Pyrethroid insecticides: poisoning syndromes, synergies, and therapy

Ultrasensitive detection of deltamethrin by immune magnetic nanoparticles separation coupled with surface plasmon resonance sensor

Small molecules or analytes present in trace level are difficult to be detected directly using conventional surface plasmon resonance (SPR) sensor, due to its small changes in the refractive index induced by the binding of these analytes on the sensor surface. In this paper, a new approach that combines SPR sensor technology with Fe3O4 magnetic nanoparticles (MNPs) assays is developed for directly detecting of deltamethrin in soybean. The Fe3O4 MNPs conjugated with antibodies specific to antigen serves as both labels for enhancing refractive index change due to the capture of target analyte, and "vehicles" for the rapid delivery of analyte from a sample solution to the sensor surface. Meanwhile, SPR direct detection format without Fe3O4 MNPs and gas chromatography (GC) analysis were conducted for detection of deltamethrin in soybean to demonstrate the amplification effect of Fe3O4 MNPs. A good linear relationship was obtained between SPR responses and deltamethrin concentrations over a range of 0.01-1 ng/mL with the lowest measurable concentration of 0.01 ng/mL. The results reveal that the detection sensitivity for deltamethrin was improved by 4 orders of magnitude compared with SPR direct detection format. The recovery of 95.5-119.8% was obtained in soybean. The excellent selectivity of the present biosensor is also confirmed by two kinds of pesticides (fenvalerate and atrazine) as controls. This magnetic separation and amplification strategy has great potential for detection of other small analytes in trace level concentration, with high selectivity and sensitivity by altering the target-analyte-capture agent labeled to the carboxyl-coated Fe3O4 MNPs.

Characteristics and magnitude of acute pesticide-related illnesses and injuries associated with pyrethrin and pyrethroid exposures--11 states, 2000-2008

BACKGROUND

Excluding disinfectants, pyrethrins and pyrethroids are the pesticides used most commonly in and around homes. Respiratory effects and paresthesia are among the concerns about pyrethrin/pyrethroid exposures.

METHODS

Acute pesticide-related illness/injury cases were identified from the Sentinel Event Notification System for Occupational Risks-Pesticides Program and the California Department of Pesticide Regulation from 2000-2008. Characteristics and incidence rates were determined for acute pyrethrin/pyrethroid-related illness/injury cases. Logistic regression analyses were performed to determine odds of respiratory and dermal symptoms in persons with illness/injury following pyrethrin/pyrethroid exposure compared to persons with illness/injury following exposure to other pesticides.

RESULTS

A total of 4,974 cases of acute pyrethrin/pyrethroid-related illness were identified. Incidence rates increased over time, reaching 8 cases/million population in 2008. The majority of cases were low severity (85%) and 34% were work-related. Respiratory effects were the most common symptoms reported (48%). Risk of acute respiratory effects were significantly elevated among persons exposed only to pyrethrins (adjusted odds ratio [aOR] 1.79; 95% confidence interval [95% CI]: 1.49-2.16), only to pyrethroids (aOR 1.99 95% CI: 1.77-2.24), to a mixture of pyrethroids (aOR 2.36; 95% CI: 1.99-2.81) or to a mixture containing both pyrethrins and pyrethroids (aOR 2.99; 95% CI: 2.33-3.84) compared to those with illness arising from exposure to other pesticides. The most common factors contributing to pyrethrin/pyrethroid-related illness included exposure from spills/splashes, improper storage, and failure to evacuate during pesticide application.

CONCLUSIONS

The magnitude of acute pyrethrin/pyrethroid-related illness/injury is relatively low but is increasing. As such, additional measures to prevent them are needed.

Severe acute illness in a toddler exposed to multiple agricultural pesticides and an insect repellent

Acute severe pesticide-related illness among farm worker children is rarely reported. The authors report a toddler with acute onset of apnea, cyanosis, somnolence, hypotonia, tachycardia, and miosis who required hospitalization. Health care providers suspected pesticide poisoning, but were unable to determine the causal agent. Investigation by a public health program documented four pesticide exposures that occurred within one-half hour of acute illness. This case illustrates the importance of a thorough environmental/occupational exposure history and obtaining biological samples. It also documents the need to strengthen the Worker Protection Standard for agricultural workers and the importance of reporting and investigating pesticide-related illness.

Status epilepticus: An association with pyrethroid poisoning

This report describes a 35 year old male who presented with seizures after consuming 4-5 bottles of “ALL-OUT” a commercial composition of pyrethroid used as insecticides. Our case report supports authors reporting an association of pyrethroid poisoning with status epilepticus.

Density shift, morphological damage, lysosomal fragility and apoptosis of hemocytes of Indian molluscs exposed to pyrethroid pesticides

Bellamya bengalensis (Gastropoda: Prosobranchia) and Lamellidens marginalis (Bivalvia: Eulamellibranchiata) are the molluscs of Indian freshwater ecosystem and important biological resources. These edible species bear economical, ecological, nutritional and medicinal importance. Natural habitat of these organisms is under the ecological threat of contamination by cypermethrin and fenvalerate, the common pyrethroid pesticides of India. Hemocytes are chief immunoeffector cells of molluscs which exhibit responsiveness against environmental toxins and perform diverse immunological functions including phagocytosis, encapsulation and cytotoxicity. Experimental exposure of cypermethrin and fenvalerate resulted in significant shift in density and morphological damage in hemocytes of B. bengalensis and L. marginalis respectively. Pyrethroid induced fragility and destabilization of hemocyte lysosomal membrane was recorded and proposed as an indication of toxin induced stress in molluscs. Apoptosis is an immunologically important cellular response which is modulated by environmental toxins. Pyrethroid exposure suppressed the physiological level of apoptosis and necrosis in hemocytes of B. bengalensis and L. marginalis indicating possible impairment of apoptosis mediated immunoprotection. Differential responses of B. bengalensis and L. marginalis hemocytes may be due to species specificity, toxin specificity, nonidentical immune strategies of Gastropoda and Bivalvia, specific habitat preference and related ecological niches.

Prallethrin poisoning: A diagnostic dilemma

Pyrethroid insecticides are very widely used in agriculture and household due to their high effectiveness and low toxicity in humans. Despite their extensive worldwide use, there are a few reports of human pyrethroid poisoning. The poisoning has a varied presentation and its symptoms overlap with those of other compounds, which can lead to misdiagnosis. We present a case of poisoning with prallethrin, a pyrethroid compound, commonly available as All-Out.

Critical consideration of the multiplicity of experimental and organismic determinants of pyrethroid neurotoxicity: a proof of concept

Pyrethroids (PYR) are pesticides with high insecticidal activity that may disrupt neuronal excitability in target and nontarget species. The accumulated evidence consistently showed that this neurophysiologic action is followed by alterations in motor, sensorimotor, neuromuscular, and thermoregulatory responses. Nevertheless, there are some equivocal results regarding the potency of PYR in lab animals. The estimation of potency is an important step in pesticide chemical risk assessment. In order to identify the variables influencing neurobehavioral findings across PYR studies, evidence on experimental and organismic determinants of acute PYR-induced neurotoxicity was reviewed in rodents. A comprehensive analysis of these studies was conducted focusing on test material and dosing conditions, testing conditions, animal models, and other determinants such as testing room temperature. Variations in the severity of the neurotoxicity, under lab-controlled conditions, was explained based upon factors including influence of animal species and age, test material features such as chemical structure and stereochemistry, and dosing conditions such as vehicle, route of exposure, and dose volume. If not controlled, the interplay of these factors may lead to large variance in potency estimation. This review examined the scope of acute toxicological data required to determine the safety of pesticide products, and factors and covariates that need to be controlled in order to ensure that predictivity and precaution are balanced in a risk assessment process within a reasonable time-frame, using acute PYR-induced neurotoxicity in rodents as an exemplar.

Pesticide exposure in children

Pesticides are a collective term for a wide array of chemicals intended to kill unwanted insects, plants, molds, and rodents. Food, water, and treatment in the home, yard, and school are all potential sources of children's exposure. Exposures to pesticides may be overt or subacute, and effects range from acute to chronic toxicity. In 2008, pesticides were the ninth most common substance reported to poison control centers, and approximately 45% of all reports of pesticide poisoning were for children. Organophosphate and carbamate poisoning are perhaps the most widely known acute poisoning syndromes, can be diagnosed by depressed red blood cell cholinesterase levels, and have available antidotal therapy. However, numerous other pesticides that may cause acute toxicity, such as pyrethroid and neonicotinoid insecticides, herbicides, fungicides, and rodenticides, also have specific toxic effects; recognition of these effects may help identify acute exposures. Evidence is increasingly emerging about chronic health implications from both acute and chronic exposure. A growing body of epidemiological evidence demonstrates associations between parental use of pesticides, particularly insecticides, with acute lymphocytic leukemia and brain tumors. Prenatal, household, and occupational exposures (maternal and paternal) appear to be the largest risks. Prospective cohort studies link early-life exposure to organophosphates and organochlorine pesticides (primarily DDT) with adverse effects on neurodevelopment and behavior. Among the findings associated with increased pesticide levels are poorer mental development by using the Bayley index and increased scores on measures assessing pervasive developmental disorder, inattention, and attention-deficit/hyperactivity disorder. Related animal toxicology studies provide supportive biological plausibility for these findings. Additional data suggest that there may also be an association between parental pesticide use and adverse birth outcomes including physical birth defects, low birth weight, and fetal death, although the data are less robust than for cancer and neurodevelopmental effects. Children's exposures to pesticides should be limited as much as possible.

Embryotoxic and teratogenic effects of pesticides in chick embryos: a comparative study using two commercial formulations

Developmental toxicity of two different classes of commercial formulations of insecticides was studied by in ovo treatment of fertilized Rhode Island Red eggs. The first one was a combination of chlorpyrifos and cypermethrin and the second one was spinosad, a fermentation product of soil bacterium, Actinomycetes. In this study, the combination pesticide and spinosad of different concentrations were administered as a single dose in ovo in volumes of 50 μL per each egg on day "0" of incubation. Embryonic growth and development, morphological and skeletal malformations, and hatchability were assessed. The combination insecticide induced explicit alterations in the embryonic growth and development and resulted in malformations particularly to the axial and appendicular skeletal structures, whereas the changes were trivial in case of the spinosad exposure.

Biological monitoring for exposure to deltamethrin: a human oral dosing study and background levels in the UK general population

An oral dose of the pyrethroid insecticide deltamethrin was administered to five volunteers at the acceptable daily intake (ADI, 0.01 mg/kg). Total urine was collected from the volunteers at timed intervals for 60h post-exposure. The metabolites 3-(2,2-dibromovinyl)-2,2-dimethyl-(1-cyclopropane)carboxylic acid (DBVA) and 3-phenoxybenzoic acid (3-PBA) were quantified in hydrolysed urine using GC-MS analysis. Both metabolites exhibited rapid elimination half-lives of 3.6 and 7.1h, respectively. Levels of DBVA quantified in urine were approximately 5 times greater than 3-PBA. Mean metabolite levels found in 24h total urine collections, normalised for a 70 kg individual, were 42.8 μmol DBVA/mol creatinine (range 34.6-63.2; CV=28%) and 8.7 μmol 3-PBA/mol creatinine (range 6.6-12.7; CV=31%). We calculate that a 70 kg person receiving a dose of deltamethrin at the ADI would be expected to have a 24-h total urine collection level of 32-53 μmol DBVA/mol creatinine (95% confidence interval). Analysis of 336 samples from adult UK residents with no known exposure to deltamethrin derives an upper reference value (95th percentile) of 0.5 μmol DBVA/mol creatinine (maximum 4.2 μmol DBVA/mol creatinine), demonstrating that general population exposure to deltamethrin in the UK is very low and well within levels expected at the ADI.

Permethrin modulates cholinergic mini-synaptic currents by partially blocking the calcium channel

Pyrethroid insecticide modulation of the voltage-gated sodium channel (VGSC) is proposed to underlie their effects on neuronal excitability by inhibiting channel inactivation and increasing channel open time. However, some in vitro evidences indicate that target sites other than VGSCs could contribute to pyrethroid disruption of neuronal activity. Cholinergic excitability in Drosophila, as in other insects and mammals, is important for activity in the central nervous system. The effects of permethrin, a putative calcium antagonist, on calcium current and cholinergic mini-synaptic transmission were investigated in the Drosophila brain. At concentration of 2.5μM, permethrin significantly decreased the calcium current and cholinergic mini-synaptic current. However, the permethrin could not antagonize the calcium current completely. Removal of calcium from the external solution produced a significant decrease of cholinergic mini-synaptic transmission. The results are consistent with the hypothesis that permethrin may modulate cholinergic mini-synaptic currents by partially blocking the calcium channel.

An unusual cause of status epilepticus

A 24-year-old female presented with status epilepticus following ingestion of a pyrethroid insecticide Deltamethrin. The pathophysiology, clinical features, and management of pyrethroid poisoning are discussed in this article.

Decreased sperm motility in rats orally exposed to single or mixed pesticides

The Brazilian Agency of Sanitary Vigilance (ANVISA) conducted a study that demonstrated the presence of residues of several pesticides in fresh fruits and vegetables that were available for purchase by the general populace. In order to evaluate potential adverse health effects of low-level exposure to agrochemicals, the reproductive toxicity of the pesticides dicofol, dichlorvos, permethrin, endosulfan, and dieldrin was evaluated in rats dosed with these chemicals individually or as mixtures. Sixty male Lewis rats (6 wk old, 200 x g) were randomly allocated to 8 groups: (1) control group, received basal diet; (2) 5 groups designated a to e received the diet containing each pesticide individually, at the respective effective doses: lowest-observed-adverse-effect level (LOAEL) for dieldrin and endosulfan, lowest-observed-effect level (LOEL) for dicofol, and lowest effect level (LEL) for dichlorvos and permethrin, respectively, depending on the published data; (3) effective dose group, which received a mixture of pesticides added to basal diet at the respective doses reported to produce adverse effects; and (4) low dose group, which received a pesticide mixture added to the basal diet, where each pesticide was at its no-observed-effect level (NOEL). After 8 wk of treatment, reproductive parameters were evaluated. Sperm morphology, daily sperm production (DSP), sperm transit time through the epididymis, hormonal levels, and histopathological evaluation of testis and epididymis did not differ significantly among the groups. However, sperm motility was significantly decreased in animals that received a mixture of dieldrin, endosulfan, dicofol, dichlorvos, and permethrin, as well as in the group receiving dicofol alone. Exposure to the individual pesticides endosulfan, dichlorvos, and permethrin did not markedly affect sperm motility. The impairment of sperm motility in the mixture of pesticides at the NOEL level indicates that reproductive effects not seen with individual pesticides may occur in presence of several pesticides due to an additive effect. However, the pesticide mixtures did not appear to affect DSP or spermatogenesis despite reduced sperm motility.

Developmental neurotoxicity of pyrethroid insecticides in zebrafish embryos

Pyrethroid insecticides are one of the most commonly used residential and agricultural insecticides. Based on the increased use of pyrethroids and recent studies showing that pregnant women and children are exposed to pyrethroids, there are concerns over the potential for developmental neurotoxicity. However, there have been relatively few studies on the developmental neurotoxicity of pyrethroids. In this study, we sought to investigate the developmental toxicity of six common pyrethroids, three type I compounds (permethrin, resmethrin, and bifenthrin) and three type II compounds (deltamethrin, cypermethrin, and lambda-cyhalothrin), and to determine whether zebrafish embryos may be an appropriate model for studying the developmental neurotoxicity of pyrethroids. Exposure of zebrafish embryos to pyrethroids caused a dose-dependent increase in mortality and pericardial edema, with type II compounds being the most potent. At doses approaching the LC(50), permethrin and deltamethrin caused craniofacial abnormalities. These findings are consistent with mammalian studies demonstrating that pyrethroids are mildly teratogenic at very high doses. However, at lower doses, body axis curvature and spasms were observed, which were reminiscent of the classic syndromes observed with pyrethroid toxicity. Treatment with diazepam ameliorated the spasms, while treatment with the sodium channel antagonist MS-222 ameliorated both spasms and body curvature, suggesting that pyrethroid-induced neurotoxicity is similar in zebrafish and mammals. Taken in concert, these data suggest that zebrafish may be an appropriate alternative model to study the mechanism(s) responsible for the developmental neurotoxicity of pyrethroid insecticides and aid in identification of compounds that should be further tested in mammalian systems.

Evidence for dose-additive effects of pyrethroids on motor activity in rats

BACKGROUND

Pyrethroids are neurotoxic insecticides used in a variety of indoor and outdoor applications. Previous research characterized the acute dose-effect functions for 11 pyrethroids administered orally in corn oil (1 mL/kg) based on assessment of motor activity.

OBJECTIVES

We used a mixture of these 11 pyrethroids and the same testing paradigm used in single-compound assays to test the hypothesis that cumulative neurotoxic effects of pyrethroid mixtures can be predicted using the default dose-addition theory.

METHODS

Mixing ratios of the 11 pyrethroids in the tested mixture were based on the ED30 (effective dose that produces a 30% decrease in response) of the individual chemical (i.e., the mixture comprised equipotent amounts of each pyrethroid). The highest concentration of each individual chemical in the mixture was less than the threshold for inducing behavioral effects. Adult male rats received acute oral exposure to corn oil (control) or dilutions of the stock mixture solution. The mixture of 11 pyrethroids was administered either simultaneously (2 hr before testing) or after a sequence based on times of peak effect for the individual chemicals (4, 2, and 1 hr before testing). A threshold additivity model was fit to the single-chemical data to predict the theoretical dose-effect relationship for the mixture under the assumption of dose additivity.

RESULTS

When subthreshold doses of individual chemicals were combined in the mixtures, we found significant dose-related decreases in motor activity. Further, we found no departure from the predicted dose-additive curve regardless of the mixture dosing protocol used.

CONCLUSION

In this article we present the first in vivo evidence on pyrethroid cumulative effects supporting the default assumption of dose addition.

Pyrethrin and pyrethroid illnesses in the Pacific northwest: a five-year review

OBJECTIVE

Pyrethrin and pyrethroid insecticides are commonly applied in homes and businesses and on some agricultural crops. This research used a two-state regional approach to analyze reports of acute pesticide poisonings due to pyrethrin and pyrethroid insecticides.

METHODS

The Washington State Department of Health and the Oregon Public Health Division collected pesticide poisoning surveillance data from 2001 through 2005. Cases were included if they involved exposure to at least one pyrethrin or pyrethroid insecticide. Descriptive statistics were calculated; differences between categories were assessed using Chi-square analysis.

RESULTS

A total of 407 cases fit our definition. Overall, the rate of poisoning in Oregon was significantly higher than in Washington (incidence rate ratio 1.70, 95% confidence interval 1.40, 2.07), and rates for both states generally increased during the time period. For both states, most exposures resulted in low severity illnesses (92%), and most were classified as possible cases (73%). Only about one-fourth of cases were related to a person's work. The most common category of clinical signs and symptoms of illness was respiratory (52% of cases), followed by neurological (40% of cases). Exposure route was predominantly inhalation; there was no association between route and case severity. There was a significant association between illness severity and losing time from work or regular activities (p<0.0001).

CONCLUSIONS

Although the majority of pyrethrin and pyrethroid poisoning cases were low in severity, adverse reactions have occurred, as transpired in Oregon in 2005. Regional analysis has the potential to improve the surveillance system and provide unique opportunities for targeting preventive interventions.

Acute toxic effects of three pesticides on Pseudomonas putida monitored by microcalorimeter

A series of calorimetric experiments were performed to investigate the toxic effects of beta-cypermethrin (BCP), bensulfuron-methyl (BSM) and prometryne (PM) on Pseudomonas putida (P. putida). The metabolic action of P. putida on the three pesticides was studied by obtaining power-time curves. The growth of P. putida was inhibited completely in each case when the concentrations of pesticides were up to 80 micro g mL(- 1). The relationships between the inhibitory ratio (k) and doses of contaminants were approximately linear for the three pesticides. The total heat dissipated per milliliter (Q(total)) for the pesticides decreased during the course of the experiment. The OD(600) of P. putida growth in the absence and presence of pesticides was also obtained. The power-time curves of P. putida growth coincided with its turbidity curves. This elucidates that microcalorimetric method agrees well with the routine microbiological method. Among these three pesticides, BSM was found to be the most toxic with an IC(50) of 19.24 micro g mL(- 1) against P. putida. PM exhibited moderate virulence with an IC(50) of 27.86 micro g mL(- 1) and BCP had the lowest toxicity with an IC(50) of 39.64 micro g mL(- 1).

Cypermethrin effects on the adult mice seminal glands

The insecticide cypermethrin acts upon the sodium channels. Their effects over animal health are not understood. Here, the effects of cypermethrin on the seminal glands (SGs) are studied (1/5 DL50 i.p.). Forty-five adult mice (CF1) were distributed in three groups: (1) untreated, (2) vehicle (oil), and (3) experimental (cypermethrin in oil). The animals were sacrificed at 1 and each 8.6 days. The SGs were processed for histology: Haematoxylin/P.A.S, Thyonin (0.6%) and Immunohistochemistry (Ki-67). In the SGs was quantified: the epithelium height, mastocytes, and cell proliferation. In the results, cypermethrin exerts an intense effect on epithelium height and cell proliferation. A net increase of both parameters was observed at 24 h (p0.05). However, the mastocytes increased drastically and progressively during the experimental period (p0.05). Then, the effects have acute manifestations, which would be responsible for the potential changes in the male's reproductive potentiality.

Pyrethroid Insecticides: Advances and Challenges in Biomonitoring

Pyrethroid insecticides have a wide variety of applications throughout the world. They are structurally diverse chemicals that are synthetically derived from naturally occurring pyrethrin insecticides. Significant advances in analytical chemistry have led to the development of biomarkers of exposure to pyrethroids, and these methods are currently being applied to study exposure in the general population. This article reviews the chemistry and toxicology of pyrethroid insecticides, with an emphasis on the development of biomarkers to assess environmental exposure. Future challenges in the application of these biomarkers in epidemiological studies are explored, as is a need for improved understanding of the toxicokinetics of pyrethroids in humans.

Topical pyrethrin toxicity leading to acute-onset stuttering in a toddler

Pyrethrin compounds can cause neurotoxicity when used in an excessive dose. A case of stuttering and general clumsiness in a toddler associated with topical pyrethrin use is described.

Lethal and sublethal effects of the pyrethroid, bifenthrin, on grass shrimp (Palaemonetes pugio) and sheepshead minnow (Cyprinodon variegatus)

This study investigated the lethal and sublethal effects of the pyrethroid insecticide bifenthrin on adult and larval grass shrimp, Palaemonetes pugio, and adult sheepshead minnows, Cyprinodon variegatus. The effects were determined by conducting 96-h aqueous static renewal tests and 24-h static tests with sediment. Oxidative stress biomarkers, lipid peroxidation, glutathione, and catalase were also assessed. The 96-h aqueous LC50 value for adult shrimp was 0.020 microg/L (95% CI: 0.015-0.025 microg/L) and for larval shrimp was 0.013 microg/L (95% CI: 0.011-0.016 microg/L). The 96-h aqueous LC50 for adult sheepshead minnow was 19.806 microg/L (95% CI: 11.886-47.250 microg/L). The 24-h sediment LC50 for adult shrimp was 0.339 microg/L (95% CI: 0.291-0.381 microg/L) and for larval shrimp was 0.210 microg/L (95% CI: 0.096-0.393 microg/L). The oxidative stress assays showed some increasing trends toward physiological stress with increased bifenthrin concentrations but they were largely inconclusive. Given the sensitivity of grass shrimp to this compound in laboratory bioassays, additional work will be needed to determine if these exposure levels are environmentally relevant.

Applications of carboxylesterase activity in environmental monitoring and toxicity identification evaluations (TIEs)

This review has examined a number of issues surrounding the use of carboxylesterase activity in environmental monitoring. It is clear that carboxylesterases are important enzymes that deserve increased study. This class of enzymes appears to have promise for employment in environmental monitoring with a number of organisms and testing scenarios, and it is appropriate for inclusion in standard monitoring assays. Given the ease of most activity assays, it is logical to report carboxylesterase activity levels as well as other esterases (e.g., acetylcholinesterase). Although it is still unclear as to whether acetylcholinesterase or carboxylesterase is the most "appropriate" biomarker, there are sufficient data to suggest that at the very least further studies should be performed with carboxylesterases. Most likely, data will show that it is optimal to measure activity for both enzymes whenever possible. Acetylcholinesterase has the distinct advantage of a clear biological function, whereas the endogenous role of carboxylesterases is still unclear. However, a combination of activity measurements for the two enzyme systems will provide a much more detailed picture of organism health and insecticide exposure. The main outstanding issues are the choice of substrate for activity assays and which tissues/organisms are most appropriate for monitoring studies. Substrate choice is very important, because carboxylesterase activity consists of multiple isozymes that most likely fluctuate on an organism- and tissue-specific basis. It is therefore difficult to compare work in one organism with a specific substrate with work performed in a different organism with a different substrate. An attempt should therefore be made to standardize the method. The most logical choice is PNPA (p-nitrophenyl acetate), as this substrate is commercially available, requires inexpensive optics for assay measurements, and has been used extensively in the literature. However, none of these beneficial properties indicates that the substrate is an appropriate surrogate for a specific compound, e.g., pyrethroid-hydrolyzing activity. It will most likely be necessary to have more specific surrogate substrates for use in assays that require information on the ability to detoxify/hydrolyze specific environmental contaminants. The use of carboxylesterase activity in TIE protocols appears to have excellent promise, but there are further technical issues that should be addressed to increase the utility of the method. The main concerns include the large amount of nonspecific protein added to the testing system, which can lead to undesirable side effects including nonspecific reductions in observed toxicity, decrease in dissolved oxygen content, and organism growth. It is probable that these issues can be resolved with further assay development. The ideal solution would be to have a commercial recombinant carboxylesterase that possessed elevated pyrethroid-hydrolysis activity and which was readily available, homogeneous, and inexpensive. The availability of such an enzyme would address nearly all the current method shortcomings. Such a preparation would be extremely useful for the aquatic toxicology community. Further work should focus on screening available esterases for stability, cost, and activity on pyrethroids, with specific focus on esterases capable of distinguishing type I from type II pyrethroids. It would also be beneficial to identify esterases that are not sensitive to OP insecticides. Many esterases and lipases are available as sets to test chemical reactions for green chemistry, enabling large-scale screening. Other potential approaches to increase the utility of the enzyme include derivatization with polyethylene glycol (PEG) or cyanuric acid chloride to increase stability and reduce microbial degradation. It is also possible that the enzyme could be formulated in a sol gel preparation to increase stability. It is likely that the use of carboxylesterase addition will increase for applications in sediment TIEs. Carboxylesterases are an interesting and useful enzyme family that deserves further study for applications in environmental monitoring as well as to increase our understanding of the fundamental biological role(s) of these enzymes. There are, of course, other enzymes that show high esterase activity on pyrethroids but are not technically carboxylesterases in the alpha/beta-hydrolase fold protein family. These enzymes should also be examined for use in TIE protocols and "esterase" arrays as well as for general applications in environmental monitoring. One can envision the creation of a standardized screen of enzymes with esterase activity to (1) identify environmental contaminants, (2) estimate the potential toxic effects of new compounds on a range of organisms, and (3) monitor organism exposure to agrochemicals (and potentially other contaminants). This approach would provide a multibiomarker integrative assessment of esterase-inhibiting potential of a compound or mixture. In conclusion, much is still unknown about this enzyme family, indicating that this area is still wide open to researchers interested in the applications of carboxylesterase activity as well as basic biological questions into the nature of enzyme activity and the endogenous role of the enzyme.

Animal models of chronic pesticide neurotoxicity

There is a wealth of literature on neurotoxicological outcomes of acute and short-term exposure to pesticides in laboratory animals, but there are relatively few studies of- long-term exposure. Many reports in the literature describing ;chronic' exposures to pesticides are, in fact, as short as five days and rarely longer than three months. Furthermore, routes of administration range from subcutaneous to dietary. Doses used in many of the studies produce signs of acute or overt toxicity. In contrast, human symptoms have been reported following exposures that are prolonged and often without obvious toxic effects. A survey of the literature was conducted to identify rodent studies with neurobehavioral and neurophysiological endpoints of pesticide exposures lasting 30 days or longer. This survey indicated that the majority of studies concentrate on cholinesterase inhibitors (organophosphorus and carbamate insecticides). Various neuromotor, cholinergic, physiological, affective and cognitive disorders were reported at doses producing cholinesterase inhibition; however, there were a fewer effects at non-inhibiting doses. Other classes of pesticides produced similar effects, with the exception of cholinergic signs. In many studies, the changes were subtle, which may correspond to the nonspecific changes in psychomotor and cognitive function reported in humans. It appears, then, that the data from animal and human pesticide exposures are generally comparable, but the specific outcomes are influenced by many experimental differences. Future research should concentrate on analogous exposures and outcomes to facilitate interpretation.

Pesticide illness among flight attendants due to aircraft disinsection

BACKGROUND

Aircraft "disinsection" is the application of pesticides inside an aircraft to kill insects that may be on board. Over a 1-year period, California's tracking system received 17 reports of illness involving flight attendants exposed to pesticides following disinsection.

METHODS

Interviews, work process observations, and a records review were conducted. Illness reports were evaluated according to the case definition established by the National Institute for Occupational Safety and Health.

RESULTS

Twelve cases met the definition for work-related pesticide illness. Eleven cases were attributed to the "Residual" method of disinsection, i.e., application of a solution of permethrin (2.2% w/w), solvents (0.8%), and a surfactant (1.4%); the method of disinsection could not be determined for one case.

CONCLUSIONS

The aerosol application of a pesticide in the confined space of an aircraft cabin poses a hazard to flight attendants. Nontoxic alternative methods, such as air curtains, should be used to minimize disease vector importation via aircraft cabins. Employers should mitigate flight attendant pesticide exposure in the interim.

Formulation-dependent toxicokinetics explains differences in the GI absorption, bioavailability and acute neurotoxicity of deltamethrin in rats

The acute neurotoxicity of pyrethroid insecticides varies markedly with the dosage vehicle employed. The objective of the present study was to assess the influence of two common vehicles on the bioavailability and toxicokinetics (TK) of a representative pyrethroid insecticide, deltamethrin (DLM), to determine whether the vehicles influence toxic potency by modifying the chemical's TK. Adult, male Sprague-Dawley rats were administered DLM iv or po, either by dissolving it in glycerol formal (GF) or by suspending it in Alkamuls (AL). Groups of rats received 10mg DLM/kg by gavage in each vehicle, as well as 2 mg/kg in GF or 10mg/kg in AL by iv injection. Serial blood samples were collected over 96 h and analyzed for their DLM content by HPLC. In a second experiment, plasma, brain, fat, liver and lung DLM concentrations were measured 2h after giving 10mg DLM/kg orally in GF or AL. In a third experiment rats received 2 or 10mg DLM/kg iv in AL or 2mg DLM/kg iv in GF. Lung DLM content was determined 15 min post injection. DLM particle size in both formulations was measured under a phase contrast microscope. DLM appeared to be completely dissolved in GF, while particle size ranged from <5 to >50 microm in AL. The bioavailability of DLM in the aqueous AL suspension was approximately 9-fold lower than in GF (1.7% versus 15%). Blood C(max) (0.95+/-0.27 versus 0.09+/-0.01 microg/ml) and AUC(0)(48h) (5.49+/-0.22 versus 0.61+/-0.14 microg.h/ml) were markedly higher in the GF gavage group. Tissue DLM levels were also significantly higher in the GF animals at 2h. The 10mg/kg po and 2mg/kg iv doses of DLM in GF produced moderate salivation and slight tremors. Rats receiving the insecticide in AL were asymptomatic. IV injection of the AL suspension resulted in trapping of much of the dose in the pulmonary capillaries. As anticipated, the injected suspension had a longer half-life and slower clearance than did the GF formulation. In summary, limited dissolution of the highly lipophilic DLM particles in the AL suspension severely limited DLM's GI absorption, bioavailability, target organ deposition and acute neurotoxic potency.

Prallethrin induced biochemical changes in erythrocyte membrane and red cell osmotic haemolysis in human volunteers

Changes in biochemical composition in erythrocyte membrane, erythrocytic osmotic haemolysis, and nitrite and nitrate levels in plasma were analyzed in 12 human volunteers who were exposed regularly to prallethrin, a type I pyrethroid mosquito repellent. The results revealed a decrease in cholesterol (C) and phospholipid (P) moieties in erythrocyte membrane with no consequent change in C:P ratio. Further, a significant decrease in the content of phosphatidyl serine suggested that PS is a sensitive phospholipid species to the pyrethroid action. Significant decrease in membrane lipid peroxidation and enhanced levels of nitrite and nitrate in plasma and erythrocyte indicate that increased generation and availability of nitric oxide might have rendered tolerance to erythrocyte membrane by protecting the cells from haemolysis. Increased NO(2) and NO(3) may be due to increased activity of nitric oxide synthase (NOS) and/or expression of isoforms of NOS. A possible involvement of free radical scavenging and antioxidant effects of nitric oxide might have contributed to the observed decrease in lipid peroxidation in the present study.

Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria endemic area in South Africa

DDT and pyrethroids were determined in 152 breast-milk samples from three towns in KwaZulu-Natal, South Africa, one of which had no need for DDT for malaria control. All compounds were found present in breast milk. Primiparae from one town had the highest mean SigmaDDT whole milk levels (238.23 microg/l), and multiparae from the same town had the highest means for permethrin (14.51 microg/l), cyfluthrin (41.74 microg/l), cypermethrin (4.24 microg/l), deltamethrin (8.39 microg/l), and Sigmapyrethroid (31.5 microg/l), most likely derived from agriculture. The ADI for DDT was only exceeded by infants from one town, but the ADI for pyrethroids was not exceeded. Since the ADI for DDT was recently reduced from 20 to 10 microg/kg/bw, we suggest that this aspect be treated with concern. We therefore raise a concern based on toxicant interactions, due to the presence of four different pyrethroids and DDT. Breastfeeding however, remains safe under prevailing conditions.

Environmental pyrethroid and organophosphorus insecticide exposures and sperm concentration

BACKGROUND

There is growing concern that poisoning and other adverse health effects are increasing because organophosphorous (OP) insecticides are now being used in combination with pyrethroid (PYR) insecticides to enhance the toxic effects of PYR insecticides on target insects, especially those that have developed PYR resistance.

OBJECTIVES

We conducted a pilot biomonitoring study to determine whether men in our reproductive cohort study were being exposed to pesticides environmentally by virtue of frequenting an agricultural setting.

METHODS

We screened 18 randomly selected urine samples collected from male participants of reproductive age for 24 parent compounds and metabolites of pesticides and examined the results in relation to sperm concentration.

RESULTS

Results showed high prevalence of exposure to OP and PYR pesticides and our preliminary analyses provided some suggestion that the higher exposure group had lower sperm concentration.

CONCLUSIONS

The potential of OP/PYR mixtures to have enhanced human toxicity needs more research attention.

A mixture of organophosphate and pyrethroid intoxication requiring intensive care unit admission: a diagnostic dilemma and therapeutic approach

The illegal mixing of organophosphates and pyrethroids in marketed agriculture insecticides is becoming prevalent in developing countries. Over a 12-mo period, 8 patients were admitted to the emergency department of a university hospital in Dharan, Nepal after ingestion of such a mixture with suicidal intent. All patients presented with a combination of miosis, bradycardia, tachypnea, and unconsciousness. The occurrence of both pupillary dilation after a small-dose infusion of atropine (0.08 to 0.2 mg/kg in 1-3 h) and seizures raised the possibility of pyrethroid poisoning. In each case, an examination of the insecticide container confirmed that it contained a mixture of organophosphate and pyrethroid. After seizure control, gastric lavage, respiratory support, hemodynamic stabilization and diuresis, seven of the patients recovered without neurological deficit. One patient suffered aspiration pneumonia and died. The early clinical picture after this mixed poisoning is based on the toxicity of organophosphates rather than pyrethroids. Because the patients responded to a small dose of atropine with mydriasis and tachycardia, it suggested a mixed poisoning. Early suspicion of mixed poisoning may have a significant prognostic impact.

Aircraft disinsection: Exposure assessment and evaluation of a new pre-embarkation method

A new "pre-embarkation" method for aircraft disinsection was investigated using two different 2% d-phenothrin containing aerosols. Five experiments in aircrafts of the type Airbus 310 (4x) and Boeing 747-400 (1x) were performed. In the absence of passengers and crew the d-phenothrin aerosol was sprayed under the seat rows and in a second step at the height of approximately 1.60 m by moving from one end of the cabin to the other. Concentration levels of d-phenothrin were determined at different time periods after application of the aerosol spray. In a B 747-400 with the air conditioning system operating the concentrations ranged between 853 and 1753 microg/m3 during and till 5 min after the beginning of spraying at different locations in the cabin. Within 5-20min after the end of the spraying concentrations of 36-205 microg/m3 and 20-40 min thereafter only ca. 1 microg d-phenothrin/m3 were detectable (average values in relation to each period of measurement). On cabin interior surfaces the median values for mainly horizontal areas ranged from 100 to 1160 ng d-phenothrin/cm2. d-Phenothrin concentrations in the air were sufficient to kill flying insects like house flies and mosquitoes within 20 min. Horizontal surfaces were 100% effective against insects up to 24 h after spraying. Doses inhaled by sprayers determined by personal measurements were calculated to be 30-235 microg d-phenothrin per 100 g spray applied (30% in the respirable fraction for Arrow Aircraft Disinsectant; 10% for Aircraft Disinsectant Denka). If passengers will board, e.g., 20 min after the end of the disinsection operation, inhalation exposure is estimated to be practically negligible. Also possible dermal exposure from residues in seats and headrests is very low for passengers during the flight. Therefore any health effects for passengers and crew members are very unlikely.

A reassessment of the neurotoxicity of pyrethroid insecticides

The pyrethroids are a widely used class of insecticides to which there is significant human exposure. They are however generally regarded as safe to man, and there have been few reports of human fatalities. Their acute toxicity is dominated by pharmacological actions upon the central nervous system (CNS), predominantly mediated by prolongation of the kinetics of voltage-gated sodium channels, although other mechanisms operate. This review summarizes our present understanding of such actions and the pharmacological options to antagonize them. One significant problem is the very clear heterogeneity of pyrethroid sensitivity that is seen across sodium channel subtypes; however, the distribution and function of these across the central nervous system are poorly characterized. The review also provides an overview of recent studies that suggest additional effects of pyrethroids: developmental neurotoxicity, the production of neuronal death, and action mediated via pyrethroid metabolites. The evidence for these is at present equivocal, but all 3 carry important implications for human health.

The effect of pesticide spraying on the rate and severity of ED asthma

We report on the incidence of emergency department (ED) asthma presentations and admissions to the Lincoln Hospital, located in the South Bronx of New York City, during the 1999 eradication program of the mosquito vector for West Nile virus. Spraying of Malathion and Resmethrin occurred in the hospital's geographic area over 4 days in September 1999. During that time, 1318 pediatric and adult patients were seen in the ED for asthma-related symptoms. Of these, 222 (16.8%) were hospitalized. Emergency department visits, during days when spraying occurred, were compared with visits during days when no spraying occurred. Comparisons were made with previous years as a reference point. Findings showed that the spraying of insecticides did not increase the rate or severity of asthma presentations as measured by the Lincoln Hospital's ED asthma census or hospital admissions for asthma.

Deltamethrin, a pyrethroid insecticide, is a potent inducer for the activity-dependent gene expression of brain-derived neurotrophic factor in neurons

The mRNA expression of brain-derived neurotrophic factor (BDNF) is controlled in an activity-dependent manner through Ca(2+) influx into neurons. Pyrethroids are widely used insecticides of low acute toxicity in mammals, but their effects on sodium channels are known to lead to hyperexcitation in neuronal cells of insects. In this study, we found that deltamethrin, a type II pyrethroid insecticide, was highly effective in inducing BDNF expression in culture and in the rat brain. Addition of deltamethrin to rat cortical cells in culture markedly increased the expression of BDNF exon III-V mRNA and protein, dependent upon the neuronal activity accompanying the influx of Ca(2+) into neurons and the Ca(2+) influx-dependent phosphorylation of extracellular signal-regulated kinases 1/2. The elevated expression was maintained for at least 48 h, even after deltamethrin was withdrawn from the culture medium. Comparison of the effects of selected pyrethroids on the expression revealed that type II but not type I pyrethroids effectively induced BDNF mRNA expression. In addition, administration of deltamethrin to rats increased the level of BDNF protein in the cerebral cortex and hippocampus. These results indicate that deltamethrin is a potent inducer of BDNF expression in neurons and that it may induce neuronal hyperexcitation if it reaches the brain.

Poisoning due to Pyrethroids

The first pyrethroid pesticide, allethrin, was identified in 1949. Allethrin and other pyrethroids with a basic cyclopropane carboxylic ester structure are type I pyrethroids. The insecticidal activity of these synthetic pyrethroids was enhanced further by the addition of a cyano group to give alpha-cyano (type II) pyrethroids, such as cypermethrin. The finding of insecticidal activity in a group of phenylacetic 3-phenoxybenzyl esters, which lacked the cyclopropane ring but contained the alpha-cyano group (and hence were type II pyrethroids) led to the development of fenvalerate and related compounds. All pyrethroids can exist as at least four stereoisomers, each with different biological activities. They are marketed as racemic mixtures or as single isomers. In commercial formulations, the activity of pyrethroids is usually enhanced by the addition of a synergist such as piperonyl butoxide, which inhibits metabolic degradation of the active ingredient. Pyrethroids are used widely as insecticides both in the home and commercially, and in medicine for the topical treatment of scabies and headlice. In tropical countries mosquito nets are commonly soaked in solutions of deltamethrin as part of antimalarial strategies. Pyrethroids are some 2250 times more toxic to insects than mammals because insects have increased sodium channel sensitivity, smaller body size and lower body temperature. In addition, mammals are protected by poor dermal absorption and rapid metabolism to non-toxic metabolites. The mechanisms by which pyrethroids alone are toxic are complex and become more complicated when they are co-formulated with either piperonyl butoxide or an organophosphorus insecticide, or both, as these compounds inhibit pyrethroid metabolism. The main effects of pyrethroids are on sodium and chloride channels. Pyrethroids modify the gating characteristics of voltage-sensitive sodium channels to delay their closure. A protracted sodium influx (referred to as a sodium 'tail current') ensues which, if it is sufficiently large and/or long, lowers the action potential threshold and causes repetitive firing; this may be the mechanism causing paraesthesiae. At high pyrethroid concentrations, the sodium tail current may be sufficiently great to prevent further action potential generation and 'conduction block' ensues. Only low pyrethroid concentrations are necessary to modify sensory neurone function. Type II pyrethroids also decrease chloride currents through voltage-dependent chloride channels and this action probably contributes the most to the features of poisoning with type II pyrethroids. At relatively high concentrations, pyrethroids can also act on GABA-gated chloride channels, which may be responsible for the seizures seen with severe type II poisoning. Despite their extensive world-wide use, there are relatively few reports of human pyrethroid poisoning. Less than ten deaths have been reported from ingestion or following occupational exposure. Occupationally, the main route of pyrethroid absorption is through the skin. Inhalation is much less important but increases when pyrethroids are used in confined spaces. The main adverse effect of dermal exposure is paraesthesiae, presumably due to hyperactivity of cutaneous sensory nerve fibres. The face is affected most commonly and the paraesthesiae are exacerbated by sensory stimulation such as heat, sunlight, scratching, sweating or the application of water. Pyrethroid ingestion gives rise within minutes to a sore throat, nausea, vomiting and abdominal pain. There may be mouth ulceration, increased secretions and/or dysphagia. Systemic effects occur 4-48 hours after exposure. Dizziness, headache and fatigue are common, and palpitations, chest tightness and blurred vision less frequent. Coma and convulsions are the principal life-threatening features. Most patients recover within 6 days, although there were seven fatalities among 573 cases in one series and one among 48 cases in another. Management is supportive. As paraesthesiae usually resolve in 12-24 hours, specific treatment is not generally required, although topical application of dl-alpha tocopherol acetate (vitamin E) may reduce their severity.

In-flight spraying in aircrafts: determination of the exposure scenario

Exposure measurements were carried out in parked aircrafts during and after application of a biocide aerosol spray (simulated in-flight spraying). The aerosol product SRA spray (Standard Reference Aerosol Spray) was used for spraying. Concentrations of the pyrethrins--the active ingredients--in the air of the passenger cabin (airborne particles, measured during spray application and 40 minutes afterwards) varied from 11 to 65 microg/m3; those of the synergist piperonyl butoxide were 200-485 microg/m3. The concentrations on surfaces of the cabin furniture differed widely. Low concentrations were determined on surfaces in vertical positions (median values: pyrethrins < or =2 ng/cm2; piperonyl butoxide < or =17 ng/cm2), while under seats, on seats and on headrests the concentrations were up to 55.5 ng/cm2 for pyrethrins and 1162.5 ng/cm2 for piperonyl butoxide (median values). The inhaled doses for sprayers (using 100 g of spray) and persons sitting in the passenger cabin were calculated to be 17 microg for pyrethrins and 200 microg for piperonyl butoxide (maximum values). Maximum total external body doses for the applicators during spraying were 830 microg for pyrethrins and 8840 microg for piperonyl butoxide. The potential dermal dose for persons sitting in the passenger cabin was about a factor of two lower.

The synaptosomal membrane bound ATPase as a target for the neurotoxic effects of pyrethroids, permethrin and cypermethrin

Pyrethroids are used widely as insecticides both in agriculture and in households. A cellular target of pyrethroids is the sodium channel in the membrane. In the present study, the activity of the membrane bound integral protein ATPase was studied as a biomarker for the membrane effect of the pyrethroids permethrin and cypermethrin. Male Sprague-Dawley rats were used for cerebral synaptosome preparation. The isolation of synaptosomes was performed with the Percoll gradient method. Both total ATPase and Mg(2+) activated ATPase were studied by determining inorganic phosphate liberated from the substrate ATP. One hour exposure to permethrin (Biokill) and cypermethrin (Ripcord) insecticide products affected ATPase activities. The activity of Na(+), K(+) ATPase decreased dose-dependently in 10-50 microM concentrations of permethrin, and Mg(2+) activated ATPase increased over twofold in the same concentrations of the active components. The effect of the cypermethrin compound Ripcord was not clearly dose-dependent. The activity of total ATPase was almost entirely lost in the concentrations of 100 microM of permethrin and cypermethrin. The results support the idea that membrane ATPases are one target of the neurotoxic effect of pyrethroid compounds.

Combined exposure to DEET (N,N-diethyl-m-toluamide) and permethrin: pharmacokinetics and toxicological effects

Permethrin and DEET are concurrently used for pests control inside homes, in public places, and in military shelters. Combined exposure to these compounds produced greater biochemical, behavioral, and metabolic alterations in animals compared to each individual compound. Concurrent application of DEET and permethrin induced urinary excretion of 3-nitrotyrosine and 8-hydroxy-2'-deoxyguanosine, markers of DNA damage and oxidative stress in rats, increased the release of rat brain mitochondrial cytochrome c, disrupted the blood-brain barrier (BBB) in rats, decreased m2 muscarinic acetylcholine receptor ligand binding density in rat brain, increased urinary excretion of 6 beta-hydroxycortisol, a marker CYP3A4 induction, altered sensorimotor and locomotor activities in rats, and changed in vivo and in vitro metabolism and pharmacokinetic profiles of the individual compound. These findings show that more research is needed to examine adverse effects of the combined use of DEET and permethrin on other biochemical/physiological system(s) and to predict mechanistic pathways for these effects, particularly mechanism of action at cellular and molecular levels and alterations of genes transcription.

Acute ingestion poisoning with insecticide formulations containing the pyrethroid permethrin, xylene, and surfactant: a review of 48 cases

BACKGROUND

Forty-eight patients poisoned with insecticide formulations containing permethrin (a Type I pyrethroid insecticide), xylene, and surfactants are reported here. These patients were diagnosed and treated in the Chang Gung Memorial Hospital in Taiwan from January 1987 to June 1999. Ten patients ingested permethrin in error and 38 patients attempted suicide. Gastrointestinal tract signs and symptoms were most common (35/48; 73%), and included sore throat, mouth ulcerations, dysphagia, epigastric pain, and vomiting. Pulmonary abnormalities were documented in 29% (14/48) of patients. Aspiration pneumonitis occurred in eight patients, including onefatal case. Pulmonary edema was observed in two patients. Sixteen patients (33%) had central nervous system involvement including confusion (6/48; 13%), coma (10/48; 21%), and seizures (4/48; 8%). Cardiovascular symptoms in 3/48 (7%) patients were limited to arrhythmias and shock. Mild renal and hepatic dysfunction was found in 5/48 (10%) and 3/48 (6%) of patients, respectively. Leukocytosis occurred in 16 patients (33%) but was not associated with infection. Only one death occurred during this 12.5-year period.

CONCLUSION

Poisoning caused by ingesting insecticides containing permethrin, xylene, and surfactant manifests primarily gastrointestinal tract symptoms and signs. The involvement of the central nervous system and lungs were less common, but clinically more significant. The relative contributions of the 20% permethrin, 70% xylene, and 10% surfactant to these toxic manifestations, however, is uncharacterized.