Mixture Of Permethrin Research Articles

Probing the potential mechanism of permethrin exposure on Alzheimer's disease through enantiomer-specific network toxicology, multi-spectroscopic, and docking approaches

Latest observations indicated that exposure of organic environmental neurotoxins may increase the potential risk of Alzheimer's diseases (AD). As a suspected food-derived risk factor, permethrin, composed of cis-isomer and trans-isomer, is widely used as a broad-spectrum pyrethroid insecticide in agricultural crops for the arthropod pests controlling. Thus, evaluating the impact of permethrin exposure is of great importance to human health. In this study, we performed the toxicological network approach to decipher AD-related mechanisms of cis-permethrin and trans-permethrin. Based on the toxicological network construction and central network topological analysis, human serum albumin (HSA) was selected as the core targets in AD-related developing. From the analysis of the steady state and time-resolved fluorescence quenching of HSA in presence of permethrin mixture, it has been inferred that the nature of the quenching mainly originates from the dynamic modes. Experimentally, the thermodynamic parameters revealed hydrophobic interactions and van der Waals forces played a major role during quenching process. Tryptophan synchronous fluorescence spectra were blue shifted whereas the position of tyrosine synchronous spectra was red shifted during the complex formation. Three-dimensional fluorescence together with FT-IR experiment confirmed that permethrin caused the secondary structure changes in HSA. To better understand the binding patterns between HSA and cis/trans -permethrin, theoretical calculation and molecular docking were implemented. According to the electrostatic potential map, the electrophilic attack region corresponds for electron rich oxygen atoms, while the nucleophilic attack regions were mainly located at over the benzene rings and methyl on cyclopropane ring of permethrins. Docking results shown that cis-permethrin and trans-permethrin located in hydrophobic pocket nearby Domain IIA with the different binding affinity (−7.6 and −9.2 kcal/mol), which consistent with the competitive displacement experiment. All these findings generated in the present study facilitated the elucidation of the molecular mechanism details between permethrin mixture and HSA, which provided fresh insights into the links between environmental exposure and AD-related adverse health outcomes.

Vagus Nerve Stimulation Ameliorates Cognitive Impairment and Increased Hippocampal Astrocytes in a Mouse Model of Gulf War Illness

Gulf war illness (GWI), is a chronic multi-symptom illness that has impacted approximately one-third of the veterans who served in the 1990 to 1991 Gulf War. GWI symptoms include cognitive impairments (eg, memory and concentration problems), headaches, migraines, fatigue, gastrointestinal and respiratory issues, as well as emotional deficits. The exposure to neurological chemicals such as the anti-nerve gas drug, pyridostigmine bromide (PB), and the insecticide permethrin (PER), may contribute to the etiologically related factors of GWI. Various studies utilizing mouse models of GWI have reported the interplay of these chemical agents in increasing neuroinflammation and cognitive dysfunction. Astrocytes are involved in the secretion of neuroinflammatory cytokines and chemokines in pathological conditions and have been implicated in GWI symptomology. We hypothesized that exposure to PB and PER causes lasting changes to hippocampal astrocytes, concurrent with chronic cognitive deficits that can be reversed by cervical vagus nerve stimulation (VNS). GWI was induced in CD1 mice by injecting the mixture of PER (200 mg/kg) and PB (2 mg/kg), i.p. for 10 consecutive days. VNS stimulators were implanted at 33 weeks after GWI induction. The results show age-related cognitive alterations at approximately 9 months after exposure to PB and PER. The results also showed an increased number of GFAP-labeled astrocytes in the hippocampus and dentate gyrus that was ameliorated by VNS.

Effect of a combination of permethrin and diesel oil on <i>Rhipicephalus sanguineus</i> and <i>Ctenocephalides canis</i> in experimentally infested dogs

Rhipicephalus sanguineus (Brown dog tick) and Ctenocephalides canis (dog and cat flea) cause heavy economic burden for dog owners in Nsukka, south-east, Nigeria, and are also major cause of vector-borne diseases worldwide. A total of 40 apparently healthy dogs were randomly assigned to 3 groups (A, B and C) and experimentally infested with Rhipicephalus sanguineus and Ctenocephalides canis. Each dog in Group A (n = 10) was treated with a mixture of permethrin and diesel oil while Groups B (n = 6) and C (n = 4) were treated with permethrin and diesel oil respectively. The remaining dogs in each group served as controls. Parasites were counted 48th hour post-treatment and efficacy estimated as percentage reduction in live parasites in treated groups compared to untreated groups. In Group A the average percentage efficacy was 99.7% while in groups B and C it was 98.3% and 72.1% respectively for R. sanguineus, Geometric mean of live parasites between treated and control groups was significantly different (p<0.05) for every day in Groups A, B and C. Tick and flea numbers can be reduced in dogs by the application of diesel oil as an acaricide.
 Keywords: Dogs; tick and flea control; diesel fuel oil; permethrin.

In vitro exposure to pyrethroid-based products disrupts development of mouse preimplantation embryos

The objective of this study was to evaluate the potential toxicity of pyrethroids (deltamethrin, permethrin, fenvalerate, λ-cyhalothrin), commercial pyrethroid-based products DECIS EW 50 (deltamethrin mixture), TOP SPOT ON STRONGER (permethrin mixture), as well as related secondary ingredients on mouse preimplantation embryo development.Two-cell stage embryos were in vitro cultured with addition of the listed chemicals until blastocyst formation. All active pyrethroids negatively affected embryonic development at 1000 μM concentration. Decreased quality of obtained blastocysts in permethrin, fenvalerate and λ-cyhalothrin-treated embryos was revealed as well. Deltamethrin showed harmful impact on embryo development at 100 μM concentration. Lower concentrations of pyrethroids (1, 10 μM) had no effect on embryo development.The presence of DECIS EW 50 containing deltamethrin at 100 μM caused degeneration of all embryos. Similarly, TOP SPOT ON STRONGER containing 100 μM of permethrin impaired embryonic development and quality of obtained blastocysts. Evaluated secondary ingredients (butylhydroxyanisol, butylhydroxytoluen, butylparaben and cyclohexanone) at corresponding concentrations showed damaging impact on preimplantation embryo development as well.Our results indicate that the embryotoxic potential of active pyrethroids is relatively low, whereas pyrethroid-based products have relatively high potential to impair mouse preimplantation development. Embryotoxicity of commercial products is probably attributable to the presence of secondary ingredients.

Synergistic effect and field control efficacy of the binary mixture of permethrin and chlorpyrifos to brown planthopper (Nilaparvata lugens)

Abstract The brown Planthopper (BPH), Nilaparvata lugens is a major pest of rice production in tropical Asia. The appearance of insecticide resistance challenges the control of BPH in field. The development of new insecticide is expensive and time-consuming. Thus, the precise and proper use of existing compounds becomes an important issue in resistance management of this pest. In this study, five commercial insecticides of BPH (permethrin, chlorpyrifos, imidacloprid, clothianidin and thiamethoxam) were tested to explore the toxicity of the binary mixture between different kinds of insecticides. In all combinations of mixture, the mixtures of permethrin and chlorpyrifos displays synergistic effect at three different mixture ratios (1:1, 1:10 and 10:1). The strongest synergism observed in permethrin/ chlorpyrifos mixtures at 1:1 ratio (Combination index, CI = 0.39). Addition of enzyme inhibitor followed by detoxification enzyme activity assays suggested that the mechanism of synergistic effect of permethrin/chlorpyrifos mixture may result from inhibition of the cytochrome P450 monooxygenase and esterase activity. This inference can be supported through two lines of evidence. One is decrease of toxicity when permethrin/chlorpyrifos mixture in a 1:1 ratio plus triphenyl phosphate (TPP) or piperonyl butoxide (PBO), but increase of toxicity when permethrin/chlorpyrifos mixture in a 10:1 ratio plus TPP or PBO. Another is exposure of the 3rd instar nymphs to permethrin/chlorpyrifos mixture after 72 h also significantly decreased both cytochrome P450 monooxygenases and esterase activity. Further field trail showed the mixture of 50 ppm permethrin +50 ppm chlorpyrifos increased the field control efficiency significantly rather than permethrin alone or chlorpyrifos alone. Our study indicated that the mixture of permethrin and chlorpyrifos in a 1:1 ratio might be an effective method for the control of BPH in paddy field.

Subchronic toxicity of low dose propoxur, permethrin, and their combination on the redox status of rat liver

Carbamates and pyrethroids are widely used pesticides. However, their joint toxicity at low doses with long-term exposure remains unknown. Therefore, we investigated the subchronic joint hepatotoxicity of the two representative pesticides within these two classes, i.e., propoxur (PR) and permethrin (PE) in rats. The male Wistar rats were orally treated with three different doses of PR, PE and their mixtures for 90 consecutive days. Liver weight, serum clinical chemistry parameters and histopathological changes were measured to access the hepatotoxicity. In addition, oxidative stress markers in liver were measured using biochemical assays. The results showed that PR reduced liver weight and lead to prominent liver histological changes. Moreover, PR dose-dependently induced lipid peroxidation and reduced superoxide dismutase activity. In contrast, PE induced a relatively mild hepatotoxicity. Intriguingly, the mixture of PR and PE did not reduce liver weight or increase serum aspartate transaminase activity. In addition, the mixture did not reduce the antioxidant enzyme activity as PR did. Thus, these results showed that PR induced prominent hepatotoxicity with subchronic exposure, and there is a potential antagonistic interaction between PR and PE on the oxidative damage in liver of rats.

Effectiveness of emergent and submergent aquatic plants in mitigating a nitrogen–permethrin mixture

ABSTRACTHydraulically connected wetland microcosms (∼50 L) in series were used to test the effectiveness of varying combinations of two common aquatic vascular plants, parrot feather (Myriophyllum aquaticum) and cattail (Typha latifolia), for mitigating contamination from a mixture of nitrogen (ammonium nitrate) and permethrin. The upstream series included Myriophyllum only (M) and Typha only (T) while the combination upstream effluent into downstream series included Myriophyllum into Myriophyllum (M + M) and Typha into Myriophyllum (T + M). During flow, M into M + M more efficiently mitigated nitrogen than T into T + M. Post-flow, nitrogen removal efficiency was greater for T versus M and M + M versus T + M. Mean aqueous dissipation half-lives (t1/2) of NH4-N and NO3-N were more rapid in T than M treatments. Ammonium and nitrate t1/2 was highly correlated with aquatic plant above-ground shoot biomass. Permethrin mitigation efficiencies and t1/2 were not significantly affected by plant species either singly or in combination. Trans-permethrin t1/2 was moderately correlated with plant biomass, but not cis-permethrin t1/2. Results of this study indicate differences in aquatic plant species and flow path influence nitrogen removal but not permethrin. However, plant species appears less important than overall plant biomass in ascertaining aquatic plant effectiveness in mitigating a nitrogen–permethrin mixture.

Do Varying Aquatic Plant Species Affect Phytoplankton and Crustacean Responses to a Nitrogen-Permethrin Mixture?

Hydraulically connected wetland microcosms vegetated with either Typha latifolia or Myriophyllum aquaticum were amended with an NH4NO3 and permethrin mixture to assess the effectiveness of both plant species in mitigating effects of the pollutant mixture on phytoplankton (as chlorophyll a) and Hyalella azteca. Phytoplankton grew in response to increased NH4NO3 in the presence of all plant species, but was unaffected by exposure to permethrin. H. azteca responses occurred rapidly (0.17days), was mitigated within 1-2days, and aqueous toxicity was unaffected by plant species type. A toxic unit model approach ascertained primary toxicity was permethrin with minimal additional toxicity from NH4NO3. Varying aquatic plant species had only modest influences on phytoplankton responses and no observable influence on animal responses during nitrogen-permethrin mixture exposures. As a result, both T. latifolia and M. aquaticum can be used as part of an effective agricultural best-management practice system for mitigating pollutant impacts of agricultural run-off.

Does cadmium affect the toxicokinetics of permethrin in Chironomus dilutus at sublethal level? Evidence of enzymatic activity and gene expression

Pyrethroids and metals were simultaneously detected in aquatic environment and showed antagonistic lethality to the benthic invertebrate, Chironomus dilutus. Accelerated biotransformation of pyrethroids in organism by the presence of metals was proposed as the likely reason for the antagonism. Mechanistic explanation for the role of toxicokinetics of pyrethroids in the antagonistic interaction would help better understanding the reasons for the joint toxicity. The goal was achieved in the current study by evaluating the impact of cadmium on toxicokinetic parameters of permethrin in C. dilutus, and by explaining the interaction through quantifying the activity and gene expression of biotransformation-related enzymes. Toxicokinetic parameters were simulated using a first-order kinetic model. Bioconcentration factors and uptake and elimination rate constants for permethrin were not significantly changed with the addition of cadmium at sublethal level, neither did the activity of enzymes, including glutathione S-transferase (GST), carboxylesterase (CarE), catalase and lipid peroxidation. Yet, the activities of metabolism-related enzymes (GST and CarE) showed an elevating tendency with adding cadmium. Furthermore, the expression of metabolism-related genes, including cytochrome P450 and glutathione S-transferase genes were significantly up-regulated in C. dilutus exposed to a mixture of permethrin and cadmium compared with permethrin only. Although co-exposure to cadmium did not induce toxicokinetic changes of permethrin in C. dilutus, it did enhance the activity of metabolic enzymes which were encoded by the metabolism-related genes, suggesting an acceleration of biotransformation of permethrin to less toxic metabolites in the midges. This possibly explained the antagonistic interaction for permethrin and cadmium.

An experimental hut evaluation of Olyset Plus, a long-lasting insecticidal net treated with a mixture of permethrin and piperonyl butoxide, against Anopheles fluviatilis in Odisha State, India.

BackgroundFast development of pyrethroid resistance in malaria vectors prompted the development of new vector control tools including combination of insecticides with different modes of action as part of resistance management strategies. Olyset Plus® is a new long-lasting insecticidal net, in which, permethrin and a synergist, piperonyl butoxide (PBO), are incorporated into filaments. Mixture nets such as this may have application against resistant mosquitoes, particularly those whose resistance is based on oxidative metabolism. There may also be enhanced activity against susceptible mosquitoes since mixed function oxidases are involved in a many metabolic activities including activation to form bioactive compounds.MethodsBio-efficacy of Olyset Plus was evaluated against susceptible malaria vector, Anopheles fluviatilis in experimental huts. Deterrence, blood feeding inhibition, induced exophily and killing effect were measured to assess the bio-efficacy. The results were compared with Olyset Net®, a polyethylene permethrin-incorporated LLIN and a conventionally treated polyester net (with permethrin) washed to just before exhaustion.ResultsResults showed significant reduction in entry (treatment: 0.4–0.8; control: 4.2 per trap-night) and increase in exit (56.3–82.9 % and 44.2 %) rates of Anopheles fluviatilis in the treatment arms compared to control (P < 0.05). While blood feeding rates declined in treatment arms (18.8–30.6 %), it increased in control (77.6 %) (P < 0.05). This was further evident from the blood-feeding inhibition rates in treatment arms (60.6–90.6 %). Total mortality was significantly higher in all treatment arms (96.3–100 %) compared to control arm (2 %) (P < 0.05). Chemical analysis for active ingredient (AI) showed retention of 75 and 88 % in Olyset plus and Olyset net respectively after 20 washes. Performance of Olyset Plus washed 20 times was equal to the CTN and Olyset Net against the susceptible malaria vector An. fluviatilis, fulfilling the WHO efficacy criteria of Phase II evaluation for LLIN. However, the benefit of incorporating PBO and permethrin together in a long-lasting treatment could not be demonstrated in the current study as the target vector species was fully susceptible to pyrethroids.ConclusionOlyset Plus, with its intrinsic bio-efficacy could be an effective vector control tool to prevent transmission of malaria by susceptible vectors like An. fluviatilis. However, the results of the current study need to be further supported by testing the net at village level (Phase III) for community acceptability. Before taking the net to village level, it needs to be verified whether the net is better than pyrethroid nets in terms of bio-efficacy against resistant An. culicifacies, another malaria vector that has developed resistance to synthetic pyrethroids in India.

A Permethrin/Allethrin Mixture Induces Genotoxicity and Cytotoxicity in Human Peripheral Blood Lymphocytes

Two pyrethroids, permethrin and allethrin, are often combined for large-scale use in public health programs to control vector-borne diseases. In this study, the genotoxic potential of a commercial formulation of permethrin and allethrin was examined using cultured human peripheral blood lymphocytes (PBL). Genotoxicity was evaluated using the cytokinesis-block micronucleus cytome (CBMN cyt) assay by measuring the frequency of micronuclei (MN), nuclear division index (NDI), formation of nucleoplasmic bridges (NPB) and nuclear buds (NBUD), as well as apoptotic and necrotic cells. Human PBL were treated with different concentrations of a permethrin/allethrin mixture (1/0.01, 5/0.07, and 10/0.14 μg/ml) for 24 or 36 h. The highest concentration (10/0.14 μg/ml) of permethrin/allethrin mixture significantly increased MN frequency and percent apoptotic cells after incubations for 24 or 36 h. The NDI was markedly decreased in response to treatment with 5/0.07 or 10/0.14 μg/ml permethrin/allethrin for both 24 and 36 h. Exposure to the permethrin/allethrin mixture did not significantly alter formation of NBUD, NPB, or percent necrotic cells. The MN frequency was significantly correlated with the number of apoptotic and necrotic cells but inversely correlated with NDI. Data demonstrated that a mixture of permethrin and allethrin induced concentration- and time-dependent cytotoxic and genotoxic damage to human PBL in vitro.

Effect of permethrin, anthracene and mixture exposure on shell components, enzymatic activities and proteins status in the Mediterranean clam Venerupis decussata

Anthracene (ANT) and permethrin (PER) are two of the more toxic compounds reaching the marine environment. This study aimed to determine the impact of these molecules on Venerupis decussata, an economically important species cultured on the Tunisian coast. Shell structure and its possible transformation upon exposure to the two contaminants were studied by X-ray diffraction and gravimetric analyses. Results revealed a phase transition in shell composition from aragonite to calcite after PER exposure, to a mixture of PER and ANT (Mix) but not for ANT alone. Catalase (CAT), superoxide dismutase (SOD) and glutathione transferase (GST) activities were determined in digestive gland and gills after exposure to ANT, PER and Mix to assess the impact of the contamination on the oxidative status of V. decussata. Enzyme activities increased in the digestive gland after PER treatment and in the gills after ANT treatment. PER exposure significantly reduced the levels of free thiols and increased levels of carbonylated proteins in the digestive gland, as compared to controls. In contrast, ANT exposure significantly reduced free thiols and increased the number of carbonylated proteins in the gills. Mix induced additive effects as measured by both enzymatic and proteomic approaches. The present study suggests that PER has a strong effect on shell structure; that PER and ANT exposure generate compound-dependent oxidative stress in the tissues of V. decussata and that a mixture of the two compounds has synergistic effects on biochemical response.

Joint toxicity of permethrin and cypermethrin at sublethal concentrations to the embryo-larval zebrafish

Pyrethroids, the widely used pesticides, are highly toxic to aquatic organisms. However, little information is so far available regarding the joint toxicity of type I and type II pyrethroids to fish. Zebrafish is a well-accepted aquatic vertebrate model for toxicity assessment due to small size, easy husbandry, high fecundity and transparent embryos. In this study, we utilized embryo-larval zebrafish to elucidate the combined effects of sublethal concentrations of permethrin (PM) and cypermethrin (CP), which are the most frequently used type I and type II pyrethroids, respectively. Fish were exposed from 3h postfertilization (hpf) to 144 hpf to binary mixtures of nominal concentrations of 100, 200, 300μgL−1 PM (PM100, PM200, PM300) and 10, 20, 30μgL−1 CP (CP10, CP20, CP30). Analytical data of the real concentrations of the chemicals showed a significant degradation of the pyrethroids but an obvious recovery after the renewal of the exposure solution. Defect rates of embryos exposed to these low concentrations of single PM or CP exhibited no statistically significant difference from the control,while the application of combination of PM and CP resulted in deleterious effects on zebrafish embryonic development. In all PM200 and PM300 exposure groups, increasing CP concentrations acted additively to the action of PM in terms of all sublethal endpoints. Co-treatment of embryos with the specific sodium channel blocker MS-222 and pyrethroids (individuals or the mixture) caused a decline in the incidences of body axis curvature and spasms compared to treatment of animals with pyrethroids alone, suggesting that the developmental toxicity of PM and CP to zebrafish was related to disruption of ion channels. We further revealed that mixture of the two pyrethroids caused greater down-regulation in the mRNA levels of proneural genes. The individual pesticides had no effect on the activity of superoxide dismutase (SOD), while the mixture exposure caused significant induction. Treatment with CP or the mixture increased the activity of catalase (CAT). Taken together, our data indicated that the mixture of PM and CP caused higher incidence of morphological defects, greater inhibition in proneural gene expression and more oxidative stress, compared to the single chemical at the corresponding doses. Our findings suggest that the combination of type I and type II pyrethroids poses a greater risk to fish in the water column.

Evidence for diazinon-mediated inhibition of cis-permethrin metabolism and its effects on reproductive toxicity in adult male mice

The potential toxicity resulting from combinatorial effects of organophosphorus and pyrethroid insecticides are not completely known. We evaluated male reproductive toxicity in mice co-exposed to diazinon and cis-permethrin. Nine-week-old male Sv/129 mice were exposed to diazinon (10μmol/kg/day) or cis-permethrin (90μmol/kg/day) alone or in combination (100μmol/kg/day), or vehicle (corn oil), for 6 weeks. Diazinon and the diazinon–permethrin mixture inhibited plasma and liver carboxylesterase activities. In the mixture group, urinary excretion of cis-permethrin metabolite 3-phenoxybenzoic acid decreased along with increased plasma and testicular concentrations of cis-permethrin, while excretion of diazinon metabolites, diethylphosphate and diethylthiophosphate, did not change, versus mice exposed to each chemical alone, which suggested that inhibition of carboxylesterase decreased the metabolic capacity to cis-permethrin. Though the co-exposure decreased testosterone biosynthesis, increased degenerate germ cells in seminiferous tubule and sperm morphological abnormalities versus controls more clearly than exposure to cis-permethrin alone, the expected potentiation of toxicity was not evident.

The Joint Toxicity of Type I, II, and Nonester Pyrethroid Insecticides

Evidence suggests that there are separate binding domains for type I and II pyrethroid insecticides on the voltage gated sodium channel of the nerve cell axon, but there are no studies that have examined the mixture toxicity of nonester pyrethroids and type I and II pyrethroids. Therefore, we examined the effect of nonester pyrethroid (etofenprox), type I (permethrin), and type II (cypermethrin) pyrethroid insecticides alone and in all combinations to Drosophila melanogaster Meigen. The combination of permethrin + etofenprox and permethrin + cypermethrin demonstrated antagonistic toxicity, while the combination of cypermethrin + etofenprox demonstrated synergistic toxicity. The mixture ofpermethrin + cypermethrin + etofenprox demonstrated additive toxicity. The toxicity of permethrin + cypermethrin was significantly lower than the toxicity of cypermethrin alone, but the combination was not significantly different from permethrin alone. The toxicity of permethrin + cypermethrin + etofenprox was significantly greater than the toxicity of both permethrin and etofenprox alone, but it was significantly lower than cypermethrin alone. The mixture of permethrin and etofenprox was significantly less toxic than permethrin. The explanation for the decreased toxicity observed is most likely because of the competitive binding at the voltage-gated sodium channel, which is supported by physiological and biochemical studies of pyrethroids. Our results demonstrate that the assumption that the mixture toxicity of pyrethroids would be additive is not adequate for modeling the mixture toxicity of pyrethroids to insects.

A comparison of mixture toxicity assessment: Examining the chronic toxicity of atrazine, permethrin and chlorothalonil in mixtures to Ceriodaphnia cf. dubia

Pesticides predominantly occur in aquatic ecosystems as mixtures of varying complexity, yet relatively few studies have examined the toxicity of pesticide mixtures. Atrazine, chlorothalonil and permethrin are widely used pesticides that have different modes of action. This study examined the chronic toxicities (7-d reproductive impairment) of these pesticides in binary and ternary mixtures to the freshwater cladoceran Ceriodaphnia cf. dubia. The toxicity of the mixtures was compared to that predicted by the independent action (IA) model for mixtures, as this is the most appropriate model for chemicals with different modes of action. Following this they were compared to the toxicity predicted by the concentration addition (CA) model for mixtures. According to the IA model, the toxicity of the chlorothalonil plus atrazine mixture conformed to antagonism, while that of chlorothalonil and permethrin conformed to synergism. The toxicity of the atrazine and permethrin mixture as well as the ternary mixture conformed to IA implying there was either no interaction between the components of these mixtures and/or in the case of the ternary mixture the interactions cancelled each other out to result in IA. The synergistic and antagonistic mixtures deviated from IA by factors greater than 3 and less than 2.5, respectively. When the toxicity of the mixtures was compared to the predictions of the CA model, the binary mixture of chlorothalonil plus atrazine, permethrin plus atrazine and the ternary mixture all conformed to antagonism, while the binary mixture of chlorothalonil plus permethrin conformed to CA. Using the CA model provided estimates of mixture toxicity that did not markedly underestimate the measured toxicity, unlike the IA model, and therefore the CA model is the most suitable to use in ecological risk assessments of these pesticides.

Pesticides induced oxidative stress in thymocytes

The role of oxidative stress in immune cell toxicity caused by the pesticides lindane, malathion and permethrin was investigated in thymic cells from C57BL/6 mice. Thymocytes treated with any of these pesticides (concentrations ranging between 50-150 microM) were found to generate both superoxide ((*)O(2) (-)) and H(2)O(2). The production of (*)O(2) (-) was detected with hydroethidine-ethidium bromide assay. H(2)O(2) production was monitored with a flow cytometric fluorescent (DCFH-DA) assay. All three pesticides stimulated (*)O(2) (-) release after 5 min exposure. Lindane and permethrin, but not malathion, continued to have significant (p < or = 0.05) effects on (*)O(2) (-) generation following 15 min of exposure. The lindane + malathion mixture was found to cause more-than-additive increase in (*)O(2) (-) production compared to individual pesticide treatments (at both 5 and 15 min). However, the effect of the lindane + permethrin mixture was not significantly different than individual components of this mixture. The effects of these pesticides on levels of antioxidant enzymes were also investigated, and only mixtures were found to have significant (p < or = 0.05) effects. Thus, lindane + malathion and lindane + permethrin mixtures increased total superoxide dismutase (SOD) specific activity, had no effect on catalase levels and inhibited GSH-peroxidase and GSH-reductase specific activities. Although the results of these studies do not explain the mechanism of action of these pesticides on the generation of (*)O(2) (-) and H(2)O(2), it is worthy of note that mixtures of these chemicals have oxidative responses greater than those of single chemicals.

Melon aphid (&lt;i&gt;Aphis gossypii&lt;/i&gt;) resistance to pesticides

Eleven pesticides were applied at their recommended concentrations through a Potter Tower to melon aphid (Aphis gossypii), (Homoptera: Aphididae) from potted chrysanthemums (Chrysanthemum x morifolium) in Auckland. The aphids were either topically sprayed or placed on spray residues on chrysanthemum leaf discs embedded in agar. Mortality was assessed after 48 h. The LC 50 for topical application of pirimicarb was also assessed and was over 10 times the recommended field spray concentration. The synthetic pyrethroids, lambda-cyhalothrin and tau-fluvalinate, caused low mortality. The residues of dichlorvos, demeton-s-methyl, methamidophos, acephate, methomyl, maldison and pirimiphos methyl/ permethrin mixture, gave lower mortality than topical applications. Mortality was similar for maldison and methomyl in both tests. Endosulfan gave 100% mortality in both tests. Growers are recommended to implement a melon aphid resistance management strategy.

Pesticide Tracers for Measuring Orchard Spray Drift

Airborne spray and ground level deposits of permethrin were measured downwind from semi-dwarf apple trees sprayed with an orchard air sprayer. Collectors were located from ground level to an elevation of 10 m (32.8 ft) and out to 240 m (787 ft) downwind from the sprayed tree row. A mixture of permethrin and water was sprayed at 468 L/ha (50 gal/acre) during nine passes on days 1, 2, and 3. The wind was light and variable on day 1 but wind speed was about 4 to 6 m/s (6.4 to 9.7 mile/h) on days 2 and 3. Ground level deposits decreased as downwind distance increased. On day 1, no permethrin was detected beyond 60 m (197 ft) from the tree row. At 30 m (98 ft) from the tree row, deposits on Line 1 (sprayed without trees) was about the same as deposits on Lines 2 and 3 (sprayed through trees). Airborne spray permethrin deposits were affected by wind speed; at all sample sites, deposits on strings at elevations from 1.5 to 4.5 m (4.9 to 14.8 ft) were less when wind speed was less. At the 60 m (197 ft) location, deposits tended to be more uniform over elevation than at locations closer to the sprayed trees. In general, deposits on string decreased with increased elevation.

Effect of four spray regimes on the development of permethrin and dichlorvos resistance, in the laboratory, by the house fly (Diptera: Muscidae).

A Musca domestica L. strain possessing latent resistance to pyrethroid insecticides was selected in the laboratory, using four spray regimes involving single selections each generation with either permethrin, dichlorvos, permethrin, and dichlorvos alternated each generation, or a 1:1 mixture of permethrin and dichlorvos. After eight generations of selection, resistance to permethrin at the LC50 level was 73-fold in the permethrin-selected strain, 4-fold in the dichlorvos-selected house flies, 31-fold in the alternately selected strain, and 6-fold in the mixture-selected strain. Dichlorvos resistance was 4-, 27-, 10-, and 7-fold in the respective strains after eight generations. Resistance levels declined in the four strains after the selection pressure was removed. A 10:1 mixture of piper only but oxide and permethrin increased permethrin susceptibility fivefold and reduced heterogeneity in the resistant (permethrin-selected) strain. The feasibility of alternating insecticides, using mixtures, or using synergists to postpone pyrethroid resistance development in the field is discussed.