in the HCI solution (control) at the same pH. The RLE was greater at pH 4 than at pH 3, and it decreased for the elements in the order Fe > Ca > Mg > Al ≈ Si > K ≈ Na. This indicates that natural organic solutes are more important weathering agents at higher than lower pH and for weathering of mafic minerals rich in Ca, Fe and Mg than of felsic minerals such as K- and Na-feldspars. For all elements and at both pHs, RLE was strongly correlated with the concentration of DOC, which was also closely correlated with titratable acidity of the organic solutes. The important effect of soil type and tree species in producing weathering-promoting organic solutes therefore seems to be expressed through the concentration and not the composition of the organic soil solutes.     

Fluoro‐mobilization of metals in a Slovak forest soil affected by the emissions of an aluminum smelter

Depositions originating from a central Slovak Al smelter may increase metal solubility in adjacent soils because they contain F (mainly HF). The reason for fluoro‐mobilization of metals may be the formation of soluble fluoro‐metal complexes or the mobilization of organic matter and subsequent formation of organo‐metal complexes. The objectives of our work were (1) to assess the extent of metal mobilization by fluoride in a Slovak Lithic Eutrochrept affected by the emissions of an Al smelter and (2) to model the dissolved metal species with the help of a chemical equilibrium model (MINEQL+). The O (Moder), A, and B horizons were equilibrated with solutions at F concentrations of 0, 0.9, 2.7, and 9.0 mmol l^—1. In the extracts, the concentrations of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Zn, dissolved organic carbon (DOC), free and complexed F, and the pH and electrical conductivity (EC) were determined. The heavy metal concentrations in the O horizon (Cd: 0.99, Cr: 18.0, Cu: 44, Ni: 26, Pb: 110, and Zn: 84 mg kg^—1) were 2.5 to 9 times larger than those in the A and B horizons. The concentrations of H₂O‐soluble F decreased from the O (261 mg kg^—1) to the A (103 mg kg^—1) and B horizon (92 mg kg^—1). In batch experiments increasing addition of F increased the equilibrium concentrations of Al, Cr, Cu, Fe, Ni, Pb, and DOC in all samples, of Cd in the A, and of K in the B horizon. At the same time the concentrations of complexed F and pH increased whereas EC decreased. Chemical equilibrium modelling indicated that the mobilizing effect of F resulted from the formation of fluoro‐Al complexes and organo‐complexes of all other metals.     

Aluminum and iron estimated by Mehlich‐3 extractant in mine soils in Galicia,northwest Spain

Abstract

The efficiency of Mehlich‐3 reagent as an extractant for aluminum (Al) and iron (Fe) was studied in Galician coal mine soils, in the process of reclamation. Mehlich‐3 Al and Fe values were compared to those from other Al and Fe tests and with phosphorus (P) sorption. The soils are very heterogeneous, consisting mainly of carbonaceous and non‐carbonaceous clays and shales, which are often rich in pyrite. Some of them have been amended with topsoil or fly ash. One hundred forty samples, from 0 to 15 or 15 to 30 cm, were analyzed. The pH values ranged from 2.7 to 8.4; oxalate and pyrophosphate Al from 0 to 1.17%, and 0.02 to 0.58%, respectively; and oxalate and pyrophosphate Fe from 0.02 to 2.25% and 0 to 1.28%, respectively; PSI (P sorption index) values varied between 0 and 55.1. The Mehlich‐3 Al values ranged from 24 to 2600 mg kg^‐1. A close relationship was observed between Mehlich‐3 and oxalate Al values (r=0.77), although the regression line tended to be curvilinear. Mehlich‐3 Al was better correlated than oxalate Al to pyrophosphate Al (r=0.66 vs. r=0.59) and also to pH‐NaF (r=0.89 vs. r=0.74). The Mehlich‐3 Al is almost as good as oxalate Al in estimating non‐crystalline Al, the correlation coefficients between log PSI and log (Mehlich‐3 Al) or log (oxalate Al) being 0.51 and 0.57, respectively. The Mehlich‐3 Fe correlated to available (r=0.63), exchangeable (r=0.65) and soluble Fe (r=0.66), but not to non‐crystalline Fe.     

Production, purification, and properties of an endoglucanase produced by the hyphomycete Chalara (Syn. Thielaviopsis) paradoxa CH32

The hyphomycete Chalara (syn. Thielaviopsis) paradoxa produces endoglucanase activity during the late trophophase. The low molecular mass (35 kDa) endoglucanase purified from cultured broths works optimally at 37 degrees C and pH 5.0. The enzyme inactivates at pH below 3.0 and also at temperatures of 50 degrees C or higher, but it is stable at lower temperatures, including refrigeration temperature and freezing. The enzyme is inhibited by detergents, by EDTA, and by the divalent cations Hg(2+) and Ag(2+). It is also inhibited to some extent by 10 mM Zn(2+), Fe(2+), and Mg(2+), but it is stimulated by Mn(2+). Enzyme activity is not affected by reducing agents. In the presence of low concentrations of water miscible organic solvents (20%) endoglucanase activity is inhibited by 7% (for methanol) to 50% (for acetonitrile), and it is totally inhibited at higher solvent concentrations (50%). Enzyme activity is not affected by the water immiscible solvent ethyl acetate. Carboxymethylcellulose is the preferred substrate (K(m(app)) = 8.3 g/L; V(max(app)) = 1.1 microM/min). Hydrolysis of crystalline cellulosic substrates is very limited, but it is greatly enhanced by phosphoric acid swelling. The purified enzyme shows no activity toward disaccharides or aryl-glucosides. Its activity is inhibited by cellobiose.     

Leaching of metals from the A-horizon of a spruce forest soil

The study quantifies the amount of metals (Na, K, Mg, Ca, Al, Fe, Mn, Ni, Cr, V, Cu, Zn, Cd, Pb) leached from the A-horizon of a podzolic spruce forest soil in southern Sweden during 2.5 yr, and offers statistical evidence of environmental conditions of importance to metal release. Considerable losses of Pb, Cr, Ni and V may occur from the A-horizon of forest soils under conditions favoring leaching of organic matter, Fe, and Al, i.e. during periods of comparably high soil temperature and moisture. Metals with a larger fraction present in exchangeable form (Na, Mg, Ca, Zn, Cd) are more susceptible to minor pH changes. An accelerated deposition or internal production of acidic matter therefore will reduce the retention times of these elements particularly.     

Effect of soil pH on mineral element concentrations of two erythroxylum species

Erythroxylum coca var. coca Lam. (E. coca) and Erythroxylum novogranatense var. novogranatense (Morris) Hieron (E. n. novogranatense) are two of four Erythroxylum species grown in the tropics of South America for cultural medicines and the alkaloid benzoylmethylecgonine. In a published study of biomass production over a soil pH range of 3.5 to 7.0, E. coca grew best at a pH equal to and below 5.5, and E. n. novogranatense grew best within the pH range of 4.7 to 6.0. Erythroxylum coca was tentatively classified as more tolerant to metal toxicities [aluminum (Al) and manganese (Mn)] than E. n. novogranatense, however, concentration patterns of mineral elements for E. coca and E. n. novogranatense tissue have not been reported, nor have the mechanisms of differential acid‐soil‐tolerance been elucidated. In the current study, the effects of soil pH on concentrations of Al, calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), Mn, and zinc (Zn) in leaves, stems, and roots were investigated. At pH 3.5, roots of both species accumulated high concentrations of Al that decreased as soil pH increased, however, there was no pH × species interaction. The highest concentration of Ca was found in the leaves of both species, however, E. coca accumulated more Ca as soil pH increased than did E. n. novogranatense. Manganese and Zn levels were highest in roots of both species (E. coca and E. n. novogranatense); levels in all tissues decreased with increasing pH. Manganese concentration was highest in roots of E. coca and Zn concentration was highest in tissues of E. n. novogranatense. Copper, Fe, K, and Mg levels were erratic with increasing pH, indicating that sufficient amounts of these nutrients are acquired at low pH levels. Root concentrations of Fe and K in E. coca increased markedly between pH 3.5 and 4.7. At pH 3.5, E. coca demonstrated no symptoms of mineral deficiency and/or toxicity, however, chlorosis, leaf distortion and root atrophy were prevalent at pH 6.5 and 7.0. By contrast, E. n. novogranatense demonstrated diminished growth and root atrophy at soil pH 3.5, whereas at pH 6.5 and 7.0, although biomass production was reduced, no symptoms of mineral deficiency and/or toxicity were present. The species obviously behave differentially at pH extremes and E. coca appears to be most tolerant of extremely acid soils; the two species may also differ in mineral sensitivities between the species at higher pH levels. Erythroxylum coca may compete more effectively with Al for Ca binding sites within the root, and may have greater internal tolerance of Mn, compared with E. n. novogranatense.     

Nature of impurities in fertilizers containing EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+) chelates.

Iron chelates derived from ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid (EDDHMA), ethylenediaminedi(2-hydroxy-5-sulfophenylacetic) acid (EDDHSA), and ethylenediaminedi(5-carboxy-2-hydroxyphenylacetic) acid (EDDCHA) are remarkably efficient in correcting iron chlorosis in plants growing in alkaline soils. This work reports the determination of impurities in commercial samples of fertilizers containing EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+). The active components (EDDHMA/Fe(3+), EDDHSA/Fe(3+), and EDDCHA/Fe(3+)) were separated easily from other compounds present in the fertilizers by HPLC. Comparison of the retention times and the UV-visible spectra of the peaks obtained from commercial EDDHSA/Fe(3+) and EDDCHA/Fe(3+) samples with those of standard solutions showed that unreacted starting materials (p-hydroxybenzenesulfonic acid and p-hydroxybenzoic acid, respectively) were always present in the commercial products. 1D and 2D NMR experiments showed that commercial fertilizers based on EDDHMA/Fe(3+) contained impurities having structures tentatively assigned to iron chelates of two isomers of EDDHMA. These findings suggest that current production processes of iron chelates used in agriculture need to be improved.     

Pectin adsorption on amorphous Fe/Al hydroxides and its effect on surface charge properties and Cu(II) adsorption

Purpose

The purpose of this study was to elucidate the mechanisms for pectin-enhanced adsorption of heavy metal cations on variable charge minerals.

Materials and methods

Batch experiments were conducted to investigate the adsorption of pectin and copper(II) by amorphous Fe/Al hydroxides. The morphology, mineralogy, and functional groups of pectin–Fe/Al hydroxides were examined using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy analysis.

Results and discussion

The amount of pectin adsorbed by amorphous Al(OH)₃ was much greater than that by amorphous Fe(OH)₃ at pH values between 3.5 and 6.5 due to the higher positive charge density on Al(OH)₃ and greater electrostatic attraction between the hydroxide and pectin compared with Fe(OH)₃. The addition of pectin decreased the positive surface charge on amorphous Fe and Al hydroxides. The presence of pectin enhanced the adsorption of Cu(II) by the Fe and Al hydroxides. The increase in Cu(II) adsorption on amorphous Fe hydroxide was more obvious at low pH values than at higher pH values, while an opposite changing trend was observed for amorphous Al hydroxide. At pH 3.9, 4.3, and 4.9, pectin increased Cu(II) adsorption by Fe hydroxide from 24.4, 76.6, and 177.0 mmol/kg to 61.6, 98.8, and 192.0 mmol/kg, i.e., Cu(II) adsorption was increased by 37.2, 22.2, and 15.0 mmol/kg, respectively. At pH 4.3 and 4.9, pectin increased Cu(II) adsorption by Al hydroxide from 3.7 and 27.0 mmol/kg to 17.3 and 69.4 mmol/kg, i.e., Cu(II) adsorption was increased by 13.6 and 42.4 mmol/kg, respectively. The greater adsorption of pectin by Al hydroxide was mainly responsible for the larger enhancement of pectin on Cu(II) adsorption on Al hydroxide at higher pH values compared with Fe hydroxide.

Conclusions

The adsorption of pectin on Fe and Al hydroxides decreased the positive charge on the hydroxides and thus enhanced the adsorption of Cu(II) by the hydroxides.

     

Reactions of fulvic acid with metal ions

Fulvic acid is a water-soluble humic material that occurs widely in soils and waters and that tends to form water-soluble and water-insoluble complexes with a variety of metal ions, some of which are toxic. This paper presents information on the conditions under which the different types of FA-metal complexes are formed. The solubility in water, separately and after mixing, of FA (2 to 30 mg/100 ml) and eleven metal ions (Fe(III), Al, Cr(III), Pb, Cu, Hg(II), Zn, Ni, Co, Cd and Mn; 1 × 10^?5 moles of each metal ion) was investigated over the pH range 4 to 9. After mixing, the solubility of the components was significantly affected by pH only when less than 20 mg of FA was present. As the systems became richer in FA (22 to 30 mg), most of the metal ions remained in the aqueous phase, likely due to the formation of FA-metal complexes, inhibiting the formation of metal hydroxides. The order in which the eleven metal ions tended to form water-insoluble FA-metal complexes depended on the pH. At pH 6 it was: Fe = Cr = Al > Pb = Cu > Hg > Zn = Ni = Co = Cd = Mn. This order appeared to correlate with the valence, 1st hydrolysis constants and effective hydrated ionic diameters of the metal ions. In general, FA/metals weight ratios of > 2 favored the formation of water-soluble FA-metal complexes; at lower ratios, water-insoluble complexes, which could accumulate in soils and sediments, were formed.     

Studies on water transport through the sweet cherry fruit surface. 7. Fe3+ and Al3+ reduce conductance for water uptake

The effects of the chloride salts LiCl, CaCl(2), MgCl(2), AlCl(3), EuCl(3), and FeCl(3) and the iron salts FeCl(2), FeCl(3), Fe(NO(3))(3), FeSO(4), and Fe(2)(SO(4))(3) on water conductance of exocarp segments (ES) and rates of water uptake into detached sweet cherry fruit (Prunus avium L. cv. Adriana, Early Rivers, Namare, Namosa, and Sam) were studied. ES were excised from the cheek of mature fruit and mounted in stainless steel diffusion cell; water penetration was monitored gravimetrically from donor solutions containing the above mineral salts into a PEG 6000 (osmolality = 1.14 osM, pH 4.8, 25 degrees C) receiver solution. Conductance of ES was calculated from the amount of water taken up per unit of surface area and time by dividing by the gradient in water activity across ES. LiCl, CaCl(2), MgCl(2), FeCl(2), and FeSO(4) had no significant effect on conductance, but AlCl(3), FeCl(3), Fe(NO(3))(3), and Fe(2)(SO(4))(3) significantly reduced conductance compared to water only as a donor. Also, EuCl(3) lowered conductance; however, this effect was not always significant. Effects of salts on water conductance of ES and rates of water uptake into detached fruit were closely related (R 2 = 0.97***). Upon application of an FeCl(3)-containing donor conductance decreased instantaneously. FeCl(3) concentrations of <6.6 x 10(-)(4) M had no effect on conductance, but concentrations at or above this threshold decreased conductance. FeCl(3) lowered water conductance at a receiver pH of 4.8, but not at pH < or =2.6. The effect of FeCl(3) on conductance was largest in cv. Namare and smallest in cv. Adriana. There was no significant effect of FeCl(3) on conductance for transpiration. Formation of aluminum and iron oxides and hydroxides in the exocarp as a result of a pH gradient between donor and receiver solution is discussed as the potential mechanism for Fe(3+) and Al(3+) reducing conductance for water uptake.