Library

Notes: A study has been made of the effect of properties and composition of soils on the adsorption of ethofumesate. Adsorption isotherms of ethofumesate by agricultural and natural soils and by montmorillonite and humic acid were obtained. The correlations between the Freundlich K constants, and Kd distribution coefficients and the soil parameters were determined. Significant correlations (P〈0.05) were found between K and clay content and between Kd and smectite content for the agricultural soils but the correlation with organic matter content was of borderline or no significance.Considering the agricultural and natural soils together or the soils with an organic matter content 〉2%, a highly significant correlation was found between K and the organic matter content. According to the r2 determination coefficient, the organic matter content accounts for 88.4% of the variability in adsorption in the first case, and 92.2% in the second case. The log10 Kdom values of soils with an organic matter content 〉2% were similar and confirm the importance of the organic matter as a determinant parameter in the adsorption of ethofumesate by these soils. The adsorption of the herbicide by montmorillonite and humic acid confirmed the results obtained with the soils and point to the importance of the exchangeable cation nature of the samples and of the temperature in the adsorption process. Adsorption de l'éthofumesate dans des sols agri-coles et naturels L'effet des propriétés et de la composition du sol sur l'adsorption de l'ethofumesate a étéétudié. Les isothermes d'adsorption de 1'éthofumesate par des sols agricoles et naturels ainsi que par la montmorillonite et des acides humiques ont été déterminés. Les corrélations entre les caractéris-tiques du sol, les constantes de Freundlich K d'une part et les coefficients de distribution Kd d'autre part ont été déterminées. Des corrélations significatives (P〈0.05) ont été mises en évidence entre K et la teneur en argile ainsi qu'entre Kd et la teneur en smectite pour les sols agricoles mais la correlation avec la teneur en matisre organique etait tout juste ou non significative.Lorsqu'on considérait les sols agricoles et naturels ensemble ou les sols dont la teneur en matière organique est supérieure à 2%, une corrélation hautement significative existait entre K et la teneur en matière organique. Le coefficient de détermination r2 montre que la teneur en matière organique explique 88.4% de la vari-abilité de l'adsorption dans le premier cas et 92.2% dans le second cas. Le log10 Kdométait similaire pour les sols de teneur en matière organique 〉2%, ce qui confirme l'importance du paramètre matière organique dans l'adsorption de 1'ethofumesate par ces sols. L'adsorption de I'herbicide par la montmorillonite et les acides humiques a confirmé les résultats obtenus avec les sols et a montre 1'importance de la température du process et de la nature des cations d'échange des échantillons. Adsorption von Ethofumesat in Acker- and natürlichen Böden Bei der Untersuchung der Wirkung der Eigen-schaften und der Zusammensetzung von Böden auf die Adsorption von Ethofumesat wurden Adsorplions-Isothermen mit Acker- und natürlichen Böden sowie mit Montmorillonit und Huminsäure ermittelt. Die Korrelationen zwischen den Freundlich-Konstanten K sowie den Verteilungskoeffizienten Kd und den Bodenparametern wurden bestimmt. Signifikante Korrelationen (P〈0.05) wurden für K und den Tongehall und für Kd und den Smectit-Gehalt in Ackerböden gefunden, doch die Korrelation mit dem Gehalt an organischer Substanz war marginal oder nicht signifikant. Für Acker-und natürliche Böden insgesamt oder Böden mit einem Gehalt an organischer Substanz von 〉2% wurde eine hochsignifikante Korrelation zwischen K und dem Corg.-Gehalt gefunden. Das Bestimmtheitsmaß (r2) für die organische Substanz lag swischen 88.4% im ersten und 92.2% im zweiten Fall. Die log10Koc-Werte Böden mit einem Corg.-Gehalt von 〉2 % waren ähnlich und bestätigen die Bedeutung der organischen Substanz als bestimmenden Parameter für die Adsorption von Ethofumesat in diesen Böden. Die Adsorption des Herbizids an Montmorillonit und Huminsäure unterstreichen die an den Böden gewonnenen Ergebnisse und die Bedeutung der Kationen-Austauschfähigkeit der Proben.

Notes: Abstract. A study was carried out on the sorption of two sparingly water-soluble pesticides (diazinon and linuron) by a sandy loam soil modified with different exogenous organic materials (EOMs) containing humic-like substances: city refuse compost (CRC), peat (P), commercial “humic” acid (HA), liquid “humic” acid (LHA), and two (nonhumic) model compounds (surfactants), tetradecyltrimethylammonium bromide (TDTMA) and sodium dodecyl sulphate (SDS), before and after 2- and 8-month incubation periods with the soil. In all cases, the isotherms fitted the Freundlich sorption equation (x/m = KC e n ), generally with r 2 values greater than 0.99. The value of the sorption constant K for the natural soil was 8.81 for diazinon and 2.29 for linuron. These values increased significantly for EOM modified soils with respect to natural soil, with the exception of the samples modified with SDS and LHA, in which cases they decreased, possibly due to the micellar properties of these compounds. Incubation of EOMs with soil increased their sorption capacity: the K oc values were increased proportionally to the incubation time for both pesticides and for all treatments carried out. Accordingly, the sorption capacity of hydrophobic pesticides increases with the degree of evolution in the soil of EOMs with “humic”-type compounds, possibly due, among other causes, to the increase in the EOMs' colloidal properties and the modifications occurring in the hydrophobic-hydrophilic characteristics of the soil surfaces. The main conclusion is that application to the soil of carbon-rich wastes, especially those with a high degree of maturity, may offer an important strategy for reducing pesticide leaching and for eliminating pesticide residues from soil with the use of anionic surfactants.

Notes: Abstract The thermal decomposition of the interlayer complexes of homoionic samples of montmorillonite with the carbamate insecticide pirimicarb (2-dimethylamino-5, 6-dimethyl pyrimidin 4-yl-dimethyl carbamate) was studied using TG and DSC techniques. The decomposition of the organic compound was followed by IR spectroscopy and X-ray diffraction. It was observed that the thermal decomposition of pirimicarb is catalyzed by adsorption by the clay. Both the catalytic capacity of the clay and the values of the decomposition enthalpies depend on the characteristics of the interlayer cation of the montmorillonite.

Notes: Abstract Using adsorption isotherms, a study was performed of the adsorption of two organophosphorus pesticides, azinphosmethyl (sparingly soluble in water) and dichlorvos (moderately soluble in water), by montmorillonites saturated with the cations hexadecyltrimethylammonium (HDTMA+), dodecyltrimethylammonium (DDTMA+) and tetramethylammonium (TMA+) in aqueous media. The results were compared with those obtained for the adsorption of these pesticides by natural montmorillonite, humic acid and by the soil organic matter and with the octanol-water partition coefficient (Kow) of the compounds. Results indicated that regarding the capacity to remove azinphosmethyl from water the organic matter derived from the organic cations HDTMA+ and DDTMA+ is 5–10 times more effective than humic acid; 10–20 times more effective than the organic matter from the soil and 20–50 times more efficient than octanol. However, both organic phases, that derived from the organic matter of the soil and that of the organic cations, have similar effectiveness for removing dichlorvos from water, in turn, their efficiency is 50 times higher than that of octanol. These findings may find application in the removal of azinphosmethyl or other sparingly water soluble organophosphorus pesticides from aquifers.