Metalaxyl In Soil Research Articles

Quantitative Assessment of Degradation Degree of Metalaxyl in Soil and Plant by Compound-Specific Isotope Analysis

Quantitative Assessment of Degradation Degree of Metalaxyl in Soil and Plant by Compound-Specific Isotope Analysis

Enantiomer-specific stable carbon isotope analysis (ESIA) to evaluate degradation of the chiral fungicide Metalaxyl in soils

Chiral pesticides are often degraded enantioselectively in soils, leading to disparity among enantiomers that may display different toxicity levels. Monitoring pesticide degradation extents and processes remains out of reach in the field using conventional bulk and enantiomer concentration analyses. Enantioselective stable carbon isotope analysis (ESIA) combines compound specific isotope analysis (CSIA) and enantioselective analysis, and bears potential to distinguish enantiomer degradation from non-destructive dissipation. We developed ESIA of the fungicide Metalaxyl, providing the 13C/12C ratios for S-Metalaxyl and R-Metalaxyl separately, and applied it to follow degradation in soil incubation experiments. Significant enantioselective degradation (kS-MTY = 0.007–0.011 day−1 < kR-MTY = 0.03–0.07 day−1) was associated with isotope fractionation (Δδ13CS-MTY ranging from 2 to 6‰). While R-Metalaxyl degradation was rapid (T1/2≈10 days), concomitant enrichment in heavy isotopes of the persistent S-Metalaxyl occurred after 200 days of incubation (εS-Metalaxyl ranging from −1.3 to −2.7‰). In contrast, initial racemic ratios and isotopic compositions were conserved in abiotic experiments, which indicates the predominance of microbial degradation in soils. Degradation products analysis and apparent kinetic isotope effect (AKIE) suggested hydroxylation as a major enantioselective degradation pathway in our soils. Altogether, our study underscores the potential of ESIA to evaluate the degradation extent and mechanisms of chiral micropollutants in soils.

Metalaxyl Degradation by Mucorales Strains Gongronella sp. and Rhizopus oryzae.

In this study, the degradation of metalaxyl was investigated in the presence of two Mucorales strains, previously isolated from soil subjected to repeated treatments with this fungicide and selected after enrichment technique. Fungal strains were characterised by a polyphasic approach using phylogenetic analysis of the Internal Transcribed Spacer (ITS) gene region, phenotypic characterisation by Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) spectral analysis, and growth kinetics experiments. The strains were identified as Gongronella sp. and Rhizopus oryzae. The fungal growth kinetics in liquid cultures containing metalaxyl fits with Haldane model. Under laboratory conditions, the ability of Gongronella sp. and R. oryzae cultures to degrade metalaxyl was evaluated in liquid cultures and soil experiments. Both species were able to: (a) use metalaxyl as the main carbon and energy source; and (b) degrade metalaxyl in polluted soils, with rates around 1.0 mg·kg−1 d−1. This suggests these strains could degrade metalaxyl in soils contaminated with this fungicide.

Effect of synthetic clay and biochar addition on dissipation and enantioselectivity of tebuconazole and metalaxyl in an agricultural soil: Laboratory and field experiments

Laboratory and field experiments were conducted to assess how the addition of oleate-modified hydrotalcite (clay) and biochar (BC) to an agricultural soil affected the sorption, leaching, persistence, and enantiomeric composition of soil residues of two chiral fungicides, tebuconazole and metalaxyl. Laboratory experiments showed that the sorption of both fungicides ranked as follows: unamended soil<BC-amended soil<clay-amended soil. The addition of clay at a rate of 1% increased metalaxyl soil sorption coefficient (Kd) from 0.34 to 3.14Lkg−1 and that of tebuconazole from 2.4 to 47.4Lkg−1. In our experimental set-up, field plots were either unamended or amended with clay (2tha−1) or BC (4tha−1), and subsequently treated with a mixture of tebuconazole and metalaxyl at 3 and 6kgha−1, respectively. The leaching, persistence, and enantiomer composition of fungicides residues were monitored by sampling at different soil depths (0–5, 5–10, 10–20cm) for 98days. No significant changes in the scarce mobility and long persistence of tebuconazole upon amending the soil with clay or BC were observed. In contrast, sorption to clay and BC particles reduced the leaching and degradation of metalaxyl and the clay increased its persistence in the topsoil compared to the unamended soil. The enantioselective analysis of tebuconazole and metalaxyl soil residues indicated that tebuconazole remained mostly racemic along the experiment, whereas for metalaxyl the concentration of S-enantiomer was greater than the concentration of R-enantiomer, more so at longer experimental times and deeper horizons. Nevertheless, for the top 0–5cm soil layer metalaxyl remained more racemic in clay- and BC-amended soil than in unamended soil. Our results show that addition of amendments with high sorptive capacities can be beneficial in reducing leaching and degradation losses of chiral pesticide enantiomers from the topsoil, and that sorption by the amendments can influence the final enantiomeric composition of pesticide residues.

Environmental fate of the fungicide metalaxyl in soil amended with composted olive-mill waste and its biochar: An enantioselective study

A large number of pesticides are chiral and reach the environment as mixtures of optical isomers or enantiomers. Agricultural practices can affect differently the environmental fate of the individual enantiomers. We investigated how amending an agricultural soil with composted olive-mill waste (OMWc) or its biochar (BC) at 2% (w:w) affected the sorption, degradation, and leaching of each of the two enantiomers of the chiral fungicide metalaxyl. Sorption of metalaxyl enantiomers was higher on BC (Kd≈145Lkg−1) than on OMWc (Kd≈22Lkg−1) and was not enantioselective in either case, and followed the order BC-amended>OMWc-amended>unamended soil. Both enantiomers showed greater resistance to desorption from BC-amended soil compared to unamended and OMWc-amended soil. Dissipation studies revealed that the degradation of metalaxyl was more enantioselective (R>S) in unamended and OMWc-amended soil than in BC-amended soil. The leaching of both S- and R-metalaxyl from soil columns was almost completely suppressed after amending the soil with BC and metalaxyl residues remaining in the soil columns were more racemic than those in soil column leachates. Our findings show that addition of BC affected the final enantioselective behavior of metalaxyl in soil indirectly by reducing its bioavailability through sorption, and to a greater extent than OMWc. BC showed high sorption capacity to remove metalaxyl enantiomers from water, immobilize metalaxyl enantiomers in soil, and mitigate the groundwater contamination problems particularly associated with the high leaching potential of the more persistent enantiomer.

First evidence for covalent linkage of acidic metabolites of metalaxyl and DDT as non-extractable pesticide residues in soil and sediment

Soils and sediments are a major sink for lipophilic organic pollutants. The remobilization potential of non-extractable residues is an important aspect of the environmental risk assessment and is directly linked to the binding modes of xenobiotics to macromolecular geopolymers. For instance, weak binding will favour rapid release of toxic metabolites, whereas strong binding will favour release in the long run. So far there is few strong evidence on the precise nature and strength of pollutant binding to organic matter. We used 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (DDT) contaminated sediment and metalaxyl spiked microbial active soil for alkaline hydrolysis reaction with 18O-sodium hydroxide (Na18OH). Gas chromatography–mass spectrometry analyses showed 2 Da shifts in molecule ions of 2,2-bis(chlorophenyl)acetic acid methylester (DDA-methylester) and additionally in fragment ions of 18O-metalaxyl indicating monolabeled derivatives of both pesticide metabolites.18O-labeling of the carboxyl moiety during hydrolysis proved the cleavage of the metabolites from organic macromolecules. This is the first concrete evidence for stable ester linkage of acidic metabolites of DDT and metalaxyl in soil and sediment matrices.

Quantitative and enantioselective analyses of non-extractable residues of the fungicide metalaxyl in soil

The remobilization of non-extractable residues (NER) is a potential source for enhanced ecotoxicity and bioavailability in aquatic and terrestrial systems. The objective of this study is to investigate the influence of microbial and extracellular enzyme-assisted transformation of the fungicide metalaxyl and the formation of its non-extractable residues with special interest on the enantioselectivity of these processes. Soil sterilization using mercuric chloride treatment and chloroform fumigation allowed us to inhibit microbial activity without substantial alteration of the extracellular enzyme activity. Under sterilized and non-sterilized conditions, incubation experiments with rac-metalaxyl were carried out for a short-term (10 days) and a long-term (92 days) period. Particle size fractionation delivered sand, organo-silt, and organo-clay fractions of the agricultural soil. Extractable residues (water and solvent soluble) were separated from insoluble proportion of the organo-mineral components (organo-clay, organo-silt). The latter were subdivided into humic subfractions (fulvic acids, humic acids, and humin) and non-humic substances. All these subfractions were subjected to alkaline hydrolysis treatment delivering hydrolyzable proportion of NER of metalaxyl. All fractions were analyzed quantitatively by gas chromatography–mass spectrometry (GC/MS), and the enantioselectivity was determined by means of chiral-GC/MS. In all experimental set-ups, most of the metalaxyl residues were found in the water-soluble fraction. The amount of total extractable metalaxyl residue decreased in the time period of 10–92 days from approximately 95 to 75 % under sterilized and non-sterilized conditions. Chiral analyses showed the dissipation of R-metalaxyl (enantiomer fraction (EF) > 0.5) after 92 days even in sterilized samples, indicating a direct influence of not only microbial but also extracellular enzymatic activity in the enantioselective fungicide degradation processes. The metabolite metalaxyl acid was predominantly found in the water-soluble fraction (30 %) and in hydrolyzable NER fraction (2 %) under non-sterilized condition. Chiral-GC/MS showed an enrichment of the previously dissipated R-metalaxyl in these fractions (EF < 0.5). There is evidence of microbial as well as extracellular enzyme-assisted formation of non-extractable metalaxyl residues. Higher availability of the transformation product metalaxyl acid allowed also higher amounts of hydrolyzable NER in the non-sterilized samples. Hereby, a strong incorporation of the acid metabolite was evident. Chiral analyses provide insights into the stereoselectivity not only of the metabolic transformation processes but also of the formation of NER of the fungicide metalaxyl.

Enhanced non-extractable residue formation of 14C-metalaxyl catalyzed by an immobilized laccase

We studied the influence of an immobilized laccase from Trametes versicolor on non-extractable residue (NER) formation of the systemic fungicide 14C-metalaxyl in soil. We added the enzyme (130 mU/g DW) to soil sterilized by gamma irradiation and observed that the amount of NER (6.3 % of applied radioactivity) after 10 days of incubation was enhanced about twofold compared to the sterile soil without laccase addition. Residues formed within samples without enhanced enzyme activity were mainly bound via ester linkages to all fractions of humic matter, i.e., fulvic acids, humic acids, non-humines, and humines, respectively. In contrast, residues formed in presence of immobilized laccase were more strongly bound by covalent linkages such as ether and C-C bonds, especially to humic acids. After chemical degradation of the humic matter, it could be observed that all NER contained the first major transformation product, i.e., metalaxyl acid. The findings underline that the residue formation of metalaxyl in soil may be partly catalyzed by immobilized extracellular oxidative enzymes through oxidative coupling reactions within the humic matter.

Controlled Release of Agrochemicals Intercalated into Montmorillonite Interlayer Space

Periodic application of agrochemicals has led to high cost of production and serious environmental pollution. In this study, the ability of montmorillonite (MMT) clay to act as a controlled release carrier for model agrochemical molecules has been investigated. Urea was loaded into MMT by a simple immersion technique while loading of metalaxyl was achieved by a rotary evaporation method. The successful incorporation of the agrochemicals into the interlayer space of MMT was confirmed by several techniques, such as, significant expansion of the interlayer space, reduction of Barrett-Joyner-Halenda (BJH) pore volumes and Brunauer-Emmett-Teller (BET) surface areas, and appearance of urea and metalaxyl characteristic bands on the Fourier-transform infrared spectra of the urea loaded montmorillonite (UMMT) and metalaxyl loaded montmorillonite (RMMT) complexes. Controlled release of the trapped molecules from the matrix was done in water and in the soil. The results reveal slow and sustained release behaviour for UMMT for a period of 10 days in soil. For a period of 30 days, MMT delayed the release of metalaxyl in soil by more than 6 times. It is evident that MMT could be used to improve the efficiency of urea and metalaxyl delivery in the soil.

Enantioselective separation and transformation of metalaxyl and its major metabolite metalaxyl acid in tomato and cucumber

Many studies have shown the enantioselective transformation of metalaxyl in soil and animals, but little is known about the enantioselective biotransformation of metalaxyl in plants. In this study, a sensitive and convenient chiral liquid chromatography–tandem mass spectrometry method was developed for simultaneous measurement of the enantiomers of metalaxyl and its major metabolite, metalaxyl acid, in tomato and cucumber. Separation was by reversed-phase chromatography on a Chiralcel OD-RH column under isocratic conditions using acetonitrile–water (60/40, v/v) as mobile phase. The proposed method was successfully applied to investigate the possible enantioselective transformation of metalaxyl as well as the formation of metalaxyl acid in tomato and cucumber. In both vegetables, the (−)-R-enantiomer was preferentially degraded, resulting in relative enrichment of the (+)-S-enantiomer. Furthermore, formation of the metalaxyl acid enantiomers was also shown to be enantioselective, with the R-metalaxyl acid formed at a faster rate. This is the first evidence of enantioselective transformation of metalaxyl in vegetables, and the results should be considered in future environmental risk and food safety evaluations.

Influence of pine or oak wood on the degradation of alachlor and metalaxyl in soil

The objective of this work was to study the influence pine or oak wood added to soil as an amendment (5% w/w) had on the degradation rate of two pesticides, alachlor and metalaxyl, with different hydrophobic character. The formation of pesticide metabolites and the soil dehydrogenase activity in non-amended and amended soil samples were also monitored. The degradation of metalaxyl followed first-order kinetics, while the degradation of alachlor followed first-order or biphasic kinetics in the soil samples studied. The results indicated that the degradation rate was slower for metalaxyl than for alachlor, and for both pesticides followed the order: pine amended soil < oak amended soil < non-amended soil. The faster degradation rate in non-amended soil was attributed to the higher sorption of pesticides by wood amended soils. The alachlor ethane sulfonic acid (ESA), and two metalaxyl metabolites (2-[(2,6-dimethylphenyl)-methoxyacetylamino]-propionic acid and N-(2,6-dimethylphenyl)-2-methoxy-acetamide) were detected during the incubation period. Soil dehydrogenase activity recorded close values in non-amended and amended soil treated with alachlor, but it was higher in wood amended soil treated with metalaxyl. Pine and oak wood increase the immobilization of the pesticides studied, but they also limit their bioavailability in soil by decreasing their degradation rate in amended soil.

COMPORTAMENTO DO FUNGICIDA METALAXIL EM SOLOS BRASILEIROS ARENOSOS E ARGILOSOS

Utilizou-se a cromatografia a líquido de alta eficiência (CLAE) para quantificar o coeficiente de adsorção (Kd) e a degradação do metalaxil suplementado em quatro diferentes solos brasileiros nas concentrações de 0,003 e 0,03 g Kg-1. Os resultados mostraram que o metalaxil não foi degradado em solos autoclavados durante o período de avaliação. Estudos preliminares “in vitro” têm demonstrado que microrganismos do solo podem degradar N-(2,6-dimetilfenil)-N-(2-metoxiacetil)-alanina metil éster (metalaxil), fungicida usado na agricultura para o controle de doenças causadas por fungos da ordem dos Peronosporales. Os resultados da avaliação por CLAE revelaram (em ambas as concentrações testadas do fungicida) altos valores de Kd e maior degradação de metalaxil nos solos argilosos que nos demais tipos de solos investigados. Esses dados evidenciaram que o comportamento do metalaxil em solos varia conforme as taxas de aplicação, características do solo e atividade microbiana.

Enantioselective degradation of metalaxyl in soils: chiral preference changes with soil pH.

Chiral pesticides are often degraded enantio-/stereoselectively in soils. Degradation is typically studied with one or a small number of soils so that it is not possible to extrapolate the findings on chiral preference to other soils. For this study, the fungicide metalaxyl was chosen as a "chiral probe" to investigate its enantioselective degradation in 20 different soils, selected primarily to cover a wide range of soil properties (e.g., acidic/alkaline, aerobic/ anaerobic) rather than to consider soils of agricultural importance. Racemic metalaxyl was incubated in these soils under laboratory conditions, and the degradation of the enantiomers as well as the enantioselective formation/ degradation of the primary major metabolite, metalaxyl acid, was followed over time, using enantioselective GC-MS after ethylation with diazoethane. In aerobic soils with pH > 5, the fungicidally active R-enantiomer was degraded faster than the S-enantiomer (k(R) > k(S)), leading to residues with a composition [S] > [R]. However, in aerobic soils with pH 4-5, both enantiomers were degraded at similar rates (k(R) approximately k(S)), and in aerobic soils with pH < 4 and in most anaerobic soils, the enantioselectivity was reversed (k(R) < k(S)). These considerable soil-to-soil variations were observed with soils from locations close to each other, in one case even within a single soil profile. Liming and acidification of a "nonenantioselective" soil prior to incubation resulted in enantioselective degradation with k(R)> k(S) and k(R) < k(S), respectively. While the enantioselectivity (expressed as ES = (k(R) - k(S))/(k(R) + k(S))) of metalaxyl degradation in aerobic soils apparently correlated with soil pH, no such correlation was found for metalaxyl acid. Reevaluation of published kinetic data for the herbicides dichlorprop and mecoprop indicated similar correlations between soil pH and ES as for metalaxyl.

골프장 그린 토양에서 Metalaxyl의 흡ㆍ탈착 특성

Laboratory experiments were conducted to examine the behavior of metalaxyl in environment which was used as pesticide in green soil of golf course and as functions of the characteristics of adsorption, desorption and degradation in soil texture and organic matter contents. Acid water containing metalaxyl was conducted to evaluate the effects on adsorption, desorption and degradation. The adsorption of metalaxyl played more significant role in organic contents than clay contents, and pH Increases more pH 2.5 than pH 5.6. The desorption of metalaxyl from contaminants soil decreased higher organic contents LS-soil than S-soil, but the desorption amount of metalaxyl increased more pH 5.6 than pH 2.5. The rate of degradation of metalaxyl in green soil environmental increased higher organic contents LS-soil than S-soil and decreased more pH 2.5 than pH 5.6. These results indicated that the behavior of metalaxyl of the green soil was affected the soil texture of the golf course. Increasing of organic contents, the adsorption amount of metalaxyl on soil increased. Moreover the decrease of the pH of solution increased adsorption amounts and decreased desorption amounts. As the results, the transportation of metalaxyl in soil decreased the acidic rates. The acidification of soil by the acid rain increased the adsorption amount of metalaxyl, but the degradation of metalaxyl decreased. Therefore, it is possible to sustain contamination in run-off the stream and ground water by residuals in soil.

Influence of biotic and abiotic factors on dissipating metalaxyl in soil

Under laboratory condition, dissipation of metalaxyl in sterile and non-sterile soils, its sorption behaviour and fate in presence of light have been studied. The half-life value of metalaxyl was found in the range of 36–73 d in non-sterile soil. 5.3–14.7% dissipation was observed due to abiotic factors other than light. Metalaxyl was found photostable in soil showing half-life of 188–502 h under simulated sunlight. In adsorption study, a non-linear relationship between concentration of metalaxyl and its adsorption into soils was observed. Estimated k OC value increased as organic carbon content decreased. Adsorption and desorption k D values ranged between 53.5 and 151.1.

Reduced persistence of metalaxyl in soil associated with its failure to control cavity spot of carrots

Metalaxyl was used to control Pythium diseases of carrots in experiments on farms with a history of cavity spot. The first experiment compared the method of application (sprayed, banded or broadcast) and rate (0, 1.5, 3 or 6 kg a.i. ha−1) one week after sowing. Three additional experiments compared the rate (0, 0.75, 1.5 or 3 kg a.i. ha−1) and time (sowing, 1‐ to 2‐ or 4‐ to 5‐true‐leaf stage) of application. In expt 1, the application of metalaxyl, but not the method by which it was applied, increased yield by 20% and significantly reduced the incidence of cavity spot, forking and misshapen carrots. In expts 2, 3 and 4, neither the rate nor time of application affected yield or reduced the incidence of Pythium diseases. Comparison of the sites showed that they differed in past metalaxyl usage. Metalaxyl had not been used on the site of expt 1, but had been used previously at sites 2, 3 and 4. Laboratory experiments were conducted to determine whether these differences in efficacy resulted from reduced sensitivity of Pythium isolates to metalaxyl, or reduced persistence of metalaxyl in soil. ED50 values showed that there was no reduction in metalaxyl sensitivity. The half‐life of metalaxyl was 82 days in soil from expt 1, but was 10 days or fewer in soils from expts 2, 3 and 4. Thus the failure of metalaxyl to control Pythium diseases was associated with reduced persistence in soil, not reduced sensitivity of the target fungi.

Control Options for Greenhouse Cucumber Damping-Off Disease

ABSTRACT Greenhouse cucumber plants were transplanted into soil treated in five different ways to test for reduction of damping-off disease. The non-chemical and methyl bromide treatments involved the replacement of a small area of soil around the transplants to allow for maturity of the plants to a less susceptible stage of growth. Untreated fallow field soil, solarized soil, methyl bromide treated soil and metalaxyl soil drench treatments were all effective in preventing infection from Pythium aphanidermatum, the causal agent for damping-off of cucumber seedlings in this Study.

Adsorption and movement of metalaxyl in soils under unsaturated flow conditions

Adsorption and mobility of the fungicide metalaxyl was studied in three soil types, viz., Hessaraghatta loamy sand (HLS), Bellary clay (BC), and Ooty clay (OC) soils, under laboratory conditions. The K values obtained from the Freundlich adsorption isotherms were 0.04, 10.65 and 13.32 µg/g for HLS, BC and OC soils respectively. Mobility of metalaxyl in these soils was inversely related to K values (r = −0.97). Although, metalaxyl persisted for over 60 days in all the soils, it did not move beyond a depth of 17.5 cm in any of the soils under unsaturated flow conditions. Mobility of metalaxyl was fastest in HLS and slowest in OC soils.

The influence of a peat amendment and turf density on downward migration of metalaxyl fungicide in creeping bentgrass sand lysimeters

Downward migration of the fungicide, metalaxyl (N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alanine methyl ester) in irrigated creeping bentgrass ( Agrostic palustris Huds) sand lysimeters was studied as a function of two factors: (1) amending sand with peat and (2) density of the bentgrass turf. Based on the determination of metalaxyl in leachates collected at specific intervals following fungicide application, the presence of peat in the sand delayed the downward migration of the fungicide. The percentages of total applied metalaxyl found in the collected leachates generally decreased as turf density and surface organic matter increased. Literature on the subject of the downward migration of metalaxyl in soils is reviewed.

The Relationship of Infection byPythiumspp. to Root System Morphology of Alfalfa Seedlings in the Field

Alfalfa root system morphology was evaluated in relation to root infection by Pythium spp. in developing seedlings in the field. Metalaxyl treatments (soil drench, seed treatment, or nontreated) were used to produce differing levels of root infection in the field. Experiments were conducted at an upland site on a research farm in Missouri in two consecutive years. Quantitative assessments of root system morphology were made using morphometric and topological classification techniques. A metalaxyl soil drench treatment reduced root colonization by Pythium spp. per unit root length compared with either the metalaxyl-treated seed treatment or untreated control in 1991 through the first 4 weeks after emergence. Root colonization by Pythium spp. was low in 1992 and no differences among treatments could be detected. In the 1991 field test, the metalaxyl soil treatment resulted in increased root system growth and complexity (greater length, more branches, faster growth rates) compared with the seed and control treatments over the first 4 weeks of seedling development. However, no effect of root infection on root system branching structure could be detected in either year. These results suggested that, under favorable environmental conditions, sublethal root infections of alfalfa seedlings by Pythium spp. can cause reductions in root system size and complexity under natural field conditions.