Different Concentrations Of Cypermethrin Research Articles

Evaluation of Acute Toxicity and Lethal Concentration (LC50) of Cypermethrin (25% EC) in Adults of Cyprinus carpio (Linnaeus 1758)

The present study attempted to determine the acute toxicity and medial lethal concentrations of Cypermethrin (25% EC) for common carp Cyprinus carpio using Finney’s static bioassay (1971), probit analysis method. The LC50 values for 24, 48, 72 and 96 hr were found to be 3.962 µl Lit-1, 3.767 µl Lit-1, 3.349 µl Lit-1 and 2.924 µl Lit-1 respectively. Fish (weight 90–100 g, length up to 18±2 cm) were exposed to different concentrations of cypermethrin which were 1.5 µl Lit-1, 2.0 µl Lit-1, 2.5 µl Lit-1, 3.0 µl Lit-1, 3.5 µl Lit-1, 4.0 µl Lit-1 and 4.5 µl Lit-1 up to 96 hr. LC50 value decreases with an increase in exposure time. During this exposure period, abnormal behaviors like restlessness, hyperactivity, erratic movements, increased opercular movements, and loss of equilibrium and response were noticed in carp. Over secretion of mucous all over the body surface along with respiratory stress and mortality was also observed.

Impact Assessment of Cypermethrin (A Pyrethroid) Induced Chronic Toxicity on Vitals of Adult Cyprinus carpio L.

The acute toxicity evaluation of cypermethrin, a pyrethroid to common carp i.e. Cyprinus carpio was done with an emphasis on histopathological effects. In this investigation, fish were exposed to different concentrations of Cypermethrin (25% EC) for 21 days. C. carpio were treated with different sublethal concentrations i.e. (5, 10, 15, and 20 percent of 96 hr LC50 value i.e. 2.924 µl/L) of cypermethrin for three different exposure periods, 7, 14, and 21 days. Control and exposed fish were sacrificed at an interval of 7 days and the vital tissues like brain, gills, and kidney were taken to analyze the histopathological alterations. During this experimental period, respiratory stress and erratic swimming activities, disrupted equilibrium, and response were observed which continuously varied with the increasing toxicant concentration. In gills, the proliferation of cells of filament, inflammation, hemorrhage, epithelial cell destruction, fusion of secondary lamellae, and necrosis were noticed. Hence it is concluded that cypermethrin poses a serious threat to aquatic fauna of the ecosystem which can be assessed via histological studies.

Assessment of the exposure of two pesticides on common carp (Cyprinus carpio Linnaeus, 1758): Are the prolonged biomarker responses adaptive or destructive?

Chlorpyrifos (CPF) and cypermethrin (CYP) are two insecticides that have a proven negative effect on non-target aquatic organisms when they enter the surface waters. However, literature on the comparative effects of these pesticides on important aquaculture fish species, such as common carp (Cyprinus carpio Linnaeus, 1758) is not yet scientifically detailed, especially over the long-term. The idea of conducting a long-term exposure is to find out how the observed biomarkers would change compared to the short-term exposure. In the natural environment, toxicants are not present alone, but in combination. By monitoring the long-term impact of individual substances, the state of aquatic ecosystems exposed to various toxicants could be predicted. Thus, this study aimed to evaluate the toxicity of different concentrations of CYP (0.0002, 0.0003, and 0.0006 μg/L) and CPF (0.03, 0.05, and 0.10 μg/L) in 50-L glass tanks on C. carpio, exposed for 30 days under laboratory conditions. A set of histological and biochemical biomarkers in the gills and liver were applied with the chemical analyses of water and fish organs. Furthermore, the condition and hepatosomatic index were calculated to assess the physiological status of the treated carps. The behavioral responses were also monitored, and the respiration rate was analyzed. The results suggest that CYP had a more prominent effect on the histological structure of fish organs, biochemical responses of anti-oxidant enzymes, behavior, and respiration rate compared to the effect of CPF. In addition, the results also indicate that the liver is more susceptible to chronic and chemically induced cellular stress compared to the gills, with overall destructive changes in the histological biomarkers rather than adaptive. Regardless of the scenario, our results provide novel insights into pesticide exposure and the possible biological impacts on economically important freshwater fish, exposed to lower CYP and CPF concentrations, based on the EU legislation (maximum allowable concentrations, MAC-EQS).

EFFECTS OF CYPERMETHRIN ON HAEMATOLOGICAL MARKERSIN WALLAGO ATTU

Wallago attu was exposed to five different concentrations of cypermethrin for 30 days and found a remarkable change in haemoglobin, TLC, PCV and TEC values. A surging rise was noticed in all the four parameters on exposure to the different concentration of cypermethrin on day 1 but there was a slight reduction in the haemoglobin content, PCV and TEC with a slight rise in TLC after few days. Wallago attu exposed to cypermethrin showed an increase in blood glucose level. Cypermethrin has potent piscicidal activity against Wallago attu and adversely affects.

Combination of cypermethrin and thymol for control of Rhipicephalus microplus: Efficacy evaluation and description of an action mechanism

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites in the tropical and subtropical regions of the world. Synthetic pyrethroids are widely used to control this tick, and the selection of resistant populations is a huge problem worldwide. The activity of thymol, a natural monoterpene, free or in combination with other compounds, has been demonstrated against different species of ticks. However, the mode of action is not fully understood. The present study aimed to evaluate the efficacy and the potential mode of action of the combination of cypermethrin and thymol on ticks from two populations with different levels of susceptibility to cypermethrin (low and high susceptibility). The isolated acaricidal activity of cypermethrin and thymol on larvae was carried out in different concentrations. The combination with different concentrations of cypermethrin and fixed concentrations of thymol (1300µg/mL for the low susceptibility population; 690µg/mL for the high susceptibility population) were performed. Adult engorged females were divided into five experimental groups (n=20): 1) Control group untreated; 2) Control group: 2.0% (v/v) DMSO; 3) Thymol group: 1300µg/mL thymol; 4) Cypermethrin group: 3700µg/mL cypermethrin; 5) Association of cypermethrin (3700µg/mL)+thymol (1300µg/mL). A subgroup was used to study the efficacy of the reproductive parameters and another subgroup, with ten adults from each treatment, was used to quantify thymol and cypermethrin by HPLC chromatographic analysis. All compounds tested were effective on larvae from both populations, and the combination with thymol decreased the LC50 of cypermethrin (232.4 to 52.7µg/mL) on the low-susceptibility population. The combination of thymol and cypermethrin was effective in both populations of R. microplus (reproductive performance of engorged females) when compared to the untreated control group, even with higher percent control values (pop. 1: 93.5±5.6% and pop. 2: 92.7±1.1%) than the group treated only with cypermethrin (pop. 1: 87.3±7.3% and pop. 2: 83.5±1.2%). From the HPLC analyzes, a higher concentration of cypermethrin (pop. 1: 30.3±6.9 and pop. 2: 45.4±17.7ng/mg) was detected in the tissues of engorged females treated with the combination compared to analyte concentrations in groups treated with cypermethrin only (pop. 1: 12.4±4.4 pop. 2: 25.5±9.4ng/mg). This was the first study to investigate the acaricidal efficacy of the combination of thymol+cypermethrin on R. microplus and demonstrate that the presence of thymol increases the concentration of cypermethrin in the internal tissues of engorged females through a possible mechanism for increasing the penetration of cypermethrin at the cuticular level.

Impacts of changes in temperature and exposure time on the median lethal concentrations (LC50) of a combination of organophosphate and pyrethroid in the control of Culex quinquefasciatus, say (Diptera: Culicidae)

Climate change factors such as rainfall, heat waves, rising temperatures and flooding have positively impacted insect vector population. This scenario poses considerable demand on chemical control. This study was carried out with the specific aim to examine the influence of changes in temperature and exposure time of C. quinquefasciatus to toxicities of pyrethroid (Cypermethrin), organophosphate (2, 2- dichlorovinyl dimethyl phosphate) and their mixtures. Eggs of C. quinquefasciatus were collected at the Federal University of Technology, Akure, Nigeria, in an area far from residential and cultivated zones, with a remote chance of the mosquitoes being exposed to insecticides. The eggs were allowed to hatch into larvae/pupae in the field at 27–29 °C temperature, 70–85% RH, 14:10 (L: D) photoperiod. F3 adult generation reared were transferred to the Entomology Laboratory and exposed to different concentrations of Cypermethrin and DDVP applied singly and in mixtures at varying temperatures and exposure time with mortality recorded. The median lethal concentration (LC50) values for the insecticides were higher when the insecticides were applied singly than when applied as mixtures. Therefore, mixtures of cypermethrin and DDVP have enhanced toxicity. Again, temperature changes also affect insecticide toxicity and because climate change has a characteristic temperature variability, it poses a barrier to insecticide toxicity. Hence, it is expedient to have a climate change adaptation policy in synergy with modality of chemical applications. Further study of toxico-kinetic of the insecticides in mosquito control is also recommended.

Cypermethrin- and fipronil-based insecticides cause biochemical changes in Physalaemus gracilis tadpoles.

Insecticides used for agricultural pest control, as cypermethrin-based insecticide (CBI) and fipronil-based insecticide (FBI), are constant threats to non-target aquatic organisms. This study aimed to investigate the effect of different concentrations of cypermethrin and fipronil on neurotoxicity and oxidative stress in Physalaemus gracilis. Physalaemus gracilis tadpoles were exposed to five insecticide concentrations and a control treatment, with six replicates. During the experimental period, the tadpole mortality rate was evaluated and after 168 h, the neurotoxic enzyme activity and metabolite quantification related to the antioxidant system were measured. Tadpoles reduced acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities when exposed to 20 μg L-1 CBI and at all FBI concentrations, respectively. Glutathione S-transferase (GST) and superoxide dismutase (SOD) activities showed an increase from concentrations of 6 μg L-1 and 20 μg L-1 of CBI, respectively. After exposure of P. gracilis tadpoles to FBI, inhibitions of AChE and BChE were observed at the highest concentrations evaluated (500 and 1500 μg L-1). SOD activity decreased from 50 μg L-1 of FBI; however, catalase (CAT) and GST activities and carbonyl protein levels increased, regardless of the evaluated dose. We observed that both insecticides promoted oxidative stress and neurotoxic effects in P. gracilis tadpoles. These results suggest that biochemical biomarkers can be used for monitoring toxicity insecticides for the purpose of preservation of P. gracilis.

Toxicological Responses of African Mud Catfish (Clarias gariepinus, Burchell, 1822) Fingerlings Exposed to Culture Water Contaminated with Different Concentrations of Cypermethrin

Toxicological Responses of African Mud Catfish (Clarias gariepinus, Burchell, 1822) Fingerlings Exposed to Culture Water Contaminated with Different Concentrations of Cypermethrin

Exposure to anti-mosquito insecticides utilized in rice fields affects survival of two non-target species, Ischnura elegans and Daphnia magna

Insecticides are commonly utilized to control mosquito larvae in rice fields. They can, however, have negative effects on both vertebrates and non-target invertebrate species. In this study, we examined the effects of pulse exposition to different concentrations of cypermethrin (0.15, 0.015, 0.0015 mg/L) and diflubenzuron (0.15, 0.015, 0.0015 mg/L) on egg hatching rate, larval growth, and larval survival in a damselfly, Ischnura elegans, and on survival of a crustacean, Daphnia magna. Insecticide exposure had significant negative effects on hatching rate in damselfly eggs. Exposed damselfly larvae also grew less and showed a higher mortality than control larvae. In Daphnia, the acute toxicity test (ISO 6341 in Water quality—determination of the inhibition of the mobility of Daphnia magna Straus (Cladocera, Crustacea)—acute toxicity test, Int Organ Stand Geneve, Geneva, 2012) showed an increased inhibition of mobility in the presence of insecticides. We observed a proportional response in relation to insecticide concentration, such that the highest exposure levels showed the largest reduction of vital performances. Our highest tested values correspond to those currently employed in agriculture. This study suggests that exposure to two common insecticides strongly affects non-target invertebrates even at very low concentration levels (cypermethrin 0.0015 mg/L and diflubenzuron 0.0015 mg/L).

Toxicity of cypermethrin on the embryo and larvae of Gangetic mystus, Mystus cavasius.

The objective of the present study was to elucidate the effects of cypermethrin on the embryo and the larvae of Gangetic mystus, Mystus cavasius. Therefore, fertilized eggs (n=100) and 1-day-old larvae (n=100) were exposed to six different concentrations of cypermethrin (0, 2, 4, 8, 16 and 32μg L-1) in each of the 18 plastic bowls. Each of the treatment and control was maintained in three replicates. The LC10 and LC50 values for Gangetic mystus embryos and larvae were calculated using probit analysis. Results showed the mortality of embryos significantly increased with increasing cypermethrin concentrations. The 24-h LC10 and LC50 (with 95% confidence interval) values of cypermethrin for embryo were 0.42 (0.14-0.81) and 5.60 (4.16-7.19) μg L-1, respectively. Hatching success decreased and mortality of larvae increased significantly with increasing cypermethrin concentrations. The 24-h LC10 and LC50 values (with 95% confidence limits) of cypermethrin for larvae were 1.72 (1.24-2.20) and 11.57 (10.09-13.42) μg L-1, respectively; the 48-h LC10 and LC50 for larvae were 1.34 (0.83-1.89) and 8.25 (6.87-9.91) μg L-1, respectively; the 72-h LC10 and LC50 for larvae were 1.13 (0.63-1.66) and 6.12 (4.91-7.47) μg L-1, respectively. Furthermore, results showed several malformations in embryos and larvae when exposed to the two highest concentrations of cypermethrin. The findings of the study suggest that 2μg L-1 cypermethrin concentration in the aquatic environment may have deleterious effects on the development and the reproduction of Gangetic mystus.

Total and differential white blood cell counts in Caiman latirostris after in ovo and in vivo exposure to insecticides

Agricultural activities associated mainly with soybean crops affect the natural environment and wildlife by habitat destruction and the extensive use of agrochemicals. The aim of this study was to evaluate immunotoxic effects of the insecticides cypermethrin (CYP) and endosulfan (END) in Caiman latirostris analyzing total blood cell count (TWBC) and differential white blood cell count (DWBC) after in ovo and in vivo exposure. Eggs (in ovo) and hatchlings (in vivo) from nests harvested in natural habitats were artificially incubated and reared under controlled conditions in the Proyecto Yacaré (Gob.Santa Fe/MUPCN) facilities. Exposure of embryos was performed by topication on the eggshell during the first stage of development. The treatments were distilled water (negative control; NC), ethanol (vehicle control; VC), four groups treated with different concentrations of CYP and four groups with END. In vivo exposure was performed by immersion; treatments were NC, VC, two groups exposed to CYP and two to END. After embryonic exposure to the insecticides, no differences were found in TWBC or DWBC among the neonates exposed to pesticides versus controls. In the in vivo scenario, similar results were obtained for TWBC, but DWBC data showed differences between NC hatchlings and CYP-1 hosts for heterophil, lymphocyte and monocyte levels, and between NC and END-1 hosts for lymphocyte and monocyte levels. Research on the effects of pesticide exposure on this species is of special interest not only to assess the impact on caiman populations, but also to further characterize the species as a potential sentinel of ecosystem health.

The in vitro effect of cypermethrin on quality and oxidative stress indices of rainbow trout Oncorhynchus mykiss spermatozoa

There is limited information on the scientific literature about the effect of in vitro exposure of fish sperm to pesticides. In vitro effect of cypermethrin on sperm quality and oxidative stress has not yet been fully investigated. Therefore, the effects of cypermethrin, a type II pyrethroid insecticide, on quality and oxidative stress of spermatozoa were examined in vitro. To explore the potential in vitro toxicity of cypermethrin, fish spermatozoa were incubated with different concentrations of cypermethrin (1.025, 2.05 and 4.1μg/l) for 2h. The motility rate and duration of sperm were determined after exposure to cypermethrin. Reduced glutathione (GSH), glutathione peroxidase (GSH-Px), catalase (CAT) and malondialdehyde (MDA) in spermatozoa were analyzed for determination of oxidant and antioxidant balance. Our results indicated that spermatozoa motility and duration significantly decreased with exposure to cypermethrin. Additionally, activity of GSH-Px (P<0.05) and MDA and GSH levels increased in a concentration-dependent manner while CAT activity decreased (P<0.05). Consequently, the oxidant and antioxidant status and sperm quality were affected by quantitative changes and different concentrations of cypermethrin.

Hepatic Enzymes Activity in the Fish Prochilodus Lineatus (Valenciennes, 1836) After Sublethal Cypermethrin Exposure

Prochilodus lineatus, a fish, was exposed to sublethal concentrations of cypermethrin: 0.075, 0.150, and 0.300μgL(-1) and a control group (without cypermethrin) for 96h. Five specimens were exposed in each concentration for triplicate (n=60). Hepatic biochemical values and behavioral changes were studied. The results revealed a significantly higher level of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase in hepatic tissue at different concentrations of cypermethrin tested compared to control (p<0.05). A decrease in total protein was observed in exposed groups but not significantly (p>0.05). This study provides information to know toxic mechanisms of cypermethrin on hepatic enzymes of P. lineatus that are poorly understood.

Alkaline Comet Assay for Genotoxic Effect Detection in Neotropical Fish Prochilodus lineatus (Pisces, Curimatidae)

Toxicants on fish may induce genetic alterations that can be used as genotoxic markers. We evaluated DNA damage using alkaline comet assay applied on erythrocytes after in vivo exposure of Prochilodus lineatus to different concentrations of Cypermethrin (0.300, 0.150, 0.075 and 0.000 microg/L) as a probable chemical mutagen. The results revealed a significantly higher level of DNA damage at all concentrations of Cypermethrin tested compared to control and background level (p < 0.05). We have standardized the technique for one of the most common native fish species that will be useful for biomonitoring genotoxicity in polluted waters of the region.

Evaluation of in vivo genotoxicity of cypermethrin in Drosophila melanogaster using the alkaline Comet assay.

The single cell gel electrophoresis (SCGE) assay, also known as the Comet assay, is one of the most promising genotoxicity tests developed in recent years to measure and analyse DNA damage in single cells. The present study was undertaken to assess the in vivo genotoxicity of the synthetic pyrethroid cypermethrin in brain ganglia and anterior mid gut of Drosophila melanogaster. Freshly emerged first instar larvae (22 +/- 2 h) were placed in different concentrations of cypermethrin (0.0004, 0.0008, 0.002, 0.2 and 0.5 p.p.m.) mixed in standard Drosophila food and allowed to grow. At 96 +/- 2 h, brain ganglia and anterior midgut from control and treated larvae were dissected out, single cell suspensions were prepared and a Comet assay was performed. Our results revealed a significant dose-dependent increase in DNA damage in the cells of brain ganglia and anterior midgut of D.melanogaster exposed to cypermethrin as compared with controls (P < 0.05 at 0.002 p.p.m.; P < 0.001 at 0.2 and 0.5 p.p.m.). The present study shows in vivo genotoxicity of cypermethrin even at very low concentrations, which proves D.melanogaster as a model for in vivo genotoxicity assessment using the Comet assay.

Toxicity of cypermethrin: hsp70 as a biomarker of response in transgenic Drosophila

Heat shock protein induction is often associated with a cellular response to a harmful environment or to adverse life conditions. The main aims of our study were (1) to evaluate the cytotoxic potential of cypermethrin; and (2) to investigate the suitability of stress-induced heat shock protein Hsp70 as a biomarker for environmental pollutants in transgenic Drosophila melanogaster (Hsp70-lacZ)Bg9. Different concentrations of cypermethrin (0.002, 0.2, 0.5 and 50.0 p.p.m.) were mixed with food. Third instar larvae of transgenic Drosophila melanogaster were allowed to feed on these mixtures for different time intervals (2, 4, 6, 12, 24 and 48h). Following feeding, hsp70 induction and tissue damage were evaluated. In the highest concentration treatment group (50 p.p.m.), 100% larval mortality was recorded after 12 h exposure. Hsp70 was found to be induced even at the lowest concentration (0.002 p.p.m.) of the insecticide, while tissue damage was observed in the larvae exposed for 48 h. While an insignificant decline in hsp70 expression was observed in the larvae exposed to cypermethrin at a dietary concentration of 0.002 p.p.m. after 48 h compared with those exposed for 24 h, in the next two higher concentrations of the toxicant, a similar but significant decline in hsp70 expression was evident in the exposed larvae after 48 h. The present study reveals the cytotoxic potential of cypermethrin and further proposes that hsp70 induction in transgenic Drosophila melanogaster could be used as a sensitive biomarker in risk assessment.

Acute Mortality of Soft Shell Clam, Mya arenaria, Larvae, Green Sea Urchin Strongylocentrotus droenbachiensis, Larvae, and Rotifers, Brachionus plicatilis, Exposed to Cypermethrin (Excis ™)

ABSTRACT The acute effects of Cypermethrin (Excis (tm)) on soft shell clam, Mya arenaria, larvae, green sea urchin, Strongylocentrotus droenbachiensis, larvae, and rotifers, Brachionus plicatilis, were studied in the laboratory. Cypermethrin (Excis(tm)) is used at a concentration of 5 μg/L as a bath treatment of salmonids against sea lice, predominantly, Lepeophtheirus salmonis. Zooplankton were exposed for 1, 6, and 12 hours to different concentrations of Cypermethrin, at water salinity levels of 32 (±0.6) ppt and a temperature of 12° C. Clams, urchins, and rotifers were exposed to Cypermethrin concentrations of 0, 0.005, 0.05, 0.5, 5.0, 50, 500, 5,000, and 50,000 μg/L. These concentrations correspond to 0,1/1000,1/100,1/10,1,10,100,1,000, and 10,000 times the manufacturer's recommended treatment concentration. Only at concentrations of between 10-10 000 times greater than the recommended treatment dose of 5 μg/L, did Cypermethrin treatment cause statistically significant mortality in the clam larvae (P < 0.05), sea urchin larvae (P < 0.05) and rotifers (P < 0.05). The LC50 values for soft shell clam larvae mortality after 1, 6 and 12 hours of exposure were calculated at 13,490; 11,749; and 10,715 μg/L, respectively. For the sea urchin larvae the LC50 values after exposure for 1, 6, and 12 hour treatment durations were 21,5207; 39,716; and 16,982 μg/L, respectively. All LC50 values for the rotifer were > 50,000 μg/L. Soft shell clam larvae, green sea urchin larvae, and rotifers are not significantly affected by exposure to Cypermethrin concentrations below the manufacturer's recommended treatment dose.

EFFECT OF CYPERMETHRIN ON ISOLATED MALE AND FEMALE RAT HEPATOCYTES

Cypermethrin is a synthetic pyrethroid that belongs to a group of insecticides with low mammalian toxicity but high insecticidal activity. The present study was designed to investigate the toxicity of cypermethrin on freshly isolated hepatocytes from male and female rats. Hepatocytes were harvested by a collagenase perfusion technique and were exposed to different concentrations of cypermethrin (100, 200, 400, or 800 ng/2×106 cells) for up to 2 h. Cell viability and the leakage of aspartate transaminase (AST) and alanine transaminase (ALT) were determined throughout the incubation period. The cell viability of the hepatocytes from male and female rats exposed to 400 ng and 800 ng was significantly reduced after 60 and 30 min of incubation, respectively. With cells from female rats, viability was also reduced upon exposure to 200 ng cypermethrin for 2 h. The decrease in cell viability was dose and time dependent. The leakage of ALT and AST was significantly increased with 400 and 800 ng concentrations at 60 and 30 min, respectively. ALT leakage from female hepatocytes was significantly increased at 60 min of incubation with the 200-ng dose, whereas 2 h of incubation was required for the leakage of ALT from the cells of male rats. The present data indicate that cypermethrin has toxic effects on male and female rat hepatocytes in a dose- and time-dependent manner. The data suggest that female rat hepatocytes may be more sensitive to the toxic effects of cypermethrin than male cells.

EFFECT OF CYPERMETHRIN ON ISOLATED MALE AND FEMALE RAT HEPATOCYTES

Abstract Cypermethrin is a synthetic pyrethroid that belongs to a group of insecticides with low mammalian toxicity but high insecticidal activity. The present study was designed to investigate the toxicity of cypermethrin on freshly isolated hepatocytes from male and female rats. Hepatocytes were harvested by a collagenase perfusion technique and were exposed to different concentrations of cypermethrin (100, 200, 400, or 800 ng/2×106 cells) for up to 2 h. Cell viability and the leakage of aspartate transaminase (AST) and alanine transaminase (ALT) were determined throughout the incubation period. The cell viability of the hepatocytes from male and female rats exposed to 400 ng and 800 ng was significantly reduced after 60 and 30 min of incubation, respectively. With cells from female rats, viability was also reduced upon exposure to 200 ng cypermethrin for 2 h. The decrease in cell viability was dose and time dependent. The leakage of ALT and AST was significantly increased with 400 and 800 ng concentrations at 60 and 30 min, respectively. ALT leakage from female hepatocytes was significantly increased at 60 min of incubation with the 200-ng dose, whereas 2 h of incubation was required for the leakage of ALT from the cells of male rats. The present data indicate that cypermethrin has toxic effects on male and female rat hepatocytes in a dose- and time-dependent manner. The data suggest that female rat hepatocytes may be more sensitive to the toxic effects of cypermethrin than male cells.