Neonicotinoid insecticides in global agricultural surface waters - Exposure, risks and regulatory challenges

Dihydroxyl modified UiO-66 as dispersive solid-phase extraction sorbent coupled with ultra-high performance liquid chromatography tandem mass spectrometry for detection of neonicotinoid insecticides

The extensive usage of neonicotinoid insecticides (NIs) has raised many concerns about their potential harm to environment and human health. Thus, it is of great importance to develop an efficient and reliable method to determine NIs in food samples. In this work, three Zr4+-based metal-organic frameworks functionalized with various numbers of hydroxyl groups were fabricated with a facile one-pot solvothermal method. Among them, dihydroxy modified UiO-66 (UiO-66-(OH)2) exhibited best adsorption performance towards five target NIs. Then, a sensitive and efficient method for detection of NIs from vegetable and fruit samples was established based on dispersive solid phase extraction (dSPE) with UiO-66-(OH)2 as adsorbent coupled with ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Key parameters affecting the dSPE procedure including amounts of adsorbent, adsorption time, eluent solvents and desorption time were investigated. Under the optimal conditions, rapid adsorption of NIs within five minutes was achieved due to the high affinity of UiO-66-(OH)2 towards NIs. The developed method exhibited high sensitivity with limits of detection (LODs) varied from 0.003 to 0.03 ng/mL and wide linearity range over 3-4 orders of magnitude from 0.01 to 500 ng/mL. Furthermore, the established method was applied for determining trace NIs from complex matrices with recoveries ranging from 74.6 to 99.6 % and 77.0-106.8 % for pear and tomato samples, respectively. The results indicate the potential of UiO-66-(OH)2 for efficient enrichment of trace NIs from complex matrices.

Agricultural film-derived microplastics elevate the potential risk of pesticides in soil ecosystem: The inhibited leaching by altering soil pore

The residue of mulch film is a crucial source of microplastics (MPs) in agricultural fields. The effects of mulch film-derived MPs on the environmental behavior of pesticides in agriculture remain unclear. In the present study, the effects of MPs of different sizes (5 mm, 1 mm, 30 µm, and 0.3 µm) at environmentally relevant concentrations on pesticide transport were evaluated, and the mechanism was explored with respect to adsorption and pore structure using fluorescence visualization, the extended Derjaguin-Landau-Verwey-Overbeek model, and microcomputed tomography. MPs were found to be retained in the soil due to size limitation, pore capture, and surface adhesion. The presence of mm-sized MPs (5 and 1 mm) at a concentration of 0.25 % inhibited the leaching behavior of atrazine, metolachlor, and tebuconazole. MPs did not significantly alter the pesticide adsorption ability of the soil. The reduced leaching originated from the impact of MPs on soil pore structure. Specifically, the porosity increased by 16.2-25.0 %, and the connectivity decreased by 34.5 %. These results demonstrate that mm-sized MPs inhibit pesticide leaching by obstructing the pores and altering the transport pathways, thereby potentially elevating environmental risks, particularly to the soil ecosystem.

FePO4/WB as an efficient heterogeneous Fenton-like catalyst for rapid removal of neonicotinoid insecticides: ROS quantification, mechanistic insights and degradation pathways

Iron-based catalysts for peroxymonosulfate (PMS) activation hold considerable potential in water treatment. However, the slow conversion of Fe(III) to Fe(II) restricts its large-scale application. Herein, an iron phosphate tungsten boride composite (FePO4/WB) was synthesized by a simple hydrothermal method to facilitate the Fe(III)/Fe(II) redox cycle and realize the efficient degradation of neonicotinoid insecticides (NEOs). Based on electron paramagnetic resonance (EPR) characterization, scavenging experiments, chemical probe approaches, and quantitative tests, both radicals (HO• and SO4⋅-) and non-radicals (1O2 and Fe(IV)) were produced in the FePO4/WB-PMS system, with relative contributions of 3.02 %, 3.58 %, 6.24 %, and 87.16 % to the degradation of imidacloprid (IMI), respectively. Mechanistic studies revealed that tungsten boride (WB) promoted the reduction of FePO4, and the generated Fe(II) dominantly activated PMS through a two-electron transfer to form Fe(IV), while a minority of Fe(II) engaged in a one-electron transfer with PMS to produce SO4⋅-, HO•, and 1O2. In addition, four degradation pathways of NEOs were proposed by analyzing the byproducts using UPLC-Q-TOF-MS/MS. Besides, seed germination experiments revealed the biotoxicity of NEOs was significantly reduced after degradation via the FePO4/WB-PMS system. Meanwhile, the recycling experiments and continuous flow reactor experiments showed that FePO4/WB exhibited high stability. Overall, this study provided a new perspective on water remediation by Fenton-like reaction. ENVIRONMENTAL IMPLICATION: Neonicotinoids (NEOs) are a type of insecticide used widely around the world. They've been found in many aquatic environments, raising concerns about their possible negative effects on the environment and health. Iron-based catalysts for peroxymonosulfate (PMS) activation hold great promise for water purification. However, the slow conversion of Fe(III) to Fe(II) restricts its large-scale application. Herein, iron phosphate tungsten boride composite (FePO4/WB) was synthesized by a simple hydrothermal method to facilitate the Fe(III)/Fe(II) redox cycle and realize the efficient degradation of NEOs. The excellent stability and reusability provided a great prospect for water remediation.

Neonicotinoid insecticides in a large-scale agricultural basin system-Use, emission, transportation, and their contributions to the ecological risks in the Pearl River Basin, China

Neonicotinoid pollution has increased rapidly and globally in recent years, posing significant risks to agricultural areas. Quantifying use and emission, transport and fate of these contaminants, and risks is critical for proper management of neonicotinoids in river basin. This study elucidates use and emissions of neonicotinoid pesticides in a typical large-scale agriculture basin of China, the Pearl River Basin, as well as the resulting agricultural non-point source pollution and related ecological risks using market surveys, data analysis, and the Soil and Water Assessment Tool. Neonicotinoid use in the basin was estimated at 1361 t in 2019, of which 83.1 % was used in agriculture. After application, approximately 99.1 t neonicotinoids were transported to the Pearl River, accounting for 7.2 % of the total applied. Estimated aquatic concentrations of neonicotinoids showed three seasonal peaks. Several distinct groups of neonicotinoid chemicals can be observed in the Pearl River, as estimated by the model. An estimated 3.9 % of the neonicotinoids used were transported to the South China Sea. Based on the present risk assessment result, several neonicotinoids posed risks to aquatic organism. Therefore, the use of alternative products and/or reduced use is deemed necessary. This study provides novel insights into the fate and ecological risks of neonicotinoid insecticides in large-scale watersheds, and underscores the need for greater efficiency of use and extensive environmental monitoring.

Flupyradifurone negatively affects survival, physical condition and mobility in the two-spotted lady beetle (Adalia bipunctata)

Lady beetles play a crucial role in natural ecosystems and agricultural settings. Unfortunately, these insects and more specifically the two-spotted lady beetle (Adalia bipunctata) are currently facing a severe decline in populations due to various stressors, with pesticide exposure being a significant threat. Flupyradifurone is a relatively newly introduced insecticide and as existing research is mainly elucidating its effects on bees there remains a limited understanding of its effects on non-hymenopteran insects, including lady beetles. In this study we investigated the impact of acute orally applied flupyradifurone doses on survival and sublethal parameters such as physical condition and mobility on A. bipunctata. Our findings revealed a significant increase in mortality among individuals subjected to flupyradifurone doses of 19 ng/individual (corresponding to >1.5-2.0 ng active substance (a.s.)/mg body weight (bw). The calculated LD50 of flupyradifurone at 48 h was 2.11 ng a.s./mg bw corresponding to an amount of 26.38 ng/individual. Sublethal consequences were observable immediately after pesticide application. Even at doses as low as 2 ng/individual (corresponding to >0.0-0.5 ng a.s./mg bw), flupyradifurone induced trembling and temporary immobility in treated animals. Furthermore, pesticide intoxication led to hypoactivity, with less distance covered and a decline in straightness of locomotion. In conclusion, our study underscores the harmful effects of flupyradifurone on the two-spotted lady beetle at doses notably lower than those affecting bees. These findings stress the importance of additional research to attain a more holistic understanding of pesticide impacts not only on a broader range of non-target arthropods species, but also on various exposure routes as well as lethal and sublethal effects.

Role of brain monoamines in acetamiprid-induced anxiety-like behavior

Neonicotinoid (NN) pesticides have been linked to increased brain dysfunction in mammals, such as anxiety-like behavior; this is thought to involve monoamines (MA), neurotransmitters that control behavior, memory, and learning. However, the mechanism by which NNs affect the central nervous system is not fully understood. In this study, we aimed to investigate whether MAs affect NNs-induced anxiety-like behavior. Mice were orally administered acetamiprid (ACE), an NN, at the no observed adverse effect level (NOAEL) of mouse (20 mg/kg body mass) set by the Food Safety Commission of Japan, and the elevated zero-maze (EZM) test was performed 30 min after administration. After behavioral analysis, levels of four MA (dopamine, 3-MT, serotonin, and histamine) in selected brain regions were determined by liquid chromatography mass spectrometry (LC/MS/MS). In the exposed group, a trend toward increased anxiety-like behavior was observed, and at least one MA concentration was significantly increased in each region. Further, significant correlations were found between behavioral test results and hippocampal serotonin and striatal dopamine concentrations, as well as between dopamine and serotonin concentrations, in the exposed group. As anxiety can influence activity in the behavioral tests, the activity of neurons in the raphe nuclei (RN), a brain region greatly involved in anxiety via the serotonergic system, was examined by staining with anti-serotonin antibodies, and increased serotonergic activity was observed. Taken together, these results suggest that ACE regulates MA levels, notably serotonin levels in the hippocampus and that RN plays an important role in ACE-induced anxiety-like behavior.

Glycometabolic disorder induced by chronic exposure to low-concentration imidacloprid in zebrafish

The health risks induced by chronic exposure to low concentrations of imidacloprid (IMI) to zebrafish were investigated in this study. The results indicated that the growth of zebrafish was inhibited after being exposed to 10, 100, and 500 μg/L of IMI for 90 days. Moreover, the blood glucose levels in the IMI-exposed groups were significantly higher compared to the control group. Investigation into the development of zebrafish larvae revealed that IMI exposure hindered the development of the liver and pancreatic islets, organs crucial for glucose metabolism. In addition, the IMI-exposed groups exhibited reduced liver glycogen and plasma insulin levels, along with changes in the activity of enzymes and the transcription levels of genes associated with liver glucose metabolism. These findings suggest that IMI induces glycometabolic disorders in zebrafish. The analysis of intestinal flora revealed that several key bacteria associated with an elevated risk of diabetes were significantly altered in IMI-exposed fish. Specifically, a remarkable decrease was found in the abundance of the genera Aeromonas and Shewanella, which have been found closely related to the development of pancreatic islets. This implies that the alteration of key bacteria in the fish gut by IMI, which in turn affects the development of organs such as the pancreatic islets, may be the initial trigger for abnormalities in glucose metabolism. Our results revealed that chronic exposure to low concentrations of IMI led to glycometabolic disorder in fish. Therefore, considering the pervasive existence of IMI residues in the environment, the health hazards posed by low-concentration IMI to fish cannot be overlooked.

Those That Remain Caught in the "Organic Matter Trap": Sorption/Desorption Study for Levelling the Fate of Selected Neonicotinoids

With projections suggesting an increase in the global use of neonicotinoids, contemporary farmers can get caught on the "pesticide treadmill", thus creating ecosystem side effects. The aim of this study was to investigate the sorption/desorption behavior of acetamiprid, imidacloprid, and thiacloprid that controls their availability to other fate-determining processes and thus could be useful in leveling the risk these insecticides or their structural analogues pose to the environment, animals, and human health. Sorption/desorption isotherms in four soils with different organic matter (OC) content were modelled by nonlinear equilibrium models: Freundlich's, Langmuir's, and Temkin's. Sorption/desorption parameters obtained by Freundlich's model were correlated to soil physico-chemical characteristics. Even though the OC content had the dominant role in the sorption of the three insecticides, the role of its nature as well as the chemical structure of neonicotinoids cannot be discarded. Insecticides sorbed in the glassy OC phase will be poorly available unlike those in the rubbery regions. Imidacloprid will fill the sorption sites equally in the rubbery and glassy phases irrespective of its concentration. The sorption of thiacloprid at low concentrations and acetamiprid at high concentrations is controlled by hydrophilic aromatic structures, "trapping" the insecticides in the pores of the glassy phase of OC.

Neonicotinoid insecticides in waters of the northern Jiangsu segment of the Beijing-Hangzhou Grand Canal: Environmental and health implications

Neonicotinoid (NEO) insecticides have been frequently detected in natural aquatic environments. Nevertheless, the distribution of NEOs in artificial environments is not clear. The Beijing-Hangzhou Grand Canal is the longest canal in the world. The northern Jiangsu segment of the Grand Canal was selected to study the spatiotemporal variation and source of eight NEOs in the canal water and assess their ecological and health risks. The total NEO concentration in the canal water was 12-289 ng L-1 in the dry season and 18-373 ng L-1 in the wet season, which were within the concentration range in other 11 natural rivers worldwide. The average total NEO concentrations were not statistically different between the seasons; only the concentrations of imidaclothiz, thiacloprid (THI), acetamiprid, and dinotefuran were different. At city scale, the total NEO concentration in the dry season showed a decreasing trend along the water flow from Xuzhou City to Yangzhou City. The total NEO concentrations were found to be positively correlated with the sown area of farm crops and the rural labour force, indicating the agricultural influence on the spatial distribution of NEO concentrations. In the wet season, relatively high NEO concentrations were distributed in downstream sites under the influence of artificial regulation. The primary contributor to the NEO inputs into the canal was the nonpoint source in the dry and wet seasons, with a relative contribution of 68 %. THI, imidacloprid, clothianidin and thiamethoxan would produce chronic ecological risks in both seasons. Further consideration needs to be given to the above four NEOs and NEO mixtures. The human health risks that NEOs posed by drinking water were assessed based on the chronic daily intake (CDI). The maximum CDI for adults and children was lower than the reference doses. This suggested public health would not be at risk from canal water consumption.

Design, synthesis, and evaluation of novel arecoline-linked amino acid derivatives for insecticidal and antifungal activities

A series of arecoline derivatives with amino acid moieties were designed and synthesised using an acylamide condensation strategy, taking arecoline as the foundational structure. The insecticidal efficacy of these compounds against Aphis craccivora and Tetranychus cinnabarinus was evaluated. Notably, derivatives 3h and 3i demonstrated superior insecticidal activity compared with arecoline. Additionally, 3h and 3i showed good fungicidal effectiveness against two types of plant fungi. Moreover, molecular docking analyses suggested that 3h and 3i could affect the nervous systems of A. craccivora and T. cinnabarinus by binding to neuronal nicotinic acetylcholine receptors. These findings suggest that compounds 3h and 3i represent promising leads for further development in insecticide and fungicide research.

Pesticides in Ethiopian surface waters: A meta-analytic based ecological risk assessment

In most developing countries, including Ethiopia, a conspicuous gap exists in understanding risk of pesticides and establishing robust regulatory frameworks for their effective management. In this context, we present a detailed assessment of pesticide risks within Ethiopian aquatic ecosystems in at least 18 distinct surface water bodies, including 46 unique sample locations. Measured environmental concentrations (MECs; n = 388) of current-use pesticides (n = 52), sourced from existing field studies, were compared against their respective regulatory threshold levels (RTLs). The results indicated a scarcity of pesticide exposure data across the majority of Ethiopian water bodies situated within agricultural watersheds. Importantly, surface water pesticide concentrations ranged from 0.0001 to 142.66 μg/L, with a median concentration of 0.415 μg/L. The available dataset revealed that 142 out of 356 MECs (approximately 40 %) of the identified pesticides entail significant acute risks to aquatic ecosystems, with the highest RTL exceedances up to a factor of 8695. Among the pesticide use groups, insecticides exhibited the highest exceedance rate, while this was rarer for fungicides and herbicides. Furthermore, a species-specific insecticide risk assessment indicated aquatic invertebrates (54.4 %) and fishes (38.4 %) are more exposed to pesticide risks, attributable to pyrethroids and organophosphates. In conclusion, our findings demonstrate that the presently registered pesticides in Ethiopia carry elevated risks towards aquatic environments under real-world settings. This challenges the notion that pesticides approved through Ethiopian pesticide regulatory risk assessment entail minimal environmental hazards. Consequently, we advocate for the adoption of more refined risk assessment strategies, a post-registration reevaluation process, and, if deemed necessary, the imposition of bans or restrictions on highly toxic pesticides.

Imidacloprid affects the visual behavior of adult zebrafish (Danio rerio) by mediating the expression of opsin and phototransduction genes and altering the metabolism of neurotransmitters

Imidacloprid poses a significant threat to aquatic ecosystems. In this study, we investigated the visual toxicity of imidacloprid and the underlying molecular mechanisms in adult zebrafish. After exposure to imidacloprid at environmental relevant concentrations (10 and 100μg/L) for 21 days, the detectable contents of imidacloprid were 23.0 ± 0.80 and 121 ± 1.56 ng/mg in eyes of adult zebrafish, respectively. The visual behavior of adult zebrafish was impaired including a reduced ability to track smoothly visual stimuli and visually guided self-motion. The immunofluorescence experiment showed that the content of Rhodopsin (Rho) in the retina of zebrafish was changed significantly. The expression rhythm of genes played key roles in capturing photons in dim (rho) and bright (opn1mw3, opn1lw2 and opn1sw2) light, and in phototransduction (gnb3b, arr3a and rpe65a), was disrupted significantly throughout a 24-h period in adult zebrafish. Targeted metabolomics analysis showed that the content of 16 metabolites associated with neurotransmitter function changed significantly, and were enriched in top three metabolism pathways including Arginine biosynthesis, Alanine, aspartate and glutamate metabolism, and Tryptophan metabolism. These results indicated that imidacloprid exposure at environmentally relevant concentrations could cause optical toxicity through disturbing the expression of opsins and affecting the phototransduction in the retina of zebrafish adults.

A synthesis of anthropogenic stress effects on emergence-mediated aquatic-terrestrial linkages and riparian food webs

Anthropogenic stress alters the linkage between aquatic and terrestrial ecosystems in various ways. Here, we review the contemporary literature on how alterations in aquatic systems through environmental pollution, invasive species and hydromorphological changes carry-over to terrestrial ecosystems and the food webs therein. We consider both the aquatic insect emergence and flooding as pathways through which stressors can propagate from the aquatic to the terrestrial system. We specifically synthesize and contextualize results on the roles of pollutants in the emergence pathway and their top-down consequences. Our review revealed that the emergence and flooding pathway are only considered in isolation and that the overall effects of invasive species or pollutants on food webs at the water-land interface require further attention. While very few recent studies looked at invasive species, a larger number of studies focused on metal transfer compared to pesticides, pharmaceuticals or PCBs, and multiple stress studies up to now left aquatic-terrestrial linkages unconsidered. Recent research on pollutants and emergence used aquatic-terrestrial mesocosms to elucidate the effects of aquatic stressors such as the mosquito control agent Bti, metals or pesticides to understand the effects on riparian spiders. Quality parameters, such as the structural and functional composition of emergent insect communities, the fatty acid profiles, yet also the composition of pollutants transferred to land prove to be important for the effects on riparian spiders. Process-based models including quality of emergence are useful to predict the resulting top-down directed food web effects in the terrestrial recipient ecosystem. In conclusion, we present and recommend a combination of empirical and modelling approaches in order to understand the complexity of aquatic-terrestrial stressor propagation and its spatial and temporal variation.

Neonicotinoids in tea leaves and infusions from China: Implications for human exposure

The ingestion of contaminated tea involves the risk of human exposure to residues of neonicotinoids (NEOs). Nevertheless, there is little empirical research about this topic; to bridge the current knowledge gap, we collected 220 samples of various tea products from four geographical areas in China, including unfermented green tea, semi-fermented white tea and oolong tea, completely fermented black tea, and post-fermented dark tea. A total of six NEOs were detected from the tea leaves and infusions, namely, dinotefuran (DIN), thiamethoxam (THM), clothianidin (CLO), imidacloprid (IMI), acetamiprid (ACE), and thiacloprid (THI). The detection frequencies (DFs) and concentrations of all target NEOs were relatively high across the investigated tea samples, and the DIN, IMI and ACE residues measured in some samples exceeded the maximum residue level (MRL) standards for the European Union. Samples representing the Jiangnan area exhibited greater levels of total target NEOs (∑6NEOs) than samples representing the Jiangbei area (p < 0.001). Moreover, dark tea samples were found to have far higher levels of NEO residues than green (p < 0.001), white (p < 0.05), or oolong (p < 0.001) samples. The health risks associated with exposure to NEO residues via tea were small for both children and adults in terms of acute, chronic, and cumulative dietary exposure risk assessments. The transfer rates (TRs) of NEOs observed in white, black, and dark tea infusions gradually decreased after the third brewing time. As such, it is recommended to only consume tea that has been brewed at least three times. The presented results not only describe the extent of NEO contamination in Chinese tea leaves and infusions, but also provide tea drinking guidelines for consumers.

Determination of organic contaminants in L'Albufera Natural Park using microporous polyethylene tube passive samplers: An environmental risk assessment

L'Albufera Natural Park (Valencia, Spain) is a protected wetland of international significance that provides critical habitats to endemic and threatened bird and plant species. This study aims to use multiple cross-validation techniques to generate an accurate estimation of the environmental risk of organic contaminants (OCs) in an internationally important coastal wetland, to identify compounds of concern and their potential sources and risk factors. Microporous polyethylene tube (MPT) passive samplers were deployed at 12 locations across L'Albufera Natural Park with concurrent grab samples collected. A subset of MPT samplers were also analysed by an additional laboratory in Australia to widen the range of contaminants and assess interlaboratory reproducibility of results. Forty-three pesticides, 20 pharmaceuticals and personal care products (PPCPs), 20 per-and polyfluoroalkyl substances (PFAS) and 4 organophosphorus flame retardants (OPFRs) were detected in the MPT samplers. The fungicides tebuconazole and difenoconazole were detected at the highest concentrations in passive samplers (maximum concentrations, 153 ng sampler-1 and 106 ng sampler-1, respectively). Several other pesticides were detected in all locations (mean concentrations >1 ng sampler-1). The compounds fenamiphos, propyzamide, difenoconazole, propiconazole, metsulfuron methyl, sodium bis (perfluorohexyl) phosphinate (6:6 PFPiA), 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), 6:2 fluorotelomersulfonate (6:2 FTS), citalopram desmethyl and citalopram were reported in the wetland for the first time. Spatial distribution analysis revealed higher pesticide concentrations in the North of L'Albufera. A risk quotient (RQ) analysis showed that ibuprofen is of concern in the area. Overall, the MPT sampling approach is promising as a risk assessment tool for better understanding the transport and fate of OCs in protected areas.

Binary mixtures of imidacloprid and thiamethoxam do not appear to cause additive toxicity in fathead minnow larvae (Pimephales promelas)

Introduction: Considerable use of neonicotinoid insecticides has resulted in their detection in surface waters globally, with imidacloprid (IM) and thiamethoxam (TM) frequently found together. Neonicotinoids are selective agonists for invertebrate nicotinic acetylcholine receptors (nAChR) leading to paralysis and death. While not overtly toxic to vertebrates, growing evidence suggests that chronic exposure to individual neonicotinoids can cause adverse health effects in fish. This work examined whether chronic exposure to binary mixtures of imidacloprid (IM) and thiamethoxam (TM) would be more toxic to fathead minnow (Pimephales promelas) larvae than either insecticide alone. Materials and Methods: Embryos were exposed to a 1:1 mixture of IM and TM (0.2, 2, 20, 200 or 2,000 μg/L of each pesticide) or a 1:5, 1:10, or 1:20 mixture of IM and TM (0.02 μg/L of IM with 0.1, 0.2, or 0.4 μg/L of TM) for a total of 8 days. Survival, developmental toxicity, embryonic motor activity, and startle escape responses were quantified. Results: Survival and growth were reduced, and hatching induced by exposure to a 1:1 mixture containing > 2 μg/L of each insecticide, but not following exposure to mixtures containing environmentally-relevant concentrations. Acute exposure to a 1:1 mixture did not alter embryonic motor activity; however, chronic exposure to these mixtures resulted in a slight but significant decrease in embryonic movements. Only 1:1 mixtures of high concentrations of IM and TM altered the startle escape response by increasing latency of response; however, a significant proportion of fish exposed to 1:1 mixtures had altered latency and burst speed. Taken together, these behavioral indicators of nAChR activation suggest that in mixtures, neonicotinoids could interfere with nAChR signaling despite their low affinity for the nAChR. Conclusion: Our findings suggest that toxicity of binary mixtures of IM and TM is primarily driven by IM, and that mixtures of IM with TM do not appear to cause significant additive toxicity when compared with our previous studies evaluating each neonicotinoid alone. Given the limited toxicological data available for mixtures of neonicotinoid insecticides in fish, further study is required to better understand the ecological risks these insecticides may pose to aquatic ecosystems.

Occurrence, source, and risk assessment of neonicotinoid insecticides in the Huai River, China

Neonicotinoids (NEOs) are the most widely used insecticides in the world. Nevertheless, the occurrence and distribution of NEOs in agricultural areas are not well understood. This study investigated the concentration, sources, ecological risks, and health risks of eight NEOs in the water of the Huai River, which flows through a typical agricultural area in China. The total concentration of NEOs in the river water ranged from 1.02 to 191.2 ng L-1, with an average of 64.1 ng L-1. Thiamethoxam was the dominant compound, with an average relative contribution of 42.5%. The average concentration of the total NEOs in downstream was significantly higher than that in upstream (p < 0.05). This may be related to the intensity of agricultural activities. The riverine NEO fluxes increased by approximately 12 times from the upper site to the lower site. More than 1.3 tons of NEOs in 2022 were transferred into Lake Hongze, the largest regulative lake on the Eastern Route of the South-to-North Water Diversion Project. Nonpoint sources were the major contributor to the total NEO inputs, and water use was the main output pathway. The risk assessment indicated that the individual NEOs in the river water presented low ecological risks. The NEO mixtures would produce chronic risks to aquatic invertebrates in 50% of the sampling sites, which were mostly distributed in downstream. Thus, more attention should be given to the downstream. Based on the Monte Carlo simulation, the health risks of NEOs via water consumption were estimated. The maximum chronic daily intakes were 8.4 × 10-4, 2.25 × 10-4, 1.27 × 10-4, 1.88 × 10-4 mg kg-1 day-1 for boys, girls, men, and women, respectively, which were approximately 2 orders of magnitude lower than the acceptable daily intake. Therefore, river water consumption would not be a concern for the public health.

Aquatic-terrestrial transfer of neonicotinoid insecticides in riparian food webs

Current-use pesticides are ubiquitous in freshwaters globally, often at very low concentrations. Emerging aquatic insects can accumulate pesticides during their aquatic development, which can be retained through their metamorphosis into terrestrial adults. Emerging insects thus provide a potential, yet largely understudied linkage for exposure of terrestrial insectivores to waterborne pesticides. We measured 82 low to moderately lipophilic organic pesticides (logK_ow: -2.87 to 6.9) in the aquatic environment, emerging insects and web-building riparian spiders from stream sites impacted by agricultural land use. Insecticides, mainly neuro-active neonicotinoids were ubiquitous and had the highest concentrations in emerging insects and spiders (∑ insecticides: 0.1-33 and 1-240 ng/g, respectively), although their concentrations in water were low, even when compared to global levels. Furthermore, neonicotinoids, although not considered to be bioaccumulative, were biomagnified in riparian spiders. In contrast, concentrations of fungicides and most herbicides decreased from the aquatic environment to the spiders. Our results provide evidence for the transfer and accumulation of neonicotinoids across the aquatic-terrestrial ecosystem boundary. This could threaten food webs in ecologically sensitive riparian areas worldwide.

Potential to reduce pesticides in intensive apple production through management practices could be challenged by climatic extremes

Apples are the third most produced fruit in the world, but their production is often pesticide-intensive. Our objective was to identify options for pesticide reduction using farmer records from 2549 commercial apple fields in Austria during five years between 2010 and 2016. Using generalized additive mixed modeling, we examined how pesticide use was related to farm management, apple varieties, and meteorological parameters, and how it affected yields and toxicity to honeybees. Apple fields received 29.5 ± 8.6 (mean ± SD) pesticide applications per season at a rate of 56.7 ± 22.7 kg ha^-1, which included a total of 228 pesticide products with 80 active ingredients. Over the years, fungicides accounted for 71 % of the pesticide amounts applied, insecticides for 15 %, and herbicides for 8 %. The most frequently used fungicides were sulfur (52 %), followed by captan (16 %) and dithianon (11 %). Of insecticides, paraffin oil (75 %) and chlorpyrifos/chlorpyrifos-methyl (6 % combined) were most frequently used. Among herbicides, glyphosate (54 %), CPA (20 %) and pendimethalin (12 %) were most often used. Pesticide use increased with increasing frequency of tillage and fertilization, increasing field size, increasing spring temperatures, and drier summer conditions. Pesticide use decreased with increasing number of summer days with maximum temperatures >30 °C and number of warm, humid days. Apple yields were significantly positively related to the number of heat days, warm humid nights, and pesticide treatment frequency, but were not affected by frequency of fertilization and tillage. Honeybee toxicity was not related to insecticide use. Pesticide use and yield were significantly related to apple varieties. Our analysis shows that pesticide use in the apple farms studied can be reduced by less fertilization and tillage, partly because yields were >50 % higher than the European average. However, weather extremes related to climate change, such as drier summers, could challenge plans to reduce pesticide use.