Tracing the source of methomyl using stable isotope analysis

RATIONALE

Pesticide self-poisoning is a major method of suicide in many agricultural communities worldwide. In addition, there are a number of known crime cases related to people being harmed by insecticides. Methomyl, a prohibited insecticide in the Republic of Korea, has high toxicity and is frequently used for self-poisoning. In this study, we investigated the source of origin of methamyl in a fatal poisoning case using stable isotope ratio analysis.

METHODS

Two bottles of Soju from a crime scene were seized and nine different brands of methomyl products were collected from the neighborhood for analysis. In addition, the gastric contents and energy drink from the person who had committed suicide were analyzed. Isotope analysis using GC/Isolink/IRMS was conducted to determine the source of the methomyl by comparing their carbon and nitrogen isotope ratios. Linear discriminant analysis was utilized to verify the results.

RESULTS

Isotope ratio analysis showed that the isotope ratio ranges of methomyl found in the Soju, the gastric contents of the suicide victim, and the energy drink bottle were similar to those of a seized methomyl product, Samgong methomyl 2011 (SG11). Thus, it was assumed that SG11 was used in this fatal poisoning case.

CONCLUSIONS

This study demonstrates the potential of stable isotope ratio analysis for the determination of insecticide origin in fatal poisoning cases.

OCCUPATIONAL CARBAMATE POISONING IN THAILAND

Carbamate insecticide is a leading cause of poisoning in Thailand. The objective of this study was to characterize the clinical manifestations and modes of occupational exposure in carbamate poisoning cases. We retrospectively studied all the cases of carbamate poisoning due to occupational exposure recorded in the Ramathibodi Poison Center Toxic Exposure Surveillance system during 2005 to 2010. Demographic data, clinical manifestations and severity were analyzed statistically. During the study period, 3,183 cases were identified, of which 170 (5.3%) were deemed to be due to occupational exposure. Ninety-six cases (56.5%) and 35 cases (20.6%) were poisoned by carbofuran and methomyl, respectively. Carbofuran is sold as a 3% grain and applied by sowing; methomyl is sold as a liquid and is applied by spraying. The majority of poisoned patients did not wear personal protective equipment (PPE) while applying the carbamates. The clinical manifestations of occupational carbofuran poisoning recorded were nausea and vomiting (82.3%), headaches (56.3%) and miosis (19.8%). The clinical manifestations of methomyl poisoning were nausea and vomiting (74.3%), headaches (57.1%) and palpitations (11.4%). Most patients in both groups had mild symptoms. Only one case in each group required endotracheal intubation and mechanical ventilation support. There were no deaths and the lengths of hospitalization ranged from 2 hours to 2 days. Occupational carbamate poisoning cases in our series were mostly mild and the patients recovered quickly. There were only rare cases of serious symptoms. Lack of knowledge and inadequate PPE were the major factors contributing to occupational poisoning. Educating agricultural workers about correct precautions and pesticide use could minimize this type of poisoning.

An outbreak of food borne illness due to methomyl pesticide intoxication in Korea

On February 21, 2013, 6 elderly people collapsed abruptly after eating bean sprout bibimbab (boiled rice mixed with bean sprouts and seasoned with soybean sauce) at a countryside restaurant in the Chungbuk Province, Korea. Minutes after eating the meal, all of the patients lapsed into a state of stupor. Respiratory arrest developed in 2 patients; and one of two patients died of cardiac arrest. The autopsy identified methomyl and methanol in the deceased patient's gastric contents and in the remaining soybeanbean sauce seasoning. Five of the 6 patients ingested one spoonful of the soybeanbean sauce seasoning and survived, while one patient who died of cardiac arrest, ingested approximately two spoons. Symptoms of toxicity presented quickly in the subjects and progressed rapidly, including chest tightness, an unusual sensation in the pit of the stomach, dizziness, ataxia, and finally, collapse. Three patients who drank ethanol with the meal experienced only mild toxic symptoms. Our analysis of the clinical observations in these cases suggests that ingestion of methomyl pesticide and the additive toxicity of methanol may have been responsible for the intoxication.

An unusual cause of atrial fibrillation: exposure to insecticides

BACKGROUND

Although there are many well-known cardiac results of insecticide poisoning, atrial fibrillation (AF) has not been reported as the result of insecticide intoxication.

CASE

Twenty-six-year-old male, complaining of nausea and vomiting, presented to the emergency department with a history of methomyl dust exposure. All physical examination findings were normal except irregular heart rate on cardiac auscultation. The electrocardiogram of the patient showed AF with normal ventricular response. Patient's acetylcholinesterase (ACE) level was 3,319 IU/L in presentation and pralidoxim use was seen unnecessary for the treatment. The patient's rhythm spontaneously returned to sinus rhythm 24 hr after the presentation and no cardiopulmonary pathology was found during the follow-up. The patient was discharged without symptoms.

CONCLUSION

AF is a rare complication of insecticide intoxication. In this case, treatment of symptoms was adequate until a normal sinus rhythm returned.

Acute pancreatitis subsequent to voluntary methomyl and dichlorvos intoxication

INTRODUCTION

Acute pancreatitis subsequent to methomyl (Lannate) had not been reported until 2005, when Markides published the first case. In our study, we report for the first time 2 cases of acute pancreatitis complicating voluntary methomyl intoxication and compare them with 5 cases of pancreatitis subsequent to dichlorvos poisoning admitted to our toxicological unit during the same period, between July 2001 and June 2003.

CASE REPORTS

Patients included in this study were seriously poisoned because all developed muscarinic and nicotinic syndromes. Deep coma and respiratory failure requiring mechanical ventilation were noted in all methomyl-poisoned patients and in only 3 dichlorvos-poisoned patients. Acute pancreatitis occurred 24 to 72 hours after dosing and was characterized by painless abdominal paralytic ileus and vomiting. Clinical features and laboratory examinations were normalized by the fifth day under medical treatment. Complications such as intrapancreatic fluid collection occurred later between days 10 and 20 in 1 methomyl-poisoned patient who required secondary surgical drainage and in 1 dichlorvos-poisoned patient who was treated conservatively. Outcome was favorable in all cases.

CONCLUSION

The developing of acute pancreatitis is a serious adverse effect following insecticide intoxication and is better known with dichlorvos than methomyl.

A case of poisoning in a man who drank a nutrition supplement containing methomyl, a carbamate pesticide

A 50-year-old man was admitted to the emergency room complaining oppression on his chest, sweating and vomiting. He had drunk a 30 ml volume nutrition supplement 60 minutes before. As myosis and decrease of serum choline esterase activity were observed on admission examination, poisoning was suspected and toxicological analyses were carried out on the heeltap of the drink. Drug screening by gas chromatography-mass spectrometry (GC/MS) revealed the presence of methomyl and the concentration of methomyl in the heeltap determined by liquid chromatography was 2.1 mg/ml. Methomyl concentrations in the serum and urine were determined after converting methomyl to its oxime form followed by derivatization and GC/MS. Methomyl concentration in the serum collected 6 hours after ingestion was 0.63 microg/ml, and that in the urine collected 7-20 hours after ingestion was 0.10 microg/ml. Based on these values and reported data, the amount of methomyl contaminated to the drink was considered to be a toxic dose.

Chronic neuropsychological sequelae of cholinesterase inhibitors in the absence of structural brain damage: two cases of acute poisoning

Here we describe two cases of carbamate poisoning. Patients AMF and PVM were accidentally poisoned by cholinesterase inhibitors. The medical diagnosis in both cases was overcholinergic syndrome, as demonstrated by exposure to cholinesterase inhibitors. The widespread use of cholinesterase inhibitors, especially as pesticides, produces a great number of human poisoning events annually. The main known neurotoxic effect of these substances is cholinesterase inhibition, which causes cholinergic overstimulation. Once AMF and PVM had recovered from acute intoxication, they were subjected to extensive neuropsychological evaluation 3 and 12 months after the poisoning event. These assessments point to a cognitive deficit in attention, memory, perceptual, and motor domains 3 months after intoxication. One year later these sequelae remained, even though the brain magnetic resonance imaging (MRI) and computed tomography (CT) scans were interpreted as being within normal limits. We present these cases as examples of neuropsychological profiles of long-term sequelae related to acute poisoning by cholinesterase inhibitor pesticides and show the usefulness of neuropsychological assessment in detecting central nervous system dysfunction in the absence of biochemical or structural markers.

A fatal poisoning caused by methomyl and nicotine

A 35-year-old male was found lying in a prone position in his room. He was in cardiopulmonary arrest on arrival to hospital and was pronounced dead. There was no attempt at resuscitation. No miosis was observed on admission. At post-mortem his stomach contained 170 g greenish liquid with a small amount of shredded tobacco leaves. The serum cholinesterase activities were 47-90 IU (normal range for male: 200-440 IU). GC and GC-MS analyses showed nicotine (21.8 mg), methomyl (304 mg), and triazolam (1.69 mg) in his stomach. He had consumed tobacco leaves, Lannate containing water soluble methomyl (45%), and Halcion tablets containing 0.25 mg triazolam. Methomyl concentrations in blood were 3-8 ng/ml. Substantial amounts of methomyl (2260-2680 ng/ml) were detected in cerebrospinal fluid and vitreous humor. Nicotine concentrations in blood ranged from 222 to 733 ng/ml. A small amount of triazolam was detected only in bile (176 ng/ml) and liver (23 ng/g). The cause of death was respiratory paralysis produced by the additive effects of methomyl and nicotine shortly after consumption.

Methomyl-induced severe acute pancreatitis: possible etiological association

CONTEXT

N-methyl carbamate insecticides are widely used in homes, gardens and agriculture. They share the capacity to inhibit cholinesterase enzymes with organophosphates and therefore share similar symptomatology during acute and chronic exposures. One of the serious effects of organophosphate and carbamate intoxication is the development of acute pancreatitis and subsequent intrapancreatic fluid formation.

CASE REPORT

An 18-year old Caucasian man was admitted to our Intensive Care Unit with cholinergic crisis symptomatology, after the ingestion of an unknown amount of a carbamate insecticide (methomyl). Pseudocholinesterase levels were 2 kU/L on the day of admission (reference range: 5.4-13.2 kU/L). Two days after admission, an abdominal CT scan revealed blurring of the peripancreatic fat planes, inflammation and swelling of the pancreas, and a substantial amount of ascitic fluid in the left anterior pararenal space and pelvis. Paracentesis and analysis of the ascitic fluid demonstrated findings diagnostic of pancreatic ascites. There had been no other evident predisposing factors for acute pancreatitis, other than methomyl intoxication. Eleven days after admission, pseudocholinesterase levels returned to normal, while a new abdominal CT scan revealed the formation of intrapancreatic fluid collection. The patient was discharged in good physical condition two weeks after admission. A follow up abdominal CT scan performed one month later showed a significant reduction in the size of the intrapancreatic fluid.

DISCUSSION

Acute pancreatitis is not uncommon after organophosphate intoxication and carbamates share the same risk as organophosphorus pesticides. The development of acute pancreatitis and subsequent intrapancreatic fluid collection after methomyl intoxication has not previously been reported. This is the first case reported of acute pancreatitis and pancreatic ascite formation after anticholinesterase insecticide ingestion.

An Outbreak of Food‐borne Illness Due to Methomyl Contamination

BACKGROUND

On December 26, 2002, 124 dinners took ill while eating lunch at a seafood restaurant in the town of Chiching in Kaohsiung municipality of Taiwan. Sixty-nine people were sent to the emergency departments of the Municipal Chiching Hospital and Yuan's General Hospital.

METHODS

We analyzed the clinical symptoms, detailed food history, and ingested amount of each food from 59 hospitalized adult patients and identified the source of the outbreak.

RESULTS

The median latency period from beginning eating to first symptoms was 5 min. Twenty-six symptoms and signs were recorded. The most commonly reported clinical effects were general weakness (84%), ataxia (82%), dizziness (82%), vomiting (80%), sweating (75%), floating sensation (71%), headache (69%), dyspnea (69%), and blurred vision (67%). Thirty-one patients had residual symptoms 7 days after ingestion. Of the six residual symptoms reported, the most frequent ones were dizziness (40%), poor appetite and dry mouth (11%), and gastrointestinal disturbance (11%). The presence of residual symptoms correlated with the severity of the initial complaints (p < 0.01). Almost all patients ate cooked rice (93%) and leaf vegetable stir-fried with crab claw (93%). The amount of each food eaten by the patients was not associated with the severity of symptoms (p > 0.05). High levels of methomyl in leaf vegetables of "leaf vegetables stir-fried with crab claws" (380 ppm) and fried mussels (1113 ppm) were found by the Food Inspection Center at the Department of Health. The food history and chemical analysis of the poison indicated methomyl was the cause of this outbreak. Twenty-four patients recovered completely within 7 days.

CONCLUSION

Food-related methomyl intoxication produced a rapid onset of significant clinical toxicity in 124 individuals. Based on the analysis of 55 adult patients, the most common effects were gait ataxia, dizziness, generalized weakness, and vomiting.

An outbreak of food-borne illness associated with methomyl-contaminated salt

CONTEXT

On January 5, 1999, the California Department of Health Services was notified of the repeated occurrence (December 21, 1998, and January 2, 1999) of gastrointestinal tract illness among patrons at a Thai restaurant in central California.

OBJECTIVE

To identify the source of the outbreak.

DESIGN

Case-control study; microbiological and toxicological laboratory testing of samples of food, stool, and vomitus.

SETTING

Thai food restaurant in central California.

PARTICIPANTS

Patrons of the restaurant. A case (n = 107) was defined as dizziness, nausea, or vomiting occurring in a person who ate at the restaurant between December 20, 1998, and January 2, 1999, with onset of symptoms within 2 hours of eating. A control (n = 169) was a person who ate at the restaurant during the same period but reported no symptoms.

MAIN OUTCOME MEASURES

Odds ratios (ORs) of illness associated with food exposures; ORs of shifts during which illness occurred associated with certain cooks; laboratory results.

RESULTS

The median latency period was 40 minutes from beginning eating to first symptom and was 2 hours to onset of diarrhea. The median duration of symptoms was 6 hours. Twenty-six persons (24%) visited the emergency department or were treated by a physician; no person required hospitalization. Patients reported nausea (95%), dizziness (72%), abdominal cramps (58%), headache (52%), vomiting (51%), chills (48%), and diarrhea (46%). Fifty-one cases (48%) included dizziness, lightheadedness, or a feeling of disequilibrium as the initial symptom. Illness was statistically associated with several foods and ingredients, but no single dish or ingredient explained a substantial number of cases. The analysis of food exposures included salt added by cooks, as estimated by using the amount of salt in the recipe for each dish and the amount of each dish eaten by respondents. This association was stronger with increasing levels of salt: ORs for illness among persons who consumed more than 0.42 to 0.84, more than 0.84 to 1.25, and more than 1.25 tsp of salt added to foods in the kitchen were 1.9 (95% confidence interval [CI], 0.6-5.7), 3.0 (95% CI, 1.0-8.8), and 4.0 (95% CI, 1.3-13.5) compared with persons who consumed less than 0.42 tsp (P value for trend =.004). Methomyl, a highly toxic carbamate pesticide, was identified in a sample of vomitus (20 ppm) and in salt taken from containers in the storeroom (mean, 5600 ppm) and the stovetop (mean, 1425 ppm). The oral toxic dose causing illness in 50% of those exposed to methomyl was estimated to be 0.15 mg/kg of body weight (estimated range, 0.09-0.31 mg/kg of body weight). The presence of cook A was associated with shifts during which cases of illness occurred (OR, 10.4; 95% CI, 1.2-157.4).

CONCLUSION

This outbreak of gastrointestinal illness was associated with the consumption of food seasoned with methomyl-contaminated salt. To allow rapid assessment for further investigational and control measures by health officials, physicians should report suspected outbreaks of illness to public health departments, however trivial the symptoms or cause may seem.

[Acute poisoning with methomyl and other pesticides in the province of Ragusa, Sicily]

In 1995-96, the Occupational Medicine Service of the province of Ragusa, Sicily, examined all cases of pesticide poisonings among persons seen in two local emergency departments, identifying 86 cases due to unintentional pesticide exposure. Methomyl, a highly toxic carbamate, was indicated for 51% of all cases. The most frequently reported symptoms included nausea and vomiting (48%), excessive perspiration (33%), and dyspnea (16%). Fifty-nine cases (69%) were hospitalized, 5 in intensive care. The methomyl cases occurred more frequently during summer months while the cases from all other pesticides showed no seasonal patterns. These observations point out the relevance of identifying acute pesticide poisonings in the province of Ragusa and suggest that ongoing registration of these events should be a public health priority.

[Stimulation single fiber electromyography in rats with myasthenia induced by organophosphorus insecticides and their mixtures poisoning]

OBJECTIVE

To study the neuromuscular function and its relation with the occurrence of myasthenia in rats poisoned by dimethoate (D), phoxim (P), methomyl (M), M + D and M + P respectively.

METHODS

The stimulation single fiber electromyography(SSFEMG) at different stimulus frequencies(5, 10 and 20 Hz) was used. The whole blood cholinesterase (ChE) activity was measured 1 h before and after poisoning.

RESULTS

(1) Myasthenia occurred in 5 out of 9.5 out of 10.5 out of 5, and 8 rats poisoned by D, P, M + D, and M + P, respectively. (2) The average mean consecutive differences(MCD) at 5, 10, and 20 Hz in myasthenic rats were significantly higher than those of poisoned rats without myasthenia and the control ones. (3) SSFEMG changes at 5, 10 and 20 Hz were significantly consistent with the clinical manifestation of myasthenia, especially at 10 Hz and 20 Hz. (4) ChE activity was significantly lower in rats with P or D poisoning while ChE inhibition was of no difference in rats with M, M + D, and M + P poisoning. In the D poisoning and P poisoning groups, there was no significant difference in ChE inhibition between the rats with and without myasthenia.

CONCLUSION

Muscle weakness was associated with neuromuscular transmission dysfunction, but not well correlated with ChE inhibition. The SSFEMG with stimulus frequency at 10 Hz or 20 Hz could be used to detect the neuromuscular dysfunction during myasthenia induced by organophosphate insecticides and their mixtures poisoning.

[A case of carbamate poisoning in which GCMS was useful to identify causal substance and to decide the appropriate treatment]

We often have cases of insecticide poisoning where the patient is unconscious and the causal substances are unknown. We report an 83-year-old unconscious man who had apparently ingested several agricultural chemicals, possibly organophosphate or carbamate. According to his family, there were three kinds of containers of agricultural chemicals with their caps opened around him. When he was transferred to our hospital, he presented hypertension, hypersalivation, and muscle fasciculation. His pupils were markedly miotic. In order to identify the substances ingested we used a gas chromatographymass spectrometer (GCMS) using his gastric content. Within 30 minutes we were able to identify the causal substance as methomyl, one of the popular carbamates, thereby eliminating the need to use pralidoxime (PAM). GCMS makes it possible to identify unknown substances quickly and accurately and is therefore extremely useful in deciding the appropriate treatment.

Children's plasma cholinesterase activity and fatal methomyl poisoning

There is a case of a couple who intentionally killed their children with methomyl insecticide. This was presented as our initial investigation of plasma cholinesterase (ChE) activity in Thai children. A hundred and five healthy Thai children 5-6 years of age, participated in the project. Their plasma was drawn to measure ChE activity. Mean +/- standard deviation of the children ChE was 7,417 +/- 1,620 U/L. The enzyme activity of the children was not significantly different between gender and parents' occupations. However, the mean of female ChE activity appeared to be lower than male ChE. Children whose parents were farmers appeared to have lower ChE activity than those whose parents were employees, merchants, government officers, unemployed parents, or private business owners. Two victims of child homicide were presented with ChE activity approximately 6 and 9 per cent of the average, considering healthy children. It was concluded that children's plasma ChE activity lower than 10 per cent of normal, could be a lethal indicator of anti-ChE insecticide poisoning.

Toxicity of methomyl following intravenous administration in the horse

Methomyl (S-methyl-N-((methylcarbamoyl)oxy) thioacetimidate) toxicity was studied in horses using i.v. dosages from 0.01 to 3.0 mg/kg. Doses of 1-3 mg methomyl/kg produced increased GI motility and respirations, facial fasiculations, salivation, lacrimation and convulsions. The only effect at 0.5 mg/kg was increased GI sounds in 1/4 horses. This extensively used crop insecticide had been associated with episodes of morbidity and mortality and led to speculation that it was extremely potent to the horse. This was not supported by these clinical studies.

Sensitive determination of methomyl in blood using gas chromatography-mass spectrometry as its oxime tert.-butyldimethylsilyl derivative

A sensitive, selective and reliable method was developed to determine methomyl ¿methyl-N-[(methylcarbamoyl)oxy]-thioacetimidate¿, a carbamate insecticide in human blood, using gas chromatography-mass spectrometry. Dimethylglyoxime served as an internal standard (I.S.). Methomyl in the blood was converted to its oxime form by sodium hydroxide. The solution made acidic with hydrochloric acid was poured into a column packed with Extrelut. Methomyloxime and I.S. were eluted from the column with a mixture of dichloromethane-ethyl acetate-chloroform (65:25:10), transformed to tert.-butyldimethylsilyl derivatives, and analyzed by gas chromatography-mass spectrometry in the electron impact mode. The calibration curves were linear in the concentration range from 1 ng/g to 100 ng/g and 100 ng/g to at least 5000 ng/g. The lower limit of detection was 0.5 ng/g. The absolute recoveries were 72-93% and within-day coefficients of variation were 3.1-5.6% at blood concentrations of 10 and 1000 ng/g. Two practical forensic applications are described.

New treatment regimens in organophosphate (diazinon) and carbamate (methomyl) insecticide-induced toxicosis in fowl

The objective of this work was to determine optimal treatment regimens for organophosphate (OP) or carbamate insecticide toxicoses in fowl using the antidotes atropine sulfate and pralidoxime chloride (2-PAM). Broiler chicks in treatment groups, each comprising 3 replicates of 6-7 birds/replicate, were gavaged on a body weight (BW) basis with the OP and carbamate insecticides, diazinon and methomyl, respectively, at lethal dosages. Treatment groups were injected with either or both of the antidotes at various dosages as soon as clinical signs appeared. Birds appearing healthy 24 h thereafter were regarded as having been treated successfully. At a dosage of 100 mg/kg BW, atropine was mildly toxic and at 200 mg/kg 2-PAM was severely toxic (but not lethal), whereas at dosages of 50 and 100 mg/kg BW, respectively, the antidotes were at their most effective. With diazinon, atropine alone was only partially effective (12/20 survivors), whereas 2-PAM was extremely efficacious. (20/20 survivors); the combination of the 2 antidotes at 2 dosages was slightly less effective (19/20 survivors) than 2-PAM alone. For methomyl toxicity, atropine was largely successful (18/20 survivors), whereas 2-PAM was mostly unsuccessful (10/20 survivors); the combination at high dosage was less effective (15/20 survivors) than atropine alone, but at a low dosage the combination was the most successful (20/20 survivors). The results indicate that anticholinesterase insecticide toxicoses in fowl should not be treated according to textbook recommendations, and antidotal dosage with atropine should be up to 100 times greater than is commonly recommended. The specific cause of the toxicoses should ideally be determined before treatment is given, but as this is often unknown, a combination of antidotes may be the optimal treatment protocol.

Carbamate poisoning in early childhood and in adults

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.

The analysis of methomyl, a carbamate pesticide, in post-mortem samples

Extraction procedures and analytical methods are described for the quantitation of methomyl, a carbamate insecticide, in autopsy tissue and fluid samples. The analytical results from case work demonstrate the rapid metabolism of methomyl in the body.

Acute poisoning with carbamate pesticides: the Cretan experience

In Crete, in southern Greece, a number of fatal carbamate poisonings were investigated over a period of 2 years, from 1991 to 1993. Five cases are reported, involving the fatal ingestion of methomyl (Lannate), a cholinesterase-inhibiting carbamate insecticide. Analysis of samples of blood plasma and serum showed more than 90% inhibition of cholinesterase. The blood methomyl concentrations had a mean value of 26.7 mg/l, and a range of 5.6-57.0 mg/l. These values are much higher than those previously reporter in similar cases (0.57-1.4 mg/l). Methomyl concentrations in organs and tissues were found to be significantly lower than those in blood and vitreous humour.

Exposure evaluation is a crucial step for quantitative risk assessment of methomyl

Methomyl, methyl N-[[(methylamino)carbonyl]oxy]ethanimidothioate is a carbamate insecticide with anticholinesterase activity. As a broad spectrum insecticide, it is one of the most frequently used pesticides in tangerine orchards in Thailand. Although methomyl is said to be rapidly eliminated from experimental animals (1) high incidence of acute poisonings was reported among patients occupationally exposed to a powder formulation of methomyl (2, 3). In this passive dosimetry study of tangerine growers, during mixing and overhead spraying of a 90% powder formulation of methomyl, ocular and nasal exposure was measured. Exposure data are discussed in terms of the "potentially absorbed" or "internal dose".

Carbamate poisoning and oxime treatment in children: a clinical and laboratory study

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.

Methomyl in the blood of a pilot who crashed during aerial spraying

An aerial-spray pilot died when his aircraft crashed while he was spraying methomyl. We measured the pesticide in his blood by gas chromatography with flame photometric detection and confirmed the results by mass spectrometry with direct liquid injection through a liquid chromatography interface. The whole blood methomyl concentration was 570 ng/mL.

Management of methomyl poisoning

Eleven patients who suffered methomyl poisoning were admitted to the intensive care unit. All of them showed cholinergic symptoms similar to that produced by organophosphate insecticides but of lesser intensity. Plasma cholinesterase activity was normal in four patients and moderately lower in the remainder (always above 32%). All of the patients showed miosis and none presented with bradycardia. No complications were detected in the acute stage or on further examination a month later. The treatment applied was: (1) gastric lavage or washing the skin; (2) the administration of activated charcoal; (3) small doses of atropine according to symptoms (average of total dose 4.3 mg). All of the patients recovered within 24-48 h. In conclusion, we can assume that methomyl poisoning does not produce serious complications if moderate surveillance is assumed. Only small doses of atropine are required to counteract symptoms.

Fatal and non-fatal methomyl intoxication in an attempted double suicide

A 79-year-old man and his 73-year-old wife attempted double suicide by ingesting methomyl powder. The woman died 19 h after ingestion in spite of intensive care. At autopsy a large number of miliary hemorrhages were found in both thalami of the brain. Her husband, however, recovered after 10 days of treatment. Methomyl (CAS No. 16752-77-5, Lannate) in the biological materials was analyzed by gas chromatography-mass spectrometry. The methomyl concentration was 44 micrograms/g in the wife's serum sample collected 1 h after ingestion, and 0.2 microgram/g in the blood sample collected at autopsy. The methomyl concentration in the husband's blood sample collected 28 h after ingestion was from 0.01 to 0.1 microgram/g. It is suggested that prompt and adequate intensive care including a direct hemoperfusion is necessary to effect the recovery of patients with lethal blood levels of methomyl. The miliary hemorrhages found in the thalami of the brain are suspected to have been caused by asphyxia induced by methomyl intoxication.

The laboratory's role in environmental health emergency investigations

An emergency environmental health investigation of a mass poisoning of unknown origin is a multidiscipline effort that requires the cooperation and close communication of epidemiologists, toxicologists, and chemists. The laboratory's role in this effort is important; special instruments, knowledge, and experience are needed. Our approach to such an investigation is discussed and past cases are used as illustrations. The role of the analytical chemist is presented, and the major resources needed for these investigations are described.

Propanil-chloracne and methomyl toxicity in workers of a pesticide manufacturing plant

In a survey of occupationally acquired disease in workers at a pesticide plant, we found that 11 (11%) of 102 workers had been hospitalized for illness related to chemical exposures; highest hospitalization rates occurred in packaging (27%), production (22%), and maintenance (9%) workers. Commonest causes of hospitalization were intoxication by the carbamate pesticide methomyl [1-(methylthio)ethylideneamino methyl carbamate], a reversible cholinesterase inhibitor, and methemoglobinemia following exposure to 3,4-dichloroaniline. On clinical evaluation, five (46%) of 11 packaging workers, the group with the highest exposure to methomyl, had experienced blurred vision or pupillary constriction. Seventeen (61%) of 28 production workers with exposure to dichloroaniline and propanil (3'4'-dichloropropionanilide) had chloracne, an acne-form dermatosis caused by the contaminant tetrachlorazobenzene in propanil and dichloroaniline. The chloracnegenic potentials of propanil and dichloroaniline were verified by rabbit ear tests. These findings reemphasize the hazards inherent in the the manufacture and formulation of pesticides and herbicides.

A fatal episode of accidental methomyl poisoning

Three fatalities from the accidental ingestion of methomyl, a carbamate pesticide, are reported. The methomyl had been stored in an unlabeled tin can and was accidentally used in preparing "roti," an Indian dish. The identification of the source of the poison through animal tests and further chemical identification is described. The lethal dose of methomyl was estimated to have been between 12 and 15 mg/kg body weight.

Poisoning by carbamate pesticides

In recent years the number of carbamate pesticides registered for use in New South Wales has increased. Some of the newer carbamates are very toxic and have cholinergic properties similar to those of the organic phosphates, though the effect is of much shorter duration. Because of this, separate tests for plasma and red blood cell levels of cholinesterase should be conducted as soon as possible after exposure in order to obtain meaningful results. A typical case of carbamate poisoning is described in which both plasma and red blood cell cholinesterase values were lowered. The substitution of a liquid pesticide formulation for the original powder formulation has reduced the operator inhalation hazard in the case of methomyl.