Degradation Of Metolachlor Research Articles

Microplastic-Induced Oxidative Stress in Metolachlor-Degrading Filamentous Fungus Trichoderma harzianum.

While there has been intensive research on the influence of microplastics (MPs) on aquatic organisms and humans, their effect on microorganisms is relatively little-known. The present study describes the response of the Trichoderma harzianum strain to low-density polyethylene (LDPE) microparticles. MPs, either separately or with metolachlor (MET), were added to the cultures. Initially, MP was not found to have a negative effect on fungal growth and MET degradation. After 72 h of cultivation, the content of fungal biomass in samples with MPs was almost three times higher than that in the cultures without MPs. Additionally, a 75% degradation of the initial MET was observed. However, due to the qualitative and quantitative changes in individual classes of phospholipids, cell membrane permeability was increased. Additionally, MPs induced the overproduction of reactive oxygen species. The activity of superoxide dismutase and catalase was also increased in response to MPs. Despite these defense mechanisms, there was enhanced lipid peroxidation in the cultures containing the LDPE microparticles. The results of the study may fill the knowledge gap on the influence of MPs on filamentous fungi. The findings will be helpful in future research on the biodegradation of contaminants coexisting with MPs in soil.

Enantioselectivity and mechanisms of chiral herbicide biodegradation in hydroponic systems

This study demonstrates the enantioselective removal dynamics and mechanisms of the chiral herbicide metolachlor in a hydroponic system of Phragmites australis. It presents the first work to elucidate plant-microbial driven enantioselective degradation processes of chiral chemicals. The results showed a degradation efficiency of up to 95.07 ± 2.81% in the hydroponic system driven by a notably high degradation rate constant of 0.086 d−1. P. australis was demonstrated to rapidly increase the contribution of biodegradation pathways in the hydroponic system to 82.21 ± 4.81% within 4 d with an enantiomeric fraction (EF) drop to 0.26 ± 0.02 to favour the enantioselective degradation of S-Metolachlor (kS-Metolachlor = 0.568 d−1 and kR-Metolachlor = 0.147 d−1). Comparatively, the biodegradation pathways in the control constituted less than 25%, with an EF value of circa 0.5. However, the enantioselective biodegradation pathways exhibited complete reversal after about 4 d to favour R-Metolachlor. Plants promoted the degradation of R-Metolachlor, evidenced by an increase in EF to 0.59 ± 0.03. Nonetheless, metolachlor showed an inhibitory effect on plants reflected by the reduction of plant growth rate, chlorophyll content, and electron transport rate to −7.85 ± 1.52%, 1.33 ± 0.43 mg g−1, 4.03 ± 1.33 μmol (m2 s)−1, respectively. However, rhizosphere microorganisms aided plants to catalyze excessive reactive oxygen species production by the antioxidant enzymes to protect plants from oxidative damage and restore their physiological activities. High-throughput analysis of microbial communities demonstrated the enrichment of Massilia (40.63%) and Pseudomonas (8.16%) in the initial stage to promote the rapid degradation of S-Metolachlor. By contrast, the proliferation of Brevundimonas (32.29%) and Pseudarthrobacter (11.03%) in the terminal stage was closely associated with the degradation of R-Metolachlor. Moreover, as symbiotic bacteria of plants, these bacteria aided plants protection from reactive oxygen damages and promoted the recovery of plant metabolic functions and photosynthesis. Overall, these results demonstrate biodegradation mediated by plant-microbe mechanisms as the main driver for the enantioselective degradation of metolachlor in hydroponic systems.

Removal of Chloroacetanilide Herbicides from Water Using Heterogeneous Photocatalysis with TiO2/UV-A

Chloroacetanilide herbicides are widely used in the agricultural sector throughout the world. Because of their poor biodegradability, high water solubility, and long persistence, chloroacetanilide herbicides have a high potential to contaminate water, and conventional water treatment processes do not ensure sufficient removal. Therefore, heterogeneous photocatalysis using TiO2/UV-A was investigated for the degradation of alachlor, acetochlor, and metolachlor from water. Two commercially available TiO2 (P25 and AV-01) were used as photocatalysts. Different experimental setups were also tested. In addition, the toxicity of single herbicides and mixtures of their photocatalytic degradation products to the freshwater alga Chlorella kessleri was investigated via a growth inhibition test. The maximum removal efficiency for alachlor, acetochlor, and metolachlor was 97.5%, 93.1%, and 98.2%, respectively. No significant differences in the removal efficiency of chloroacetanilide herbicides were observed for the photocatalysts used. Although the concentrations of all herbicides during photocatalysis decreased, the toxicity of the resulting mixtures of degradation products increased or remained the same, indicating the formation of toxic degradation products.

Effects of three surfactants on the degradation and environmental risk of metolachlor in aquatic environment

Surfactants and pesticides can be simultaneously detected in the environment by the reason of their widespread use and large amounts of emissions. Due to the special amphipathicity of surfactants, it may have special effects on the environmental behaviors and toxic effects of other substances in the environment. There are few relevant studies at present. In this study, the effects of three surfactants on the degradation of the amide pesticide metolachlor in water-sediment system were investigated. The study found that the three surfactants had no significant effect on the degradation of metolachlor in the system at environmental concentrations. However, at critical micelle concentration, cationic surfactant octadecyl trimethyl ammonium bromide and nonionic surfactant nonylphenol polyoxyethylene ether promoted the degradation of metolachlor in water-sediment system. Anionic surfactant odium dodecylbenzene sulfonate (SDBS) prolonged the degradation half-life of metolachlor. The presence of surfactants not only affected the environmental behavior of pesticides. When they coexisted with pesticides, the joint toxicity to aquatic organisms cannot be ignored. This study found that the combined effects of three surfactants and metolachlor on the acute developmental toxicity of zebrafish embryos were all synergistic effects. The combined effects of two ionic surfactants and metolachlor on the acute toxicity of adult zebrafish were synergistic effects. Further study showed that co-exposure of SDBS and metolachlor increased the absorption of metolachlor by zebrafish. Combined exposure of SDBS and metolachlor caused oxidative stress in brain, gill and liver of zebrafish. The results showed that the simultaneous presence of anionic surfactants and pesticides in the environment may increase the environmental risk of pesticides.

Degradation of Mcpa, Metolachlor and Propiconazole in the Hyporheic Zone of an Agriculturally Impacted River

Degradation of Mcpa, Metolachlor and Propiconazole in the Hyporheic Zone of an Agriculturally Impacted River

Impact of Soil Aeration on the Environmental Fate of Pre-Emergent Herbicide Metolachlor

The impact of the aeration status of soils on the environmental fate of the soil-applied pre-emergent herbicide metolachlor is of significance to sustainable agriculture practices and has not been investigated thoroughly by existing research works. To address this knowledge gap, we examined the adsorption, desorption, degradation, and mineralization of radioactively labeled [14C] metolachlor in Catlin, Flanagan, and Drummer soils under aerobic and anaerobic conditions. Based on our findings, anaerobic conditions in the soil significantly reduced the adsorption of 14C-metolachlor while also promoting its desorption, thereby potentially releasing a greater amount of herbicide from the soil after a field application. The first-order degradation and mineralization kinetics of 14C-metolachlor were distinctively enhanced by anaerobic conditions in all the soils tested. Furthermore, the degradation and mineralization rates of 14C-metolachlor in non-sterilized versus sterilized soil microcosms clearly indicated microbial activity in the degradation of metolachlor in soil. The results from this study suggest that soil redox conditions could impact the bioavailability and environmental fate of herbicide metolachlor and should be taken into consideration as part of sustainable weed management programs.

Isolation, Degradation Performance and Field Application of the Metolachlor-Degrading Fungus Penicillium oxalicum MET-F-1

Metolachlor is extensively used and the most persistent chloroacetamide herbicide, thereby which its metabolites have been frequently detected in soils and surface and groundwaters. Microbial degradation is predominantly responsible for the removal of metolachlor from soil and water. However, few microbial strains reported previously are highly efficient in degrading potentials for metolachlor. We isolated the fungal strain MET-F-1 from an activated sludge, characterized as Penicillium oxalicum, which could degrade 88.6% of 50 mg/L metolachlor coupled with 0.1% glucose plus 0.1% yeast extract within 384 h under optimal conditions. Compared with metabolites produced by previously isolated microorganisms, different degradation products, i.e., MOXA, M2H, and MDES, detected by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), were produced through hydrolytic and reductive dechlorination by MET-F-1. This is the first report on the degradation of metolachlor by Penicillium oxalicum sp. Furthermore, field plot experiments using the wheat bran inoculum method were performed and demonstrated good metolachlor-degrading activity of this strain. This study serves as a steppingstone to promote MET-F-1 strain usage as a promising agent for metolachlor-contaminated soil remediation.

The metolachlor degradation kinetics and bacterial community evolution in the soil bioelectrochemical remediation

Herbicide-polluted soils have posed a threat to the crop growth and agro-product quality and safety. Even worse, the low-content of residue is still appreciable for a long time in subsurface soils. The soil bioelectrochemical remediation system (BERS) provides an inexhaustible electron acceptor to cause in situ indigenous microorganisms to generate biocurrent and accelerate the removal of metolachlor (ML). As a result of carbon fiber amendment, the highest current density (637 ± 19 mA/m2) to date has been generated in a soil BERS. The ML half-life and complete removal time decreased from 21 to 3 d and from 245 to 109 d, respectively. Importantly, the soil BERS was verified to be an effective treatment method for low-polluted sediments/soils, whether by ML or by its degradates. The quantitative degradates of ML showed that the first step was dechlorination based on the bioelectrochemical degradation pathway. The biocurrent selectively enriched special species, e.g., Geobacter and Thermincola for bioelectricity generation and Ralstonia, Phyllobacterium and Stenotrophomonas for degradation in soils. Meanwhile, Flavisolibacter and Gemmatimonas occupied the core niche in strengthening interspecific relationships by the biocurrent. This study firstly revealed the explicit abundance of Geobacter in agricultural soils and laid a foundation for the function design of mixed bacteria in the sediment/soil BERS.

Nitrogen-doping positively whilst sulfur-doping negatively affect the catalytic activity of biochar for the degradation of organic contaminant

Developing low-cost and efficient metal-free carbon-based catalysts is of great importance but remains a challenge. In this work, rice straw derived biochar was prepared and doped with heteroatoms (N and S) for the catalytic degradation of metolachlor (MET) through activating peroxymonosulfate (PMS). Adsorption process played a critical role for the subsequent degradation process. Surface ketone C (-C = O) was the catalytic active sites for the PMS decomposition. Interestingly, N-doping positively whilst S-doping negatively influenced the MET degradation process. Through experimental investigation and theoretical calculations, N-doping was demonstrated to be beneficial for the interaction between biochar and PMS, thus accelerating the catalytic degradation process. The reactive oxidative species involved in the degradation process were explored by EPR analysis. The degradation pathways were elucidated based on the liquid chromatography time-of-flight mass (LC-TOF-MS) analysis of the degradation products. This study highlights the applications of biochar for the environmental catalysis.

Sunlight Photolysis of Safener Benoxacor and Herbicide Metolachlor as Mixtures on Simulated Soil Surfaces.

Benoxacor is a safener paired with the high-use herbicide S-metolachlor. Commercial formulations containing both compounds are sprayed onto soil pre-emergence to enhance yields of corn. In this study, we evaluated the sunlight photolysis of metolachlor and benoxacor, individually and as mixtures, in three different reaction environments: in water and on two soil-simulating surfaces (quartz and kaolinite). When irradiated individually, benoxacor degraded at least 19 times faster than metolachlor in each reaction environment, consistent with its higher molar absorptivity within the solar spectrum than metolachlor. When metolachlor and benoxacor were irradiated as mixtures, benoxacor promoted metolachlor degradation on quartz and, to a lesser extent, in water, but not on kaolinite. On quartz, at a benoxacor/metolachlor molar ratio of 0.1:1, metolachlor degraded 1.8 times faster than in the absence of benoxacor; as the benoxacor/metolachlor ratio increased, metolachlor degradation rate also increased. The photolysis rate of benoxacor depended on its initial surface concentration and was promoted by metolachlor. Benoxacor photoproducts were capable of absorbing sunlight and serving as photosensitizers for metolachlor degradation. These results illustrate how a safener can influence the photochemistry of its coformulated herbicide and suggest that such mixture effects should be considered when evaluating the environmental fate of agrochemicals.

From rice straw to magnetically recoverable nitrogen doped biochar: Efficient activation of peroxymonosulfate for the degradation of metolachlor

Conversion of agricultural biomass waste to value-added biochar based catalysts receives tremendous interests because it falls into the scope of resource recycle concept. In this work, a magnetic nitrogen doped biochar-supported CoFe2O4 composite (MNBC) was synthesized by using rice straw, an abundant agricultural waste as the precursor. The prepared catalyst exhibited excellent performance in catalytic degradation of metolachlor (MET), a broad-spectrum chloroacetanilide herbicide, by coupling with peroxymonosulfate (PMS). The pyrolysis temperature played a significant role in the activity of the resultant catalysts. Among others, MNBC800 catalyst performed the best stability and reusability. In-situ (EPR) analysis revealed that SO4•−, •OH and 1O2 participated into the degradation process and the SO4•− was the major contributor. The degradation was promoted at neutral and weak basic conditions, whilst significantly inhibited at strong basic condition (pH = 11). Eleven degradation intermediates were successfully identified through liquid chromatography – quadrupole time-of-flight – mass spectrometer (LC-Q-TOF-MS). The degradation mainly occurred via hydroxylation, dechlorination, and dealkylation reactions. Additionally, though the degradation was greatly inhibited in real wastewater, it was not remarkably influenced in river and groundwater, implying its applicability in river/groundwater remediation. Eventually, the easy separation and low toxicity make the catalyst promising for the degradation of MET from several aquatic systems. This study would pave the way to the catalytic degradations of organic pollutants by low-cost biochar based catalysts.

Sulfate radical induced catalytic degradation of metolachlor: Efficiency and mechanism

Efficient removal of residual metolachlor (MET), a frequently used herbicide from aquatic system is highly desirable but remains a challenge. In the present study, the emerging sulfate radical based advanced oxidation processes (SR-AOPs) is developed for the degradation of MET from aqueous solution. At the conditions of [MET] = 10 mg L−1, [Peroxymonosulfate (PMS)] = 3 mM, [Catalyst] = 0.2 g L−1, pH = 6.5, the degradation process could be accomplished within 40 min and the derived pseudo-first-order kinetic rate constant (kapp) was 0.11 min−1. The effects of reaction conditions including pH, oxidant dosage, temperature, concomitant anions and humic acid on the degradation process were comprehensively investigated. Sulfate radical was identified to be the main contributor to the degradation process through radical scavenging and electron paramagnetic resonance (EPR) analysis. The second-order rate constant for reaction of SO4− with MET was determined to be 2.17 × 109 M−1s−1 by competition kinetic method. The degradation showed a moderate pH-tolerance. Specifically, alkaline/neutral conditions were beneficial for the MET degradation whilst acidic condition exhibited a detrimental effect on the degradation. Through LC-Q-TOF-MS analysis, eleven aromatic derivatives were detected and their molecular structures were tentatively proposed. A tentative mechanism was proposed based on the detected derivatives. The toxicity test further revealed that the degradation products performed a less toxicity than MET. The results pave an avenue toward the applications of SR-AOPs for MET elimination from aquatic environment.

Stimulation of earthworms (Eisenia fetida) on soil microbial communities to promote metolachlor degradation

Degradation of metolachlor in surface soil is extremely important to its potential mobility and overall persistence. In this study, the effects of earthworms (Eisenia fetida) on the degradation of metolachlor at two concentration levels (5 and 20 mg kg−1) in soil were investigated via the column experiment. The degradation kinetics of metolachlor indicate that addition of earthworms enhances metolachlor degradation significantly (P < 0.05), with the enhanced degradation rate of 30% and 63% in the low and high concentration treatments at the 15th day, respectively. Fungi rather than bacteria are primarily responsible for metolachlor degradation in soil, and earthworms stimulate metolachlor degradation mainly by stimulating the metolachlor-degrading functional microorganisms and improving fungal community structure. Earthworms prefer to promote the possible fungal degraders like order Sordariales, Microascales, Hypocreales and Mortierellales and the possible bacteria genus Rubritalea and strengthen the relationships between these primary fungi. Two metabolites metolachlor oxanilic (MOXA) and moetolachlor ethanesulfonic acid (MESA) are detected in soil and earthworms in the high concentration treatments. Earthworms stimulate the formation of MOXA and yet inhibit the formation of MESA in soil. Another metabolite metolachlor-2-hydroxy (M2H) is also detected in earthworms, which is reported firstly. The study provides an important information for the remediation of metolachlor-polluted soil.

Restructured fungal community diversity and biological interactions promote metolachlor biodegradation in soil microbial fuel cells

Soil microbial fuel cells (MFCs) provide an inexhaustible electron acceptor for the removal of metolachlor and in situ biocurrent stimulation for fungal activity was investigated. The metolachlor degradation rates enhanced by 33%–36% upon the introduction of electrodes after 23 d. In closed MFCs, the abundance of Mortierella as the most dominant genus increased to 43%–54% from 17% in the original soil, whereas those of Aphanoascus and Penicillium decreased to 0.24%–0.39% and 0.38–0.72% from 14% to 11%, respectively. Additionally, a 10-fold amplification of unique OTUs was observed, mainly from increase on the electrode surface. The different treatments were clustered, especially samples near the cathode. The linear discriminant analysis showed that Aphanoascus fulvescens acted as a biomarker between the original and treated soils. The co-occurrence networks demonstrated that Mortierella universally competed for growth with coexisting species while Cladosporium exhibited the most affiliations with species from the 36 other genera present. The correlation analysis indicated that the species associated with degradation belonged to Mortierella, Kernia, Chaetomium and Trichosporon, while the species associated with electrogenesis were Debaryomyces hansenii and Mortierella polycephala. Importantly, this study is the first to reveal fungal community structure in soil MFCs with degrading pollutants and producing electricity.

ROS production and removal of the herbicide metolachlor by air non-thermal plasma produced by DBD, DC− and DC+ discharges implemented within the same reactor

There is a long-time interest in non-thermal plasma research applied to different environmental issues. We have recently developed a reactor for water treatment by air non-thermal plasma, which can be energized by either DC (positive or negative polarity) or AC high voltage. This paper reports and discusses the results of a study in which the performance of this reactor was tested under the three discharge regimes, DC− and DC+ corona and DBD. Comparative experiments were carried out to characterize the system with regard to ROS (OH radicals, hydrogen peroxide and ozone) production and efficiency of treatment of the persistent herbicide metolachlor. DC− discharges turned out to be significantly more effective in the production of ROS than either DC+ and DBD: higher ozone and hydrogen peroxide concentrations were obtained at any given energy input and OH radical formation was more efficient. Specifically, the rate of OH radical formation was (16.2 ± 1.2), (6.34 ± 0.11) and (4.15 ± 0.13) μM kJ−1 for DC−, DBD and DC+, respectively. In view of these findings, it was not surprising that DC− discharge regime sustained the most efficient process of metolachlor removal. The efficiency was evaluated considering the decay of metolachlor concentration as a function of time and of energy input, the G50 parameter and the extent of mineralization achieved. The results clearly show that according to all these indicators DC− discharges appear to be the best choice among the three which can be implemented in this reactor. HPLC/UV–Vis and HPLC/MSn analyses revealed that, regardless of the type of discharge employed, the same oxidation intermediates are formed from metolachlor, although at different rates depending on the discharge type. These observations therefore suggest that the same mechanisms and reactive species are probably involved in the degradation of metolachlor by DC−, DC+ and DBD air non-thermal plasma.

Holistic assessment of occurrence and fate of metolachlor within environmental compartments of agricultural watersheds

BackgroundMetolachlor [(RS)-2-Chloro-N-(2-ethyl-6-methyl-phenyl)-N-(1-methoxypropan-2-yl)acetamide] and two degradates (metolachlor ethane-sulfonic acid and metolachlor oxanilic acid) are commonly observed in surface and groundwater. The behavior and fate of these compounds were examined over a 12-year period in seven agricultural watersheds in the United States. They were quantified in air, rain, streams, overland flow, groundwater, soil water, subsurface drain water, and water at the stream/groundwater interface. The compounds were frequently detected in surface and groundwater associated with agricultural areas. A mass budget approach, based on all available data from the study and literature, was used to determine a percentage-wise generalized distribution and fate of applied parent metolachlor in typical agricultural environments. ResultsIn these watersheds, about 90% of applied metolachlor was taken up by plants or degraded, 10% volatilized, and 0.3% returned as rainfall. One percent was transported to surface water, while an equal amount infiltrated into the unsaturated zone soil water. <0.02% reached the groundwater. Subsurface flow paths resulted in greater degradation of metolachlor because degradation reactions had more time to proceed. ConclusionsAn understanding of the residence times of water in the different environmental compartments, and the important processes affecting metolachlor as it is transported along flowpaths among the environmental compartments allows for a degree of predictability of metolachlor's fate. Degradates with long half-lives can be used (in a limited capacity) as tracers of metolachlor, because of their persistence and widespread occurrence in the environment.

Adsorption and Degradation of Metolachlor in Alluvial Soils: Effect of Poultry Litter

Soils in the Southern Mississippi Valley Alluvium (MLRA 131) have low organic matter content (&lt; 20 g kg-1) and application of poultry (Gallus gallus domesticus) litter to these soils may improve their quality. However, after litter application, chemical weed control practice such as herbicide application for row crop production remains the same. In soils where soybean [Glycine max (L.) Merr.] is grown, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl] acetamide] is applied as a pre-emergent herbicide to control broadleaf and annual grasses. There is an opportunity for metolachlor to leach to the groundwater during and after rainfall events. We hypothesize that metolachlor applied to these alluvial soils amended with poultry litter may degrade rapidly when compared to unamended (control) soils. Soil samples were collected from the top 10 cm of Commerce silt loam (Aeric Fluvaquents) and Sharkey clay (Vertic Haplaquepts). The samples were air dried and amended with poultry litter to increase the organic matter content to 20 g kg-1. Control samples received no poultry litter but were subjected to similar protocols as the amended samples. Batch experiments indicated significant increase in metolachlor adsorption for the amended soils, although adsorption was higher in Sharkey clay. Kinetics experiments showed that equilibrium was established 2 h for Commerce silt loam and 24 h for Sharkey clay. Metolachlor degradation was 6 times faster in the amended Commerce soil and 2.5 times faster in the amended Sharkey soil. Degradation rate in the amended Commerce soil was 2.3 times faster than the amended Sharkey clay. We conclude that adding poultry litter to these alluvial soils will increase metolachlor adsorption and further increase rates of degradation. However, appropriate amounts of poultry litter when applied, are promising for enhancing remediation of metolachlor.

Aspect of the degradation and adsorption kinetics of atrazine and metolachlor in andisol soil

Summary The degradation kinetics and sorption characteristics of atrazine and metolachlor in Japanese andisol soil were evaluated using laboratory incubation of soil samples. The water content of the soil was set to field capacity while three different temperatures (5, 25 and 35°C) were considered for the experiment. First order model fitted the degradation kinetics of both herbicides under the investigated temperature range with half-lives ranging from 19.2 to 46.9 days for atrazine and from 23.4 to 66.9 days for metolachlor, respectively. The activation energies (Ea) of atrazine and metolachlor calculated using Arhenius equation were 21.47 and 23.91 kJ mol−1, respectively. The soil sorption study was conducted using the batch equilibrium process. The adsorption behaviors of atrazine and metolachlor were investigated using linear, Freundlich and Langmuir isotherms although the linear and Freundlich isotherms gave relatively high correlation coefficient (R2 ) and very low standard error of estimate (SEE). The free energy (ΔG°) values were in the range −30.6 to −32.0 kJ/mol, and −32.1 to −41.5 kJ/mol for atrazine and metolachlor, respectively. Thermodynamic parameters indicated that the adsorption is spontaneous, endothermic accompanied by increase in entropy. The understanding of atrazine and metolachlor sorption processes is essential to determine the pesticide fate and availability in soil for pest control, biodegradation, runoff and leaching.

Effect of fly ash amendment on metolachlor and atrazine degradation and microbial activity in two soils

The study reports the effect of Inderprastha (IP) and Badarpur (BP) fly ashes on degradation of metolachlor and atrazine in Inceptisol and Alfisol soils. Metolachlor dissipated at faster rate in Alfisol (t1/2 8.2-8.6days) than in Inceptisol (t1/2 13.2-14.3days). The fly ashes enhanced the persistence of metolachlor in both the soils; however, the extent of effect was more in Inceptisol (t1/2 16.6-33.8days) than Alfisol (t1/2 8.4-12days) and effect increased with fly ash dose. 2-Ethyl-6-methylacetanilide was detected as the only metabolite of metolachlor. Atrazine was more persistent in flooded soils (t1/2 10.8-20.3days) than nonflooded soils (t1/2 3.7-12.6days) and fly ash increased its persistence, but effect was more pronounced in the flooded Inceptisol (t1/2 23.7-31days) and nonflooded Alfisol (t1/2 6.3-10.1days). Increased herbicide sorption in the fly ash-amended soils might have contributed to the increased pesticide persistence. TheIP fly ash inhibited microbial biomass carbon at 5% amendment levels in both the soils, while BP fly ash slightly increased microbial biomass carbon(MBC) content. Dehydrogenase activity was inhibited by both fly ashes in both the soils with maximum inhibition observed in the IP fly ash-amended Alfisol. No significant effect of fly ash amendment was observed on the fluorescein diacetate activity.

Photocatalytic-assisted ozone degradation of metolachlor aqueous solution

Photocatalytic-assisted ozone degradation of metolachlor (MTLC) aqueous solutions was investigated using neat TiO2 (prepared by sol-gel method) and TiO2/carbon composite (prepared from commercial available metal oxide and carbon phase) as catalysts. In terms of MTLC degradation, O3 on its own is enough to achieve 100% removal, but the introduction of light increased the rate of removal. On the other hand, the combination of O3 with light and the tested catalysts is mandatory to reach high mineralization in short reaction times. After 60min of reaction, the TOC removal was 87% and 75% in the presence of the prepared composite and TiO2, respectively. The concentration of two short chain carboxylic acids, oxalic and oxamic acids, was followed during MTLC degradation. The amount of these acids decreased when O3 and light were combined.In general, nitrogen ions, such as nitrate and ammonium, were detected in the studied processes. All treatments released ammonium and light based processes also produced nitrate.Microtox® analysis showed that the combined process in the presence of the prepared catalysts led to a remarkable reduction in the toxicity of the treated solution, decreasing the inhibition of luminescent activity of Vibrio Fisheri from 74% to 12%.