Fate Of Herbicides Research Articles

Potential impacts of seasonal variation on atrazine and metolachlor persistence in andisol soil.

To estimate the potential effect of seasonal variation on the fate of herbicides in andisol soil, atrazine and metolachlor residues were investigated through the summer and winter seasons during 2013 and 2014 under field condition. The computed half-lives of atrazine and metolachlor in soil changed significantly through the two seasons of the trial. The half-lives were shorter in summer season with 16.0 and 23.5days for atrazine and metolachlor, respectively. In contrast, the half-lives were longer during the winter season with 32.7 and 51.8days for atrazine and metolachlor, respectively. The analysis of soil water balance suggested that more pesticide was lost in deeper soil layers through infiltration in summer than in winter. In addition, during the summer season, metolachlor was more likely to leach into deeper soil layer than atrazine possibly due to high water solubility of metolachlor.

Degradation of Herbicide Mesotrione in Three Soils with Differing Physicochemical Properties from China.

The movement and fate of herbicides in soils under various environmental factors are important in evaluating their mobility and ecological impact. The effects of sterilization, solarization, and soil physicochemical properties on the degradation of herbicide mesotrione in three soils from China were evaluated using laboratory incubation method, and the degradation kinetics were also simulated using pseudo first-order reaction model. The calculated half-lives () of mesotrione were found to be 3.78- to 5.24-fold increased in sterilized soils than nonsterilized soils, which indicated that the degradation of mesotrione was strongly affected by soil microbial activity. A certain role of promoting degradation effect of natural light was found, and the values appeared to be only 7.90, 15.89, and 25.29 d in the surface of paddy soil, sandy loess, and silt clay loam, respectively. Correlation analysis between the observed first-order reaction rate constant () values and the selected soil properties revealed that the degradation of mesotrione was highly dependent on soil pH value ( > 0.992) and organic matter content ( > 0.932), but less related with clay content (<0.02 mm) with < 0.761 and nonrelated with cation exchange capacity (CEC) ( < 0.164). Data obtained in this study are helpful for further research on the prediction of the movement and fate of mesotrione in soils in limiting its environmental impact.

Role of Alumina and Montmorillonite in Changing the Sorption of Herbicides to Biochars.

The influence of biochars on the fate of herbicides in soil depends mostly on environmental factors among which the role of soil minerals is not clear. Two wood-derived biochars produced at 400 °C (BC400) and 600 °C (BC600) were treated with alumina and montmorillonite to investigate their interaction with biochars and the influence of herbicide sorption. Both minerals exhibited a pore-expanding effect that was likely relative to the removal of authigenic organic matter away from the biochars' surface. Alumina brought more remarkable pore expansion by doubling the surface area of the BC400 biochar and the mesopore area of the BC600 biochar. Consequently, more adsorption sites were accessible for herbicide molecules, which resulted in higher sorption of herbicides (acetochlor and metribuzin) to the mineral-treated biochars than to the untreated biochars. The results are useful for understanding the change of surface and sorption properties of biochars with soil applications.

Reduced mobility of fomesafen through enhanced adsorption in biochar-amended soil.

The residual soil material resulting from biomass thermochemical transformation during carbon separation, known as biochar, has been introduced as a soil amendment because of its numerous environmental benefits, including uses for contaminated land management. Adsorption and leaching of fomesafen in soils amended with 3 different rates of rice hull biochar (0.5%, 1%, and 2% w/w) under laboratory conditions were investigated, and studies were performed following a batch equilibration adsorption-desorption procedure and a column experiment for leaching. Adsorption-desorption data fit with the Freundlich equation well. The adsorption coefficient of fomesafen sharply increased from 0.59 to 0.99 to 8.02 to 22.23 when the amount of biochar amendment in the soil increased from 0% to 2% (w/w). In addition, a strong correlation was found between the amount of adsorbed fomesafen and the rate of amended biochar (r > 0.992, p < 0.01). Furthermore, biochar amendments reduced the desorption percentage of fomesafen in the soils. The outcomes of the leaching experiment also illustrated that the lowest fomesafen concentration in the leachate (21.4%) occurred in the soil amended with 2% (w/w) biochar. Moreover, the adsorption coefficients (K(f)(ads)) of the soil were positively correlated with the total amount of adsorbed fomesafen in the corresponding soil columns (r = 0.990, p < 0.01) and negatively correlated with the leachate percentage (r = 0.987, p < 0.05). The results of the present study suggest that biochar amendments in agricultural soils likely alter the fate of herbicides by decreasing their transport through enhanced adsorption.

Modeling atrazine transport in soil columns with HYDRUS-1D

Both physical and chemical processes affect the fate and transport of herbicides. It is useful to simulate these processes with computer programs to predict solute movement. Simulations were run with HYDRUS-1D to identify the sorption and degradation parameters of atrazine through calibration from the breakthrough curves (BTCs). Data from undisturbed and disturbed soil column experiments were compared and analyzed using the dual-porosity model. The study results show that the values of dispersivity are slightly lower in disturbed columns, suggesting that the more heterogeneous the structure is, the higher the dispersivity. Sorption parameters also show slight variability, which is attributed to the differences in soil properties, experimental conditions and methods, or other ecological factors. For both of the columns, the degradation rates were similar. Potassium bromide was used as a conservative non-reactive tracer to characterize the water movement in columns. Atrazine BTCs exhibited significant tailing and asymmetry, indicating non-equilibrium sorption during solute transport. The dual-porosity model was verified to best fit the BTCs of the column experiments. Greater or lesser concentration of atrazine spreading to the bottom of the columns indicated risk of groundwater contamination. Overall, HYDRUS-1D successfully simulated the atrazine transport in soil columns.

Effect of rice husk gasification residue application on herbicide behavior in micro paddy lysimeter.

Effects of rice husk gasification residues (RHGR) application on the fate of herbicides, butachlor and pyrazosulfuron-ethyl, in paddy water were investigated using micro paddy lysimeters (MPLs). The dissipation of both herbicides in paddy water was faster in the RHGR treated MPL than in the control MPL. The average concentrations of butachlor and pyrazosulfuron-ethyl in paddy water in the lysimeter treated with RHGR during 21 days were significantly reduced by 51% and 48%, respectively, as compared to those in the lysimeter without RHGR application. The half-lives (DT50) of butachlor in paddy water for control and treatment were 3.1 and 2.3 days respectively, and these values of pyrazosulfuron-ethyl were 3.0 and 2.2 days, respectively. Based on this study, RHGR application in rice paddy environment is an alternative method to reduce the concentration of herbicide in paddy field water and consequently to reduce potential pollution to aquatic environment.

ADSORPTION BEHAVIOUR OF HAZARDOUS ORGANIC SOLUTIONS ONTO NEW POLYMERIC SORBENT

The fate of herbicides in soil, and surface and groundwaters is determined by several factors including retention, transformation, and transport processes. Environmental pollutants removed from waters of these chemicals is important for all biologic life. In this study, adsorption of textile dyestuffs or adsorption of pesticides such as bisphenol A, 4-amino nitrophenol, phenoxyacetic acid were examined on PVBCIm. This polymer was obtained by modifying polyvinyl benzyl chloride (PVBC) resin with imidazole. This method, has been extended to chloro methyl group to preparepoly (N-vinyl imidazole) (PVIm) graft chains on crosslinked polyvinyl benzyl chloride (PVBC) polymer. In the aqueous solution the adsorption of organic waste was determined by UV-vis spectrophotometer. For different concentrations of hazardous organic wastes in aqueous solution, Freundlich, Langmuir, and BET isotherms were applied at 25 oC.

Abiotic and Biotic Processes Governing the Fate of Phenylurea Herbicides in Soils: A Review

Phenylurea herbicides are world widely used for controlling the development of various broad leaf weeds in cereal crops. Despite their agronomic interest, these herbicides are of environmental concern because they are often detected at concentrations above the threshold concentration imposed by legislation in soil and water worldwide. Understanding the fate of these pollutants is as such of major importance and has been the subject of many scientific studies in the last decades. This review article presents an overview of the abiotic and biotic processes governing the environmental fate of phenylurea herbicides after their application to agricultural fields. More precisely, it highlights the pivotal role of biodegradation in natural attenuation of pesticides in agricultural soils. The recent advances in the microbial aspects of their degradation in the field as well as in pure cultures are presented including metabolic pathways, processes, and factors that control the biodegradation of phenylurea herbicides.

Study of Cytotoxic Effects of Benzonitrile Pesticides.

The benzonitrile herbicides bromoxynil, chloroxynil, dichlobenil, and ioxynil have been used actively worldwide to control weeds in agriculture since 1970s. Even though dichlobenil is prohibited in EU since 2008, studies addressing the fate of benzonitrile herbicides in the environment show that some metabolites of these herbicides are very persistent. We tested the cytotoxic effects of benzonitrile herbicides and their microbial metabolites using two human cell lines, Hep G2 and HEK293T, representing liver and kidneys as potential target organs in humans. The cell viability and proliferation were determined by MTT test and RTCA DP Analyzer system, respectively. The latter allows real-time monitoring of the effect of added substances. As the cytotoxic compounds could compromise cell membrane integrity, the lactate dehydrogenase test was performed as well. We observed high toxic effects of bromoxynil, chloroxynil, and ioxynil on both tested cell lines. In contrast, we determined only low inhibition of cell growth in presence of dichlobenil and microbial metabolites originating from the tested herbicides.

Identification of sethoxydim degradation products in natural waters under different light sources by HPLC-QTOF-MS

Photodegradation process is one of the most important abiotic factors affecting the fate of pesticides in aquatic ecosystems. As consequence of this transformation pathway, different photoproducts can be formed with unknown toxicity, mobility and persistence in aqueous media. The information obtained is even more valuable for new families of pesticides, like cyclohexanedione herbicides, because the scientific literature about their environmental behavior and persistence is quite limited.Although there are evidences that the persistence of sethoxydim, a cyclohexanedione herbicide, in aquatic media is largely affected by reactions initiated by solar radiation, there are no studies about the photoproducts formed in natural waters. Therefore, we studied for the first time the photoproducts formed during the irradiation of sethoxydim herbicide under natural and simulated sunlight in different sources of waters. Ten photoproducts of sethoxydim were separated and identified by means of the HPLC-ESI-Qtof-MS technique. Main phototransformation processes of sethoxydim involved isomerization of oxime ether bond, oxidation of sulfur atom and cleavage of oxime ether bond. Photoproducts dealkoxy ketone, dealkoxy sulfoxides and dealkoxy sethoxydim resulted to more photostable than sethoxydim hence probably more persistent in the environmental. Both radiation and water sources influenced the concentrations of photoproducts formed during the irradiation of sethoxydim.These findings highlight the need for further insight in the study of photoproducts to understand the environmental fate of sethoxydim herbicide.

Catabolism of terbuthylazine by mixed bacterial culture originating from s-triazine-contaminated soil.

The s-triazine herbicide terbuthylazine (TERB) has been used as the main substitute of atrazine in many EU countries for more than 10years. However, the ecological consequences of this substitution are still not fully understood. Since the fate of triazine herbicides is primarily dependent on microbial degradation, in this paper, we investigated the ability of a mixed bacterial culture, M3-T, originating from s-triazine-contaminated soil, to degrade TERB in liquid culture and soil microcosms. The M3-T culture grown in mineral medium with TERB as the N source and citrate as the C source degraded 50mgL(-1) of TERB within 3days of incubation. The culture was capable of degrading TERB as the sole C and N source, though at slower degradation kinetics. A thorough LC-MS analysis of the biodegradation media showed the formation of hydroxyterbuthylazine (TERB-OH) and N-t-butylammelide (TBA) as major metabolites, and desethylterbuthylazine (DET), hydroxydesethylterbuthylazine (DET-OH) and cyanuric acid (CA) as minor metabolites in the TERB degradation pathway. TBA was identified as a bottleneck in the catabolic pathway leading to its transient accumulation in culture media. The supplementation of glucose as the exogenous C source had no effect on TBA degradation, whereas citrate inhibited its disappearance. The addition of M3-T to sterile soil artificially contaminated with TERB at 3mgkg(-1) of soil resulted in an accelerated TERB degradation with t 1/2 value being about 40 times shorter than that achieved by the native microbial community. Catabolic versatility of M3-T culture makes it a promising seed culture for accelerating biotransformation processes in s-triazine-contaminated environment.

Aqueous photodegradation of sethoxydim herbicide: Qtof elucidation of its by-products, mechanism and degradation pathway

The photochemical fate of sethoxydim herbicide in water was studied under simulated sunlight radiation (Suntest apparatus). This compound exhibited a rapid degradation rate in water with a half-life of approximately 1h, which is in accordance with the high calculated value of the quantum yield (Φ=0.26). Consequently, the photolysis of sethoxydim should be considered as an efficient route of sethoxydim removal in aqueous media.During the photodegradation studies, ten by-products were detected, and their identification was accomplished using high-performance liquid chromatography (HPLC) coupled with quadrupole time-of-flight mass spectrometry (Qtof) and electrospray ionization in positive mode (ESI+). A detailed and exhaustive study of the mass spectra of the precursor ions and their MS/MS fragmentation patterns allowed for their identification. The photodegradation products resulted from the cleavage and isomerization of the NO bond of the oxime, oxidation of the sulfur atom, oxidative CS bond cleavage and Beckmann rearrangement followed by intramolecular cyclization.Additionally, the reactive species involved and a plausible mechanism for the photodegradation of sethoxydim in water are discussed. Finally, based on the identified products, a rational pathway for the photodegradation of sethoxydim in water is proposed.

The Novel BacterialN-Demethylase PdmAB Is Responsible for the Initial Step ofN,N-Dimethyl-Substituted Phenylurea Herbicide Degradation

The environmental fate of phenylurea herbicides has received considerable attention in recent decades. The microbial metabolism of N,N-dimethyl-substituted phenylurea herbicides can generally be initiated by mono-N-demethylation. In this study, the molecular basis for this process was revealed. The pdmAB genes in Sphingobium sp. strain YBL2 were shown to be responsible for the initial mono-N-demethylation of commonly used N,N-dimethyl-substituted phenylurea herbicides. PdmAB is the oxygenase component of a bacterial Rieske non-heme iron oxygenase (RO) system. The genes pdmAB, encoding the α subunit PdmA and the β subunit PdmB, are organized in a transposable element flanked by two direct repeats of an insertion element resembling ISRh1. Furthermore, this transposable element is highly conserved among phenylurea herbicide-degrading sphingomonads originating from different areas of the world. However, there was no evidence of a gene for an electron carrier (a ferredoxin or a reductase) located in the immediate vicinity of pdmAB. Without its cognate electron transport components, expression of PdmAB in Escherichia coli, Pseudomonas putida, and other sphingomonads resulted in a functional enzyme. Moreover, coexpression of a putative [3Fe-4S]-type ferredoxin from Sphingomonas sp. strain RW1 greatly enhanced the catalytic activity of PdmAB in E. coli. These data suggested that PdmAB has a low specificity for electron transport components and that its optimal ferredoxin may be the [3Fe-4S] type. PdmA exhibited low homology to the α subunits of previously characterized ROs (less than 37% identity) and did not cluster with the RO group involved in O- or N-demethylation reactions, indicating that PdmAB is a distinct bacterial RO N-demethylase.

Transformation of organic wastes in soil: Effect on bentazone behaviour

The aim of this study was to evaluate the impact of two organic wastes from olive oil production on the fate of bentazone in soil, and to assess the influence of the transformation of organic matter from these wastes under field conditions. Results on freshly laboratory-amended soils were compared to those with soils amended in the field for nine consecutive years. Two amendments and two doses were studied. Sorption of bentazone increased upon amendment with Kd values from 0.03 to 1.7. The increase was higher for freshly amended soils than for the field amended soils and for the higher dose. Degradation was correlated with sorption in the case of field amended soils, whereas higher persistence in freshly amended soils may be related to the easier microbial availability of DOC molecules than bentazone molecules. The increase in non-conducting pores in amended soils favours sorption and degradation processes reducing leaching. Important differences revealed in herbicide fate between freshly amended soils and aged field amended soils limit further extrapolation of laboratory studies to field studies.

Fate of napropamide herbicide in selected Malaysian soils

This study was carried out to determine the sorption-desorption, degradation and leaching of napropamide in selected Malaysian soils. The sorption capacities of the selected Malaysian soils for napropamide were the following in descending order: Linau > Teringkap > Gunung Berinchang > Jambu > Rudua > Baging soil. The results indicate that napropamide degradation decreased with increasing soil sorption capacity. Napropamide was leached out earlier in the Baging soil than the other soils. Overall, the application of napropamide in the selected Malaysian soils would not pose a threat to the environment except in soil with low organic matter and clay content and high hydraulic conductivity, such as the Baging soil.

Relating nutrient and herbicide fate with landscape features and characteristics of 15 subwatersheds in the Choptank River watershed

Excess nutrients and agrochemicals from non-point sources contribute to water quality impairment in the Chesapeake Bay watershed and their loading rates are related to land use, agricultural practices, hydrology, and pollutant fate and transport processes. In this study, monthly baseflow stream samples from 15 agricultural subwatersheds of the Choptank River in Maryland USA (2005 to 2007) were characterized for nutrients, herbicides, and herbicide transformation products. High-resolution digital maps of land use and forested wetlands were derived from remote sensing imagery. Examination of landscape metrics and water quality data, partitioned according to hydrogeomorphic class, provided insight into the fate, delivery, and transport mechanisms associated with agricultural pollutants. Mean Nitrate-N concentrations (4.9 mg/L) were correlated positively with percent agriculture (R 2 = 0.56) and negatively with percent forest (R 2 = 0.60). Concentrations were greater ( p = 0.0001) in the well-drained upland (WDU) hydrogeomorphic region than in poorly drained upland (PDU), reflecting increased denitrification and reduced agricultural land use intensity in the PDU landscape due to the prevalence of hydric soils. Atrazine and metolachlor concentrations (mean 0.29 μg/L and 0.19 μg/L) were also greater ( p = 0.0001) in WDU subwatersheds than in PDU subwatersheds. Springtime herbicide concentrations exhibited a strong, positive correlation (R 2 = 0.90) with percent forest in the WDU subwatersheds but not in the PDU subwatersheds. In addition, forested riparian stream buffers in the WDU were more prevalent than in the PDU where forested patches are typically not located near streams, suggesting an alternative delivery mechanism whereby volatilized herbicides are captured by the riparian forest canopy and subsequently washed off during rainfall. Orthophosphate, CIAT (6-chloro- N-(1-methylethyl)-1,3,5-triazine-2,4-diamine), CEAT (6-chloro- N-ethyl-1,3,5-triazine-2,4-diamine), and MESA (2-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl)amino]-2-oxoethanesulfonic acid) were also analyzed. These findings will assist efforts in targeting implementation of conservation practices to the most environmentally-critical areas within watersheds to achieve water quality improvements in a cost-effective manner.

Dissipation and Transport of Clopyralid in Soil: Effect of Application Strategies

At present there are no herbicide uses registered for broadleaf weed control in buckwheat. Clopyralid, mixed with desmedipham, was anticipated to provide early-season broadleaf weed suppression with minimal crop injury. However, field trials resulted in limited success, which brought into question the fate and availability of clopyralid for weed control. A 4-year field study was conducted in Lithuania to evaluate the dissipation of clopyralid in Haplic Luvisol sandy loam soil and the influence of application rate, application timing, and coapplication with desmedipham on its degradation and transport. Clopyralid dissipation was rapid; 50% dissipation times, in the surface 5 cm, averaged over the 4 years of the study, were <7 days. Application rate (90 versus 180 g ai ha(-1)), timing (pre-emergence versus postemergence), and coapplication with desmedipham (360 g ai ha(-1)) did not significantly influence clopyralid dissipation. Clopyralid dissipation by leaching was not a significant factor; at 7-21 days after application, <8 μg kg(-1) was found at the 10-20 cm depth. Understanding the dissipation of herbicides and the influence of application strategies on herbicide fate will allow for informed decisions and improved efficacy of weed control. On the basis of the results of this research, weed scientists can now determine whether increased rates of clopyralid would provide sufficient residual chemical for adequate weed control without crop injury.

A Field Study of the Fates of Arsenal and Escort Applied on the Cumberland Plateau in Tennessee

Problem statement: The low organic soils of the Cumberland Plateau, as well as the karst geology of the region, may promote increased transport of herbicides outside of application sites. We have studied the fates of imazapyr and metsulfuron-methyl applied to a privately owned tract on the Cumberland Plateau in Tennessee and compared the field results with herbicide fate predicted by the computer model GLEAMS. Approach: The fate of the two herbicides, applied for pine release at a site on the Cumberland Plateau, was monitored over a sixteen month period. Concentrations in soil water were monitored using vacuum soil lysimeters. Grab samples were taken of water in ephemeral streams draining the clearcut area and of a perennial stream which receives water from the study area. Uncut streamside management zones of about 50 m bordered the streams. The field results were compared with those obtained using the GLEAMS computer model. Results: Concentrations of both herbicides in soil water dropped significantly within the first two months after application, imazapyr to less than 50 µg L-1 and metsulfuron-methyl to less than 3 µg L-1 and decreased more gradually in the following months. The maximum concentrations observed in soil water were 252 µg L-1 (imazapyr) and 13 µg L-1 (metsulfuron-methyl). Except on two dates occurring 5 months after application, the herbicides were not detected in the stream samples. GLEAMS predicted that very little herbicide should have been lost from the site in runoff or erosion sediment. The model predicted greater retention of the herbicides by the soil than was found through the field measurements. Conclusion/Recommendation: The rapid transport of imazapyr and metsulfuron we observed indicates that further study is justified at other locations on the Cumberland Plateau. Streamside management zones effectively prohibited contamination of receiving streams by herbicides at the study site.

Abiotic Reduction of Pendimethalin and Trifluralin in Controlled and Natural Systems Containing Fe(II) and Dissolved Organic Matter

The environmental fate of dinitroaniline herbicides is poorly understood, despite their classification as Persistent Bioaccumulative Toxins by the U.S. Environmental Protection Agency. This study investigated the abiotic reduction of pendimethalin and trifluralin in controlled laboratory systems in the presence of Fe(II) and fulvic acids isolated from various surface waters and in sediment pore waters containing naturally abundant levels of dissolved Fe(II) and dissolved organic matter (DOM). It was found that Fe(II) was necessary for pendimethalin and trifluralin reduction to occur in controlled systems and that higher concentrations of DOM slowed Fe(II)-mediated reactions. Pendimethalin and trifluralin reduction in natural pore waters was roughly an order of magnitude slower compared to controlled Fe(II)-DOM solutions, indicating that the reactive Fe(II) species responsible for reduction are concentration-limited in natural pore waters relative to controlled systems. The results show that caution must be exercised when extrapolating results from controlled system reactions to natural systems and that abiotic reduction of both trifluralin and pendimethalin is observed within 3-7 days in anaerobic sedimentary pore waters containing high concentrations of both dissolved Fe(II) and DOM.

Fate of Two Herbicides in Zero‐Tension Lysimeters and in Field Soil

In Germany, zero-tension lysimeters are used as part of the registration requirements in case pesticides pose a potential threat to contaminate the groundwater. However, the water regime and the method of pesticide sampling differ between the lysimeters and the field. We monitored the transport of the two herbicides ethidimuron [1-(5- ethylsulfonyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea] (ETD) and methabenzthiazuron [1-benzothiazol-2-yl-1,3-dimethyl-urea] (MBT) and their main metabolite, accompanied with bromide as conservative tracer, in zero-tension lysimeters filled with undisturbed soil and in the field. The herbicides were applied as a short pulse to the bare soil surface. Herbicide concentrations were analyzed in the drainage water of the 1.2-m-deep lysimeters and from soil cores taken from the field during six campaigns. Soil coring in the field emphasized matrix flow and allowed us to estimate the field-based dissipation and sorption parameters. Based on mass recovery calculations, the field fate half-life was 870 d for ETD compared with 389 d for its main metabolite. The initially fast field-based dissipation of MBT with a half-life value of approximately 1 mo was followed by a much slower dissipation. The retardation factor was estimated from the concentration profiles by inversely solving the convection-dispersion equation and yielded 18.2 +/- 1.3 for ETD and 36.9 +/- 17.5 for MBT. For the lysimeters, a leaching period of 2 1/2 yr was too short to monitor bulk herbicide mass through the soil matrix. Only 1.7% of the applied EDT and 1.4% of the applied MBT were sampled in the drainage water at 1.2 m depth. Despite contrasting sorption and dissipation properties, both herbicides appeared fast and at the same time in the drainage water, hinting at preferential flow phenomena. Compared with field fate of herbicides measured by soil coring, zero-potential lysimeters emphasize the transport of small amounts of herbicides triggered by preferential flow events.