Herbicide Clopyralid Research Articles

Biocompatible Nano-Cocrystal Engineering for Targeted Herbicide Delivery: Enhancing Efficacy through Stimuli-Responsive Release and Reduced Environmental Losses.

In addressing the critical challenges posed by the misuse and inefficiency of traditional pesticides, we introduce a Nano-Cocrystal material composed of the herbicide clopyralid and coformer phenazine. Developed through synergistic supramolecular self-assembly and mechanochemical nanotechnology, this Nano-Cocrystal significantly enhances pesticide performance. It exhibits a marked improvement in stability, with reductions in hygroscopicity and volatility by approximately 38%. Moreover, it intelligently modulates release according to environmental factors, such as temperature, pH, and soil inorganic salts, demonstrating decreased solubility by up to four times and improved wettability and adhesion on leaf surfaces. Importantly, the herbicidal activity surpasses that of pure clopyralid, increasing suppression rates of Medicago sativa L. and Oxalis corniculata L. by up to 27% at the highest dosage. This Nano-Cocrystal also shows enhanced crop safety and reduced genotoxicity compared to conventional formulations. Offering a blend of simplicity, cost-effectiveness, and robust stability, our findings contribute a sustainable solution to agricultural practices, favoring the safety of nontarget organisms.

Incorporating climate projections in the environmental risk assessment of pesticides in aquatic ecosystems.

Global climate change will significantly impact the biodiversity of freshwater ecosystems, both directly and indirectly via the exacerbation of impacts from other stressors. Pesticides form a prime example of chemical stressors that are expected to synergize with climate change. Aquatic exposures to pesticides might change in magnitude due to increased runoff from agricultural fields, and in composition, as application patterns will change due to changes in pest pressures and crop types. Any prospective chemical risk assessment that aims to capture the influence of climate change should properly and comprehensively account for the variabilities and uncertainties that are inherent to projections of future climate. This is only feasible if they probabilistically propagate extensive ensembles of climate model projections. However, current prospective risk assessments typically make use of process-based models of chemical fate that do not typically allow for such high-throughput applications. Here, we describe a Bayesian network model that does. It incorporates a two-step univariate regression model based on a 30-day antecedent precipitation index, circumventing the need for computationally laborious mechanistic models. We show its feasibility and application potential in a case study with two pesticides in a Norwegian stream: the fungicide trifloxystrobin and herbicide clopyralid. Our analysis showed that variations in pesticide application rates as well as precipitation intensity lead to variations in in-stream exposures. When relating to aquatic risks, the influence of these processes is reduced and distributions of risk are dominated by effect-related parameters. Predicted risks for clopyralid were negligible, but the probability of unacceptable future environmental risks due to exposure to trifloxystrobin (i.e., a risk quotient >1) was 8%-12%. This percentage further increased to 30%-35% when a more conservative precautionary factor of 100 instead of 30 was used. Integr Environ Assess Manag 2024;20:384-400. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Probabilistic risk assessment of pesticides under future agricultural and climate scenarios using a bayesian network

The use of Bayesian networks (BN) for environmental risk assessment has increased in recent years as they offer a more transparent way to characterize risk and evaluate uncertainty than the traditional risk assessment paradigms. In this study, a novel probabilistic approach applying a BN for risk calculation was further developed and explored by linking the calculation a risk quotient to alternative future scenarios. This extended version of the BN model uses predictions from a process-based pesticide exposure model (World Integrated System for Pesticide Exposure - WISPE) in the exposure characterization and toxicity test data in the effect characterization. The probability distributions for exposure and effect are combined into a risk characterization (i.e. the probability distribution of a risk quotient), a common measure of the exceedance of an environmentally safe exposure threshold. The BN model was used to account for variabilities of the predicted pesticide exposure in agricultural streams, and inter-species variability in sensitivity to the pesticide among freshwater species. In Northern Europe, future climate scenarios typically predict increased temperature and precipitation, which can be expected to cause an increase in weed infestations, plant disease and insect pests. Such climate-related changes in pest pressure in turn can give rise to altered agricultural practices, such as increased pesticide application rates, as an adaptation to climate change. The WISPE model was used to link a set of scenarios consisting of two climate models, three pesticide application scenarios and three periods (year ranges), for a case study in South-East Norway. The model was set up for the case study by specifying environmental factors such as soil properties and field slope together with chemical properties of pesticides to predict the pesticide exposure in streams adjacent to the agricultural fields. The model was parameterized and evaluated for five selected pesticides: the three herbicides clopyralid, fluroxypyr-meptyl, and 2-(4-chloro-2-methylphenoxy) acetic acid (MCPA), and the two fungicides prothiocanzole and trifloxystrobin. This approach enabled the calculation and visualization of probability distribution of the risk quotients for the future time horizons 2050 and 2085. The risk posed by the pesticides were in general low for this case study, with highest probability of the risk quotient exceeding 1 for the two herbicides fluroxypyr-meptyl and MCPA. The future climate projections used here resulted in only minor changes in predicted exposure concentrations and thereby future risk. However, a stronger increase in risk was predicted for the scenarios with increased pesticide application, which can represent an adaptation to a future climate with higher pest pressures. In the current study, the specific BN model predictions were constrained by an existing set of climate projections which represented only one IPCC scenario (A1B) and two climate models. Further advancement of the BN modelling demonstrated herein, including more recent climate scenarios and a larger set of climate models, is anticipated to result in more relevant risk characterization also for future climate conditions. This probabilistic approach will have the potential to aid targeted management of ecological risks in support of future research, industry and regulatory needs.

Using the Pesticide Toxicity Index to show the potential ecosystem benefits of on-farm biobeds.

The influent and effluent of two single-cell biobeds (Province of Alberta, Canada) and two dual cell-biobeds (Province of Saskatchewan, Canada) were monitored during a number of growing seasons. A total of 59 unique pesticide active ingredients were detected, with all biobed influent samples (n=54) and 93% of effluent samples (n=54) containing pesticide mixtures. About one-half of the effluent samples in both single-cell (56%) and dual-cell (45%) biobeds contained active ingredients that have Groundwater Ubiquity Score (GUS) values >2.8 and so were more likely to move through the biomatrix materials into effluent. The Pesticide Toxicity Index (PTI) calculated for aquatic indicator species (i.e., vascular and nonvascular plants, invertebrates, and fish) was always larger for influent samples (e.g., median PTI>500 for invertebrates in dual-cell biobed) than effluent samples (i.e., median PTI<1). As such, this study demonstrates the potential ecosystem benefits of the broad adoption of on-farm biobeds in the Canadian Prairies for recycling tank rinsate as a strategy to accelerate a green economy. Although biobeds were highly effective in reducing the concentrations for pesticides with a wide range of soil organic carbon coefficient and half-life values, the biobed effectiveness was relatively poor for the herbicides clopyralid, diclofop, fluroxypyr, and imazethapyr. Clopyralid (3.02), fluroxypyr (3.70), and imazethapyr (3.90) all have relatively high GUS values(>2.8) and are thus more likely to be detected in effluent than active ingredients with smaller GUS values. This suggests that further improvements in biosystem design need to be made for optimizing the recycling of these pesticides.

Effect of Herbicide Clopyralid and Imazamox on Dehydrogenase Enzyme in Soil of Regenerated Pedunculate Oak Forests

Clopyralid and imazamox are successfully used for weed control during the first years of regeneration of pedunculate oak forests. Hence, the question that arises is how these herbicides affect microorganisms, especially the activity of dehydrogenase enzyme, when they reach the soil. Two study sites were selected in regenerated pedunculate oak forests, and the two herbicides were applied in two doses that are used for weed control (clopyralid, 100 g a.i. ha−1 and 120 g a.i. ha−1; imazamox, 40 g a.i. ha−1 and 48 g a.i. ha−1). The effect of the herbicides was evaluated 7, 14, 21, 30, and 60 days after application. A significant reduction in dehydrogenase activity was found on days 7 and 14 at both sites. However, after 14 days there was a recovery of dehydrogenase activity for all treatments such that the values obtained on day 21 did not differ from the control values. The effect of clopyralid and imazamox on dehydrogenase activity was not dose-dependent. Dehydrogenase activity also depended on soil properties, soil sampling time and climatic conditions during the investigation years. The results show that clopyralid and imazamox can reduce soil dehydrogenase activity, but this effect is transient. This can be attributed to the ability of microorganisms to overcome the stress caused by the herbicide by developing the capability to utilize herbicides as a nutrient source and proliferating in such an environment.

Perturbation of clopyralid on bio-denitrification and nitrite accumulation: Long-term performance and biological mechanism

The contaminant of herbicide clopyralid (3,6-dichloro-2- pyridine-carboxylic acid, CLP) poses a potential threat to the ecological system. However, there is a general lack of research devoted to the perturbation of CLP to the bio-denitrification process, and its biological response mechanism remains unclear. Herein, long-term exposure to CLP was systematically investigated to explore its influences on denitrification performance and dynamic microbial responses. Results showed that low-concentration of CLP (<15 mg/L) caused severe nitrite accumulation initially, while higher concentrations (35–60 mg/L) of CLP had no further effect after long-term acclimation. The mechanistic study demonstrated that CLP reduced nitrite reductase (NIR) activity and inhibited metabolic activity (carbon metabolism and nitrogen metabolism) by causing oxidative stress and membrane damage, resulting in nitrite accumulation. However, after more than 80 days of acclimation, almost no nitrite accumulation was found at 60 mg/L CLP. It was proposed that the secretion of extracellular polymeric substances (EPS) increased from 75.03 mg/g VSS at 15 mg/L CLP to 109.97 mg/g VSS at 60 mg/L CLP, which strengthened the protection of microbial cells and improved NIR activity and metabolic activities. Additionally, the biodiversity and richness of the microbial community experienced a U-shaped process. The relative abundance of denitrification- and carbon metabolism-associated microorganisms decreased initially and then recovered with the enrichment of microorganisms related to the secretion of EPS and N-acyl-homoserine lactones (AHLs). These microorganisms protected microbe from toxic substances and regulated their interactions among inter- and intra-species. This study revealed the biological response mechanism of denitrification after successive exposure to CLP and provided proper guidance for analyzing and treating herbicide-containing wastewater.

Design, synthesis and mode of action of novel 3-chloro-6-pyrazolyl picolinate derivatives as herbicide candidates.

Picolinate/picolinic acid compounds are an important class of synthetic auxin herbicides. To explore the herbicidal activity of 6-pyrazolyl picolinate compounds, a series of 3-chloro-6-pyrazolyl-picolinate derivatives was designed and synthesized. Twenty-five 3-chloro-6-pyrazolyl-picolinate derivatives synthesized were tested for herbicidal activity and the IC50 value of compound c5 to the growth of Arabidopsis thaliana root was 27 times lower than that of the commercial herbicide clopyralid. Compound c5 displayed better post-emergence herbicidal activity and broader (Picloram, Clopyralid, Aminopyralid) herbicidal spectrum at a dosage of 400 g ha-1 in comparison with clopyralid; it also was safe to wheat and maize at this dosage. Arabidopsis thaliana phenotypes and expression of auxin-response genes demonstrated that compound c5 might be a novel auxin-type herbicide. Molecular docking analyses revealed that compound c5 had stronger binding ability to receptor AFB5 (auxin signaling F-box protein 5) than clopyralid. These 6-pyrazolyl picolinate compounds could be used as potential lead structures for the discovery of a novel synthetic auxin herbicide. © 2021 Society of Chemical Industry.

Towards a higher photostability of ZnO photo-electrocatalysts in the degradation of organics by using MMO substrates

In this work, it is proposed a novel strategy to increase the photostability of the ZnO photoelectrocatalyst under prolonged light irradiation, without the addition or deposition of metals and/or semiconductor oxides during their synthesis. This strategy is based on the use of a mixed metal oxide (MMO-Ru0.3Ti0.7O2) coating as the substrate for the electrodeposition of ZnO. To assess it, the electrodeposition of ZnO films on Ti and Ti/MMO substrates and the photoelectrocatalytic activity of these materials for the degradation of the herbicide clopyralid were studied. The results showed that the substrate directly influenced the photo-stability of the ZnO film. Under the incidence of UV light and polarization, the novel Ti/MMO/ZnO electrode showed greater photocurrent stability as compared to Ti/ZnO, which is a very important outcome because the behavior of these electrodes was similar when compared in terms of the degradation of clopyralid. Single electrolysis was not able to degrade efficiently clopyralid at the different potentials studied. However, the irradiation of UV light on the polarized surface of the Ti/ZnO and Ti/MMO/ZnO electrodes increased markedly the degradation rate of clopyralid. A synergistic effect was observed between light and electrode polarization, since the rate of degradation of clopyralid was twice as high in photoelectrocatalysis (PhEC) than in photocatalysis (PhC) and different intermediates were formed. From these results, mechanisms of degradation of clopyralid for the PhC and PhEC systems with the Ti/ZnO and Ti/MMO/ZnO electrodes were presented. Therefore, the Ti/MMO/ZnO electrode could be a cheap and simple alternative to be applied in the efficient photodegradation of organic pollutants, presenting the great advantage of having a facile synthesis and high capacity to work at relatively low potentials.

Selectivity and efficacy of herbicide GF-3488, containing synthetic auxins halauxifen-methyl and clopyralid, in winter oilseed rape crops in Ukraine

Halauxifen-methyl is a new synthetic auxin, which in combination with another auxin-like herbicide clopyralid is the active ingredient of complex herbicide GF-3488, that is used for dicotyledonous weeds control in winter oilseed rape crops. The reason of this study was a necessity to test crop selectivity and efficacy of GF-3488 to control dicotyledonous weeds in winter oilseed rape crops in Ukraine and also the possibility of GF-3488 application in the tank mixture with graminicide or/and insecticide to control monocotyledonous weeds and insects. A randomized block experiment was conducted in 2015—2017 in 4 locations. It was found that under spring applying, the GF-3488 is not inferior to another widely used herbicide Galera Super on selectivity to the crop. Herbicide GF-3488 at the rate 1.0 l/ha was significantly better than Galera Super at the rate 0.3 l/ha in controlling of annual dicotyledonous weeds Papaver rhoeas L., Galium aparine L., Consolida regalis S.F. Gray and was effective to control of certain types of cruciferous weeds, which are resistant to Galera Super. Adding graminicide Fusilade Forte and insecticide Nurelle D did not affect the GF-3488 selectivity to the crop and had no negative impact on dicotyledonous weeds control. Efficacy of monocotyledonous weeds control by graminicide did not change in the mixture with GF-3488. It was concluded that herbicide GF-3488 is effective on winter oilseed rape against dicotyledonous weed species. Therefore for the simultaneous control of dicotyledonous and monocotyledonous weeds in winter oilseed rape in the spring after the renewal of the crop vegetation herbicide GF-3488 is advisable to be used in a tank mixture with graminicides, and for simultaneous protection against weeds and pests it can be mixed with insecticides.

Detection of herbicide clopyralid at nanogram per gram level in agricultural products using easy-to-use micro liquid–liquid extraction followed by analysis with ultraperformance liquid chromatography–tandem mass spectrometry

A new sample preparation method was developed for auxin-like herbicide clopyralid residue in agricultural products. The method uses extraction with sulfuric acid – acidified acetonitrile, with cleanup of sample extracts using solid-phase extraction (diatomaceous earth) and micro liquid–liquid extraction, followed by ultraperformance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS). This sample preparation method greatly reduces the influence on ionization during determination with UPLC–MS/MS. Quantification was achieved using external calibrators prepared in matrix-free 0.1% formic acid. The proposed analytical method supported good recovery of 73.7–91.4% with less than 8% relative standard deviation. Method quantification limits (MQL) of samples were 0.6–1.0 ng g–1. The method was applied to determine clopyralid residue in several crop samples. The herbicide was detected as near the MQLs in all samples.

Testing the role of electrode materials on the electro-Fenton and photoelectro-Fenton degradation of clopyralid

This work studies the effect of the anode and cathode materials on the degradation of the herbicide clopyralid. Different electrochemical advanced oxidation processes (EAOPs), including electrochemical oxidation with electrogenerated hydrogen peroxide (EO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF) were carried out. The first experiments were focused on the effect of the cathode, where the use of the hydrophobic carbon felt modified by the deposition of carbon black & PTFE mixture (MCF) improves the H2O2 production in comparison to a conventional carbon felt (CF), regardless of the anode material employed. On the other hand, a laser-made Ti/Ru0.3Ti0.7O2 mixed metal oxide (MMO) and a commercial boron-doped diamond (BDD) were compared as anodes. Results obtained point out that the MMO anode promotes the accumulation of this oxidant (H2O2) in bulk. Once characterized by the production of hydrogen peroxide, the second part of this study focused on the degradation of clopyralid with the MCF cathode with different EAOPs. Results demonstrate that clopyralid fastly degrades in the sequence EO-H2O2 < EF < PEF, and almost complete mineralization occurs for EF and PEF employing MMO or BDD as the anode. Synergy effect study shows that irradiation of 9 W UVC produces a positive synergistic effect of 81.7% and 41.55% (for the PEF-MMO and PEF-BDD, respectively), ascribed to the additional removal of aromatic intermediates by the UVC and the activation of H2O2. At the end of the treatment, mineralization of the herbicide was attained at 1.22 kW h (g−1 TOC). Finally, considering the lower cost of the prepared MMO, these findings demonstrate the potentiality of using modified carbon felt combined with the laser-made Ti/Ru0.3Ti0.7O2 anode for the treatment of polluted waters.

Improving biodegradability of clopyralid wastes by photoelectrolysis: The role of the anode material

In this work, the removal of the non-readily biodegradable herbicide clopyralid by electrochemical (EC) and photoelectrochemical (PhEC) oxidation with different anode materials were conducted looking to improve not only its oxidation but also its biodegradability. First, in order to find out optimal conditions, it was carried out EC and PhEC degradations in chloride medium, at current densities ranging from 30 to 100 mA cm−2 during 1 h (0.8–2.7 A h L−1), using as anodes MMO-RuO2TiO2, MMO-RuO2IrO2, MMO-IrO2Ta2O5 and boron-doped diamond (BDD). Results show better efficiencies on clopyralid removal for MMO-RuO2IrO2 and BDD anodes at lower current densities. Then, the influence of all anodes on clopyralid transformation was evaluated, extending the electrolysis and photoelectrolysis for 8 h applying 30 mA cm−2 (6.4 A h cm−3). At these conditions, better outcomes are observed for PhEC degradation, where complete pollutant removal is attained for BDD anode and 88.7% for MMO-RuO2IrO2, while COD removal is 47.7% for MMO and 43.1% for BDD anode. Then, short-term biodegradability tests, conducted for EC and PhEC processes, pointed out that MMO-RuO2TiO2 is the most promising anode material, being capable of improving biodegradability in 48.2% and 53% for EC and PhEC degradation, respectively. The toxicity of treated solutions using MMO-RuO2TiO2 and BDD anodes in both EC and PhEC degradation were compared, employing the inhibitory effect in the bioluminescence of marine bacteria Vibrio Fisheri. Toxicity assessments show that toxicity significantly reduces by using the MMO-RuO2TiO2 in NaCl and Na2SO4 medium for both processes. Finally, this study demonstrates that photoelectrolysis with MMO anodes was the most effective strategy in order to increase biodegradability in chloride media, as well as to reduce the toxicity of the treated waste.

The Intercalation Behaviour and Physico-Chemical Characterisation of Novel Intercalated Nanocomposite from Zinc/Aluminium Layered Double Hydroxides and Broadleaf Herbicide Clopyralid

The Intercalation Behaviour and Physico-Chemical Characterisation of Novel Intercalated Nanocomposite from Zinc/Aluminium Layered Double Hydroxides and Broadleaf Herbicide Clopyralid

Highly sensitive analytical method for herbicide clopyralid residue in cattle manure compost with ultraperformance liquid chromatography tandem mass spectrometry.

A micro liquid-liquid extraction has been applied to sample preparation in the current authorized method for clopyralid in compost. The method rendered matrix effects practically negligible during determination with ultraperformance liquid chromatography-electrospray ionization tandem mass spectrometry with an improved limit of quantification of 0.7 µg/kg dry weight. Moreover, it had good accuracy and reproducibility. Therefore, the method is proposed as a highly effective routine analytical technique for investigating the actual status of clopyralid residue in compost.

Electro-irradiated technologies for clopyralid removal from soil washing effluents

In this work, electrolysis and electro-irradiated technologies, i.e. sonoelectrolysis, photoelectrolysis and photosonoelectrolysis have been evaluated in order to improve the biodegradability of soil washing effluents polluted with the herbicide clopyralid. Results obtained showed that simple electrolysis with carbon felt anodes improved the biodegradability of the effluent and that combination of electrolysis with irradiation technologies lead to very different operative results. Photoelectrolysis produced a synergistic effect in clopyralid removal and mineralization, while sonoelectrolysis and photosonoelectrolysis did not generate any positive effect, showing antagonisms. Regarding the biodegradability of the effluents, photoelectrolysis was the only technology which demonstrated a significant enhancement; nevertheless, it has associated an important energy consumption in comparison to simple electrolysis processes.

Removal of aqueous Clopyralid by Photoctalytic-ozonation process on Activated carbon under solar radiation: Catalyst characterization and kinetic study

Solar photocatalytic ozonation has been used to oxidize the herbicide clopyralid in aqueous solution. Activated carbon used as a catalyst was characterized by Scanning Electron Microscopy (SEM) images showed the presence of irregular cavities and pores, which have different sizes and shapes, with a great surface area of BETand a high pHpzc. The adsorption kinetics was found to follow the pseudo-second-order kinetic mode. Catalyst stability was tested by means of consecutive reuse cycles. After five cycle of reuse the adsorption efficiency reached 75% of the clopyralid removal.Clopyralid elimination kinetic by direct ozonation has been studies. The system O3/AC/Daylight significantly improves clopyralid and mineralization rate abatement if compared to runs conducted in the absence of radiation and/ or activated carbon. Clopyralid total abatement was achieved in less than 30 min when 0.5 g/L of activated carbon and under solar radiation (300-800 nm) were used. Thus, TOC removal in 180 min treatments increased from 20 to about 90 % in O3 and O3/OSAC/Daylight, respectively, under similar operating conditions.

Electrochemical dewatering for the removal of hazardous species from sludge

This work focuses on the evaluation of the electrochemical dewatering of sludge polluted with model hazardous species. To do this, two sludge samples taken from the outlet of the anaerobic digesters of the municipal Wastewater Treatment Facility of Ciudad Real were polluted with herbicide clopyralid (CP) and with antibiotics amoxicillin (AMX) and ampicillin (AMP), respectively. These sludge samples underwent first dewatering by press filtration and then, the dewatering continued by the application of an electrochemically assisted driven process with increasing electric fields (1.0, 2.0 and 3.0 V cm−1). Results demonstrate that the electrochemically-assisted process can help to exhaust the pollutant adsorbed onto the sludge and attain a supplemental removal (up to 15%) of water in both cases. This is a highly important result, because it can help to develop technologies for sludge treatment that avoid the diffusion of hazardous pollution during the land application of the sludge. No reactivity of the pollutants was observed during the tests.

2,4-D–Resistant Buckhorn Plantain (Plantago lanceolata) in Managed Turf

AbstractA population of buckhorn plantain with suspected resistance to 2,4-D was identified in central Indiana following 30 yr of 2,4-D–containing herbicide applications. Our objectives were to (1) confirm and quantify the level of herbicide resistance in the buckhorn plantain population using dose–response experiments and (2) find alternative herbicides that could be used to control this population. Greenhouse experiments were conducted to quantify the dose–response of resistant (R) and susceptible (S) biotypes of buckhorn plantain to both 2,4-D and triclopyr, two synthetic auxin herbicides from different chemical families. The R biotype was ≥6.2 times less sensitive to 2,4-D than the S biotype. The efficacy of triclopyr was similar on both the R and S biotypes of buckhorn plantain, suggesting the absence of cross-resistance to this herbicide. This is the first report of 2,4-D resistance in buckhorn plantain and the first report of 2,4-D resistance in turf. The resistance mechanism was limited to within a chemical family (phenoxycarboxylic acid) and did not occur across all WSSA Group 4 synthetic auxin herbicides, as the pyridinecarboxylic acid herbicides clopyralid and triclopyr and the arylpicolinate herbicide halauxifen-methyl provided control in our experiments.

Development of a modified electrode by using a nanocomposite containing acid-activated multi-walled carbon nanotube and fumed silica for the voltammetric determination of clopyralid

This is the first study in the literature, which presents the voltammetric determination of herbicide clopyralid (CLD). A novel modified glassy carbon electrode was developed by using the nanocomposite containing acid-activated multi-walled carbon nanotube (A-MWCNT) and fumed silica (FS). The effective surface area of the electrode (8 times) and the reduction peak current values of CLP (369 times) increased in the presence of A-MWCNT-FS nanocomposite. This revealed that the electrode had an electro-catalytic effect on the electrochemical reduction of CLP. Cyclic voltammetry and electrochemical impedance measurements indicated that electron transfer rate of Fe(CN)64−/3− redox couple on the modified electrode was much higher over the bare electrode. Scanning electron microscopy images showed that A-MWCNT and FS formed a homogeneous nanocomposite by dispersing each other. It was observed that electrochemical reduction of CLP was more favourable in pH values between 2 and 4. Electrochemical reduction of CLP on the modified electrode was an adsorption-controlled process. Electrochemical reduction peak currents linearly increased with CLP concentrations in the range of 0.005μM and 10.0μM. The detection limit was calculated as 0.8nM. Measurement and fabrication reproducibilities of the modified electrode were obtained as 2.94% (N: 10) and 3.34% (N: 5), respectively. Electrochemical reduction behaviour of CLP was not affected by the presence of different substances in the measurement solution. The GC/A-MWCNT-FS electrode allowed to determine the CLP in real samples such as urine, river water, sugar beet, wheat and herbicide formulations (Phaeton and Lontrel). The results indicated that the electrochemical sensor prepared in this study could be a very promising alternative to current analytical methods used to determine CLP.

Cross-resistance to auxinic herbicides in dicamba-resistant Chenopodium album

ABSTRACTThe responses of two dicamba-resistant Chenopodium album (fathen) populations (L and M) were compared with the responses of two dicamba-susceptible populations (A and P) to the auxinic herbicides mecoprop, clopyralid, 2,4‐D and aminopyralid in a preliminary experiment. The dicamba-resistant fathen was cross-resistant to the pyridine carboxylic acid herbicides clopyralid and aminopyralid, but not the phenoxy acid herbicides, 2,4-D and mecoprop. The level of cross-resistance to aminopyralid and picloram (another pyridine carboxylic acid herbicide) was investigated in two separate dose-response experiments. The results of the first dose-response experiment showed populations L and M were 12 and 19 times more resistant to aminopyralid, respectively, than susceptible populations (A and P). The dicamba-resistant fathen populations were also shown to be resistant to picloram although the levels of resistance ranged from three- to 17-fold. These levels of cross-resistance for both herbicides were confirmed in the second dose-response experiment. The results of this study help with planning control strategies for this resistance problem.