Hydrolysis and adsorption of cyhalofop-butyl and cyhalofop-acid on soil colloids

A study was undertaken to investigate the stability of cyhalofop-butyl (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]butylpropanoate (CyB), an aryloxyphenoxy-propionic herbicide, at different pH values. The hydrolysis of CyB was faster in nonsterile than in sterile water. In sterile medium, CyB degraded only to (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid (CyA), whereas in nonsterile water, also the metabolites (2 R)-2-[4-(4-carbamoyl-2-fluorophenoxy)phenoxy]propanoic acid (CyAA) and (2 R)-2-[4-(4-carboxyl-2-fluorophenoxy)phenoxy]propanoic acid (CyD) were detected. The adsorption of CyB onto clays, iron oxide, and dissolved organic matter (DOM), using a batch equilibrium method, was also studied. A lipophilic bond is responsible for CyB adsorption on DOM. CyB was adsorbed on Fe(III)- and Ca-clays through hydrogen bonding between the carbonyl oxygen and water surrounding the exchangeable cations. In the interlayer of K-clay, CyB was hydrolyzed to CyA, which remained adsorbed therein as a monomer. The acid CyA was adsorbed only by the Fe-oxide through complexation. The CyA-Fe-oxide complex was stable and did not undergo degradation.     

Kinetic properties and stability of potato acid phosphatase immobilized on Ca-polygalacturonate

 Acid phosphatase from potato was adsorbed and immobilized on a pre-formed network of Ca-polygalacturonate, a substrate which has a composition and morphology similar to the mucigel present at the root-soil interface. The influence of different types of organic buffers on enzyme adsorption and activity was investigated. The highest enzyme activity, for free and adsorbed enzyme, was obtained with Na-maleate buffer at pH 6.0, which was used for all subsequent experiments. The Michaelis-Menten kinetic parameters, V_max and K_m, were determined for free and adsorbed phosphatase. V_max showed a 60% decrease upon adsorption (2.09±0.30 U/mg, for the soluble form and 0.84±0.15 U/mg, for the adsorbed enzyme), whereas K_m increased from 0.49±0.15 mM for the free enzyme to 0.99±0.20 mM for adsorbed phosphatase. Phosphatase adsorption decreased as the concentration of NaCl increased, indicating that the enzyme is bound to the carrier gel through coulombic interactions. Adsorption increased stability of the enzyme as compared with the free enzyme (t _1/2 of the activity was 9.4 days and 5.8 days, respectively), but increased thermal and proteolytic inactivation. The pH/activity profile revealed no change in terms of shape or optimum pH (4.5) upon adsorption of the enzyme. These results indicate that adsorption of acid phosphatase on Ca-polygalacturonate induces changes in the kinetic properties and stability of the enzyme, and the same type of response can be extrapolated from these results for acid phosphatases of the rhizosphere. Received: 1 July 1997     

Effect of undesalted dissolved organic matter from composts on persistence, adsorption, and mobility of cyhalofop herbicide in soils

The effect of undesalted dissolved organic matter (DOM) extracted from composts on the degradation, adsorption, and mobility of cyhalofop herbicide in soils was studied. A paddy-field sediment poor in organic matter (OM), an OM-rich forest soil, and DOM from agroindustrial or municipal waste compost were used. DOM increased the cyhalofop-acid but not the cyhalofop-butyl solubility in water. The degradation of cyhalofop-butyl in the sediment was slow, giving cyhalofop-acid as the only metabolite, whereas in forest soil, the process was faster, and three byproducts were detected. Soil pretreatment with DOM did not modify the degradation pattern but only reduced the adsorption of cyhalofop-butyl by soil, whereas it increased the adsorption of cyhalofop-acid. Among the cationic components of DOM solutions, the potassium ion seems to be related to the increased adsorption of the cyhalofop-acid in both OM-poor and OM-rich soils, yielding reversible complexes with the former and favoring hydrophobic interactions with the latter.     

Agreement among three different equine venipuncture sites with regard to measurement of packed cell volume and total solids

The primary objective of this study was to determine the agreement between the packed cell volume (PCV) and total solids (TS) values in blood collected from the jugular vein (JV) in comparison with the cephalic vein (CV) and the transverse facial venous sinus (TFVS) in healthy adult horses. A total of 72 samples were taken from 24 horses. We found high agreement that reflects no clinically relevant differences between the PCV and TS values obtained from the CV or the TFVS in comparison with the JV in standing healthy adult horses.     

Interactions Among Different Devices and Electrical Stimulus on the Electroejaculation of Captive Agoutis (Dasyprocta leporina)

The interactions among different electroejaculation devices associated with serial or continuous stimuli were investigated to improve the efficiency of the electroejaculation for semen collection in agoutis. Ten sexually matured male Dasyprocta leporina were restrained by the intramuscular administration of xylazine–ketamine association. Each individual was randomly subjected to four electroejaculation protocols, by combining two devices (one presenting longitudinal electrodes emitting square waves and other presenting ring electrodes emitting sine waves) and two electrical stimuli protocols (serial or continuous). A total of 40 attempts for electroejaculation were conducted in agoutis, being 10 per treatment. The most efficient treatment in providing ejaculates containing sperm (p < 0.05) was that using and electroejaculator connected to a probe with ring electrodes and associated with serial stimuli (4/7; 57%). In spite of semen parameters obtained by sine waves were adequate for using the samples for assisted reproduction, higher values for sperm motility and functional membrane integrity were obtained in the use of the square wave, independently of the electric stimulation protocol used (p < 0.05). In conclusion, we verified that the use of a device presenting a probe with ring electrodes and emitting sine waves, associated with a serial stimuli protocol, improves the efficiency for semen obtaining by electroejaculation in adults D. leporina.     

On the Lipidic Fraction of some Typical Mediterranean Soils from Micaschists

The lipidic fraction extracted from Rankers and Cambisols developed under the same pedoclimatic conditions was studied using chemical and physical methods. Their amounts extracted from different horizons varied from 0.10 to 0.66 g/100 g soil or from 2.7 to 33.3 g/100 g soil organic matter. UV-visible, NMR and IR analyses indicate a rather homogeneous constitution of the lipidic fraction of the examined soils, characterized by a prevalence of long aliphatic saturated chains and only traces of aromatic compounds. X-ray diffractometry gives evidence of the presence in all horizons of ozocerite, a crystalline mineral wax which can be considered an accumulation metabolic product. The characteristics of the lipids of these soils, shown by the acid number and by the E₂/E₃ ratio, can be used as an index of their bioactivity.     

Effects of lead pollution on different soil enzyme activities

We studied the effects of Pb pollution on soil dehydrogenase and phosphatase activity. Samples of four soils (Saxe, Podestà, Porto Teulada, and Sa Xia Manna) were collected from various locations in southwestern Sardinia, Italy. The soils, which differ mainly in heavy metal contents of pedologic origin (Cu, Zn, Cd, and Pb), were treated with Pb (0, 100, 500, 1000, and 5000 g Pb g^-1 soil) and incubated in the laboratory. Samples of the incubated soils were collected periodically (0, 1, 2, 4, 8, and 16 weeks) and the enzymes were measured. Soil dehydrogenase activity was influenced by both the Pb additions and variations in soil moisture content. Only the addition of 5000 g Pb g^-1 soil led to a significant decrease in dehydrogenase activity compared to the controls, while the other doses of Pb did not always result in a clear reduction in enzyme activity. Drying the soil led to a considerable reduction in dehydrogenase activity, sometimes so far as to render the differences found between the various treatments not statistically significant. Soil phosphate activity was also influenced by the Pb additions, but the effect of the variation in soil moisture content was less than that found for the dehydrogenase. After the 2nd week of incubation, the phosphate activity in the Podestà and Saxe soils had decreased proportionally to the increase in Pb content. At the end of the incubation period, in the Porto Teulada and Sa Xia Manna soils, a net reduction in phosphatase activity versus controls was found only at the highest Pb concentration. Although both enzyme activities were influenced by the Pb additions, the phosphate activity was less sensitive to variations in the soil moisture content and may thus be a more suitable indicator for soil pollution by Pb.     

13C NMR spectra of soil organic fractions extracted with organic solvents

Soil organic fractions extracted in sequence with ethyl ether, acetone, benzene and dioxane have been investigated with ¹³C NMR spectroscopy. The spectra of ethyl ether and acetone fractions are identical and show the presence of signals assigned to normal long chain (C_23±2) fatty acids. A very similar spectral pattern is displayed by the benzene fraction which appears to consist of a mixture (50 ± 10)% of normal fatty acids and normal alkanes (C_21±3). A comparison with data in the literature indicates that the well developed signals at 14, 23, 30 (very intense) and 32 ppm are a common feature of the lipid fraction extracted from different soils.A completely different spectrum has been obtained from the dioxane fraction. Most signals appearing in the range 55–75 ppm can be attributed to oxygen bonded sp³ carbon atoms. The lack of aromatic signals seems to exclude the possibility that this fraction was derived from lignin residues.The comparison with ¹H NMR spectra and the occurrence of distinct and sharp signals indicate that ¹³C NMR is a valuable tool in the study of soil organic fractions extracted with organic solvents.