S-metolachlor Research Articles

Gender-Specific Toxic Effects of S-Metolachlor and Its Metabolite on Hibernating Lizards: Implications for Reproductive Health and Ecosystem Vulnerability.

Reptiles rely on hibernation to survive harsh winters, but climate change and pesticide use in agriculture jeopardize their survival, making the ecosystem vulnerable. S-metolachlor (SM), a commonly found herbicide in soil, and its metabolite metolachlor oxanilic acid (MO) induce oxidative stress and disrupt reproductive hormones. In this study, lizards were exposed to SM- and MO-contaminated soil for 45 days during hibernation. Weight loss and deaths occurred at the beginning of hibernation in all groups. Furthermore, the exposure group experienced severe oxidative stress and damage in the liver, kidney, heart, gonad, and brain. The testosterone levels significantly decreased in male lizards in both the SM and MO groups, whereas estradiol levels increased significantly in female lizards in the SM group. Gender-specific expression of steroidogenic-related genes in the brains and gonads of lizards was observed. Histological analysis revealed toxic effects induced by both SM and MO in vital organs during hibernation. Moreover, MO induced more severe reproductive toxicity in male lizards during hibernation. Therefore, this study suggests gender-specific toxic effects were observed in hibernating lizards exposed to SM and MO, underscoring the importance of vigilant monitoring of pesticide application in agriculture and assessing the potential harm of its metabolites.

Volatilization of three herbicides applied to corn

Secondary drift of herbicides through volatilization can become a significant source of airborne concentrations of the active ingredients. The physicochemical properties, such as vapor pressure, of the active ingredients play a significant role in the rate of volatilization post application. This study utilized a laboratory-scale wind tunnel exposed to ambient conditions to evaluate the volatilization of three herbicides with a range of vapor pressures following application to corn at the V3 growth stage: S-metolachlor (SMOC), bicyclopyrone (BIR), and pendimethalin (PDM). A series of air samples were collected from the wind tunnel with sampling durations of 8-, 16- and 24-h to characterize the temporal profile of pesticide volatilization. About 19% of SMOC application volatilized during the first 8 h while 5% volatilized during next 40 h of sampling. Relative lower fluxes of about 0.5% application were measured for PDM and BIR. All measurements of BIR samples were below laboratory detection limits except for one 8-h sample. Experimental results from this study were also compared to results from three predictive models ranging from a simple linear regression to mechanistic models utilizing physio-chemical properties to predict volatilization rates. The two mechanistic models captured the magnitude and diurnal behavior of the SMOC volatilization rate. However, the volatilization rate of PDM, which has relatively high leaf adsorption characteristics, was significantly overpredicted by all the models, with the exception of the Scholtz's model (scenario II). This specific scenario simulates a wetleaf with no active ingredient on the surface of the leaf. Pesticide uptake by the cuticle is accounted for in this scenario, and it provided the best estimates for all three herbicides.

Acute toxicity and genotoxicity of the S-metolachlor-based herbicide Dual Gold® on Leptodactylus luctator (Hudson, 1892) tadpoles (Anura: Leptodactylidae).

Herbicides used in agriculture and their metabolites are frequently detected in surface water bodies, where they can persist and cause adverse effects on aquatic organisms. The aim of this study was to evaluate the acute toxicity and genotoxic effects of the S-metolachlor (SM)-based herbicide Dual Gold® (DG®), on Leptodactylus luctator tadpoles (Anura: Leptodactylidae). To assess the toxicity of the herbicide, including the median lethal concentration (LC50) at 24h, the no-observed-effect concentration (NOEC), and the lowest-observed-effect concentration (LOEC), tadpoles were exposed to five nominal concentrations of DG® (5.0, 6.2, 7.8, 9.8, and 12.2 mg/L), and to dechlorinated water as a negative control (NC). The LC5024h of DG® was 7.0 mg/L, the NOEC was 5.0 mg/L and the LOEC=6.2 mg/L. L. luctator tadpoles were sensitive to the herbicide, reaching 100% mortality after 24 h of exposure to the highest concentration tested (12.2 mg/L). To evaluate the potential genotoxicity of the herbicide, the frequencies of micronuclei (MN) and other erythrocyte nuclear abnormalities (ENA) were determined in larvae exposed to three nominal concentrations of DG® (1.0, 5.0, and 6.2 mg/L) for 48 and 96 h. The frequencies of MN and ENA were compared with a positive control (40 mg/L of Cyclophosphamide) and a negative control. The frequencies of MN and ENA in the erythrocytes of tadpoles exposed to the test concentrations of DG® and Cyclophosphamide were significantly higher than in the negative control group at both 48 and 96 h (with the only exception of MN at 1.0 mg/L at 48 h). Our results confirm the genotoxic and cytotoxic effects of this widely used herbicide in agriculture, a fact that represents a potential risk to amphibians that develop in ponds associated with or immersed in agroecosystems.

Mulching vs. organic soil amendment: Effects on adsorption-desorption of herbicides

Mulching and organic soil amendment are two agricultural practices that are being increasingly used to preserve soil from degradation, although they may modify the fate of herbicides when applied in soils subjected to these practices. This study has set out to compare the impact of both agricultural practices on the adsorption-desorption behaviour of the herbicides S-metolachlor (SMOC), foramsulfuron (FORAM), and thiencarbazone-methyl (TCM) involving winter wheat mulch residues at different stages of decomposition and particle size, and unamended soils or those amended with mulch. The Freundlich Kf adsorption constants of the three herbicides by mulches, and unamended and amended soils ranged between 1.34 and 65.8 (SMOC), 0–34.3 (FORAM), and 0.01–1.10 (TCM). The adsorption of the three compounds was significantly higher in mulches than in soils (unamended and amended). The adsorption of SMOC and FORAM increased significantly with mulch decomposition, with this positive impact also being observed on the adsorption of FORAM and TCM after mulch milling. Simple and multiple correlations between mulches, soils, and herbicide properties, and adsorption-desorption constants (Kf, Kd, Kfd) reflected the organic carbon (OC) content and/or dissolved organic carbon (DOC) content of the adsorbents as main variables controlling the adsorption and/or desorption of each herbicide. The statistic R2 revealed that >61 % of the variability in the adsorption-desorption constants could be explained by jointly considering the OC of mulches and soils and the hydrophobicity (for Kf) or water solubility of herbicides (for Kd or Kfd). The same trend observed for Kfd desorption constants as for Kf adsorption ones resulted in higher percentages of herbicide remaining adsorbed after desorption in amended soils (33 %–41 % of SMOC, 0 %–15 % of FORAM, and 2 %–17 % of TCM) than in mulches (< 10 %). The results reveal a higher efficiency of organic soil amendment than mulching as an agricultural practice for immobilising the herbicides studied when winter wheat mulch residues are used as a common adsorbent, and as a better strategy for avoiding groundwater contamination.

UV-Vis Activated Cu2O/SnO2/WO3 Heterostructure for Photocatalytic Removal of Pesticides.

A three-steps sol–gel method was used to obtain a Cu2O/SnO2/WO3 heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO3 acting as substrate for SnO2 development. The SnO2/WO3 sample provide nucleation and grew sites for Cu2O formation. Diffraction evaluation indicated that all samples contained crystalline structures with crystallite size varying from 42.4 Å (Cu2O) to 81.8 Å (WO3). Elemental analysis confirmed that the samples were homogeneous in composition and had an oxygen excess due to the annealing treatments. Photocatalytic properties were tested in the presence of three pesticides—pirimicarb, S-metolachlor (S-MCh), and metalaxyl (MET)—chosen based on their resilience and toxicity. The photocatalytic activity of the Cu2O/SnO2/WO3 heterostructure was compared with WO3, SnO2, Cu2O, Cu2O/SnO2, Cu2O/WO3, and SnO2/WO3 samples. The results indicated that the three-component heterostructure had the highest photocatalytic efficiency toward all pesticides. The highest photocatalytic efficiency was obtained toward S-MCh (86%) using a Cu2O/SnO2/WO3 sample and the lowest correspond to MET (8.2%) removal using a Cu2O monocomponent sample. TOC analysis indicated that not all the removal efficiency could be attributed to mineralization, and by-product formation is possible. Cu2O/SnO2/WO3 is able to induce 81.3% mineralization of S-MCh, while Cu2O exhibited 5.7% mineralization of S-MCh. The three-run cyclic tests showed that Cu2O/SnO2/WO3, WO3, and SnO2/WO3 exhibited good photocatalytic stability without requiring additional procedures. The photocatalytic mechanism corresponds to a Z-scheme charge transfer based on a three-component structure, where Cu2O exhibits reduction potential responsible for O2 production and WO3 has oxidation potential responsible for HO· generation.

Ageing of copper, zinc and synthetic pesticides in particle-size and chemical fractions of agricultural soils

The transformation and mobility of heavy metals and synthetic pesticides in soil depend on ageing, involving their chemical and physical distributions among soil fractions over time. Heavy metals and synthetic pesticides often co-occur in soil, although their ageing is usually evaluated separately and in bulk soil. Here, contrasting vineyard and crop soils were spiked with copper (Cu; 700 mg kg−1) and zinc (Zn; 200 mg kg−1) a and/or synthetic pesticides (5 mg kg−1), i.e., the fungicide metalaxyl (MTY) and herbicide S-metolachlor (SMET), to evaluate within 200 days their distribution among soil physical and chemical fractions. More than 90% of MTY and SMET in soil was released into the water phase, even 200 days after spiking. This emphasizes the potential mobilization of MTY and SMET from the soil following field application. MTY, SMET, Cu and Zn were associated mainly with the silt fraction and to a lesser extent (<30%) with the sand and clay fractions. Overall, the ageing of MTY, SMET, Cu and Zn in agricultural soil was affected mainly by the soil type and sterilization and only to a minor extent by their co-occurrence. Sorption controlled the dissipation of MTY and SMET in soil, while biodegradation contributed to less than 10%. A large fraction (37 ± 2%) of Cu was associated with Fe oxides after 200 days of ageing, while Zn was found (33 ± 2%) in the residual soil fraction. The silt fraction of the nonsterile vineyard soil became enriched in 65Cu over time (Δδ65Cu = 0.25 ± 0.07‰), whereas the clay fraction was depleted in 65Cu (Δδ65Cu = −0.20 ± 0.07‰). Cu isotope fractionation mirrored the Cu distribution in soil chemical fractions, suggesting that Cu stable isotopes may help to follow-up Cu ageing. In contrast, no significant Zn isotope fractionation was observed among soil experiments or over time. Overall, our study emphasizes the variability in ageing of synthetic pesticides and heavy metals co-occurring in agricultural soils and their interplay in physical and chemical fractions of the soil.

Carrier effect of S-metolachlor by microplastics and environmental risk assessment

Organic pesticide pollutants have obvious negative effects on organisms in the environment. As an emerging organic contaminant, the ubiquitous microplastics (MPs) are undoubtedly regarded as the focus of global attention. MPs originate from the fragmentation of large plastic waste or direct environmental emissions. This research explored the adsorption characteristics of S-metolachlor (S-MET) by three types of MPs, namely polyvinyl chloride (PVC), polypropylene (PP) and polyethylene (PE). The effects of factors such as initial pH, contact time, dosage and ionic strength on the reaction were explored. SEM, XRD, FT-IR and other analytical methods were used to study its physical and chemical properties. Adsorption kinetics, isotherm and mechanism of S-MET on MPs were carried out. The environmental and risk assessment between MPs and S-MET were analyzed. The results showed that the saturated adsorption capacities of S-MET on PVC, PP and PE are 17.67 μg/g, 14.71 μg/g and 14.41 μg/g, respectively. In addition, adsorption has both physical and chemical adsorption processes, and physical adsorption is the main process. The main adsorption mechanism may be the process of hydrogen bonding and ligand complexation. The experimental results can provide a theoretical basis for the transfer and conversion of S-MET in areas with plastic pollution. The environmental benefits and risk assessment provide a reference for controlling the pollution of MPs and S-MET in the environment.

Indigenous functional microbial communities for the preferential degradation of chloroacetamide herbicide S-enantiomers in soil

This study investigated indigenous functional microbial communities associated with the degradation of chloroacetamide herbicides acetochlor (ACE), S-metolachlor (S-MET) and their enantiomers in repeatedly treated soils. The results showed that biodegradation was the main process for the degradation of ACE, S-MET and their enantiomers. Eight dominant bacterial genera associated with the degradation were found: Amycolatopsis, Saccharomonospora, Mycoplasma, Myroides, Mycobacterium, Burkholderia, Afipia, and Kribbella. The S-enantiomers of ACE and S-MET were preferentially degraded, which mainly relied on Amycolatopsis, Saccharomonospora and Kribbella for the ACE S-enantiomer and Amycolatopsis and Saccharomonospora for the S-MET S-enantiomer. Importantly, the relative abundances of Amycolatopsis and Saccharomonospora increased by 146.3%–4467.2% in the S-enantiomer treatments of ACE and S-MET compared with the control, which were significantly higher than that in the corresponding R-enantiomer treatments (25.3%–4168.2%). Both metagenomic and qPCR analyses demonstrated that four genes, ppah, alkb, benA, and p450, were the dominant biodegradation genes (BDGs) potentially involved in the preferential degradation of the S-enantiomers of ACE and S-MET. Furthermore, network analysis suggested that Amycolatopsis, Saccharomonospora, Mycoplasma, Myroides, and Mycobacterium were the potential hosts of these four BDGs. Our findings indicated that Amycolatopsis and Saccharomonospora might play pivotal roles in the preferential degradation of the S-enantiomers of ACE and S-MET.

Effects of S-metolachlor on wheat (Triticum aestivum L.) seedling root exudates and the rhizosphere microbiome

S-metolachlor (S-ME) is a common chloroacetanilide herbicide. Here, we investigated the effects of S-ME on wheat seedling growth and explored via metabolomics the driver through which S-ME changes the rhizosphere microbiome. The results indicated that 4 mg/kg S-ME had a strong inhibitory effect on plant growth by inducing hydrogen peroxide (H2O2) levels. The richness of the rhizosphere microbiome markedly decreased after S-ME treatment, although the abundance of some potential beneficial rhizobacteria, such as Rhizobiaceae and Burkholderiaceae, increased suggesting that plants recruited potential beneficial microorganisms to resist S-ME-induced stress. Spearman correlation analysis revealed that Rhizobiaceae and Burkholderiaceae were positively correlated with organic acids secreted by plants after S-ME treatment, implying that potential beneficial microorganisms may be attracted mainly by organic acids. Our results demonstrated the phytotoxicity of S-ME on crop growth and indicated both that S-ME could influence rhizosphere microorganism abundance and that recruitment of potential beneficial microorganisms could be the result of root exudate regulation.

Herbicide Uptake and Regrowth Ability of Tall Fescue and Orchardgrass in S-Metolachlor-Contaminated Leachates from Sand Pot Experiment

The ability of tall fescue (Festuca arundinacea L.) and orchardgrass (Dactylis glomerata L.), to remediate leachates polluted with S-metolachlor (SMR) has been assessed in static hydroponic cultures. Different SMR concentrations (0.25, 1.00, and 2.00 mg L−1) were applied in the growth media to test the capacity of the two grasses to tolerate and uptake this herbicide, and to regrowth after mowing. S-metolachlor did not severely affect the dry weight aerial biomass of D. glomerata and F. arundinacea, which were reduced by 5% and 10%, respectively, when compared to the untreated control, regardless of the SMR concentrations in the leachate. The regrowth ability of aerial biomass after mowing was reduced at the different SMR concentrations, according to a dose–response model. The SMR concentrations, which reduced the regrowth ability of F. arundinacea and D. glomerata of 10% and 30%, were found to be EC10 (Effective Concentration) of 0.21 and 0.38 mg L−1 and EC30 of 0.45 and 0.74 mg L−1, respectively. These values could be assumed as the SMR concentrations that were well tolerated by both the species, without compromising their aerial biomass regrowth. Finally, tall fescue was found to be more effective and faster than orchardgrass in decreasing the SMR in the leachate and, therefore, this species should be preferred to be used in the vegetative buffer strips (VBS).

Effects of residual S-metolachlor in soil on the phyllosphere microbial communities of wheat (Triticum aestivum L.)

S-metolachlor (S-ME) is a widely used chiral herbicide that can cause potential ecological risks via long-term usage. In this work, we chose a model plant, wheat, as the test material to determine the effects of applying 10 mg/kg S-ME to soil on its fresh weight, chlorophyll and malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity and the diversity and structural composition of the phyllosphere microorganisms after 7 and 14 days of exposure. Our work showed that this concentration of residual S-ME in soil only slightly decreased plant biomass and had little effect on lipid peroxidation, the antioxidant enzyme system and chlorophyll content. Interestingly, although the test concentration of S-ME did not exert strong inhibitory effects on the physiological activities of wheat, it decreased the diversity of phyllosphere microbial communities and changed their structure, indicating that microorganisms were more sensitive stress indicators. S-ME reduced the colonization by some beneficial bacteria related to plant nitrogen fixation among the phyllosphere microorganisms, which influenced the growth and yield of wheat because these bacteria contribute to plant fitness. In addition, S-ME affected the association between the host and the composition of the phyllosphere microbial communities under different growth conditions. Our work provides insights into the ecological implications of the effects of herbicides on the phyllosphere microbiome.

Reactivity of vadose-zone solids to S-metolachlor and its two main metabolites: case of a glaciofluvial aquifer.

The vulnerability of groundwater to pesticides is governed in part by sorption mechanisms in the vadose zone, commonly studied in soil but less well-known in the geological solids. To alleviate this lack of knowledge, adsorption of the herbicide S-metolachlor (SMOC) and of two of its metabolites-metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOXA)-was studied with batch equilibrium method on seventeen surface soils and three geological solids of the vadose zone overlying a glaciofluvial aquifer. In grainsize terms, the latter three were sand for the first two samples and gravel for the third. Adsorption is ordered as follows: SMOC > > MESA > MOXA, except for one of the geological solids for which MESA adsorption was slightly higher than that of SMOC (Kd = 0.73 vs. 0.44Lkg-1). The low MOXA adsorption could only be quantified for the gravel sample (Kd = 0.74Lkg-1), which was also more reactive than all the other samples to MESA and SMOC (Kd = 2.08 and 28.8Lkg-1, respectively). Statistical multivariate tests related the highest Kd values for SMOC with the soils and geological solids with the highest organic-carbon and clay-fraction contents. The highest Kd values for MESA were found in the samples containing high oxide concentrations. Our results shed a new light on the adsorption of SMOC, MESA and MOXA suggesting that during their transfer to groundwater, pesticides and metabolites can be adsorbed in the vadose zone on both soils and geological solids.

Dissipation of S-metolachlor and butachlor in agricultural soils and responses of bacterial communities: Insights from compound-specific isotope and biomolecular analyses

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 μg/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 μg/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 (Δδ13C) 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 reducers 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.

Effects of olive mill wastes with different degrees of maturity on behaviour of S‑metolachlor in three soils

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.

Effects of S-metolachlor and its degradation product metolachlor OA on marbled crayfish (Procambarus virginalis)

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 < 0.01). Antioxidant biomarker levels remained different from controls after a 28-day recovery period. Differences in behaviour including speed of movement and velocity, and histopathological damage to gill and hepatopancreas were associated with S-M and M-OA exposure and persisted after 28 days in S-M- and M-OA-free water. Results suggest harmful effects of low concentrations of S-M and its metabolite M-OA on non-target organisms and provide information for assessing their effects at environmentally relevant concentrations.

Impacts of S-metolachlor and terbuthylazine in fatty acid and carbohydrate composition of the benthic clam Scrobicularia plana

S-metolachlor (SMOC) and terbuthylazine (TBA) are herbicides that commonly appear as active ingredients (a.i.) in the composition of plant protection products. In a previous work, experimental bioassays were performed using those chemicals to find suitable molecular biomarkers to assess its toxicity to the non-target species Scrobicularia plana. The results obtained showed that the pollutants produce mortality and biochemical changes at the species, namely in protein contents and enzymatic activity levels. Thus, for a better understanding of the total biochemical impacts of those pollutants in S. plana, the composition of fatty acids (FA) and carbohydrates (CH) of the survival organisms are investigated here. In addition, since this species is edible its biochemical profile is directly related to its nutritious quality, which is analysed in this study. Furthermore, the analyses were performed in two types of tissue - the muscle and visceral mass of each survival organism. The greatest changes in FA composition are observable in small size class, being the most sensitive size class both at the toxicological and biochemical level. FA contents are higher in small organisms, both at the field and under laboratory conditions, being the disparity between size classes higher in visceral masses than in muscles. Indeed, muscles adequately represent the FA profile since those molecules appear in higher content in this tissue compared to visceral masses, becoming the better indicator tissue of biochemical changes. Besides, using muscles, less amount of biomass is needed, so it turns out to be the most cost-effective tissue to be used as endpoint in future studies. FA profiles observed at SMOC and TBA exposure are different, organisms from TBA exposure presenting a lower nutritious quality, in terms of FA abundance and diversity, than the organisms exposed to SMOC. Still, SMOC produces reductions of HUFA, essential fatty acids that cannot be synthesized by the species. Moreover, HUFA (mostly EPA and DHA) occupied the greatest part of the FA composition of organisms exposed to the control treatments and to TBA; however, the decreases of HUFA caused by the SMOC exposure change the profiles and make SFA the most dominant group. These findings represent a risk of low occurrence of essential fatty acids in entire aquatic environments exposed to the chemicals studied. Regarding CH, glucose is the only monosaccharide found in S. plana which was expected since glycogen is the main polysaccharide in animal tissues. In general, the glucose content increases with a concentration of pollutants, whereas the glycogen concentration decreases, suggesting that the glucose is being released as a response to chemical stress. Thus, this work presents tools to assess biochemical impacts of S-metolachlor and terbuthylazine in aquatic systems and to goes deeper in the knowledge of these pollutants’ toxicity to non-target species to predict its propagation through aquatic trophic webs.

Biomarkers’ responses of the benthic clam Scrobicularia plana to the main active ingredients (S-metolachlor and Terbuthylazine) of a common herbicide

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.

S-metolachlor promotes oxidative stress in green microalga Parachlorella kessleri - A potential environmental and health risk for higher organisms

The estimation of the toxic influences of herbicide products on non-target aquatic organisms is essential for evaluation of environmental contamination. We assessed the effects of the herbicide S-metolachlor (S-MET) on unicellular green microalga Parachlorella kessleri during 4–72 in vitro exposure to concentrations in the range 2–200μg/L. The results have shown that S-MET had a significant effect on algae, even in doses 10 and 20 times lower than the EC50 values obtained for P. kessleri (EC50-72h=1090μg/L). It generates reactive oxygen species in algae, decreases their growth and photosynthetic pigment concentration, changes their ultrastructure and alters the cellular antioxidant defence capacities. The levels of protein adducts with the reactive aldehyde 4-hydroxy-2-nonenal (HNE), the end-product of lipid peroxidation, were significantly elevated in S-MET treated cells revealing the insufficient effectiveness of P. kessleri antioxidant mechanisms and persistent lipid peroxidation. Since algae are fundamental aquatic food component, the damaged algal cells, still capable of dividing while having persistently increased content of HNE upon S-MET contamination could represent an important environmental toxic factor that might further affect higher organisms in the food chain.

Correction to Degradation and Transport of the Chiral Herbicide S-Metolachlor at the Catchment Scale: Combining Observation Scales and Analytical Approaches.

Evaluating pesticide degradation and transport in the soil-surface water continuum remains challenging at the catchment scale. Here we investigated the dissipation of the chiral herbicide S-metolachlor (SM) in soil in relation to its transport in runoff. Analyses of SM, transformation products (TPs, i.e., MESA and MOXA), and enantiomers were combined to determine SM degradation at plot and catchment scales. Assisted by modeling, we found that the main dissipation pathways of SM at the plot scale were degradation (71%), volatilization (5%), leaching (8%) and runoff (3%), while 13% of SM persisted in topsoil. This highlights the relevance of degradation processes. TPs could trace the different discharge contributions: MOXA prevailed in runoff water, whereas MESA was associated with slower flowpaths. At the catchment outlet, 11% of SM applied was exported in dissolved or particulate phases or as TPs (in SM mass equivalent). A single event 1 week after application exported 96% of SM, which underlined the pote...

Behaviour of S-metolachlor and its oxanilic and ethanesulfonic acids metabolites under fresh vs. partially decomposed cover crop mulches: A laboratory study

At the time of spring pre-emergent herbicide application, the soil surface in conservation agriculture is most of the time covered by cover crops (CC) mulches. The state of these mulches depends on their destruction date and on the selected species. Sorption and degradation of 14C-S-metolachlor on and within 8 decaying CC-covered (2 species × 4 initial decomposition state) soils corresponding to conservation agriculture were compared to its fate in bare soil (BS) corresponding to conventional agriculture. 14C-S-metolachlor and its metabolites distribution between mineralized, extractable and non-extractable (NER) fractions was determined at 5 dates during a 20 °C/84-d period. Herbicide mineralization was weak (<2%) for both CC and BS. Extractability of 14C in BS was intermediate between CC that were decomposed 28 or 56 days and 0 or 6 days before application. Degradates consisted in up to 43% of total radioactivity, with specificities according to the CC or soil compartment. NER formation was equivalent in BS and in the much decomposed CC-amended microcosms, and was stronger in less decomposed CC. S-metolachlor DT50 was 23-d in BS, and 9, 15, 39 and 25-d for CC ordered by increased decomposition state at the time of application. These results were attributed to the proportion of 14C intercepted by CC, and to higher levels of organic matter and microbial activity in less decomposed CC as compared with more decomposed ones. Then the state of decomposition level of CC residues determines the behaviour of SMOC (S-metolachlor) sprayed on the mulch in the conditions of conservation agriculture.