Metolachlor Research Articles

Degradation ability of Trichoderma spp. in the presence of poly(butylene adipate-co-terephthalate) microparticles

Investigating the effects of microplastics remains a pertinent issue given the extensive biodiversity of exposed organisms, variations in the mechanisms of action among individual polymers, and their reliance on environmental conditions. Therefore, the objective of the study was to investigate some interactions of the popular biodegradable plastic poly(butylene adipate-co-terephthalate) (PBAT) on some aspects of the physiology of filamentous fungi Trichoderma spp., integral components of the soil microbiome known for promoting plant growth and aiding in pollution remediation. In the two Trichoderma strains examined, a positive influence on fungal growth was observed in the presence of microplastics (MPs). The capability to degrade MPs with the involvement of cytochrome P450 monooxygenases was confirmed through the detection of terephthalic acid (TPA) in postculture extractions. Additionally, inhibition of degradative activity in the presence of MPs was observed for metolachlor (MET) and 2,4-dichlorophenoxyacetic acid (2,4-D). Moreover, biodegradation pathways with the involvement several dechlorinated or hydroxylated metabolites were proposed for examined compunds. Concentration-dependent shifts in oxidative stress enzymes activity and slight modifications in phospholipid profiles were noted for the tested PBAT concentrations. In summary, this study enhances our understanding of PBAT's impact on the physiology of filamentous fungal and their degradative capacities important for mitigating environmental pollution by xenobiotics and plastics.

In vitro and in silico analyses reveal the toxicity of metolachlor to grass carp hepatocytes and the antagonism of melatonin

Due to the widespread use of metolachlor (MET), the accumulation of MET and its metabolites in the environment has brought serious health problems to aquatic organisms. At present, the toxicity of MET on the physiological metabolism of aquatic animals mainly focused on the role of enzymes. There is still a lack of research on the molecular mechanisms of MET hepatotoxicity, especially on antagonizing MET toxicity. Therefore, this study focuses on grass carp hepatocytes (L8824 cells) closely related to toxin accumulation. By establishing a MET exposed L8824 cells model, it is determined that MET exposure induces pyrolytic inflammation of L8824 cells. Subsequent mechanistic studies found that MET exposure induces pyroptosis in L8824 cells through mitochondrial dysfunction, and siCaspase-1 inhibits the MET induced ROS production, suggesting a regulation of ROS-NLRP3- Caspase-1 pyroptotic inflammation cycling center in MET induced injury to L8824 cells. Molecular docking revealed a strong binding energy between melatonin (MT) and Caspase-1. Finally, a model of L8824 cells with MT intervention in MET exposure was established. MT can antagonize the pyroptosis induced by MET exposure in L8824 cells by targeting Caspase-1, thereby restoring mitochondrial function and inhibiting the ROS-pyroptosis cycle. This study discovered targets and mechanisms of MT regulating pyroptosis in MET exposed-L8824 cells, and the results are helpful to provide new targets for the design of MET antidotes.

Widely used herbicide metolachlor can promote harmful bloom formation by stimulating cyanobacterial growth and driving detrimental effects on their chytrid parasites

Metolachlor (MET) is a widely used herbicide that can adversely affect phytoplanktonic non-target organisms, such as cyanobacteria. Chytrids are zoosporic fungi ubiquitous in aquatic environments that parasitize cyanobacteria and can keep their proliferation in check. However, the influence of organic pollutants on the interaction between species, including parasitism, and the associated ecological processes remain poorly understood. Using the host-parasite system consisting of the toxigenic cyanobacterium Planktothrix agardhii and its chytrid parasite Rhizophydium megarrhizum, we investigated the effects of environmentally relevant concentrations of MET on host-parasite interactions under i) continuous exposure of chytrids and cyanobacteria, and ii) pre-exposure of chytrids. During a continuous exposure, the infection prevalence and intensity were not affected, but chytrid reproductive structures were smaller at the highest tested MET concentration. In the parasite's absence, MET promoted cyanobacteria growth possibly due to a hormesis effect. In the pre-exposure assay, MET caused multi- and transgenerational detrimental effects on parasite fitness. Chytrids pre-exposed to MET showed reduced infectivity, intensity, and prevalence of the infection, and their sporangia size was reduced. Thus, pre-exposure of the parasite to MET resulted in a delayed decline of the cyanobacterial cultures upon infection. After several parasite generations without MET exposure, the parasite recovered its initial fitness, indicating that detrimental effects are transient. This study demonstrates that widely used herbicides, such as MET, could favor cyanobacterial bloom formation both directly, by promoting cyanobacteria growth, and indirectly, by inhibiting their chytrid parasites, which are known to play a key role as top-down regulators of cyanobacteria. In addition, we evidence the relevance of addressing multi-organism systems, such as host-parasite interactions, in toxicity assays. This approach offers a more comprehensive understanding of the effects of pollutants on aquatic ecosystems.

Evaluating binding and interaction of selected pesticides with serum albumin proteins by Raman, 1H NMR, mass spectrometry and molecular dynamics simulation

Addressing the acute pesticide poisoning and toxicity to humans, is a global challenge of top priority. Serum albumin is the most abundant plasma protein, capable of binding with herbicide and pesticide residues. This study reports multifaceted approaches for in-depth and robust investigation of the molecular interactions of selected pesticides, including propanil (PPL), bromoxynil (BXL), metolachlor (MLR) and glyphosate (GPE) with bovine serum albumin (BSA) proteins using experimental (Raman and FTIR spectroscopy, native mass spectrometry and high field 1H NMR), molecular dynamics (MD) simulation and principal component analysis (PCA). The binding of pesticides with BSA resulted in BSA amide I and amide II Raman spectral shifts. PCA of Raman spectra of serum-pesticide complexes showed the grouping of pesticides on the score plot based on the similarities and differences in pesticides’ chemical structures. Native mass spectrometry results revealed strong adduct formation of the pesticides with the protein. The observed changes in chemical shifts, peak broadening or peak disappearance of characteristic proton signals of the pesticides, indicated altered chemical environments due to binding BSA-pesticides interactions. The results of MD simulation conducted for over 500 ns revealed strong pesticides interaction with LEU197, LEU218, LEU237, TRP213, SER286 and ILE289 residues to the site I of BSA. Free energy landscapes provided insights into the conformational changes in BSA on the binding of pesticides. Overall, the experimental and computational results are in consonant and indicate the binding of pesticides into the site I and site II (sub-domain IIA) of the BSA via hydrogen bonding, non-covalent and hydrophobic interactions. Communicated by Ramaswamy H. Sarma

Palmelloid-like phenotype in the alga Raphidocelis subcapitata exposed to pollutants: A generalized adaptive strategy to stress or a specific cellular response?

This work focuses on the formation of palmelloid-like phenotype in the freshwater alga Raphidocelis subcapitata (formerly known as Pseudokirchneriella subcapitata and Selenastrum capricornutum), when exposed to adverse conditions generated by the presence of organic [the antibiotic erythromycin (ERY) and the herbicide metolachlor (MET)] or inorganic [the heavy metals, cadmium (Cd) and zinc (Zn)] pollutants, at environmentally relevant concentrations. This alga in absence of stress or when exposed to ERY or Zn, up to 200 µg/L, essentially showed a single-nucleus state, although algal growth was reduced or stopped. R. subcapitata “switched” to a multinucleated state (palmelloid-like morphology) and accumulated energy-reserve compounds (neutral lipids) when stressed by 100–200 µg/L MET or 200 µg/L Cd; at these concentrations of pollutants, growth was arrested, however, the majority of the algal population (≥83 %) was alive. The formation of palmelloid-like phenotype, at sub-lethal concentrations of pollutants, was dependent on the pollutant, its concentration and exposure time. The multinucleated structure is a transitory phenotype since R. subcapitata population was able to revert to a single-nucleus state, with normal cell size, within 24–96 h (depending on the impact of the toxic in the alga), after being transferred to fresh OECD medium, without pollutants. The obtained results indicate that the formation of a palmelloid-like phenotype in R. subcapitata is dependent on the mode of action of toxics and their concentration, not constituting a generalized defense mechanism against stress. The observations here shown contribute to understanding the different strategies used by the unicellular alga R. subcapitata to cope with severe stress imposed by organic and inorganic pollutants.

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.

Metolachlor metal-organic framework nanoparticles for reducing leaching, ecotoxicity and improving bioactivity.

The adverse effects of pesticides has led to a series of ecological, environmental and public health issues. Amide herbicides are an important agrochemical, yet many are prone to leach and pollute the environment, which limits their further application. In this study, metolachlor (METO) was selected as a model pesticide and a controlled released nanoparticle (NP) system was constructed employing a zeolitic imidazolate framework-8 hybrid inorganic-organic porous material (METO@ZIF-8). The synthesis parameters of METO@ZIF-8 were optimized, and the loading content of METO@ZIF-8 was maximized by a central composite design of response surface test. The NPs were regular dodecahedron with uniform size (mostly 54.3nm diameter). METO@ZIF-8 had high specific surface area and good dispersal in water. Moreover, it endowed the active ingredient with a pH-responsive release property. The nanocarrier effectively improved the adsorption capacity of METO in soil and reduce the leaching by 10.3-21.7%. Pot experiments suggested that the control effect of METO@ZIF-8 was 16.6 and 48.4% higher than that of METO emulsifiable concentrate (EC) and METO technical concentration (TC) at the recommended dose. Based on the excellent controlled release profiles, METO@ZIF-8 did not affect corn plant growth and significantly reduced the risk of phytotoxicity induced by METO. METO@ZIF-8 effectively reduced acute toxicity in zebrafish compared with METO EC. This study explored the fabrication of a nanocarrier for improving the efficacy and promoting the environmental safety of leachable amide herbicides. © 2022 Society of Chemical Industry.

Evaluation of the toxicological effects of atrazine-metolachlor in male rats: in vivo and in silico studies.

The types and mechanisms of atrazine-metolachlor toxicity, an herbicide composed of atrazine (ATR) and metolachlor (MET), need to be further investigated. This study evaluated the toxic actions of ATR-MET by in vivo and in silico methods. Here, varying doses of ATR-MET were orally administered to rats once daily for twenty-one days using normal saline as control. Molecular docking was used to characterize the binding of ATR and MET with androgen receptor (AR) to predict their potential endocrine-disrupting effects, using testosterone as benchmark. ATR-MET-induced-testicular toxicity (reduced sperm motility, count, and daily sperm production and increased live/dead ratio) was accompanied with testicular oxidative stress (diminished level of reduced glutathione, activities of glutathione-S-transferase, superoxide dismutase and catalase and increased level of malondialdehyde). Furthermore, ATR-MET induced cardiovascular toxicity (increased levels of plasma total cholesterol, HDL-cholesterol, LDL-cholesterol, and triglycerides) with concomitant induction of renal toxicity (increased plasma creatinine and urea levels), and hepatotoxicity (increased plasma bilirubin, alkaline phosphatase, acid phosphatase, alanine aminotransferase and aspartate aminotransferase). Binding energy and amino acid interactions from in silico study revealed that MET possessed endocrine-disrupting capacity. In conclusion, exposure to atrazine-metolachlor could promote cardiovascular, renal, hepatic, as well as reproductive impairment in experimental male albino rats.

Occurrence of Banned and Currently Used Herbicides, in Groundwater of Northern Greece: A Human Health Risk Assessment Approach.

The presence of pesticide residues in groundwater, many years after their phase out in European Union verifies that the persistence in aquifer is much higher than in other environmental compartments. Currently used and banned pesticides were monitored in Northern Greece aquifers and a human health risk assessment was conducted. The target compounds were the herbicides metolachlor (MET), terbuthylazine (TER), atrazine (ATR) and its metabolites deisopropylatrazine (DIA), deethylatrazine (DEA) and hydroxyatrazine (HA). Eleven sampling sites were selected to have representatives of different types of wells. Pesticides were extracted by solid-phase extraction and analyzed by liquid chromatography. MET was detected in 100% of water samples followed by ATR (96.4%), DEA and HA (88.6%), DIA (78.2%) and TER (67.5%). ATR, DIA, DEA, HA, MET and TER mean concentrations detected were 0.18, 0.29, 0.14, 0.09, 0.16 and 0.15 μg/L, respectively. Obtained results were compared with historical data from previous monitoring studies and temporal trends were assessed. Preferential flow was the major factor facilitating pesticide leaching within the month of herbicide application. Moreover, apparent age of groundwater and the reduced pesticide dissipation rates on aquifers resulted of long-term detection of legacy pesticides. Although atrazine had been banned more than 18 years ago, it was detected frequently and their concentrations in some cases were over the maximum permissible limit. Furthermore, human health risk assessment of pesticides was calculated for two different age groups though drinking water consumption. In all examined wells, the sum of the HQ values were lower than the unity. As a result, the analyzed drinking water wells are considered safe according to the acute risk assessment process. However, the presence of atrazine residues causes concerns related with chronic toxicity, since ATR R values were greater than the parametric one of 1 × 10−6 advised by USEPA, for both age groups.

Metolachlor adsorption using walnut shell biochar modified by soil minerals

The removal of pesticide residues in soil is a research hotspot. The metolachlor (MET) adsorption by walnut shell biochar (BC) modified with montmorillonite (MBC), illite (IBC), and kaolinite (KBC), as well as the original BC (OBC) was investigated. The characteristics of samples were studied by scanning electron microscopy and mapping analysis, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry, and chemical stability analysis. The effects of the dosage, ionic strength, and pH, and determined the adsorption kinetics and isotherms for MET with the BCs were analyzed. In addition, response surface methodology regression model analysis was conducted and the adsorption mechanisms were investigated. The results showed that the thermal stability and chemical stability of MBC, IBC, and KBC were higher than those of OBC, and MBC had the greatest stability. The MET adsorption rates of OBC, MBC, IBC, and KBC were 62.15%, 92.47%, 87.97%, and 83.31%, respectively. The kinetic fitting results and adsorption mechanisms showed that the modification of BC with minerals enhanced the physical adsorption of MET. The maximum MET adsorption capacities by OBC, MBC, IBC, and KBC were 39.68 mg g−1, 68.49 mg g−1, 65.79 mg g−1, and 65.36 mg g−1, respectively. Hydrogen bonds, π–π bonds, coordination bonds, and hydrophobic interactions were the key adsorption mechanisms. Therefore, the mineral-modified BCs were characterized by high adsorption rates and stability. This approach can make BC more efficient, with higher performance as a low cost soil amendment.

Degradation potential of MCPA, metolachlor and propiconazole in the hyporheic sediments of an agriculturally impacted river

Hyporheic sediments are influenced by physical, biological, and chemical processes due to the interactions with river water and has been shown to play an important role in the environmental fate of pesticides.Therefore, this study evaluated the bacterial degradation potential of MCPA, metolachlor and propiconazole in hyporheic sediments sampled along a 20 km long stretch of an agriculturally impacted river dominated primarily by water losing conditions. Water physicochemical parameters in the river and nearby groundwater wells were assessed along with pesticide sorption to sediments and bacterial community composition. Degradation and mineralisation batch experiments were set up from six locations (five water losing, one water gaining) using environmentally relevant concentrations of pesticides (10 μg kg−1). Highly variable DT50 values from 11 to 44 days for MCPA, 11–27 days for metolachlor (MTC) and 60–147 days for propiconazole were calculated based on ~140 day studies. Degradation of MTC led to accumulation of the transformation products MOA and MESA in batch experiments. Noteworthy, MESA was detected in the groundwater wells adjacent to the part of the river impacted by losing conditions suggesting that degradation processes in hyporheic sediments may lead to the formation of transformation products (TP) leaching towards groundwater. Further, from propiconazole was identified a persistent transformation product being different from 1,2,4-triazole.Specific calculated DT50 values could not the linked to bacterial diversity. However, generally all sediment samples were characterised by high bacterial diversity, where approximately 80% of the relative sequence abundances were < 1%, which may increase the likelihood of finding contaminant-degrading genes, thereby explaining the general high contaminant-degrading activity. The studied sediments revealed a high potential to degrade pesticides despite only being exposed to low diffuse pollutant concentrations that is similar to calculated DT50 values in agricultural soils.

Stereoselective degradation pathway of amide chiral herbicides and its impacts on plant and bacterial communities in integrated vertical flow constructed wetlands

This study demonstrates the stereoselective degradation patterns and biodegradation mechanisms of metolachlor (MET) and napropamide (NAP) in integrated vertical flow constructed wetlands (IVCW). The higher interphase transferability of NAP resulted in higher degradation rates of 90.60 ± 4.09%. The enantiomeric fraction (EF) values of 0.38 ± 0.02 and 0.54 ± 0.03, respectively, recorded for the enantiomers S-MET and R-NAP, with higher herbicidal activities, demonstrated their highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants showed positive correlations with the degradation efficiency and enantioselectivity of MET and NAP. Adaptive regulations by plants promoted the proliferation of microbial genera like Enterobacter and unclassified_Burkholderiales, which could facilitate plant growth. Moreover, enrichment of the herbicide-degrading functional bacteria Terrimonas (5.10%), Comamonas (4.05%) Pseudoxanthomonas (4.49%) and Mycobacterium (1.42%) demonstrably promoted the preferential degradation of S-MET and R-NAP. Furthermore, the abundance of Ferruginibacter favored the use of R-NAP as carbon source to achieve co-removal of R-NAP and NO3–-N.

Effective adsorption of metolachlor herbicide by MIL-53(Al) metal-organic framework: Optimization, validation and molecular docking simulation studies

Effective removal and optimization models of metolachlor (MET) adsorption was carried out using MIL-53(Al) metal–organic framework (MOF), response surface methodology (RSM), artificial neural network (ANN) and molecular docking simulation. The MOF was hydrothermally synthesized and characterized using the Field Emission Scanning Electron Microscopy (FESEM), Powdered X-ray diffraction (XRD), Fourier Transformed Infrared (FTIR) and Brunauer, Emmett and Teller (BET). High adsorption capacity of MET was recorded (241.617 mg/g) with fast equilibration time of ∼ 25 min at 0.999 coefficient of determination (R2) which was due to the high surface area of the MOF (1104 m2/g). The kinetics followed the pseudo-second order model describing a chemisorption adsorption process. The isotherm showed a multilayer adsorption process of the Freundlich model with R2 of 0.990. The thermodynamic parameters followed an endothermic and spontaneous adsorption. The optimization by the RSM was significant with minimum number of experimental runs, lesser error and showed a simultaneous interaction of the adsorption parameters in predicting MET adsorption capacity. The ANN learning algorithm performed significantly in predicting and validating the experimental conditions designed by the RSM model. Both the RSM and ANN model provide remarkable values that are very similar with the experimental results. The binding mode and binding affinity of MIL-53(Al) and MET were determined by the docking simulation. Prospect for the reusability potential of the MOF was explored and the findings were significant. Hence, the results showed the potential of the MOF for the effective remediation of MET in aqueous medium.

Analytical method for sequential determination of persistent herbicides and their metabolites in fish tissues by UPLC–MS/MS

A novel and accurate liquid chromatography–tandem mass spectrometry method was developed to sequentially determine three persistent herbicides (atrazine (ATZ), acetochlor (ACE), and metolachlor (MET)) and seven characteristic metabolites (desethylatrazine (DEA), deisopropylatrazine (DIA), diaminochlorotriazine (DACT), MET–oxanilic acid (MET-OA), MET-ethanesulfonic acid (MET-ESA), ACE-ESA, and ACE-OA) in fresh fish tissues from six fish species. A modified QuEChERS method was conducted to extract the target compounds from fish tissues. Matrix-matched calibrations of the target analytes were carried out at spiking levels of 1, 10, 100, and 1000 ng g−1. The method was validated in accordance with Codex guidelines (CAC/GL 71–2009). Recoveries for the target analytes were 67–120% with relative standard deviations below 20%, and the matrix effects ranged from −58.7% to 59.3%. The limits of detection and quantitation were 0.01–1.90 and 0.02–6.35 ng g−1, respectively. Moreover, the method was successfully applied to analyze the concentrations of the target chemicals in fresh tissue samples of six fish species (n = 67) collected from four markets in Nanning City, Guangxi Province, China. The concentrations in all samples were 1.1–140.5 ng g−1. Interestingly, this study was the first to measure DEA and DIA in fish liver, and their highest concentrations were 10.7 and 14.2 ng g−1, respectively. This method provides a basis for studying the pathways of biotransformation, bioaccumulation, detoxification, and exposure patterns of ACE, ATZ, MET, and their metabolites in aquatic environments.

Adsorption of metolachlor by a novel magnetic illite–biochar and recovery from soil

In this study, we investigated a highly efficient adsorbent that can be recycled from the soil. Walnut shells were used as raw materials to prepare original ecological biochar (OBC), illite modified biochar (IBC), FeCl3 modified biochar (magnetic biochar; MBC), and illite and FeCl3 modified biochar (IMBC), which were tested as low-cost adsorbents. The agents were used to remove metolachlor (MET) from soil. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, magnetic sensitivity curve analysis, and a series of adsorption experiments were conducted to study the interaction between illite and MBC, and the effect on MET adsorption. Compared with OBC, IMBC had more adsorption sites on the surface. IMBC improved the hole filling effect during the adsorption process. IMBC had more oxygen-containing functional groups and it performed better at removing organic matter through π-π interactions. According to the Langmuir model, the Q0 values for IBC, MBC, and IMBC were 91.74 mg g−1, 107.53 mg g−1, and 129.87 mg g−1, respectively, which were significantly higher than that for OBC (72.99 mg g−1). The response surface model was used to explore the optimal adsorption conditions for IMBC. After three regeneration cycles, the MET adsorption rate with IMBC was still 81.38% and the MET recovery rate was 98.12%. Therefore, IMBC was characterized as an adsorbent with high efficiency, low cost, and good recyclability. In addition, we propose a suitable agricultural system for recovering MBC on site in the field.

Metolachlor-adsorption on the walnut shell biochar modified by the fulvic acid and citric acid in water

In this study, we used fulvic acid (FA) and citric acid (CA) to soak walnut shell powder. The soaked walnut shell powder is then burned at 700 °C into biochar (BC). The modified BC is due to the removal of metolachlor (MET) in the aqueous solution. Firstly, in the study of kinetics and isotherm, it was found that the optimal modified concentrations of FA and CA on BC were both 800 mg L–1. Then characterize the BCs (FBC and CBC) with the best modification effect (SEM, FTIR, XRD). The element composition and surface functional groups of FBC and CBC are analyzed. According to the Langmuir model, the maximum adsorption capacity of FBC and CBC are 99.01 mg g–1 and 74.07 mg g–1, respectively, which are significantly higher than the original OBC (51.28 mg g–1). It can be seen that both FBC and CBC have good adsorption performance, but the adsorption effect of FBC is better. Finally, the results of adsorption regeneration experiments in agricultural wastewater show that FBC and CBC not only have better adsorption in agricultural wastewater, but also have good regeneration performance. These results help to study the adsorption mechanism and process optimization further.

Micellar-enhanced thermochemically induced fluorescence derivatization (ME-TIFD) method for the determination of metolachlor herbicide residues in water

A sensitive micellar-enhanced thermochemically induced fluorescence derivatization (ME-TIFD) method for a rapid determination of metolachlor (MET) residues based on the O-phthalaldehyde (OPA)-thermoproduct complex of MET (OPA-MET) was investigated. Both SDS and Brij-700 have been used as surfactant micelles. This study advocates the TIFD method analytical parameters curation. Fluorescence enhancement and its stabilization were highlighted for the OPA-MET equimolar complex in micellar aqueous solutions. The new analytical features (K: binding constant and ΔG°: Gibbs energy) for controlling thermodynamic interactions were carried out at 25 °C. Under the optimized conditions, the calibration curves were linear with correlation coefficients ranging from 0.9788 to 0.9896 at the concentration level of 10-580 ng mL–1, and the limits of detection were 0.04-0.7 ng mL−1 at a signal-to-noise (S/N) of 3. The SPE/ME-TIFD applications combined with analysis of well and tap water spiked samples with metolachlor yield satisfactory mean recoveries (RSD) 102.2–108.1% (5.1–7.3%) and 103.6–106.0% (6.3–7.6%), respectively.

Comparative effect of weed control methods on Mexican sunflower (Tithonia diversifolia) in maize

Mexican sunflower management in arable crops is becoming increasingly important due to its prevalent growth habit. The field experiments were conducted to compare weed suppressive abilities of two cover crops and two maize herbicides on Mexican sunflower. The treatments consist of the pre-emergence application of Primextra Gold (atrazine + metolachlor) at 4 l/ha, a post-emergence application of Aminoforce (2, 4-D) at 1.6 l/ha, two cover crops, Centrosema pubescens (Centro) at 2.5 kg/ha and Pueraria phaseoloides (Puero) at 2.0 kg/ha, hand weeding at 2 and 5 weeks after sowing (WAS) and no weeding. The experimental design was a randomized complete block design with four replications. Pre-emergence herbicide produced taller plants at 8 and 12 WAS and higher number of leaves at 12 WAS. Despite two hand weedings (at 2 and 5 WAS), the weed biomass of hand weeding treatment was not different from no weeding. Higher weed densities produced by hand weeding and no weeding at 12 WAS indicated that the two herbicides and the two cover crop treatments gave better weed control than both weed checks. Weed control was 4, 7 and 8 times better in pre-emergence, post-emergence and Centro; respectively, than no weeding at 8 WAS. Although Centro provided long term weed control, the herbicides were able to provide early protection for the maize plants. The highest maize yield of 2.21 t/ha obtained from Primextra Gold (atrazine + metolachlor) at 4l/ha was significantly higher than yields from the other treatments. Yield reduction of 24.5, 27.7, 34.4, 40.8 and 94.2% was obtained in 1.6 l/ha Aminoforce, Centro, hand weeding, Puero and no weeding, respectively, when compared to maize yield from Primextra Gold. Key words: Mexican sunflower, cover crops, herbicides, hand weeding, weed control.

Strong adsorption of metolachlor by biochar prepared from walnut shells in water.

In this study, we investigated the removal of metolachlor (MET) by biochar (BC) prepared from walnut shells (W-BC) compared with BCs made from cow dung (D-BC) and corn cobs (C-BC) by characterizing the adsorption kinetics, pH, adsorbent dose, and ionic strength, and using isotherm models. Weight analysis was also conducted to understand the adsorption capacity and adsorption mechanisms. The results showed that the MET removal rates were 87.89% (W-BC), 52.91% (D-BC), and 10.91% (C-BC), respectively. According to the results fitted to the Langmuir isotherm model, the saturated adsorption capacities for MET were 96.15 mg g-1, 37.88 mg g-1, and 11.98 mg g-1 with W-BC, D-BC, and C-BC, respectively. The results demonstrated that W-BC was particularly effective at MET removal. Analyses based on the weights of different factors showed that the correlation coefficient was highest for the BC type with 46.11% in the MET adsorption process, followed by the initial concentration of MET (19.29%). The adsorption of MET by BCs was probably influenced mostly by electron donor-acceptor interactions and pore filling. These results may facilitate further studies of the adsorption mechanism and optimization of the process.

Exposure of the alga Pseudokirchneriella subcapitata to environmentally relevant concentrations of the herbicide metolachlor: Impact on the redox homeostasis

This study investigated the effect of the herbicide metolachlor (MET) on the redox homeostasis of the freshwater green alga Pseudokirchneriella subcapitata. At low MET concentrations (≤40 μg L−1), no effects on algal cells were detected. The exposure of P. subcapitata to 45–235 μg L−1 MET induced a significant increase of reactive oxygen species (ROS). The intracellular levels of ROS were particularly increased at high (115 and 235 μg L−1) but environmentally relevant MET concentrations. The exposure of algal cells to 115 and 235 μg L−1 MET originated a decrease in the levels of antioxidants molecules (reduced glutathione and carotenoids) as well as a reduction of the activity of scavenging enzymes (superoxide dismutase and catalase). These results suggest that antioxidant (non-enzymatic and enzymatic) defenses were affected by the excess of MET. As consequence of this imbalance (ROS overproduction and decline of the antioxidant system), ROS inflicted oxidative injury with lipid peroxidation and damage of cell membrane integrity. The results provide further insights about the toxic modes of action of MET on a non-target organism and emphasize the relevance of toxicological studies in the assessment of the impact of herbicides in freshwater environments.