Bensulfuron-methyl Concentration Research Articles

Assessment of methyl 2-({[(4,6-dimethoxypyrimidin-2-yl)carbamoyl] sulfamoyl}methyl)benzoate through biotic and abiotic degradation modes

AbstractDetoxification and management of environmental contaminants is an exigent issue of current times. Sulfonylurea herbicide, Bensulfuron-methyl was investigated for its degradation demeanour in soils, through biotic and abiotic modes (biodegradation and hydrolysis). Solid-liquid extraction of the herbicide was followed by GC-MS and UV-visible spectrophotometry analysis. The main metabolites observed were pyrimidinamine [149 m/z] and benzylsulfonamide [182 m/z]. The rate of biodegradation achieved by Aspergillus niger and Penicillium chrysogenum was 95% and 71%, respectively. The maximal decline in Bensulfuron-methyl concentration through hydrolysis was 48%. Furthermore, hydrolytic elimination was also evaluated based on time and pH. Both these parameters had a strong influence on the rate of transformation. Soils with lower pH exhibited an increased rate of degradation while a temperature of 27±2°C gave ideal conditions for herbicide decomposition. Percentage degradation and rate constant (k) followed first order reaction kinetics. Non-inoculated soils displayed less amounts of degradation. Furthermore, relative standard deviations were calculated for the residuals extracted in all soils. Analysis of variance (ANOVA) provided a p value < 0.05 for both strains with R2 closer to 1 signifying the significance of the results. Both fungal strains proved their potential for Bensulfuron-methyl remediation in soils.

Chlorination of bensulfuron-methyl: Kinetics, reaction factors and disinfection by-product formation

The kinetics of bensulfuron-methyl chlorination were studied at pH 4–9 at room temperature (25 ± 1 °C), which can be described well by a second-order kinetic model, first-order in chlorine and first-order in bensulfuron-methyl concentrations. Bensulfuron-methyl reacted very rapidly with aqueous chlorine with the maximum reaction rate constant at pH 6 and minimum at pH 9. The superior reactions were the reactions between HOCl and ionized/nonionized bensulfuron-methyl. The reaction factors including bromide and ammonium concentrations as well as temperature were also evaluated. It was found that bromide accelerated the chlorination of bensulfuron-methyl and the reaction rate increased linearly with the increase of bromide concentration. In contrast, the presence of ammonium inhibited the degradation of bensulfuron-methyl due to its quick conversion of chlorine to chloramines. Bensulfuron-methyl chlorination is an endothermic reaction with the activation energy being estimated as 13.74 kJ/mol using the Arrhenius equation. Four volatile disinfection by-products (DBPs) were identified after bensulfuron-methyl chlorination, including chloroform, dichloroacetonitrile, 1,1,1-trichloroacetone and nitrotrichloromethane. Trihalomethanes were the dominant species with a maximum reached at pH 8, which could cause potential risks to public health during bensulfuron-methyl chlorination, especially with the presence of bromide because the concentration and species of brominated DBPs increased with increasing bromide concentration.

Biodegradation of bensulfuron-methyl and its effect on bacterial community in paddy soils

Bensulfuron-methyl (BSM) is a new kind of sulfonylurea herbicide widely used to control broad-leaf weeds in rice paddies. The aim of this work was to study BSM biodegradation in paddy soils with BSM-degrading bacteria Bacillus megaterium L1 and Brevibacterium sp. BH and its effect on the structures of soil bacterial community. More than 90 % of BSM could be degraded in paddy soils with 0.0355 mg kg⁻¹ BSM concentration. Addition of BSM-degrading bacterial strains Bacillus megaterium L1 into BSM contaminated paddy soil could have the half-life time of BSM compared to treatment without Bacillus megaterium L1 inoculation. Denaturing gradient gel electrophoresis and principle component analysis indicated that the diversity of the soil microbial community structure changed along with the addition of BSM, which recovered at the end of the experiment (5 weeks). Addition of BSM-degrading bacteria Bacillus megaterium L1 enriched the diversity of soil microbial community structure in paddy soils. This study provides information on the biodegradation of BSM and BSM's influences on the soil bacteria microbial community structures.

Isolation and characterization of Rhodococcus sp.BX2 capable of degrading bensulfuron-methyl

Bensulfuron-methyl (BSM) is a widely applicable sulfonylurea herbicides. However, BSM remains in environment for extended period of time (over 100 days) and causes a series of environmental problems. In this study, BX2, a strain presents high BSM degradation abilities, was isolated from an activated sludge sample using a continuous enrichment method and determined to be a member of the genus Rhodococcus based on its physiobiochemical characteristics and 16S rRNA gene sequence. Strain BX2 degradated 92% BSM from an initial concentration of 20 mg/L within a 7- day incubation at 35℃. The specific degradation rate increased with an increase in the initial BSM concentration and the maximum specific degradation rate obtained was 0.146 mg/(mg·d) at 140 mg/L. BSM degradation by strain BX2 can be presented by Haldane’s inhibition equation and the kinetic parameters were: = 16.75 mg/(mg·d), = 7809.36 mg/L and = 2.41 mg/L, respectively. These results indicated that the strain BX2 could be an excellent candidate for bioremediation of BSM-contaminated environments due to its high BSM-degradative ability. Key words: Bensulfuron-methyl (BMS), Rhodococcus sp.BX2, isolation, biodegradation.

Plant Species Mediate Rhizosphere Microbial Activity and Biodegradation Dynamics in a Riparian Soil Treated with Bensulfuron-methyl

A pot experiment was conducted to investigate microbial characteristics and the biodegradation process of bensulfuron-methyl (BSM) in a rhizosphere soils planted with different riparian plants. The results showed that microbial population decreased with BSM addition in the rhizosphere, especially for bacteria and fungi. The activities of the dehydrogenase (DHase) were stimulated firstly, due to BSM addition, but then were inhibited, and recovered to the initial level, while the activities of the phosphatase and urease showed obviously decreasing trend throughout the whole experiment. Rhizosphere soil substrate-induced respiration (SIR) was depressed by BSM, especially at the initial 14 days of incubation. Compared to Zizania aquatica and Phragmites australis, Acorus calamus showed a significantly (p < 0.05) higher DHase activity and larger SIR in the rhizosphere soils treated with BSM, which means that A. calamus can effectively alleviate inhibitory effect of the sulfonylurea herbicide addition on microbial activity. There were significant (p < 0.05) differences in microbial degradation dynamics of BSM in the rhizosphere soils among three kinds of riparian plants. A. calamus displayed a significantly (p < 0.05) higher degradation efficiency of BSM in the rhizosphere soils, followed by Z. aquatica and P. australis. The residual BSM concentration in A. calamus rhizosphere soil was 23.1 and 32.2% lower than that in Z. aquatica and P. australis rhizosphere soils, respectively, indicating a greater improvement effect on biodegradation of BSM in A. calamus rhizosphere soils.

Behavior of bensulfuron-methyl in an agricultural alkaline soil

A field experiment to determine the available bensulfuron-methyl (BSM) in the upper soil layer was conducted in an agricultural area in the South of Spain. To facilitate herbicide analysis, two application rates were employed, 200 g ha−1 and 5 kg ha−1. Samples of upper soil and soil solution were collected. Soil solution was sampled by means of metallic samplers, placed at a depth of 35 cm. In the plots receiving the lower dose ceramic suction, porous cups were also installed. Results from soil solution samples showed that the maximum BSM concentration was found after 8-10 days for the high irrigation supply (945 mm) and after 18-25 days for the lower irrigation regime (405 mm). The mathematical model FOCUSPELMO 1.1.1 was applied to interpret the data obtained in the field experiments. In general, there was a reasonable agreement between experimental and simulated data for soil samples, although the model did not acceptably predict herbicide concentrations in water soil samples. Ceramic cups sampled a higher soil water volume and more frequently than did the metallic samplers. However some variable results were attributed to preferential flow.

Susceptibilities of some aquatic ferns to paddy herbicide bensulfuron methyl

Paddy herbicides have the potential to cause adverse effects on non‐target plants. Susceptibilities of some aquatic ferns (Azolla japonica Franch. et Savat., Isoetes japonica A. Braun, Marsilea quadrifolia L. and Salvinia natans All.) and duckweeds (Lemna minor L. and Spirodela polyrhiza Schleid.) to paddy herbicide bensulfuron methyl (BSM) were evaluated with a 20 day exposure experiment using 200 cm2 pots. The BSM concentrations in the surface water of monitoring pots with no plants dissipated exponentially with half lives of 3.5 and 3.9 days at application rates of 15 and 150 g ha−1, respectively. The BSM concentrations in the surface water 1 day after application in the culture pots were comparable among plant species, and were lower than those in the monitoring pots. Bensulfuron methyl reduced the plant growth in all species. I. japonica showed the lowest intrinsic relative growth rate (RGR) and the lowest susceptibility with an effective dose resulting in 50% growth inhibition (ED50) of 21 g ha−1. Except for I. japonica, the RGR of the duckweeds was similar to the ferns, and ED50 for the duckweeds was higher than the ferns. ED50 for Sa. natans, A. japonica and M. quadrifolia were 1.1, 1.8 and 1.2 g ha−1, respectively, which were smaller than 1/20 of the recommended field dose (51–75 g ha−1) and ranged from 1/2 to 1/6 of ED50 for L. minor and Sp. polyrhiza (6.5 and 3.2 g ha−1, respectively). These results suggest that BSM application in paddy fields and its runoff in some localities is expected to have adverse effects on the growth of Sa. natans, A. japonica and M. quadrifolia.

Cross-resistance to bispyribac-sodium and bensulfuron-methyl in Echinochloa phyllopogon and Cyperus difformis

Water-seeded and continuously flooded rice in California is mostly grown as a continuous crop and weeds are the most serious rice production problem. Echinochloa phyllopogon (Stapf) Koss and Cyperus difformis L. are adapted to this aquatic system and compete with rice, causing heavy economic losses. Flooding cannot fully suppress these weeds. Heavy reliance on few available herbicides resulted in the evolution of herbicide resistance in populations of both weeds in California rice fields. Resistance to bensulfuron-methyl (ALS inhibitor) is widespread among C. difformis populations. E. phyllopogon has evolved resistance to several herbicides, including bispyribac-sodium (ALS inhibitor), which has not yet been commercially used. A resistant (R) E. phyllopogon was also much more tolerant to bensulfuron-methyl than a susceptible (S) biotype. Understanding the patterns and mechanisms of cross-resistance in key weeds of rice to bensulfuron-methyl and bispyribac-sodium is relevant for the successful deployment of this new herbicide and for the management of herbicide resistance in California rice. Whole-plant bioassays were conducted to compare responses between E. phyllopogon and C. difformis to bispyribac-sodium and bensulfuron-methyl and to detect the involvement of cyt P-450 monooxygenases in E. phyllopogon resistance to bensulfuron-methyl using the cyt P-450 inhibitors piperonyl butoxide and malathion (previous studies had already shown cyt P-450-mediated resistance to bispyribac-sodium). ALS activity was assayed on leaf extracts from young R and S plants of both species for a range of bispyribac-sodium and bensulfuron-methyl concentrations. The dose–response studies confirmed cross-resistance in R E. phyllopogon ; minimum and maximum ratios (R/S) of the GR 50 values of resistant to susceptible plants were 9 and >25.5 for bispyribac-sodium and bensulfuron-methyl, respectively. cyt P-450 contributed to bensulfuron-methyl resistance in R E. phyllopogon. C. difformis was also cross-resistant (R/S ratios: >10 for bispyribac-sodium and >26 for bensulfuron-methyl). ALS assays demonstrated that, unlike R E. phyllopogon, cross-resistance in R C. difformis was due to reduced ALS sensitivity. C. difformis ALS was more sensitive to bispyribac-sodium ( I 50=138.87 nM) than to bensulfuron-methyl ( I 50=6724.56 nM) . Also, ALS inhibition in R and S E. phyllopogon was higher with bispyribac-sodium. Thus, binding differences between both herbicides at the target site are suggested. This study reveals that cross-resistance between bensulfuron-methyl and bispyribac-sodium in both weeds involves degradation enhancement through monooxygenases and target-site alteration.

Surface Water Monitoring Survey for Bensulfuron Methyl Applied in Paddy Fields

Water samples from rice paddies, paddy drains, connecting streams, rivers and lakes have been analyzed for the rice herbicide bensulfuron methyl (BSM). BSM concentrations of river and lake water were in the range of < 0.1-2.3 μg/l. Peak concentrations correlated with release of paddy water and diminished rapidly to non-detectable level within 1-2 months. BSM was not detected in any tap water samples taken during peak discharge periods. Samples from rice paddies had initial concentrations of 106 μg/l of BSM (at a maximum use rate of 75 g a.i./ha), dissipating with an average DT 50 of about 2 days. Concentrations of BSM in water released from the paddies rapidly decreased as the drainage water moved downstream. These levels of BSM do not generally exceed EC 50 for several aquatic organisms.

Hydrilla tuber formation in response to single and sequential bensulfuron methyl exposures at different times

Hydrilla (Hydrilla verticillata (L.f.) Royle) grown in outdoor tanks was exposed to bensulfuron methyl concentrations of 25, 50, or 100 ppb on June 16, August 20 or October 15; 50 ppb June 16 and August 20, or 25 ppb on June 16, July 21, August 20, and October 15, 1990, with a 35-day contact time. Hydrilla was also exposed to the compound on August 9, 1991 at concentrations of 10, 20, 30, 40, or 50 ppb. In 1990, the August 20 exposure resulted in the greatest inhibition of tuber production for a single application. Exposure in June caused hydrilla to produce at least twice as many tubers as unexposed plants by April 10, 1991. Exposure in October arrested tuber production, which had already begun. Exposure in June and August delayed tuber formation until after February 9, 1991. Exposure in June, July, August, and October inhibited tuber formation for the entire growing season. Hydrilla treated with all concentrations of bensulfuron methyl on August 9, 1991 produced tubers only sporadically through March 16, 1992, compared to unexposed hydrilla, which produced an average of 48 tubers/531 sq cm by January 4, 1992. With the onset of warmer weather after March 16, tubers produced by unexposed hydrilla more than doubled, and comparable numbers of new tubers were produced by plants that were exposed to 10 or 20 ppb. Tuber production was inhibited for the entire growing season by exposure to 50 ppb on August 9, 1991. In spite of the promise that bensulfuron methyl showed for use in aquatic plant management, the Experimental Use Permit was not renewed in 1992 and efforts to register the compound were discontinued.

Acetolactate Synthase of Suspension-Cultured Carrot Cells Resistant to Bensulfuron Methyl.

Activities of acetolactate synthase (ALS) of 10-8 M bensulfuron methyl (BSM)-resistant carrot cells were compared with those of susceptible (normal) cells.ALS activity, assayed by measuring acetoin formed by decarboxylation of acetolactate, was inhibited in normal cells by low concentrations of BSM. However, nearly or more than half of the total activity was not inhibited by 10-6M BSM at pH lower than 7.5. Acetoin amounts produced in undecarboxylated samples almost coincided with those inhibited by high concentrations of BSM, 10-6 and 10-4M, in normal and resistant cells, respectively. This might indicate the presence of a direct acetoin producing system in ALS assay. Net ALS activity could be obtained by subtracting the undecarboxylated value from the total activity.Optimum pHs were broad, around 8.5 for ALS and 7.0 for direct acetoin producing activity. ALS was saturated at 40mM pyruvate and apparent Km value for ALS was 5-6mM.ALS from resistant cells was inhibited by BSM less than the normal cells. The BSM concentrations inhibiting ALS activity by 50% (I50) were 1×10-8M and 6×10-7M for normal and resistant cells, respectively. As this I50 value of the resistant cells was about 10 times higher than that reported previously (5.2×10-8M), the probability is that insensitivity of ALS to BSM of the resistant cells developed during long-term culture.