Environmental fate and impact assessment of thiobencarb application in California rice fields using RICEWQ

Modelling pesticide concentrations in Japanese paddy fields using the RICEWQ model

Increasing concerns about plant protection products in surface waters have highlighted the importance of pesticide monitoring and modelling, both nowadays integral components of the pesticide registration process. The Rice Water Quality (RICEWQ) model predicts the fate and transport of pesticides under various paddy environmental conditions. The model has been used widely for regulatory purpose in the U.S., while its use in Europe has been limited to regulatory submissions, despite multiple recommendations to adopt RICEWQ as a high tier assessment model for regulatory purposes. The applicability of the RICEWQ model under Japanese agricultural conditions remains unexplored. This study leverages field experimental data to evaluate the RICEWQ model's capability to simulate daily concentrations of two herbicides, mefenacet and pretilachlor, in paddy water and paddy soil in Japan. The RICEWQ model provided a reasonable level of performance for predicting the fate and transport of the two herbicides by ensuring that the simulated daily water balance corresponded with field observations and with minor pesticide-specific calibration. To further improve the performance of the simulations, we implemented a straightforward calibration framework. Calibrating the RICEWQ model improved the accuracy of all simulations; for both herbicides and in both paddy water and paddy soil compartments, the lowest Nash-Sutcliffe efficiency achieved was 0.725, demonstrating excellent performance. However, the RICEWQ model consistently underestimated the peak concentrations of herbicides in paddy water within the first three days of simulation. Simulation results suggested that approximately 50 % of the total applied herbicide was lost from the paddy system. Increasing the duration of the water holding period after pesticide application or increasing the storage capacity of the rice field via excess water storage depth management has the potential to reduce greatly herbicide loss to below 10 % of the total applied herbicide.

Unveiling six novel bacterial strains for fipronil and thiobencarb biodegradation: efficacy, metabolic pathways, and bioaugmentation potential in paddy soil

Introduction

Soil bacteria offer a promising approach to bioremediate pesticide contamination in agricultural ecosystems. This study investigated the potential of bacteria isolated from rice paddy soil for bioremediating fipronil and thiobencarb, common agricultural pesticides.

Methods

Bacterial isolates capable of degrading fipronil and thiobencarb were enriched in a mineral salt medium. A response surface methodology with a Box-Behnken design was utilized to optimize pesticide degradation with the isolated bacteria. Bioaugmentation tests were performed in paddy soils with varying conditions.

Results and discussion

Six strains, including single isolates and their mixture, efficiently degraded these pesticides at high concentrations (up to 800 µg/mL). Enterobacter sp., Brucella sp. (alone and combined), and a mixture of Stenotrophomonas sp., Bordetella sp., and Citrobacter sp. effectively degraded fipronil and thiobencarb, respectively. Notably, a single Pseudomonas sp. strain degraded a mixture of both pesticides. Optimal degradation conditions were identified as a slightly acidic pH (6-7), moderate pesticide concentrations (20-50 µg/mL), and a specific inoculum size. Bioaugmentation assays in real-world paddy soils (sterile/non-sterile, varying moisture) demonstrated that these bacteria significantly increased degradation rates (up to 14.15-fold for fipronil and 5.13-fold for thiobencarb). The study identifies these novel bacterial strains as promising tools for bioremediation and bioaugmentation strategies to tackle fipronil and thiobencarb contamination in paddy ecosystems.

Efficacy of novel bacterial consortia in degrading fipronil and thiobencarb in paddy soil: a survey for community structure and metabolic pathways

Introduction

Fipronil (FIP) and thiobencarb (THIO) represent widely utilized pesticides in paddy fields, presenting environmental challenges that necessitate effective remediation approaches. Despite the recognized need, exploring bacterial consortia efficiently degrading FIP and THIO remains limited.

Methods

This study isolated three unique bacterial consortia-FD, TD, and MD-demonstrating the capability to degrade FIP, THIO, and an FIP + THIO mixture within a 10-day timeframe. Furthermore, the bioaugmentation abilities of the selected consortia were evaluated in paddy soils under various conditions.

Results

Sequencing results shed light on the consortia's composition, revealing a diverse bacterial population prominently featuring Azospirillum, Ochrobactrum, Sphingobium, and Sphingomonas genera. All consortia efficiently degraded pesticides at 800 µg/mL concentrations, primarily through oxidative and hydrolytic processes. This metabolic activity yields more hydrophilic metabolites, including 4-(Trifluoromethyl)-phenol and 1,4-Benzenediol, 2-methyl-, for FIP, and carbamothioic acid, diethyl-, S-ethyl ester, and Benzenecarbothioic acid, S-methyl ester for THIO. Soil bioaugmentation tests highlight the consortia's effectiveness, showcasing accelerated degradation of FIP and THIO-individually or in a mixture-by 1.3 to 13-fold. These assessments encompass diverse soil moisture levels (20 and 100% v/v), pesticide concentrations (15 and 150 µg/g), and sterile conditions (sterile and non-sterile soils).

Discussion

This study offers an understanding of bacterial communities adept at degrading FIP and THIO, introducing FD, TD, and MD consortia as promising contenders for bioremediation endeavors.

Using a Bayesian Network Model to Predict Risk of Pesticides on Aquatic Community Endpoints in a Rice Field-A Southern European Case Study

Bayesian network (BN) models are increasingly used as tools to support probabilistic environmental risk assessments (ERAs), because they can better account for uncertainty compared with the simpler approaches commonly used in traditional ERA. We used BNs as metamodels to link various sources of information in a probabilistic framework, to predict the risk of pesticides to aquatic communities under given scenarios. The research focused on rice fields surrounding the Albufera Natural Park (Valencia, Spain), and considered three selected pesticides: acetamiprid (an insecticide), 2-methyl-4-chlorophenoxyacetic acid (MCPA; a herbicide), and azoxystrobin (a fungicide). The developed BN linked the inputs and outputs of two pesticide models: a process-based exposure model (Rice Water Quality [RICEWQ]), and a probabilistic effects model (Predicts the Ecological Risk of Pesticides [PERPEST]) using case-based reasoning with data from microcosm and mesocosm experiments. The model characterized risk at three levels in a hierarchy: biological endpoints (e.g., molluscs, zooplankton, insects, etc.), endpoint groups (plants, invertebrates, vertebrates, and community processes), and community. The pesticide risk to a biological endpoint was characterized as the probability of an effect for a given pesticide concentration interval. The risk to an endpoint group was calculated as the joint probability of effect on any of the endpoints in the group. Likewise, community-level risk was calculated as the joint probability of any of the endpoint groups being affected. This approach enabled comparison of risk to endpoint groups across different pesticide types. For example, in a scenario for the year 2050, the predicted risk of the insecticide to the community (40% probability of effect) was dominated by the risk to invertebrates (36% risk). In contrast, herbicide-related risk to the community (63%) resulted from risk to both plants (35%) and invertebrates (38%); the latter might represent (in the present study) indirect effects of toxicity through the food chain. This novel approach combines the quantification of spatial variability of exposure with probabilistic risk prediction for different components of aquatic ecosystems. Environ Toxicol Chem 2024;43:182-196. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Thiobencarb induces phenotypic abnormalities, apoptosis, and cardiovascular toxicity in zebrafish embryos through oxidative stress and inflammation

Thiobencarb is a representative herbicide used on rice paddies. Because thiobencarb is used extensively on agricultural lands, especially on paddy fields, there is a high risk of unintended leaks into aquatic ecosystems. For this reason, several studies have investigated and reported on the toxicity of thiobencarb to aquatic species. In European eels, thiobencarb affected acetylcholinesterase levels in plasma and impaired adenosine triphosphatase activity in their gills. In medaka, thiobencarb-exposed embryos showed lower viability. However, molecular mechanisms underlying thiobencarb-mediated embryotoxicity have yet to be clarified. Therefore, the objective of our study was to investigate its mechanism of toxicity using zebrafish embryos. The viability of zebrafish embryos decreased upon exposure to thiobencarb and various phenotypic abnormalities were observed at concentrations lower than the lethal dose. The developmental toxicity of thiobencarb was mediated by pro-inflammatory cytokines (il1b, cxcl8, cxcl18b, and cox2a) and excessive generation of reactive oxygen species due to the downregulation of genes such as catalase, sod1, and sod2, which encode antioxidant enzymes. In addition, severe defects of the cardiovascular system were identified in response to thiobencarb exposure. Specifically, deformed cardiac looping, delayed common cardinal vein (CCV) regression, and interrupted dorsal aorta (DA)-posterior cardinal vein (PCV) segregation were observed. Our results provide an essential resource that demonstrates molecular mechanisms underlying the toxicity of thiobencarb on non-target organisms, which may contribute to the establishment of a mitigation strategy.

Evaluation of thiobencarb runoff from rice farming practices in a California watershed using an integrated RiceWQ-AnnAGNPS system

The development of modeling technology to adequately simulate water and pesticide movement within the rice paddy environment faces several challenges. These include: (1) adequately representing ponded conditions; (2) the collection/implementation of temporal/spatial pesticide application data at field scales; (3) the integration of various mixed-landuses simulation schemes. Currently available models do not fully consider these challenges and results may not be sufficiently accurate to represent fate and transport of rice pesticides at watershed scales. Therefore, in this study, an integrated simulation system, "RiceWQ-AnnAGNPS", was developed to fully address these challenges and is illustrated in a California watershed with rice farming practices. The integrated system successfully extends field level simulations to watershed scales while considering the impact of mixed landuses on downstream loadings. Moreover, the system maintains the application information at fine spatial scales and handles varying treated paddy areas via the "split and adjust" approach. The new system was evaluated by investigating the fate and transport of thiobencarb residues in the Colusa Basin, California as a case study. Thiobencarb concentrations in both water and sediment phases were accurately captured by the calibrated RiceWQ model at the edge of field. After spatial upscaling, the integrated system successfully reflected both the seasonal pattern of surface runoff and the timing of monthly thiobencarb loadings. Incorporating future enhancements can further improve model performance by including more detailed water drainage schedules and management practices, improving the accuracy of summer runoff estimations, and incorporating a more sophisticated in-stream process module. This integrated system provides a framework for evaluating rice pesticide impacts as part of a basin level management approach to improve water quality, which can be extended to other rice agrochemicals, or other areas with fine-scale spatial information of pesticide applications.

Using a multi-dimensional approach for catchment scale herbicide pollution assessments

Worldwide herbicide use in agriculture, whilst safeguarding yields also presents water quality issues. Controlling factors in agricultural catchments include both static and dynamic parameters. The present study investigated the occurrence of herbicides in streams and groundwater in two meso-scale catchments with contrasting flow controls and agricultural landuse (grassland and arable land). Using a multi-dimensional approach, streams were monitored from November 2018 to November 2019 using Chemcatcher® passive sampling devices and groundwater was sampled in 95 private drinking water wells. The concentrations of herbicides were larger in the stream of the Grassland catchment (8.9-472.6 ng L^-1) dominated by poorly drained soils than in the Arable catchment (0.9-169.1 ng L^-1) dominated by well-drained soils. Incidental losses of herbicides during time of application and low flows in summer caused concentrations of MCPA, Fluroxypyr, Trichlorpyr, Clopyralid and Mecoprop to exceeded the European Union (EU) drinking water standard due to a lack of dilution. Herbicides were present in the stream throughout the year and the total mass load was higher in winter flows, suggesting a persistence of primary chemical residues in soil and sub-surface environments and restricted degradation. Losses of herbicides to the streams were source limited and influenced by hydrological conditions. Herbicides were detected in 38% of surveyed drinking water wells. While most areas had concentrations below the EU drinking water standard some areas with well-drained soils in the Grassland catchment, had concentrations exceeding recommendations. Individual wells had concentrations of Clopyralid (619 ng L^-1) and Trichlorpyr (650 ng L^-1). Despite the study areas not usually associated with herbicide pollution, and annual mass loads being comparatively low, many herbicides were present in both surface and groundwater, sometimes above the recommendations for drinking water. This whole catchment assessment provides a basis to develop collaborative measures to mitigate pollution of water by herbicides.

National assessment of spatiotemporal loss in agricultural pesticides and related potential exposure risks to water quality in China

Pesticide loss during agricultural development has a serious effect on related water quality, and the critical concern is quantifying the potential exposure risks that pesticide loss pose to water quality at the national scale. In this study, an integrated assessment framework is proposed to scale emission factors from 232 monitoring plots to the national scale, while also considering the physicochemical properties of pesticides in dissolved or adsorbed forms. Based on the results of this study, the total pesticide emissions increased by 29.39% from 146.55 tons in 2004 to 189.62 tons in 2013 and the average loss intensities of insecticides, herbicides and fungicides were 35.25 g/km², 44.24 g/km² and 48.57 g/km², respectively. Central and Southeastern China are identified as hotspots for pesticide loss, while the proportions of high or extremely high-risk areas mainly comprise >50% of farmland. In addition, single-field crops and single-crop rice are the major cropping patterns for pesticide loss in Northern and Southern China. Our results identify key areas for the management of pesticides at the national scale and have direct implications for environmental policies on reducing the potential exposure risk of agricultural pesticides to water quality.

A review of pesticide fate and transport simulation at watershed level using SWAT: Current status and research concerns

The application of pesticides in agriculture is a widely-used way to alleviate pest stresses. However, it also introduces various environmental concerns due to the offsite movement of pesticide residues towards receiving water bodies. While the application of process-based modeling approaches can provide quantitative information on pesticide exposure, there are nonetheless growing requirements for model development and improvement to better represent various hydrological and physico-chemical conditions at watershed scale, and for better model integration to address environmental, ecological and economic concerns. The Soil and Water Assessment Tool (SWAT) is an ecohydrological model used in over 3000 published studies, including about 50 for simulating pesticide fate and transport at the watershed scale. To better understand its strengths and limitations, we conducted a rigorous review of published studies that have used SWAT for pesticide modeling. This review provides recommendations for improving the interior algorithms (fate simulation, pathway representation, transport/pollution control, and other hydrological related improvement) to better represent natural conditions, and for further extension of pesticide exposure modeling using SWAT by linking it with other models or management tools to effectively address the various concerns of environmental researchers and local decision makers. Going beyond past studies, we also recommend future improvement to fill research gaps in developing modularized field level simulation, improved BMPs, new in-pond and in-stream modules, and the incorporation of soft data. Our review pointed out a new insight of pesticide fate and transport modeling at watershed level, which should be seen as steps leading to the direction for model development, as well as better addressing management concerns of local stakeholders for model implementation.

Nitrate Runoff Contributing from the Agriculturally Intensive San Joaquin River Watershed to Bay-Delta in California

Nitrogen loading from agricultural landscapes can trigger a cascade of detrimental effects on aquatic ecosystems. Recently, the spread of aquatic weed infestations (Eichhornia crassipes, Egeria densa, Ludwigia spp., and Onagraceae) in the Sacramento-San Joaquin Delta of northern California has raised concerns, and nitrogen loading from California’s intensive farming regions is considered as one of the major contributors. In this study, we employed the Soil and Water Assessment Tool (SWAT) to simulate nitrogen exports from the agriculturally intensive San Joaquin River watershed to the Delta. The alternate tile drainage routine in SWAT was tested against monitoring data in the tile-drained area of the watershed to examine the suitability of the new routine for a tile nitrate simulation. We found that the physically based Hooghoudt and Kirkham tile drain routine improved model performance in representing tile nitrate runoff, which contributed to 40% of the nitrate loading to the San Joaquin River. Calibration results show that the simulated riverine nitrate loads matched the observed data fairly well. According to model simulation, the San Joaquin River plays a critical role in exporting nitrogen to the Delta by exporting 3135 tons of nitrate-nitrogen annually, which has a strong ecological implication in supporting the growth of aquatic weeds, which has impeded water flow, impairs commercial navigation and recreational activities, and degrades water quality in Bay-Delta waterways. Since nitrate loadings contributed by upstream runoff are an important nutrient to facilitate weed development, our study results should be seen as a prerequisite to evaluate the potential growth impact of aquatic weeds and scientific evidence for area-wide weed control decisions.