Influence of pine or oak wood on the degradation of alachlor and metalaxyl in soil

Sustainable agricultural practices influence s-metolachlor, foramsulfuron and thiencarbazone-methyl degradation and their metabolites formation

The effect of sustainable agricultural practices, such as mulching or the application of straw residues as an organic amendment, on the degradation, dissipation and persistence in the soil of S-metolachlor (SMOC), foramsulfuron (FORAM) and thiencarbazone-methyl (TCM) is still unclear. The objective here was to conduct a laboratory experiment to evaluate the impact of milled wheat straw (WS) simulating its individual use as mulch or applied as an organic amendment to two agricultural soils: unamended and WS-amended soils on the degradation kinetics of the herbicides SMOC, FORAM and TCM, and on the formation of their major metabolites at two incubation temperatures (14 °C and 24 °C). The degradation rate of SMOC on WS was 6.9-16.7 times faster than that observed for FORAM and TCM at both temperatures. The half-life (DT50) values were 1.1-10.6 times lower for FORAM than for SMOC and TCM in the unamended and WS-amended soils at 14 °C and 24 °C. The application of WS to soils increased the DT50 values from 1.1 to 11.2 times for all the herbicides at both incubation temperatures due to their higher adsorption and lower bioavailability. The herbicides recorded a faster degradation at 24 °C (1.2-3.9 times) than at 14 °C, according to Q10 values >1. SMOC metabolites were more persistent in WS-amended soils than in unamended ones, in agreement with the DT50 values recorded for the parent compound. The results indicate that the effect of the mulch applied to soils as an organic amendment was different depending on the herbicide and incubation temperature. The outcomes of this research can give key suggestions for reducing the effects of residual herbicides following sustainable agricultural practices by avoiding soil and groundwater contamination, which is one of the challenges involved in the application of chemical inputs.

Environmental contaminant 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide remediation via Xanthomonas axonopodis and Aspergillus niger

Alachlor, a chloroacetanilide endocrine disruptor herbicide is precarious for humans as well as the environment. Though banned by the European Union and classified as moderately hazardous by WHO, yet it is nevertheless used in several countries posing austere human and environmental health issues. Alachlor attenuation was scrutinized through simulated biodegradation experiments using soil-isolated microbes. Bio-disintegrative assays of pure three fungal and one bacterial strain; Aspergillus flavus (AF), Penicillium chrysogenum (PC), Aspergillus niger (AN) and Xanthomonas axonopodis (XA), respectively were utilized. Initial Alachlor concentration (10 mg/L) was prepared with individual microbial suspension and monitored for 35 d. Alachlor bio-transformation was analyzed quantitatively and qualitatively by gas chromatography mass spectroscopy. XA and AN displayed maximal potential to metabolise the herbicide while forming residues; 1-chloroacetyl, 2,3- dihydro-7 ethylindole, 7 ethylindole, 7-ethyl-3-methyl-2-methoxy-2,3-dihydroindole, N- (2,6-diethylphenyl)-methyleneamine and 7-Ethyl-N-methylindole. Alachlor degradation by AF, PC, AN and XA was found to be 17.1%, 5.5%, 72.6% and 82.1%, respectively, after 35 d. Microbes have displayed cometabolism as the main mechanism for Alachlor degradation. This research can influence imperative and significant environmental friendly bio-remedial strategies for xenobiotic eradication.

Influence of agroforestry plant species on the infiltration of S-Metolachlor in buffer soils

Agroforestry practices have been acknowledged for reducing pesticide losses while maintaining land productivity. Pesticide removal from overland flow results from great infiltration capacities of the buffer soils. This can in turn threaten the quality of groundwater in case of poor pesticide sorption and degradation in the root-influenced zone. These mechanisms and their balance are likely to be influenced by plant species. However, little is known about the role of agroforestry species in the infiltration of herbicides. The aim of this study was thereby to evaluate how popular agroforestry species modulate the infiltration of water and of a widely used herbicide. We established large buffer microcosms by planting Brome grass, Black walnut, Pin oak and Poplar trees in repacked soil columns. After a growth season of 4 months, we performed ponded infiltration experiments with bromide and S-Metolachlor. We used then the HYDRUS 1D model to compare the hydrodynamic properties and S-Metolachlor transport patterns between the microcosms. In addition, we compared the sorption properties of the rhizosphere and bulk soils. We found that the tree species increased the sorption of S-Metolachlor in soil with Kd being 3 times greater than in the un-vegetated and Brome grass microcosms. Poplar trees increased the hydraulic conductivity (Ksat) compared to the control and was associated to a low retardation of S-metolachlor, which increases the risk of groundwater contamination. With slightly reduced Ksat and retardation factor in the root zone, 1.6 to 1.8 times greater than in the control treatment, Black walnut appears as an optimal species for mitigating S-Metolachlor. The Brome grass and oak microcosms had the lowest Ksat of all treatments and S-Metolachlor retardation factors were equal and slightly increased compared to the control, respectively. These results show that agroforestry buffer's efficiency can be optimized by selecting appropriate species.

Previous degradation study of two herbicides to simulate their fate in a sandy loam soil: Effect of the temperature and the organic amendments

A laboratory study was designed to assess the following: i) the degradation kinetics of chlorotoluron and flufenacet at two different temperatures, 6 °C and 16 °C, in an unamended agricultural soil and one amended with spent mushroom substrate (SMS) and green compost (GC), and ii) the formation of the main metabolites of both herbicides with potential risk for water pollution over degradation time. The aim was to determine the dependence of these herbicide degradations on temperature (Q₁₀ factor) using kinetic parameters, which is essential information for the later simulation of herbicide environmental fate with FOCUS models. SMS and GC were applied in situ to the natural soil as organic amendments at rates of 140 or 85 t residue ha^-1, respectively. Unamended and amended soils were taken from the 0-10 cm topsoil of experimental plots (three replicates/treatment) located on an agricultural farm. Samples of soil + herbicides were incubated at 6 °C or 16 °C under laboratory conditions. The degradation curves of chlorotoluron and flufenacet were fitted to single first-order and first-order multicompartment kinetic models, respectively. The flufenacet degradation, the more hydrophobic herbicide, was slower than that of chlorotoluron in all the treatments. The application of the organic amendments to soil increased the half-lives (DT₅₀) for both herbicides incubated at 6 °C (1.3-1.9 times) and 16 °C (1.4-1.9 times) due to their higher sorption and lower bioavailability for degradation in amended soils. The herbicides recorded a faster degradation at 16 °C than at 6 °C (Q₁₀ = 1.9-2.8) due to the increased microbial biomass and/or activity with temperature. The metabolites desmethyl chlorotoluron, flufenacet ESA and flufenacet OA were detected in all the soil treatments at both incubation temperatures. The determination of Q₁₀ factors in amended soils is very valuable for generating accurate input data for pesticide fate models such as FOCUS in order to improve the evaluation of the leaching of herbicides and their transformation products, which is a relevant goal to maintain the sustainability of agricultural systems.

Assessing the use of sand, peat soil, and pine bark for the attenuation of polar pesticides from agricultural run-off: a bench-scale column experiment

Biofilters have been shown to be efficient for removing pollutants from different water effluents, but little information is available about their capacity to remove highly polar pesticides from agricultural run-off waters. In this study, we assess the capacity of three different biofilter-supporting materials (sand, peat soil, and pine bark) to remove five phenoxyacid herbicides (mecoprop, dicamba, MCPA, dichlorprop and 2,4-D) and five non-ionic pesticides (atrazine, simazine, fenitrotion, diazinon, and alachlor) from real agricultural run-off waters. The experimental design included three columns 120 cm in length and 15 cm in diameter, each filled with 100 cm of one of the selected supporting materials. After 30 days of acclimation, the columns were fed with agricultural run-off water spiked at 10 μg L^-1 with each of the studied pesticides for 20 days at a hydraulic loading rate (HLR) of 0.32 m day^-1. The results show that the sand filter was the best supporting material for removing phenoxyacid herbicides (77% on average), whereas peat soil and pine bark were best for removing non-ionic pesticides (72% on average). The attenuation of mecoprop and dichlorprop correlated negatively with the enantiomeric fraction. Therefore, this study shows that the use of waste-to-product materials in biofilter systems is a good solution for removing pollutants from agricultural run-off waters.

Metalaxyl Degradation by Mucorales Strains Gongronella sp. and Rhizopus oryzae

In this study, the degradation of metalaxyl was investigated in the presence of two Mucorales strains, previously isolated from soil subjected to repeated treatments with this fungicide and selected after enrichment technique. Fungal strains were characterised by a polyphasic approach using phylogenetic analysis of the Internal Transcribed Spacer (ITS) gene region, phenotypic characterisation by Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) spectral analysis, and growth kinetics experiments. The strains were identified as Gongronella sp. and Rhizopus oryzae. The fungal growth kinetics in liquid cultures containing metalaxyl fits with Haldane model. Under laboratory conditions, the ability of Gongronella sp. and R. oryzae cultures to degrade metalaxyl was evaluated in liquid cultures and soil experiments. Both species were able to: (a) use metalaxyl as the main carbon and energy source; and (b) degrade metalaxyl in polluted soils, with rates around 1.0 mg kg^-¹ d^-¹. This suggests these strains could degrade metalaxyl in soils contaminated with this fungicide.

Application of mesotrione at different doses in an amended soil: Dissipation and effect on the soil microbial biomass and activity

The aim of this work was to estimate the dissipation of mesotrione applied at three doses (2, 10 and 50 mg kg(-1) dw) in an unamended agricultural soil, and this same soil amended with two organic residues (green compost (C) and sewage sludge (SS)). The effects of herbicide and organic residue on the abundance and activity of soil microbial communities were also assessed by determining soil microbial parameters such as biomass, dehydrogenase activity (DHA), and respiration. Lower dissipation rates were observed for a higher herbicide dose. The highest half-life (DT50) values were observed in the SS-amended soil for the three herbicide doses applied. Biomass values increased in the amended soils compared to the unamended one in all the cases studied, and increased over the incubation period in the SS-amended soil. DHA mean values significantly decreased in the SS-amended soil, and increased in the C-amended soil compared to the unamended ones, under all conditions. At time 0 days, respiration values were significantly higher in SS-amended soils (untreated and treated with mesotrione) than in the unamended and C-amended soils. The effect of mesotrione on soil biomass, DHA and respiration was different depending on incubation time and soil amendment and herbicide dose applied. The results support the need to consider the possible non-target effects of pesticides and organic amendments simultaneously applied on soil microbial communities to prevent negative impacts on soil quality.

Effect of different organic amendments on the dissipation of linuron, diazinon and myclobutanil in an agricultural soil incubated for different time periods

Dissipation kinetics of pesticides belonging to three chemical groups (linuron, diazinon and myclobutanil) was studied in an unamended agricultural soil and in this soil amended with three organic residues: sewage sludge (SS), grape marc (GM) and spent mushroom substrate (SMS). The soils were incubated with the residues outdoors for one and 12 months. Mineralized, extracted and non-extractable fractions were also studied for (14)C-linuron and (14)C-diazinon. The dissipation kinetics was fitted to single first-order or first-order multicompartment models. The dissipation rate (k) decreased in the order diazinon>linuron>myclobutanil, and DT50 values decreased for linuron (1.6-4.8 times) or increased for myclobutanil (1.7-2.6 times) and diazinon (1.8-2.3 times) in the amended soils relative to the unamended soil. The lowest DT50 values for the three pesticides were recorded in GM-amended soil, and the highest values in SMS-amended soil. After 12 months of soil incubation, DT50 values decreased in both the unamended and amended soils for linuron, but increased for the unamended and SMS-amended soil for diazinon and myclobutanil. A certain relationship was observed between the sorption of pesticides by the soils and DT50 values, although it was significant only for myclobutanil (p<0.05). Dissipation mechanism recorded the lowest mineralization of (14)C-pesticides in the GM-soil despite the highest dissipation rate in this soil. The extracted (14)C-residues decreased with incubation time, with increased formation of non-extractable residues, higher in amended soils relative to the unamended soil. Soil dehydrogenase activity was, in general, stimulated by the addition of the organic amendments and pesticides to the soil after one month and 12 months of incubation. The results obtained revealed that the simultaneous use of amendments and pesticides in soils requires a previous study in order to check the environmental specific persistence of these compounds and their effectiveness in amended soils.

Degradation of pesticide mixture on modified matrix of a biopurification system with alternatives lignocellulosic wastes

The biobed systems were designed to retain and to degrade pesticides through the properties of a biomixture composed of straw (ST), topsoil and peat (PT) 2:1:1 v/v. The ST is the main substrate in the biomixture, as it allows the proliferation of fungi that promotes pesticide degradation. The use of readily available components in the biomixture is an important aspect to build a biobed. Therefore, potential use of readily available wastes as barley husk (BH), sawdust (SW) and oat husk (OH), as total or partial substitutes of ST were tested in pesticide degradation studies. Metabolite formation and the biological activities were also evaluated. Biomixture composed of OH was highly efficient in pesticide degradation, with t½ values of 28.6, 58.9 and 26.8 d for atrazine (ATZ), chlorpyrifos (CHL) and isoproturon (ISP). On the other hand, comparable for degrading capacities with the ST based biomixture were obtained with SW and BH, but only as partial replacement. Contrarily, high t½ values (more than 100 d) were obtained in biomixtures with total substitution of ST by SW or BH. Metabolite formation was observed in all biomixtures tested, but without clear formation patterns. Moreover, high and stable biological activity was observed in the biomixtures composed of OH. Therefore, our results demonstrated that ST can be partial or totally replaced by OH in the biomixture allowing an efficient degradation of pesticide mixture. However, it is recommended that ST can be only partially replaced by BH and SW in the biomixture to allow efficient pesticide degradation.

Dissipation of fungicides in a vineyard soil amended with different spent mushroom substrates

The degradation kinetics and formation of metabolites for fungicides of different chemical classes (iprovalicarb, metalaxyl, penconazole, and pyrimethanil) and determination of bound residues for metalaxyl and penconazole were studied in both an unamended vineyard soil and in the same soil amended with two spent mushroom substrates (composted (C-SMS1) and fresh (F-SMS2)). The degradation kinetics was fitted to single first-order or first-order multicompartment patterns. Degradation rates decreased in C-SMS1-amended soils for all fungicides as compared to unamended soil, but in F-SMS2-amended soils, they decreased only for iprovalicarb and penconazole. The DT(50) values were higher by up to 1.8 (metalaxyl), 3.8 (pyrimethanil), 4.1 (iprovalicarb), and >1000 (penconazole) times in the soil plus C-SMS1 compared to those for soil plus F-SMS2 or unamended soil. The dissipation mechanism recorded the highest mineralization in the unamended soil for (14)C-metalaxyl and (14)C-penconazole, with the highest formation of nonextractable residues in the F-SMS2-amended soil for (14)C-metalaxyl. The results are consistent with (1) the chemical characteristics of each SMS (total and soluble organic carbon) controlling sorption and the bioavailability of fungicides and (2) the microbial activity of SMS-amended soils, which affects fungicide biodegradation. The findings of this work highlight the potential of SMS amendments with different characteristics to decrease or increase the degradation rate of a fungicide in a vineyard soil.

Effects of the organic matter from swine wastewater on the adsorption and desorption of alachlor in soil

The application of swine wastewater to the soil for agricultural purposes results in the addition of total and dissolved organic matter to the soil, which may interfere with the dynamics of pesticides in the soil. The objective of this study was to evaluate the effects of the application of total and dissolved organic matter from a biodigester and a treatment lagoon of swine wastewater in the adsorption and desorption of alachlor [2-chloro-2,6-diethyl-N(methoxymethyl acetamide)]. The assay was performed by the batch equilibrium method, and the results were fitted to the Freundlich model. The curve comparison test revealed a greater adsorption of alachlor in the soil treated with swine wastewater from the biodigester. The adsorption and desorption of alachlor increased in the soils where swine wastewater was added, and hysteresis was observed in all of the treatments.