Inhibitor Report for: Aldicarb

Aldicarb, a carbamate pesticide banned in France since 2008, represents a persistent risk of human poisoning. There is no up-to-date picture of aldicarb intentional poisonings associated to detailed diagnosis and clinical management of cases to evaluate the effect of its ban on intoxication risk reduction, including suicide. This retrospective epidemiological study describes cases of suicidal intoxication from the Hauts-de-France region between 2012 and 2021 and illustrates this situation through one analytically documented case. 60 cases were collected, mostly presenting a pathognomonic symptomatology. Thirty-five victims presented a muscarinic syndrome (58.3%), 14 a nicotinic syndrome (23.3%), and 37 a central nervous system impairment (61.7%). Hospitalization was necessary for 44 cases (73.3%), with 2 fatal evolutions. Diagnosis was based on the blood cholinesterase activities. Among the 25 cases with toxicology results, 45.8% presented a moderate decrease of acetylcholinesterase activity, whereas 87.5% presented a strong decrease of butyrylcholinesterase activity. Blood or urine detection of aldicarb and its metabolites may be considered in therapeutic management, although their quantification is unlikely to change the emergency medical care. Our study updates epidemiology of aldicarb poisoning at a regional level, highlighting a persisting health threatening situation with banned pesticides. More than 65% of national cases occurred in this agricultural area, aldicarb remaining available from storage of previously purchased products. Robust evidence is presented that acute poisoning is an ongoing major global public health challenge. There is a need for continued international efforts in risk reduction, knowledge, and information strategies.

BACKGROUND: The potential for enhanced degradation of the carbamoyloxime nematicides aldicarb and oxamyl and the organophosphate fosthiazate was investigated in 35 UK agricultural soils. Under laboratory conditions, soil samples received three successive applications of nematicide at 25 day intervals.
RESULTS: The second and third applications of aldicarb were degraded at a faster rate than the first application in six of the 15 aldicarb-treated soils, and a further three soils demonstrated rapid degradation of all three applications. High organic matter content and low pH had an inhibitory effect on the rate of aldicarb degradation. Rapid degradation was observed in nine out of the ten soils treated with oxamyl. In contrast, none of the fosthiazate-treated soils demonstrated enhanced degradation. CONCLUSION: The potential for enhanced degradation of aldicarb and oxamyl was demonstrated in nine out of 15 and nine out of ten soils respectively that had previously been treated with these active substances. Degradation of fosthiazate occurred at a much slower rate, with no evidence of enhanced degradation. Fosthiazate may provide a useful alternative in cases where the efficacy of aldicarb and oxamyl has been reduced as a result of enhanced degradation.

In an attempt to understand underlying mechanism(s) of salinity-induced aldicarb toxicity in Japanese medaka (Oryzias latipes), aldicarb uptake, biotransformation, and its effect on acetylcholinesterase (AChE) were examined. Salinity had no effect on aldicarb uptake. However, gill microsomal flavin-containing monooxygenase (FMO) activity and a 57-kDa FMO1-like protein increased as the salinity was raised from 0.15 to 2.0%. Sulfoxidation of 14C-aldicarb by liver and gill microsomal incubations showed ninefold and 1.8-fold increases, respectively, as the salinity was raised from 0.15 to 2.0%. Formation of aldicarb sulfoxide was not affected by incubation with carbon monoxide, indicating that cytochrome P450 (CYP450) was not a primary pathway in the formation of the sulfoxide. Muscle AChE activity showed no significant relationship with salinity, although the IC50 of aldicarb to muscle AChE differed significantly between 6.21 +/- 1. 253 and 2.97 +/- 0.597 microM for 0.15 and 2.0% salinity, respectively. Aldicarb sulfoxide was 40 times more potent than aldicarb in inhibiting muscle AChE in Japanese medaka. Based on these results, we conclude that salinity-induced enhancement of aldicarb toxicity to Japanese medaka might be partly attributed to the upregulation of FMO(s), which, in turn, increase the biotransformation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of AChE than aldicarb. In addition, salinity also seems to potentiate the anticholinesterase activity of aldicarb (the parent) through an unknown mechanism.

Aldicarb, a carbamate pesticide banned in France since 2008, represents a persistent risk of human poisoning. There is no up-to-date picture of aldicarb intentional poisonings associated to detailed diagnosis and clinical management of cases to evaluate the effect of its ban on intoxication risk reduction, including suicide. This retrospective epidemiological study describes cases of suicidal intoxication from the Hauts-de-France region between 2012 and 2021 and illustrates this situation through one analytically documented case. 60 cases were collected, mostly presenting a pathognomonic symptomatology. Thirty-five victims presented a muscarinic syndrome (58.3%), 14 a nicotinic syndrome (23.3%), and 37 a central nervous system impairment (61.7%). Hospitalization was necessary for 44 cases (73.3%), with 2 fatal evolutions. Diagnosis was based on the blood cholinesterase activities. Among the 25 cases with toxicology results, 45.8% presented a moderate decrease of acetylcholinesterase activity, whereas 87.5% presented a strong decrease of butyrylcholinesterase activity. Blood or urine detection of aldicarb and its metabolites may be considered in therapeutic management, although their quantification is unlikely to change the emergency medical care. Our study updates epidemiology of aldicarb poisoning at a regional level, highlighting a persisting health threatening situation with banned pesticides. More than 65% of national cases occurred in this agricultural area, aldicarb remaining available from storage of previously purchased products. Robust evidence is presented that acute poisoning is an ongoing major global public health challenge. There is a need for continued international efforts in risk reduction, knowledge, and information strategies.

BACKGROUND: The potential for enhanced degradation of the carbamoyloxime nematicides aldicarb and oxamyl and the organophosphate fosthiazate was investigated in 35 UK agricultural soils. Under laboratory conditions, soil samples received three successive applications of nematicide at 25 day intervals.
RESULTS: The second and third applications of aldicarb were degraded at a faster rate than the first application in six of the 15 aldicarb-treated soils, and a further three soils demonstrated rapid degradation of all three applications. High organic matter content and low pH had an inhibitory effect on the rate of aldicarb degradation. Rapid degradation was observed in nine out of the ten soils treated with oxamyl. In contrast, none of the fosthiazate-treated soils demonstrated enhanced degradation. CONCLUSION: The potential for enhanced degradation of aldicarb and oxamyl was demonstrated in nine out of 15 and nine out of ten soils respectively that had previously been treated with these active substances. Degradation of fosthiazate occurred at a much slower rate, with no evidence of enhanced degradation. Fosthiazate may provide a useful alternative in cases where the efficacy of aldicarb and oxamyl has been reduced as a result of enhanced degradation.

A couple showing signs of cholinergic crisis was admitted to the hospital. Analyses with high-performance liquid chromatography and gas chromatography-mass spectrometry conducted on serum, urine, and stomach contents that were collected few hours after first symptoms showed the presence of aldicarb, which is the most potent carbamate insecticide on the market. A murder attempt was suspected because the patients showed the first signs some minutes after drinking coffee upon returning home and no commercial products containing aldicarb were found in the house. Because of the reversibility of inhibition of acetylcholinesterase, the patients recovered after treatment with atropine and toxogonin. They left the hospital after 12 days. To our knowledge, the serum concentrations of aldicarb reported in this paper are the highest reported for a nonfatal case.

Young organisms are often more sensitive to the toxic effects of pesticides, and this finding has spurred research on further characterization of this susceptibility. The neurotoxic effects of cholinesterase (ChE)-inhibiting pesticides are of particular concern for human health risk assessment due to the widespread exposure potential in children. This study evaluated age-related differences in susceptibility for a carbamate (aldicarb) and an organophosphorus pesticide (methamidophos). Comparisons were made between preweanling (Postnatal Day 17, PND17), postweanling (PND27), and adult (approximately PND70) male and female rats. All were acute studies using oral administration. Sensitivity was quantified by (1) determination of maximally-tolerated doses (MTDs); (2) measurement of brain and blood ChE inhibition; and (3) neurobehavioral evaluation using end points known to be sensitive indicators of exposure to anticholinesterases. MTD data showed that preweanling rats were twice as sensitive as adults to aldicarb, but there was no differential sensitivity to methamidophos. The dose-response data for brain ChE inhibition followed a similar pattern of age-related differences, and similar levels of inhibition were measured at the MTD regardless of age. Dose-response and time course studies of neurobehavioral end points indicated that differential effects due to age depend on the behavioral end point examined. Following aldicarb administration, the dose-response curves for a few end points overlapped; however, the young rats otherwise showed fewer signs of toxicity than did the adults despite similar levels of brain ChE inhibition. Motor activity assessment showed that aldicarb did not produce any activity depression in PND17 rats, whereas the data for the PND27 and adult rats overlapped. With methamidophos, the dose-response curves for most end points for preweanling and adult rats were quite similar. Aldicarb-induced ChE inhibition was readily reversible in all age groups, whereas with methamidophos, enzyme activity recovered more rapidly in the young. Most behavioral alterations had recovered by 24 h with either pesticide. The results of these studies indicate that (1) ChE-inhibiting pesticides are not all the same regarding relative sensitivity of the young; (2) age-related differences were reflected in both the MTDs and degree of ChE inhibition; and (3) age-related differences in neurobehavioral measures depended on the pesticide and on the end points examined.

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in mammals, birds, and fish, and is readily biotransformed by most organisms studied. Metabolic products of aldicarb include the more toxic sulfoxide and the less toxic sulfone as two of the major products. Both the cytochrome P450 (CYP) and the flavin monooxygenase systems (FMO) are involved in this process. This study examined the capacities of liver microsomes of male channel catfish (Ictalurus punctatus), which lack FMO, to biotransform aldicarb in vitro. In addition, the acetylcholinesterase inhibitory potencies of aldicarb and its sulfoxide and sulfone derivatives were determined. For metabolism studies, incubations of [14C]-aldicarb (0.1mM) were carried out for up to 15-90 min using 1.0 mg/mL of hepatic microsomal protein. Total NADPH- dependent biotransformation was low (< 3.0% conversion to polar metabolites), and was inhibited by carbon monoxide. The only metabolite detected was aldicarb sulfoxide (Kmapp = 53.8 +/- 25.3 microM; Vmaxapp = 0.040 +/- 0.007 nmol/min/mg). Treatment of fish with the CYP modulators beta-naphthoflavone (BNF, 50 mg/kg) and ethanol (EtOH, 1.0% aqueous) had no effect on sulfoxide production. No correlation existed between CYP isoform expression (determined by western blot) and aldicarb sulfoxidation rates, suggesting the involvement of an unmeasured CYP isoform or involvement of several isoforms with low specificity. This study indicates that a low rate of bioactivation of aldicarb to aldicarb sulfoxide may be responsible for the resistance of channel catfish to aldicarb toxicity relative to that of other piscine species.

In an attempt to understand underlying mechanism(s) of salinity-induced aldicarb toxicity in Japanese medaka (Oryzias latipes), aldicarb uptake, biotransformation, and its effect on acetylcholinesterase (AChE) were examined. Salinity had no effect on aldicarb uptake. However, gill microsomal flavin-containing monooxygenase (FMO) activity and a 57-kDa FMO1-like protein increased as the salinity was raised from 0.15 to 2.0%. Sulfoxidation of 14C-aldicarb by liver and gill microsomal incubations showed ninefold and 1.8-fold increases, respectively, as the salinity was raised from 0.15 to 2.0%. Formation of aldicarb sulfoxide was not affected by incubation with carbon monoxide, indicating that cytochrome P450 (CYP450) was not a primary pathway in the formation of the sulfoxide. Muscle AChE activity showed no significant relationship with salinity, although the IC50 of aldicarb to muscle AChE differed significantly between 6.21 +/- 1. 253 and 2.97 +/- 0.597 microM for 0.15 and 2.0% salinity, respectively. Aldicarb sulfoxide was 40 times more potent than aldicarb in inhibiting muscle AChE in Japanese medaka. Based on these results, we conclude that salinity-induced enhancement of aldicarb toxicity to Japanese medaka might be partly attributed to the upregulation of FMO(s), which, in turn, increase the biotransformation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of AChE than aldicarb. In addition, salinity also seems to potentiate the anticholinesterase activity of aldicarb (the parent) through an unknown mechanism.

Laboratory toxicity data contrasting responses of aquatic organisms to insecticides are important for focusing on sensitive species (steepest exposure-response slope) exposed to aqueous concentrations of these insecticides in field studies. These data also allow prediction of expected responses of aquatic species to a range of insecticide concentrations in situ. Aqueous 48-h toxicity tests were performed to contrast responses of Daphnia magna Straus, Hyalella azteca Saussure, Chironomus tentans Fabricius, and Pimephales promelas Rafinesque to acetylcholinesterase-inhibiting insecticides: chlorpyrifos, aldicarb, and chlordane. As expected, invertebrates tested (H. azteca, C. tentans, and D. magna) were >/= 200 times more sensitive than the vertebrate P. promelas to chlorpyrifos exposures. H. azteca was approximately 3.5 times more sensitive to chlorpyrifos (453% mortality/&mgr;g/L) than D. magna (128% mortality/&mgr;g/L). For both aldicarb and chlordane, C. tentans was the most sensitive species tested (2.44 and 2.54% mortality/&mgr;g/L, respectively). Differences in chlordane potency for test species varied only by a factor of approximately 2-3 (0.88% mortality/&mgr;g/L for H. azteca to 2.54% mortality/&mgr;g/L for C. tentans). Although point estimates of population responses such as LC50s, NOECs, and LOECs are of some utility for predicting effects of pesticides in aquatic systems, exposure-response slopes are also useful for extrapolation of laboratory data to diverse field situations, especially where sediment sorption may regulate insecticide exposure or bioavailability.

A growing body of evidence indicates that young animals exhibit an increased susceptibility to the lethal effects of cholinesterase (ChE)-inhibiting insecticides. Our laboratory is engaged in defining factors which may explain this age-related sensitivity. This report includes results from experiments designed to compare the developmental profiles, kinetic parameters and intrinsic (i.e. in vitro) sensitivity of developing male rat brain acetylcholinesterase (AChE) activity to carbamate and organophosphorus anticholinesterases. Total ChE activity in whole brain for each age was composed of about 90% AChE and 10% butyrylcholinesterase (BCHE) activity for the six ages examined. Brain AChE activity showed an age-related increase in Vmax until postnatal day 17 with no change in Km (average of all six ages approximately equal to 72 microM). Optimal substrate (acetylthiocholine) concentration for each age was 1 mM, and there was substrate inhibition (approximately 10%) at 2.5 mM. IC50s (the concentration of compound that inhibits 50% of the AChE activity in 30 min at 26 degrees C) defined concomitantly for postnatal day 4 and adult brain AChE using either aldicarb, carbaryl, chlorpyrifos-oxon or malaoxon were virtually identical at both ages with average IC50 values being: aldicarb = 2.4 microM, carbaryl = 1.7 microM, chlorpyrifos-oxon = 4.9 nM and malaoxon = 140 nM. In summary, AChE in young and adult brain differs mostly in specific activity while the Km(s), substrate profiles, and in vitro sensitivity to selected anticholinesterase insecticides are not different. Therefore, these data support the hypothesis that the greater sensitivity of the young animals to anticholinesterase pesticides is not due to the greater sensitivity of the target molecule AChE to these inhibitors.

Synaptobrevins are vesicle-associated proteins implicated in neurotransmitter release by both biochemical studies and perturbation experiments that use botulinum toxins. To test these models in vivo, we have isolated and characterized the first synaptobrevin mutants in metazoans and show that neurotransmission is severely disrupted in mutant animals. Mutants lacking snb-1 die just after completing embryogenesis. The dying animals retain some capability for movement, although they are extremely uncoordinated and incapable of feeding. We also have isolated and characterized several hypomorphic snb-1 mutants. Although fully viable, these mutants exhibit a variety of behavioral abnormalities that are consistent with a general defect in the efficacy of synaptic transmission. The viable mutants are resistant to the acetylcholinesterase inhibitor aldicarb, indicating that cholinergic transmission is impaired. Extracellular recordings from pharyngeal muscle also demonstrate severe defects in synaptic transmission in the mutants. The molecular lesions in the hypomorphic alleles reside on the hydrophobic face of a proposed amphipathic-helical region implicated biochemically in interacting with the t-SNAREs syntaxin and SNAP-25. Finally, we demonstrate that double mutants lacking both the v-SNAREs synaptotagmin and snb-1 are phenotypically similar to snb-1 mutants and less severe than syntaxin mutants. Our work demonstrates that synaptobrevin is essential for viability and is required for functional synaptic transmission. However, our analysis also suggests that transmitter release is not completely eliminated by removal of either one or both v-SNAREs.

We describe the molecular cloning and characterization of the unc-64 locus of Caenorhabditis elegans. unc-64 expresses three transcripts, each encoding a molecule with 63-64% identity to human syntaxin 1A, a membrane- anchored protein involved in synaptic vesicle fusion. Interestingly, the alternative forms of syntaxin differ only in their C-terminal hydrophobic membrane anchors. The forms are differentially expressed in neuronal and secretory tissues; genetic evidence suggests that these forms are not functionally equivalent. A complete loss-of-function mutation in unc-64 results in a worm that completes embryogenesis, but arrests development shortly thereafter as a paralyzed L1 larva, presumably as a consequence of neuronal dysfunction. The severity of the neuronal phenotypes of C. elegans syntaxin mutants appears comparable to those of Drosophila syntaxin mutants. However, nematode syntaxin appears not to be required for embryonic development, for secretion of cuticle from the hypodermis, or for the function of muscle, in contrast to Drosophila syntaxin, which appears to be required in all cells. Less severe viable unc-64 mutants exhibit a variety of behavioral defects and show strong resistance to the acetylcholinesterase inhibitor aldicarb. Extracellular physiological recordings from pharyngeal muscle of hypomorphic mutants show alterations in the kinetics of transmitter release. The lesions in the hypomorphic alleles map to the hydrophobic face of the H3 coiled-coil domain of syntaxin, a domain that in vitro mediates physical interactions with similar coiled-coil domains in SNAP-25 and synaptobrevin. Furthermore, the unc-64 syntaxin mutants exhibit allele-specific genetic interactions with mutants carrying lesions in the coiled-coil domain of synaptobrevin, providing in vivo evidence for the significance of these domains in regulating synaptic vesicle fusion.

Physostigmine, aldicarb and carbaryl were potent inhibitors of acetylcholinesterase (AChE). The physostigmine-inhibited AChE fluoresced at 300 nm excitation and 500 nm emission wavelengths, but the aldicarb and carbaryl inhibited enzyme did not. This suggests that the carbamylated active center is not the fluorescing site in AChE. The fluorescence intensity of physostigmine-inhibited AChE decreased with increasing the substrate (acetylthiocholine) concentration, thus indicating that physostigmine binding to the active site is essential for the development of fluorescence. Thus, the physostigmine-inhibited AChE fluoresces due to the binding of trimethylpyrrolo[2,3-b]indol (TMPI) moiety, formed by the hydrolysis of physostigmine, to a peripheral site in AChE. The fluorescence intensity of the physostigmine-inhibited enzyme decreased when the inhibited-enzyme was dialyzed for either 30 min that poorly reactivated the enzyme or 180 min that fully reactivated the enzyme. This suggests that dialysis dissociates the AChE-TMPI complex much faster than it reactivates the carbamylated AChE. Ephedrine, propranolol and phenothiazines including trifluoparazine (TPZ) caused non-competitive inhibition, while hexamethonium caused an uncompetitive inhibition of AChE activity. TPZ, upon binding with AChE, formed a fluorescent TPZ-enzyme complex. The fluorescence intensity of TPZ-AChE complex was effectively decreased by ephedrine, but not by propranolol or hexamethonium. This indicates that TPZ and ephedrine bind to the same site in AChE which is different from the site/or sites to which propranolol or hexamethonium bind. Hexamethonium protected AChE from inhibition by carbamates and decreased the fluorescence intensity of the physostigmine-inhibited AChE. Phenothiazines and ephedrine did not modulate the enzyme inhibition or the fluorescence intensity of the physostigmine-inhibited AChE. Propranolol and TPZ potentiated the enzyme inhibition and increased the fluorescence intensity in the presence of physostigmine. These compounds, however, did not affect the inhibition of AChE by carbaryl or aldicarb. Ephedrine blocked the effects of TPZ, but did not alter the effects of propranolol on physostigmine-inhibited AChE. AChE, therefore, contains multiple peripheral binding sites which, upon binding to specific ligands, transduce differential signals to the active center.

Categorical regression is a mathematical tool that can be adapted to estimate potential health risk from chemical exposures. By regressing ordered categories of toxic severity or pathological staging on exposure dose, this method can estimate the likelihood of observing any of the categories of severity at any dose level. Depending on the nature of the available data, these estimates can take the form of incidence rates for any of the categories in an exposed population or the probability of a new study conducted at a specified dose level being classified as one of the categories. Categorical regression is illustrated using toxicity data on aldicarb. For aldicarb, the data fall into three different groups: human clinical studies, dietary exposures in experimental animals, and accidental human exposure by contaminated crops. The U.S. EPA has assessed this literature and developed a reference dose (RfD) of 0.001 mg/kg-day. The results of applying categorical regression to data from human clinical studies suggests a maximum likelihood risk estimate of adverse effects of 0.008% at a 10-fold higher dose than the RfD when blood cholinesterase inhibition is not considered as an adverse effect. When blood cholinesterase inhibition of 20% or more is considered as an adverse effect, a maximum likelihood risk estimate of adverse effects is 0.1% at a dose 10-fold higher than the RfD.

The importance of recovery following pulsed and continuous exposure was determined by measuring the acute toxicity of two organophosphorus (parathion and malathion) and four carbamate (aldicarb, carbaryl, carbofuran and propoxur) insecticides. Two 1-h pulses caused significantly fewer symptoms of intoxication than 2 h of continuous exposure if at least 2 to 6 h in clean water were provided between doses for the four carbamates. Two 1-h pulses were equally toxic as a single 2-h continuous exposure for the two organophosphorus insecticides. Acetylcholinesterase activity in midges given two 1-h pulses of carbaryl separated by 24 h in clean water showed reactivation to control levels between the two exposures. These results contribute to the belief that episodic exposure to insecticides is less toxic if recovery in clean water is provided.

An air sampling and analytical method was developed for organonitrogen pesticides using a combined filter and XAD-2 sorbent sampler and high performance liquid chromatography-ultraviolet detection. The method was evaluated for 14 organonitrogen pesticides by National Institute for Occupational Safety and Health evaluation guidelines and procedures. Evaluation experiments addressed limits of detection and quantitation, analytical recovery, sampler capacity, sample stability, and precision and bias over a range of 12 to 240 micrograms per sample. Samples were stable when stored for up to 30 days under either ambient or refrigerated conditions. Based on the finding of this work, 10 of the 14 compounds studied (aldicarb, captan, carbaryl, carbofuran, chlorpropham, diuron, formetanate, methiocarb, oxamyl, propham) can be successfully determined simultaneously using one method with an accuracy of better than +/- 25% of the true value with 95% confidence. Two other compounds (carbendazim/benomyl, methomyl) can be measured with the same accuracy over a more limited concentration range. The remaining two compounds (propoxur, thiobencarb) may meet this criterion, but additional samples would need to be included in the data analysis. With the current data, these two compounds can be determined with an accuracy of better than +/- 27% of the true value with 95% confidence.

Using a combination of in vitro assays we have examined the capacities of contemporary-exposure chemicals to modulate human estrogen and human progesterone receptor (hER and hPR) activity in human breast and endometrial cancer cells. The carbamate insecticides aldicarb, Baygon (propoxur), bendiocarb, carbaryl, methomyl, and oxamyl were used in this study. The carbamates alone weakly activated estrogen- or progesterone-responsive reporter genes in breast and endometrial cancer cells. All of the carbamates decreased estradiol- or progesterone-induced reporter gene activity in the breast and endometrial cancer cells. In whole cell competition binding assays, the carbamates demonstrated a limited capacity to displace radiolabeled estrogen or progesterone from ER or PR. Based on the results presented here, the carbamate insecticides may represent a class of chemicals which function through a mechanism separate from ligand-binding and, therefore, may act as general endocrine modulators in mammalian cells.

OBJECTIVE: Retrospective evaluation of the clinical course of carbamate poisoning in young children and adults. DESIGN: Thirty-six children aged 1 to 8 years (median 2.5 years) and 24 adults aged 17 to 41 years (median 22 years) ingested rat poison resulting in carbamate poisoning. The ingested poisons in all cases were positively identified as methomyl or aldicarb by gas chromatography-mass spectrometry. RESULTS: Symptoms of intoxication in children were compared to those in adults with similar depression of the serum cholinesterase. The predominant symptoms in young children were central nervous system depression and hypotonia. The most common muscarinic effect was diarrhea. In adults, the main signs were miosis and fasciculations. Fasciculations in children were less frequent. Central nervous system depression, hypotonia, and diarrhea were uncommon in adults. CONCLUSION: Based on a relatively large number of carbamate poisonings in young children, we conclude that the clinical presentation differs from adult poisoning manifestations. The absence of classic muscarinic effects does not exclude the possibility of carbamate poisoning in young children with central nervous system depression.

Although rodenticides historically have been among the most toxic substances available to the public and have been implicated as agents in both unintentional and suicidal exposures the anticoagulant agents currently in use such as coumadin and their long-acting derivatives e.g brodifacoum are relatively safe In 1995 most persons who reported exposure to anticoagulant rodenticides did not develop symptoms or require specific therapy However during 1994-1997 the New York City Poison Control Center NYCPCC was consulted about 25 patients primarily persons who had emigrated from the Dominican Republic who had manifestations consistent with the cholinergic toxidrome which is not characteristic of poisoning by the anticoagulant rodenticides after ingesting a rodenticide known as Tres Pasitos Three Little Steps In each case the product had been purchased at a neighborhood store for use as a household rodenticide The Environmental Investigation Unit of the New York State Department of Environmental Conservation NYDEC investigated the poisoning incidents Laboratory analysis indicated that the product contained the carbamate pesticide aldicarb 2-methyl-2-(methylthio)-propionaldehyde O methylcarbamoyl oxime which is not registered for use as a rodenticide in the United States This report presents a detailed description of two of these cases and a summary of the remaining cases

Rab molecules regulate vesicular trafficking in many different exocytic and endocytic transport pathways in eukaryotic cells. In neurons, rab3 has been proposed to play a crucial role in regulating synaptic vesicle release. To elucidate the role of rab3 in synaptic transmission, we isolated and characterized Caenorhabditis elegans rab-3 mutants. Similar to the mouse rab3A mutants, these mutants survived and exhibited only mild behavioral abnormalities. In contrast to the mouse mutants, synaptic transmission was perturbed in these animals. Extracellular electrophysiological recordings revealed that synaptic transmission in the pharyngeal nervous system was impaired. Furthermore, rab-3 animals were resistant to the acetylcholinesterase inhibitor aldicarb, suggesting that cholinergic transmission was generally depressed. Last, synaptic vesicle populations were redistributed in rab-3 mutants. In motor neurons, vesicle populations at synapses were depleted to 40% of normal levels, whereas in intersynaptic regions of the axon, vesicle populations were elevated. On the basis of the morphological defects at neuromuscular junctions, we postulate that RAB-3 may regulate recruitment of vesicles to the active zone or sequestration of vesicles near release sites.

1. The rate of sulphoxidation of aldicarb (2-methyl-2-(methylthio) propanal O-[(methylamino) carbonyl oxime], Temik) in rat hepatic, renal and pulmonary microsomes was determined by quantitating the levels of aldicarb sulphoxide and aldicarb sulphone produced during incubations. Under in vitro experimental conditions used in the present study, aldicarb sulphoxide was the only metabolite produced, and further metabolism of aldicarb sulphoxide to aldicarb sulphone was negligible. 2. The average maximal velocity (mumol/min/mg protein) for the sulphoxidation of aldicarb, based on measurements of product formation, in liver, kidney and lung microsomes was 5.41, 39.51 and 2.45 respectively. The corresponding values for the Michaelis constant (microM) were 184, 1050 and 188 respectively. 3. These results imply that under in vivo conditions (1) aldicarb sulphoxidation is not likely to be saturable even at lethal doses in the rat, and (2) aldicarb clearance in rat liver and kidney will be limited by the rate of blood flow and not metabolizing enzyme levels.

The suitability of Empore-activated carbon disks (EACD), Envi-Carb graphitized carbon black (GCB) and CPP-50 graphitized carbon for the trace enrichment of polar pesticides from water samples was studied by means of off-line and on-line solid-phase extraction (SPE). In the off-line procedure, 0.5-2 l samples spiked with a test mixture of oxamyl, methomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. After evaporation, a sample was injected onto a C18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detection. EACD performed better than EnviCarb cartridges in terms of breakthrough volumes (> 2 l for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n = 3) and sampling speed (100 ml/min); detection limits in drinking water were 0.05-0.16 microgram/l. In the on-line experiments, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10 x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the strong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C18 analytical column. The final on-line procedure was also applied for the less polar propoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than EACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n = 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a CPP-50 precolumn also showed better performance than when Bondesil C18/OH or polymeric PLRP-S was used, but chromatographic resolution was similar. With the CPP-50-based system, detection limits of the test compounds were 0.05-1 microgram/l in surface water.

The clinical signs of intoxication produced by cholinesterase inhibitors, many of which are used as pesticides, are considered important information for regulatory purposes. We conducted acute studies of cholinesterase inhibitors to compare their effects as determined by a functional observational battery (FOB) and motor activity. The acute effects of two carbamates (carbaryl, aldicarb) and five organophosphates (OP) (chlorpyrifos, diazinon, parathion, fenthion, and diisopropyl fluorophosphate, or DFP) were evaluated on the day of dosing at the time of peak effect, at 1 and 3 days, and 1 week after dosing (oral gavage, in corn oil). A high dose was selected that produced clear cholinergic signs, and lower doses were chosen to produce a range of effects. Generally all cholinesterase inhibitors produced autonomic signs of cholinergic overstimulation (salivation, lacrimation, and miosis), hypothermia, mild tremors and mouth-smacking (chewing motions), lowered motor activity, decreased tail-pinch response, and altered neuromuscular function (gait changes and increased foot splay). The measures generally found to be most sensitive on the day of dosing were body temperature, motor activity, gait, and the presence of mouth-smacking and fine tremors. However, no single measure was the most sensitive across all compounds; for example, the lowest dose of fenthion decreased motor activity by 86% but did not alter the tail-pinch response, whereas the lowest dose of parathion did not lower activity but did decrease the tail-pinch response. For some measures, differences in the slopes of the dose-response curves were evident. Many effects were still observed at 24 h, but recovery was apparent for all compounds. Interestingly, residual effects at 72 h were obtained with the carbamates (carbaryl, aldicarb) as well as with the Op fenthion, but not with the other compounds. Thus, the overall clinical picture of toxicity was similar for these cholinesterase inhibitors, but compound-specific differences emerged in terms of the individual measures, dose-response, and time course.

Groups of rats were treated with graded doses of zineb or aldicarb solely or in association with copper sulphate for nine consecutive weeks. Body weight gain was retarded and thymus gland weight was decreased in all treated groups. A pronounced synergism between copper sulphate and zineb was noticed in lowering the weights of thymus, testes, and adrenal glands. Various degrees of reduction in hemoglobin concentration, red blood cells and platelet counts occurred after treatment with the above-mentioned agrochemical regimen. Copper sulphate synergised the elevation of serum alkaline phosphatase (AP) activity, and bilirubin concentration as well the reduction of hemoglobin concentration by zineb. Alanine aminotransferase (ALT) activity was significantly increased, while cholinesterase (ChE) activity was decreased in all treated groups. Serum triglycerides (TGs) were lowered in rats treated with medium or high doses of zineb or aldicarb.

Aldicarb is the most potent of the commercially available carbamate pesticides and is an unusual source of acute human poisonings. We present the case of a 43-year-old man exposed to aldicarb who developed severe cholinergic symptoms and progressive weakness requiring intubation for 5 days. Both his red blood cell cholinesterase and plasma pseudocholinesterase levels were depressed for a minimum of 44 hours. He demonstrated neuromuscular improvement concurrent with pralidoxime administration. The pertinent medical literature on aldicarb poisoning is reviewed.

OBJECTIVE (1) Retrospective evaluation of the clinical course of carbamate poisoning and the effect of oxime therapy in children. (2) In vitro study of the effect of oximes on the reactivation of carbamylated cholinesterase. DESIGN: (1) Clinical survey: The records of 26 children intoxicated with carbamates were examined retrospectively. The poisoning agents in all cases were positively identified as methomyl or aldicarb by gas chromatography-mass spectrometry. (2) Laboratory study: The direct effect of obidoxime and of pralidoxime on acetylcholinesterase activity in vitro was investigated in normal human packed red blood cells pretreated with an organophosphate (paraoxon) or a carbamate (aldicarb or methomyl). CLINICAL SETTING: Pediatric intensive care unit of a teaching hospital. PATIENTS: Twenty-six infants and young children (aged 1 to 8 years) admitted to the pediatric intensive care unit with severe carbamate intoxication. INTERVENTIONS: All cases had been treated with repeated doses of atropine sulfate (0.05 mg/kg) administered every 5 to 10 minutes until muscarinic symptoms disappeared. Obidoxime chloride (Toxogonin, 6 mg/kg) was administered on admission, and again after 4 to 5 hours. RESULTS: Predominant symptoms were related to central nervous system and nicotinic effects. All the patients showed marked improvement within several hours and recovered completely within 24 hours. None of the children deteriorated and none showed exacerbation of cholinergic symptoms after obidoxime treatment. In vitro, oximes reactivated acetylcholinesterase inhibited with paraoxon, whereas no significant effect of oximes on carbamylated enzyme activity was observed. CONCLUSIONS: Based on the recovery of all cases, as compared with other reports of carbamate poisoning treated with atropine alone, it is concluded that, in the case of aldicarb or methomyl poisoning, oxime therapy apparently does not contribute to the recovery of poisoned patients. In cases of poisoning by an unknown pesticide or of mixed poisoning, oxime therapy can prove beneficial because no negative effects of the therapy can be discerned.

To optimize conditions for sample collection, preparation, storage, and analysis and to assure the validity of our previously published liquid chromatographic (LC) method for carbamate analysis in tissue, stabilities of 16 N-methylcarbamates in beef, duck, and chicken liver tissues were studied by using 2 sampling protocols. Tissue samples were fortified at room temperature to a concentration 5 to 10 times greater than either the Environmental Protection Agency tolerance level for each compound (if established) or the concentration used in the previously published method. Thereafter, samples were continuously frozen at -4 degrees C for varying time intervals. In the first study, samples were analyzed one day (initial) and 0.5, 1, 1.5, 2, 3, 4, 5, and 6 months after fortification. In the second study, samples were analyzed one day (initial) and 0.5, 1, 2, 3, and 6 months after fortification. For each residue and species, a minimum of 4 samples were analyzed by LC at each point in time, and the mean represented analyte concentration at the end of each time interval. Rates of residue depletion varied among analytes and among species. Depletion rates were greater in duck livers than in beef livers. Methomyl and oxamyl were depleted completely within 2 weeks. Between 2 and 6 months after sample fortification, residue depletions to levels below detection limits were observed for aldicarb, aldicarb sulfoxide, aldicarb sulfone, dioxacarb, promecarb, propoxur, and bendiocarb. The initial loss of certain carbamates during sample preparation in tissues exposed to room temperature for up to 8 h was greater than the subsequent rate of loss. Results indicate that cryogenic conditions are required for sample preparation and storage.

Zinc chloride-diphenylamine reagent, whose use has been reported for the detection of organochlorine insecticides by thin layer chromatography, was further studied for its ability to detect the organophosphorus insecticides phorate, phosphamidon, DDVP, and phosalone and the carbamate insecticide carbaryl and aldicarb. These insecticides give intense blue-green spots with this reagent. The procedure can be applied to the detection of the insecticides in biological materials and thus has a potential use in forensic toxicology.

Organosphosphorus and carbamate insecticides are quite often used in greenhouses. They represent a group of active principles of toxicological relevance. Initial residues on the surface of cucumber, tomato and ornamental plants, and half-life periods for residue degradation are outlined for carbendazim, dimethoate, fenazox, malathion, methamidophos and pirimiphos-methyl. Residues on plants, concentration in the air, dermal exposition, and inhibition of serum choline esterase activity are shown for methamidophos and aldicarb, respective reentry times being discussed. On harvest and cultivation in greenhouses, dermal exposition as a rule is more relevant than inhalation.

A simplified method is described for determining 7 N-methyl carbamates (aldicarb, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, and propoxur) and 3 related metabolites (aldicarb sulfoxide, aldicarb sulfone, and 3-hydroxy carbofuran) in fruits and vegetables. Residues are extracted from crops with methanol; coextractives are then separated by gel permeation chromatography (GPC) or GPC with on-line Nuchar-Celite cleanup for crops with high chlorophyll and/or carotene content (e.g., cabbage and broccoli). Carbamates are separated on a reverse-phase liquid chromatography column, using a methanol-water gradient mobile phase. Separation is followed by postcolumn hydrolysis to yield methylamine, and the formation of a fluorophore with o-phthalaldehyde and 2-mercaptoethanol prior to fluorescence detection. Recovery data were obtained by fortifying 5 different crops (apples, broccoli, cabbages, cauliflower, and potatoes) at 0.05 and 0.5 ppm. Recoveries averaged 93% at both fortification levels except for the very polar aldicarb sulfoxide for which recoveries averaged around 52% at both levels. The coefficient of variation of the method at both levels is less than 5% and the limit of detection, defined at 5 times baseline noise, varies between 5 and 10 ppb, depending on the compound.

Toxicity was determined for 15 acaricides against a laboratory strain of northern fowl mites, Ornithonyssus sylviarum (Canestrini and Fanzago). Adult females were exposed to residues on filter paper for 24 h. Three organophosphorous compounds (monocrotophos, cythioate, and famphur) were more toxic to the northern fowl mite than was carbaryl, the most commonly used pesticide in the poultry industry. The other tested compounds were less toxic to the mite than was carbaryl. Four of these, not used previously for northern fowl mite control, had low LC50's for northern fowl mites:aldicarb (0.46); pirimiphos-methyl (0.73); exo, exo-2,8-dichloro-4-thiatricyclo[3.2.1.0.]octane-4-oxide (AI3-63182) (0.87); and diazinon (2.48).

Inhibition of four acetylcholinesterases (AChE) and a butyrylcholinesterase (BCHE) by 3-(2,3-dihydro-2,2-dimethyl-benzofuran-'7-yl)-5-methoxy-1,3,4-oxadiaz ol-2(3H)-one (DBOX) and 3-(2-methoxyphenyl)-5-methoxy-1,3,4-oxadiazol-2(3H)-one (MPOX) was measured by the Ellman spectrophotometric method. Both oxadiazolidinones inhibited AChE and BCHE irreversibly and with quasi first order kinetics. DBOX was 2-3 orders of magnitude more potent than MPOX. Housefly brain AChE and horse serum BCHE were more sensitive than AChEs of red blood cells or eel and Torpedo electric organs. Aldicarb, a carbamate anticholinesterase, which protected Torpedo AChE against irreversible phosphorylation by DFP, also protected it against irreversible inhibition by DBOX and MPOX. It is suggested that the nonesteratic oxadiazolidinones are converted to carbanillates on the surface of the enzyme, then acylate the active site of ChEs, producing carbanillated enzymes. At higher concentrations, the two oxadiazolidinones also affected the specific binding of (125I) alpha-bungarotoxin (alpha-BGT) and [3H]perhydrohistrionicotoxin (H12-HTX) to Torpedo nicotinic ACh-receptors, but did not affect the specific binding of [3H]quinuclidinyl benzilate (QNB) to rat brain muscarinic ACh-receptors.

Four laboratories obtained 177 carbamate recovery values using a liquid chromatographic method. The average recovery of 11 carbamates (aldicarb, aldicarb sulfone, bufencarb, carbaryl, carbofuran, 3-hydroxy carbofuran, 3-keto carbofuran, methiocarb, methiocarb sulfoxide, methomyl, and oxamyl) from 14 crops was 99% with a coefficient of variation of 8% (0.03-1.8 ppm fortification levels). No statistical difference in recovery was found between oxime and phenyl carbamates, or between parent and metabolite carbamates. Average recovery of aldicarb sulfoxide was 59% due to loss in the liquid-liquid partitioning because of the polarity of this compound. A fifth laboratory contributed 34 carbamate recoveries (average 99%) on table-ready food products for 4 carbamates. Bendiocarb, dioxacarb, isoprocarb, and propoxur are also quantitatively recovered through the method. Previously reported carbamate and noncarbamate recovery data are also discussed. In the Food and Drug Administration's (FDA) analysis of 319 samples (mainly crops), 86 (27%) were found to contain residues of carbamate insecticides and/or toxic carbamate metabolites. Carbaryl and methomyl were the most common carbamate residues found on the food products excluding the aldicarb sulfone and sulfoxide residues found on potatoes. In one FDA Total Diet Program "market basket", 11 of 69 table-ready food commodities contained from 0.005 to 0.094 ppm carbamate residues. Carbaryl was the most prevalent residue. Several laboratories reported adverse effects on the determinative system when inadequately purified reagents were used.

A method for determining residues of aldicarb, aldicarb sulphoxide, aldoxycarb, oxamyl and methomyl in soil, groundwater and surface water is described. Subsoils were extracted with water and topsoils were extracted with acetone. The aqueous samples were either directly injected after acidification or concentrated by extraction with chloroform. The organic extracts were evaporated to dryness and redissolved in acidified mobile phase. The compounds were detected with a variable wavelength U.V. detector or with a fluorometric detector after a post-column reaction. Compounds within a concentration range from 0.5 ng/ml to 200 micrograms/ml could be determined with a maximum coefficient of variation of 7.5%. Recoveries varied from 77.0% to 98.8%.

The pH-disappearance rate profiles were determined at ca. 25 degrees C for 24 insecticides at 4 or 5 pH values over the range 4.5 to 8.0 in sterile phosphate buffers prepared in water-ethanol (99:1 v/v). Half-lives measured at pH 8 were generally smaller than at lower pH values. Changes in half lives between pH 8.0 and 4.5 were largest (greater than 1000x) for the aryl carbamates, carbofuran and carbaryl, the oxime carbamate, oxamyl, and the organophosphorus insecticide, trichlorfon. In contrast, half lives of phorate, terbufos, heptachlor, fensulfothion and aldicarb were affected only slightly by pH changes. Under the experimental conditions described half lives at pH8 varied from 1-2 days for trichlorfon and oxamyl to greater than 1 year for fensulfothion and cypermethrin. Insecticide persistence on alumina (acid, neutral and basic), mineral soils amended with aluminum sulfate or calcium hydroxide to different pH values and four natural soils of different pH was examined. No correlation was observed between the measured pH of these solids and the rate of disappearance of selected insecticides applied to them. These observations demonstrate the difficulty of extrapolating the pH dependent disappearance behaviour observed in homogeneous solution to partially solid heterogeneous systems such as soil.

This method for determining carbamates is based on the inhibiting action of these substances on acetylcholinesterase activity. The use of radioactively labelled acetylcholine as a substrate, the ensuing extractive separation of the radioactive acetic acid (formed by hydrolysis) and its radiometric determination permit to detect very small amounts of carbamates. The limit of detection for aldicarb, baygon, benomyl, bux, carbaryl, CIPC, matacil, phenmedipham and promecarb lies in the picogram range; that for barban and methomyl, in the nanogram range. The lower, linear parts of the curves for the different carbamates fall within the range 0.001-10 ng. The sensitivity (expressed as delta% inhibition/delta lg ng carbamate) ranges from 1.0 to 9.7.