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Herbicide degradation is one of the key processes determining whether the use of herbicide will have any impact on environmental quality, and it is dependent on various biotic and abiotic factors. The present study evaluates the impact of various abiotic factors such as soil type, application rate, incubation temperature, soil pH, soil microorganisms and sunlight on persistence of metribuzin and its effect on soil enzymes. Half-lives (DT50) varied significantly with application rate of metribuzin and physicochemical properties of soil and ranged from 15.17 to 46.59 days. Metribuzin degraded 2.2 to 6.5 times slower in sterilised soil (DT50 = 35.21 to 115.60 days) as compared to unsterilised soil, indicating microbial degradation is one the most predominant contributors towards degradation of metribuzin in soil. Increase in degradation rate on exposure to sunlight indicated photodegradation also contributes significantly to the degradation of metribuzin. Deaminometribuzin, diketometribuzin and deaminodiketometribuzin metabolites of metribuzin were detected in all treatments. Dehydrogenase and alkaline phosphatase activities were significantly affected by application of metribuzin while urease activity remained unaffected. The physicochemical properties viz. pH, organic matter content and temperature should be considered along with application rate of metribuzin in order to achieve satisfactory weed control and reduce environmental risk associated with the use of metribuzin in different crops. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of application rate, soil type and temperature on the degradation dynamics of mesosulfuron methyl and iodosulfuron methyl and their effect on soil enzymatic and microbial activity under laboratory conditions. Mixture of mesosulfuron methyl + iodosulfuron methyl was applied to soils at application rates of 14.4, 28.8, 43.2 and 57.5 g ha−1. Residues of herbicides were extracted using ultrasonic-assisted extraction method and analyzed with high-performance liquid chromatography. Degradation was dependent on soil type and application rate of herbicides with DT50 (50% degradation time) and DT90 (90% dissipation time) of 8.71 to 47.08 and 28.95 to 156.43 days for mesosulfuron methyl while 7.17 to 38.24 and 20.81 to 127.07 days for iodosulfuron methyl. Increase in temperature enhanced the dissipation of herbicides. The fastest dissipation was observed in loam 1 soil probably because in acidic soil abiotic hydrolysis was a predominant contributor in degradation. Among both herbicides, mesosulfuron methyl was more persistent in studied soils. Various metabolites of mesosulfuron methyl and iodosulfuron methyl, viz. mesosulfuron (M1) and 2-[3-(4-hydroxy-6-methoxypyrimidin-2-yl) ureidosulfonyl] – 4 – methane sulfonamidomethyl benzoate (M2), 4,6-dimethoxypyrimidine-2-yl-urea (M4), 2-amino-4,6-dimethoxypyrimidine (M5), metsulfuron methyl (I1), methyl-2-amino-sulfonyl benzoate (I2), 4-methoxy-6-methyl-1,3,5-triazine-2-amine (I3) and saccharin (I4), were also detected in the studied soils and their appearance and disappearance varied with soil type and application rate. The application of herbicides showed short-lived harmful effects on dehydrogenase, alkaline phosphatase and acid phosphatase activity and soil microbial activity while urease activity remained unaffected. The results indicated that studied herbicides have low to moderate persistence and transitory adverse effects on soil microbial activity depending on pH, organic matter content and temperature conditions. [ABSTRACT FROM AUTHOR]

For developing mitigation methods to decrease or eliminate the risk of water contamination around crop areas, a thorough understanding of the leaching process is required. It also affects the efficacy of herbicides towards the target weeds. The study investigated the leaching of penoxsulam and bispyribac sodium in soils with varied physicochemical properties. Quantification was done using liquid chromatography tandem mass spectrometer. Penoxsulam was found to be moderately mobile and 86.3–90.2% of the applied herbicide was detected in soil column and residues in leachate were below the limit of quantification (0.008 µg mL−1). On the contrary, only 20.8–29.9% of the applied bispyribac sodium was detected in the soil columns and 62.8–87.12% was present in leachates. The highest leachability of penoxsulam and bispyribac sodium was found in loamy sand followed by sandy loam, loam, silt loam and clay loam. The results corroborated well with index-based leaching model using principal component analysis. Therefore, it is important to propose remediation method to avoid the potential adverse effect of herbicide behaving as leachar compound. [ABSTRACT FROM AUTHOR]

A simple, efficient and cost-effective ultrasound-assisted extraction method for the quantification of penoxsulam, anilofos, bispyribac sodium, butachlor and pretilachlor from soil and rice was developed and validated. Three independent variables, including ultrasonication temperature, ultrasonication time, type and volume of solvent, were studied by single-factor experiments. Box–Behnken design (BBD) was also used to determine the optimal parameters for efficient extraction of penoxsulam, anilofos, bispyribac sodium, butachlor and pretilachlor herbicides from soil and rice. Under optimum conditions, the mean percent recoveries ranged from 82.1 ± 3.32 to 93.8 ± 2.56 from soil and rice grain with relative standard deviation <10% and limit of quantification less than the maximum residue limits imposed by principal regulatory agencies. Results depicted that the experimental values were consistent with the predicted values, indicating that RSM is accurate and reliable method to find the optimal UAE extraction conditions for studied herbicides from soil and rice. Furthermore, the greenness was evaluated using AGREE metrics, and UAE was found to be a greener and efficient method for the determination of herbicides from soil and rice. The developed method was extended to the analysis of real samples and concentration of herbicides at 0 day in soil samples varied from 0.483 ± 1.65 to 1.420 ± 1.41 µg g−1. At harvest, the concentrations of herbicides in soil and rice were below the permissible limit (<0.01 µg g−1). [ABSTRACT FROM AUTHOR]

As adsorption-desorption behaviour of herbicide plays an important role in determining leachability, release rate and availability to target species, the present study aims to evaluate the influence of soil properties, temperature and ionic state of imazamox on its adsorption-desorption behaviour. The sorption was significantly influenced by above evaluated parameters and Freundlich adsorption coefficient varied from 0.24 × 103 to 7.60 × 103 mg1−1/n kg−1 L1/n. In soils with pH in the range of 6.4–9.5, sorption of imazamox decreased with increase in solution pH while in acidic soil (pH 2.3 to 5.9), adsorption increased with increase in solution pH. At low solution pH adsorption occurs mainly through cationic form while at high solution pH adsorption was predominantly through anionic form. The presence of electrostatic attractive and repulsive forces, ∏→∏ charge transfer, hydrogen bonding and van der waals forces was key mechanism affecting the adsorption of imazamox. Greater adsorption hysteresis was observed in soils having pH in the range of 6.2–9.5 suggesting relatively less adsorption and difficult desorption of imazamox in these soils. Due to irreversible binding in high pH soil, it can be speculated that it may enhance the chances of crop injury in these soils. [ABSTRACT FROM AUTHOR]

Application of organic amendments to soil is a frequent agricultural practice for avoiding the irreversible soil degradation. However, this practice could modify the behaviour of applied herbicide. This study evaluates the impact of organic matter (OM) amendment on dissipation and leaching of penoxsulam. The addition of OM amendments enhanced the degradation rate of penoxsulam and 91.27, 89.46, 89.05 and 81.03% degradation was observed in press mud (PM), farmyard manure (FYM), poultry manure (POM) and vermicompost (VC)-amended soils after 30 days in comparison to 67.31% degradation in unamended soil. PM OM amendment was most effective in enhancing the degradation of penoxsulam. Three metabolites of penoxsulam were detected and depending upon the type of amendment there was variation in appearance and persistence of these metabolites in soil. The analysis of penoxsulam at different soil depths showed that it leached up to the depth of 30–40 cm in unamended and VC and FYM amended soil whereas to a depth of 20–30 cm in POM and PM-amended soil. The residual amounts of penoxsulam at lower depths were lesser in the amended soils than in unamended soil. None of the leachate fractions showed the presence of penoxsulam residues. The use of OM amendment in soil is an effective management practice for controlling potential pollution caused by penoxsulam to the environment. [ABSTRACT FROM AUTHOR]

Adsorption desorption behavior of herbicide in soil plays important role in assessing the fate of herbicide. Batch equilibrium method was used to assess the effect of physicochemical properties of soil and temperature on adsorption-desorption of penoxsulam in Punjab soils under laboratory conditions. The adsorption of penoxsulam in studied soils followed pseudo-second-order kinetics and fitted well into Freundlich and Langmuir model. Freundlich adsorption coefficient varied from 0.858 to 1.585 µg1−1/n g−1ml1/n indicating strong binding of penoxsulam on soil matrix. Adsorption increased with increase in temperature and thermodynamic parameters showed that adsorption process was feasible, spontaneous and endothermic. Desorption was slow with hysteresis coefficient ranging from 0.016 to 0.207. Adsorption was dominant by surface adsorption at low equilibrium concentration while partition at high equilibrium concentration. Principal component analysis (PCA) indicated that penoxsulam was moderately mobile in soil and can potentially contaminate groundwater. Highest leachability of penoxsulam was in loamy sand followed by sandy loam, loam, silt loam and clay loam. Remedial methods like the addition of organic amendments helps in reducing downward movement of penoxsulam and avoid its potential adverse effects. [ABSTRACT FROM AUTHOR]

The effect of long-term application of pretilachlor to paddy in rice–wheat cropping system was investigated from 1997 to 2015. Additionally, in 2013, field experiment was also conducted where pretilachlor was applied to paddy field having no background of its application. The residues of pretilachlor were quantified using high-performance liquid chromatography (HPLC). The average recoveries of pretilachlor from paddy soil, paddy grain and straw samples ranged from 80.7% to 93.8% using HPLC with standard deviation less than 10%. The dissipation rate of pretilachlor in paddy soil followed first-order kinetics and half-life ranged from 9.58 to 21.19 days. In 2015, HPLC was compared with gas chromatography–tandem mass spectrometry (GC–MS/MS) for quantification of residues. Average recoveries of pretilachlor using GC–MS/MS from paddy soil, paddy grain and straw samples ranged from 81.4% to 98.3% with standard deviation less than 10%. Both HPLC and GC–MS/MS offered high reproducibility; however GC–MS/MS was more sensitive and the limit of detection was 3.0 and 1.0 ng g−1for HPLC and GC–MS/MS, respectively. At harvest, the residues of pretilachlor in the paddy soil and crop were below the maximum residue limit and no dangerous accumulation was observed after its prolonged application. [ABSTRACT FROM AUTHOR]