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Atrazine Hydrolysis in Soil1
Abstract
An important pathway of atrazine degradation in perfusion systems of three soils was chemical hydrolysis to hydroxyatrazine. Ultraviolet spectrophotometric analyses of the perfusates showed the presence and accumulation of hydroxyatrazine. Atrazine degradation followed first‐order kinetics in soil‐free, sterilized soil and perfusion systems. An increased rate of atrazine hydrolysis in an acid soil was consistent with the effect of pH on hydrolysis. No microbial degradation of atrazine was detected following inoculation of a soil‐free atrazine medium with perfusates. An increased rate of hydrolysis in the presence of sterilized soil was postulated to result from soil adsorption of atrazine. Soil pH and organic matter content largely controlled the rate of atrazine hydrolysis; for soils of similar pH, atrazine degradation rates increased with increased atrazine adsorption.
... Degradation of atrazine to hydroxyatrazine under anaerobic conditions is consistent with the finding of earlier studies (Chung et al., 1996;Seybold et al., 2001). Hydrolysis of atrazine to hydroxyatrazine has been attributed to chemical degradation through adsorption of atrazine to organic matters, sediments and particles (Armstrong et al., 1967;Lerch et al., 1999;Seybold et al., 2001;Stevenson, 1972). Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. ...
... Hydrolysis of atrazine to hydroxyatrazine has been attributed to chemical degradation through adsorption of atrazine to organic matters, sediments and particles (Armstrong et al., 1967;Lerch et al., 1999;Seybold et al., 2001;Stevenson, 1972). Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. In equilibrium with atmosphere, the pH of the aerobic bioreactors remained the same as the influent at about 7.5, while in anaerobic conditions the pH dropped to an average of 6.5 (Table S4), which could have contributed in atrazine hydrolysis to hydroxyatrazine (Armstrong et al., 1967;EPA, 2006;Gamble and Khan, 1985;Geller, 1980). ...
... Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. In equilibrium with atmosphere, the pH of the aerobic bioreactors remained the same as the influent at about 7.5, while in anaerobic conditions the pH dropped to an average of 6.5 (Table S4), which could have contributed in atrazine hydrolysis to hydroxyatrazine (Armstrong et al., 1967;EPA, 2006;Gamble and Khan, 1985;Geller, 1980). Mandelbaum et al. (1993) provided evidence that microbial activity, such as the production of enzymes, enhanced atrazine hydrolysis at neutral pH values in both aerobic and anaerobic conditions. ...
Atrazine and nitrate NO3−N are two agricultural pollutants that occur widely in surface and groundwater. One of the pathways by which these pollutants reach surface water is through subsurface drainage tile lines. Edge-of-field anaerobic denitrifying bioreactors apply organic substrates such as woodchips to stimulate the removal of NO3−N from the subsurface tile waters through denitrification. Here we investigated the co-removal of NO3−N and atrazine by these bioreactors. Laboratory experiments were conducted using 12-L woodchips-containing flow-through bioreactors, with and without the addition of biochar, to treat two concentrations of atrazine (20 and 50 μg L −1) and NO3−N (1.5 and 11.5 mg L −1), operated at four hydraulic retention time, HRT, (4 h, 8 h, 24 h, 72 h). Additionally, we examined the effect of aerating the bioreactors on atrazine removal. Furthermore, we tested atrazine removal by a field woodchip denitrifying bioreactor. The removal of both NO3−N and atrazine increased with increasing HRT in the laboratory bioreactors. At 4 h, the woodchip bioreactors removed 65% of NO3−N and 25% of atrazine but, at 72 h, the bioreactors eliminated all the NO3−N and 53% of atrazine. Biochar-amended bioreactors removed up to 90% of atrazine at 72-h retention time. We concluded that atrazine removal was primarily via adsorption because neither aeration nor NO3−N levels had an effect. At 4-h retention time, the field bioreactors achieved 2.5 times greater atrazine removal than the laboratory bioreactors. Our findings thus highlighted hydraulic retention time and biochar amendments as two important factors that may control the efficiency of atrazine removal by denitrifying bioreactors. In sum, laboratory and field data demonstrated that denitrifying bioreactors have the potential to decrease pesticide transport from agricultural lands to surface waters.
... Degradation of atrazine to hydroxyatrazine under anaerobic conditions is consistent with the finding of earlier studies (Chung et al., 1996;Seybold et al., 2001). Hydrolysis of atrazine to hydroxyatrazine has been attributed to chemical degradation through adsorption of atrazine to organic matters, sediments and particles (Armstrong et al., 1967;Lerch et al., 1999;Seybold et al., 2001;Stevenson, 1972). Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. ...
... Hydrolysis of atrazine to hydroxyatrazine has been attributed to chemical degradation through adsorption of atrazine to organic matters, sediments and particles (Armstrong et al., 1967;Lerch et al., 1999;Seybold et al., 2001;Stevenson, 1972). Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. In equilibrium with atmosphere, the pH of the aerobic bioreactors remained the same as the influent at about 7.5, while in anaerobic conditions the pH dropped to an average of 6.5 (Table S4), which could have contributed in atrazine hydrolysis to hydroxyatrazine (Armstrong et al., 1967;EPA, 2006;Gamble and Khan, 1985;Geller, 1980). ...
... Armstrong et al. (1967) suggested that the enhanced hydrolysis of atrazine in soils can occur due to the presence of catalytic metals on the surface of soil mineral particles, in addition to a low soil pH that can facilitate acid hydrolysis. In equilibrium with atmosphere, the pH of the aerobic bioreactors remained the same as the influent at about 7.5, while in anaerobic conditions the pH dropped to an average of 6.5 (Table S4), which could have contributed in atrazine hydrolysis to hydroxyatrazine (Armstrong et al., 1967;EPA, 2006;Gamble and Khan, 1985;Geller, 1980). Mandelbaum et al. (1993) provided evidence that microbial activity, such as the production of enzymes, enhanced atrazine hydrolysis at neutral pH values in both aerobic and anaerobic conditions. ...
... En conditions acides (HCI 0,1 M), les t1/2 sont de 9,5 jours pour l'atrazine et de 7,9 jours pour la terbuthylazine, et de 5 et 12 jours respectivement en conditions alcalines (NaOH 0,1 M). Ainsi de nombreux auteurs observent un accroissement de l'hydrolyse lors d'une baisse de pH (Armstrong et al., 1967;Obien et Green, 1969;Khan, 1978). Ces résultats vont dans le même sens que ceux de Khan (1978) qui montrent que l'énergie d'activation de la réaction d'hydrolyse augmente quand le pH de la solution s'accroît. ...
... L'hydrolyse acide, quant à elle, résulterait d'une protonation de l'azote du noyau ou des chaînes amino-alkyles, suivie par une cassure de la liaison C-CI par l'eau. En effet, la protonation de l'azote augmenterait la déficience en électrons du carbone lié au chlore et favoriserait le déplacement nucléophile du chlore par l'eau (Armstrong et al., 1967). Par ailleurs, Harris (1967) a montré que l'hydrolyse de l'atrazine est plus rapide dans les sols à haute teneur en matière organique. ...
... Par ailleurs, Harris (1967) a montré que l'hydrolyse de l'atrazine est plus rapide dans les sols à haute teneur en matière organique. Les substances humiques catalyseraient l'hydroxylation par leur propriété acide , plus précisément par l'intermédiaire de centres actifs constitués par des groupes carboxyliques (Maslennikova et Kruglov, 1975 (Armstrong et al., 1967). ...
L'objectif de ce travail était de comparer la mobilité de l'atrazine et de la terbuthylazine dans trois types de sol : un sol brun calcique, un sol brun calcaire et un pélosol, et d'évaluer les risques de contamination des nappes phréatiques par ces xénobiotiques. Des études d'adsorption et de désorption en batch ont été menées au laboratoire. Les résultats ont montré que les trois sols possèdent une affinité plus élevée pour la terbuthylazine que pour l'atrazine. 1\ n'a pas été observé de relation entre l'adsorption et le taux d'argile. L'adsorption de ces triazines augmente non seulement avec la teneur en carbone organique, mais aussi avec le degré d'humification et de polymérisation de la matière organique des sols. Des incubations en conditions contrôlées au laboratoire ont montré une biodégradation plus rapide de l'atrazine par rapport à la terbuthylazine, et une formation de résidus "non extractibles" plus importante dans le cas de la terbuthylazine, 38% contre 22% pour l'atrazine. Des expériences ont été conduites en colonne de laboratoire avec des sols reconstitués afin d'apprécier les possibilités de lessivage des deux triazines. Les profils de distribution des deux herbicides montrent que les quantités d'atrazine désorbées en surface se redistribuent plus profondément que pour la terbuthylazine. De plus, la vitesse de migration des deux triazines est plus élevée dans le sol brun calcique que dans les deux autres sols. Parallèlement à ces modèles de laboratoire, la mise en place de Iysimètres en plein champ a permis d'étudier, sous conditions naturelles, les différences de comportement de l'atrazine dans les trois sols. La persistance de l'atrazine est alors deux à trois fois supérieure à celle estimée au laboratoire. Par ailleurs, les résultats indiquent une migration plus importante des résidus s-triaziniques dans le sol brun calcaire par rapport aux deux autres sols. Ainsi, les pertes par lessivage sont de 3,3% de la quantité d'atrazine appliquée pour le sol brun calcaire, contre 1,1 % pour le pélosol et 0,9% dans le sol brun calcique.
... Atrazine metabolites produced by N-dealkylation reactions (i.e., DEA and DIA) are considered products of biodegradation [47], and the half-life of atrazine under field conditions is about 26 days [41]. In contrast, the dechlorination reaction of atrazine (i.e., OH-ATZ metabolite) can be either abiotic or biotic, with the former (via hydrolysis) being widely accepted [47,48]. Hydrolysis of atrazine is governed by pH; under acidic and alkaline conditions, hydrolysis of atrazine increases [48]. ...
... In contrast, the dechlorination reaction of atrazine (i.e., OH-ATZ metabolite) can be either abiotic or biotic, with the former (via hydrolysis) being widely accepted [47,48]. Hydrolysis of atrazine is governed by pH; under acidic and alkaline conditions, hydrolysis of atrazine increases [48]. Atrazine binds to soil particles (i.e., particulate soil-bound atrazine); however, in this study, only the dissolved form of atrazine was quantified. ...
Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the removal of sediment and particulate phosphorus (P) through an aggregate bed. However, conventional limestone used in blind inlets does not remove dissolved P, which is a stronger eutrophication agent than particulate P. Steel slag has been suggested as an alternative to limestone in blind inlets for removing dissolved P. The objectives of this study were to construct a blind inlet with steel slag and evaluate its ability to remove dissolved P, nitrogen (N), and herbicides. A blind inlet was constructed with steel slag in late 2015; data from only 2018 are reported due to inflow sampling issues. The blind inlet removed at least 45% of the dissolved P load and was still effective after three years. The dissolved P removal efficiency was greater with higher inflow P concentrations. More than 70% of glyphosate and its metabolite, and dicamba were removed. Total N was removed in the form of organic N and ammonium, although N cycling processes within the blind inlet appeared to produce nitrate. Higher dissolved atrazine and organic carbon loads were measured in outflow than inflow, likely due to the deposition of sediment-bound particulate forms not measured in inflow, which then solubilized with time. At a cost similar to local aggregate, steel slag in blind inlets represents a simple update for improving dissolved P removal.
... had more influence on atrazine degradation compared to previously reported impacts of soil organic matter content (Gavrilescu, 2005). Increasing soil pH increased the concentrations of atrazine metabolites, which may be due to hydrolysis of atrazine (Armstrong et al., 1967). Li et al. (2021b) further compared the adsorption processes of atrazine in neutral and acidic soils, showing that atrazine tended to be protonated to the cationic form that has a greater affinity to negatively charged colloids in soils when the soil pH is decreased. ...
Diffusive gradient in thin films (DGT) for organics has received considerable attention for studying the chemical dynamics of various organic pollutants in the environment. This review investigates current limitations of DGT for organics and identifies several research gaps for future studies. The application of a protective outer filter membrane has been recommended for most DGT applications, however, important questions regarding longer lag times due to significant interaction or adsorption of specific groups of compounds on the outer membrane remain. A modified DGT configuration has been developed that uses the diffusive gel as the outer membrane without the use of an extra filter membrane, however use of this configuration, while largely successful, remains limited. Biofouling has been a concern when using DGT for metals; however, effect on the performance of DGT for organics needs to be systemically studied. Storage stability of compounds on intact DGT samplers has been assessed in select studies and that data is synthesized here. DGT has been used to describe the kinetic desorption of antibiotics from soils and biosolids based on the soil/biosolid physical-chemical characteristics, yet applications remain limited and requires further research before wide-scale adoption is recommended. Finally, DGT for organics has been rarely, albeit successfully, combined with bioassays as well as in vivo bioaccumulation studies in zebrafish. Studies using DGT combined with bioassays to predict the adverse effects of environmental mixtures on aquatic or terrestrial biota are discussed here and should be considered for future research.
... A previous study has shown that heavy metals have a tendency to catalyze the photodegradation of pesticides in pure water systems, similar to our experimental conditions (Liu et al. 2007). In addition, the rate of ATZ hydrolysis depends largely on the pH environment, and rapid hydrolysis occurs under highly acidic or alkaline conditions (Armstrong et al. 1967). It has also been reported that pH is the most significant environmental factor that may be related to the degradation pattern of pesticides (Fang et al. 2019), and the degradation efficiency of ATZ is favorable at a lower pH (Kong et al. 2016). ...
To understand the influence of Cd on atrazine (ATZ) degradation in aqueous solution, the degradation of different initial levels of ATZ (0.1, 0.5, 1.0, and 2.0 mg·L⁻¹) was investigated in the presence and absence of Cd²⁺ in a 20-day laboratory experiment. It was found that Cd²⁺ caused a significant decrease in ATZ degradation and increased its half-life from 17–34 days to 30–57 days (p < 0.0001). Regarding the three most common metabolites of ATZ, deethylatrazine (DEA) and deisopropylatrazine (DIA) were detected in water earlier than hydroxyatrazine (HYA). The DEA content was several times higher than the DIA and HYA contents, regardless of the presence or absence of Cd²⁺. In the presence of Cd²⁺, the DIA content was significantly lower and the HYA content was significantly higher. Furthermore, Cd²⁺ had a dose-dependent effect on HYA formation. Our results indicated that the coexistence of Cd²⁺ and ATZ resulted in greater herbicide persistence, thereby possibly increasing the risk of environmental contamination. DEA was still the predominant ATZ degradation product detected in water under the combined pollution, which was similar to the ATZ tendency.
... and run-off during irrigation (Rothstein et al. 1996;Shipitalo and Owens 2003), it is detected above the permissible limits i.e. 2 μg L −1 in ground and drinking water (WHO 2003;de Albuquerque Arraes, de SáBarreto and de Araújo 2008). The reported half-life of atrazine varies from 10-109 days in soil (Armstrong, Chesters and Harris 1967;ATSDR 2003). Atrazine may undergo abiotic hydrolysis to hydroxyatrazine under acidic condition (Mandelbaum, Wackett and Allan 1993;WHO 2003) or get converted into hydroxyatrazine, deethylatrazine or deisopropylatrazine by soil microorganisms (Fig. 1;Geller 1980). ...
Soil isolate Pseudomonas sp. strain AKN5 degrades atrazine as the sole source of nitrogen. The strain showed expeditious growth on medium containing citrate as the carbon source and ammonium chloride as the nitrogen source as compared to citrate plus atrazine or cyanuric acid. Biochemical and nitrogen-source-dependent enzyme induction studies revealed that atrazine is metabolized through hydrolytic pathway and has two segments: the upper segment converts atrazine into cyanuric acid while the lower segment metabolizes cyanuric acid to CO2 and ammonia. Bioinformatics and co-transcriptional analyses suggest that atzA, atzB and atzC were transcribed as three independent transcripts while atzDEF were found to be transcribed as a single polycistronic mRNA indicating operonic arrangement. Transcriptional analysis showed inducible expression of atzA/B/C/DEF from atrazine grown cells while cyanuric acid grown cells showed significantly higher expression of atzDEF. Interestingly, growth profiles and enzyme activity measurements suggests that strain utilizes a simple nitrogen source (ammonium chloride) over the complex (atrazine or cyanuric acid) when grown on dual nitrogen source. These results suggest that atrazine degradation genes were up-regulated in the presence of atrazine but repressed in the presence of simple nitrogen source like ammonium chloride.
... L'atrazine est une molécule emblématique de cette famille chimique, fréquemment retrouvées dans les cours d'eau européens (Loos et al., 2013). La Jalle de Blanquefort ne fait pas exception et présente une contamination de 1,2 ± 0,8 ng.L -1 , associée à son produit de transformation dans les sols : l'hydroxyatrazine (Armstrong et al., 1967;Radosevich et al., 1995), retrouvée à 29,4 ± 25,8 ng.L -1 . De même l'acétochlore ESA, quantifié à des concentrations moyennes de 26,6 ± 18,3 ng.L -1 , est un des produits de transformation de l'herbicide acétochlore interdit depuis 2011 dans l'ensemble de l'Union Européenne en raison de son écotoxicité . ...
L’augmentation globale de la démographie couplée à une amélioration du niveau de vie conduit à l’augmentation de la pression anthropique pesant sur les ressources en eau. Cette pression passe entre autre par une consommation et donc un rejet de multiples molécules organiques, parmi lesquelles les pesticides représentent des contaminants emblématiques. Longtemps utilisés en agriculture afin d’en augmenter la productivité, ces substances sont aujourd’hui utilisées également de façon importante dans notre quotidien (traitements vétérinaires, protection des matériaux de construction, peintures, papier, textiles, etc.). Cela conduit à identifier les rejets urbains comme des vecteurs de pesticides au travers des effluents de station de traitement des eaux usées ou des effluents d’exutoires pluviaux, qui viennent s’ajouter aux apports induits par l’agriculture. Cette multiplicité de sources couplée à une toxicité intrinsèque avérée en font des molécules à fort enjeu environnemental dont il est essentiel de hiérarchiser les apports afin de pouvoir mettre en place des mesures de réduction.Dans ce cadre, un continuum péri-urbain situé sur la Métropole de Bordeaux (France) a permis de mettre en évidence des profils de contamination différents entre les eaux naturelles, les effluents urbains et les exutoires pluviaux, tant sur l’aspect qualitatif que sur l’aspect quantitatif. Si les eaux de surface sont principalement quantitativement marquées par des phytopharmaceutiques (métolachlore, glyphosate), les molécules identifiées comme potentiellement impactantes (en termes d’effets potentiels) proviennent d’avantage d’effluents urbains (fipronil, imidaclopride). En effet, les stations de traitement des eaux usées sont identifiées comme d’importants vecteurs en biocides et antiparasitaires à usages vétérinaires en raison de leur faible capacité de traitement vis-à-vis de ces contaminants. Toutefois, ces effluents ne sont que le reflet des utilisations en amont du réseau. L’investigation de ce dernier a conduit à identifier les usages domestiques comme responsables de l’introduction de certaines molécules préoccupantes tels les antiparasitaires à usages vétérinaires (fipronil et imidaclopride). En parallèle, bien que non majoritaires en ce qui concerne les apports en pesticides, les exutoires pluviaux ne sont toutefois pas négligeables et apportent en quantités conséquentes des biocides de protection (comme la carbendazime, le diuron, le propiconazole ou la terbutryne) de par le lessivage de surfaces traitées en zones urbaines. Le cas du glyphosate semble complexe puisque aucune des voie d’apport n’est clairement identifiée comme majoritaire. L’apport est très global, probablement du fait de sa multiplicité d’usages, tant en agriculture que par certains professionnels ou par les particuliers.L’échantillonnage passif par les POCIS (Polar Organic Chemicals Integrative Sampler) a été appliqué avec succès afin de calculer des flux plus précis dans les eaux de surfaces, permettant ainsi une identification plus fine des sources majoritaires. Cet outil montre toutefois ses limites en ce qui concerne le suivi d’échantillons complexes telles que les eaux brutes, en présentant des cinétiques d’accumulation trop courtes pour permettre un suivi quantitatif du réseau d’assainissement sur de longues périodes. Ces observations ont été confirmées à l’occasion de calibrations in-situ en rivière et en entrée de station de traitement des eaux usées et qui ont donné lieu au développement de nouveaux outils. Les mini-POCIS et les POCIS-T, plus légers et plus petits ont été calibrés à la fois en laboratoire et en station de traitement des eaux usées. Ils se sont révélés plus adaptés que la forme classique pour suivre la contamination des eaux usées car ils permettent d’augmenter la durée du suivi. Ils représentent une alternative intéressante pour le suivi du réseau d’assainissement.
... Simazine remains stable in neutral pH range, but becomes unstable under extremely acidic or alkaline conditions. Simazine has been known to undergo hydrolytic dechlorination due to protonation of lone-pair electrons on the N atom in the aromatic ring structure and subsequent cleavage of C-Cl bond due to electron deficiency under acidic conditions and to the direct nucleophilic substitution of Cl by OH under alkaline conditions [69,70]. ...
Biochar has received considerable attention as an eco-friendly bio-sorbent; however, multifarious characteristics caused by pyrolysis and feedstock pose difficulties in its application. We characterized the pH-dependent sorption of the pesticide simazine on Miscanthus biochar produced at two pyrolysis temperatures (400 and 700 oC; hereafter B-400 and B-700). The specific surface-area (SSA) of the micro- and nanopores, elemental composition, surface acidity and infrared spectra were determined. The SSA was greater in B-700 than in B-400, and the former had greater SSA in micro-pores and lower SSA in nanopores than the latter. During pyrolysis, the single-bond structures of the feedstock were converted to aromatic structures, and further pyrolysis led to ligneous structures. Alterations in pore structure and concave-up Scatchard plot corroborated the presence of two sorption mechanisms: electrostatic attractions (Ses ) and hydrophobic attractions (Shp ). Decreases in maximum sorption in the qmax-L with increasing pH was due to decreased Ses via deprotonation of carboxylic groups on biochar, while those in the qmax-H with increasing pyrolysis temperature were due to decreased Shp , resulting from pore structure deformation. We believe that our approach, which addresses the pH-dependence of charge density of sorbate and sorbent, could contribute to a better understanding of the behavior of simazine.
... (3) formation de produits de transformation qui peuvent être ultérieurement dégradés de façon biologique (Parochetti, 1978). (Armstrong et al., 1987). ...
La contamination des ressources en eau par les pesticides dépend de leur transfert dans le sol. L'objectif de notre étude est de préciser et de comprendre l'influence conjointe de l'eau (humidité et dynamique dans le sol) et du temps, sur le transfert vertical des pesticides dans les sols. Trois niveaux d'investigation ont été adoptés : une étude de la mobilité d'un pesticide (isoproturon) et d'un traceur de l'eau (bromure) en cases lysimétriques, des simulations de ces transferts par le modèle Agriflux et une caractérisation de la dissipation de pesticides (isoproturon, bentazone) au laboratoire. A l'échelle du profil de sol, le suivi des quantités d'isoproturon et de bromure exportées par percolation a mis en évidence une variabilité corrélée à la différence de fonctionnement hydrodynamique des sols. Une hétérogénéité entre les répétitions de sol a également été observée. La simulation avec Agriflux a fourni des résultats cohérents avec les observations de terrain. L'utilisation du modèle a par ailleurs souligné l'importance des processus lents d'adsorption/désorption sur la disponibilité du pesticide au transfert dans l'eau mobile. Les expérimentations en laboratoire ont permis de montrer successivement : la relation entre l'humidité du sol au moment du traitement et la mobilité du pesticide ; puis l'entraînement par diffusion dans l'eau immobile intra-agrégat des molécules étudiées ; et enfin, l'effet du temps de résidence sur leur immobilisation croissante
... The persistence of chlorimuron-ethyl increases with increasing pH. Atrazine is almost non-volatile and its half-life in soil, water, and sediments ranges from few weeks to more than 2 years depending on various environmental factors like pH, moisture content, temperature and soil humus and clay minerals [14][15][16][17]. Hydrolysis of atrazine is rapid under acidic or basic conditions but is slower at neutral pHs [18]. ...
Chlorimuron-ethyl and atrazine are two herbicides with long half-lives in soil; their long-term and excessive application has led to a series of environmental problems. In this study, the strains Chenggangzhangella methanolivorans CHL1 and Arthrobacter sp. ART1 were combined and used for the remediation of chlorimuron-ethyl, atrazine and combined contaminated soils in a microcosm experiment. Changes in chlorimuron-ethyl and atrazine concentrations in soils were monitored, and variations in the soil microbial community were studied by phospholipid fatty acid (PLFA) analysis. The two inoculated degrading strains accelerated the degradation of chlorimuron-ethyl and atrazine in soil, especially in the combined contaminated soil. Addition of the two herbicides and their combination generally decreased the concentrations of total PLFAs, total bacterial PLFAs, Gram-negative and Gram-positive bacterial PLFAs and Shannon-Wiener indices, and changed microbial community composition, whilst stimulating fungal PLFA concentrations. In addition, the combined herbicide treatment had more impact on microbial biomass than the single herbicide treatments. Inoculation treatments significantly relieved the effects of herbicides on soil microbial biomass, diversity and community structure. This study demonstrated that strains CHL1 and ATR1 have the potential to remediate chlorimuron-ethyl, atrazine and combined contaminated soils, and provided valuable information for remediation of chlorimuron-ethyl, atrazine and combined contaminated soils in situ.
... The highest concentration of HA-ATR was detected in pol-MERC-treated soil, after 20 days of incubation. Interestingly, HA-ATR formation was associated with anaerobic or oxygen-limited conditions, like those found in flooded soil (Armstrong et al., 1967). Chung et al. (1996) reported a linear isotherm study where HA-ATR showed sixfold higher adsorption to soil than ATR did (Chung et al., 1996). ...
The absence of suitable terminal electron acceptors (TEA) in soil might limit the oxidative metabolism of environmental microbial populations. Bioelectroventing is a bioelectrochemical strategy that aims to enhance the biodegradation of a pollutant in the environment by overcoming the electron acceptor limitation and maximizing metabolic oxidation. Microbial electroremediating cells (MERCs) are devices that can perform such a bioelectroventing. We also report an overall profile of the (14) C-ATR metabolites and (14) C mass balance in response to the different treatments. The objective of this work was to use MERC principles, under different configurations, to stimulate soil bacteria to achieve the complete biodegradation of the herbicide (14) C-atrazine (ATR) to (14) CO2 in soils. Our study concludes that using electrodes at a positive potential [+600 mV (versus Ag/AgCl)] ATR mineralization was enhanced by 20-fold when compared to natural attenuation in electrode-free controls. Furthermore, ecotoxicological analysis of the soil after the bioelectroventing treatment revealed an effective clean-up in < 20 days. The impact of electrodes on soil bioremediation suggests a promising future for this emerging environmental technology.
... Microbes present in the soil have the ability to degrade chemical compounds, but sometimes (due to environmental factors), the rate of degradation process decreases or sometimes does not take place at all. [26][27][28] These chemicals can be the chlorinated aromatic herbicides (triazine) and pesticides used in the agricultural field or for gardening. They have ability to persist in the soil for very long time, and many of them have half-life in years and vary according to the environmental conditions. ...
Any foreign chemical substance that is unusually present within an organism or is unexpectedly found in the environment at a higher concentration than the permissible limits can be termed a xenobiotic or a pollutant. Such substances include carcinogens, drugs, food additives, hydrocarbons, dioxins, polychlorinated biphenyls, pesticides or even some natural compounds. Pollutants are known for their higher persistence and pervasiveness, and along with their transformed products, they can remain in and interact with the environment for prolonged periods. In this article, the classification of such substances based on their nature, use, physical state, pathophysiological effects, and sources is discussed. The effects of pollutants on the environment, their biotransformation in terms of bioaccumulation, and the different types of remediation such as in situ and ex situ remediation, are also presented.
... Microbial metabolism is one of the most recognised mechanisms for degradation of xenobiotic compounds in soil (Armstrong et al. 1967;Häggblom 1992). However, it may become compromised under low moisture and nutrient conditions, where the persistence of triazines and other xenobiotic compound may increase (Yadav and Loper 2000). ...
Any substance foreign to a biological system is known as xenobiotic compound. The manufacturing and processing of xenobiotic chemicals on the large scale have led to serious surface and subsurface soil contamination. Biotransformation
of the hazardous pollutants to less toxic substances or their complete mineralization represents an economical substitute to clean up soil and water. In principle, fungi by virtue of their enzymes can biodegrade any naturally existing biopolymers and some of the synthetic polymers as well. Degradation of polymers largely depends on the fungal extracellular enzymes, namely, oxidoreductases and hydrolases. White-rot ligninolytic fungal strains such as T. versicolor and P. ostreatus have been recognized to be the major decomposers of biopolymers via laccase-mediated transformation. Moreover, the ligninolytic fungal strains carrying enzyme Mn-peroxidase activity demonstrated the maximum degradation of naphthalene (69 %). Many non-ligninolytic species degrade polycyclic aromatic hydrocarbons (PAHs) via cytochrome P450 monooxygenase and epoxide hydrolase-catalyzed reactions to form transdihydrodiols. Remediation of nitro-aromatics along with their recalcitrant carcinogenic intermediates, possessing the worst degree of toxicity hazardous rating 3, has been described by utilizing fungal species such as Phanerochaete chrysosporium or Pseudomonas sp. ST53. Additionally, white-rot fungi possessing oxidative enzymes have the ability of TNT degradation and mineralization to CO2. On the other hand, fungal laccases have been reported to catalyze the transformation of the model endocrine disruptors, alkylphenols and biphenyls. For instance, T. versicolor catalyzed the partial transformation of nonylphenol into carbon dioxide. Discovering the new beneficial fungal strains in addition to isolation, engineering, and sequencing of new useful enzymes is highly desirable to further strengthen the biodegradation of contaminated soil.
... Microbial metabolism is one of the most recognised mechanisms for degradation of xenobiotic compounds in soil (Armstrong et al. 1967;Häggblom 1992). However, it may become compromised under low moisture and nutrient conditions, where the persistence of triazines and other xenobiotic compound may increase (Yadav and Loper 2000). ...
The different xenobiotic compounds, such as insecticides, fungicides, herbicides, chlorinated derivatives and polycyclic aromatic hydrocarbons (PAHs), which are widely used in agricultural activities for increased crop production and other human benefits, can enter the soil and water environments and cause significant toxic impacts on the soil health, microorganisms, ecosystem, human health and environmental quality. The application of biochar to soil can improve soil health and fertility, soil organic matter, nutrient content, pH and soil water retention and aggregation, but reduce soil greenhouse gas emissions, soil bulk density, erosion potential and leaching of pesticides and nutrients to surface and groundwater and mitigate climate change impacts. The biochar has high potential to remediate the soils contaminated by xenobiotic compounds reducing their mobility and bioavailability in soil. This book chapter has reviewed (1) biochar production properties and their effects on soil fertility, physical, chemical and biological properties; (2) the fate and behaviour of xenobiotics in soil, illustrating their interaction with soil constituents and uptake by plants; and (3) the remediation techniques to reduce mobility and bioavailability of the xenobiotic compounds through biochar application to soil. Depending on the type, amount of biochar applied and the physicochemical properties of the biochar itself, it may change the soil properties as well as impact the use, rates, efficacious properties and fates of xenobiotic compounds used in agronomic management. The effects of biochar on the fate and mobility of xenobiotic compounds in soil ecosystems depend on the soil types and properties. Since biochars contain colloidal-sized particles that move through soil pore water flows, colloid-facilitated transport could actually enhance mobility and leaching of xenobiotic compounds in the presence of biochar. Increased sorption to soils and recalcitrance of pesticides leading to longer residence times in the environment is desirable if bioactivity is still acceptable, and it controls the target pest. However, longer residence time may also create some environmental problems, such as greater leaching potential or carry-over problems into the following season.
Background
Bacterial community found in biodynamic preparations (BD500–BD507) can help improve soil health, plant development, yield, and quality. The current work describes a metagenomic investigation of these preparations to identify the bacterial communities along with the functional diversity present within them.
Results
Metagenome sequencing was performed using the Illumina MiSeq platform, which employs next-generation sequencing (NGS) technology, to provide an understanding of the bacterial communities and their functional diversity in BD preparations. NGS data of BD preparations revealed that maximum operational taxonomic units (OTUs) of the phylum Proteobacteria were present in BD506 (23429) followed by BD505 (22712) and BD501 (21591), respectively. Moreover, unclassified phylum (16657) and genus (16657) were also highest in BD506. Maximum alpha diversity was reported in BD501 (1095 OTU) and minimum in BD507 (257 OTU). Further, the OTUs for five major metabolic functional groups viz carbohydrate metabolism, xenobiotic degradation, membrane transport functions, energy metabolism, and enzyme activities were abundant in BD506 and BD501.
Conclusion
The bacterial communities in BD506 and BD501 are found to be unique and rare; they belong to functional categories that are involved in enzyme activity, membrane transport, xenobiotic degradation, and carbohydrate metabolism. These preparations might therefore be thought to be more effective. The investigation also found a highly varied population of bacteria, which could explain why BD preparations work well in the field. In view of this, the BD preparations may be utilized for unexploited bacterial communities for sustainable agriculture production.
“Xenos,” is a Greek word meaning “stranger.” These are some chemical compounds used by mankind for several domestic, agricultural, and industrial purposes; however, they are present as micro-pollutants in the environment, and their impact on the environment as well as on mankind is nonnegotiable because of its toxic effects, limited biodegradation, and prolonged persistence in the environment. Besides, microbial-mediated biodegradation is marked as the most standard way to eradicate these compounds. There is an array of microorganisms, namely, Microbacterium, Micrococcus, Methanospirilium, Flavobacterium, Rhodococcus, Aspergillus, and Penicillum, that show tremendous potential to degrade xenobiotics from polluted natural environment such as soil or water. This chapter provides insights on different types of xenobiotics and the capability of microbes to degrade xenobiotics and its compounds. In addition, this chapter summarizes the advanced techniques, such as omics approaches, to understand their metabolic machinery in the degradation process. The in-depth study of these techniques can also resolve various issues that are arising in the degradation of these xenobiotic compounds.
The Arab Maghreb countries (Morocco, Algeria and Tunisia) are located in a fragile zone, in majority semi-arid or Saharan. One of the priorities of the governments of these countries after their independence was the interest of the agricultural sector to ensure their food. They have devoted their efforts to developing laws, plans (PMV, PNDA and PDAR) and strategies to this end. However, policies were not sufficient to achieve self-sufficiency. Land users were not as up to updates of agricultural development. Using intensive agriculture, this has been accelerating in recent years. Farmers have deeply plowed the land, causing the destruction of the physical and chemical structure of the soil. They irrigated at random crops with systems that save not water, resulting in water depletion, organic and mineral matter, soil degradation and salinity in large areas. Through their excessive use of mineral fertilizers and phytosanitary products, they have caused edaphic, atmospheric and aquatic pollution, including contamination of soils, groundwater and surface water by nitrates and phosphates; thus intoxication and cancerous diseases announced by medical reports and university studies; not to mention the deforestation to carry out certain agricultural or industrial activities, by eliminating the biodiversity of the flora and the fauna, causing a climate change and a complete change of the ecosystem. These problems push the countries of the Arab Maghreb out of the path of sustainable agro-socio-economic development, which produces, preserves the environment and natural wealth for future generations. Although there were tests to mitigate the risks of pollution and climate change, deserves to be expanded and deepened as the sub-projects of integration of climate change in the implementation of the Green Morocco Plan (PICCPMV), the adoption of administrative, legislative and economic provisions for the effective and sustainable management of water resources, including the pricing of irrigation water, and the National Irrigation Program for Water Conservation (PNEEI) and the Council Higher Water and Climate (CSEC) in Morocco. Measures considered in the National Planning and Predicted Contribution (INDC) submitted at COP21 in Tunisia, which provides for the agriculture, forestry and land use sector, a mitigation plan that includes the intensification of CO2 absorption capacities of the forest and arboriculture, thanks to the intensification of reforestation, consolidation and increase of carbon stocks in forest and pastoral environments. An important agricultural heritage peculiar to these countries, it is still cultivated so that the ancestors respects the environment, needs attention and good management to intensify it, as the cultivation of dates, olives, figs, citrus fruits, cocoa and even cereals. Sustainable agriculture requires the organization of these countries: it is necessary to apply on the ground with sincerity the laws of the good management of the water in quantity or quality, either for drinking or for the irrigation of the cultures; cultivate environment-adaptive species in arid zones or climate-sensitive areas; the most important thing is to inform farmers, how to save crop irrigation water by preferably using the drip system, how to limit the use of chemicals (fertilizers and pesticides) by replacing them with organic or natural products, or apply rotations, or select healthy seeds for varieties that are adaptable to the changing environment and resistant to diseases.
Atrazine is a triazine herbicide used predominantly on corn, sorghum, and sugarcane in the US. Its use potentially overlaps with the ranges of listed (threatened and endangered) species. In response to registration review in the context of the Endangered Species Act, we evaluated potential direct and indirect impacts of atrazine on listed species and designated critical habitats. Atrazine has been widely studied, extensive environmental monitoring and toxicity data sets are available, and the spatial and temporal uses on major crops are well characterized. Ranges of listed species are less well-defined, resulting in overly conservative designations of "May Effect". Preferences for habitat and food sources serve to limit exposure among many listed animal species and animals are relatively insensitive. Atrazine does not bioaccumulate, further diminishing exposures among consumers and predators. Because of incomplete exposure pathways, many species can be eliminated from consideration for direct effects. It is toxic to plants, but even sensitive plants tolerate episodic exposures, such as those occurring in flowing waters. Empirical data from long-term monitoring programs and realistic field data on off-target deposition of drift indicate that many other listed species can be removed from consideration because exposures are below conservative toxicity thresholds for direct and indirect effects. Combined with recent mitigation actions by the registrant, this review serves to refine and focus forthcoming listed species assessment efforts for atrazine. Abbreviations: a.i. = Active ingredient (of a pesticide product). AEMP = Atrazine Ecological Monitoring Program. AIMS = Avian Incident Monitoring SystemArach. = Arachnid (spiders and mites). AUC = Area Under the Curve. BE = Biological Evaluation (of potential effects on listed species). BO = Biological Opinion (conclusion of the consultation between USEPA and the Services with respect to potential effects in listed species). CASM = Comprehensive Aquatic System Model. CDL = Crop Data LayerCN = field Curve Number. CRP = Conservation Reserve Program (lands). CTA = Conditioned Taste Avoidance. DAC = Diaminochlorotriazine (a metabolite of atrazine, also known by the acronym DACT). DER = Data Evaluation Record. EC25 = Concentration causing a specified effect in 25% of the tested organisms. EC50 = Concentration causing a specified effect in 50% of the tested organisms. EC50 RGR = Concentration causing a 50% reduction in relative growth rate. ECOS = Environmental Conservation Online System. EDD = Estimated Daily Dose. EEC = Expected Environmental Concentration. EFED = Environmental Fate and Effects Division (of the USEPA).
The effects of Fe(III) and Cu(II) on the sorption of atrazine (AT) and prometryn (PY) on clay minerals were investigated both preloaded and in solution. For smectite, Fe(III) preloading greatly enhanced AT and PY sorption at pH 4.0 and 6.0 but diminished AT sorption at pH 8.0. Cu(II) preloading promoted AT and PY sorption under alkaline conditions but suppressed AT sorption at pH 4.0. The adverse effects were not obvious for PY. While for illite and kaolinite, Fe(III) and Cu(II) had little or promotion effects due to the lower contents of them in these two minerals. In the co-sorption studies, for smectite, AT sorption remained at pH 4.0 and increased at pH 6.0 and 8.0, while PY sorption was inhabited over the pH range of 4.0-8.0 in the presence of Fe(III). AT and PY sorption were not affected by Cu(II) except for PY at pH 8.0, in which case, the sorption was promoted. For illite and kaolinite, Fe(III) and Cu(II) generally enhanced AT and PY sorption.
17 pages de références bibliographiques et 20 pages d'annexes
The synthetic s-triazines are abundant, nitrogen-rich, heteroaromatic compounds used in a multitude of applications including, herbicides, plastics and polymers, and explosives. Their presence in the environment has led to the evolution of bacterial catabolic pathways in bacteria that allow use of these anthropogenic chemicals as a nitrogen source that supports growth. Herbicidal s-triazines have been used since the mid-twentieth century and are among the most heavily used herbicides in the world, despite being withdrawn from use in some areas due to concern about their safety and environmental impact. Bacterial catabolism of the herbicidal s-triazines has been studied extensively. Pseudomonas sp. strain ADP, which was isolated more than thirty years after the introduction of the s-triazine herbicides, has been the model system for most of these studies; however, several alternative catabolic pathways have also been identified. Over the last five years, considerable detail about the molecular mode of action of the s-triazine catabolic enzymes has been uncovered through acquisition of their atomic structures. These structural studies have also revealed insights into the evolutionary origins of this newly acquired metabolic capability. In addition, s-triazine-catabolizing bacteria and enzymes have been used in a range of applications, including bioremediation of herbicides and cyanuric acid, introducing metabolic resistance to plants, and as a novel selectable marker in fermentation organisms. In this review, we cover the discovery and characterization of bacterial strains, metabolic pathways and enzymes that catabolize the s-triazines. We also consider the evolution of these new enzymes and pathways and discuss the practical applications that have been considered for these bacteria and enzymes. One Sentence Summary: A detailed understanding of bacterial herbicide catabolic enzymes and pathways offer new evolutionary insights and novel applied tools.
Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triaazine] diffused at a rate of 15.2 × 10 ⁻⁸ sq cm/sec at 25 C which was faster than the diffusion rate of 2-chloro-4,6-bis(ethylamino)- s -triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)- s -triazine (propazine) in the same soils. Diffusion rates were highly correlated with total surface area of the soil. Increasing soil moisture content, soil pH, and soil temperature resulted in greater diffusion rates. A relative indication of herbicide mobility may be obtained from some of the physical and chemical properties of the soils and herbicides involved; however, rate of diffusion appears to be governed by a combination of soil and herbicide properties.
The persistence of 2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine (atrazine) residues under greenhouse conditions was affected by levels of activated carbon added to a silica sand potting medium and by up to four consecutive crops of corn ( Zea mays L.). Degradation of atrazine within the sand and removal by the corn crops were both reduced by activated carbon. Atrazine removal by successive crops of corn reduced injury to oat seedlings grown on the sand alone, and absorption by 1.2 g of carbon per kilogram of sand prevented oat injury both with and without cropping. Although 0.4 g/kg of activated carbon inhibited atrazine removal by corn, oat seedlings were not protected from the residues remaining. When exposed to alternate freezing and thawing, the ability of 0.4 g/kg of activated carbon to deactivate atrazine was reduced causing increased oat injury.
Field studies indicated that liming an acid Bladen silt loam from pH 5.5 to 7.5 increased the phytotoxicity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine] and prometryn [2,4-bis-(isopropylamino)-6-methyoxy- s -triazine]. Liming greatly increased the persistence of atrazine, but did not affect prometryn dissipation. Liming increased the ¹⁴ C-concentration present in the shoots of corn ( Zea Mays L. ‘Pioneer 3369A’), cotton ( Gossypium hirsutum L. ‘Coker 201’), and soybeans [ Glycine Max (L.) Merr. ‘Ransom’] from soil treated with ¹⁴ C-ring labeled atrazine, prometryn, and hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)- s -triazine] in greenhouse studies. Decreases in ¹⁴ C-uptake by the crops were associated with adsorption and degradation of the compounds in the soil. Atrazine was taken up in much greater amounts than hydroxyatrazine. Cotton absorbed less of the s -triazines than soybeans or corn from soil.
The effect of soil pH on the disappearance of ¹⁴ C ring-labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine], hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)- s -triazine], and prometryne [2,4-bis(isopropylamino)-6-(methylthio)- s -triazine] were studied over a 5-month period in a Bladen silt loam soil under greenhouse conditions. Employment of an integrated system allowed simultaneous monitoring of degradation, volatilization, respiration, plant uptake, and leaching processes. A resulting balance-sheet indicated that a range of 87 to 99% of the ¹⁴ C added could be accounted for after 5 months. Degradation was found to be the primary mode of dissipation. The pattern of atrazine degradation was characteristic of nonbiological processes, while prometryne degradation was probably by microbial action. Hydroxyatrazine was the major metabolite from the atrazine treatments while prometryne yielded an unknown and hydroxypropazine [2-hydroxy-4,6-bis(isopropylamino)- s -triazine]. Ex-tractable atrazine after 5 months amounted to 35% of the initial amount added in the pH 7.5 soil and 11% in the pH 5.5 soil, while prometryne occurred as 10% in the pH 7.5 soil and 42% in the pH 5.5 soil. Plant uptake and leaching occurred to a greater extent in the more alkaline soil with each chemical, but these pathways along with volatilization and respiration were minor contributors toward the disappearance of these herbicides.
Greenhouse studies were conducted to investigate the basis for effective field control of yellow nutsedge (Cyperus esculentus L. var. esculentus) when atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -trizine] was applied late postemergence. Yellow nutsedge responded similarly to atrazine applied preemergence, early postemergence, or late postemergence. Yellow nutsedge growing with or without the presence of the mother tuber responded similarly to atrazine applied early postemergence. Atrazine application to the soil resulted in much greater yellow nutsedge injury than foliar application. The addition of oil enhanced atrazine activity when foliarly applied, but not when soil applied. Simulated rainfall immediately after postemergence applications enhanced yellow nutsedge control more than when simulated rainfall was delayed. The primary roots of yellow nutsedge appeared to be more important than other underground absorbing areas for atrazine uptake in young plants. Plants from tubers originating from lower soil depths produced secondary roots deeper, and these plants were less affected by atrazine applied preemergence than plants originating from tubers closer to the soil surface. A considerable reduction in atrazine activity was obtained when tubers were planted into soil 1 month after atrazine application.
Field studies on the persistence of simazine [2-chloro-4,6-bis(ethylamino)- s -triazine] showed less persistence under no-tillage corn (Zea mays L. ‘Pioneer 3369A’) culture than conventionally tilled corn. Bioassay studies conducted in the greenhouse using oats (Avena sativa L. ‘Compact’) as indicator crop showed the lowest level of simazine remaining in soils of low pH (5.4 and lower). Persistence of simazine in the soil increased with increasing soil pH.
Field studies and laboratory analyses were conducted to examine factors affecting degradation of ¹⁴ C-atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)- s -triazine] under field conditions. The effects of these factors on weed control under no-tillage and conventional tillage systems were also examined. The amount of radioactivity which was unextractable in 90% methanol increased with time following treatment with ¹⁴ C-atrazine. The rate of formation of unextractable ¹⁴ C compounds was greater under no-tillage and increased with decreasing pH. After 14 to 18 days, a greater amount of extractable atrazine was present in areas receiving lime. The degradation of atrazine occurred more rapidly when surface pH was less than 5.0 compared with a pH greater than 6.5. The effect of lime on the amount of parent atrazine present in the soil was directly correlated to its effect on soil pH. Extractable atrazine in the soil 45 days after treatment was significantly correlated with weed control with the greatest effect under no-tillage.
Atrazine [2-chloro-4-(ethylamino)-6-isopropylamino)- s -triazine] carryover under reduced or no-till row crop production systems was measured by planting oats ( Avena sativa L.) the following year as a field bioassay during 1970 through 1976 at Lincoln and North Platte, Nebraska. Oat yields indicate that soil persistence of normal-use rates of atrazine into the subsequent year is only a minor residue problem under reduced tillage cropping systems. Atrazine carryover in soil was less of a problem under these reduced tillage systems as compared with prior experiments with conventional tillage systems across Nebraska.
Field studies were conducted to determine the effect of soil surface (upper 5 cm) pH and tillage on weed control and corn ( Zea mays L.) yield using simazine [2-chloro-4,6-bis-(ethylamino)- s -triazine] as the herbicide for weed control. Soil pH, weed control, and corn yield were examined under no-tillage and conventional tillage systems with and without added lime and different rates of nitrogen. Increased soil pH significantly increased weed control as compared with added lime vs. no added lime, where the surface soil pH influenced the effectiveness of the applied simazine. Soil pH had a greater effect on weed control under no-tillage than under conventional tillage. Conventional tillage significantly (P<.01) increased weed control, yield, and soil pH over no-tillage. Additions of lime as compared to unlimed treatments resulted in significantly increased weed control (83% vs. 63%), yield (5,930 vs. 5,290 kg/ha) and soil pH (5.91 vs. 5.22). The poorest weed control was observed with no-tillage on unlimed plots. A significant tillage by linear effect of nitrogen interaction for all variables resulted from a greater decrease (P<.01) in weed control and soil pH and a greater increase in yield with increased nitrogen under no-tillage than with conventional tillage.
Efficacy of atrazine [2-chloro-4-(ethylamino-6-(isopropylamino)- s -triazine] applied preemergence to no-tillage and conventional-tillage corn ( Zea mays L.) was studied in the field for 2 yr at two locations. Other variables examined were lime treatments, atrazine rates, and acid-forming (NH 4 NO 3 ) vs. nonacid-forming (NaNO 3 ) nitrogen fertilizers. Mean surface soil pH levels during the growing season were higher with no-tillage than conventional tillage, because of the retention of lime in the surface in no-tillage vs. mixing it with the soil in conventional tillage, but there was no consistent increase in atrazine efficacy or longevity in one system over the other. Liming significantly increased atrazine efficacy and longevity in both no-tillage and conventional-tillage systems. Increased rates of atrazine increased weed control and longevity of the herbicide. Use of NaNO 3 as a nitrogen source resulted in increased atrazine efficacy and longevity as compared with use of NH 4 NO 3 during the first year, which was relatively dry, but had no effect during the second year, which was relatively wet.
Much of the success of modern agriculture is due to pesticide technology. Because weeds pose the greatest threat to crop yields, the largest class of pesticides used today is herbicides. Herbicides include products whose active ingredients represent a wide range of chemical families; yet most constitute a minimal potential hazard to man and the environment. Criteria typically used to determine potential hazard are mammalian and piscine toxicity, persistence, and bioaccumulation. By evaluating these criteria and assigning numerical values it is possible to devise a ranking of pesticides such as that developed by Weber (51). This list identifies those pesticides most likely to have some undesirable activity, either before or after they are applied. All herbicides ranked well below organochlorine insecticides in hazard rating and most were less hazardous than the organophosphate and carbamate insecticides. However, any substance, when used improperly, has the potential to cause problems, and for this reason all chemicals should be handled with caution.
Broadcast applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1 H ,3 H )-dione] pellets and foliar sprays were tested at four rates for hardwood control and safety to loblolly pine ( Pinus taeda L.) at each of eight study locations differing in soil characteristics. Reduction in the number of hardwoods in the stand (hardwood density reduction) was greater with the pellet on soils with more than 60% sand, while the liquid formulation was most efficacious for finely textured soils. Hardwood density reduction with the pellet was negatively correlated with percent silt, clay, soil organic matter, and cation exchange capacity, and positively correlated with percent sand. With foliar sprays, hardwood density reduction was positively correlated with hexazinone rate and negatively correlated with soil pH. Pine mortality was positively correlated to percent sand with the pellet and negatively correlated to soil pH with broadcast sprays. Regression models incorporating pine height, herbicide rate, soil texture, cation exchange capacity, soil organic matter, and acidity could explain up to 78% of the variation in hardwood density change and 77% of the variation in pine mortality. Selective control of hardwoods in young loblolly pine stands is a function of hexazinone rate, formulation, and various soil factors.
It is essential to monitor pesticides in the environment to help ensure water and soil quality. The diffusive gradients in thin-films (DGT) technique can measure quantitative in-situ labile (available) concentrations of chemicals in water, soil and sediments. This study describes the systematic development of the DGT technique for 9 current pesticides, selected to be representative of different classes with a wide range of properties, with two types of resins (HLB (hydrophilic-lipophilic-balanced) and XAD 18) as binding layer materials. The masses of pesticides accumulated by DGT devices were proportional to the deployment time and in inverse proportion to the thickness of the diffusive layer, in line with DGT theoretical predictions. DGT with both resin gels were tested in the laboratory for the effects of typical environmental factors on the DGT measurements. DGT performance was independent of: pH in the range of 4.7 - 8.2; dissolved organic matter concentrations <20 mg L-1; and ionic strength from 0.01 to 0.25 M, although it was slightly affected at 0.5 M in some cases. This confirms DGT as a sampler suitable for controlled studies of environmental processes affecting pesticides. Field applications of DGT to measure pesticides in situ in waters and controlled laboratory measurements on five different soils (prepared at fixed soil:water ratios) demonstrated DGT is a suitable tool for environmental monitoring in waters and for investigating chemical processes in soils.
Field experiments were conducted to examine the effect of tillage on atrazine [6-chloro- N -ethyl- N ′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] persistence in the soil and soybean [ Glycine max (L.) Merr.] injury. Tillage systems evaluated were no-tillage, chisel plowing, and moldboard plowing. Reduced tillage systems, such as no-tillage or chisel plowing, resulted in greater soybean injury from atrazine residue than did moldboard plowing. Regardless of atrazine residue level, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4 H )-one] resulted in the greatest injury to soybeans. Metribuzin application in combination with atrazine residue increased soybean injury under the chisel plowed system.
Although phytotoxic residues of the triazine herbicides are objectionable when, in some soils and under some environmental conditions, sensitive plants are injured the season after application, residual activity is essential for weed control and soil sterilization. Without residual activity, frequent applications of less persistent herbicides would be necessary, and costs of weed control would, therefore, be high. A good example of the advantages of residual phytotoxicity was described by Horowitz (1964), who suggested that a single application of simazine or atrazine at the beginning of winter rains in Israel would control winter weeds and maintain sorghum planted the next spring free of weeds until harvest.
Until recently, microbial decomposition was considered the main pathway for detoxication of the s-triazine herbicides in soils. Organisms have been isolated which can detoxify these herbicides (Kaufman
et al. 1965). Factors such as temperature and soil organic matter which influence soil microbial activity have been shown to correlate with the rate of s-triazine loss from the soil (Burnside
et al. 1961, Talbert and Fletchall 1964). More recent studies, however, indicate that microbial decomposition may play a less significant role in the detoxication process and various nonbiological pathways may be more important than previously thought.
Many new organic agricultural chemicals have been developed which offer great potential in the production and preservation of food and fiber (Weber 1969). In the process of developing and utilizing these chemicals we must come to understand how they affect the target organisms and what becomes of them after they have done their job. The purpose of this review is to discuss1 the behavior of one family of these organic compounds, the s-triazines, at the molecular level, in systems in which the chemicals are associated with clay minerals. Factors affecting the adsorption and release of s-triazines by clay colloids and the availability of the compounds to plant roots will also be included. The literature citations are limited to those studies in which s-triazines and clays were directly associated and situations in which other compounds behaved in a manner similar to the s-triazines.
Recalcitrant xenobiotic compounds are a major source of concern due to their resistance to degradation and persistency in the environment. Xenobiotic compounds pose a serious threat to the environment as they tend to distort the nutrient cycling and affect non-target organisms. These recalcitrant compounds include heavy metals, halocarbons, polychlorinated biphenyls, polycyclic aromatic compounds, synthetic polymers, alkyl benzyl sulphonates, nitroaromatics, dioxins, synthetic dyes, chlorophenols, certain herbicides and pesticides as well as lignins that are ubiquitous in nature. Xenobiotic compounds find their way into the environment either through intentional release as happens with pesticides and herbicides spray or accidentally in the form of oil spills and persist as sediments and complexes, thereby reducing the quality of soil and water bodies and consequently creating the need for removal and/or remediation processes. White rot fungi which degrade the most recalcitrant natural polymer, lignin, have been shown to degrade a wide range of recalcitrant xenobiotic compounds. Recently, the use of co-cultures of white rot has been a subject of research. Owing to the variation in the ligninolytic machinery and rates of degradation, the use of co-cultures is attractive as it offers the advantage of combining the degradative capabilities of different fungi to bring about complete degradation of the parent compounds as well as the metabolites.
Infrared spectroscopy was used to study the hydrolysis of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine] upon interaction with homoionic soil colloids. Montmorillonite, an allophanic soil clay, and a montmorillonitic Coker soil clay were saturated with H ⁺ , Al ³⁺ , Cu ²⁺ , and Ca ²⁺ and treated with atrazine and hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)- s -triazine]. Hydrolysis of atrazine was evaluated by the presence of a strong hydroxyatrazine carbonyl absorption band at 1745 cm ⁻¹ . The H ⁺ - and Al ³⁺ -saturated montmorillonite and montmorillonitic Coker soil clay promoted atrazine hydrolysis while Ca ²⁺ - or Cu ²⁺ -saturated montmorillonite did not. A small degree of atrazine hydrolysis was detected in the Cu ²⁺ -Coker soil clay. Dehydration of Ca ²⁺ - or Cu ²⁺ -Coker soil clay after equilibration with atrazine increased the hydrolysis of atrazine. The allophanic soil clay did not catalyze the hydrolysis of atrazine when the exchange complex was saturated with H ⁺ , Al ³⁺ , Ca ²⁺ , or Cu ²⁺ . Moreover, Al ³⁺ -allophane was not sufficiently acidic to protonate hydroxyatrazine. Thus, a major difference exists between soil allophanic colloids, montmorillonitic soil clays, and montmorillonite as catalysts in the protonation and hydrolysis of atrazine.
The aqueous environment in the vicinity of the subsurface solid matrix is different from that of the bulk water. The electric field emanating from the charged solid may strongly affect polarizable species of contaminants, and therefore, their potential for abiotic transformation is much greater at the solid–liquid interface than in natural bulk waters. Molecules in direct contact with reactive solid constituents often are subject to catalytic properties of the surface or interact with available adsorbing sites and can undergo a variety of transformations.
Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.
Synthetic organic pesticides when used properly have been of tremendous benefit to man and his environment, but when misused or used carelessly they have caused considerable harm. Fortunately, the adverse effects have been relatively minor in comparison to the great benefits from pest control. There is little doubt that pesticides have played, and most likely will continue to play, an important role in the production of food as the world’s supply of raw agricultural products continues to decline in proportion to the increase in population.
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