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Enhanced soil toxic metal fixation in iron (hydr)oxides by redox cycles
No full textThe possibility to foster toxic metals (Cd, Cu, Ni, Pb and Zn) fixation on Fe (hydr)oxides, either native or added as ameliorants, was investigated at
the laboratory scale in two heavily polluted arable and grassland soils by inducing repeated cycles of the reduction and oxidation. Soil samples were
treated with Fe-rich waste (FeW) alone or together with fresh organic waste (OW) to accelerate reduction step. The FeW (242 g Fe kg−1) was an air
dried sediment produced by treatment of olive mill waste waters and theOW(410 g C kg−1) was obtained by source separate collection of solid urban
waste. The efficiency of metals immobilization was evaluated in terms of biological availability. Phyto-availability was assessed either by 1 M NH4
acetate extraction (exchangeable fraction) and by 0.005 M DTPA/0.1 M triethanolamine (pH 7.3) extraction, whereas hazard to humans from direct
soil ingestion (oral bio-accessibility) was tested by the physiologically based extraction test (PBET).
Aerobic incubation of soils treated with FeW+OW did not cause any significant change to the exchangeable fraction of toxic metals in both
the arable and the grassland soils, whereas one to three redox cycles, applied after FeW+OWaddition, reduced Cd and Cu in both soils and Pb in
the arable soil below detection limits. Exchangeable Zn was reduced in the FeW+OW treated soil by 50 and 90% in the arable and grassland soils,
respectively.
DTPA-extractable Cd, Cu and Zn were unaffected by treatments when soils were maintained oxic, but on the contrary, decreased significantly
after one to three redox cycles by 88%, 93%, 36% and 95%, 98%, 65% in the arable and grassland soil, respectively. Lead showed a different
behaviour with a general tendency to increase its availability. This result could be explained with the progressive dissolution of Mn oxides during
the redox cycles. DTPA-extractable Ni showed in the arable soil a progressive increase, but remained constant in the grassland soil. A further
reduction in DTPA-extractable metals, particularly evident for Ni, Pb and Zn, was observed after 150 d ageing of treated soils.
Soil treatments were also effective in reducing potential hazard from direct soil ingestion in grassland soil (95%, 100%, 27% and 30% for Cd,
Cu, Pb and Zn respectively), whereas the effect was much lower in the arable soil.
The mechanisms of metal fixation are compatible with chemisorption and co-precipitation on Fe (hydr)oxides. These results suggest that redox
cycles can be applied to FeW treated soils to reduce biological availability of many toxic metals in neutral soils, but their efficiency varies
according to the element and soil composition. The addition of OW generally fosters metal fixation by intensification of the reductive process
Identificazione di un prodotto di trasformazione del metamitron nel terreno.
No full textEdizioni SBR srl, Portici (NA
Soil behaviour of metamitron in laboratory and lysimeter studies
No full textThe fate of metamitron, a sugar beet herbicide, in soil was studied in laboratory and in field lysimeters under different water regimes. Laboratory degradation followed first-order kinetics with half-lives ranging from 18.8 to 56.3 d with different incubation conditions. Lysimeter dissipation was consistently rapid with half-lives ranging from 4.4 to 8.0 d under the different water regimes. The influence of temperature on laboratory degradation was within the range reported for many other pesticides, while that of soil moisture was lower than for other pesticides. Adsorption was well described by an L-type isotherm with a 1/n value far from unity in common with most polar herbicides. Metamitron movement through the lysimeters varied with the different amounts of water supplied. Metamitron reached 60 cm in depth at day 7 after treatment and 120 cm in depth at day 14 after treatment in lysimeters that received normal water amounts and about 10 % of pesticide moved below 120 cm in lysimeters that received, in addition to the normal water, 151 mm water at day 4 after treatment, which simulates a probable spring rain event in northern Italy. The marked movement of the pesticide in these conditions suggests that it is to be considered a potential pollutant in irrigated crops but, the rapid disappearance (DT50 4-8 days) of the pesticide in the lysimeters by means other than leaching, partially reduces this risk. (© Inra/Elsevier)Étude du comportement de la métamitrone dans le sol au laboratoire et dans des cases lysimétriques. Le devenir dans le sol d'un herbicide destiné aux betteraves à sucre, la métamitrone, a été étudié au laboratoire et au champ dans des cases lysimétriques sous différents régimes hydriques. La dégradation au laboratoire a suivi une cinétique du premier ordre avec des demi-vies comprises entre 18,8 et 56,3 j pour différentes conditions d'incubation. La dégradation dans les cases lysimétriques a été sensiblement plus rapide avec des demi-vies comprises entre 4,4 et 8,0 j sous différents régimes hydriques. L'influence de la température sur la dégradation au laboratoire a été du même ordre de grandeur que celle qui est reportée pour beaucoup d'autres pesticides alors que celle de l'humidité du sol a été plus faible que pour les autres pesticides. L'adsorption est bien décrite par des isothermes en L avec une valeur de 1/n loin de l'unité comme pour la plupart des herbicides polaires. Les mouvements de la metamitrone à l'intérieur des lysimètres ont varié en fonction des différentes quantités d'eau apportées. La metamitrone a ainsi atteint la profondeur de 60 cm 7 j après son application, 120 cm 14 j après son application dans les lysimètres qui ont reçu les quantités normales d'eau. Dans les lysimètres qui ont reçu en plus de la quantité normale d'eau, 151 mm 4 j après l'application, ce qui simulait un événement pluvieux probable au printemps en Italie du nord, environ 10 % du pesticide se sont déplacés au-dessous de 120 cm. Le déplacement marqué du pesticide dans ces conditions suggère qu'il peut être considéré comme un polluant potentiel dans les cultures irriguées, mais sa disparition rapide (demi-vie : 4 à 8 j) dans les lysimètres par des mécanismes autres que le lessivage, réduit partiellement ce risque. (© Inra/Elsevier
Degradation and mobility of metolachlor and terbuthylazine in a sandy clay loam soil
No full textThe degradation of metolachlor and terbuthylazine, two maize herbicides, was studied in laboratory in a sandy clay loam soil under different temperature and soil moisture conditions and in drainage field lysimeters. Identification of the main degradation products of the two herbicides was attempted both in laboratory and field lysimeter soil samples. The results show that the degradation of the two herbicides in laboratory followed a first order kinetics influenced by temperature and soil moisture. Metolachlor disappeared in soil more rapidly than terbuthylazine. Metolachlor moved more rapidly than terbuthylazine through the soil profile in field lysimeters and noticeable quantities were found in drainage water. In the laboratory degradation studies, the main degradation products of both herbicides were found in soil samples as early as the first week of incubation, while in the field lysimeter studies only the degradation product of terbuthylazine was found in soil samples. (© Inra/Elsevier, Paris.)Adsorption, dégradation et mobilité du métolachlore et du terbuthylazine au laboratoire et dans des lysimètres de terrain. La dégradation du métolachlore et du terbuthylazine, deux herbicides du maïs, a été étudiée au laboratoire dans un sol de limon argilo-sableux dans différentes conditions de température et d'humidité du sol et dans des lysimètres de terrain. L'identification des principaux produits de dégradation des deux herbicides a été entreprise sur des échantillons de sol à la fois au laboratoire et dans des lysimètres de terrain. Les résultats montrent qu'au laboratoire la dégradation des deux herbicides a suivi une cinétique de premier ordre influencée par la température et l'humidité du sol. Le métolachlore a disparu du sol plus rapidement que le terbuthylazine et a migré plus rapidement que celui-ci à travers le profil pédologique dans les lysimètres de terrain et des quantités notables ont été retrouvées dans les eaux de drainage. Au laboratoire, les principaux produits de dégradation des deux herbicides ont été retrouvés dans les échantillons de sol dès la première semaine d'incubation, tandis que dans les lysimètres de terrain, seul le produit de dégradation du terbuthylazine a été retrouvé dans les échantillons de sol. (© Inra/Elsevier, Paris.
Interactions between Fe-cyanide complex and humic acids
No full textThe fate of cyanides in soil is strongly influenced
by the formation of Fe cyanides, which can interact with
organic and inorganic colloids and precipitate as stable
compounds. Scarce information is available on the capacity
of humic acids to interact with cyano-complexes and thus
affect the leaching and prevent the risk of contamination of
watertable. Here we show that interaction between humic
acids (HAs) and ferricyanide complex led to a formation
of ferricyanide-humo micelles, and that the interaction did
not imply changes in the original structure of ferricyanide
comple
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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