Dynamics of uptake and elimination of pyrethroid insecticides in zebrafish (Danio rerio) eleutheroembryos

Uptake/depuration kinetics, bioaccumulation potential and metabolic transformation of a complex pharmaceutical mixture in zebrafish (Danio rerio)

Uptake and elimination kinetics, bioconcentration factors (BCFs), and metabolic transformation of 20 different pharmaceutically active compounds (PhACs), covering a wide range of therapeutic categories and physico-chemical properties, were studied using zebrafish (Danio rerio). The fish were exposed to the mixture of the selected PhACs at environmentally relevant concentrations similar to 10 µg L-1. The experiments were performed in semi-static conditions and comprised a 7-day uptake period followed by a 7-day depuration period. Most of the PhACs reached a concentration plateau within the 7-day uptake-phase which was followed by an efficient depuration, with the observed uptake (ku) and depuration rate constants (kd,) ranging between 0.002 and 3.752 L kg-1 h-1, and 0.010 to 0.217 h-1, respectively. The investigated PhACs showed low to moderate BCFs. The highest BCFs of 47.8, 28.6 and 47.6 L kg-1 were determined for sertraline, diazepam and desloratadine, respectively. A high contribution of metabolic products to the total internal concentration was observed for some PhACs such as codeine (69%), sulfamethoxazole (51%) and verapamil (87%), which has to be taken into account when assessing the bioconcentration potential. Moreover, most of the metabolites exhibited significantly longer half-lives in zebrafish than their parent compounds and affected the overall depuration kinetics.

Size-dependent Effect on Foliar Utilization and Biocontrol Efficacy of Emamectin Benzoate Delivery Systems

The development of nanopesticides provides new avenues for pesticide reduction and efficiency improvement. However, the size effect of nanopesticides remains unclear, and its underlying mechanisms of influence have become a major obstacle in the design and application of pesticide nanoformulations. In this research, the noncarrier-coated emamectin benzoate (EB) solid dispersions (Micro-EB and Nano-EB) were produced under a constant surfactant-to-active ingredient ratio by a self-emulsifying-carrier solidification technique. The particle size of Micro-EB was 162 times that of spherical Nano-EB. The small size and large specific surface area of Nano-EB facilitated the adsorption of surfactants on the surface of the particles, thereby improving its dispersibility, suspensibility, and stability. The pinning effect of nanoparticles significantly suppressed droplet retraction and rebounding. Moreover, Nano-EB exhibited a 25% higher retention of the active ingredient on cabbage leaves and a 70% higher washing resistance than Micro-EB, and both were significantly different. The improvement of abilities in wetting, spreading, and retention of Nano-EB on crop leaves contributed to the increase in foliar utilization, which further resulted in a 1.6-fold enhancement of bioactivity against target Spodoptera exigua compared to Micro-EB. Especially, Nano-EB did not exacerbate the safety risk to the nontarget organism zebrafish with no significant difference. This study elaborates the size effect on the effectiveness and safety of pesticide formulations and lays a theoretical foundation for the development and rational utilization of efficient and environmentally friendly nanopesticides.

Occurrence, distribution, and health risk assessment of pyrethroid and neonicotinoid insecticides in aquatic products of China

Synthetic pyrethroid insecticides (SPIs) and neonicotinoid insecticides (NEOs), now dominant in the insecticide market, are increasingly found in aquatic environments. This study focused on six SPIs and five NEOs in aquatic products from four Chinese provinces (Shandong, Hubei, Shanxi and Zhejiang) and the risk assessment of the safety for the residents was conducted. It revealed significantly higher residues of Σ6SPIs (6.27-117.19 μg/kg) compared to Σ5NEOs (0.30-14.05 μg/kg), with SPIs more prevalent in fish and NEOs in shellfish. Carnivorous fish showed higher pesticide levels. Residues of these two types of pesticides were higher in carnivorous fish than in fish with other feeding habits. In the four regions investigated, the hazard quotient and hazard index of SPIs and NEOs were all <1, indicating no immediate health risk to human from single and compound contamination of the two types of pesticides in aquatic products. The present study provides valuable information for aquaculture management, pollution control and safeguarding human health.

Dose-dependent stress response of esfenvalerate insecticide on common carp (Cyprinus carpio): Evaluating blood parameters and gene expression

Esfenvalerate is a pyrethroid insecticide used primarily in the agriculture sector for insect management. Esfenvalerate is effective against a wide range of harmful insects, including flies, cockroaches, locusts, and many other types of bugs. It is also known that esfenvalerate has toxic effects on aquatic organisms and poses significant environmental concerns. In this study, the aim is to subchronically examine the effects of sublethal concentrations of esfenvalerate insecticide on common carp (Cyprinus carpio) by assessing changes in blood parameters and resulting gene expression. For this purpose, common carp (Cyprinus carpio) were divided into 5 groups and exposed to 0.025, 0.05, 0.1, and 0.15 μg/L concentrations of esfenvalerate for a period of 14 days. Blood and liver tissue samples were collected from the fish that underwent weight and length measurements. The effects on gene expression levels of immune, antioxidant, and stress-related genes in the liver tissue, including SOD, GST, Cortisol receptor, HSP70, H+-ATPase, Na+/K+-ATPase, Catalase, and GpX, were evaluated, as were the hematological and serum biochemical parameters. Significant decreases were observed in the levels of hematocrit, hemoglobin, erythrocytes, triglycerides and total protein and catalase, H+-ATPase, and GpX gene expression. Glucose, cholesterol, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase (LDH) and alkaline phosphatase (ALP), SOD, Cortisol receptor, Na+/K+-ATPase gene expression levels increased. As a result, it has been revealed that esfenvalerate insecticide causes oxidative stress in carp at all dose ranges.

Kinetics of uptake and depuration of synthetic pyrethroid insecticides in manila clam (Ruditapes philippinarum)

Synthetic pyrethroid insecticides (SPIs) are frequently detected in water bodies and sediments, and they show high toxicity to aquatic organisms, but their toxicity kinetics remain unknown. In this work, the kinetics of uptake and depuration of three SPIs, fenpropathrin (FP), cypermethrin (CM) and deltamethrin (DM) were evaluated in manila clams (Ruditapes philippinarum) for the first time through a bioconcentration-semi-static test. Clams were exposed to three SPIs of different concentrations (2 ng/mL and 20 ng/mL) for 4 days, followed by a 10-day depuration stage. The results indicated that adult manila clams could absorb SPIs rapidly, and the bioconcentration factor (BCF) values of SPIs were different at high and low concentrations of contaminants. The depuration rate constants (k₂) of SPIs in adult manila clams ranged from 0.024 h^-1 to 0.037 h^-1. The bioaccumulation factors ranged from 319.41 to 574.38. And the half-lives (t_1/2) were in the range of 18.49 to 29.22 h. These results showed that manila clams have a high bioconcentration capacity, and SPIs have a high cumulative risk for bivalves. Moreover, after 10 days of elimination, SPIs can still be detected in manila clams at all concentrations, indicating that the complete elimination of SPIs required a longer time.

The acute toxicity, mechanism, bioconcentration and elimination of fluxametamide on zebrafish (Danio rerio)

Fluxametamide is a completely novel and the first isoxazoline insecticide used to control agricultural pests and has high insecticidal properties. To expand its usage in the paddy field, its potential toxicological effects on fish are necessary to make clear. In this study, the acute toxicity, bioconcentration and elimination of fluxametamide to zebrafish Danio rerio, and the action mode of it on the heteromeric Drα1β2Sγ2 and Drα1β2S GABA receptor was respectively determined by HPLC and two-electrode voltage clamp technique. Fluxametamide exhibited high toxicity to D. rerio, whereas slightly inhibited the GABA-stimulated current of Drα1β2Sγ2 or Drα1β2S. It showed high bioconcentration level in D. rerio at 0.0314 mg L^-1 and 0.157 mg L^-1, with bioconcentration factors at steady state of 1491.55 and 2875.28, respectively. The concentration of fluxametamide in D. rerio rapidly decreased from 47.84 ± 0.12 to 9.77 ± 1.13 mg kg^-1 in 0.0314 mg L^-1 or from 393.19 ± 0.46 to 46.93 ± 2.88 mg kg^-1 in 0.157 mg L^-1 within 10 days, and steadily kept at a low level after 18 days. In conclusion, fluxametamide has highly acute toxicity to D. rerio, and might induce high bioconcentration in a short time. As we know, this is the first report to provide a theoretical basis for evaluating the potential risk of fluxametamide on fish, and guidance for the application of fluxametamide.

The onset of active gill respiration in post-embryonic zebrafish (Danio rerio) larvae triggers an increased sensitivity to neurotoxic compounds

Originally designed as a general alternative to acute fish toxicity testing (AFT), the fish embryo toxicity test (FET) has become subject to concerns with respect to neurotoxic substances. Whereas oxygen uptake in the fish embryo primarily occurs via diffusion across the skin, juvenile and adult fish rely on active ventilation of the gills. As a consequence, substances including, e.g., neurotoxicants which prevent appropriate ventilation of gills ("respiratory failure syndrome") might lead to suffocation in juvenile and adult fish, but not in skin-breathing embryos. To investigate if this respiratory failure syndrome might play a role for the higher sensitivity of juvenile and adult fish to neurotoxicants, a modified acute toxicity test using post-embryonic, early gill-breathing life-stages of zebrafish was developed with chlorpyrifos, permethrin, lindane, aldicarb, ziram and aniline as test substances. Additionally, a comparative study into bioaccumulation of lipophilic substances with log_Kow > 3.5 and swimbladder deflation as potential side effects of the respiratory failure syndrome was performed with 4 d old skin-breathing and 12 d old gill-breathing zebrafish. With respect to acute toxicity, post-embryonic 12 d larvae proved to be more sensitive than both embryos (FET) and adult zebrafish (AFT) to all test substances except for permethrin. Accumulation of chlorpyrifos, lindane and permethrin was 1.3- to 5-fold higher in 4 d old than in 12 d old zebrafish, suggesting that (intermediate) storage of substances in the yolk might reduce bioavailability and prevent metabolization, which could be a further reason for lower toxicity in 4 d than in 12 d old zebrafish. Whereas ziram and aniline showed no significant effect on the swimbladder, zebrafish exposed to chlorpyrifos, lindane and permethrin showed significantly deflated swimbladders in 12 d old larvae; in the case of aldicarb, there was a significant hyperinflation in 4 d old larvae. Swimbladder deflation in post-embryonic 12 d zebrafish larvae might be hypothesized as a reason for a lack of internal oxygen supplies during the respiratory failure syndrome, whereas in 4 d old embryos cholinergic hyperinflation of the swimbladder dominates over other effects. Regarding acute lethality, the study provides further evidence that the switch from transcutaneous to branchial respiration in post-embryonic zebrafish life-stages might be the reason for the higher sensitivity of juvenile and adult fish to neurotoxic substances.

The toxicokinetics and risk assessment of pyrethroids pesticide in tilapia (Oreochromis mossambicus) upon short-term water exposure

Pyrethroids pesticides (PPs) are the widely adopted synthetic pesticides for agriculture and fishery. The frequent use of these pesticides leads to the accumulation of residues in the freshwater environments in China, subsequently affecting aquatic organisms and ecosystems. However, there are few reports on the toxicological and risk assessment of aquaculture aquatic products. In this study, the uptake, depuration kinetics and potential risk to human health and ecology of fenpropathrin, cypermethrin, fenvalerate, and deltamethrin were assessed using tilapia. The results indicated that four PPs were readily accumulated by tilapia. The bioconcentration factors (BCF) of the PPs in plasma and muscle were between 71.3 and 2112.1 L/kg and 23.9-295.3 L/kg, respectively. The half-lives (t_1/2) of muscle and plasma were 2.90-9.20 d and 2.57-8.15 d. The risks of PPs residues in the muscle of tilapia and exposed water were evaluated by hazard quotient (HQ) and risk quotient (RQ). Although PPs residues in tilapia had a low dietary risk to human health, the residues in the exposed water had a high ecological risk to fish, daphnia, and green algae. Therefore, assessing the PPs content in freshwater aquaculture and monitoring their dosages and frequencies are highly necessitated to avoid their adverse effect on the aquaculture environment.

Uptake, elimination, and toxicokinetics of selected pharmaceuticals in multiple tissues of Nile tilapia (Oreochromis niloticus) exposed to environmentally relevant concentrations

Pharmaceuticals in aquatic environment displayed adverse effects to fish. The effects are usually related to the internal levels of pharmaceuticals accumulated in specific fish tissues. In this study, we investigated the uptake, elimination, and toxicokinetics of six pharmaceuticals, e.g. naproxen (NAX), diclofenac (DCF), ibuprofen (IBU), carbamazepine (CBZ), fluoxetine (FLX), and sertraline (SER), in 11 fish tissues of Nile tilapia. The experiments were conducted in a flow-through system with an 8-day uptake/8-day elimination periods. The fish exposure groups involved the control, single FLX, and mixture of six pharmaceuticals at environmentally relevant concentration of 4 μg/L. FLX and SER showed the maximum concentrations of 145 and 201 ng/g wet weight, respectively, in fish spleen tissue, while NAX and IBU were not detected in any tissue. The mean concentrations for the pharmaceuticals in Nile tilapia tissues generally followed the order: bile> kidney, gut, stomach, liver> brain, gill, spleen> plasma, skin, muscle. The steady-state bioconcentration factors in various tissues generally range at 0.74-437.58 L/kg. The uptake and elimination toxicokinetics illustrated the rapid accumulation and depuration of pharmaceuticals in fish tissues. The results help to understand the internal bioconcentration, tissue distribution, and toxicokinetics of pharmaceuticals in multiple fish biological compartments.

Enantioselective accumulation, elimination and metabolism of fenbuconazole in lizards (Eremias argus)

The enantioselective accumulation, elimination and metabolism of fenbuconazole in lizards were determined following a single-dose (25 mg/kg^bw) exposure to racemic or enantiomeric fenbuconazole. Accumulation of fenbuconazole was found in lizard fat with rac-form > enantiopure enantiomers. The enantiomer fractions (EFs) were higher than 0.5 in the blood, while EFs were less than 0.5 in the liver, brain, skin and stomach. There was conversion from (+)-fenbuconazole to (-)-fenbuconazole in lizard liver and conversion from (-)-fenbuconazole to (+)-fenbuconazole in lizard liver and blood. The results showed that enantioselective accumulation appeared in lizards, but the direction varied among blood and different tissues. The elimination half-lives (t_1/2) of (+)-fenbuconazole were higher than those of (-)-fenbuconazole in the blood and liver, suggesting that (-)-fenbuconazole eliminated faster than (+)-fenbuconazole in these tissues. In addition, both (+)-fenbuconazole and (-)-fenbuconazole eliminated faster in the liver and stomach exposed to racemate than those exposed to enantiopure enantiomers. On the contrary, the form of racemate decreased the elimination rate of fenbuconazole in lizard fat. Synergistic elimination may occur when two enantiomers coexisted in lizard liver and stomach, while the racemate produced antagonistic elimination in lizard fat. Simultaneously, three metabolites, RH-6467, RH-9029&RH-9030 and keto-mchlorophenol, were discovered in lizard liver. Only two metabolites, RH-6467 and RH-9029&RH-9030, were found in lizard blood. RH-9029&RH-9030 were the major metabolites. The discovered enantiomers of (+)-fenbuconazole metabolites were different from those of (-)-fenbuconazole. The findings of this study may provide a better understanding of the enantioselective behaviors of chiral triazole fungicides in reptiles.

Ecotoxicity of pesticides and semiochemicals used for control and prevention of conifer bark beetle (Dendroctonus spp.) outbreaks

Application of pyrethroid pesticides and semiochemicals are two treatments used worldwide to control conifer bark beetles (Dendroctonus spp.); their residues can reach water reservoirs and water currents through run off and affect non-target organisms such as freshwater invertebrates. Therefore, we assessed the 48-h lethal toxicity, chronic toxicity (reproduction inhibition), and bioaccumulation of three pyrethroid pesticides (bifenthrin, cypermethrin, and deltamethrin) and two semiochemicals (verbenone and 3-methyl-2-cyclohexen-1-one) in two freshwater invertebrates: the cladoceran Alona guttata and the rotifer Lecane papuana. Bifenthrin was the most toxic of the five chemical compounds tested followed by deltamethrin and then cypermethrin, which was the least toxic pyrethroid for both species. Semiochemicals were far less toxic than pyrethroids and verbenone was most toxic than 3-methyl-2-cyclohexen-1-one for both species. For the rotifer Lecane papuana, the pyrethroid with the highest Bioconcentration Factor was bifenthrin, and for the semiochemicals it was 3-methyl-2-cyclohexen-1-one. For the cladoceran Alona guttata, the pyrethroid with the highest bioconcentration factor was cypermethrin and for the semiochemicals it was verbenone. The pyrethroid with highest body burdens both lethal and chronic was cypermethrin. Semiochemicals showed lethal and chronic body burdens 12-fold higher than pyrethroids and were therefore less toxic than pyrethroids. These results showed that the semiochemicals verbenone and 3-methyl-2-cyclohexen-1-one are a safe tool for the freshwater invertebrates tested when compared with pyrethroid pesticides. Cypermethrin was the least toxic of the pyrethroids tested and therefore could be considered as a good candidate to control outbreaks of the conifer bark beetle.

Multi- and transgenerational effects following early-life exposure of zebrafish to permethrin and coumarin 47: Impact on growth, fertility, behavior and lipid metabolism

Transgenerational effects induced by environmental stressors are a threat to ecosystems and human health. However, there is still limited observation and understanding of the potential of chemicals to influence life outcomes over several generations. In the present study, we investigated the effects of two environmental contaminants, coumarin 47 and permethrin, on exposed zebrafish (F0) and their progeny (F1-F3). Coumarin 47 is commonly found in personal care products and dyes, whereas permethrin is used as a domestic and agricultural pyrethroid insecticide/insect repellent. Zebrafish (F0) were exposed during early development until 28 days post-fertilization and their progeny (F1-F3) were bred unexposed. On one hand, the effects induced by coumarin 47 suggest no multigenerational toxicity. On the other hand, we found that behavior of zebrafish larvae was significantly affected by exposure to permethrin in F1 to F3 generations with some differences depending on the concentration. This suggests persistent alteration of the neural or neuromuscular function. In addition, lipidomic analyses showed that permethrin treatment was partially correlated with lysophosphatidylcholine levels in zebrafish, an important lipid for neurodevelopment. Overall, these results stress out one of the most widely used pyrethroids can trigger long-term, multi- and possibly transgenerational changes in the nervous system of zebrafish. These neurobehavioral changes echo the effects observed under direct exposure to high concentrations of permethrin and therefore call for more research on mechanisms underlying effect inheritance.

Bifenthrin exposure causes hyperactivity in early larval stages of an endangered fish species at concentrations that occur during their hatching season

Bifenthrin is a pyrethroid insecticide commonly used in agricultural and urban sectors, and is found in watersheds worldwide. As a sodium channel blocker, at sublethal concentrations it causes off-target effects, including disruption of calcium signaling and neuronal growth. At the whole organism level, sublethal concentrations of bifenthrin cause behavioral effects in fish species, raising concerns about the neurotoxic properties of the compound on fish populations. Here we describe the application of a high-throughput behavioral system to evaluate contaminant impacts on the sensitive early-life stages of Delta smelt (Hypomesus transpacificus), a critically endangered teleost species endemic to the San Francisco Bay Delta (SFBD), California, USA. Leveraging the natural behavior of early-larval Delta smelt, whereby they increase movement in bright light and decrease movement in the dark, we developed a test using a cycle of light and dark periods in a closed chamber to test hyper- or hypoactivity for this species. We show that early-larval Delta smelt have a significant preference to move toward light, and utilized the behavioral test to evaluate the impact of exposure to bifenthrin at concentrations found in habitats where Delta smelt reportedly spawn, ranging up to concentrations detected in tributaries to these habitats. All tested concentrations of bifenthrin (nominal 2, 10, or 100 ng/L) caused hyperactivity, over a 96 h exposure, with noted significance determined during the light period of the test. To further understand the impact of bifenthrin exposure, expression of a suite of genes relevant to neurodevelopment, the mechanistic target of rapamycin (mTOR) signaling pathway, and biotransformation in exposed larvae were also measured. Following exposure to picomolar concentrations of bifenthrin, expression of genes in the mTOR signaling and neurogenesis pathways were altered alongside behavior. This study demonstrates how light and dark cycle behavioral tests can be used to assess sensitive alterations in swimming activity in Delta smelt at early developmental stages and how gene expression can complement these assays. This approach can be used to assess the impact of multiple compounds that occur within the restricted habitat of Delta smelt, thus having the potential to greatly inform conservation management strategies for this critically sensitive life stage.

Yolk Sac of Zebrafish Embryos as Backpack for Chemicals?

The zebrafish embryo (Danio rerio) has developed into one of the most important nonsentient animal models for the hazard assessments of chemicals, but the processes governing its toxicokinetics (TK) are poorly understood. This study compares the uptake of seven test compounds into the embryonic body and the yolk sac of the zebrafish embryo using TK experiments, a dialysis approach, thermodynamic calculations, and kinetic modeling. Experimental data show that between 95% (4-iodophenol) and 67% (carbamazepine) of the total internal amount in 26 h post fertilization (hpf) embryos and between 80 and 49% in 74 hpf embryos were found in the yolk. Thus, internal concentrations determined for the whole embryo overestimate the internal concentration in the embryonic body: for the compounds of this study, up to a factor of 5. Partition coefficients for the embryonic body and a one-compartment model with diffusive exchange were calculated for the neutral test compounds and agreed reasonably with the experimental data. For prevalently ionic test compounds at exposure pH (bromoxynil, paroxetine), however, the extent and the speed of uptake were low and could not be modeled adequately. A better understanding of the TK of ionizable test compounds is essential to allow assessment of the validity of this organismic test system for ionic test compounds.

Acute embryonic exposure of zebrafish to permethrin induces behavioral changes related to anxiety and aggressiveness in adulthood

Permethrin (PM) is one of the most used synthetic pyrethroid worldwide. Exposure to this compound during pregnancy and early childhood has been indicated as a risk factor for neurodevelopmental disorders. We evaluated the long-term effects of embryonic PM exposure in different stages of zebrafish development. Briefly, embryos (3 hpf) were exposed to sub-lethal concentrations of PM (25 and 50 μg.L^-1) during 24 h and then behavioral parameters were evaluated during embryonic (28 hpf), eleutheroembryonic (3 dpf), larval (7 dpf), and adult stages (90 dpf). PM exposure decreased spontaneous movement at 28 hpf and decreased thigmotaxis in eleutheroembryos. The long-term effects of PM include changes in non-motor behaviors such as fear and anxiety in larva and adults. Adults embryonically exposed to PM also showed a significant increase in aggressiveness parameters. These results demonstrated that embryonic exposure to PM induces persistent neurotoxic effects in adulthood, which can impair the cognitive and behavioral fitness of non-target species contributing to a rise in neurodevelopmental disorders.

The synthetic pyrethroid deltamethrin impairs zebrafish (Danio rerio) swim bladder development

Deltamethrin (DM) is a widely used insecticide and reveals neural, cardiovascular and reproductive toxicity to various aquatic organisms. It has been known that DM negatively affects motion of zebrafish (Danio rerio). However, little is known in relation to the impacts of DM on development of swim bladder, which is a key organ for motion. In the present study, zebrafish embryos were exposed to 20 and 40 µg/L DM. The changes of swim bladder morphology were observed and transcription levels of key genes were compared between DM treatments and the control. The results showed that DM treatments significantly blocked the formation of progenitor and tissue layers in swim bladder of zebrafish embryos, leading to failed inflation of swim bladder. Compared with the control, the key genes (pbx1, foxA3, mnx1, has2, anxa5b, hprt1l and elovl1a) responsible for swim bladder development also showed decreased levels in response to DM treatments, suggesting that DM might specifically affect swim bladder development. Moreover, transcription levels of genes in the Wnt (wnt5b, tcf3a, wnt1, wnt9b, fzd1, fzd3 and fzd5) and Hedgehog (ihhb, ptc1 and ptc2) signaling pathways all decreased significantly in response to DM treatments, compared with the control. Considering the importance of Wnt and Hedgehog pathways in development of swim bladder, these results suggested that DM might affect swim bladder development through inhibiting the Wnt and Hedgehog pathways. Overall, the present study reported that swim bladder might be a potential target organ of DM toxicity in zebrafish, which contributed more information to the evaluation of DM's environmental risks.

One-step ionic liquid-based ultrasound-assisted dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography for the determination of pyrethroids in traditional Chinese medicine oral liquid preparations

In this study, a simple one-step ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction technique was coupled with high-performance liquid chromatography for the analysis of four pyrethroids in three kinds of traditional Chinese medicine oral liquid preparations: simotang oral liquid, kangbingdu oral liquid, and huaji oral liquid. The extraction parameters were examined to improve extraction efficiency. The optimum extraction conditions were 50 μL of 1-octyl-3-methylimidazolium hexafluorophosphate utilized as the extraction solvent and 800 μL of acetonitrile applied as the dispersive solvent. The extraction was assisted by ultrasonication for 8 min. The limits of detection for the four pyrethroids were within 0.007–0.024 mg L⁻¹, and the limits of quantitation ranged between 0.023 and 0.080 mg L⁻¹. The accuracy of the pyrethroid determination ranged from 80.1 to 106.4%. It was indicated that the proposed ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction method had an easy operation and was accurate and environmentally friendly. This approach has potential for the analysis of pyrethroids in traditional Chinese medicine oral liquid preparations.

Behavioral, molecular and physiological responses of embryo-larval zebrafish exposed to types I and II pyrethroids

Pyrethroids are potent neurotoxicants that may elicit multiple pathways of toxicity in non-target organisms. Comparative studies on the mechanistic and developmental effects of types I and II pyrethroids against non-target aquatic species are limited. This study assessed the effects of the two pyrethroid types against embryo-larval zebrafish (Danio rerio) at environmentally relevant and laboratory concentrations. Zebrafish embryos were exposed to type-I (permethrin, bifenthrin) and type-II (deltamethrin, λ-cyhalothrin, fenvalerate, esfenvalerate) pyrethroids at 1000, 10, 0.1, 0.01, 0.0 μg/L, starting at 5-h post-fertilization (hpf) through 5-d post-fertilization (dpf) under static exposure conditions. Swimming behavior (distance traveled and velocity) was assessed at 5-dpf. The relative expression of Nrf2a, GST, Casp-9 and p53 mRNA transcripts, carboxyl esterase (CES) activity and total reactive oxygen species (ROS) were measured. The stability of the pyrethroids across 5 days was analyzed. Bifenthrin-(10 μg/L) and esfenvalerate-(1000 μg/L) significantly (p < 0.05) reduced total distance traveled by larvae while 1000 μg/L deltamethrin and λ-cyhalothrin were lethal causing body axis curvature and pericardial edema. At environmentally relevant concentrations-(μg/L) compared to control, permethrin-(0.122) upregulated Nrf2a and Casp-9 expressions while λ-cyhalothrin-(0.053) downregulated Nrf2a and fenvalerate-0.037 downregulated GST. At laboratory concentrations-(μg/L), permethrin-(1000) upregulated Nrf2a, Casp-9 and p53 expressions, bifenthrin-(10) upregulated Casp-9 while fenvalerate-(0.1) and esfenvalerate-(1000) downregulated GST. There was concentration dependent increase in CES activity which correlated positively with total ROS. Pyrethroid concentrations decreased significantly by day 5. This study showed disparity in the mechanistic effects across the pyrethroids types and their instability in aqueous media may underestimate toxicity against non-target aquatic species when exposed in their natural environment.

Statistical relationship between metabolic decomposition and chemical uptake predicts bioconcentration factor data for diverse chemical exposures

BACKGROUND

A challenge of in vitro to in vivo extrapolation (IVIVE) is to predict the physical state of organisms exposed to chemicals in the environment from in vitro exposure assay data. Although toxicokinetic modeling approaches promise to bridge in vitro screening data with in vivo effects, they are often encumbered by a need for redesign or re-parameterization when applied to different tissues or chemicals.

RESULTS

We demonstrate a parameterization of reverse toxicokinetic (rTK) models developed for the adult zebrafish (Danio rerio) based upon particle swarm optimizations (PSO) of the chemical uptake and degradation rates that predict bioconcentration factors (BCF) for a broad range of chemicals. PSO reveals a relationship between chemical uptake and decomposition parameter values that predicts chemical-specific BCF values with moderate statistical agreement to a limited yet diverse chemical dataset, and all without a need to retrain the model to new data.

CONCLUSIONS

The presented model requires only the octanol-water partitioning ratio to predict BCFs to a fidelity consistent with existing QSAR models. This success begs re-evaluation of the modeling assumptions; specifically, it suggests that chemical uptake into arterial blood may be limited by transport across gill membranes (diffusion) rather than by counter-current flow between gill lamellae (convection). Therefore, more detailed molecular modeling of aquatic respiration may further improve predictive accuracy of the rTK approach.

Bifenthrin causes transcriptomic alterations in mTOR and ryanodine receptor-dependent signaling and delayed hyperactivity in developing zebrafish (Danio rerio)

Over the last few decades, the pyrethroid insecticide bifenthrin has been increasingly employed for pest control in urban and agricultural areas, putting humans and wildlife at increased risk of exposure. Exposures to nanomolar (nM) concentrations of bifenthrin have recently been reported to alter calcium oscillations in rodent neurons. Neuronal calcium oscillations are influenced by ryanodine receptor (RyR) activity, which modulates calcium-dependent signaling cascades, including the mechanistic target of rapamycin (mTOR) signaling pathway. RyR activity and mTOR signaling play critical roles in regulating neurodevelopmental processes. However, whether environmentally relevant levels of bifenthrin alter RyR or mTOR signaling pathways to influence neurodevelopment has not been addressed. Therefore, our main objectives in this study were to examine the transcriptomic responses of genes involved in RyR and mTOR signaling pathways in zebrafish (Danio rerio) exposed to low (ng/L) concentrations of bifenthrin, and to assess the potential functional consequences by measuring locomotor responses to external stimuli. Wildtype zebrafish were exposed for 1, 3 and 5 days to 1, 10 and 50 ng/L bifenthrin, followed by a 14 d recovery period. Bifenthrin elicited significant concentration-dependent transcriptional responses in the majority of genes examined in both signaling cascades, and at all time points examined during the acute exposure period (1, 3, and 5 days post fertilization; dpf), and at the post recovery assessment time point (19 dpf). Changes in locomotor behavior were not evident during the acute exposure period, but were observed at 19 dpf, with main effects (increased locomotor behavior) detected in fish exposed developmentally to bifenthrin at 1 or 10 ng/L, but not 50 ng/L. These findings illustrate significant influences of developmental exposures to low (ng/L) concentrations of bifenthrin on neurodevelopmental processes in zebrafish.

Effect of titanium dioxide nanoparticles on the bioavailability and neurotoxicity of cypermethrin in zebrafish larvae

In aquatic environment, the presence of nanoparticles (NPs) has been reported to modify the bioavailability and toxicity of the organic toxicants. Nevertheless, the combined toxicity of NPs and the pesticides that were used world-widely still remains unclear. Cypermethrin (CYP), a synthetic pyrethroid insecticide, is commonly used for controlling agricultural and indoor pests. Therefore, the effects of titanium dioxide NPs (nTiO₂) on CYP bioconcentration and its effects on the neuronal development in zebrafish were investigated in our study. Zebrafish embryos (2- hour-post-fertilization, hpf) were exposed to CYP (0, 0.4, 2 and 10 μg/L) alone or co-exposed with nTiO₂ (1 mg/L) until 120-hpf. nTiO₂ is taken up by zebrafish larvae and also it can adsorb CYP. The zebrafish body burdens of CYP was observed and CYP uptake was increased by nTiO₂, indicating that the nTiO₂ could accelerate the bioaccumulation of CYP in larvae. Co-exposure of nTiO₂ and CYP induced the generation of reactive oxygen species. Exposure to CYP alone significantly decreased the mRNA expression of genes, including glial fibrillary acidic protein (gfap), α1-tubulin, myelin basic protein (mbp) and growth associated protein (gap-43). Besides, reductions of serotonin, dopamine and GABA concentrations were observed in zebrafish and the larval locomotion was significantly decreased in response to the lower level of the neurotransmitters. Moreover, co-exposure of nTiO₂ and CYP caused further significantly decreased in the locomotion activity, and enhanced the down-regulation of the mRNA expression of specific genes and the neurotransmitters levels. The results demonstrated that nTiO₂ increased CYP accumulation and enhanced CYP-induced developmental neurotoxicity in zebrafish.

Early life exposure of zebrafish (Danio rerio) to synthetic pyrethroids and their metabolites: a comparison of phenotypic and behavioral indicators and gene expression involved in the HPT axis and innate immune system

Ecotoxicological studies have revealed the association between synthetic pyrethroid (SP) exposure and aquatic toxicity in fish; however, research on the toxic effects of SP metabolites is still limited. In this study, the toxicity of two SPs (permethrin (PM) and β-cypermethrin (β-CP)) and their three metabolites (3-phenoxybenzoic alcohol (PBCOH), 3-phenoxybenzaldehyde (PBCHO), and 3-phenoxybenzoic acid (PBCOOH)) towards zebrafish embryos and larvae was evaluated. Both SPs and their metabolites exhibited significant developmental toxicities, caused abnormal vascular development, and changed locomotor activities in larvae. The alteration of gene expression involved in the thyroid system and the innate immune system indicated that SPs and their three metabolites have the potency to induce thyroid disruption and trigger an immune response. The results from the present study suggest that SP metabolites could induce multiple toxic responses similar to parent compounds, and their toxicity should be considered for improving the understanding of environmental risks of SPs.

Differential uptake of and sensitivity to diphenhydramine in embryonic and larval zebrafish

The zebrafish fish embryo toxicity (FET) test is increasingly employed for alternative toxicity studies, yet our previous research identified increased sensitivity of zebrafish slightly older than embryos employed in FET methods (0-4 d postfertilization [dpf]). We identified rapid steady-state accumulation of diphenhydramine across zebrafish embryo and larval stages. However, significantly (p < 0.05) lower accumulation was observed at 48 h compared to 96 h in chorionated and dechorionated embryos (0-4 dpf), but not in zebrafish at 7 to 11 and 14 to 18 dpf. Increased uptake and toxicity of diphenhydramine was further observed in zebrafish at 7 to 11 and 14 to 18 dpf compared with 0-4 dpf embryos with chorion or dechorionated, which indicates that differential zebrafish sensitivity with age is associated with accumulation resulting from gill and other toxicokinetic and toxicodynamic changes during development. Environ Toxicol Chem 2018;37:1175-1181. © 2017 SETAC.

Equilibrium sampling informs tissue residue and sediment remediation for pyrethroid insecticides in mariculture: A laboratory demonstration

Mariculture product safety in relation to sediment quality has attracted increasing attention because of the accumulation of potentially hazardous chemicals, including pyrethroid insecticides, in sediment. Passive sampling has been widely used to assess the bioavailability of sediment-associated hydrophobic organic contaminants and predict their body residue in benthic organisms. Therefore, in this study, we introduced polydimethylsiloxane (PDMS) polymer as a biomimetic "chemometer" for freely-dissolved concentrations (C_free) to assess the efficacy of different carbon sorbents in reducing the bioavailability of pyrethroids in the process of sediment remediation. Black carbon (BC)-based materials (e.g., charcoal, biochar, and activated carbon) showed the advantageous sorption capacity over humic substance-based peat soil based on both C_free and tissue residue in exposed clams. Of the tested BC-type materials, biochar appeared to be an ideal one in the remediation of pyrethroid-contaminated sediment. The predictive value of the PDMS chemometer approach to informing tissue residue was confirmed by a good agreement between the measured lipid-normalized concentrations of pyrethroids in clams and the lipid-based equilibrium concentrations calculated from C_free via lipid-water partition coefficients. The quantitative inter-compartmental relationship underlying the laboratory system of sediment-pore water-PDMS-biota was also cross-validated by a mechanistically-based bioaccumulation model, thus confirming the validity of C_free as a predictive intermediate to alert for tissue residue and guide sediment remediation. The present study revealed a great promise of sensing C_free by polymer-based equilibrium sampling in predicting tissue residue of chemicals applied in mariculture against regulatory guidelines, and, in turn, informing remediation measures when needs arise. In situ demonstration is warranted in the future to ascertain the field applicability of this approach in real mariculture systems.

Assessment of biomarkers in the neotropical fish Brycon amazonicus exposed to cypermethrin-based insecticide

The effects of cypermethrin-based insecticide (CBI), commonly used in aquaculture and agriculture, were evaluated in matrinxa (Brycon amazonicus) exposed to sub-lethal concentration (20% of LC50) for 96 h. Physiological and biochemical effects were studied through biomarkers: lipid peroxidation (LPO), glutathione (GSH), and ascorbic acid concentrations; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glucose-6-phosphate dehydrogenase (G6PDH) assays in the liver and gills. Besides, ions Na⁺, Cl^-, and K⁺; protein and glucose concentrations were measured in the plasma. Red blood cells count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), and hematimetric parameters were evaluated in the total blood. The NKA (Na⁺ /K+ ATPase) activity was assayed in the gills. The histopathological effects of CBI were also investigated in the gills. The liver and gill LPO increased 62 and 100%, respectively. The tripeptide GSH concentration reduced in the liver and increased in the gill of exposed fish. The SOD and CAT activities increased in the liver, whereas CAT reduced in the gill. Liver also presented an increase in G6PDH activity. Plasma Na⁺ and Cl^- and glucose concentrations increased in the exposed fish. Levels of Ht, Hb and RBC were significantly increased. The gill NKA activity also increased. Exposed fish exhibited histological alterations in the gills such as hypertrophy and proliferation of chloride cells, blood vessels dilation, aneurysms and hemorrhage of the lamella. The histological index indicated moderate to heavy damage to the gills. CBI provokes liver and gills oxidative stress, gill structural damages, and ionic imbalance. A multi-biomarker approach allows us to see that B. amazonicus was unable to cope with CBI exposure.

Toxicity assessment of pyriproxyfen in vertebrate model zebrafish embryos (Danio rerio): A multi biomarker study

Pyriproxyfen (2-[1-methyl-2-(4-phenoxyphenoxy) ethoxy] pyridine) (PPF), a pyridine-based pesticide widely used to control agricultural insect pests and mosquitoes in drinking water sources. However, its ecotoxicological data is limited in aquatic vertebrates particularly in fish. Hence, the present study aimed to evaluate the adverse effect of PPF in zebrafish embryo development (Danio rerio). In order to investigate the impact of PPF, embryos were exposed to 0.16, 0.33 and 1.66 μg/mL (0.52, 1.04 and 5.2 μM, respectively) for 96 hpf and various biomarker indices such as developmental toxicity (edema formation, hyperemia, heart size and scoliosis), oxidative stress (reactive oxygen species (ROS), lipid peroxidation (LPO) and nitric oxide (NO)), antioxidant responses (superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), glutathione peroxidase (GPx) and reduced glutathione (GSH)), biochemical (lactate dehydrogenase (LDH) and acid phosphatase (AP)), neurotoxicity (acetylcholinesterase (AChE)), genotoxicity (apoptosis and DNA damage) and histopathological changes were determined. The results showed that severe developmental deformities and changes in heart rate were observed in embryos treated with highest (1.66 μg/mL) concentration than the control (P < 0.05). Heart size measurement showed that, significant change in heart size (P < 0.01) was observed in embryos of 96 hpf only at 1.66 μg/mL PPF exposure. The oxidative stress was apparent at highest test concentration (1.66 μg/mL) as reflected by the elevated ROS, LPO and NO and changes in antioxidant enzyme activities including SOD, CAT, GST and GPx (P < 0.05). Besides, GSH level and AChE activity were significantly lowered in 1.66 μg/mL PPF exposed group than the control. After 96 hpf of PPF exposure, no significant changes were found in AP activity whereas, a biphasic response was observed in the LDH activity. There was no genotoxic effect in embryos exposed to PPF at 0.16 and 0.33 μg/mL, while significant (P < 0.05) DNA damage and apoptosis were found in 1.66 μg/mL treated group. Histopathological analysis revealed that exposure to PPF at 1.66 μg/mL resulted in thinning of heart muscles, pericardial edema and hyperemia while there was no obvious changes were observed in other treatment groups. Hence, the results of the present study demonstrate that PPF could cause adverse effect on early developmental stages of zebrafish at higher concentration.

Bioconcentration and Metabolism of Emodin in Zebrafish Eleutheroembryos

Emodin is a major active anthraquinone of various herbal laxatives, which can exert many pharmacological effects. However, chronic use of anthranoid laxatives, even at low dosages, may cause melanosis coli (MC). It has been suggested that the accumulation of anthraquinones is a risk factor in the MC process. To investigate the accumulation of emodin, we conducted a bioconcentration study of emodin in zebrafish eleutheroembryos. Based on the economic cooperation and development (OECD) 305 test, zebrafish eleutheroembryos were exposed to emodin at a constant concentration for 48 h, before the test media were replaced by the blank medium for 24 h of depuration. To eliminate the effect of metabolism of emodin for assessment of the bioconcentration factor (BCF), we also conducted a modified test for which zebrafish eleutheroembryos were exposed to the non-renewed test media, whose emodin concentration decreased with time. At different exposure time points, zebrafish eleutheroembryos and exposure media were sampled for analysis of emodin concentration using HPLC-MS/MS. The results showed rapid accumulation of emodin in zebrafish eleutheroembryos to reach a steady-state concentration within 24 h. Meanwhile, emodin was actively metabolized by zebrafish eleutheroembryos to result in 29.5–40.7% of its elimination. In the groups with high or low concentrations of emodin, the standardized BCF (sBCF) values in the standard test were 24.0 and 20.0, while those in the modified test were 50.4 and 52.0. These results showed that emodin could accumulate in zebrafish eleutheroembryos when used for 48 h and beyond, suggesting that the accumulation of anthraquinones may be a risk factor in the MC process. Accordingly, emodin should be unsuitable for long-term use due to its accumulation.

Tissue distribution, metabolism and hepatic tissue injury in Chinese lizards (Eremias argus) after a single oral administration of lambda-cyhalothrin

Lambda-cyhalothrin (LCT) is a widely used pyrethroid with neurotoxicity. However, little is known about the toxicokinetics of LCT in reptiles. In this study, the absorption, distribution, metabolism and excretion of LCT in Chinese lizards (Eremias Argus) were determined following a single dose (10 mg kg^-1) treatment. In the liver, brain, gonads and skin, LCT levels peaked within several hours and then decreased rapidly. However, the concentration of LCT gradually increased in the fat tissue. More than 90% of the LCT dose was excreted in the faeces. One LCT metabolite, 3-phenoxybenzoic acid (PBA), was detected in lizard plasma and tissues. PBA preferentially accumulates in the brain and plasma. The half-life of PBA in the brain was 3.2 days, which was 35.4-fold greater than that of LCT. In the plasma, the concentration of PBA was significantly higher than that of LCT. The bioaccumulation of LCT in tissues was enantioselective, and the enantiomeric fractions (EF) ranged from 0.72 to 0.26. The preferential accumulation of enantiomers changed according to exposure time, but the reasons behind this phenomenon were not clear. For pathological analysis, vacuolation of the cytoplasm and large areas of necrosis were observed in the liver sections after 168 h of dosing. The liver tissues exhibited both decreases in the hepatosomatic index and histopathological lesions during the exposure period. In this study, the effect concentration of LCT in lizards was 200-fold lower than its LD₅₀ value used in risk assessments for birds. These results may provide additional information for the risk assessment of LCT for reptiles and indicate that birds may not be an ideal surrogate for reptile toxicity evaluation.

Toxicokinetics of Polar Chemicals in Zebrafish Embryo (Danio rerio): Influence of Physicochemical Properties and of Biological Processes

The time-resolved uptake of 17 nonionic and ionic polar compounds (logD ≤ 2) with a diversity of functional groups into zebrafish embryos (ZFE) was studied over 96 h of exposure. Among them were pharmaceuticals, pesticides and plant active ingredients. Uptake rates for the diffusion controlled passive uptake through the ZFE membrane ranged from 0.02 to 24 h(-1) for the nonionic compounds and were slower for ionic compounds (<0.008-0.08 h(-1)). The study compounds did not enrich much in the ZFE (median bioconcentration factor of 1, max. 7). Biotransformation significantly influenced the internal concentration of some of the test compounds over time (benzocaine, phenacetin, metribuzin, phenytoin, thiacloprid, valproic acid). For benzocaine, valproic acid and phenacetin several transformation products (TPs) were observed by LC-MS already at early life-stages (before 28 hpf); for benzocaine the TPs comprised >90% of the initial amount taken up into the ZFE. For six compounds internal concentrations remained very low (rel. int. conc. < 0.2). Besides biotransformation (sulfamethoxazole), poor membrane permeability (cimetidine, colchicine) and also affinity to efflux transporters (atropine and chloramphenicol) are the likely reasons for these low internal concentrations. This study outlines that the uptake of polar compounds into ZFE is influenced by their physicochemical properties. However, biological processes, biotransformation and, likely, efflux can strongly affect the internal concentrations already in early developmental stages of the ZFE. This should be considered in future toxicokinetic modeling. The evaluation of the toxicity of chemicals by ZFE requires toxicokinetic studies of the test compounds and their TPs to increase comparability to effects in fish.

From the Cover: Zebrafish Larvae Are Insensitive to Stimulation by Cocaine: Importance of Exposure Route and Toxicokinetics

Zebrafish (Danio rerio) larvae have been suggested as vertebrate model to complement or even replace mammals for rapidly assessing behavioral effects of psychoactive drugs. Yet, divergent responses have been reported in mammals and fish despite the conservation of many drug targets. Cocaine, eg, acts as stimulant in mammals but no such response has been documented for zebrafish larvae. We hypothesized that differences in exposure routes (inhalation or injection in mammals vs waterborne in fish) may be a reason for differences in behavioral responses. We characterized cocaine toxicokinetics by liquid chromatography-mass spectrometry and found its rapid uptake into larvae. We used Matrix-assisted laser desorption ionization-mass spectrometry imaging for the first time to characterize internal distribution of cocaine in zebrafish larvae. Surprisingly, eyes accumulated the highest amount of cocaine and retained most of it even after 48 h depuration. We attribute this to trapping by pigment melanin, a thus far little explored mechanism that may also be relevant for other basic drugs. Cocaine also reached the brain but with levels similar to those in trunk indicating simple passive diffusion as means of distribution which was supported by toxicokinetic models. Although brain levels covered those known to cause hyperactivity in mammals, only hypoactivity (decreased locomotion) was recorded in zebrafish larvae. Our results therefore point to cocaine's anesthetic properties as the dominant mechanism of interaction in the fish: upon entry through the fish skin and gills, it first acts on peripheral nerves rapidly overriding any potential stimulatory response in the brain.

Permethrin is a potential thyroid-disrupting chemical: In vivo and in silico envidence

Permethrin (PM), one of the most heavily used synthetic pyrethroids, has the potential to interfere with thyroid hormones in mammals, however, the effect is poorly recognized in aquatic organisms. Herein, embryonic zebrafish were exposed to PM (0, 1, 3 and 10μg/L) until 72h post-fertilization. We demonstrated that PM readily accumulated in larvae with a preference for cis-PM, inhibited development and increased thyroxine and 3,5,3'-triiodothyronine levels accompanying increase in the transcription of most target genes, i.e., thyroid-stimulating hormone β, deiodinases, thyroid receptors, involved in the hypothalamic-pituitary-thyroid axis. Further Western blot analysis indicated that transthyretin (TTR) protein was significantly increased. Molecular docking analysis and molecular dynamics simulations revealed that PM fits into three hydrophobic binding pocket of TTR, one of the molecular targets of thyroid hormone disrupting chemicals (THDCs), and forms strong van der Waals interactions with six resides of TTR, including Leu8, Leu 101, Leu125, Thr214, Leu218 and Val229, thus altering TTR activity. Both in vivo and in silico studies clearly disclosed that PM potentially disrupts the thyroid endocrine system in fish. This study provides a rapid and cost-effective approach for identifying THDCs and the underlying mechanisms.

Chiral bioaccumulation behavior of tebuconazole in the zebrafish (Danio rerio)

Tebuconazole is an effective chiral fungicide, and previous studies have demonstrated that tebuconazole enantiomers exhibit enantioselective toxicity to non-target aquatic organisms. Thus, the aim of the present study was to investigate the chiral bioaccumulation behavior of tebuconazole in zebrafish (Danio rerio). Two exposure concentrations (0.107 and 1.07 mg/L) of tebuconazole were used. The uptake experiments lasted for 8 days, and subsequently, the zebrafish were transferred to another clean tank containing water without tebuconazole for depuration experiments (up to 14 days). A significant trend in enantioselective bioaccumulation was observed in these zebrafish with the preferential accumulation of (-)-R-tebuconazole at two dose levels. The results of the depuration experiments indicated that the degradation of (-)-R-tebuconazole in zebrafish was slower than that of (+)-S-tebuconazole. The BCFk values for (+)-S-tebuconazole and (-)-R-tebuconazole in a low dose of this chemical were 11.22 and 16.25, respectively, while at a high dose, these values were 9.79 and 10.31, respectively. The enantiomer fraction of tebuconazole in zebrafish and water ranged from 0.31-0.49. Hence, future research should focus on the fate of tebuconazole in the aquatic environment at the enantiomer levels.

Acute exposure to synthetic pyrethroids causes bioconcentration and disruption of the hypothalamus-pituitary-thyroid axis in zebrafish embryos

Synthetic pyrethroids (SPs) have the potential to disrupt the thyroid endocrine system in mammals; however, little is known of the effects of SPs and underlying mechanisms in fish. In the current study, embryonic zebrafish were exposed to various concentrations (1, 3 and 10 μg/L) of bifenthrin (BF) or λ-cyhalothrin (λ-CH) until 72 h post fertilization, and body condition, bioaccumulation, thyroid hormone levels and transcription of related genes along the hypothalamus-pituitary-thyroid (HPT) axis examined. Body weight was significantly decreased in the λ-CH exposure groups, but not the BF exposure groups. BF and λ-CH markedly accumulated in the larvae, with concentrations ranging from 90.7 to 596.8 ng/g. In both exposure groups, alterations were observed in thyroxine (T4) and triiodothyronine (T3) levels. In addition, the majority of the HPT axis-related genes examined, including CRH, TSHβ, TTR, UGT1ab, Pax8, Dio2 and TRα, were significantly upregulated in the presence of BF. Compared to BF, λ-CH induced different transcriptional regulation patterns of the tested genes, in particular, significant stimulation of TTR, Pax8, Dio2 and TRα levels along with concomitant downregulation of Dio1. Molecular docking analyses revealed that at the atomic level, BF binds to thyroid hormone receptor (TRα) protein more potently than λ-CH, consequently affecting HPT axis signal transduction. In vitro and in silico experiments disclosed that during the early stages of zebrafish development, BF and λ-CH have the potential to disrupt thyroid endocrine system.

The influence of size on the toxicity of an encapsulated pesticide: a comparison of micron- and nano-sized capsules

Encapsulation technology involves entrapping a chemical active ingredient (a.i.) inside a hollow polymeric shell and has been applied to commercial pesticide manufacturing for years to produce capsule suspension (CS) formulations with average particle sizes in the micron-scale. The few literature sources that investigate the environmental fate and toxicity to non-target organisms of encapsulated commercially available pesticide products with regard to capsule size report on average sizes between 20 and 50 μm. Here, we have identified a CS formulation with an average capsule size of approximately 2 μm with some capsules extending into the nanometer scale (~200 nm). Determining how carrier size influences toxicity is important to understanding if current pesticide risk assessments are sufficient to protect against products that incorporate encapsulation technology. Here, a commercial pyrethroid CS pesticide with lambda-cyhalothrin (λ-Cy) as the a.i. was separated into two suspensions, a fraction consisting of nano-sized capsules (~250 nm) and a fraction of micron-sized capsules (~2200 nm) in order to investigate the influence of capsule size on toxicity to embryonic zebrafish, Danio rerio. Toxicity was evaluated 24h after exposure to equivalent amounts of a.i. by the presence and severity of pyrethroid-specific tremors, 14 sublethal developmental impacts and mortality. Fish exposed to greater than 20 μg a.i. L(-1) technical λ-Cy or formulated product experienced curvature of the body axis, pericardial edema, craniofacial malformations, and mortality. Exposure to the unfractionated formulation, micro fraction, nano fraction and technical a.i. resulted in no significant differences in the occurrence of sublethal impacts or mortality; however, the technical a.i. exposure resulted in significantly less fish experiencing tremors and shorter tremors compared to any of the formulated product exposures. This suggests that the capsule size does not influence the toxic response of the entrapped λ-Cy, but the presence or absence of the capsules does. Testing across other encapsulated products is needed to determine if size does not have influence on toxicity regardless of encapsulation technology.

Fish embryo toxicity test: identification of compounds with weak toxicity and analysis of behavioral effects to improve prediction of acute toxicity for neurotoxic compounds

The fish embryo toxicity test has been proposed as an alternative for the acute fish toxicity test, but concerns have been raised for its predictivity given that a few compounds have been shown to exhibit a weak acute toxicity in the fish embryo. In order to better define the applicability domain and improve the predictive capacity of the fish embryo test, we performed a systematic analysis of existing fish embryo and acute fish toxicity data. A correlation analysis of a total of 153 compounds identified 28 compounds with a weaker or no toxicity in the fish embryo test. Eleven of these compounds exhibited a neurotoxic mode of action. We selected a subset of eight compounds with weaker or no embryo toxicity (cyanazine, picloram, aldicarb, azinphos-methyl, dieldrin, diquat dibromide, endosulfan, and esfenvalerate) to study toxicokinetics and a neurotoxic mode of action as potential reasons for the deviating fish embryo toxicity. Published fish embryo LC50 values were confirmed by experimental analysis of zebrafish embryo LC50 according to OECD guideline 236. Except for diquat dibromide, internal concentration analysis did not indicate a potential relation of the low sensitivity of fish embryos to a limited uptake of the compounds. Analysis of locomotor activity of diquat dibromide and the neurotoxic compounds in 98 hpf embryos (exposed for 96 h) indicated a specific effect on behavior (embryonic movement) for the neurotoxic compounds. The EC50s of behavior for neurotoxic compounds were close to the acute fish toxicity LC50. Our data provided the first evidence that the applicability domain of the fish embryo test (LC50s determination) may exclude neurotoxic compounds. However, neurotoxic compounds could be identified by changes in embryonic locomotion. Although a quantitative prediction of acute fish toxicity LC50 using behavioral assays in fish embryos may not yet be possible, the identification of neurotoxicity could trigger the conduction of a conventional fish acute toxicity test or application of assessment factors while considering the very good fish embryo-acute fish toxicity correlation for other compounds.

Methodologies, bioindicators, and biomarkers for assessing gender-related differences in wildlife exposed to environmental chemicals

Male and female organisms may have significant differences in their exposure, toxicokinetics, and response to chemicals, but gender effects have received relatively little attention, often viewed as a confounder rather than of primary importance. In this paper, we examine some of the key issues and methodologies for incorporating gender in studies of the effects of chemicals on wildlife, and explore bioindicators and biomarkers of gender effects. Examining gender-related differences in response to chemicals is complicated in wildlife because of the vast array of species, and differences in niches, lifespans, reproductive cycles and modes, and population dynamics. Further, organisms are more at risk in some ecosystems than others, which may increase the magnitude of effects. Only by studying wild animals, especially native species, can we truly understand the potential impact of gender-specific effects of chemical exposure on populations. Several factors affect gender-related differences in responses to chemicals, including exposure, age, size, seasonality, and genetic and phenotypic variation. There are clear examples where gender-related differences have had significant effects on reproductive success and population stability, including destabilization of gamete release in invertebrates, and alterations of endocrine and neuroendocrine system functioning in vertebrates. A wide range of new technologies and methods are available for examining gender-related differences in responses to chemicals. We provide examples that show that there are gender-related differences in responses to chemicals that have significant biological effects, and these gender-related differences should be taken into account by scientists, regulators, and policy makers, as well as the public.