Mobility monitoring of two herbicides in amended soils: A field study for modeling applications

Modelling herbicide distribution through soil profiles under conventional tillage and non-tillage

Conservation agricultural practices based on mulching and herbicides use are becoming more widespread. However, they cannot be simulated with pesticide fate models used for risk assessment before placing pesticides on the European market. Thus, this work sought to assess and compare the performance of PRZM and MACRO models to replicate the moisture content and vertical distribution of S-metolachlor, foramsulfuron, and thiencarbazone-methyl herbicides in two agricultural soils under conventional tillage (CT) and non-tillage (NT) over a two-year field experiment. A new approach was developed to consider the impact of the mulch on soil moisture and on the amount of herbicides reaching the NT topsoil. This involved removing the presence of the mulch layer while maintaining its impact on potential evapotranspiration and herbicide adsorption and degradation through the meteorological file and the herbicide application inputs, respectively. In addition, the Kf of S-metolachlor was calibrated for an acceptable agreement between predictions and observations. MACRO outperformed PRZM in simulating soil water content and herbicide mobility, and both models performed better under CT compared to NT. Model performances decreased the second year, especially in NT soils, because herbicide DT50 were parameterized with values measured the first year, which were less representative of the second year. This new modelling approach is appropriate for simulating moisture and herbicide transport in NT soils with MACRO on a bi-annual scale. However, to assess the fate of herbicides in NT, models require a module allowing change in DT50 according to the soil surface covered annually by the mulch.

Herbicide and metabolite mobility in soil profiles under conventional tillage and non-tillage: A two-year comparative field experiment

A two-year field experiment was conducted to compare the impact of conventional tillage (CT) and non-tillage (NT) on the mobility in two soils (S1 and S2) of the herbicides S-metolachlor (SMOC), foramsulfuron (FORAM), and thiencarbazone-methyl (TCM), and the formation of their main metabolites. Herbicide and metabolite distribution through the soil profiles (0-50 cm) was determined over two maize cycles. After the first application, the mobility of SMOC and TCM was similar under CT conditions, with higher concentrations in S2 + CT topsoil than in S1 + CT due to the higher organic carbon content in S2 and its retention ability, while both herbicides were detected in the entire S1 + CT profile over time. Under NT management, partial interception by the mulch during application reduced the amount of herbicides that initially reached the topsoil, modifying their mobility dynamics. SMOC and TCM properties facilitated their transport through the soil profile, favoured by the irrigation applied shortly after their application. The total SMOC and TCM balance in S1 and S2 profiles revealed possible leaching below 50 cm, especially in soils+CT. However, the simultaneous degradation of SMOC and TCM might also occur on the mulch and/or in soil profiles, as indicated by the continuous detection of two SMOC metabolites (ethane sulfonic acid, SMOC-ESA, and oxanilic acid, SMOC-OA) and one TCM metabolite (thiencarbazone, TCM-MET1) throughout the soil profile in all the treatments assayed. FORAM dissipated faster than SMOC and TCM in all the treatments, with a total balance in all the soil profiles <40 % after 13 days. The high water solubility and polarity of FORAM might have enhanced its leaching, although its degradation to its two main metabolites was also observed in all cases. The mobility dynamics of the three herbicides in the second experimental period were similar for both soils under CT, but differed in soils under NT compared to the first application, with higher interception by the greater amount of mulch on the soil surface in the second year.

Status and development of spent mushroom substrate recycling: A review

The edible mushroom industry is the sixth largest after grain, cotton, oil, vegetables and fruits, and the annual production of edible mushrooms in China exceeds 40 million tons. Edible mushroom cultivation produces a class of by-products consisting mainly of mycelium remnants and lignocellulosic waste, known as Spent Mushroom Substrate (SMS) or Spent Mushroom Compost (SMC). SMS/SMC is rich in nutrients and active ingredients and has an extremely high recycling potential. This review paper summarizes SMS recycling strategies from the perspectives of "environmental remediation" and "circular economy", and briefly discusses the legitimacy, possible challenges and future research of SMS recycling. It is hoped that this will assist researchers in related fields and promote the development of the SMS recycling industry, thereby contributing to sustainable environmental and economic development.Implications: The efficient management of SMS is important for many countries around the world, particularly major mushroom producing countries. Traditional disposal methods (incineration, burial, piling) can cause serious damage to the environment and waste resources. The correct disposal method can protect the natural environment and provide certain economic benefits. This study presents the main methods of SMS processing from both an "environmental remediation" and "circular economy" perspective. In general, this paper emphasizes the importance of SMS processing, introduces the current mainstream processing methods and briefly discusses the legality of their processing methods.

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.

Concomitant determination of pesticides in soil and drainage water over a potato cropping season reveal dissipations largely in accordance with respective models

Pesticides are widely used in agriculture where they do not only reach their targets but also distribute to other environmental compartments and negatively affect non-target organisms. To prospectively assess their environmental risk, several tools and models using pesticide persistence (DT50) and leaching potential (groundwater ubiquity score (GUS), EXPOSIT) have been developed. Here, we simultaneously quantified 18 pesticides in soil and drainage water during a conventionally grown potato culture at field scale with high temporal resolution and compared our findings with predictions of the above models. Overall dissipations of all freshly applied compounds in soil were in line with published DT50 field values and their occurrences in drainage water were generally consistent with GUS and EXPOSIT models, respectively. In contrast, soil concentrations of the legacy pesticide atrazine and one of its transformation products (atrazine-2-hydroxy) were constant during the entire sampling campaign. Moreover, during peak discharge atrazine concentrations in drainage water were diluted whereas those of freshly applied pesticides were maximal. This difference demonstrates that the applied risk assessment tools were capable of predicting environmental concentrations and dissipation of pesticides at the short and medium time scale of a few half-lives after application, but fell short of capturing long-term trace residues.

The role of biochar and green compost amendments in the adsorption, leaching, and degradation of sulfamethoxazole in basic soil

The fate of the antibiotic sulfamethoxazole in amended soils remains unclear, moreover in basic soils. This work aimed to assess the adsorption, leaching, and biodegradation of sulfamethoxazole in unamended and biochar from holm oak pruning (BC)- and green compost from urban pruning (CG)-amended basic soil. Adsorption properties of the organic amendments and soil were determined by adsorption isotherms of sulfamethoxazole. The leachability of this antibiotic from unamended (Soil) and BC- (Soil + BC) and GC- (Soil + GC) amended soil was determined by leaching columns using water as solvent up to 250 mL. Finally, Soil, Soil + BC, and Soil + GC were spiked with sulfamethoxazole and incubated for 42 days. The degradation rate and microbial activity were periodically monitored. Adsorption isotherms showed poor adsorption of sulfamethoxazole in unamended basic soil. BC and CG showed good adsorption capacity. Soil + BC and Soil + GC increased the sulfamethoxazole adsorption capacity of the soil. The low sulfamethoxazole adsorption of Soil produced quick and intense sulfamethoxazole leaching. Soil + BC reduced the sulfamethoxazole leaching, unlike to Soil + GC which enhanced it concerning Soil. The pH of adsorption isotherms and leachates indicate that the anion of sulfamethoxazole was the major specie in unamended and amended soil. CG enhanced the microbial activity of the soil and promoted the degradability of sulfamethoxazole. In contrast, the high adsorption and low biostimulation effect of BC in soil reduced the degradation of sulfamethoxazole. The half-life of sulfamethoxazole was 2.6, 6.9, and 11.9 days for Soil + GC, Soil, and Soil + BC, respectively. This work shows the benefits and risks of two organic amendments, BC and GC, for the environmental fate of sulfamethoxazole. The different nature of the organic carbon of the amendments was responsible for the different effects on the soil.

Selection of aquatic microbiota exposed to the herbicides flufenacet and metazachlor

Herbicides are important, ubiquitous environmental contaminants, but little is known about their interaction with bacterial aquatic communities. Here, we sampled a protected natural freshwater habitat and characterised its microbiome in interaction with herbicides. We evolved the freshwater microbiomes in a microcosm assay of exposure (28 days) to flufenacet and metazachlor at environmental concentrations of 0.5, 5 and 50 μg L-1 . Inhibitory effects of herbicides were exemplarily assessed in cultured bacteria from the same pond (Pseudomonas alcaligenes, Paenibacillus amylolyticus and Microbacterium hominis). Findings were compared to long-term concentrations as provided by local authorities. Here, environmental concentrations reached up to 11 μg L-1 (flufenacet) and 76 μg L-1 (metazachlor). Bacteria were inhibited at minimum inhibitory concentrations far above these values; however, concentrations of 50 μg L-1 of flufenacet resulted in measurable growth impairment. While most herbicide-exposed microcosm assays did not differ from controls, Acidobacteria were selected at high environmental concentrations of herbicides. Alpha-diversity (e.g., taxonomic richness on phylum level) was reduced when aquatic microbiomes were exposed to 50 μg metazachlor or flufenacet. One environmental strain of P. alcaligenes showed resistance to high concentrations of flufenacet (50 g L-1 ). In total, this study reveals that ecologic imbalance due to herbicide use significantly impacts aquatic microbiomes.

Assessment of Different Spent Mushroom Substrates to Bioremediate Soils Contaminated with Petroleum Hydrocarbons

Bioremediation techniques are being developed as substitutes for physical–chemical methodologies that are expensive and not sustainable. For example, using the agricultural waste spent mushroom substrate (SMS) which contains valuable microbiota for soil bioremediation. In this work, SMSs of four cultivated fungal species, Pleurotus eryngii, Lentinula edodes, Pleurotus ostreatus, and Agaricus bisporus were evaluated for the bioremediation of soils contaminated by petroleum hydrocarbons (TPHs). The bioremediation test was carried out by mixing the four different SMSs with the TPH-contaminated soil in comparison with an unamended soil control to assess its natural attenuation. To determine the most efficient bioremediation strategy, hydrolase, dehydrogenase, and ligninolytic activities, ergosterol content, and percentage of TPHs degradation (total and by chains) were determined at the end of the assay at 40 days. The application of SMS significantly improved the degradation of TPHs with respect to the control. The most effective spent mushroom substrate to degrade TPHs was A. bisporus, followed by L. edodes and P. ostreatus. Similar results were obtained for the removal of aliphatic and aromatic hydrocarbons. The results showed the effectiveness of SMS to remove aliphatic and aromatic hydrocarbons from C10 to C35. This work demonstrates an alternative to valorizing an abundant agricultural waste as SMS to bioremediate contaminated soils.

Leaching and degradation of S-Metolachlor in undisturbed soil cores amended with organic wastes

Organic waste (OW) reuse in agriculture is a common practice fostered by benefits in terms of waste recycling and crop production. However, OW amendments potentially affect the fate of pesticide spread on fields to protect the crops from pests and weeds. The influence of OW on the sorption, degradation, and leaching of pesticides is generally studied for each mechanism separately under artificial laboratory conditions. Our study aims at evaluating the balance of these mechanisms under more realistic conditions to clarify the influence of three common OW amendments on the fate, in soil, of the widely used herbicide S-Metolachlor. We performed leaching experiments in large undisturbed soil cores amended with raw sewage sludge, composted sludge, and digested pig slurry (digestate), respectively. We monitored S-Metolachlor and its two main metabolites MET-OA and MET-ESA in the leachates during a succession of 10 rainfall events over 126 days. We also quantified the remaining S-Metolachlor and metabolites in the soil at the end of the experiments. S-Metolachlor leaching didn't exceed 0.1% of the applied dose with or without OW amendment. Despite a soil organic carbon increase of 3 to 32%, OW amendments did not significantly affect the amount of S-Metolachlor that leached through the soil (0.01 to 0.1%) nor its transformation rate (6.0 to 8.6%). However, it affected the degradation pathways with an increase of MET-OA relative to MET-ESA formed after OW amendment (28 to 54%) compared to the controls (8%). Concentration of S-Metolachlor and metabolites in the leachates of all treatments greatly exceeded the regulatory limit for groundwater intended for human consumption in Europe. These high concentrations were probably the consequence of preferential macropore flow. Colloids had comparable levels in the leachates after S-Metolachlor application. Dissolved organic carbon was also comparable in the controls, digestate, and sludge treatments but was 65% higher in the compost-amended cores. These results, along with a great variability among replicates inherent to experiments performed under realistic conditions, partly explain the limited impact of OW on the transport of S-Metolachlor.

Effect of Organic Amendment on Mobility Behavior of Flupyradifurone in Two Different Indian Soils

Flupyradifurone is a novel neonicotinoid insecticide, mainly used in okra in subtropical conditions for controlling whitefly and jassids. The present experiment was designed to generate information on the leaching behavior of flupyradifurone, 3-[(6-chloropyridin-3-yl)methyl-(2,2-difluroethyl)amino]-2H-furan-5-one, under different rainfall conditions by using packed soil columns. Under the continuous flow conditions, a significant quantity of flupyradifurone, 67.76% and 50.61% were recovered at 0 to 5 cm soil depth in case of both clayey and sandy loam soil, respectively. A considerable amount of the residue was confined to 0 to 20 cm soil depth, with or without farmyard manure (FYM) amendment. Under varying water flow condition, distribution of the residue in the upper 0 to 5 cm soil depth got enhanced (> 90% recovery). Among the test soils, residues were detected from the leachate fraction of sandy soil (0.08 µg/mL) only. The study pointed out that leaching of flupyradifurone in sandy loam soil got decreased after using FYM. The leaching of flupyradifurone increased with the increasing amount of water (40 to 160 mL) and the residues continued to travel down to the lower depth. It can be concluded that the use of FYM may be a viable option for reducing the mobility of flupyradifurone in sandy loam soil.

Effect of Organic Residues on Pesticide Behavior in Soils: A Review of Laboratory Research

The management of large volumes of organic residues generated in different livestock, urban, agricultural and industrial activities is a topic of environmental and social interest. The high organic matter content of these residues means that their application as soil organic amendments in agriculture is considered one of the more sustainable options, as it could solve the problem of the accumulation of uncontrolled wastes while improving soil quality and avoiding its irreversible degradation. However, the behavior of pesticides applied to increase crop yields could be modified in the presence of these amendments in the soil. This review article addresses how the adsorption–desorption, dissipation and leaching of pesticides in soils is affected by different organic residues usually applied as organic amendments. Based on the results reported from laboratory studies, the influence on these processes has been evaluated of multiple factors related to organic residues (e.g., origin, nature, composition, rates, and incubation time of the amended soils), pesticides (e.g., with different use, structure, characteristics, and application method), and soils with different physicochemical properties. Future perspectives on this topic are also included for highlighting the need to extend these laboratory studies to field and modelling scale to better assess and predict pesticide fate in amended soil scenarios.

The role of two organic amendments to modify the environmental fate of S-metolachlor in agricultural soils

S-metolachlor is a widely used herbicide that may contaminate groundwater when applied to irrigated crops, especially when the soil has a low organic carbon (OC) content. The objective here was to assess the capacity of two organic wastes, namely, green compost (GC) and pelletised organo-mineral manure fertilizer (PM), applied to two soils (S) with different textures at a rate of 10% dry weight to modify the fate of S-metolachlor. The herbicide's Freundlich adsorption coefficient (Kf) increased within a range of 3.2-8.2 times in S + GC and 3.8-6.8 times in S + PM. A positive correlation between adsorption and OC and the coefficient of variation of the OC normalised adsorption coefficients (Kf_oc) higher than 20% indicated the evident influence on this process of soil OC content and its nature. The increase in adsorption did not prevent the dissipation of S-metolachlor in the amended soils, although the degradation rate decreased up to ~2 times or was not significantly modified across the different soil types. The S-metolachlor metabolites, metolachlor ethane sulfonic acid and metolachlor oxanilic acid, were detected in the herbicide's dissipation in the unamended soils, but they were not detected in the amended soils. The mobility experiments indicated leached amounts of S-metolachlor higher than 50% in unamended soil. The amounts decreased 1.1-1.7 times and 1.7-1.8 times in the S + GC and S + PM when a saturated flow was applied. Moreover, breakthrough curves indicated a slow leaching kinetics of herbicide in amended soils, with low concentrations continuously detected in the leachates together with a decrease in the maximum peak concentration. The results show the effect of the application of organic wastes especially in sandy soils to promote the immobilisation and/or degradation of S-metolachlor, avoiding its transfer to other environmental compartments.

Field insights into leaching and transformation of pesticides and fluorescent tracers in agricultural soil

The frequent detection of residues from pesticides in various natural water types has raised public awareness. This study investigated the pesticide transformation in soil and their loss to shallow groundwater in a small agricultural catchment in Northern Germany. The pesticide Flufenacet and its transformation product Flufenacet ESA were examined in Luvisol and Colluvic Gleyosol under field conditions during two consecutive years. In the second year, a fluorescent tracer experiment applying Uranine and Sulforhodamine - B was carried out to gain additional insights into leaching and formation of transformation products in soil during and after a drought. We found preferential flow in response to low precipitation as an important transport pathway for Flufenacet in dry soil, as a Flufenacet concentration (1.57 μg L^-1) was detected in shallow groundwater within 10 days after application. Leaching of Flufenacet to shallow groundwater by preferential flow posed greater risks during the dry than during the wet period. In contrast, Flufenacet ESA was detected in all groundwater samples. During the dry period, we detected no formation of TP510 (tracer transformation product) in the immediate topsoil. A fraction of both tracers remained there, suggesting also long-term residues of pesticides in the topsoil caused by limited living conditions for microorganisms under dry conditions. Newly formed transformation products of Uranine and Flufenacet were mainly trapped in upper soil if capillary flow was marginal. Formation of TP510 could be related to a soil water optimum and a soil temperature threshold. The occurrence of increased TP510 amounts in soil after drought was concurrent with the main peak of Flufenacet ESA in shallow groundwater. This suggested similar retention and transformation processes of fluorescent tracers and organic pesticides inside the soil. This study contributed to an extended understanding of the leaching and transformation of organic pollutants in agricultural soil under real field conditions.

Editorial: New Research on Soil Degradation and Restoration

The Virtual Special Issue (VSI) "New Research on Soil Degradation and Restoration" was proposed by the Guest-Editors (the authors of this editorial piece) to Journal of Environmental Management taking into account the following aspects: (a) Firstly, soil degradation is a main issue all over the world; (b) Secondly, physical, chemical and biological degradation of soil environments need detailed research, also going deeper in some new aspects poorly covered up to now; and (c) Similarly, new quality research on restoration of degraded soils, dumping sites, different areas affected by mining activities, and so on, would be clearly useful in order to prevent and/or solve critical environmental hazards. As a result, 110 manuscripts were submitted to the VSI by authors from around the world, and near 50 high quality works were finally published. The Guest-Editors of the VSI consider that the papers published will be of great interest for researchers working in this field, as well as for the overall community, as they include aspects clearly relevant at a global level.

Field measurement and modelling of chlorotoluron and flufenacet persistence in unamended and amended soils

The dissipation and persistence of two cereals herbicides, chlorotoluron and flufenacet, were studied in a field experiment including three replicated plots of unamended soil (S), soil amended with spent mushroom substrate (S + SMS), and soil amended with green compost (S + GC), during the winter wheat cultivation campaign. The SMS and GC organic residues were applied to the soil at rates of 140 or 85 t residue ha^-1, and herbicides were sprayed as Erturon® and Herold® formulations for chlorotoluron and flufenacet, respectively. Concentrations of both herbicides and of their metabolites were regularly measured in the three soil treatments (0-10 cm) from 0 to 339 days. The dissipation kinetics fitted well the single first order (SFO) model, except that of chlorotoluron that fitted the first order multi-compartment (FOMC) model better in the unamended soil. The dissipation rates of herbicides were lower in amended than in unamended soils. The results also showed that the DT₅₀ of chlorotoluron (66.2-88.0 days) and flufenacet (117-145 days) under field conditions were higher than those previously obtained at laboratory scale highlighting the importance of the changing environmental conditions on the dissipation process. Similarly, the formation of chlorotoluron and flufenacet metabolites under field conditions was different from that previously observed in the laboratory. The performance of the MACRO pesticide fate model, parameterized with laboratory data, was then tested against field data. There was a very good agreement between measured and simulated chlorotoluron residue levels in the three soil treatments, while the ability of the model to reproduce the dissipation of flufenacet was good in the unamended soil and very good in S + SMS and S + GC soils. MACRO might be used to estimate the remaining amounts of herbicides in amended soils from degradation data previously obtained at laboratory scale. This would help to manage herbicide doses in different environmental conditions to preserve the sustainability of agricultural systems.

Modelling herbicides mobility in amended soils: Calibration and test of PRZM and MACRO

Addition of organic residues to soil is a current farming practice but it is not considered in the modelling studies for pesticide risk assessment at regulatory level despite its potential impact on the pesticide dynamics in soil. Thus, the objective of this work was to examine and to compare the ability of PRZM and MACRO pesticide fate models to simulate soil water content, and bromide (Br^-, tracer), chlorotoluron and flufenacet concentrations in the soil profiles (0-100 cm) of one agricultural soil, unamended (control soil, S), amended with spent mushroom substrate (S + SMS) or amended with green compost (S + GC). Based on a two-year field-scale dataset, the models were first calibrated against measurements of water and solutes contents in the soil profiles (first year) and then tested without any further model calibration by comparison with the field observations of the second year. In general, the performance of MACRO to simulate the whole dataset in the three soil treatments was higher than that of PRZM. MACRO simulated satisfactorily the water dynamics along the soil profiles whereas it was poorly described by the capacity model PRZM. Both models predicted very well the Br^- mobility in control and amended soils after dispersion parameters were fitted to observations. No calibration was necessary to reproduce correctly herbicides vertical distribution in the control soil profile. In the amended soils, MACRO simulations were highly correlated to the observed vertical distribution of flufenacet and chlorotoluron, but calibration of the K_d of chlorotoluron was needed. On the contrary, modelling with PRZM required calibration of K_d and DT₅₀ of both herbicides to obtain an acceptable agreement between observations and predictions in the amended soils. K_d and DT₅₀ calibration was based on the initial dissolved organic carbon contents (DOC) of amended soils. It allowed to take into account the processes that decrease the herbicides sorption on the soil and enhance their bioavailability, but that are not described in PRZM and MACRO (such as the formation of herbicide-DOC mobile complexes). This work showed that models such as PRZM and MACRO are able to simulate the fate of pesticides in amended soils. However, before using these models as predictive tools in large amended soil conditions, and especially in the regulatory context, further modelling studies should focus on other pedoclimatic-pesticides-organic residues combinations, and on longer periods.