Stage-specific toxicity of cypermethrin to medaka (Oryzias latipes) eggs and embryos using a refined methodology for an in vitro fertilization bioassay

Parental exposure to Cypermethrin causes intergenerational toxicity in zebrafish offspring

Cypermethrin (CYP), a synthetic pyrethroid pesticide, has been detected in agriculture and aquaculture. However, there is limited knowledge about the transgenerational impacts. This study aimed to investigate the developmental toxicity of CYP on F1 larvae offspring of adult zebrafish exposed to various CYP concentrations (5, 10, and 20 μg/L) for 28 days. The results indicated that CYP accumulated in parental zebrafish, and CYP was below the limit of quantification in offspring. Paternal exposure impacted the hatching rate and heart rate of the F1 generation. Furthermore, CYP significantly impacted the development of swim bladders in progeny and dysregulated the genes relevant to swim bladder development. The neutrophil migrated to the swim bladder. The mRNA levels of the inflammatory factors were also significantly elevated. According to network toxicology, PI3-AKT may be the signaling pathway for CYP-influenced bladder development. Subsequent molecular docking and Western blot analysis showed CYP affected the PI3-AKT signaling pathway. Notably, MK-2206, a specific Akt inhibitor, rescued the CYP-induced damage of swim bladder development in offspring. The present study highlights the potential risks of CYP on the development of offspring and lasting impact in aquatic environments.

Compatibility of Insecticides with Rice Resistance to Planthoppers as Influenced by the Timing and Frequency of Applications

Simple Summary

The brown planthopper, Nilaparvata lugens (Stål)(BPH) is a pest of rice in Asia. Varietal resistance is proposed as an alternative to insecticides that reduces BPH densities. However, in practice, resistance is often combined with insecticide use. We examined the effects of combining seven insecticides with resistance. We applied insecticides as one, two or three applications (experiment 1), or as early or late applications (experiment 2) to resistant (IR62) and susceptible (IR64) rice in a screenhouse environment. Carbofuran and fipronil reduced BPH biomass density. Single applications of cartap hydrochloride, cypermethrin, or buprofezin reduced BPH biomass densities on IR62, but not on IR64 (i.e., synergies); however, the effects were weak and multiple applications of all insecticides (≥2) eliminated synergies. Multiple applications of deltamethrin were antagonistic to resistance as indicated by higher densities of planthoppers on treated IR62 than on treated IR64. In non-infested plants from experiment 2, late applications reduced rice yields compared to early applications. Results suggest that early applications of some insecticides risk enhancing BPH densities, whereas late applications risk reducing rice yields. To avoid negative effects, applications should be made in compliance with Integrated Pest Management principals and multiple insecticide applications to BPH resistant rice should be avoided.

Abstract

The brown planthopper, Nilaparvata lugens (Stål)(BPH) is a pest of rice in Asia. We examined the effects of seven insecticides combined with host resistance against BPH. In a screenhouse environment, we treated BPH-infested and non-infested resistant (IR62) and susceptible (IR64) rice with buprofezin, carbofuran, cartap hydrochloride, cypermethrin, deltamethrin, fipronil, or thiamethoxam + chlorantraniliprole. In one experiment, plants received one, two or three applications. In a second experiment, plants received one early or late insecticide application. Carbofuran and fipronil reduced planthopper biomass densities but resistance did not contribute to these effects (i.e., resistance was redundant). Single applications of cartap hydrochloride (at 20 or 50 days after sowing (DAS)), cypermethrin (20 DAS), or buprofezin (50 DAS) reduced BPH biomass densities on IR62 (i.e., synergies); other insecticides and application times, and multiple applications of all insecticides did not reduce BPH biomass densities on IR62 more than on IR64 (i.e., either resistance or insecticides were redundant). Deltamethrin (three applications) was antagonistic to resistance, but host resistance tended to buffer against the negative effects of single deltamethrin applications. Yields of infested IR62 were not statistically improved by insecticide applications. Late applications reduced yields of non-infested rice. We discuss how prophylactic insecticide applications could destabilize BPH populations and reduce the productivity and profitability of resistant rice.

Inhibition of swim bladder inflation in Japanese medaka (Oryzias latipes) embryos following exposure to select pharmaceuticals alone and in combination

This study leveraged the Japanese medaka fish embryo model for the assessment of effects of select contaminants on early development in fish. Fish embryos were exposed to various pharmaceutical contaminants including synthetic hormones and non-steroidal anti-inflammatory drugs and their effects on development were observed. Initial screening determined that swim bladder inflation failure was the most common endpoint detected. Swim bladder inflation failure was first explored in a study demonstrating that medaka require access to the air-water interphase to inflate their swim bladders in a time-dependent manner, and swim bladder inflation failure was correlated with mortality. Fish embryos were exposed 24-hours post fertilization until hatch to concentration ranges of various pharmaceutical contaminants including: 17β-estradiol, 17α-ethinylestradiol, and levonorgestrel (1 to 1000 µg/L), or diclofenac (0.32 to 100 mg/L). The main effect observed across all four compounds was a significant increase in failure of swim bladder inflation with increasing exposure concentration (24 to 72-hours post-hatch). Following single compound experiments combinatorial exposures using no-observed-effect concentrations were conducted. The main effect observed was a significant decrease in inflation success 24-hours post-hatch following a binary mixture of levonorgestrel and 17α-ethinylestradiol, as well as a significant decrease in swim bladder inflation success at all times following exposure to a quaternary mixture of all four compounds. This study demonstrated that embryonic exposure to pharmaceutical compounds, both alone and in combination, resulted in failure of swim bladder inflation in larval Japanese medaka.

The Effects of 17α-Ethinylestradiol on the Heart Rate of Embryonic Japanese Medaka (Oryzias latipes)

Estrogen toxicity has been an area of priority in aquatic toxicology over the last 20 yr. Currently, estrogen toxicity is primarily linked to classical estrogen signaling, the interaction of estrogen receptors alpha and beta (ERα and ERβ). Recent evidence has indicated that a rapid, nongenomic, nonclassical estrogen signaling pathway exists via the G protein-coupled estrogen receptor (GPER), which is expressed in many biological systems, with roles in the cardiovascular system. The objective of the present study was to investigate the effect of 17α-ethinylestradiol (EE2) on the heart rate of embryonic Japanese medaka (Oryzias latipes). A significant decrease (bradycardia) in embryonic heart rate was observed at all treatment concentrations (0.1, 1, 10, 100, and 1000 ng/L EE2) at 144, 168, and 192 h postfertilization (hpf; p ≤ 0.05), whereas 120 and 216 hpf embryos experienced a significant decrease from the control at 10, 100, and 1000 ng/L EE2 and 0.1, 100, and 1000 ng/L EE2, respectively (p ≤ 0.05). In addition, using select estrogen receptor modulators, it was demonstrated that estrogen-induced bradycardia appears to be linked to GPER and not ERα and ERβ. The present study highlights GPER as a novel and alternative mode of action for EE2 toxicity at environmentally relevant concentrations. Environ Toxicol Chem 2020;39:904-912. © 2020 SETAC.

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.

Dairy Products Added to Rearing Media Negatively Effect Drosophila melanogaster (Diptera: Drosophilidae) Egg Production and Larval Development

This study examined the effect of kefir, yogurt, and milk on egg production and development in Drosophila melanogaster Meigen. Kefir, yogurt, and milk were added to the Drosophila culture medium. First they were fed to mature individuals and then these females laid eggs on medium containing kefir, yogurt, and milk. Later the development of eggs and larvae was examined. The experiments were conducted on two generations, the F1 generation reared with additives in the media and F2 without the additives. The effects of these substances on the basic stages of development were also examined. In the experimental groups, the numbers of eggs and larvae decreased considerably in both the F1 and F2 generations. The comparison between the experimental groups themselves also showed a difference. In both generations, development of eggs into third instar larvae was reduced and metamorphosis was delayed. In addition, morphological abnormalities were observed in the larvae. Overall the results showed that kefir, yogurt, and milk affected egg and larva development negatively and this negative effect continued in the F2 generation. The continuation of this negative effect in the F2 generation, which was not exposed to various milk additives, is an interesting finding. These results indicate that the nutrients from the milk and the milk products used were neither utilized by nor beneficial for this insect.

Asymmetric patterns in the cranial skeleton of zebrafish (Danio rerio) exposed to sodium pentachlorophenate at different embryonic developmental stages

Bilaterally symmetric organisms display mirror copies of their structures on both sides of the body, and the development of both sides is regulated by the same set of genes. Environmental variations can directly affect phenotype, and exposure to chemical contaminants at certain stages may modify embryonic development. The pesticide sodium pentachlorophenate (NaPCP) was used at the no-observable-effect concentration (NOEC) to determine the degree of susceptibility of zebrafish (Danio rerio) embryos in different developmentally susceptible windows (zygote, blastula, gastrula, segmentation, pharyngula and larva). Shape variation in the zebrafish viscerocranium and fluctuating asymmetry (FA), which increases in direct proportion to environmental stress, induced by exposure to NaPCP were measured with geometric morphometrics. Procrustes ANOVA was performed to estimate the shape variation around a symmetric consensus that accounted for the following factors: shape variation in individuals (I), variation by sides (S), the Individuals×Sides interaction (I×S), and the stages of exposure to the toxicant (Stages). Factors I, S and IxS accounted for most of the morphological variation (p<0.0001). Extensive deformities throughout the viscerocranium occurred during the window of exposure from gastrula to larva. Embryonic mortality occurred and was dependent on the stage of exposure. The NOEC concentration of NaPCP affected embryonic development in D. rerio and also induced lethal effects in embryos. FA was determined in both unexposed and NaPCP-exposed embryos and was greater in the control than in some exposure windows; besides, no correlation was found between FA and developmental stages, so our results do not support FA as a bioindicator of chemical stress but confirm its value in the study of morphological effects of toxicants.

Dietary ascorbic acid as a means to counter the stress of cypermethrin on the growth of freshwater catfish Heteropneustes fossilis

Two months of experiments performed in outdoor vats in a 3 × 3 factorial design to evaluate the effects of three sublethal levels (0.0, 0.3 and 0.5 µg L−1) of cypermethrin on freshwater catfish Heteropneustes fossilis fed with three different levels (0.0, 0.5 and 1.0 g kg−1) of ascorbic acid (AA) in the diet. Even the lower sublethal level (0.3 µg L−1) of cypermethrin produced significant reduction in growth and deposition of protein in the body of H. fossilis. Dietary supplement of AA at 0.5 g kg−1 failed to counter these ill effects of cypermethrin on H. fossilis, but a supplement of 1.0 g kg−1 AA significantly increased the AA reserve in the body of the fish, and the ill effects of cypermethrin on growth were reversed. It was concluded that the catfish H. fossilis required an exogenous supply of AA to counter the stress of cypermethrin.

Stage-specific malformations and phenotypic changes induced in embryos of amphibian (Xenopus tropicalis) by triphenyltin

Tributyltin (TBT) and triphenyltin (TPT) can induce unique malformations in embryos of amphibian (Xenopus tropicalis). We further exposed X. tropicalis embryos to TPT during different stages. Severe malformations were observed in the embryos after exposure to 5-10 μg Sn/L TPT during S32-40 and S40-46. Comparatively, the embryos showed slight or moderate malformations after exposure during S10-25, S25-32 or S46-47. The most characteristic malformations were narrow or no fins, followed by enlarged proctodaeums and skin hypopigmentation. The developed fins were still affected after TPT exposure, but the inhibited fins could not recover even after the removal of TPT exposure. In TPT treatment groups, the proctodaeums of embryos externally expanded, and the pigment cells of embryos were poor, small and dot like. Our results suggested that TPT-induced teratogenicity was highly stage-specific. The sensitive window of fin defects indicated that TPT affected the formation rather than induction or expansion of fins.

Effect-directed analysis of municipal landfill soil reveals novel developmental toxicants in the zebrafish Danio rerio

Effect-directed analysis (EDA) is an approach used to identify (unknown) contaminants in complex samples which cause toxicity, using a combination of biology and chemistry. The goal of this work was to apply EDA to identify developmental toxicants in soil samples collected from a former municipal landfill site. Soil samples were extracted, fractionated, and tested for developmental effects with an embryotoxicity assay in the zebrafish Danio rerio. Gas chromatograph mass selective detection (GC-MSD) chemical screening was used to reveal candidate developmental toxicants in fractions showing effects. In a parallel study, liquid chromatography-hybrid linear ion trap Orbitrap mass spectrometry was also applied to one polar subfraction (Hoogenboom et al. J. Chromatogr. A2009, 1216, 510-519). EDA resulted in the identification of a number of previously unknown developmental toxicants, which were confirmed to be present in soil by GC-MS. These included 11H-benzo[b]fluorene, 9-methylacridine, 4-azapyrene, and 2-phenylquinoline, as well as one known developmental toxicant (retene). This work revealed the presence of novel contaminants in the environment that may affect vertebrate development, which are not subject to monitoring or regulation under current soil quality assessment guidelines.

Dechorionation as a tool to improve the fish embryo toxicity test (FET) with the zebrafish (Danio rerio)

Prior to hatching, the zebrafish embryo is surrounded by an acellular envelope, the chorion. Despite repeated speculations, it could not be clarified unequivocally whether the chorion represents an effective barrier and, thus, protects the embryo from exposure to distinct chemicals. Potentially, there is a risk of generating false negative results in developmental toxicity studies due to limited permeability of the chorion for some compounds. The simplest way to exclude this is to remove the chorion and expose the "naked" embryo. In the context of ecotoxicity testing, standardized protocols do not exist for fish embryo dechorionation, and survival rates of dechorionated embryos have usually not been subjected to statistical analysis. Since reproducibly high survival rates are of fundamental importance for chemical toxicity assessment, the present study was designed to develop and optimize a dechorionation procedure. With appropriate modifications of the fish embryo test protocol, embryos can be dechorionated at 24h post-fertilization (hpf) with survival rates of ≥90%. However, for fish embryo tests with dechorionated embryos, the standard positive control test substance, 3,4-dichloroaniline, should be replaced by another compound, e.g., acetone, since 3,4-dichloroaniline exerts its effects during the first 24h of development. Dechorionation of younger stages (<24 hpf) is generally possible, however with lower survival rates. The effect of dechorionation was demonstrated with the cationic polymer Luviquat HM 552, which is blocked by the chorion non-dechorionated embryos due to its molecular weight of ~400,000 Dalton, but becomes strongly toxic after dechorionation.

Assessment of potential immunotoxic effects caused by cypermethrin, fluoxetine, and thiabendazole using heat shock protein 70 and interleukin-1β mRNA expression in the anuran Xenopus laevis

The current study describes the effect of cypermethrin, fluoxetine, and thiabendazole, at environmentally relevant concentrations, on the expression of heat shock protein 70 (HSP70) and interleukin 1β (IL-1β), using Xenopus laevis larvae as animal model. Cytokines and interleukins are considered good predictors of the immunotoxic potential of xenobiotics. Tadpoles at stage 47 (normal tables of X. laevis) were exposed under static conditions to: 0.3 and 30 µg/L fluoxetine, 0.7 µg/L thiabendazole, and 0.24 µg/L cypermethrin. The effects were evaluated at 7, 24, and 72 h, and 6 and 9 d. Randomly chosen tadpoles were used as genetic material for detection of hsp70 and IL-1β mRNA induction through reverse transcription PCR. Tadpoles exposed to 30 µg/L fluoxetine showed mRNA expression of both genes at all exposure times, whereas at 0.3 µg/L a peak response for hsp70 was observed after 24 h, and the increase in IL-1β mRNA was statistically significant with respect to the control 72 h after exposure. Thiabendazole induced a high expression of mRNA for both hsp70 and IL-1β at all exposure times. Cypermethrin increased the hsp70 mRNA levels, with a peak at 24 h, and provoked high expression of IL-1β mRNA at all exposure times. Considering the relationship between HSP70 and IL-1β and their involvement (mainly of IL-1β) in immune responses, certain changes observed in their expression could be considered warning indicators of potential immunotoxic effects of these substances on Xenopus.

Cadmium toxicity to embryonic-larval development and survival in red sea bream Pagrus major

At 18 degrees C and 33 psu, 24 and 48 h LC(50) values of cadmium (Cd) for red sea bream Pagrus major embryos were 9.8 and 6.6 mgl(-1), respectively, while 24, 48, 72, and 96 h LC(50) values for larvae were 18.9, 16.2, 8.0, and 5.6 mgl(-1), respectively, indicating that embryos were more sensitive to Cd toxicity than larvae. Cd concentrations at > or =0.8 mgl(-1) led to low hatchability (0-90% in > or =0.8 mgl(-1) solutions vs. 97-100% in lower ones), delay in time to hatch, high mortality (38-100% vs. 1-10%), morphological abnormality (42-100% vs. 1-10%), reduced length (3.55-3.60 vs. 3.71-3.72 mm) in the embryos and larvae. They were Cd concentration dependent and potential biological significant endpoints for assessing the risk of Cd to aquatic organisms. Heart beat and yolk absorption of the larvae were significantly inhibited at some high concentrations but they were not as sensitive as other endpoints to Cd exposure.

Single and joint toxicity of cypermethrin and copper on Chinese cabbage (Pakchoi) seeds

The single and joint effects of Cu(2+) and cypermethrin (CPM) on the seed germination and the elongation of root and shoot of Pakchoi were investigated. The results showed that in solution low concentrations of Cu(2+) could accelerate the germination rate of Pakchoi, whereas high concentrations of Cu(2+) could inhibit it. CPM could strongly inhibit the germination of Pakchoi in solution. However, in the joint toxicity effect, CPM reduced the phytotoxicity of Cu(2+) on the germination of Pakchoi seeds under solution conditions. In the single-factor experiments and joint effect tests of CPM and copper on the seedling growth, it was found that there were significant liner relationships between concentrations of pollutants and root elongation (P<0.05). Copper and CPM had synergic effects on root elongation of Pakchoi in solution cultivation test. However, in soil culture test, these synergistic effects were not significant (P<0.05). Meanwhile, the joint toxicity was more dependent on the effect of copper than that of CPM. The toxicity of the pollutants to seed germination, shoot and root elongation is in the following sequence: root elongation>shoot elongation>germination rate.

Aquatic toxicity of cartap and cypermethrin to different life stages of Daphnia magna and Oryzias latipes

Cartap and cypermethrin, which are among the most widely used pesticides in many countries, are considered safe because of their low mammalian toxicity and their low persistence in the environment. However, recent findings of endocrine-disrupting effects and developmental neurotoxicity have raised concerns about the potential ecological impacts of these pesticides. We evaluated the aquatic toxicity of cartap [S,S'-(2-dimethylaminotrimethylene) bis(thiocarbamate), unspecified hydrochloride] and cypermethrin [(RS)-alpha-cyano-3-phenoxybenzyl-(1RS,3RS,1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate], both individually and combined, on different life stages of the freshwater cladoceran Daphnia magna and a freshwater teleost, Japanese medaka (Oryzias latipes). The 96-hr Daphnia median effective concentrations (EC50s) for cartap and cypermethrin were 91.0 microg/L and 0.00061 microg/L, respectively. Rapid recovery of Daphnia was observed after short-term pulsed exposure to cartap and cypermethrin; there were no adverse effects on reproduction or survival 20 d after a 24 hr exposure to cartap up to 1240 microg/L and cypermethrin up to 1.9 microg/L. Chronic continuous exposure (for 21 d) of 7-d-old Daphnia to cypermethrin significantly reduced the intrinsic population growth rate in a concentration-dependent manner. However, because the intrinsic population growth rates were all above zero, populations did not decrease even at the highest experimental concentration of 200 ng/L. Exposure of Daphnia neonates (< 24 hr old) to cypermethrin for 21 d caused significant, sub-lethal reproduction-related problems, such as increased time to first brood, reduced brood size, and reduced total brood number, at 0.0002, 0.002, and 0.2 ng/L cypermethrin, but the intrinsic population growth rate was not significantly affected. Oryzias latipes was relatively more resistant to both pesticides. In particular, embryos appeared to be more resistant than juveniles or adults, which may be partly due to the protective role of the chorion. The incidence of larval fish deformity was significantly higher after a 96 hr exposure to as low as 250 microg/L of cartap or 40 microg/L of cypermethrin. The mixture of both compounds showed no synergistic toxicity. The extremely high acute-to-chronic ratio suggests that the standard acute lethal toxicity assessment might not reflect the true environmental hazards of these frequently used pesticides. Ecological hazard assessments of long-term low dose or pulsed exposures to cartap and cypermethrin may reveal more realistic consequences of these compounds in surface water.