Effect of waterborne benomyl on the hematological and antioxidant parameters of the Nile tilapia, Oreochromis niloticus

The present study was conducted to determine the 96 h-LC₅₀ of benomyl to the Nile tilapia, Oreochromis niloticus and to investigate the biochemical or hematological indices of blood and the alterations in the antioxidant enzymes of this fish in response to sublethal concentrations of benomyl. Fish weighing 71.61 ± 12.05 g were used in this study; they were subjected to fasting for 4 weeks before treatment. An aqueous solution of benomyl (0, 0.5, 1, 2, 4, 8, and 16 mg L⁻¹) was administered for 96 h to determine the LC₅₀. The 96 h-LC₅₀ value of benomyl was 4.39 (3.23-5.60) mg L⁻¹ in the present study. For 5 weeks, the aqueous solution of benomyl (0, 100, 200, and 400 μg L⁻¹) was administered to investigate its effect on the hematological parameters and antioxidant enzymes. The predominant hematological findings in fish exposed to benomyl were as follows: no significant change in the Hb (g dL⁻¹) level, MCV (μm³), MCH (pg) and MCHC (%) as compared to the control. Benomyl exposure led to greater increases in the GPT, GOT (Karmen-unit), LDH (Wroblewski unit), total cholesterol, Fe, and Ca (mg dL⁻¹) values, whereas the levels of ALP (KA unit), total protein, triglyceride, albumin, and Mg (mg dL⁻¹) did not increase. Benomyl increased the in vivo HSI (%), GST (nmol min⁻¹ mg protein⁻¹), and SOD (U mg protein⁻¹) values in the fish livers in the test group, unlike those in the control group for 5 weeks. At concentrations higher than 100 μg L⁻¹, benomyl affected the GST and SOD levels of Nile tilapia in a dose- and time-dependent manner. The present findings suggest that the in vivo hepatotoxicity associated with benomyl may, in part, result from the hematological index, and antioxidants may provide limited protection against benomyl toxicity.     

Effect of chitosan on growth and plasma membrane properties of Rhizopus stolonifer (Ehrenb.:Fr.) Vuill

The effect of chitosan (0.5, 1.0 and 2.0 mg ml⁻¹) on mycelium growth, potassium efflux, pH of the incubation medium, and activity of plasma membrane H⁺-ATPase of Rhizopus stolonifer was evaluated. The mycelium growth of R. stolonifer was reduced on media amended with chitosan at 1.0 and 2.0 mg ml⁻¹. The highest antifungal index (65%) was obtained on media containing chitosan at 2.0 mg ml⁻¹. Potassium efflux induced by the addition of the three chitosan concentrations was demonstrated. The highest potassium effluxes were observed with addition of chitosan at 2.0 mg ml⁻¹. R. stolonifer grown 72 h on Potato Dextrose Broth without chitosan generated a decrease in the medium’s pH from 5.4 to 4.8. However, the addition of chitosan at all concentrations caused increases on pH of medium cultures. The highest pH increases were observed on media amended chitosan at 2.0 mg ml⁻¹ resulting in the raising of pH level to 6.9. Additionally, there was an important inhibitory effect of chitosan (1.0 and 2.0 mg ml⁻¹) on H⁺-ATPase activity in the plasma membrane of R. stolonifer (32.70%).     

Synthesis and insecticidal activities of pyridine ring derivatives of podophyllotoxin

In an attempt to find the biorational pesticides, we synthesized 12 pyridinyl derivatives of podophyllotoxin (PPT) and 4′-demthylepipodophylltoxin (4′-DMEP) in this study. Their structures and the α/β substitution at C-4 were confirmed by ¹H NMR, IR, MS spectral analyses and elemental analysis. The insecticidal activities were tested against fifth-instar larvae of Pieris rapae and the third-instar larvae of Cullex pipiens pallens at concentrations of 250 and 10 μg ml⁻¹. Four derivatives of PPT, 4.1, 4.2, 4.3 and 4.5, showed higher insecticidal activities against P. rapae than PPT, while three derivatives of PPT, 4.4, 4.5 and 4.6, displayed higher mosquito larvicidal activity than PPT, with LC₅₀ values of 1.66, 3.96 and 1.54 mg l⁻¹, respectively. Interestingly, we also found that the pyridine ring derivatives of PPT showed delayed insecticidal activity, which is different from traditional neurotic insecticides. The results suggest that 4′-OCH₃ in the PPT derivatives is essential to keep the insecticidal activity and the insecticidal activities of pyridine ring derivatives of PPT are higher than that of the derivatives of 4′-DMEP, supporting PPT has the potential to be a lead structure of semi-synthetic insecticides.     

The toxic effects of pyrethroid deltamethrin on the common carp (Cyprinus carpio L.) embryos and larvae

Deltamethrin, a synthetic pyrethroid pesticide contaminating aquatic ecosystems as a pollutant, was investigated in the present study for toxic effects on embryos and larvae of common carp, Cyprinus carpio as a model. The control and five test experiments were repeated five times. The water temperature in the experimental units was kept at 24 ± 1 °C. The number of dead embryos significantly increased in response to deltamethrin concentrations 0.005, 0.05, 0.5, 5, 25, and 50 μg L⁻¹ (p<0.05 for each cases). Dose-response decreases in hatching success were recorded as 75.2, 64.6, 47.4, 26.0, 14.4, and 9.0%, respectively. The lowest concentration of deltamethrin (0.005 μg L⁻¹) produced a significantly decrease in number of dead larvae compared to control group (p<0.05). With increasing deltamethrin concentrations, the larvae exposed duration 1-48 h significantly increased the number of dead larvae (p<0.05 for each cases). The 48 h LC₅₀ values (with 95% confidence limits) of deltamethrin for common carp embryos and larvae were estimated as 0.213 (0.103-0.404) and 0.074 (0.011-0.260) μg L⁻¹, respectively. The results provide evidence that deltamethrin pollution may have an adverse effect on the reproduction and development of carp, which should be considered when this chemical is used in agricultural areas near aquatic ecosystems.     

Comparative efficacy of strobilurin fungicides against downy mildew disease of pearl millet

Three commercial formulations of strobilurins, viz., azoxystrobin, kresoxim-methyl, and trifloxystrobin were evaluated for their efficacy against pearl millet downy mildew disease caused by Sclerospora graminicola. In vitro studies revealed inhibition of S. graminicola sporulation, zoospore release, and zoospore motility at 0.1-2 μg ml⁻¹ of all the three fungicides. The fungicides were evaluated for phytotoxic effects on seed quality parameters and for their effectiveness against downy mildew disease by treating pearl millet by: (1) seed dressing, (2) seed dressing followed by foliar spray, and (3) also by foliar spray alone. The highest non-phytotoxic concentrations of 5, 10, and 10 μg ml⁻¹ for azoxystrobin, trifloxystrobin, and kresoxim-methyl, respectively, were selected for further studies. Under greenhouse conditions, these fungicides showed varying degrees of protection against downy mildew disease. Among the three fungicides, azoxystrobin proved to be the best by offering disease protection of 66%. Further, seed treatment along with foliar application of these fungicides to diseased plants showed enhanced protection against the disease to 93, 82, and 62% in treatments of azoxystrobin, kresoxim-methyl and trifloxystrobin respectively. Foliar spray alone provided significant increase in disease protection levels of 91, 79, and 59% in treatments of azoxystrobin, kresoxim-methyl, and trifloxystrobin, respectively. Disease curative activity of azoxystrobin was higher compared to trifloxystrobin and kresoxim-methyl. Tested fungicides showed weaker translaminar activity, as the disease inhibition was marginal when applied on adaxial leaf surface. Partial systemic activity of azoxystrobin was evident by root uptake, while trifloxystrobin and kresoxim-methyl showed lack of systemic action in pearl millet. A trend in protection against downy mildew disease similar to greenhouse results was evident in the field trials. Grain yield was significantly increased in all strobilurin fungicide treatments over control and maximum increase in yield of 1673 kg ha⁻¹ was observed in combination treatments of seed treatment and foliar spray with azoxystrobin.     

Oxygen consumption and ammonia excretion of the freshwater crab Trichodactylus borellianus exposed to chlorpyrifos and endosulfan insecticides

The effects of lethal and sublethal concentrations of chlorpyrifos and endosulfan on oxygen consumption and ammonia excretion rate of the crab Trichodactylus borellianus were evaluated. Oxygen consumption and energy expenditure had significant effect in relation to exposure times. Regarding endosulfan, a significant difference in consumption among times of exposure was registered in 625 μg L⁻¹. Moreover, at the highest concentration, energy expenditure rate was observed stabilized during 1-3 h. A significant increase in ammonia excretion was evidenced in 150 and 300 μg L⁻¹ of chlorpyrifos. The O:N ratio showed a decrease in chlorpyrifos and in 2500 μg L⁻¹ of endosulfan. This indicated a shift towards protein primary metabolism. An increment in the O:N ratio was observed in the lower endosulfan solutions. The relation oxygen:nitrogen showed a shift towards lipid and carbohydrate primary metabolism. This work indicated the complexity of the metabolism in the freshwater crab affected by xenobiotic elements.     

Cytogenetic effects of commercially formulated atrazine on the somatic cells of Allium cepa and Vicia faba

In the present study cytogenetic effects of atrazine herbicide, were examined on the root meristem cells of Allium cepa and Vicia faba. Test concentrations were chosen by calculating EC₅₀ values of formulated atrazine against both the test systems which determined to be 30 mg l⁻¹ for A. cepa and 35 mg l⁻¹ for V. faba, respectively. For cytogenetic effects root meristem cells of A. cepa were exposed to 15, 30 or 60 mg l⁻¹ whereas V. faba to 17.5, 35 or 70 mg l⁻¹ for 4 or 24 h. Roots exposed for 4 or 24 h, after sampling, were left in water for 24 h recovery and sampled at 24 h post-exposure. A set of onion bulbs or seedlings of V. faba exposed to DMSO (0.3%) was run parallel for negative control. Treatment of atrazine significantly and dose-dependently inhibited the mitotic index (MI) and induced micronucleus formation (MN) chromosome aberrations (CA) and mitotic aberrations (MA) in both the test systems at 4 or 24 h. Root meristem cells examined at 24 h post-exposure also revealed significant (p < 0.001) frequencies of MN, CA or MA despite considerable decline. Chromosome breaks and fragments were found to be major CA whereas C-metaphase, chromosome bridges and laggards were prevalent MA. Results of our study, indicate that atrazine may produce genotoxic effects in plants. Further, both the plant bioassays found to be sensitive indicators for the genotoxicity assessment as the outcome of majority of in vivo/in vitro mammalian tests are comparable.     

Inhibitory effects of Schiff analogs of salicylidene aniline on phenoloxidase from Pieris rapae L. (Lepidoptera: Pieridae)

In order to gain insight into the development of insecticides with novel modes of action, the effects of salicylidene aniline (a), salicylidene-4-chloroaniline (b), salicylidene-4-bromoaniline (c), and salicylidene-4-nitroaniline (d) on partially purified phenoloxidase (PO) from Pieris rapae L. were investigated. The results showed that the 4 compounds could inhibit PO activity, and the inhibitor concentrations leading to a loss of 50% activity (IC₅₀) were estimated to be 0.025 mmol L⁻¹, 0.732 mmol L⁻¹, 0.471 mmol L⁻¹, and 0.675 mmol L⁻¹, respectively. Meanwhile, all the inhibitors showed reversible competitive inhibition, except (d), which showed reversible mixed inhibition. The K_I values were determined as 0.106 mmol L⁻¹, 10.059 mmol L⁻¹, 8.390 mmol L⁻¹, and 20.198 mmol L⁻¹ for the four compounds, respectively. The UV-vis spectra of (a) and (d) in the presence of copper ions and the enzyme showed that (a) could directly chelate the copper ions of PO; however, (d) could neither chelate the additional copper ions nor the copper ions of PO.     

Purification, characterization and inhibition studies of α-amylase of Rhyzopertha dominica

Rhyzopertha dominica causes extensive damage to stored wheat grains. α-Amylase, the major insect digestive enzyme, can be an attractive candidate to control the insect damage by inhibiting the enzyme through α-amylase inhibitors. R. dominica α-amylase (RDA) was purified to homogeneity by differential ammonium sulphate fractionation, Sephadex G-25 and Sephadex G-100 column chromatography. The homogenous α-amylase has a molecular weight of 52 kDa. The pH optima was 7.0 and temperature optima was 40 °C. Activation energy of RDA was 3.9 Kcal mol⁻¹. The enzyme showed high activity with starch, amylose and amylopectin whereas dextrins were the poor substrates. The purified enzyme was identified to be α-amylase on the basis of products formed from starch. The enzyme showed Km of 0.98 mg ml⁻¹ for starch as a substrate. Citric acid, oxalic acid, salicylic acid, HgCl₂, tannic acid and α-amylase inhibitors from wheat were inhibitors whereas; Ca²⁺ and Mg²⁺ were the activators of RDA. Ki values calculated from Dixon graphs with salicylic acid, citric acid, oxalic acid and wheat α-amylase inhibitors were 6.9, 2.6-8.2, 3.2 mM and 0.013-0.018 μM, respectively. The Lineweaver-Burk plots with different inhibitors showed mixed type inhibition. Wheat α-amylase inhibitor showed mainly competitive inhibition with some non-competitive behaviour and other inhibitors showed mainly non-competitive inhibition with some un-competitive behaviour. Feeding trials with salicylic acid, citric acid, oxalic acid and wheat α-amylase inhibitor showed significant effect of salicylic acid and oxalic acid along with wheat α-amylase inhibitor in controlling the multiplication of R. dominica.     

Comparison of kinetic properties of a hydrophilic form of acetylcholinesterase purified from strains susceptible and resistant to carbamate and organophosphorus insecticides of green rice leafhopper (Nephotettix cincticeps Uhler)

A hydrophilic form of acetylcholinesterase (AChE) was purified from N-methyl carbamate susceptible (SA) and highly N-methyl carbamate-resistant (N3D) strains of the green rice leafhopper (GRLH), Nephotettix cincticeps Uhler. Both of purified AChE from SA and N3D strains displayed the highest activities toward acetylthiocholine (ATCh) at pH 8.5. In the SA strain, the optimum concentrations for ATCh, propionylthiocholine (PTCh), and butyrylthiocholine (BTCh) were about 1 × 10⁻³, 2.5 × 10⁻³, and 1 × 10⁻³ M, respectively. However, in the N3D strain, substrate inhibition was not identified for ATCh, PTCh, and BTCh to 1 × 10⁻² M. The K_m value in the SA strain was 51.1, 39.1, and 41.6 μM and that in the N3D strain was 91.8, 88.1, and 85.2 μM for ATCh, PTCh, and BTCh, respectively. The K_m value in the N3D strain indicated about 1.80-, 2.25-, and 2.05-fold lower affinity than that of the SA strain for ATCh, PTCh, and BTCh, respectively. The V_max value in the SA strain was 70.2, 30.5, and 4.6 U/mg protein and that in the N3D strain was 123.0, 27.0, and 14.5 U/mg protein for ATCh, PTCh, and BTCh, respectively. The V_max value in the N3D strain was 1.75- and 3.15-fold higher for ATCh and BTCh than that in the N3D strain. However, it was 1.13-fold lower for PTCh. The increased activity of AChE in the N3D strain is due to the qualitatively modified enzyme with a higher catalytic efficiency. The bimolecular rate constant (k_i) for propoxur was 27.1 × 10⁴ and 0.51 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain and that for monocrotophos was 0.031 × 10⁴ and 2.0 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain. AChE from the N3D strain was 53-fold less sensitive than SA strain to inhibition by propoxur. In contrast, AChE from the N3D strain was 65-fold more sensitive to inhibition by monocrotophos than AChE from the SA strain. This indicated negatively correlated cross-insensitivity of AChE to propoxur and monocrotophos.     

Ultra-structural changes in the integument induced by the use of three of six forms of allylisothiocyanate tested against Plutella xylostella and Pieris rapae larvae

The insecticidal activity of four forms of Hong Jing (HJ) allylisothiocyanate (AITC), AITC + cypermethrin (HJ_A, HJ_B, and HJ_C) with ratio of (1:1, 4:1, and 2:1), pure AITC (HJ_D), and two forms of Hong Du (HD) AITC, AITC + chlorpyrifos (HD_A and HD_B) with ratio of (2:1 and 2:1), respectively, were studied on the major cruciferous insect larvae Plutella xylostella (L.) and Pieris rapae (L.) by combining both spraying and dipping methods. The P. rapae was more susceptible than P. xylostella larvae. The LC₅₀ values 72 h after treatment of AITC forms (HJ_B, HJ_A, HJ_C, HJ_D, HD_B, and HD_A) on the P. rapae were; 0.07, 0.08, 0.16, 0.83, 0.26, 1.08 gL⁻¹, and 0.69, 0.26, 5.45, 0.93, 3.01, 5.98 gL⁻¹ on the P. xylostella, respectively. The toxicity of some of the AITC forms was very close to or better than that of the commercial contact insecticides such as chlorpyrifos (LC₅₀ = 0.03 and 0.04 gL⁻¹ on P. rapae and P. xylostella, respectively), and cypermethrin (0.65 and 0.78 gL⁻¹, respectively, against P. rapae and P. xylostella). The ultrastructural studies on the integument of the third larval instar of P. xylostella treated by sub-lethal concentration (LC₂₀) of HJ_B, HJ_D, and HD_B were carried out by using transmission electron microscope. The more pronounced alterations in the hypodermis and mitochondria cells. They exhibited changes in all treated samples. The hypodermis was almost completely destroyed, and the mitochondria exhibited morphological alterations, represented by enlargement, matrix rarefaction and vacuolization of the mitochondria matrix, quantity of cristae reduced, and density electron matrix lessened. These AITC forms have potential as contact insecticides, and the ultra structural observations confirm the insecticidal efficiency of different AITC forms on P. rapae and P. xylostella.     

Ameliorative effects of Mesorhizobium sp. MRC4 on chickpea yield and yield components under different doses of herbicide stress

The present study was conducted to assess the plant growth promoting activities of Mesorhizobium sp. in the presence of technical grade herbicides and its ameliorating effects on herbicide toxicity to chickpea grown in herbicide treated soils. The quizalafop-p-ethyl and clodinafop-tolerant Mesorhizobium isolate MRC4 recovered from the nodules of chickpea plants significantly produced IAA, siderophores, hydrogen cyanide and ammonia in medium amended with or without technical grade quizalafop-p-ethyl and clodinafop. Quizalafop-p-ethyl at 40, 80 and 120 μg kg⁻¹ soil and clodinafop at 400, 800 and 1200 μg kg⁻¹ soil in general, decreased the growth attributes of chickpea plants inoculated with Mesorhizobium MRC4 and un-inoculated chickpeas. The three concentrations of quizalafop-p-ethyl were comparatively more toxic and substantially decreased biomass, nodulation and leghaemoglobin content, nutrient uptake, seed yield and grain protein over the un-inoculated chickpea. Interestingly, Mesorhizobium isolate MRC4 with any concentration of the two herbicides significantly increased the measured parameters when compared to the plants grown in soils treated solely (without inoculant) with similar concentration of each herbicide. Conclusively, Mesorhizobium isolate MRC4 could be exploited as bio-inoculant for facilitating chickpea growth under herbicide stress.     

Binding of phenthoate to bovine serum albumin and reduced inhibition on acetylcholinesterase

Organophosphorus pesticides (OPs) are of environmental significance due to their high toxicity to animals. Binding to plasma proteins may effective influence the toxicological properties of xenobiotics. In an attempt to evaluate the affinity of phenthoate (PTA) to bovine serum albumin (BSA) and inhibitory ability of bound PTA to acetylcholinesterase (AChE), we investigated the interactions between phenthoate (PTA) and bovine serum albumin (BSA) using tryptophan fluorescence quenching and subsequent inhibition on AChE activity by PTA. The results showed that PTA caused the fluorescence quenching of BSA because of the formation of a PTA-BSA complex. Quenching constants (K_sv), determined using the Sterns-Volmer equation to provide a measure of the binding affinity between PTA and BSA at 303, 306, 310 and 313 K were (3.4295 ± 0.0763) × 10⁻⁴, (3.2446 ± 0.0635) × 10⁻⁴, (3.0434 ± 0.0856) × 10⁻⁴ and (2.8262 ± 0.0569) × 10⁻⁴ M⁻¹, respectively. The thermodynamic parameters, ΔH and ΔS were −25.04 kJ mol⁻¹ and 168.94 J mol⁻¹ K⁻¹, respectively, which indicated that the electrostatic interactions played a major role in PTA-BSA association. The presence of BSA consistently reduced the inhibitory ability of PTA on AChE, with the relative activity being increased from 46.98 to 61.71% for the concentration range of BSA between 0 and 4.0 g L⁻¹.     

Effects of insecticides on plant-growth-promoting activities of phosphate solubilizing rhizobacterium Klebsiella sp. strain PS19

In this study, four technical grade insecticides, fipronil, pyriproxyfen, imidacloprid and thiamethoxam were applied at the recommended and the higher doses to investigate their effects on plant growth-promoting activities of phosphate-solubilizing Klebsiella sp. strain PS19, isolated from mustard rhizosphere. All tested insecticides displayed a concentration-dependent inhibition in plant growth promoting traits, like, inorganic phosphate solubilization, biosynthesis of phytohormones and siderophores, of rhizobacterial strain PS19. For example, the phosphate-solubilizing activity of Klebsiella sp. PS 19 was reduced maximally by 95%, at 3900 μg l⁻¹ pyriproxyfen over control. At the recommended rate, the magnitude of toxicity of insecticides to plant growth promoting traits was less severe compared to the higher doses. The sequence of insecticide-toxicity expressed as percent decrease, determined at highest dose rate of each insecticide, over control was: pyriproxyfen (95) = imidacloprid (95) > thiamethoxam (94) > fipronil (85), for phosphate-solubilizing activity while for salicylic acid (SA) it was: thiamethoxam > pyriproxyfen = imidacloprid > fipronil. The impact of the highest dose rate of insecticides on 2,3-dihydroxybenzoic acid (DHBA) was almost equal to those observed for SA. Thiamethoxam decreased the indole acetic acid (IAA) synthesis maximally by 86% whereas fipronil had least toxicity and reduced it by 67% relative to the control. Among the experimental insecticides, pyriproxyfen at 3900 μg l⁻¹ in general, had the greatest toxic effects for plant growth promoting activities of the test strain. The study inferred that insecticides affect the plant beneficial activities of rhizobacteria adversely. These findings are likely to add a new insight into the pest management practices.     

Oligochitosan induces cell death and hydrogen peroxide accumulation in tobacco suspension cells

Oligochitosan has been shown to induce several plant defense responses. In the present work, the effect of oligochitosan on tobacco cell survival was investigated. The results showed that oligochitosan caused tobacco cell death in a dose-dependent manner. About 40.6 % tobacco cells died when cultured for 72 h after 500 μg ml⁻¹ oligochitosan treatment. Certain aspects of this cell death process appeared to be similar to apoptosis in animal cells. These included shrinkage of cytoplasm and condensation of chromatin. Oligochitosan also induced H₂O₂ accumulation in tobacco cell suspension culture. The role of H₂O₂ in the signal transduction that leads to cell death was investigated. Co-treatment of tobacco cells with oligochitosan and catalase inhibited H₂O₂ accumulation but did not inhibit the induction of cell death. The results suggested that apoptosis-like cell death of tobacco cells induced by oligochitosan is independent of H₂O₂ signal pathway.     

Nile tilapia (Oreochromis niloticus), liver morphology, CYP1A activity and thyroid hormones after Endosulfan dietary exposure

Endosulfan is a worldwide used insecticide suspected to be highly toxic to aquatic organisms, including fish. Most of the available studies have focused in water exposures, although this pollutant can be transferred through food chain. Therefore, in the present study, the effects of Endosulfan on tilapia (Oreochromis niloticus), when administered through the diet. Fish were fed 21 days with diets containing 1 and 0.5 μg g⁻¹ of Endosulfan, after which qualitative histological liver analysis showed that Endosulfan induced hepatocyte destruction, vessel endothelium rupture and increased melanomacrophages aggregates. To test lower environmentally relevant doses of Endosulfan could induce hepatic damage, as well as other negative effects, such as altered phase I metabolism and plasma thyroid hormone levels. Hence, tilapia were orally exposed to 0.1 and 0.001 μg g⁻¹ for 35 days. Low environmentally realistic doses of Endosulfan were still able to induce liver histopathological damage such as increased hepatocyte vacuolization and increased eosinophil granular cell aggregates. Liver cytochrome P450 1A activity, evaluated through ethoxyresorufin-o-deethylase (EROD), was enhanced in tilapia exposed to 0.001 μg g⁻¹, whereas the highest dose had no measurable effects in this enzyme activity. Fish exposed to 0.1 μg g⁻¹ of Endosulfan had depressed T4 plasma levels. Overall, the results of the present study further demonstrate the toxic effects of Endosulfan in tilapia when administered in the diet at environmentally relevant concentrations, which indicates that in the field food chain transfer may also be an importance source of this pollutant.     

Effect of fenvalerate on oxidative stress biomarkers in the brackish water prawn Penaeus monodon

The toxicity of fenvalerate to the prawn Penaeus monodon was evaluated using biomarkers of stress. In a preliminary bioassay test, P. monodon was exposed to a series of fenvalerate concentrations, which showed 4, 6.5 and 8.5 μg L⁻¹ to be sublethal, median lethal and lethal, respectively. Sublethal effect of fenvalerate was further evaluated in hepatopancreas, muscle and gills of prawns with reference to oxidative stress biomarkers. Significant induction of lipid peroxidation and glutathione-S-transferase activity was found in hepatopancreas, muscle and gills of prawns exposed to fenvalerate when compared to control (P < 0.001, P < 0.05 and P < 0.05). On the contrary, the activities of Superoxide dismutase, catalase, glutathione peroxidase, vitamin C, vitamin E and glutathione were found to be reduced in the experimental group of prawns when compared to control. The results suggest that the animals were under oxidative stress when exposed to sublethal concentration of fenvalerate.     

Avermectin exposure induces apoptosis in King pigeon brain neurons

The effect of avermectin was studied on King pigeon brain nerve cells by cytotoxicity [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide, MTT] and apoptosis [acridine orange/ethidium bromide (AO/EB) assay, transmission electron microscope (TEM) evaluation, measurement of mitochondrial membrane potential (Δψm), phosphatidylserine (PS) exposure, caspases activities, DNA fragmentation, reactive oxygen species (ROS) and caspase-3 mRNA expression] within the 2.5–10 μg L⁻¹ concentration-range. The results revealed that within the concentrations of 2.5–10 μg L⁻¹, avermectin showed obvious cytotoxicity and induced apoptosis in a dose-dependent manner to neurons of King pigeon in vitro. Cell viability were 99.93 ± 8.52%, 82.02 ± 4.99% and 78.23 ± 5.67% after 24 h of treatment with avermectin at the concentrations of 0, 2.5 and 5 μg L⁻¹, which decreased to 56.36 ± 2.17% of 10 μg L⁻¹. Treated cells showed typical apoptosis morphological changes including cytoplasmic vacuolation, chromatin condensation, unclear nuclear membrane and decreased/swollen mitochondria. Typical biochemical hallmarks of apoptosis including Δψm loss, PS exposure, activations of caspase-3, caspase-8 and caspase-9, DNA fragmentation were observed too. Moreover, the levels of ROS in the avermectin treatment groups increased significantly compared to control group. Furthermore, the caspase-3 mRNA levels increased significantly following AVM treatment. In conclusion, our experimental results show that avermectin has cytotoxicity to brain neurons of King pigeon in vitro and the mechanism of neurotoxicity induced by avermectin is closely related to apoptosis.