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

Biochemical and Behavioral Responses in the Killer Shrimp Dikerogammarus villosus Following Acute Exposure to Thiacloprid and Calypso®

Neonicotinoids are insecticides that are used globally and can persist in soil and surface water, posing a threat to ecosystems. In this study, we exposed the invasive freshwater amphipod Dikerogammarus villosus to environmentally relevant and relatively high concentrations of thiacloprid, a widely used agricultural neonicotinoid active ingredient and its commercial form Calypso® for two days. The acute effects were investigated at the behavioral (immobility time) and biochemical [glutathione S-transferase (GST) and acetylcholine esterase (AChE) activity] levels. Calypso® concentrations of 10 µg/l and 100 µg/l a significantly increased the immobility time, while thiacloprid exerted such an effect only at 100 µg/l. The GST enzyme activity did not change in the thiacloprid-treated groups; however, the 10 µg/l and 100 µg/l Calypso® concentrations significantly increased the GST activity. All Calypso® concentrations significantly decreased AChE activity until the highest Calypso® concentration was reached, and an interesting outcome was the 'U-shaped dynamics' of AChE activity. In contrast, thiacloprid had no significant blocking effect on AChE activity at any of the concentrations tested. Neonicotinoid insecticides are neurotoxins that selectively target nicotinic acetylcholine receptors in the insect central nervous system. However, their widespread use has a growing impact on nontarget animals. This study confirms the risk of neonicotinoids to aquatic invertebrates by providing evidence that neonicotinoids can also affect both behavioral and biochemical processes in D. villosus.

Neonicotinoid insecticide causes multigenerational impairment of inducible antipredator defenses in Daphnia

Nowadays organisms encounter not only natural challenges from predators but also significant anthropogenic stressors, such as insecticides, which can profoundly disrupt their normal growth and behavior. However, the knowledge on their potential interactions remains largely unknown, particularly regarding how insecticides may affect predator-prey interactions and prey responses across multiple generations. Here, we conducted a multigenerational experiment exposing two generations of Daphnia sinensis to predator kairomone from fish (Carassius auratus) and imidacloprid (a widely used neonicotinoid insecticide), both individually and in combination, followed by rearing two generations in a clean medium to examine effects on a series of traits including morphology, behavior, physiology, growth rate and reproduction. We found that fish kairomone and imidacloprid affected D. sinensis in different ways across generations, with effects remaining detectable even two generations after removing the threats. Combined stressors induced more pronounced adverse long-term effects than single stressors, affecting traits such as body size, thoracic limb movement, age at first reproduction and offspring number. Exposure to imidacloprid over generations led to a cumulative weakening of essential antipredator defenses, especially in the development of tail spine and reproductive traits, with more pronounced effects observed in the second exposure generation. Our findings highlight the complex interplay between natural and anthropogenic stressors and underscore the importance of considering multigenerational responses to fully understand their ecological impacts on aquatic ecosystems. Further research is essential to explore the underlying mechanisms driving these effects and to inform strategies for mitigating the ecological risks posed by continuous insecticide exposure.

Evaluating the impact of neonicotinoids on aquatic non-target species: A comprehensive review

Neonicotinoid insecticides (NNIs) are the fastest-growing class in agricultural protection. They target nicotinic acetylcholine receptors (nAChR) in pests, stimulating the nervous system at low doses and causing paralysis and death at higher concentrations. NNIs are used in crop protection, seed treatment, forestry, agriculture, and flea control in domestic cattle. Effective at lower concentrations and offering long-term control, NNIs are favoured for their systemic activity. However, due to their water solubility, mobility, and moderate persistence, NNIs easily contaminate adjacent aquatic environments via runoff, leaching, or spray drift. While less toxic to vertebrates, their widespread use poses threats to aquatic and terrestrial organisms, causing neurotoxicity, nephrotoxicity, cytotoxicity, genotoxicity, immunotoxicity, hepatotoxicity, endocrine disruption, and reproductive malformations. This review synthesizes research to address knowledge gaps on the environmental impact of NNIs and proposes policies to mitigate their harmful effects on aquatic non-target species.

β-ionone inhibits the grazing of Daphnia sinensis by reducing the activity of acetylcholinesterase

β-ionone is a volatile metabolite of Microcystis aeruginosa that is toxic to aquatic organisms. Using Daphnia sinensis as model, our present study found that β-ionone could significantly reduce heart rate and feeding rate, and induce intestinal emptying. Transcriptomic analysis showed that β-ionone could significantly inhibit the expression of acetylcholinesterase (AchE) mRNA, while metabolomics further revealed that β-ionone could significantly increase the level of acetylcholine (Ach) in D. sinensis. These results indicated that β-ionone might act as an AchE inhibitor, resulting in an increase in Ach levels. To test this hypothesis, both in vivo and in vitro experiments demonstrated that β-ionone could significantly reduce AchE activity. Furthermore, the inhibitory effects of β-ionone on heart rate and feeding rate could be blocked by the M-type Ach receptor (mAchR) blocker. These findings confirm that β-ionone is a novel AchE inhibitor. β-ionone could inhibit the activity of AchE, which in turn resulted in an increase of Ach in D. sinensis. Consequently, elevated levels of Ach could suppress the heart rate and feeding rate of D. sinensis by activating the mAchR, while concurrently accelerating the rate of intestinal emptying by stimulating intestinal peristalsis, thereby obstructing the digestion of algae within the intestinal tract.

Optimization of assay conditions to quantify ECOD activity in vivo in individual Daphnia magna. Assay performance evaluation with model CYP 450 inducers/inhibitors

Screening the activity of the cytochrome P450 (CYP450) mixed function oxidase system in aquatic invertebrates received seldom applications in ecotoxicology due to low baseline enzymatic activities characteristic for these organisms. In this study, an existing in vivo spectrofluorometric assay method based on quantifying the cytochrome P450 mediated conversion of 7-ethocycoumarin (EtC) used as substrate to the product 7-hydroxycoumarin (HCm) called: ethoxycoumarin-O-deethylase (ECOD) activity, initially applicable on pooled samples of Daphnia magna, was optimized for use on individual organisms. Optimal assay conditions have been established for as small as 3- and 6 days old individuals, and the limits of spectrofluorometric detection of HCm excreted by daphnids in the incubation media were defined. The modified assay was tested by screening the modulation of ECOD activity in daphnids following 24 h exposure to β-naphthoflavone (β-NF, reference CYP450 inducer) and to prochloraz (PCZ), a potent CYP450 inhibitor. Maximal ECOD activity levels in daphnids were recorded following 2 hours of incubation to 200 nM EtC. The limit of spectrofluorometric detection of HCm in the incubation media was 6.25 nM, achieved by more than 80% of three days old daphnids and all six days old individuals. Exposure of daphnids to β-NF demonstrated a bell-shaped ECOD activity induction potential, while PCZ elicited partial (60%) inhibition of ECOD activity. This optimized in vivo ECOD activity assay may serve as a cost-effective tool to study the responsiveness of Phase-I metabolism in D. magna to toxic pressure and its applicability to other aquatic invertebrates is also worth for consideration.

Acute and chronic effects of triclosan on the behavior, physiology, and multigenerational characteristics of the water flea Moina macrocopa

Triclosan, a chlorinated biphenyl ether is widely used in industrial products and cosmetics due to its antibiotic activity. Although relatively levels of triclosan have been detected in aquatic ecosystems, limited information is available regarding the acute and chronic impacts of triclosan on aquatic invertebrates, especially planktonic crustaceans. In this study, we analyzed the acute (24 h) and chronic (14 days exposure across three generations) effects of different concentrations of triclosan [1/10 of the no observed effect concentration (NOEC), the NOEC, and 1/10 of the LC50] calculated from the 24 h acute toxicity value, on the water flea Moina macrocopa. In the acute exposure experiment, the 1/10 LC50 value of triclosan significantly reduced survival, feeding rate, thoracic limb activity, heart activity, and acetylcholinesterase activity. In response to the 1/10 LC50 value, intracellular reactive oxygen species increased along with elevated levels of malondialdehyde and glutathione. Enzymatic activities of catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase were significantly increased by the 1/10 LC50 value, suggesting active protection of the antioxidant defense system against oxidative stress. Chronic exposure to the 1/10 NOEC and NOEC values revealed multigenerational adverse impacts of triclosan. The second generation was found to be the most sensitive to triclosan, as the NOEC value significantly reduced the survival rate, body length, and the number of neonates per brood, along with a delayed hatching period. Taken together, these results indicate that even sublethal levels of triclosan can have detrimental effects on the water flea population's maintenance through intergenerational toxicity.

Toxic Effects of Methylene Blue on the Growth, Reproduction and Physiology of Daphnia magna

Methylene blue (MB) is a disinfectant used in aquaculture to prevent and treat fish diseases. However, the release of MB can pose a risk to the receiving water bodies. Zooplankton are the most sensitive organisms among aquatic life. Hence, this study examined the acute and chronic toxic effects of MB on zooplankton using Daphnia magna (D. magna) as a test organism to provide basic data for risk assessment. The results show that 48 h-EC₅₀ and 24 h-LC₅₀ were 61.5 ± 2.3 and 149.0 ± 2.2 μg/L, respectively. Chronic exposure to MB affected the heart rate, beat frequency of the thoracic limbs, and reproductive ability of D. magna at environmental concentrations higher than 4.7 μg/L. The cumulative molts, time to production of the first brood, and total number of living offspring were affected at different MB concentrations, while "abortions" were observed in high-exposure groups. The activity of superoxide dismutase was increased, while glutathione S-transferase activity was stimulated at low concentrations and inhibited at high concentrations. In addition, the malondialdehyde content increased with increasing concentrations of MB. Our findings demonstrate the impact of MB on the reproduction and growth of freshwater species, as well as their physiological responses. These results have implications for establishing guidelines on the use of MB in aquaculture and setting discharge standards.

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.

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.