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International audience; The soil dissipation of the widely used herbicides S-metolachlor (SM) and butachlor (BUT) was evaluated in laboratory microcosms at two environmentally relevant doses (15 and 150 mg/g) and for two agricultural soils (crop and paddy). Over 80% of SM and BUT were dissipated within 60 and 30 days, respectively, except in experiments with crop soil at 150 mg/g. Based on compound-specific isotope analysis (CSIA) and observed dissipation, biodegradation was the main process responsible for the observed decrease of SM and BUT in the paddy soil. For SM, biodegradation dominated over other dissipation processes, with changes of carbon isotope ratios (Dd 13 C) of up to 6.5‰ after 60 days, and concomitant production of ethane sulfonic acid (ESA) and oxanilic acid (OXA) transformation products. In crop soil experiments, biodegradation of SM occurred to a lesser extent than in paddy soil, and sorption was the main driver of apparent BUT dissipation. Sequencing of the 16S rRNA gene showed that soil type and duration of herbicide exposure were the main determinants of bacterial community variation. In contrast, herbicide identity and spiking dose had no significant effect. In paddy soil experiments, a high (4:1, V/V) ESA to OXA ratio for SM was observed, and phylotypes assigned to anaerobic Clostridiales and sulfur re-ducers such as Desulfuromonadales and Syntrophobacterales were dominant for both herbicides. Crop soil microcosms, in contrast, were associated with a reverse, low (1:3, V/V) ratio of ESA to OXA for SM, and Alphaproteobacteria, Actinobacteria, and Bacillales dominated regardless of the herbicide. Our results emphasize the variability in the extent and modes of SM and BUT dissipation in agricultural soils, and in associated changes in bacterial communities.

Chloroacetamide herbicides, namely acetochlor and metolachlor, are common herbicides used on corn and soybean fields. Dichloroacetamide safeners, namely benoxacor and furilazole, are commonly used in formulations containing chloroacetamide herbicides. Extensive reports on adsorption of chloroacetamide herbicides are available, yet little information exists regarding adsorption potential of co-applied safeners. Herein, the adsorption and desorption characteristics of selected herbicide safeners to granular activated carbon (GAC) and in agricultural soils are reported. Further, soil column studies were performed to understand the leaching behaviour of the herbicide Dual II Magnum. Equilibrium sorption experiments of safeners to three agricultural soils and one GAC showed that adsorption was best fitted by the Freundlich isotherm. The Freundlich adsorption constant, Kf, for benoxacor and furilazole sorption onto three agricultural soils ranged from 0.1 to 0.27 and 0.1 to 0.13 (mg/g) × (mg/L)ˆ(1/n), respectively. The Kf for benoxacor and furilazole to GAC was 6.4 and 3.4 (mg/g) × (mg/L)ˆ(1/n), respectively, suggesting more favorable sorption of benoxacor to GAC than furilazole to GAC. The sorption to soils was reversible as almost 40%–90% of both safeners was desorbed from three soils. These results were validated in four replicated soil column studies, where S-metolachlor was shown to leach similarly to the safener benoxacor, originating from the herbicide formulation. The leaching of S-metolachlor and benoxacor was influenced by soil texture. Cumulatively, these results show that safeners will move through the environment to surface waters similarly to the active ingredients in herbicides, but may be removed during drinking water treatment via GAC.

Weeds are one of the most important biological constraint to cotton production, and resulting in a yield losses of up to 90%. The evolution of hundreds of resistant weed species, the lack of new herbicide chemistries, and the increase in weed management costs are all making weed management more arduous for the growers. Hence, a field experiment was conducted to investigate the efficacy of allelopathic crop water extracts (ACWEs) alone and in combination with one third rate of S-metolachlor (717 g a.i. ha−1) for effective weed management in cotton. The treatments investigated were; weedy check, sorghum + brassica water extract (WE) at 1.5 L ha−1, sorghum + sunflower WE at 1.5 L ha−1, sorghum + brassica + sunflower WE at 1.5 L ha−1, sorghum + brassica WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, sorghum + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, sorghum + brassica WE + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i.ha−1, and S-metolachlor at recommended rate of 2.15 kg a.i. ha−1. Results revealed that pre-emergent application of sorghum + brassica water extract (WE) at 1.5 L ha−1 was the best treatment in terms of effective dry biomass reduction (40%) of Trianthema portulacastrum and Cyperus rotundus, and increase in seed cotton yield (12%). The second best treatment was sorghum + sunflower WE at 1.5 L ha−1 + S-metolachlor at 717 g a.i. ha−1 with yield increase of 11% over the weedy control. In comparison, S-metolachlor at recommended rate 2.15 kg a.i. ha−1 recorded only 4% decrease in weeds dry biomass reduction and 8% increase in seed cotton yield. Hence, it can be predicted that binary combination of sorghum and brassica WE at 1.5 L ha−1 or binary combination of sorghum + sunflower WE at 1.5 L ha−1 with one third dose of S-metolachlor (717 g a.i. ha−1) can be used for effective weed management and increase in seed cotton yield. Furthermore, adoption of this technique will also reduce the herbicide application, which is not only beneficial for the ecosystem but, also minimize the evolution of herbicide-resistant weed species. Keywords: Allelopathy, Chemical weed control, Herbicide, Weeds, Biomass, Seed cotton yield, Environment

Due to the increasing use of chlorinated organic compounds, environmental pollution is a key issue in agricultural and industrial areas. In this study, biodegradation of chloroacetanilide herbicides, such as alachlor and metolachlor, by eight fungal strains of Trichoderma spp. originating from different microorganism collections was investigated. The tested fungi converted 80–99% of alachlor and 40–79% of metolachlor after 7 days of incubation. Biotransformation of herbicides was performed mainly by dechlorination and hydroxylation reactions. Eight alachlor metabolites and four byproducts of metolachlor conversion were detected in Trichoderma cultures, including two metolachlor intermediates for the first time identified in fungi. Moreover, in the cultures of six Trichoderma strains supplemented with chloroacetanilides, a decrease in toxicity was observed toward tested Artemia franciscana crustaceans. Simultaneously, 7 days after the application of the spores of T. koningii IM 0956, T. citrinoviride IM 6325, T. harzianum KKP 534, T. viride KKP 792 and T. virens DSM 1963 the length of roots and shoots of rapeseed seedlings treated with alachlor or metolachlor significantly increased. All tested strains exhibited plant growth-promoting traits, such as siderophore production, 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity, and phosphate solubilization, even in the presence of chloroacetanilide herbicides.

Agricultural chemicals are normally used as mixtures of several isomers, e.g. , enantiomers. In theory, in order to minimize the pesticides dose, it is desirable to use the most target-active isomer. Metolachlor is a typical multichiral herbicide belonging to amide herbicides. An asymmetric carbon atom and a chiral axis yield four stereoisomers. In this study, a novel laboratory method was developed to prepare the S -metolachlor and the four stereoisomers using high performance liquid chromatography. The separated isomers had a purity of >99%, with their absolute configurations assigned by electronic circular dichroism. The enantioseparation by ultra performance convergence chromatography tandem mass spectrometry was also performed for the rapid and sensitive detection of metolachlor stereoisomers. The enantioselective herbicidal activity toward the target weed ( Echinochloa crusgalli ) was systematically assessed for the first time by measuring the morphology of the weed after treatment with rac -, S -metolachlor and the four stereoisomers, respectively. Among the commercial pesticides, S -metolachlor was more effective in weed inhibition than rac -metolachlor, and to the four stereoisomers, the herbicidal activities were ranked as: SS > SR ≫ RS > RR , and the RR -isomer even had some stimulative effect to the weed growth at lower concentration (1 ppm). Thus, we concluded that in these cases, the chiral carbon feature played a major role in herbicidal activity rather than the chiral axis feature, and the higher bioactivity of the S -isomers was confirmed by more effective uptake and stronger interaction with target enzymes that were involved in the gibberellic acid biosynthesis. Although the SS -isomer shows the highest herbicidal activity, controlling the major chiral feature is still much easier and more economical than controlling two chiral features.

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.

Laboratory and field experiments were conducted on three Mediterranean agricultural soils in so as to investigate the effects of de-oiled two-phase olive mill waste (D) and two-phase olive mill waste (W) and their level of organic matter maturity on the environmental fate of the herbicide S‑metolachlor (SM). Three Mediterranean agricultural soils were amended with fresh (D and W) and composted W (CW) wastes under laboratory conditions. Furthermore, under field conditions, one of the soils was also amended with both wastes (D and W) over 9 years in order to assess the effects of the “aging” transformation (AD and AW treatments, respectively). Significant increases in SM adsorption were observed in all the amended soils, with no reduction in the herbicide's effectiveness. The adsorption process was more reversible with the fresh organic amendments (D or W) than with CW or (even more so) with AD or AW. The fresh amendments also increased the persistence of SM; however the field-aged and composted amendments enhanced its dissipation as a result increased soil microbial activity showed by high levels of soil dehydrogenase activity. The AD- and AW-amended soils, showed the greatest decrease in leaching loss of SM (from 51.9% in original soil to 9.33% in AD and 8.05% in AW), reflecting the strong influence of adsorption-desorption processes on SM leaching. This study has shown that the application of olive mill wastes as organic amendments may be considered a useful strategy to reduce leaching of SM in soils poor in organic matter, especially if those wastes have a high level of organic matter maturity.

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.

Increasing production of energy crops in Europe, mainly maize and rapeseed, has altered patterns of pesticide use in recent decades. The long-term effects of S-metolachlor (S-M) and of its metabolite metolachlor OA (M-OA) at the environmentally relevant concentration of 4.2 μg L−1 and at 42 μg L−1 (ten-fold concentration) on marbled crayfish (Procambarus virginalis) were evaluated in a 28-day exposure and after a subsequent 28-day recovery period. Indicators assessed were behaviour; biochemical haemolymph profile; oxidative and antioxidant parameters of gill, hepatopancreas, and muscle; and histology of hepatopancreas and gill. Results showed biochemical haemolymph profile (lactate, alanine aminotransferase, aspartate aminotransferase, inorganic phosphate), lipid peroxidation in hepatopancreas, and antioxidant parameters (catalase, reduced glutathione, glutathione S-transferase) of hepatopancreas and gill of crayfish exposed to S-M and M-OA to significantly differ from controls (P

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

The adsorption of S-metolachlor herbicide from aqueous solution by benzenesilica materials was studied. The materials were synthesized with 1,4-bis(triethoxysilyl)benzene as organosilica precursor and Brij 76 and Pluronic P123 as surfactants. Additionally, 1,3,5-triisopropylbenzene (TPB) was used as porogen to produce microporosity. Those materials obtained by Brij-76 and P123 showed well-structured ordering. However, a disordered microporous benzenesilica material was obtained in presence of P123 and TPB. All materials proved to be efficient adsorbents for S-metolachlor. Among them, the material synthesized with Brij 76 showed the highest adsorption capacity due to its ordered structure and, mainly, to its higher proportion of mesopores.

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.

A low-cost, simple to use portable rainfall simulator is developed for use over a 5 m2 plot. The simulator is easy to transport and assemble in the field, thereby allowing for necessary experimental replicates to be done. It provides rainfall intensities of between 20 and 100 mm/h by changing the number and type of silicon nozzles used. The Christiansen coefficient of uniformities obtained in the field are appropriate and vary from 79 to 94% for rainfall intensities ranging from 30 to 70 mm/h. In addition, the median volumetric drop diameters measured for rainfall intensities of 30, 50, and 70 mm/h are in the lower range of that of natural rainfall and equal to 1.10±0.08, 1.69±0.21, and 1.66±0.20 mm, respectively. The velocities of the raindrops with diameters less than 1.2 mm reached terminal velocities, while raindrops less than 2.0 mm achieved velocities reasonably close to the terminal velocity of natural rainfall. Furthermore, the average time-specific kinetic energy (KET) for rainfall intensities of 30, 50, and 70 mm/h are 257.7, 760.1, and 1645.2 J/m2/h, respectively accounting for about 78.0 and 86.5% of the KET of natural rainfall for 50 and 70 mm/h rainfall intensity, respectively. The applicability of the portable rainfall simulator for herbicide transport study is investigated using two herbicides (atrazine and metolachlor); herbicide losses in runoff and sediment samples are in the ranges reported in the literature. As a percentage of the amount of herbicide applied, 5.29% of atrazine and 2.15% of metolachlor are lost due to combined water and sediment runoff. The results show that the portable rainfall simulator can be effectively used in studying processes such as pesticide runoff, infiltration mechanisms, and sediment generation and transport at a field plot scale with an emphasis on how surface characteristics such as slope and soil properties affect these processes.

Transformation products (TPs) can be formed from organic micropollutants in the water cycle through both biological and technological processes. Despite the TPs' potentially altered toxicity compared to their parent compounds, transformation processes are not routinely monitored, and in particular those induced by drinking water treatment remain elusive. This lack of information is mainly due to the technical challenges in analyzing TPs, which are often unknown compounds occurring in low concentrations. Their analysis requires sophisticated analytical techniques such as non-target screening (NTS) based on high-resolution tandem mass spectrometry (HRMS/MS) methods combined with novel data analysis approaches. Here, we addressed the challenges of TP analysis and the scarcity of TP research concerning studies in drinking water. We performed lab-scale experiments to monitor TP formation of three organic micropollutants prevalent in drinking water sources, i.e. carbamazepine, clofibric acid and metolachlor, during rapid sand filtration and ozonation, two readily applied biotic and abiotic drinking water treatments, respectively. To facilitate TP identification in the NTS data, halogenated and/or isotopically labeled parent compounds were used, revealing potential TPs through their isotopic patterns. The experimental results showed that degradation of the parent compounds and TP formation were treatment and compound specific. In silico TP prediction and literature mining enabled suspect screening of the non-target data and thereby significantly enhanced TP identification. Overall, the developed workflow enables an efficient and more comprehensive assessment of drinking water quality changes during water treatment.

The overexploitation of the farmlands in the Mediterranean region contributes to an overuse of herbicides that have the potential to pollute surrounding aquatic systems, like the Mondego estuary, located near the city of Figueira da Foz (Portugal). Primextra® Gold TZ is the most-used herbicide in this area and it is constituted by two main active ingredients, S-metolachlor (SMOC) and terbuthylazine (TBA) that have exhibited toxicity to aquatic animal species in previous studies. The benthic bivalve species Scrobicularia plana was selected to carry out bioassays because of its capacity to filter pollutants and its important position in the structure and functioning of estuarine communities. Organisms of two size classes (big and small) were exposed individually to a range of concentrations of the mentioned compounds to assess their responses in terms of mortality. S. plana showed a clear higher sensitivity to SMOC (big – LC50 = 40.702 mg/L; small – LC50 = 41.517 mg/L) than to TBA (big – LC50 = 118.590 mg/L; small – LC50 = 108.418 mg/L), and big size class organisms, generally, showed to be more tolerant than the ones of small size class. In order to evaluate contaminated aquatic systems, it is necessary to develop laboratory strategies to rapidly assess the potential impacts of pollutants in the environment and in human health. Thus, a battery of biomarkers was selected, including the activity of antioxidant enzymes (glutathione peroxidase (tGPx), glutathione reductase (GRed) and glutathione-S-transferase (GST)) and the lipid peroxidation occurrence (by quantification of TBARS levels). This work reports that GRed and GST activate under the chemicals’ exposure at concentrations that surpass the levels for environment protection. Moreover, GRed shows specificity to detect TBA presence and GST results more accurate to assess SMOC contamination.

To study spray drift contributions to non-targeted habitats, pesticide concentrations in stemflow (water flowing down the trunk of a tree during a rain event), throughfall (water from tree canopy only), and surface water in an agriculturally impacted wetland area near Tifton, Georgia, USA were measured (2015–2016). Agricultural fields and sampling locations were on the University of Georgia's Gibbs Research Farm, Tifton, GA. Samples were screened for more than 160 pesticides, and cumulatively, 32 different pesticides were detected across matrices. Data indicate that herbicides and fungicides were present in all types of environmental samples analyzed while insecticides were only detected in surface water samples. The highest pesticide concentration observed was 10.50 μg/L of metolachlor in an August 2015 surface water sample. Metolachlor, tebuconazole, and fipronil were the most frequently detected herbicide, fungicide, and insecticide, respectively, regardless of sample origin. The most frequently detected pesticide in surface water and stemflow samples was metolachlor (0.09–10.5 μg/L), however, the most commonly detected pesticide in throughfall samples was biphenyl (0.02–0.07 μg/L). These data help determine the importance of indirect chemical exposures to non-targeted habitats by assessing inputs from stemflow and throughfall into surface waters.

Background: Little is known about modifiable risk factors for thyroid disease. Several pesticides have been implicated in thyroid disruption, but clinical implications are not clear. Objective: We assessed associations between pesticide use and other farm exposures and incident hypothyroidism and hyperthyroidism in female spouses of farmers in the Agricultural Health Study (AHS). Methods: We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals for risk of thyroid disease in 24,092 spouses who completed at least one follow-up questionnaire. Results: We identified 1627 hypothyroid and 531 hyperthyroid cases over 20 years of follow-up. The fungicides benomyl, maneb/mancozeb, and metalaxyl, the herbicide pendimethalin, and among those over 60 years of age the insecticides parathion and permethrin (applied to crops) were associated with elevated hypothyroidism risk, with HR ranging from 1.56–2.44. Conversely, the insecticide phorate, and the herbicides imazethapyr and metolachlor were associated with decreased risk (HR ranging 0.63–0.73), as were long-term farm residence and other farm-related activities (HR ranging 0.69–0.84). For hyperthyroidism, the insecticide diazinon, the fungicides maneb/mancozeb, and the herbicide metolachlor were associated with increased risk (HR ranging 1.35–2.01) and the herbicide trifluralin with decreased risk (HR: 0.57). Conclusions: Several individual pesticides were associated with increased risk of hypothyroidism and hyperthyroidism, although some pesticides were associated with decreased risk. Some of the findings, specifically associations with fungicides, are consistent with results from an earlier analysis of prevalent diseases in AHS spouses. Keywords: Pesticides, Hypothyroidism, Hyperthyroidism, Agricultural Health Study

The degradation and mineralization ability of electrochemical processes like electro-oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA-assisted photoelectro-Fenton (PEF) has been comparatively studied for solutions of the herbicide S-metolachlor. Solutions of 100 mL have been treated using an undivided cell equipped with an air-diffusion cathode and a boron-doped diamond (BDD) anode. The effect of pH, current density, and Fe2+ and S-metolachlor concentrations has been thoroughly studied. The total organic carbon removal profiles have demonstrated the feasibility of almost overall mineralization by EF and PEF after 9 h at 300 mA. The herbicide decays in both treatments informed about the complexation of Fe(III) ions formed from Fenton’s reaction, which decelerated S-metolachlor removal. However, the high oxidation power of BDD anode allowed the gradual mineralization of such complexes. The identification of chlorinated and non-chlorinated degradation byproducts by GC–MS has allowed the proposal of main degradation routes.

An ever-increasing diversity of potentially toxic chemical compounds are being developed and released into the environment as a result of human activities (e.g. agriculture, drugs, and cosmetics). Among these, pesticides have been shown to affect non-targeted wildlife since the 1960s. A range of ecotoxicological tests are used to assess the toxicity of pesticides on various model organisms. However most model organisms are metazoans, while the majority of Eukaryotes are unicellular microorganisms known as protists. Protists are ubiquitous organisms of key functional roles in all ecosystems but are so far little studied with respect to pesticide impact. To fill this gap, we developed a new ecotoxicological test based on Euglypha rotunda, a common soil amoeba, grown in culture flask with Escherichia coli as sole food source. We tested this assay with the herbicide S-metolachlor, which is known to affect cell division in seedling shoots and roots of weeds. Reproducible growth conditions were obtained for E. rotunda. The growth of E. coli was not affected by the herbicide. The growth of E. rotunda was affected by the herbicide in a non-linear way, growth being significantly reduced at ca. 15 μg/L, but not at 150 μg/L. Our results show the potential for using soil protists in ecotoxicology and adds to the growing body of evidence for non-linear impacts of pesticides on non-target organisms. With the acquisition of additional data, the protocol should be suitable for standard ecotoxicological tests.

A premix of atrazine, bicyclopyrone, mesotrione, and S-metolachlor (ABMS) has recently been registered for broad-spectrum weed control in corn (Zea mays L.) in the USA. The objectives of this study were to compare the efficacy of ABMS applied preemergence (PRE) with other commonly used PRE herbicides for weed control, corn injury, and yield in no-tillage (no-till) and reduced-tillage (reduced-till) corn production systems, and to determine the biologically effective doses of ABMS for controlling Palmer amaranth (Amaranthus palmeri S. Wats.) in field conditions. Field experiments were conducted in 2015 and 2016 at South Central Agricultural Laboratory, Clay Center, Nebraska, USA. ABMS applied at the labeled dose (2.89 kg ai ha−1) resulted in 92–99% Palmer amaranth control in both tillage systems. A similar level of Palmer amaranth control (86–99%) was observed with mesotrione plus rimsulfuron in the no-till system; however, the control was higher with ABMS than with other premixes in the reduced-till system at 42 days after treatment (DAT) and at harvest. Applications of ABMS at 2.89 kg ai ha−1 provided 99 and 81% control of velvetleaf (Abutilon theophrasti Medik.) and foxtail (Setaria spp.), respectively, in the no-till system at 28 DAT, whereas control was ≥93% in the reduced-till system. ABMS applied at 2.89 kg ai ha−1 resulted in 3% corn injury at 14 DAT regardless of the tillage system, whereas 15% corn injury was observed with acetochlor plus clopyralid plus flumetsulam, and dimethenamid-P plus saflufenacil in the reduced-till. ABMS or mesotrione plus rimsulfuron at labeled doses resulted in 16.0–16.3 t ha−1 corn yield, comparable to the weed-free control (16.4 t ha−1). The biologically effective doses of ABMS to provide 90% control (ED90) of Palmer amaranth at 42 DAT were 2.44 and 2.81 kg ai ha−1 in no-till and reduced-till systems, respectively. The efficacy of ABMS for broadleaf weed control and early-season grass weed control, and corn yield was the same or sometimes better than most of the PRE herbicides tested in this study; therefore, ABMS can be considered as an additional option for management of problem weeds, including Palmer amaranth in corn in the USA.

The aim of this study was to explore the efficiency of three horizontal subsurface flow (HSF) constructed wetlands (CWs) to remove S-metolachlor from contaminated water. The three CWs, with code names MG-R, MG-C and MG-Z, all contained medium gravel as porous media. MG-R and MG-C were planted with Phragmites australis and Typha latifolia, respectively, and MG-Z was left unplanted and used as control unit to study the effect of vegetation. The CWs units in this experiment operated continuously for one year but they were mature systems operating in various experiments for more than fourteen years. The results showed that the mean percent S-metolachlor removal values were 68.9%, 47.8% and 40.8% for MG-R, MG-C and MG-Z units, respectively. The vegetation (Phragmites australis) and the hydraulic residence time were found as the most important parameters affecting the CW capacity in herbicide removal. The current data suggest that HSF CWs are an efficient and low-cost technology in treating S-metolachlor-contaminated surface runoff in agricultural areas.

Nanoparticle incorporated membranes are potential tools to remove hazardous organic pollutants from drinking water sources. Cellulose acetate membranes were impregnated by incorporating zinc nanoparticles, which had been produced using a green synthesis in Mentha plant extract utilizing microwave energy. The synthesized nanoparticles were extensively characterized using ultraviolet–visible spectroscopy, X-ray diffraction, Scanning electron microscopy, energy dispersive X-ray and Nanoparticle tracking analysis. The spectroscopy results showed an absorbance peak at 300nm, confirming the successful synthesis, while X-ray diffraction confirmed that the particles are crystalline with a particle size of 36 nm. The surface roughness and topography of the zinc nanoparticles impregnated membranes was studied using atomic force microscopy to check the homogeneity of dispersion of the nanoparticles in the membrane. The efficiency of the zinc nanoparticles and the zinc nanoparticle loaded cellulose acetate membranes for adsorption of organic herbicides such as metolachlor and acetochlor was studied. The particles themselves and the particle-embedded membranes proved to be very adsorbent due to their unique structural properties, providing large surface area and high adsorption capacity. The incorporation of zinc nanoparticles into the membrane decreased the time needed for the removal of the selected herbicides relative to that of the nanoparticles alone, and provides a promising method for water purification.

Biochar (BC) will gradually age over time after its application to soil due to the effects of environmental factors, such as long-term oxidation and acid rain. The changes in the physical and chemical properties and structure of BC after aging are not well understood. In this study, soil burial (S), oxidation (O), and acidification (A) methods were used to simulate the aging of walnut shell BC based on comparisons with fresh BC (F-BC). The differences in the physicochemical properties and structure of the BC before and after aging were studied using an elemental analyzer, scanning electron microscopy, and Fourier transform infrared spectroscopy. We found that the hydrophilicity of BC increased after aging whereas the aromaticity decreased. The surface pore structures were severely damaged on O-BC and A-BC compared with F-BC. Many clay particles were attached to the surface of BC. The adsorption performance of S-BC was not significantly lower than that of F-BC. According to the Langmuir model, the Q 0 values for F-BC, S-BC, O-BC, and A-BC were determined as 33.78 mg g − 1 , 32.47 mg g − 1 , 18.62 mg g − 1 , and 19.12 mg g − 1 , respectively. Finally, based on the three types of aging processes, we analyzed the adsorption mechanism for BC after aging in its natural state and evaluated the environmental benefits of BC aging. Our results provide a theoretical basis for practical applications of BC aging in soil.

Agriculturally-dominated waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at varying life stages. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic perturbation in the form of a complex mixture of agricultural stressors. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d in situ exposure to an agrichemical pulse event. Minnow larvae were sampled after 14 and 28days to characterize developmental plasticity through growth measures and relative gene expression. Concentrations of agrichemical contaminants measured in water using polar organic chemical integrative samplers and composite sediment samples throughout the 28-d exposure were quantified using gas chromatography-mass spectrometry. Elevated concentrations of acetochlor, atrazine, and metolachlor were indicative of inputs from agricultural sources and were associated with reductions in body mass, condition factor, and androgenic gene expression in river exposed fathead minnow larvae. However, following a 14-d in situ depuration during the post-pulse period, river exposed larvae overcompensated in previously suppressed biological endpoints. These results indicate that fathead minnow larvae are capable of compensatory responses following episodic exposure to agrichemical stressors.

Highlights • 71 water samples from the Danube River and its tributaries were analysed. • Most relevant micropollutants were benzotriazoles, pharmaceuticals, organophosphorus compounds, and PFOS/A. • PFOS concentrations exceed its environmental quality standard (EQS). • Concentrations and loads are similar for the years 2007 and 2013., Graphical abstract Image 1, In the third Joint Danube Survey (JDS3), emerging organic contaminants were analysed in the dissolved water phase of samples from the Danube River and its major tributaries. Analyses were performed using solid-phase extraction (SPE) followed by ultra-high-pressure liquid chromatography triple-quadrupole mass spectrometry (UHPLC-MS-MS) and gas chromatography–mass spectrometry (GC–MS). The polar organic compounds analysed by UHPLC-MS-MS were 1H-benzotriazole, methylbenzotriazoles, carbamazepine, 10,11-dihydro-10,11-dihydroxy-carbamazepine, diclofenac, sulfamethox-azole, 2,4-D (2,4-dichlorophenoxyacetic acid), MCPA (2-methyl-4-chlorophenoxyacetic acid), metolachlor, cybutryne (irgarol), terbutryn, DEET (N,N-diethyl-m-toluamide), and several perfluoroalkyl acids (C6–C9; C8 = perfluorooctanoic acid (PFOA)) and perfluorooctansulfonic acid (PFOS). In addition, several organophosphorus flame retardants were analysed by GC-MS. The most relevant compounds identified in the 71 water samples, in terms of highest median and maximum concentrations, were 1H-benzotriazole, tris(1-chloro-2-propyl)phosphate (TCPP), methylbenzotriazoles, carbama-zepine and its metabolite, DEET, sulfamethoxazole, tris(isobutyl)phosphate (TiBP), tris(2-chloroethyl)phosphate (TCEP), PFOA, PFOS and diclofenac. The concentrations of these compounds in the samples were generally below the environmental quality standard (EQS) threshold values, with the exception of PFOS, the concentration of which exceeded the annual average water EQS limit of 0.65 ng/L along the whole river, and also exceeded the fish biota EQS of 9.1 μg/kg. In addition, the proposed EQS for diclofenac, of 0.1 μg/L, was exceeded in the Arges River in Romania (255 ng/L).

Glutathione S-transferases (GSTs) have been widely studied in relation to their role in herbicide tolerance and detoxification. However, a detailed characterization of GSTs from herbicide tolerant and sensitive maize cultivars is still lacking. In this study, we determined the mechanism of differential tolerance between two maize cultivars which had 4-fold difference tolerance to metolachlor. The metabolism rate of metolachlor was more rapid in the tolerant cultivar (Zea mays L. cv Nongda86) than the susceptible one (Zea mays L. cv Zhengda958). Addition of the GST inhibitor ethacrynic acid reduced the metabolism of metolachlor indicating the involvement of GSTs in the differential detoxification of metolachlor. The expression profiles of 32 GST isozymes were measured using quantitative RT-PCR. The results showed the expression of GST genes were slightly up-regulated in Nongda86, but severely inhibited in Zhengdan958 24h after metolachlor treatment. The genes GSTI, GSTIII, GSTIV, GST5, GST6 and GST7, which can detoxify chloroacetanilide herbicides, were all expressed higher in Nongda86 compared to Zhendgan958. The result of GST activity was consistent with the gene expression profiles. Collectively, higher-level expression of GST genes, leading to higher GST activity and faster herbicide detoxification, appears to be responsible for the difference in tolerance to metolachlor in two maize cultivars.

This study sheds light on the occurrence of emerging pesticides and their transformation products (TPs) in an urban river in Beijing that is mainly supplemented with treated wastewater. To this end, suspect and non-target screening was conducted using a database of 557 commercial pesticides and over 1400 predicted TPs. Finally, 30 pesticides and 20 TPs were identified, with 12 pesticides and 10 TPs detected in all samples. Eleven pesticides and 17 TPs were detected in Beijing for the first time. Among these, 18 compounds were confirmed using authentic standards. Concentrations of the confirmed and suspected compounds were determined by quantification and semi-quantification, respectively, based on 18 authentic standards. Fungicides and their TPs constituted the largest group and exhibited the highest total concentration (26 compounds; 52.2 μg/L), followed by insecticides (14 compounds; 51.3 μg/L) and herbicides (10 compounds; 24.5 μg/L). DEET, carbendazim, prometryn, ω-carboxylic acid, 2-aminobenzimidazole, metolachlor TP, hexaconazole TP, metalaxyl TP, and azoxystrobin TP exhibited relatively high mean concentration (>100 ng/L). Among the 20 TPs, approximately 65% showed higher concentrations than their parent compounds. Correlation analysis revealed that 6 pesticides and 10 TPs in the river were mainly contributed by the discharge from a wastewater treatment plant. Although a majority of the emerging pesticides had low toxicity, 10 pesticides exhibited high risks to aquatic systems, especially invertebrates.

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.

This study involved the monitoring and risk assessment of current-use pesticides in surface water from the northwestern section of the Taihu Lake Basin (China) in 2019. In particular, 114 current-use pesticides were measured in samples collected during four campaigns spread across the wet, dry, and normal seasons. Pesticide concentrations were measured by means of a novel analytical method involving online solid-phase extraction coupled to LC-MS/MS. In total, 1 plant growth regulator, 34 herbicides, 23 insecticides, and 25 fungicides were detected. Detection frequencies greater than 90% were recorded for 26 pesticides; furthermore, acetamiprid, azoxystrobin, bentazone, carbendazim, isoprothiolane, metolachlor, paclobutrazol, and triadimenol were present in every sample. The measured pesticide concentrations varied widely, from below the detection limit to 10,600 ng/L (tricyclazole). The highest median concentrations for the fungicide, herbicide, and insecticide families were observed for carbendazim (135 ng/L), metolachlor (40 ng/L), and imidacloprid (31 ng/L), respectively. Twenty-two pesticides were quantitatively reported in Chinese surface water for the first time. The number and concentration of detected pesticides were significantly higher in June and September (wet season) compared to March and December (dry season). Agricultural areas of the study area were more contaminated than the residential and industrial sections. Imidacloprid was the only pesticide that exhibited high risk to sensitive ecological species (RQmedian > 1) in all four seasons. Isoproturon, isoprothiolane, and pretilachlor were identified as high risk in March (RQmedian = 4.5), September (1.3), and June (1.1), respectively; moreover, another eight pesticides posed a high ecological risk at specific sites. Seven pesticides recorded moderate risks (i.e., RQmedian = 0.1-1.0). Of the 18 pesticides with cases of high risk, a novel risk index, which accounted for frequency of PNEC exceedance, ranged from 6.7 (imidacloprid) to 7.1 × 10-5 (propiconazole). The integrated consideration of ecological risk and frequency of risk inform priorities for regional pesticide management and control.

Pesticides applied to agricultural land can enter aquatic ecosystems through runoff or leaching during precipitation events. In a lotic system, these events result in a pulse of exposure to biota living in these systems. The concentration of pesticide increases, peaks, and then gradually declines, and this pulsed exposure may occur multiple times over the course of a growing season. The dynamic nature of exposure to pesticides in the environment is not often mimicked in the laboratory testing of the toxicity of pesticides. The present study investigated the potential latent effects of a 24-h pulsed exposure of metolachlor, metribuzin, MCPA (2-methyl-4-chlorophenoxyacetic acid), MCPP (methylchlorophenoxypropionic acid or mecoprop), dicamba, and 2,4-D to the aquatic macrophyte Lemna minor followed by a 5-day recovery period. The relative sensitivity of L. minor to the herbicides were, in this decreasing order: metolachlor > metribuzin >2,4-D > MCPA > MCPP > dicamba. This study also investigated the effects of short-term exposures of the diamide insecticides cyantraniliprole and chlorantraniliprole on the survival of the larvae of the parthenogenetic mayfly Neocloeon triangulifer. The median lethal concentrations (96-h LC50s) for cyantraniliprole and chlorantraniliprole were 8.60 and 2.92 μg/L, respectively.

Groundwater is a major drinking water resource but its quality with regard to organic micropollutants (MPs) is insufficiently assessed. Therefore, we aimed to investigate Swiss groundwater more comprehensively using liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). First, samples from 60 sites were classified as having high or low urban or agricultural influence based on 498 target compounds associated with either urban or agricultural sources. Second, all LC-HRMS signals were related to their potential origin (urban, urban and agricultural, agricultural, or not classifiable) based on their occurrence and intensity in the classified samples. A considerable fraction of estimated concentrations associated with urban and/or agricultural sources could not be explained by the 139 detected targets. The most intense nontarget signals were automatically annotated with structure proposals using MetFrag and SIRIUS4/CSI:FingerID with a list of >988,000 compounds. Additionally, suspect screening was performed for 1162 compounds with predicted high groundwater mobility from primarily urban sources. Finally, 12 nontargets and 11 suspects were identified unequivocally (Level 1), while 17 further compounds were tentatively identified (Level 2a/3). amongst these were 13 pollutants thus far not reported in groundwater, such as: the industrial chemicals 2,5-dichlorobenzenesulfonic acid (19 detections, up to 100 ng L−1), phenylphosponic acid (10 detections, up to 50 ng L−1), triisopropanolamine borate (2 detections, up to 40 ng L−1), O-des[2-aminoethyl]-O-carboxymethyl dehydroamlodipine, a transformation product (TP) of the blood pressure regulator amlodipine (17 detections), and the TP SYN542490 of the herbicide metolachlor (Level 3, 33 detections, estimated concentrations up to 100–500 ng L−1). One monitoring site was far more contaminated than other sites based on estimated total concentrations of potential MPs, which was supported by the elucidation of site-specific nontarget signals such as the carcinogen chlorendic acid, and various naphthalenedisulfonic acids. Many compounds remained unknown, but overall, source related prioritisation proved an effective approach to support identification of compounds in groundwater., Water Research, 196, ISSN:0043-1354, ISSN:1879-2448

Soil contamination caused by the widespread use of pesticides is one of the main environmental problems facing conservation organizations. (S)-metolachlor (SM) is a selective pre-emergent herbicide that poses potential risks to soil-related organisms such as reptiles. The present study elucidated the toxic effects of SM (3 and 30 mg/kg soil weight) in Eremias argus. The results showed that growth pattern was similar between the sexes in breeding season. For males, both kidney coefficient (KC) and testis coefficient in the exposure group were significantly different from those in the control group, while only KC in the high-dose group was significantly higher for females. Based on histopathological analysis, the livers of female lizards were more vulnerable than those of males in the exposure group. A reduction in total egg output was observed in SM exposed lizards. Accumulation studies indicated that skin exposure may be an important route for SM uptake in E. argus, and that the liver and lung have strong detoxification abilities. In addition, the body burdens of the lizards increased with increasing SM concentration in the soil.

By the year 2050, the population of the United States is expected to reach over 418 million, while the global population will reach 9.6 billion. To provide safe food and fiber, agriculture must balance pesticide usage against impacts on natural resources. Challenges arise when storms cause runoff to be transported to aquatic receiving systems. Vegetated systems such as drainage ditches and constructed wetlands have been proposed as management practices to alleviate pesticide runoff. Twelve experimental mesocosms (1.3×0.71×0.61m) were filled with sediment and planted with a monoculture of one of three wetland plant species (Typha latifolia, Leersia oryzoides, and Sparganium americanum). Three mesocosms remained unvegetated to serve as controls. All mesocosms were amended with 9.2±0.8μg/L, 12±0.4μg/L, and 3.1±0.2μg/L of atrazine, metolachlor, and diazinon, respectively, over a 4hr hydraulic retention time to simulate storm runoff. Following the 4hr amendment, non-amended water was flushed through mesocosms for an additional 4hr. Outflow water samples were taken hourly from pre-amendment through 8hr, and again at 12, 24, 48, 72, and 168hr post-amendment. L. oryzoides and T. latifolia had mean atrazine, metolachlor, and diazinon retentions from 51%-55% for the first 4hr of the experiment. Aside from S. americanum and atrazine (25% retention), unvegetated controls had the lowest pesticide retention (17%-28%) of all compared mesocosms. While native aquatic vegetation shows promise for mitigation of pesticide runoff, further studies increasing the hydraulic retention time for improved efficiency should be examined.

Volatilization represents a significant loss pathway for many pesticides, herbicides and other agrochemicals. One common method for measuring the volatilization of agrochemicals is the flux-gradient method. Using this method, the chemical flux is estimated as the product of the vertical concentration gradient and a turbulent-transfer coefficient (eddy diffusivity). For computational simplicity, the evaluation height needed to calculate the eddy diffusivity is typically approximated as either the geometric or logarithmic mean. Both of these estimation methods are based on simplifying assumptions and can be a significant source of error, particularly when the separation distance between the measurement heights is large. Using data collected over an eight-year period at the USDA-ARS OPE3 experimental watershed, this study compared fluxes of metolachlor, a commonly-used herbicide, computed using the approximated evaluation heights with those calculated using the exact evaluation height. While it was found that the primary factor influencing the accuracy of the flux estimates using the approximate evaluation heights was atmospheric stability, errors in the estimate of the evaluation height can result in significant (>10%) errors in the flux estimates. Based on these results, it is recommended that the exact evaluation height be used with the flux-gradient technique.

A simple method to prepare a 2,6-disubstituted aniline containing a N-sec-alkyl group and a carbonyl on one ortho substituent is reported. This method was used to accomplish the first synthesis of side chain oxidized ethylsulfonic acid (ESA) and oxanilic acid (OXA) metabolites of S-Metolachlor (S-Moc) herbicide. The 2,6-disubstituted aniline functionality was installed by a Sugasawa reaction of readily available ortho-toluidine. The N-sec alkyl group was introduced by a Mitsunobu alkylation of the nosyl-activated 2-acetyl-6-methyl-substituted aniline. This crucial step enabled access to the key 2,6-disubstituted aniline intermediate which was used in the divergent synthesis of S-Moc metabolites. A bioinspired synthesis of the keto-ESA metabolite was achieved in one step from the hydroxyl-ESA metabolite using a ruthenium-catalyzed oxidation. Download : Download full-size image

The chirality of herbicides has been the focus of research. However, there is little information on the enantioseparation of amide herbicides with different chiral elements. In this study, the need for different chiral stationary phases (CSPs), mobile phases, temperatures and flow rates for the separation of napropamide, acetochlor and propisochlor was discussed in detail and compared to metolachlor. Resolution of C-chiral enantiomers was easier than that of axial-chiral enantiomers. Metolachlor and acetochlor could achieve baseline separation only on AY-H and AS-H columns, respectively. Propisochlor had satisfactory separations on OD-H and AS-H columns. Napropamide was separated on OJ-H, AY-H and AS-H columns. Both the structures of the compounds and CSPs and the interactions between them played significant roles in the enantioseparations. Molecule dockings were also used to elucidate the separation mechanisms. C-chiral enantiomers had perfect symmetry in their optical properties, whereas the axial-chiral enantiomers did not. The elution order for napropamide, acetochlor and propisochlor, with a single chiral location, was R- prior to S-. These results were the first that compare the enantioseparations of four amide herbicides with different chirality, and they provided the absolute configurations for the herbicides. The paper also illustrated certain mechanisms for enantioseparations.

Groundwater discharge zones in streams are important habitats for aquatic organisms. The use of discharge zones for thermal refuge and spawning by fish and other biota renders them susceptible to potential focused discharge of groundwater contamination. Currently, there is a paucity of information about discharge zones as a potential exposure pathway of chemicals to stream ecosystems. Using thermal mapping technologies to locate groundwater discharges, shallow groundwater and surface water from three rivers in the Chesapeake Bay Watershed, USA were analyzed for phytoestrogens, pesticides and their degradates, steroid hormones, sterols and bisphenol A. A Bayesian censored regression model was used to compare groundwater and surface water chemical concentrations. The most frequently detected chemicals in both ground and surface water were the phytoestrogens genistein (79%) and formononetin (55%), the herbicides metolachlor (50%) and atrazine (74%), and the sterol cholesterol (88%). There was evidence suggesting groundwater discharge zones could be a unique exposure pathway of chemicals to surface water systems, in our case, metolachlor sulfonic acid (posterior mean concentration = 150 ng/L in groundwater and 4.6 ng/L in surface water). Our study also demonstrated heterogeneity of chemical concentration in groundwater discharge zones within a stream for the phytoestrogen formononetin, the herbicides metolachlor and atrazine, and cholesterol. Results support the hypothesis that discharge zones are an important source of exposure of phytoestrogens and herbicides to aquatic organisms. To manage critical resources within the Chesapeake Bay Watershed, more work is needed to characterize exposure in discharge zones more broadly across time and space.

The mixture of herbicides is a widely used technique in weed control in several crops, including maize. However, interactions that might potentially result from mixing herbicides are a matter of constant concern and research. Soil capacity to retain herbicides directly influences the final destination of these molecules in the environment. The aim of this study was to evaluate sorption and desorption of mesotrione applied alone and mixed with S -metolachlor + terbuthylazine in samples from seven Brazilian sites cultivated with maize. Mesotrione sorption (alone and mixed) was evaluated five concentrations with 0.125, 1.042 and 0.625 mg kg − 1 corresponding to the field dose of mesotrione, S -metolachlor and terbuthylazine, respectively. Sorption of mesotrione applied alone and mixed had K d (sorption coefficient) values ranging from 0.08 to 5.05 kg L − 1 and from 0.09 to 5.20 kg L − 1 , respectively, with similar behavior across soils. Mesotrione sorption was influenced primarily by the clay mineral (CM) content and the soil pH. The mode of application (alone or mixed) did not influence sorption or desorption. Mesotrione sorption was relatively low in soils, which creates the potential for leaching in maize producing areas.

Metolachlor is a chiral herbicide consisting of four stereoisomers, which is typically used as a racemic mixture or is enriched with the herbicidally active 1'S-isomers. Because studies on the enantioselective behavior of phyto-biochemical processes and the environmental fate of metolachlor have become significant, a practical method for analyzing and separating metolachlor stereoisomers must be developed. In the present study, the enantiomeric separation of metolachlor was achieved using OD-H, AS-H, OJ-H and AY-H chiral columns. The effects of different organic modifiers in an n-hexane-based mobile phase were investigated, and various temperatures and flow rates, which may influence metolachlor separation, were also explored. The optimal resolution was obtained using an AY-H column with n-hexane/EtOH (96/4) as the mobile phase at a rate and temperature of 0.6mLmin(-1) and 25°C, respectively. The absolute configuration of the four stereoisomers was identified as αSS, αRS, αSR, αRR using computed and experimentally measured ECD and VCD spectra. Thermal interconversion and solvent stability experiments were also performed. Pure metolachlor stereoisomers in different organic solvents and water at 4°C or 30°C were stable. These results were used to establish a sound method for analyzing, preparing, characterizing, and preserving individual metolachlor stereoisomers in most natural environments.

To better address how much groundwater contributes to the loadings of pollutants from agriculture we developed a specific dating tool for groundwater residence times. This tool is based on metolachlor ethane sulfonic acid, which is a major soil metabolite of metolachlor. The chiral forms of metolachlor ethane sulfonic acid (MESA) and the chiral forms of metolachlor were examined over a 6-year period in samples of groundwater and water from a groundwater-fed stream in a riparian buffer zone. This buffer zone bordered cropland receiving annual treatments with metolachlor. Racemic (rac) metolachlor was applied for two years in the neighboring field, and subsequently S -metolachlor was used which is enriched by 88% with the S -enantiomer. Chiral analyses of the samples showed an exponential increase in abundance of the S -enantiomeric forms for MESA as a function of time for both the first order riparian buffer stream ( R 2 = 0.80) and for groundwater within the riparian buffer ( R 2 = 0.96). However, the S -enrichment values for metolachlor were consistently high indicating different delivery mechanisms for MESA and metolachlor. A mean residence time of 3.8 years was determined for depletion of the initially-applied rac-metolachlor. This approach could be useful in dating groundwater and determining the effectiveness of conservation measures. One sentence summary A mean residence time of 3.8 years was calculated for groundwater feeding a first-order stream by plotting the timed-decay for the R -enantiomer of metolachlor ethane sulfonic acid.

Herbicide runoff from cropping fields has been identified as a threat to the Great Barrier Reef ecosystem. A field investigation was carried out to monitor the changes in runoff water quality resulting from four different sugarcane cropping systems that included different herbicides and contrasting tillage and trash management practices. These include (i) Conventional - Tillage (beds and inter-rows) with residual herbicides used; (ii) Improved - only the beds were tilled (zonal) with reduced residual herbicides used; (iii) Aspirational - minimum tillage (one pass of a single tine ripper before planting) with trash mulch, no residual herbicides and a legume intercrop after cane establishment; and (iv) New Farming System (NFS) - minimum tillage as in Aspirational practice with a grain legume rotation and a combination of residual and knockdown herbicides. Results suggest soil and trash management had a larger effect on the herbicide losses in runoff than the physico-chemical properties of herbicides. Improved practices with 30% lower atrazine application rates than used in conventional systems produced reduced runoff volumes by 40% and atrazine loss by 62%. There were a 2-fold variation in atrazine and >10-fold variation in metribuzin loads in runoff water between reduced tillage systems differing in soil disturbance and surface residue cover from the previous rotation crops, despite the same herbicide application rates. The elevated risk of offsite losses from herbicides was illustrated by the high concentrations of diuron (14μgL(-1)) recorded in runoff that occurred >2.5months after herbicide application in a 1(st) ratoon crop. A cropping system employing less persistent non-selective herbicides and an inter-row soybean mulch resulted in no residual herbicide contamination in runoff water, but recorded 12.3% lower yield compared to Conventional practice. These findings reveal a trade-off between achieving good water quality with minimal herbicide contamination and maintaining farm profitability with good weed control.

The occurrence and spatiotemporal variation of 26 contaminants of emerging concern (CECs) were evaluated in 68 water samples in 2011-2012 in the Zumbro River watershed, Minnesota, U.S.A. Samples were collected across a range of seasonal/hydrological conditions from four stream sites that varied in associated land use and presence of an upstream wastewater treatment plant (WWTP). Selected CECs included human/veterinary pharmaceuticals, personal care products, pesticides, phytoestrogens, and commercial/industrial compounds. Detection frequencies and concentrations varied, with atrazine, metolachlor, acetaminophen, caffeine, DEET, and trimethoprim detected in more than 70% of samples, acetochlor, mecoprop, carbamazepine, and daidzein detected in 30%-50% of samples, and 4-nonylphenol, cotinine, sulfamethoxazole, erythromycin, tylosin, and carbaryl detected in 10%-30% of samples. The remaining target CECs were not detected in water samples. Three land use-associated trends were observed for the detected CECs. Carbamazepine, 4-nonylphenol, erythromycin, sulfamethoxazole, tylosin, and carbaryl profiles were WWTP-dominated, as demonstrated by more consistent loading and significantly greater concentrations downstream of the WWTP and during low-flow seasons. In contrast, acetaminophen, trimethoprim, DEET, caffeine, cotinine, and mecoprop patterns demonstrated both seasonally-variable non-WWTP-associated and continual WWTP-associated influences. Surface water studies of CECs often target areas near WWTPs. This study suggests that several CECs often characterized as effluent-associated have additional important sources such as septic systems or land-applied biosolids. Finally, agricultural herbicide (atrazine, acetochlor, and metolachlor) profiles were strongly influenced by agricultural land use and seasonal application-runoff, evident by significantly greater concentrations and loadings at upstream sites and in early summer when application and precipitation rates are greatest. Our results indicate that CEC monitoring studies should consider a range of land uses, seasonality, and transport pathways in relation to concentrations and loadings. This knowledge can augment CEC monitoring programs to result in more accurate source, occurrence, and ecological risk characterizations, more precisely targeted mitigation initiatives, and ultimately, enhanced environmental decision-making.

Herbicide metolachlor (MET) and insecticide buprofezin (BUP) were determined in natural waters by means of a newly-developed, simple and sensitive thermochemically-induced fluorescence derivatization (TIFD) method. The TIFD approach is based on the thermolysis transformation of naturally non-fluorescent pesticides into fluorescent complex O-phthalaldehyde-thermoproduct(s) in water at 70°C for MET and at 80°C for BUP. The TIFD method was optimized with respect to the temperature, pH, complex formation kinetic and pesticides concentrations. The limit of detection (LOD=0.8ngmL(-1) for MET and 3.0ngmL(-1) for BUP) and quantification (LOQ=2.6ngmL(-1) for MET and 9.5 ngmL(-1) for BUP) values were low, and the relative standard deviation (RSD) values were small (between 1.2% and 1.8%), which indicates a good analytical sensitivity and a great repeatability of TIFD method. Recovery studies were performed on spiked well, sea and draining waters samples collected in the Niayes area by using the solid phase extraction (SPE) procedure. Satisfactory recovery results (84-118%) were obtained for the determination of MET and BUP in these natural waters.

In agriculture, herbicides are applied to improve crop productivity. During and after rain event, herbicides can be transported by surface runoff in streams and rivers. As a result, the exposure pattern in creeks is time-varying, i.e., a repeated pollution of aquatic system. In previous studies, we developed a model to assess the effects of pulse exposure patterns on algae. This model was validated for triazines and phenylureas, which are substances that induce effects directly after exposure with no delay in recovery. However, other herbicides display a mode of action characterized by a time-dependency effect and a delay in recovery. In this study, we therefore investigate whether this previous model could be used to assess the effects of pulse exposure by herbicides with time delay in effect and recovery. The current study focuses on the herbicide S-metolachlor. We showed that the effect of the herbicide begins only after 20 h of exposure for the alga Scenedesmus vacuolatus based on both the optical density and algal cells size measurements. Furthermore, the duration of delay of the recovery for algae previously exposed to S-metolachlor was 20 h and did not depend on the pulse exposure duration or the height of the peak concentration. By accounting for these specific effects, the measured and predicted effects were similar when pulse exposure of S-metolachlor is tested on the alga S. vacuolatus. However, the sensitivity of the alga is greatly modified after being previously exposed to a pulse of S-metolachlor. In the case of scenarios composed of several pulses, this sensitivity should be considered in the modelling. Therefore, modelling the effects of any pulse scenario of S-metolachlor on an alga is feasible but requires the determination of the effect trigger, the delay in recovery and the possible change in the sensitivity of the alga to the substance.

This study presents monitoring data on the spatial and temporal occurrence of pesticide residues in arable soils of the Czech Republic and relates it to soil properties, pesticide usage and data on application provided by farmers. In total, 34 soils were sampled during 2014–2017, amounting to 136 samples which were analyzed for 60 pesticides and four transformation products. Conazole fungicides were frequently present in soils above the limit of quantification and/or above the 0.01 mg/kg threshold. Of the other pesticide types, the herbicides diflufenican, chlorotoluron, metolachlor, pendimethalin and terbuthylazine, fungicides azoxystrobin, carbendazim, fenpropidin, fenpropimorph and prochloraz and the insecticide methoxyfenozide were found in ≥20% of soils in at least one sampling campaign. Soils typically (>50%) contained 2–7 residues with a maximum of 14. For the 136 samples, 116 different mixtures were identified. The occurrence of pesticides was driven by their annual usage, their half-lives in soil, and their hydrophobicity. A comparison of the monitoring data and pesticide application data provided by farmers revealed that 63% of the applied pesticides are not likely to persist until the following growing season while up to 69% of pesticide residues found in soils could be inherited from the previous growing season(s).

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 pollution in watersheds containing significant cropland area is generally problematic. Conservation practices intended to reduce nitrate-N (NO3--N) export from watersheds are being implemented by many regions without necessary tools to assess effectiveness of abatement. A commonly used herbicide metolachlor degrades in the vadose zone of croplands to form two metabolites (metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOXA)) which are both highly soluble in soils. Study of metabolite fates in a first order watershed provided evidence that transport of these metabolites to stream water is highly correlated to transport of agricultural NO3--N that also forms in the cropland vadose zone. Linear models describing the relationships of stream flux of MESA and MOXA to NO3--N flux generated goodness of fit values of 0.93 and 0.81, respectively. These findings support a conclusion that both MESA and MOXA act as excellent transport analogs of NO3--N and become strongly correlated to agricultural NO3--N leaching from the cropland vadose zone. Moreover, their use as conservative tracers in agricultural watersheds can provide valuable information concerning movement and fate of agricultural nitrogen at watershed scales of observation.

Synergistic biodegradation of earthworms and soil microorganisms plays a key role in the removal of organic pollutants in soil, yet microbially mediated processes remain unclear, especially regarding the succession of soil microbial interactions. Herein, soil biochemical evaluation, microbial community characterization, and interaction network construction were combined to understand the mechanisms dominating microbial community succession during synergistic bioremediation of metolachlor-polluted soils. The results of the network analysis indicated that metolachlor could render more complex relations but weaker connection strength among soil microorganisms. The addition of earthworms significantly alleviated the stress of metolachlor on soil microbial interactions and resulted in the restoration of interactions to a great extent. Additionally, the soil physicochemical properties, enzyme activities, and microbial community changed greatly with the addition of metolachlor and earthworms. Some soil microorganisms became significantly correlated with soil properties, metolachlor concentrations, and enzyme activities. These results, dominated by the succession of soil microbial communities, provide a new perspective for assessing the remediation effect of contaminated soil by organic pollutants.

Laboratory and field trials evaluated the efficacy of three methods of detecting aquatic pesticide concentrations. Currently used pesticides: atrazine, metolachlor, and diazinon and legacy pesticide dieldrin were targeted. Pesticides were extracted using solid-phase extraction (SPE) of water samples, titanium plate passive samplers coated in ethylene vinyl acetate (EVA) and eastern oysters (Crassostrea viginica) as biosamplers. A laboratory study assessed the extraction efficiencies and precision of each method. Passive samplers yielded the highest precision of the three methods (RSD: 3–14% EVA plates; 19–60% oysters; and 25–56% water samples). Equilibrium partition coefficients were derived. A significant relationship was found between the concentration in oyster tissue and the ambient aquatic concentration. In the field (Housatonic River, CT (U.S.)) water sampling (n = 5) detected atrazine at 1.61–7.31 μg L−1, oyster sampling (n = 2 × 15) detected dieldrin at n.d.–0.096 μg L−1 SW and the passive samplers (n = 5 × 3) detected atrazine at 0.97–3.78 μg L−1 SW and dieldrin at n.d.–0.68 μg L−1 SW.