Mobility Of Metribuzin Research Articles

Effect of biochar on the mobility and photodegradation of metribuzin and metabolites in soil‒biochar thin-layer chromatography plates

ABSTRACTBiochars obtained by biomass pyrolysis have been proposed as a soil amendment to improve soil properties and fertility as well as to retain pesticides and other environmental contaminants. The present study investigates the degradation of metribuzin herbicide and its metabolites deamino- (DA), deaminodiketo- (DADK) and diketo- (DK) metribuzin under simulated solar light and dark conditions as well as their mobility using TLC plates coated with soil and soil‒biochar mixtures at 1% and 5% w/w ratio. Biochar was characterised by X-Ray diffraction, porosimetry, scanning electron microscopy and Fourier transform infrared spectroscopy. Degradation under light conditions followed biphasic kinetics, with bi-exponential model fitted better for the soil substrate, while the Gustafson–Holden model was found more appropriate to describe degradation kinetics in 1% soil/biochar mixture. In soil, DA presented the lowest degradation rate (DT50:440.9 h), followed by metribuzin (DT50:208.0 h), DADK (DT50:110.8 h) and DK (DT50:106.5 h). The addition of biochar reduced drastically the degradation or even inhibited the photolytic process for the studied reaction period. The mobility retention factor (Rf) in soil ranged from 0.49 for metribuzin to 0.63 for DADK. The addition of biochar practically immobilises the compounds in the surface layer as Rf ranged from 0.14 to 0.10 for metribuzin and from 0.23 to 0.16 for DADK in soil/biochar mixtures 1% and 5%, respectively. In conclusion, the addition of biochar reduced dramatically the photodegradation rates as well as the mobility of metribuzin and its metabolites due to increased adsorption.

Reduced downward mobility of metribuzin in fly ash-amended soils

Metribuzin, a triazine herbicide, is poorly sorbed in the soils, therefore leaches to lower soil profile. Fly ash amendment, which enhanced metribuzin sorption in soils, may play a significant role in reducing the downward mobility of herbicide. Therefore, the present study reports the effect of Inderprastha fly ash amendment on metribuzin leaching in three soil types. Fly ash was amended at 1, 2 and 5% levels in the upper 15 cm of 30 cm long packed soil columns. Results suggested a significant reduction in the leaching losses of metribuzin in fly ash-amended columns of all the three soil types and effect increased with increase in the level of fly ash. Even after percolating water equivalent to 362 mm rainfall no metribuzin was recovered in the leachate of 5% fly ash-amended columns. Fly ash application affected both metribuzin breakthrough time and its maximum concentration in the leachate. Further, it resulted in greater retention of metribuzin in the application zone and better effect was observed in the organic carbon poor soils.

Effect of the Presence of Nonionic Surfactant Brij35 on the Mobility of Metribuzin in Soil

Given the water scarcity becoming endemic to a large portion of the globe, arid region irrigation has resorted to the use of treated, partially treated, or even untreated wastewaters. Such waters contain a number of pollutants, including surfactants. Applied to agricultural lands, these surfactants could affect the fate and transport of other chemicals in the soil, particularly pesticides. A field lysimeter study was undertaken to investigate the effect of nonionic surfactant, Brij35, on the in-soil fate and transport of a commonly used herbicide, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one]. Nine PVC lysimeters, 1.0 m long × 0.45 m diameter, were packed with a sandy soil to a bulk density of 1.35 mg m−3. Antibiotic-free cattle manure was applied (10 mg ha−1) at the surface of the lysimeters. Metribuzin was then applied to the soil surface of all lysimeters at a rate of 1.00 kg a.i. ha−1. Each of three aqueous Brij35 solutions, 0, 0.5 and 5 mg L−1 (i.e., “good”, “poor” and “very poor” quality irrigation water) were each applied to the lysimeters in triplicate. Analysis for metribuzin residues in samples of both soil and leachate, collected over a 90-day period, showed the surfactant Brij35 to have increased the mobility of metribuzin in soil, indicating that continued use of poor quality water could influence pesticide transport in agricultural soils, and increase the risk of groundwater contamination.

Novel System for Reducing Leaching of the Herbicide Metribuzin Using Clay−Gel-Based Formulations

Metribuzin is an herbicide widely used for weed control that has been identified as a groundwater pollutant. It contaminates the environment even when it is used according to the manufacturer's instructions. To reduce herbicide leaching and increase weed control, new controlled release formulations were developed by entrapping metribuzin within a sepiolite-gel-based matrix using two clay/herbicide proportions (0.5/0.2 and 1/0.2) (loaded at 28.6 and 16.7% a.i.) as a gel (G28, G16) or as a powder after freeze-drying (LF28, LF16). The release of metribuzin from the control released formulations into water was retarded, when compared with commercial formulation (CF) except in the case of G28. The mobility of metribuzin from control released formulations into soil columns of sandy soil was greatly diminished in comparison with CF. Most of the metribuzin applied as control released formulations (G16, LF28 and LF16) was found at a depth of 0-8 cm depth. In contrast, residues from CF and G28 along the column were almost negligible. Bioassays from these control released formulations showed high efficacy at 0-12 cm depth. The use of these novel formulations could minimize the risk of groundwater contamination while maintaining weed control for a longer period.

Metribuzin mobility in soil columns as affected by urea fertiliser

Application of urea fertilisers to soils influences the soil solution characteristics and thus may affect the sorption of soil-applied herbicides. The present investigation reports the influence of urea co-application on sorption and leaching of metribuzin, a triazine herbicide. Urea application at 60 and 120 kg N ha(-1) increased metribuzin sorption in soils over that in untreated natural soil. The Kf (Freundlich adsorption coefficient) values of metribuzin for natural, 60 and 120 kg N ha(-1) treatments were 0.43, 0.46 and 0.84 microg(1 - 1/n) g(-1) ml1/n respectively. Downward mobility of metribuzin was studied in packed soil columns (300 mm length x 59 mm i.d.) at two irrigation intensities, 720 m3 ha(-1) (72 mm) and 3600 m3 ha(-1) (360 mm). After 720 m3 ha(-1) irrigation, metribuzin did not leach out of any column and was not detected in the leachate. Urea amendment slowed the leaching of metribuzin by 20 and 40% in 60 and 120 kg N ha(-1) urea-treated columns respectively. Also, following urea application, greater amounts of metribuzin were retained in the application zone. Upon increasing the irrigation intensity fivefold, urea application did not have any effect on metribuzin mobility, and its breakthrough from both natural and urea-amended columns occurred after 126 mm irrigation. However, there was a marked difference in the maximum concentration of metribuzin in the breakthrough curves obtained from natural and urea-amended columns. The study indicated that co-application of metribuzin and urea fertiliser is a safe practice as far as leaching of herbicide is concerned.

Retention and degradation of metribuzin in sandy loam and clay soils of Lebanon

SummaryThe retention and degradation of metribuzin herbicide were studied under two environmental conditions. Field studies were carried out on two soils, a sandy loam soil (soil A) and a clay soil (soil B). Metribuzin was applied with a jet sprayer at 1060 g a.i. ha−1 and 1960 g a.i. ha−1 on soils A and B respectively. Reconstituted soil columns were used to study the herbicide movement and metabolism in the two soils. Analyses of metribuzin and its metabolites were carried out using standardized methods. The results indicated a very weak capacity of adsorption of metribuzin in the two soils, and the weak adsorbed fraction is easily desorbed. Degradation and mobility of metribuzin in the field and laboratory soil columns were very intense and rapid. Soil A favoured reductive deamination whereas soil B favoured oxidative desulphuration and the respective metabolites deaminometribuzin and diketometribuzin yield the same product deaminodiketometribuzin. Both leaching by rainfall and degradation were important in the disappearance of metribuzin from the soils.

Soil Column Mobility of Metribuzin from Alginate-Encapsulated Controlled Release Formulations

The mobility ofmetribuzin [4-amino-6-(1,1-dimethylethyl)-3-methylthio)-1,2,4-triazin-5(4H)-one] from alginate-encapsulated controlled release (CR) formulations was investigated in four contrasting soil profiles. Two CR formulations based on sodium alginate (1%), kaolin (10%), and Tween 20 (0.5%) were compared to technical grade (TG) metribuzin and to a commercial liquid (CL) metribuzin formulation (Sencor 4L). In addition to the basic components, the CR-Oil formulation contained 4% linseed oil and the CR-N formulation did not. All herbicide treatments were labeled with [ 14 C]-metribuzin and were applied to duplicate soil columns containing a surface and a subsoil horizon. Each horizon was packed to a depth of 12.5 cm, giving a total column length of 25 cm. The columns were leached with 21 (420 mL) to 30 cm (600 mL) of 0.01 M CaCl 2 for a period of 7-10 days. For the TG treatment, the total amounts of [ 14 C]metribuzin leached were 85, 62, 66, and 58% for the Evesboro, Ochlocknee, Conover, and Commerce soils, respectively. This is compared to 91, 52, 51, and 43% for the CL formulation. The CR-Oil formulation leached 9, 13, 9, and 9% of the applied [ 14 C]metribuzin, compared to 49, 53, 41, and 48% for the CR-N formulation. The CR-Oil formulation also increased the amount of [ 14 C]metribuzin retained in the soil surface horizon (13-27%), compared to the CR-N (2-5%), TG (2-3%), and CL (1-2%) formulations

Phytotoxicity, Adsorption, and Mobility of Metribuzin and Its Ethylthio Analog as Infuenced by Soil Properties

The phytotoxicity, adsorption, and mobility of metribuzin and ethyl-metribuzin3were studied in five soils to determine if differential soil behavior could explain: a) the greater activity of both chemicals in western Oregon than in eastern Oregon, and b) the greater activity of metribuzin than ethyl-metribuzin under similar conditions. Metribuzin had higher activity on oats than ethyl-metribuzin in all soils and in quartz sand. Metribuzin was adsorbed less and moved more than ethyl-metribuzin in all soils. Activity of both herbicides decreased as sand content increased, and activity in quartz sand was lower than in soil. Activity of both herbicides increased in a bioassay in which leaching was prevented, indicating that leaching may be important in the loss of activity of metribuzin and ethyl-metribuzin. Lowest herbicide adsorption and greatest movement were observed in coarser textured soils.

Effect of Soil pH on Microbial Degradation, Adsorption, and Mobility of Metribuzin

Metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)one] degradation by soil microorganisms decreased as the soil pH decreased. Metribuzin and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] mobility increased with increasing concentration and soil pH.14C-metribuzin had greater mobility on soil thin-layer plates than14C-atrazine because of differences in water solubility and basicity. Adsorption increased with decreasing soil pH. The pKa for metribuzin was 0.99 ± 0.08. Adsorption increased gradually as the soil pH decreased toward the pKa of metribuzin. Protonation of the amine group with subsequent adsorption to soil colloids was the postulated reason for the reduction in phytotoxicity, microbial degradation, and mobility of metribuzin at low soil pH levels.

Behavior and Fate of Metribuzin in Eight Ontario Soils

The adsorption, desorption, and mobility of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] in eight Ontario soils were investigated. The distribution coefficients varied from 0.56 for the least adsorptive Fox sandy loam soil to 31.67 for the most highly adsorptive Leamington muck soil. Most of the adsorbed metribuzin was desorbed from the mineral soils after six aqueous extractions, however substantial amounts of the herbicide remained adsorbed on the muck soils after 10 aqueous extractions. The herbicide was relatively mobile in mineral soils but was immobile in the muck soils. Mobility was inversely correlated with the amount of soil organic matter. Bioassay studies indicated that phytotoxicity of metribuzin also decreased with increasing organic matter content of the soil. Persistence of metribuzin was dependent on microbial degradation. In a field study with Guelph loam, the half-life of metribuzin was approximately 3 months.