Relative chronic sensitivity of neonicotinoid insecticides to Ceriodaphnia dubia and Daphnia magna

Assessment of toxic effects of imidacloprid on freshwater zooplankton: An experimental test for 27 species

The neonicotinoid pesticide imidacloprid has been used worldwide since 1992. As one of the most important chemicals used in pest control, there have been concerns that its run-off into rivers and lakes could adversely affect aquatic ecosystems, where zooplankton play a central role in the energy flow from primary to higher trophic levels. However, studies assessing the effects of pesticides at the species level have relied on a Daphnia-centric approach, and no studies have been conducted using species-level assessments on a broad range of zooplankton taxa. In the present study, we therefore investigated the acute toxicity of imidacloprid on 27 freshwater crustacean zooplankton (18 cladocerans, 3 calanoid copepods and 6 cyclopoid copepods). The experiment showed that a majority of calanoid copepods and cladocerans were not affected at all by imidacloprid, with the exception of one species each of Ceriodaphnia and Diaphasoma, while all six cyclopoid copepods showed high mortality rates, even at concentrations of imidacloprid typically found in nature. In addition, we found a remarkable intra-taxonomic variation in susceptibility to this chemical. As many cyclopoid copepods are omnivorous, they act as predators as well as competitors with other zooplankton. Accordingly, their susceptibility to imidacloprid is likely to cause different responses at the community level through changes in predation pressure as well as changes in competitive interactions. The present results demonstrate the need for species-level assessments of various zooplankton taxa to understand the complex responses of aquatic communities to pesticide disturbance.

Temperature related toxicity features of acute acetamiprid and thiacloprid exposure in Daphnia magna and implications on reproductive performance

This study investigated the potential for elevated temperature to alter the toxicity of acetamiprid (ACE) and thiacloprid (Thia) in the ecotoxicity model Daphnia magna. The modulation of CYP450 monooxygenases (ECOD), ABC transporter activity (MXR) and incident cellular reactive oxygen species (ROS) overproduction was screened in premature daphnids following acute (48 h) exposure to sublethal concentrations of ACE and Thia (0.1-, 1.0 μM) at standard 21 °C and elevated 26 °C temperatures. Delayed outcomes of acute exposures were further evaluated based on the reproduction performance of daphnids monitored over 14 days of recovery. Exposures to ACE and Thia at 21^o C elicited moderate induction of ECOD activity, pronounced inhibition of MXR activity and severe ROS overproduction in daphnids. In the high thermal regime, treatments resulted in significantly lower induction of ECOD activity and inhibition of MXR activity, suggesting a suppressed metabolism of neonicotinoids and less impaired membrane transport activity in daphnids. Elevated temperature on its own, caused a three-fold rise in ROS levels in control daphnids, while ROS overproduction upon neonicotinoid exposure was less accentuated. Acute exposures to ACE and Thia caused significant decreases also in the reproduction of daphnids, indicating delayed outcomes even at environmentally relevant concentrations. Both the cellular alterations in exposed daphnids and decreases in their reproductive output post exposures evidenced closely similar toxicity patterns and potentials for the two neonicotinoids. While elevated temperature elicited only a shift in baseline cellular alterations evoked by neonicotinoids, it significantly worsened the reproductive performance of daphnids following neonicotinoid exposures.

Chronic toxicity of three formulations of neonicotinoid insecticides and their mixture on two daphniid species: Daphnia magna and Ceriodaphnia dubia

Neonicotinoid insecticides represent nearly a quarter of the global insecticide market and are widely used in agriculture but also for lawn, garden care, and pest control. They are highly water-soluble, persistent in soil, may enter the aquatic compartment via spray drift, runoff, or leaching, and contribute to downstream aquatic toxicity. Although insects appear to be the most sensitive group to neonicotinoids, other groups, such as crustaceans, may also be affected. Furthermore, most studies focus on single-insecticide exposure and very little is known concerning the impact of neonicotinoid mixtures on aquatic invertebrates. The present study was designed to test potential toxicological effects of an environmentally relevant mixture of imidacloprid, clothianidin, and thiamethoxam on populations of Ceriodaphnia dubia and Daphnia magna under controlled conditions. Chronic toxicity tests were conducted in the laboratory, and survival and reproduction were measured for both species under environmentally relevant, 'worst-case' concentrations for each compound separately and in combination as pesticides are often detected as mixtures in aquatic environments. The neonicotinoids did not appear to affect the survival of C. dubia and D. magna. Reproduction of C. dubia was affected by the mixture whereas all three individual insecticides as well as the mixture caused a significant reduction in the reproduction of D. magna. Our results highlight the complexity of pesticide toxicity and show that traditional toxicological approaches such as, acute mortality studies and tests with single compounds can underestimate negative impacts that occur in the environment.

Imidacloprid: Comparative toxicity, DNA damage, ROS production and risk assessment for aquatic non-target organisms

Imidacloprid is a neonicotinoid systemic insecticide used worldwide. Despite its hazardous impact on non-target organisms, few studies have been conducted concerning the potential eco-genotoxic effects in invertebrates of surface waters where this pesticide is detected from units of ng/L to tens of μg/L. The aim of the present work was to determine the acute, the sub-chronic and the chronic toxicity of imidacloprid in producers and primary consumers of the freshwater trophic chain. The organisms under investigation were the green alga Raphidocelis subcapitata, the rotifer Brachionus calyciflorus, the cladoceran crustacean Ceriodaphnia dubia and the benthic ostracod Heterocypris incongruens. In addition, potential DNA damage and ROS production were evaluated in C. dubia. Furthermore, in accordance with European guidelines, toxicological risk assessment of imidacloprid was performed for all continents considering its global occurrence in surface waters. In addition, we assessed the genotoxicological risk and median inhibition of reproduction was observed at units of mg/L for rotifers and daphnids. Algae showed the lowest level of sensitivity to the pesticide with effective concentrations from units to hundreds of mg/L. DNA lesions were marked from 7 μg/L with a significant increase in damage as concentrations increased. Chronic toxicity risk quotient values were generally below to a threshold value of 1, with no consequential environmental concern other than for the Canadian areas. On the contrary, the genotoxicological risk quotient values were found higher than the threshold value in all continents.

Behavioral and biochemical alterations induced by acute clothianidin and imidacloprid exposure in the killer shrimp, Dikerogammarus villosus

Neonicotinoids are widely used insecticides around the world and are preserved permanently in soils and appear in surface waters posing an increased threat to ecosystems. In the present study, we exposed adult specimens of amphipod Dikerogammarus villosus to environmentally relevant and higher concentrations of two widely used agricultural neonicotinoids, clothianidin (CLO) and imidacloprid (IMI), for 2 days. The acute effects were investigated at the behavioral (immobility time and swimming activity) and biochemical (glutathione S-transferase [GST] and acetylcholine esterase [AchE] activity) levels. All CLO concentrations used (64 nM, 128 nM, 192 nM) significantly decreased the immobility time and swimming activity. In the case of IMI, the immobility time decreased significantly only at the highest concentration applied (977 nM), but the distance travelled by the animals significantly decreased even at lower concentrations (78 nM and 313 nM). The GST enzyme activity did not change in the CLO-treated groups, however, the 626 nM and 977 nM IMI concentrations significantly increased the GST activity. Similarly, to the behavioral level, all CLO concentrations significantly decreased the AchE activity. In contrast, IMI has a significant stimulating effect on the AchE activity at the 313 nM, 626 nM, and 977 nM concentrations. Based on the authors' best knowledge, this is the first study to investigate the effects of CLO and IMI at environmentally-relevant concentrations on D. villosus. Our findings contribute to the understanding of the physiological effects of neonicotinoids.

Long-term effects of neonicotinoids on reproduction and offspring development in the copepod Acartia tonsa

Neonicotinoids (NEOs) are neurotoxic pesticides acting as nicotinic acetylcholine receptor agonists. NEOs' efficacy against pest insects has favoured their spreading use in agriculture, but their proven effectiveness against non-target insects in terrestrial and aquatic ecosystems also raised concern over their environmental impact. Crustaceans were often studied for the impacts of NEOs due to their economic values and nervous' system similarity with insects. However, most studies on crustaceans focused on acute effects or exposure of early-life stages, while long-term effects were seldom explored. The present study aimed to assess the potential long-term effects of four commercially available NEOs on the reproduction and offspring of the calanoid copepod Acartia tonsa, a key species in the food webs of several coastal and estuarine environments. NEOs were confirmed as potent interferents of copepod reproduction. The first-generation compound acetamiprid significantly inhibited egg production and hatching ratio at 10 ng L-1, while larval survival and development were affected at 81 ng L-1. Similarly, the first-generation compound thiacloprid significantly inhibited the hatching ratio and larval development at 9 ng L-1, while it did not affect egg production and larval survival. Second-generation compounds were less toxic than acetamiprid and thiacloprid: clothianidin affected significantly only larval development of the offspring at 62 ng L-1, while thiamethoxam was not toxic at both the tested concentrations (8 ng L-1 and 84 ng L-1). These data evidenced that effects on copepods may occur at concentrations below the chronic aquatic life benchmarks reported by USEPA for acetamiprid (2100 ng L-1) and thiacloprid (970 ng L-1), suggesting that long-term effects of NEOs have been underestimated. A comparison with environmental concentrations evidenced that NEO-mediated effects on copepods are more liable in coastal areas receiving discharge from wastewater treatment plants or diffuse inputs from agricultural land during pesticide application periods.

Ecological risk of imidacloprid on the Brazilian non-target freshwater organisms Chironomus sancticaroli and Poecilia reticulata

Imidacloprid (IMI) is a neonicotinoid insecticide widely used in agriculture worldwide. This pesticide has been found in freshwater ecosystems, including Brazilian freshwaters. For this reason, studies are being conducted to detect the presence of IMI in freshwater and understand its effects on the aquatic biota. In the present study, the acute toxic effect of the imidacloprid commercial formulation (ICF) Galeão^® on the Brazilian non-target aquatic organisms Chironomus sancticaroli and Poecilia reticulata was evaluated. Enzymatic activities (glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX)) were also determined. Moreover, we considered 11 studies that detected IMI concentrations up to 3.65 µg.L^-1 in 28 different Brazilian freshwaters to evaluate the acute ecological risk of IMI in these environments. From the ecotoxicological assays, we determined the LC₅₀ values for C. sancticaroli (LC_50-48 h 1.52 µg.L^-1) and P. reticulata (LC_50-96 h 122.65 mg.L^-1). The high sensitivity of C. sancticaroli demonstrates that this species could be used as a bioindicator in studies investigating the contamination of freshwater by IMI. Enzymatic activity changes were observed in both organisms and offered sublethal responses to the effects of the pollution by IMI on aquatic biota. Our results suggest that the presence of IMI in Brazilian aquatic ecosystems can represent a potential ecological risk for the aquatic insect populations and, consequently, cause an imbalance in these ecosystems. The present study provides relevant and comparable toxicity information that may be useful to develop public policies to protect the Brazilian aquatic ecosystem from IMI contamination.

Physiological and metabolic alterations induced by commercial neonicotinoid formulations in Daphnia magna

Neonicotinoid insecticides are widely used agents in agriculture to control a broad range of insect pests. Although use of neonicotinoid pesticides has resulted in the widespread contamination of surface waters, sublethal toxicity data of these products in relation to non-target aquatic biota are still poor. Therefore, the objective of this study was to assess the effects of two neonicotinoid pesticides with widespread use on the basic physiological functions: the thoracic limb activity and heart rate of Daphnia magna, and to screen for their potential to affect the cytochrome P450 monooxygenase system (ECOD activity) of daphnids. The considered pesticides were the acetamiprid- and thiacloprid based products Mospilan 20 SG and Calypso 480 SC, respectively. The dose-dependent variation in the three biological endpoints considered were assessed following 24 h exposures. The two neonicotinoid formulations elicited significant depression on the thoracic limb activity and heart rate of daphnids at doses close to the immobility thresholds of formulations (48h-EC₅₀: Mospilan 20 SG = 190 mg L^-1; Calypso 480 SC = 120 mg L^-1), an effect mainly attributable to the overall drop in the general health status of the organisms. The alterations in the physiological traits were significant at exposures to 190 mg L^-1 for Mospilan 20 SG and 48 mg L^-1 for Calypso 480 SC. The dose related variation in the ECOD activity of daphnids exposed to the selected neonicotinoid formulations followed a biphasic pattern, with starting effective doses for Mospilan 20 SG of 6.3 mg L^-1 (=1/20 of 48h-EC₅₀ for Daphnia neonates), and for Calypso 480 SC of 0.034 mg L^-1 (=1/4000 of 48h-EC₅₀). Maximal ECOD activity (2.2 fold increase vs. controls) was induced by Mospilan 20 SG in daphnids exposed to 114 mg L^-1 product (=48 h-EC₂₀), and by Calypso 480 SC (1.8 fold increase) at 5.2 mg L^-1 dose (=1/20 of 48 h-EC₅₀). Our results outlined significant alterations in the physiological traits and ECOD activity in exposed daphnids at concentrations below the immobility thresholds (48 h-EC₅₀) of the products used as benchmarks to rate their toxicity risks to aquatic biota. Therefore, we think our findings might deserve consideration in the environmental risk evaluation of these products.

Physiological Effects of Neonicotinoid Insecticides on Non-Target Aquatic Animals-An Updated Review

In this paper, we review the effects of large-scale neonicotinoid contaminations in the aquatic environment on non-target aquatic invertebrate and vertebrate species. These aquatic species are the fauna widely exposed to environmental changes and chemical accumulation in bodies of water. Neonicotinoids are insecticides that target the nicotinic type acetylcholine receptors (nAChRs) in the central nervous systems (CNS) and are considered selective neurotoxins for insects. However, studies on their physiologic impacts and interactions with non-target species are limited. In researches dedicated to exploring physiologic and toxic outcomes of neonicotinoids, studies relating to the effects on vertebrate species represent a minority case compared to invertebrate species. For aquatic species, the known effects of neonicotinoids are described in the level of organismal, behavioral, genetic and physiologic toxicities. Toxicological studies were reported based on the environment of bodies of water, temperature, salinity and several other factors. There exists a knowledge gap on the relationship between toxicity outcomes to regulatory risk valuation. It has been a general observation among studies that neonicotinoid insecticides demonstrate significant toxicity to an extensive variety of invertebrates. Comprehensive analysis of data points to a generalization that field-realistic and laboratory exposures could result in different or non-comparable results in some cases. Aquatic invertebrates perform important roles in balancing a healthy ecosystem, thus rapid screening strategies are necessary to verify physiologic and toxicological impacts. So far, much of the studies describing field tests on non-target species are inadequate and in many cases, obsolete. Considering the current literature, this review addresses important information gaps relating to the impacts of neonicotinoids on the environment and spring forward policies, avoiding adverse biological and ecological effects on a range of non-target aquatic species which might further impair the whole of the aquatic ecological web.

Development of an Alternative Test System for Chronic Testing of Lotic Macroinvertebrate Species: A Case Study with the Insecticide Imidacloprid

There are currently few suitable test systems for the chronic toxicity testing of aquatic macroinvertebrates under stream conditions. Therefore, a new test system mimicking running water conditions was developed for testing with lotic insects. This system uses small test cages, with 10 of these suspended inside each 25-L container and rotating at 0.1 m/s, to create a water flow for the individual organism inside each cage. To test the performance of the new exposure system, chronic effects (21 d) of the neonicotinoid imidacloprid were investigated with field-collected larvae of the stonefly Protonemura sp. Endpoints were survival, growth, and/or emergence (depending on the developmental stage of the larvae at the start of the exposure). Two experiments conducted 1 yr apart showed good reproducibility: growth 10% effect concentration (EC10) values were 15.3 and 18.5 μg/L and no-observed-effect concentration (NOEC) values were 30.3 and 21.5 μg/L. A third experiment, performed with further-developed larval instars, showed a significant effect of imidacloprid on emergence (with EC10 of 5.97 μg/L and NOEC of 2.89 μg/L) and a significant effect on survival (with median lethal concentration of 44.7 µg/L). The results of the present study show that the newly developed test system provides a suitable approach for toxicity testing with stonefly larvae and potentially for other lotic macroinvertebrate species. Environ Toxicol Chem 2021;40:2229-2239. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Pulsed exposure of the macrophyte Lemna minor to herbicides and the mayfly Neocloeon triangulifer to diamide insecticides

Pesticides applied to agricultural land can enter aquatic ecosystems through runoff or leaching during precipitation events. In a lotic system, these events result in a pulse of exposure to biota living in these systems. The concentration of pesticide increases, peaks, and then gradually declines, and this pulsed exposure may occur multiple times over the course of a growing season. The dynamic nature of exposure to pesticides in the environment is not often mimicked in the laboratory testing of the toxicity of pesticides. The present study investigated the potential latent effects of a 24-h pulsed exposure of metolachlor, metribuzin, MCPA (2-methyl-4-chlorophenoxyacetic acid), MCPP (methylchlorophenoxypropionic acid or mecoprop), dicamba, and 2,4-D to the aquatic macrophyte Lemna minor followed by a 5-day recovery period. The relative sensitivity of L. minor to the herbicides were, in this decreasing order: metolachlor > metribuzin >2,4-D > MCPA > MCPP > dicamba. This study also investigated the effects of short-term exposures of the diamide insecticides cyantraniliprole and chlorantraniliprole on the survival of the larvae of the parthenogenetic mayfly Neocloeon triangulifer. The median lethal concentrations (96-h LC50s) for cyantraniliprole and chlorantraniliprole were 8.60 and 2.92 μg/L, respectively.

Joint toxicity of imidacloprid and azoxystrobin to Chironomus dilutus at organism, cell, and gene levels

Pesticides occur in the environment as mixtures, yet the joint toxicity of pesticide mixtures remains largely under-explored and is usually overlooked in ecological risk assessment. In the current study, joint toxicity of a neonicotinoid insecticide (imidacloprid, IMI) and a strobilurin fungicide (azoxystrobin, AZO) was investigated with Chironomus dilutus over a wide range of concentrations and at different effect levels (organism, cell, and gene levels). The two pesticides, both individually and in combination, were found to induce oxidative stress and cause lethality in C. dilutus. Median lethal concentrations for IMI and AZO were 3.98 ± 1.17 and 52.9 ± 1.1 μg/L, respectively. Mixtures of the two pesticides presented synergetic effects at environmentally relevant concentrations whilst antagonistic effects at high concentrations, showing concentration-dependent joint toxicity. Investigation on the expressions of 12 genes (cyt b, coi, cox1, cyp4, cyp12m1, cyp9au1, cyp6fv1, cyp315, gst, Zn/Cu-sod, Mn-sod, and cat) revealed that the two pesticides impaired mitochondrial respiration, detoxification, and antioxidant system of C. dilutus, and the joint effects of the two pesticides were likely due to an interplay between their respective influences on these physiological processes. Collectively, the synergistic effects of the two pesticides at environmentally relevant concentrations highlight the importance to incorporate combined toxicity studies into ecological risk assessment of pesticides.

Responses of Aquatic Nontarget Organisms in Experiments Simulating a Scenario of Contamination by Imidacloprid in a Freshwater Environment

Several studies have indicated the presence of the neonicotinoid insecticide imidacloprid (IMI) in aquatic ecosystems in concentrations up to 320.0 µg L^-1. In the present study, we evaluated the effects of the highest IMI concentration detected in surface water (320.0 µg L^-1) on the survival of Chironomus sancticaroli, Daphnia similis, and Danio rerio in three different scenarios of water contamination. The enzymatic activities of glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX) in D. rerio also were determined. For this evaluation, we have simulated a lotic environment using an indoor system of artificial channels developed for the present study. In this system, three scenarios of contamination by IMI (320.0 µg L^-1) were reproduced: one using reconstituted water (RW) and the other two using water samples collected in unpolluted (UW) and polluted (DW) areas of a river. The results indicated that the tested concentration was not able to cause mortality in D. similis and D. rerio in any proposed treatment (RW, UW, and DW). However, C. sancticaroli showed 100% of mortality in the presence of IMI in the three proposed treatments, demonstrating its potential to impact the community of aquatic nontarget insects negatively. Low IMI concentrations did not offer risks to D. rerio survival. However, we observed alterations in GST, CAT, and APX activities in treatments that used IMI and water with no evidence of pollution (i.e., RW and UW). These last results demonstrated that fish are more susceptible to the effects of IMI in unpolluted environments.

Toxicogenomics provides insights to toxicity pathways of neonicotinoids to aquatic insect, Chironomus dilutus

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01-0.08) (mean (95% confidence interval) and 0.05 (0.04-0.06) μg L^-1, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23-0.79) μg L^-1; 10% burrowing behavior concentration: 0.30 (0.22-0.43) μg L^-1). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms' nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms.

Acute Effects of Binary Mixtures of Imidacloprid and Tebuconazole on 4 Freshwater Invertebrates

Receiving waters from agricultural areas can contain multiple pesticides such as the neonicotinoid imidacloprid and the fungicide tebuconazole, leading to the potential for aquatic life to be exposed to such mixtures. In the present study, the effects of tebuconazole were tested alone and in binary mixtures with imidacloprid on 4 aquatic invertebrates: Chironomus dilutus, Hyalella azteca, Lumbriculus variegatus, and Neocloeon triangulifer. Acute (96-h) median lethal concentrations (LC50s) were derived for individual compounds and used to design a binary mixture study to determine cumulative effects. The LC50s showed that imidacloprid was more potent than tebuconazole by 1 to 3 orders of magnitude for the 4 species. Lethality data from mixture experiments were analyzed using MIXTOX to determine deviations from independent action, followed by the model deviation ratio (MDR) technique to determine the biological significance and reproducibility of observed mixture effects. MIXTOX showed that the cumulative toxicities of imidacloprid-tebuconazole differed between the species: for C. dilutus there was no deviation from independent action; however, for H. azteca the mixture was antagonistic (specifically dose ratio-dependent), and for N. triangulifer it was synergistic. The MDR method showed that only observations with H. azteca significantly deviated from independent action. Because of the lack of evidence of a clear deviation from independent action and the much greater potency of imidacloprid, the weight of evidence indicates that the presence of tebuconazole is unlikely to appreciably increase the hazard from imidacloprid exposure to aquatic invertebrates. Environ Toxicol Chem 2019;00:1-17. © 2019 SETAC.