Chromatographie et purification des diphenol oxydases du sol

Neutral sterile and lyophilized extracts of fresh soil (NAFS Extract) degraded the following substrates: p-cresol: dl-3(3.4-dihydroxyphenylalanine)(dl DOPA): d(+) catechin and p-phenylcnediamine respectively (19.7); (5.3); (5.7) and (4.4) nmoles O₂ mg C^?1 min^?1 as specific activity (sp. act.). NAFS Extract was fractionated by G100 Sephadex column chromatography into two major peaks (K_D ~ 0 and ~ 1) without an increase in sp. act. DEAE DE 52 cellulose chromatography separated NAFS Extract into three fractions. The first fraction was free from humic acid, relatively homogeneous on polyacrylamide gel electrophoresis and had sp. act.: dl DOPA (17.2): d(+) catechin (8.5): p-phenylenediamine (22.9). The o- and p-diphenol oxidases which accompanied this fraction were well separated as complexes on G100 Sephadex column and were liberated by dialysis against distilled water. Following isolation, we obtained an o-diphenol oxidase on dl DOPA (23.4) and a laccase activity on p-phenylenediamine (33.8) in the free state; these activities being associated with nucleoprotein. Fractions (II) and (III) appeared to be relatively homogeneous in the form of “humic acid—enzyme complexes”. Specific activity were high in fraction (III): dl DOPA (10.8): d(+) catechin (0.7); p-phenylenediamine (5.4). The diphenol oxidase activity extracted from soil (NAFS Extract) was treated by salmine and SP Sephadex C25 to remove humic matter. The EFS Extract obtained had the following sp. act.: dl DOPA (14.0); p-phenylenediamine (6.3). This EFS Extract was separated into three fractions by means of G100 Sephadex column chromatography. The Kn were (I) ~0; (II) ~ 0.52; (III) ~ 1.3 respectively. The first fraction showed an increase of sp. act. only with p-phenylenediamine (9.1) and in the following two fractions the sp. act. were not augmented. The first fraction was further fractionated by means of DEAE cellulose chromatography into four fractions: the-first and the second had no activity on dl DOPA and p-phenylenediamine. The third was an o-diphenol oxidase on dl DOPA (11.0) with traces of laccase: p-phenylenediamine (0.7). The fourth was pure laccase: p-phenylenediamine (18.1). These results suggested that electrostatic, covalent and van der Waals forces contributed to the formation of humic acid enzymes complexes, associated in the tetramer to monomer forms of diphenol oxidases.     

Proprietes des diphenol oxydases extraites des sols

Properties of diphenol oxidases extracted from salts. Salmine and SP-Sephadex C-25 were used to separate the enzyme system associated with humic materials in the neutral extracts of fresh soils (NAFS Extract). Electrophoresis on polyacrylamide gel shows that this preparation is heterogeneous. The elementary analysis of the soil enzyme is C 43·13%; N 5·09%; H 7·21%; O 44·58%. Chromatographic analyses indicate that the soil enzyme contains 53 per cent amino acids, 36 per cent sugars and amino sugars and 10 per cent ammonium and inorganic materials. The soil enzyme has a maximum absorption at 270–280 nm. The soil enzyme degrades the following substrates at the relative rate mentioned in parentheses : d-catechin (298);p-cresol (251); catechol (156); dl-DOPA (100);p-phenylene diamine (59);p-quinol (20) in terms of rate of oxygen absorption. This enzymatic preparation has the properties of an o- and p-diphenol oxidase. The rate of decarboxylation was measured using a radiorespirometer. The following relative values are dl-DOPA-l-¹⁴C (100); dl-tyrosine-l-¹⁴C (35) ; dl-tyrptophan-1-¹⁴C (7); dl-phenylalanine-l-¹⁴C (2). The dl-DOPA-2-¹⁴C was partially degraded to ¹⁴CO₂. The O₂ absorbed and CO₂ (carboxyl) evolved in case of dl-DOPA was in the ratio of 1·8 at 37°C. The activation energy on dl-DOPA was 3·1 and 7·9 kcal/mole/°C for oxygen absorption and decarboxylation respectively. The enzymatic activity on dl-DOPA-l-¹⁴C was optimum in air and inhibited in a N₂ atmosphere. Decarboxylation on dl-DOPA-l-¹⁴C followed the Michaelis-Menten law, from which we found that K_m = 8·3 × 10^?4M for decarboxylation. The oxidative decarboxylation was inhibited by H₂O₂ (74%); KCN (75%); ascorbate (92%); BAL (97%);DIECA(90%).Melanogenesis of dl-DOPA followed first order kinetics. The maximum absorption at 305 nm during melanogenesis shows the formation of dopachrome.     

Relationship between molecular characteristics of soil humic fractions and glycolytic pathway and krebs cycle in maize seedlings

A humic acid (HA) isolated from a volcanic soil was separated in three fractions of decreasing molecular size (I, II and III) by preparative high performance size exclusion chromatography (HPSEC). The molecular content of the bulk soil HA and its size fractions was characterized by pyrolysis-GC-MS (thermochemolysis with tetramethylammonium hydroxide) and NMR spectroscopy. All soil humic materials were used to evaluate their effects on the enzymatic activities involved in glycolytic and respiratory processes of Zea mays (L.) seedlings. The elementary analyses and NMR spectra of the humic fractions indicated that the content of polar carbons (mainly carbohydrates) increased with decreasing molecular size of separated fractions. The products evolved by on-line thermochemolysis showed that the smallest size fraction (Fraction III) with the least rigid molecular conformation among the humic samples had the lowest content of lignin moieties and the largest amount of other non-lignin aromatic compounds. The bulk HA and the three humic fractions affected the enzyme activities related to glycolysis and tricarboxylic acid cycle (TCA) in different ways depending on molecular size, molecular characteristics and concentrations. The overall effectiveness of the four fractions in promoting the metabolic pathways was in the order: III>HA>II>I. The largest effect of Fraction III, either alone or incorporated into the bulk HA, was attributed to a flexible conformational structure that promoted a more efficient diffusion of bioactive humic components to maize cells. A better knowledge of the relationship between molecular structure of soil humic matter and plant activity may be of practical interest in increasing carbon fixation in plants and redirect atmospheric CO₂ into bio-fuel resources.     

Physical protection and biochemical quality of organic matter in mediterranean calcareous forest soils: a density fractionation approach

Physical protection is one of the most important ways for stabilization of organic carbon (OC) in soils, and in order to properly manage soils as a sink for carbon, it is necessary to know how much OC a given soil could protect. To this end, we studied individual horizons taken from 16 soil profiles under Quercus rotundifolia stands, all over calcareous parent materials. Horizons were subjected to a sequential extraction using solutions of sodium polytungstate (NaPT) of increasing density: (i) NaPT d=1.6, using slight hand agitation, to obtain the free light fraction (FL); (ii) NaPT d=1.6 and ultrasonic dispersion, to obtain the Occluded Fraction I (Ocl I); (iii) NaPT d=1.8, to obtain the Occluded Fraction II (Ocl II); and (iv) NaPT d=2.0, to obtain the Occluded Fraction III (Ocl III). The fraction of density>2.0 are taken as dense fraction (DF). The free organic matter was further divided into FL>50 (retained by a 50 μm mesh: coarse organic fragments) and FL<50 (non-retained: fine organic fragments). The fractions FL>50 and FL<50 were taken together as free organic matter. The rest of the fractions are taken together as protected organic matter. The obtained fractions were analyzed for total OC, total N, and carbohydrate content. The percentage of non-hydrolyzable OC and N in each fraction was taken as an indicator of OC and N recalcitrance, respectively.For both OC and N, the fractions FL>50 and DF are dominant; the rest of the fractions are of much lower quantitative importance. In H horizons and in most A horizons, most of the OC and N are free, whereas in B horizons both OC and N are mostly protected. Overall, the percentages of free OC and N are very high and are currently amongst the highest ever recorded.Organic matter recalcitrance is lowest in the two most protected fractions (Ocl III and especially DF), and highest in the first occluded fractions (Ocl II and especially Ocl I). The free organic matter (FL>50 fraction) has an intermediate quality: it includes recognizable plant fragments, but the indicators tested (recalcitrance, carbohydrate content, cellulose to total carbohydrates ratio) suggest that it is not always the most fresh and non-decomposed fraction.There are clear maxima for both protected OC and N, which can be approached by curve fitting. By exponential fit, the obtained maxima are 84.1 g of OC and 7.7 g of N kg⁻¹ of mineral particles <20 μm. These maxima are much higher than the upper limits obtained by other authors. Differences in the sampling approach are suggested as the reason for such discrepancies.     

EPR spectra of humic acids and their metal complexes

On the basis of ESR spectra, humic substances are believed to be hydroquinone type polymer radicals with considerable cation exchange and redox capacity. All 3d-transition metal humates appear to be ionic high spin complexes. Manganese (II) ions doped in raw peats and peat humic acids are coordinated octahedrally with six oxygen-containing functional groups, e.g., carboxylate, phenolic, hydroxyl, carbonyl ligands, whereas copper (II) ions are in square planar arrangement with two carboxylate and two aliphatic nitrogen ligands. Doping with vanadyl(II) ions results in a square pyramidal arrangement with four oxygen-containing ligands. Diamagnetic manganese(VII), chromium(VI), molybdenum (VI) and vanadium(V) oxoanions in acidic solution are reduced by humic acids into paramagnetic manganese(II), chromium(III), molybdenum(V) and vanadium(IV) ions. Diamagnetic copper(I) ions, on the other hand, are oxidized by humic acids into paramagnetic copper(II) ions.In contrast to polyronic acid gels with outer-sphere structure, 3d-transition metal ions are generally bound to humic acids as inner-sphere chelate complexes.     

Sawdust: Cost Effective Scavenger for the Removal of Chromium(III) Ions from Aqueous Solutions

Cr(III) ions sorption onto sawdust of spruce (Picea smithiana) has been studied thoroughly using radiotracer technique. Maximum sorption (94%) of Cr(III) ions (8.98×10^?5 M) onto sorbent surface is achieved from deionized water in 20 min agitation time using 200 mg of sawdust. The sorption data followed the Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms. Freundlich constants l/n = 0.86 ± 0.07 and C _e = 85.0 ± 25.8 mmole g^?1 have been estimated. Sorption capacity, X _m = 0.82± 0.3 mmole g^?1, β = ?0.00356± 0.00017 kJ² mole^?2 and energy, E = 11.9± 0.3 kJ mole^?1 have been evaluated using D-R isotherm. The Langmuir constants Q = 5.8± 0.2 μmole g^?1 and b = (7.4± 0.5)×10⁴ dm³ mole^?1 have been calculated. The variation of sorption with temperature yields thermodynamic parameters Δ H = ?11.6± 0.3 kJ mole^?1, Δ S = ?16.2± 0.9 J mole^?1 K^?1 and Δ G = ?6.8± 0.3 kJ mole^?1 at 298 K. The negative value of enthalpy and free energy reflect the exothermic and spontaneous nature of sorption respectively. Among the anions studied oxalate, citrate, carbonate and borate have reduced the sorption. The cations Y(III), Ce(II) and Ca(II) suppressed sorption. The sawdust column can be used to separate Cr(III) ion from Cs(I), I(I),Tc (VII) and Se (IV).     

Reduction of Cr(VI) by soil humic acids

The rate of hexavalent chromium reduction by a soil humic acid (SHA) was investigated in aqueous solutions where concentrations of Cr(VI), H⁺, and SHA were independently varied. Rate experiments were done with a large excess of SHA over Cr(VI). Rates of reduction depend strongly on [H⁺], increasing with decreasing pH. Typical Cr(VI)-SHA reactions display a nonlinear reduction of Cr(VI) with time that cannot be modelled with simple first- or second-order rate equations. An empirical rate equation is developed for Cr(VI)-soil humic acid reactions over a range of experimental conditions. The model is in part based on a reactive continuum concept developed for soil fulvic acids. The rate equation describing Cr(VI) reduction by SHA is: R= -(k₀+k[H⁺]^1/2)[HCrO₄^?]^1/2X_e^?1, where k₀ is (8·3 ± 1·2) × 10^?12, s^?1k is (2·04 ± 0·05) × 10^?9 l^1/2 mol^?1/2 s^?1, and X_e is the equivalent fraction of SHA oxidized. The rate equation adequately models Cr(VI) reduction in an experiment with [Cr(VI)]₀ four times greater than the maximum concentration used in its derivation. Cr(VI) reduction at pH 3 by two other SHAs can also be modelled using the rate equation. The difference between the rate coefficients for the humic acid and the fulvic acid from the same soil was greater than the difference in the rate coefficients for humic acids from different soils.     

Effect of humic acid on copper adsorption by Kaolin

Varying amounts of humic acid (Na-salt; 0 to 10 ppm) were first equilibrated with a dilute suspension of H⁺ -Kaolin and then with spiked (high activity radioactive ⁶⁴Cu) water. After filtration, through a 0.45 µm Millipore membrane, the amount of radioactivity on the filter and the filtrate was measured separately using a Gamma ray well counter. Adsorption of Cu (expressed as distribution coefficient — K _d ) was plotted against humic acid concentration. K _d values decreased sharply upto 1 ppm humic acid concentration and thereafter remained constant up to 10 ppm.     

Remediation of Atrazine-contaminated Soil and Water by Nano Zerovalent Iron

Atrazine-contaminated soil may require remediation to mitigate ground and surface water contamination. We determined the effectiveness of nano zerovalent iron (nano ZVI) to dechlorinate atrazine (2-chloro-4ethylamino-6-iso-propylamino-1,3,5-triazine) in contaminated water and soil. This study determined the effects of iron sources, solution pH, Pd catalyst and presence of Fe or Al sulfate salts on the destruction of atrazine in water and soil. Our results indicate nano ZVI can be successfully used to remediate atrazine in water and soil. Aqueous solution of atrazine (30 mg l^?1) was treated with 2% (w/v) of nano ZVI and 5% (w/v) of commercial ZVI. Although, iron dose in nano ZVI treatment was less than that in commercial ZVI treatment, atrazine destruction kinetic rate (k _obs) of nano ZVI treatment (1.39 days^?1) was around seven times higher than that of commercial ZVI treatment (0.18 days^?1). Reductive dechlorination was the major process in destruction of atrazine by nano ZVI. The dechlorination product was 2-ethyl-amino-4-isopropylamino-1,3,5-triazine. Lowering the pH from 9 to 4 increased the destruction kinetic rates of atrazine by nano ZVI. Moreover, nano ZVI/Pd enhanced destruction kinetic rates of atrazine (3.36 day^?1). Pd played the important role as a catalyst during treatment of atrazine by nano ZVI. Atrazine destruction kinetic rates were greatly enhanced in both contaminated water and soil treatments by nano ZVI when sulfate salts of Fe(II), Fe(III) or Al(III) was add with the following order of removal rates: Al (III) (2.23 day^?1) > Fe (III) (2.04 day^?1) > Fe(II) (1.79 day^?1). The same results were found in atrazine-nano ZVI-soil incubation experiments.     

A field study of cadmium dynamics in periphyton and in Hyalella azteca (crustacea: amphipoda)

We studied the dynamics of Cd uptake and depuration in epilithic periphyton and in the grazing amphipod Hyalella azteca. Both stable Cd, sufficient to achieve an aqueous concentration of 90 ng L^?1, and its radiotracer ¹⁰⁹Cd, were added during 1987 to the epilimnion of oligotrophic Lake 382 of the Experimental Lakes Area in northwestern Ontario. Cadmium dynamics within both periphyton and Hyalella were rapid, with equilibrium being approached within two weeks. For periphyton, the Cd uptake rate constant (K _uw ) was 3.8×10⁴ d^?1 with a depuration rate of 0.29 d^?1. For Hyalella the depuration rate was 0.36 d^?1, 10% due to growth dilution and 90% to excretion or desorption. The total Cd uptake rate (k _ut ) by Hyalella was 6.1×10⁴ d^?1, with more of the uptake (58%) derived from food (periphyton) than from water. Hyalella assimilated 80% of ingested Cd. Steady-state bioconcentration factors (BCF) were at least 10-fold higher than previously published values for Amphipoda. In periphyton and Hyalella the BCF were 1.2×10⁵ and 3.2×10⁵, respectively.     

Effects of urease and nitrification inhibitors on the efficient use of urea for pastoral systems

Abstract

The humic substances contained in an animal organic waste were extracted and the total extract separated into three humic fractions with different molecular weights (low, F₁ <10³; medium, F₂, with molecular weights ranging from 10³ to 10⁴; and high, F₃ >10⁴). The C content was highest in F₂, the same fraction also showing the lowest N content. The molecular weight of the humic fractions influenced the electrical conductivity, the highest molecular weight resulting in the lowest degree of electrical conductivity. Membrane-controlled ultrafiltra-tion (the method used to separate the various fractions from the whole extract) was also suitable for purifying such enzymes as phosphatase and β-glucosidase: the total activity obtained from the three fractions was considerably greater than that determined in the whole extract, Pyrolysis-gas chromatography (Py-GC) applied to the whole extract and humic fractions showed that in the F₃ fraction (highest molecular weight) benzene was the major fragment while furfural was the major fragment of F₁ (lowest molecular weight). For this reason, the humification index benzene/toluene indicates that the fraction with the highest molecular weight was the most humified while the furfural/pyrrole ratio indicates that the fraction with the lowest molecular weight was the most degradable. The whole extract and the fraction F₁ had a negative effect on seed germination when the concentration was equivalent to 100 mg kg^?1 of C, while the germination index was higher than that of the control when only 10 mg kg^?1 were used. The F₂ fraction had a positive effect on germination regardless of the concentration used. When 10 mg kg^?1 of C of the humic substances studied were added to the nutrient solution for growth experiments with maize plants, F₃ led to increases in root weight and F₂ led to increases in shoot weight. An inhibitor effect was observed for fraction F₁.     

Simple Formulation of the Soil Water Effect on Residue Decomposition

Soil water content, θ, is a major factor affecting residue decomposition, but simple formulation of this factor is often lacking. We observed that θ significantly (P < 0.001) affected the residue decomposition constant, k _d. When θ varied from 0.09 g g^?1 to 0.23 g g^?1, k _d ranged from 0.009 to 0.013 d^?1 and from 0.009 to 0.022 d^?1 for residues with carbon to nitrogen ratio (C/N) > 30 and C/N < 25, respectively. A θ factor was formulated in terms of the field capacity θ _FC and the air‐dry θ _d in the form f _w = (θ ? θ _d) / (θ _FC ? θ _d), and this was used to modify the potential k _d as θ varied. Coupling f _w with a first‐order residue decomposition equation resulted in the prediction of the decomposition of four residue types in the greenhouse (R² = 0.94; relative root mean square error, RRMSE, = 0.06) and in the field (R² = 0.93; RRMSE = 0.11).     

Influence of soil applied boron on yield of berseem (Trifolium alexandrium L.) and soil boron fractions in calcareous soils

A greenhouse experiment was conducted in North-west India to study the effect of soil applied boron on yield of berseem (Trifolium alexandrium L.) and soil boron fractions in boron deficient calcareous soils. Three soils with varying calcium carbonate content viz. 0.75% (Soil I), 2.6% (Soil II), and 5.7% (Soil III) were collected from different sites of Ludhiana, Bathinda, and Shri Muktsar Sahib districts, Punjab, India. The treatments consisted of six levels of soil applied boron viz. 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0 mg B kg^?1 along with control. The green fodder yield and dry matter yield increased significantly at 0.75 mg B kg^?1 soil treatment level in the first cutting, while these were significant at 1.0 mg B kg^?1 soil treatment level in all soils at second, third, and fourth cuttings. Among all three calcareous soils, Soil I with lower calcium carbonate was the best soil in respect of mean yield in comparison to Soil II and Soil III. Combined effect of boron level and soils had significant effect on yield of berseem. There was a significant increase in mean dry root biomass at 1.0 mg B kg^?1 soil level over control and then remained non-significant with further high levels of soil applied boron. The mean dry root biomass decreased significantly for the soils having 0.75%, 2.6%, and 5.7% calcium carbonate levels. Readily soluble fraction is considered to be easily available fraction of B for plant uptake and consisted of 0.47–0.62% in Soil I, 0.31–0.43% in Soil II, and 0.24–0.34% in Soil III of the total boron. Among all B fractions, mean readily soluble, specifically adsorbed, and oxide-bound fractions got increased significantly with increase in B levels. Readily soluble and organically bound B fractions were more in Soil I as compared to Soil II and Soil III. Specifically adsorbed boron, oxide bound fraction, residual and total boron were more in Soil III in comparison to Soil I and Soil II. Among all fractions, residual fraction accounted for the major portion of the total B. It comprised of 92.71–93.90% in Soil I, 94.51–95.40% in Soil II, and 94.91–95.25% in Soil III of the total boron.     

Chemical Behavior of U(VI) in the Presence of Soil Components

Soil components from different environments (forest (OF), semiarid (SZ), and sand (AS)) were separated from fulvic and humic substances, characterized by DRX, EDS(SEM), and zero-charge points were determined. The sorption of U(VI) by these materials was determined considering contact time, concentration of U(VI), pH, ionic strength, and presence of sodium chloride and humic acids. The time to reach the kinetic sorption equilibrium was ca. 1 min for the components of the SZ and AS soils, whereas those from OF required longer times. The zero-charge points of the materials indicate that in the experimental conditions, the surfaces of the materials are positively charged, as are uranyl ions. The sorption kinetic data were well fitted to the pseudo-second-order model, which indicates chemical sorption. The maximum sorption capacities for U(VI) obtained from data fitted to the Langmuir model of OF and SZ were 49 and 19.8 mg g^?1 respectively. Sorption isotherm data for AS were best fitted to the Freundlich model (q_e?=?5.4 mg g^?1). The maximum values of distribution coefficients (K_d) were 23?±?7 L kg^?1, 545?±?64 L kg^?1, and 1178?±?229 L kg^?1 for AS, SZ, and OF, respectively; these values may depend on pH, contact time, initial concentration of U(VI), and the composition of the materials. Sodium chloride in the aqueous solutions affects U(VI) sorption by the materials SZ and AS. The effect of humic acids depends on pH, only in acid media soluble humate complexes may be formed.     

Evaluation of different fractions of the organic matter of peat on tetracycline retention in environmental conditions: in vitro studies

Purpose

Due to the modernization of the agro-industrial sector, compounds with different toxicity and effects on human health and animal have been used and consequently affecting the environment. Among them, tetracycline (TC) stands out as one of the antibiotics most commonly used worldwide. This study evaluated the TC interaction with different fractions of peat in natura and humic substances, humic acid, fulvic acid, and humin.

Materials and methods

The different fractions of the organic matter were characterized by organic matter content, elemental analysis, spectroscopic analysis (E₄/E₆), and nuclear magnetic resonance of carbon 13 (NMR ¹³C), and the interaction between TC and different fractions of organic matter was made by fluorescence spectrometry. We used the tangential ultra-filtration system for determining the complexation capability of humic substances (HSs), fulvic acids (FA), humic acids (HA), and humin (HUM) from peat with TC. Finally, we evaluated sorption kinetic experiments between TC and peat in natura.

Results and discussion

The peat samples, humic substances, FAs, HAs, and HUM were characterized by organic matter (OM), atomic ratio (H/C and C/O) calculated from elemental analysis data, functional groups quantified by NMR ¹³C data, and E₄/E₆ ratio, and the results show significant differences in the structural characteristics of the fractions of OM influenced by the type of microorganisms and environmental factors associated with this decomposition. Data analysis revealed the strongest interaction between HUM and TC (59.19 mg g^?1), followed by interaction between HS and TC (43.36 mg g^?1 HS). In the sorption studies, these conditions showed the best model to describe the system under consideration using the Freundlich model.

Conclusions

The results showed that the different fractions of the OM extracted from peat show different contributions that affect the bioavailability of contaminants to the environment.

     

Characteristics of an amidase isolated from a soil bacterium

Amidase was extracted from a bacterium isolated from soil, and its properties were compared with those of amidase in soil. Amidase activity of the bacterial protein was lower than that of soil amidase, respectively, in its optimal pH (7.0 vs 8.5), optimal temperature (50 vs 60°C), K_m constant calculated by the Lineweaver-Burk plot (5.6 vs 17.9 mm), activation energy (18.9 vs 43.3 kJmol^?) and Q₁₀ (av. = 1.28 vs 1.75). Bacterial amidase was stable at temperatures ranging from 10 to 50°C and denatured at 55°C. Toluene inhibited both bacterial and soil amidase.When the inhibitions by 21 trace elements were compared by using 2 μmol 0.1 mg^?1 protein, the most effective inhibitors of bacterial amidase (> 25% inhibition) were: Ag(I), Cd(II), Cu(II), Hg(II), Ni(II), Pb(II), Zn(II), Al(III) and Se(IV). The effect of 16 pesticides on bacterial amidase varied considerably. By using 2 μg of active ingredient of pesticide 0.1 mg^?1 protein, the inhibition of bacterial amidase ranged from 7 to 49% with Dinitroamine and Butylate, respectively. The results show that soil constituents have a considerable influence on the reaction catalyzed by this enzyme.     

Salinity,chloride, and density relationships in ion enriched Onondaga Lake,NY

The relationship between salinity (S), chlorinity (Cl) and density (d) for the ion polluted (S = 3 to 4.5‰) and stratified Onondaga Lake are presented. The data base includes 220 determinations of the major ionic components collected from ten equally spaced depths. The salinity (S) and ionic strength (I) in the lake can be estimated from S = 1.85 Cl ? 0.28, where Cl is in g kg^?1 and I = 1.456 [Cl^?] ? 0.039, where [Cl] is in mmol L^?1. Due to the high concentration of Ca²⁺ in the lake, the seawater equation of state (Chen and Millero, 1977a) could not be used to estimate reliable densities for the lake (Δd ～ 100 × 10^?6 g cm^?3). A reliable equation of state for Onondaga Lake was derived from the composition data $$d = d_0 + A_v {\text{ }}CL + B_v {\text{ }}Cl^{3/2} $$ where d ₀ is the density of water (g cm^?3), A _v is a temperature dependent parameter related to the infinite dilution apparent molal volumes and B _v is related to the ion-ion interactions of the lake salts. The high ionic content of the lake depresses the temperature of maximum density to 3.18°C and alters the stratification of the lake. The salinity component of the stratification represents 40% of the total density stratification.     

THE MECHANISM OF PHOSPHATE ADSORPTION BY KAOLINITE, GIBBSITE, AND PSEUDOBOEHMITE

The adsorption isotherms (20°C) of phosphate on two potassium kaolinites and two aluminium oxides have been determined at pH values from 3 to 10 and at concentrations ranging from 10^?4 to 10^?2M. The reversibility of the adsorption with respect to pH and concentration has also been examined. The isotherms result from at least three types of adsorption site (regions I, II, and III) of widely different reactivities. The number of adsorption sites increases to a limit with decrease in pH for regions I and II. The behaviour of region III is more complex. The different adsorbents behave in essentially the same manner and differ only in the number of adsorption sites. It is tentatively suggested that regions I and II are located on an edge –Al(OH)₂ of the adsorbents, while region III results from penetration into some amorphous region of the crystal surface.     

Reductive transformation of pentachlorophenol on the interface of subtropical soil colloids and water

Ten soil colloids were obtained from three kinds of Fe-rich (> 50 g kg^− 1) subtropical soil parent materials (Basalt, Sandshale, and Quaternary Period Red Earth) collected in nine sites in Guangdong of China. Effect of the Fe-rich soil colloids and adding Fe(II) and oxalic acid on reductive dechlorination transformation of pentachlorophenol (PCP) were studied on colloids interfaces of reaction suspension. Mineralogical properties and specific surface area of the soil colloids were characterized by X-ray powder diffraction and Brunauer-Emmett-Teller (BET) methods, respectively. A series of reductive experiments were designed to determine PCP transformation and chloride ion release, and to calculate rate constant (k values) of pseudo first-order kinetics. Our results showed that reductive transformation of PCP occurred with k values from 0.007 to 0.057 d^− 1, and relevant chloride was released in the suspension of the ten soil colloids. Soil colloid developed from Basalt presented higher transformation rates (0.040-0.057 d^− 1) than that from Sandshale (0.007-0.033 d^− 1) and Quaternary Period red earth (0.012 d^− 1). Two paddy soil colloids developed from Sandshale (0.032-0.033 d^− 1) were more active than other three Sandshale soil colloids (0.007-0.011 d^− 1). The k values were significantly and positively correlated to the BET surface area (P < 0.01, n = 10). Addition of oxalic acid (0.022-0.231 d^− 1) or Fe(II) (0.029-0.256 d^− 1) into suspension of soil colloids gave arise to increase by 1.2-9.4 times in the k values. The release of chloride ion was simultaneously elevated. The enhancement of oxalic acid or Fe(II) on reductive transformation of PCP was attributed to increase of surface-bound Fe(II), which possess high reductive reactivity. The k values adding 1.0 mM oxalic acid were significantly and positively correlated to BET surface area and soil pH (P < 0.01), while k values adding 1.0 mM Fe(II) were related to total Fe (P < 0.001). The results may give new insight to understand the contribution of PCP abiotic reductive transformation in subtropical and tropical soils, and also in permeable reactive barriers.     

Decarboxylation des acides amines aromatiques-1-14C par les extraits de sol

Decarboxylation of the aromatic amino acids-1-¹⁴C by soilextracts: Neutral aseptic extracts of fresh soils (NAFS Extract) from forest, meadow and cultivated soils decarboxylate dl-DOPA-l-¹⁴C; dl-tyrosine-l-¹⁴C; dl-tryptophane-l-¹⁴C and dl-phenylalanine-l-¹⁴C with relative decarboxylation rates of 100; 30; 10; 0 respectively. The decarboxylation rate of dl-DOPA-l-¹⁴C has a highly significant correlation with the concentration of mineral fraction in the NAFS Extract. This result suggests that, in soil, the enzymatic system is protected by the easily extracted soil minerals. Considering the high value of E_act. (23 kcal/mole/degree), the catalytic power of the enzymatic system associated with the NAFS Extract is low. The decarboxylation rate of dl-DOPA-l-¹⁴C is optimum under aerobic conditions at pH 7 and at 37°C.The kinetic of the reaction follows the Michaelis-Menten law with K_m = 2·1 × 10^?3 M. The nature of the enzymatic system associated with the NAFS Extract is discussed.