F. Sánchez-Rasero

A role for leaf peroxisomes in the catabolism of purines

Summary The presence of purines and allantoin in peroxisomes purified from pea ( Pisum sativum L.) leaves was studied. Purified intact peroxisomes were pretreated to remove proteins, and analyzed by an HPLC method to identify and quantify the levels of the metabolites xanthine, hypoxanthine, uric acid, and allantoin in leaf peroxisomes. Uric acid and xanthine were clearly detected in leaf peroxisomes, 20 μg of xanthine and 21 μg of uric acid per mg peroxisomal protein. Allantoin also seemed to be present in peroxisomes, but hypoxanthine was not identified. The existence of allantoin in peroxisomes was verified enzymatically by determining the concentration of this ureide with commercial allantoinase, and an amount of about 7μg allantoin per mg peroxisomal protein was measured. In purified intact peroxisomes xanthine oxidase and urate oxidase activities were found to be present, but allantoinase activity was not detected. These results show for the first time that purines and allantoin are present in leaf peroxisomes and that xanthine can be catabolized to uric acid and allantoin inside these organelles. The N-rich ureide allantoin could be further used by leaf cells for synthesis of amino acids and proteins.

Photodegradation of mecoprop and dichlorprop on dry, moist and amended soil surfaces exposed to sunlight

The effects of environmental conditions on the photodecomposition of two phenoxy-alkanoic acid herbicides were investigated on different soil surfaces conditions under sunlight exposition. A technique has been developed to study this process on moist nonsterile soil surfaces. A slow rate of disappeareance occurs in the three soils exposed to sunlight in absence of water. Photolysis of these herbicides is controlled by soil texture and its adsorption capacity. The organic matter does not have a sensitizing effect on the photodecomposition of these herbicides on dry soil surfaces. On nonsterile moist soil surfaces exposed to sunlight, the photolytic process prevails in the two first days of exposure and the transformation kinetics fits the Hoerl function better than the first-order exponential equation.

Methidathion degradation in soil amended with biosolids and a cationic surfactant: use of different kinetic models

The influence of the addition of a municipal biosolid and the cationic surfactant tetradecyl trimethyl ammonium bromide (TDTMA) on the degradation of an organophosphorus insecticide, methidathion, in a soil was investigated. Before incubation, top soil samples were amended with 4% of biosolid (SB), TDTMA (SS) and both amendments (SBS). Two additional samples of top soil, unamended (Ss) and amended with the biosolid (SBs), were sterilised to check for abiotic degradation. The amendments did not markedly affect insecticide degradation in any sample, with minute changes attributed to small sorption differences. Measurements of the dehydrogenase activity (DHA) seem to support the hypothesis that methidathion degradation is carried out by soil micro-organisms. The presence of the biosolid increases methidathion persistence in the sterile samples. Experimental data were fitted to three mathematical equations: a first-order one (monophasic model), a biexponential model and the Hoerl function (biphasic models). Biphasic models better predict the results obtained in top soil amended or not, while for sterile samples all the proposed equations are good descriptors.

Adsorption of cyanazine on peat and montmorillonite clay surfaces.

The adsorption of cyanazine by peat and montmorillonite is studied as a function of the crystal chemical characteristics of exchangeable cations and temperature. The adsorption kinetics of cyanazine on peat shows that the adsorption equilibrium is reached within 1 h. The values of the rate constants of the reaction seem to indicate that the adsorption rate of cyanazine by peat is mainly controlled by the diffusion process. The order of adsorption of cyanazine by peat is as follows: H+-peat > Cu2+-peat > Ca2+-peat > Co2+-peat > Mg2+-peat > K+-peat. The thermodynamic parameters seem to point to an adsorption mechanism by hydrogen bonds, although in the acidic and Cu2+ samples a protonation process and adsorption of the protonated species is also likely. The values of the adsorption rate constant of cyanazine by montmorillonite is ten times higher than that for peat. The adsorption of cyanazine by montmorillonite follows this order: Cu2+-mont > Co2+-mont > H+-mont; the adsorption on Cu2+-mont is five times greater than on the other samples. For the Cu2+ samples, the thermodynamic parameters seem to point to a mechanism of direct coordination cyanazine-Cu2+. The most probable mechanism for the adsorption of cyanazine by the Co2+ sample is by physical bonding. For the H+ sample there is a physical adsorption and an ionic one according to the following reaction: H+-mont + cyanazine → mont – H+-cyanazine.

Use of a solid phase extraction method for the analysis of pesticides in groundwater by gas chromatography with electron capture and flame photometric detectors

Organophosphorous, organochlorine and electron-capture sensitive pesticides were extracted from water in a single step using a C18 solid phase extraction cartridge, eluted with ethyl acetate and isooctane and determined by GC with electron-capture and flame photometric detection. Analytical aspects of the method were studied with a linear regression model, including the linearity of the responses, repeatability and detection limits, which ranged from 3 to 35 µg l–1. The method of concentration employed did not contribute to a noticeable loss of the chemicals, with recoveries of over 90%, except for fenthion. The present method is applied to the analysis of 27 pesticides in groundwater, most of which are recovered at >70% efficiency which complies with the EPA criteria.

Adsorption of mecoprop and dichlorprop on calcareous and organic matter amended soils: Comparative adsorption of racemic and pure enantiomeric forms

Abstract The adsorption isotherms of mecoprop [R,S‐2‐(4‐chloro‐2‐ methylphenoxy) propanoic acid] and dichlorprop [R,S‐2‐(2,4‐dichlorophenoxy)propanoic acid] on twelve calcareous soils were studied. All the isotherms fit the Freundlich equation. The distribution coefficients (Kf) were low and were only significantly related with the organic matter content of the soils. The main adsorption mechanism at the pH of these soils was found to be by cation bridging between the anionic forms of the two herbicides, and the external surfaces of the organic matter and/or negatively charged clay. The Koc values for mecoprop (R,S‐ MCPP) and dichlorprop (R,S‐ DCPP) adsorption predicted a high mobility of these herbicides in the soils. Their corresponding enantiomeric forms, R (biologically active) and S (biologically inactive) were adsorbed at the same ratio on these soils. The organic matter amended soils showed a significant increase on the retention capacity of both molecules.

Bentazone Leaching in Spanish Soils

Adsorption, incubation and soil-column experiments with bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were carried out in ten different soils from the marches surrounding the Donana National Park (Huelva, SW Spain). Adsorption isotherms for the different soils showed a good fit with the Freundlich equation. Bentazone was poorly adsorbed in all the soils studied, with no significant relationship between the K f values and soil characteristics. A significant correlation was obtained between the soil organic matter content and the distribution constant values (K d ) calculated at an equilibrium concentration of 200 μg cm -3 . The low adsorption and non-degradation of bentazone on these soils suggest that the herbicide readily percolates through soils to reach the surface and ground waters. The mobility of bentazone through three soil columns was also studied. The mass balances carried out showed that bentazone was totally eluted from the soil columns. The theoretical model applied to explain bentazone leaching under our experimental conditions seems to be suitable for soil columns with a uniform water-flow rate.

Simultaneous determination and enantiomeric resolution of mecoprop and dichlorprop in soil samples by high-performance liquid chromatography and gas chromatography-mass spectrometry

Abstract A rapid, precise and sensitive method was developed for the quantitative simultaneous determination of mecoprop and dichlorprop in soil samples by reversed-phase high-performance liquid chromatography (HPLC), thus making it very appropriate for degradation studies where many samples have to be analysed. This method was supplemented with a simple gas chromatography–mass spectrometry (GC–MS) ion trap method developed using a chiral permethylated-β-cyclodextrin stationary phase in order to determine the relative amounts of the R and S enantiomeric forms of these herbicides. Recovery rates for natural soils were around 80% at concentrations of 0.5 and 1.0 μg/g. Lower recoveries were achieved for the 10% peat-modified soil samples. The analytical sensitivity of the HPLC technique was 0.11 and 0.07 ng/μl, for 20 μl injections, for mecoprop and dichlorprop, respectively.

Effect of Storage on the Recovery of Different Types of Pesticides Using a Solid-phase Extraction Method

Recoveries of different pesticide groups after storage either on C 18 cartridges or as dried residues from organic solutions, and their analysis by gas chromatography with electron capture and flame photometric detection, were studied. Two storage temperatures, 4 and -18 °C, and three storage periods, 3, 7 and 30 d, were considered. The effect of storage temperature and storage time on the recovery of 27 pesticides in water was investigated. In general, the pesticide recoveries were ≥70% after 30 d of storage at -18 °C on C 18 cartridges. Exceptions included captan and folpet. The storage of the dried residues generally did not affect the pesticide recovery when kept at -18 °C for up to 30 d.

Simultaneous determination of various pesticides in water by solid-phase extraction/HPLC with photodiode array detection

Abstract A solid-phase extraction/high-performance liquid chromatographic method with photodiode array detection has been developed for the simultaneous determination of carbendazim, thiophanate-methyl, lenacil, methabenzthiazuron, diuron, phenmedipham, captan and diflubenzuron in water at the low ng/ml level. Recoveries (82–102%) and precision (R.S.D. 0.5–2.8%) are quite good and the detection limits achieved are up to 2.5 times lower than the maximum limit permitted by the E.C.