Red Cell Cholinesterase Research Articles

O-EV002. Auditory event-related potential changes over 6 months following acute organophosphate insecticide poisoning: A follow-up study

Introduction . Ingestion of organophosphate insecticides (OPIs) is a common method of self-harm and a major clinical problem is Asia. Apart from acute cholinergic effects, OPIs are also claimed to be associated with long-term neurobehavioural deficits. However, neurophysiological evidence for such long-term deficits is scarce in humans. We aimed to assess long-term changes in the pre-attentive (N1) and attentive (P3b) components of auditory event-related potentials (ERPs) following acute OPI self-poisoning. Methods . We recruited 203 patients (147 men) hospitalised following OPI ingestion (OP Group; all had significant red cell cholinesterase inhibition) and 50 patients (23 men) hospitalised with paracetamol overdose (Control Group) as a means of self harm. We recorded their EEG in an auditory oddball task and derived the averaged ERPs. The subjects underwent three testing sessions: on discharge from hospital (around 14 days post-ingestion), 6 weeks and 6 months post-ingestion. We compared the reaction time and ERP indices of the two groups at each time point, adjusting for sex, age, education and psychiatric comorbidities in multiple regression models. Results . After adjusting for covariates, OP Group had significantly slower reaction time than the Control Group on discharge (mean difference [SE] = 65[20] ms, p = 0.001) and at 6 weeks (mean difference [SE] = 45[20] ms, p = 0.024), but not at 6 months. Parietal (PZ) P3b amplitudes were significantly smaller in the OP group on discharge (mean difference [SE] = 2.23[0.84] V, p = 0.009) and at 6 months (mean difference [SE] = 3.34[1.43] V, p = 0.021). P3b latencies or frontal (FZ) N1 component did not show significant intergroup differences. Conclusion . Acute exposure to clinically significant doses of OPIs seem to cause impairment in behavioural and neurophysiological indices of stimulus discrimination, that outlast the cholinergic phase of intoxication. The behavioural impairment seems to disappear over months, but the underlying neurophysiological deficits of attentive processing seem to last even after 6 months post-exposure.

The pharmacokinetics and pharmacodynamics of severe aldicarb toxicity after overdose

Objective. To describe the clinical effects, pharmacokinetics, and pharmacodynamics of plasma and acetylcholinesterase in an aldicarb overdose. Case Report. A 57-year-old female was found unconscious and incontinent of urine after ingesting aldicarb. She was bradycardic, hypotensive, hypersalivating, clammy, had small pupils, and generalized weakness. She was intubated, ventilated, and treated with large atropine doses (50 mg and 20 mg/h infusion) and adrenaline. She improved hemodynamically over 24 h, but remained comatose for another 24 h, before recovering without sequela. Aldicarb concentration at admission was 2.18 μg/ml and concentration–time data best fitted a two compartmental model with first order absorption and a time of ingestion 4.5 h preadmission. The half-life of distribution was 0.4 h and half-life of elimination, 13 h. Plasma cholinesterase concentration at admission was 0.3 kU/L (Reference range[RR]:4.3–10.6 kU/L) and red cell cholinesterase was 10 U/gHb (RR:38–66 U/gHb). The IC50 was 0.15 μg/ml and 0.26 μg/ml for plasma and red cell cholinesterase, respectively. Discussion. Aldicarb poisoning causes rapid onset severe toxicity with muscarinic and nicotinic excess, seizures, and decreased consciousness. Cholinesterases rapidly recover once aldicarb concentrations decrease and precede clinical recovery.

Regeneration of Red Cell Cholinesterase Activity Following Pralidoxime (2-PAM) Infusion in First 24 h in Organophosphate Poisoned Patients

Oximes such as pralidoxime chloride reactivate acetylcholinesterase. However their role in management of organophosphate poisoning is controversial. The study was carried out to find effectiveness of pralidoxime chloride (2-PAM) in regenerating red cell acetyl cholinesterase in first 24h following administration of it in dose recommended by WHO. Eight patients with OPP [chlorpyriphos (3), phorate (3), dichlorvos (1) and monocrotophos (1) who fulfilled the criteria for inclusion were investigated. In addition to decontamination and atropine, all these patients were administered 30mg/kgbodywt of 2-PAM as bolus dose followed by 7.5mg/kgbodywt/h with maximum dose being 500mg/h as continuous infusion till first 24h. Red cell AChE activity was estimated every 15min for first 4h, one hourly for next 4h and then 2 hourly till 24h and subsequently without 2-PAM every 12h till 7days or discharge or death which ever earlier. In all the patients maximum increase in activity was observed in first 4h following which rise was very slow despite continued 2-PAM infusion and reaching a steady state in 20h in all the cases. The increase in red cell AChE activity observed in diethyl group at 24h of 2-PAM infusion was 154% vs. 81% in dimethyl group. At 7days the increase in activity was 215% vs. 118% respectively. However on multiple repeated ANOVA, no statistically significant difference was observed between diethyl and dimethyl groups at admission and discharge (P>0.05). Similarly no significant difference was observed in three groups when patients were categorized according to WHO classification of organophosphates (P>0.05). The maximum increase in red cell AChE activity occurs in first 4h of 2-PAM administration followed by a slow increase despite 2-PAM infusion till 24h.

Comparison of red cell cholinesterase and plasma cholinesterase activities in early detection of organo-phosphorus toxicity in exposed industrial workers in Port Harcourt, Nigeria

The Niger Delta region of Nigeria has a high concentration of companies using organo-phosphorus compounds with workers who have been exposed to these compounds for varying lengths of time resulting in toxic manifestations in some of the workers. Studies have revealed that plasma cholinesterase and red cell cholinesterase levels are reduced following organo-phosphorus toxicity. This study looks at cholinesterase levels in plasma and red cell in the occupationally exposed groups and control with a view to determining which will be more useful in the early detection of organo-phosphorus toxicity. Fourty seven subjects with early symptoms of organo-phosphorus toxicity who have worked for more than 4 years with organo-phosphorus compounds were selected from five companies localized around the same area in Port Harcourt. Fifty subjects who do not work directly with organo-phosporus compounds from the same companies as the 47 workers above but not working directly in the organo-phosphorus units were also studied while 50 persons working in the civil service were recruited as controls. The kinetic colorimetric method was used for measuring plasma and red cell cholinesterase activity Result: The results showed significant reduction in the mean plasma cholinesterase activity in the chronically exposed subjects (4614. +/- 532) who showed symptoms of toxicity when compared with that of the control group (8095 +/- 575). There was no statistical difference in the mean red cell cholinesterase activity of the chronically exposed group (7998. +/- 948) when compared with that of the control (8115. +/- 712) P > 0.05 CONCLUSION: The effect of organo-phosphorus poisoning occurs early and is more marked in plasma cholinesterase than in the red cell cholinesterase. Plasma cholinesterase is thus more useful in early detection of organo-phosphorus toxicity than red cell cholinesterase.

Correlación y conversión entre valores de colinesterasa eritrocitaria medida con las técnicas de Michel y EQM®

Several techniques are available to measure red cell cholinesterase; therefore, evaluations with several methods provide a measure of concordance. An equation was formulated to transform native data of reference values to reference units of cholinesterase activity as measured by Michel and EQM tests. The experimental design was descriptive, transversal and prospective. The group sampled was a representative adult working population, aged 18-75, without previous exposure to cholinesterase inhibitors pesticides. The individuals were affiliated to the Social Security System and resided in Valle de Aburrá and Cercano Oriente Antioqueño (Antioquia Province, northwestern Colombia). Of 827 individuals, quantitative erythrocytes (Michel y EQM) tests exhibited "r" coefficients between 0.67 and R2 coefficient of 44%.,This indicated that one test explained the results in other test in 44% of the cases. The corelation was higher in Aburrá than in Oriente. The linear model for the 827 individuals was as follows: EQM U/g oxy-hemoglobin = 9.575 U/ g oxy-hemoglobin + 29.791 (Michel delta pH/hour). Michel delta pH/hr = 0.3312 delta pH/hour + 0.0149 (EQM U/g oxy-hemoglobin), where EQM was expressed in U/g oxy-hemoglobin and Michel pH change/hr. Inter-sections (coefficient a) and inclines (coefficient b) were significant in this model. In the adjusted equations, after exclusion of 12 extreme data (1.5% of 827), the r coefficient increased from 0.67 to 0.72 The adjusted equations were as follows: EQM U/g oxy-hemoglobin = 8.1884 U/g oxy-hemoglobin + 31.3920 (Michel delta pH/hour); Michel delta pH/hr = 0.2925 delta pH/hr + 0.0161 (EQM U/g oxy-hemoglobin). This system of linear equations permitted the transformation of Michel (delta PH/ hr) units to EQM (U/g oxy-hemoglobin) units and vice versa. This will facilitate data comparisons by clinicians and epidemiologists who are using these methods of cholinesterase measurement.

Problems in monitoring overexposure among spray workers in fruit orchards chronically exposed to diluted organophosphate pesticides

Objectives: Farmworkers applying diluted pesticides are chronically exposed to low levels of toxic substances such as organophosphates (OPs). Monitoring of serum and red cell cholinesterase (ChE) levels are often used to determine whether these workers are overexposed to OPs. There are major problems with the interpretation of ChE levels: differing definitions of `overexposed'; measurement variation and biological variation over time; and confounding factors such as alcohol misuse and certain liver conditions. The purpose of this study was to conduct a survey under field conditions to determine the extent of possible overexposure and the problems with biological monitoring using ChE levels in a spray worker population chronically exposed to OPs. Methods: A survey of 134 spray workers from 44 deciduous fruit farms in the Western Cape, South Africa, was conducted three times during the production season. Both ChE levels were determined at the end of 6 months lay-off (no spraying); during peak spraying; and at the end of the spray season. A group of 51 packshed workers with no exposure to OPs was used for comparison. Results: Despite exhaustive statistical analyses, the proportions of lowered ChE levels could not be shown to differ between the exposed and unexposed groups. The variation in ChE levels observed could be explained statistically by the high levels of alcohol misuse among the participants (76% in the exposed group, 59% in the unexposed group). Unhealthy lifestyle habits were highly prevalent amongst these workers (e.g. 83% smoked), which have long-term implications for their health and, importantly, hamper the diagnosis of overexposure. Alcohol intake was statistically associated with lowered ChE levels. Conclusions: According to different definitions of `lowered', different conclusions could be reached, which hamper reliable application in the field. The interpretation of ChE levels as an indicator of overexposure to OPs is complex, and the risk of misinterpretation in such a worker population is considerable.

Factors Affecting Initial Cholinesterase Levels from a Pilot Study of Central Wisconsin Farmers

Measurement of cholinesterase levels can serve as an indirect estimate of exposureto organophosphate or carbamate insecticides. In addition to individual variability,there are potential predictable confounding factors that may affect the result. In aconvenience sample of producers that were being evaluated for general healthconcerns, we performed a pilot study to evaluate parameters that might affect thegroup cholinesterase levels. Cholinesterase levels were found to be related to the typeof grower, even though all claimed not to be exposed at the time of the tests. Theplasma and red cell cholinesterase levels did not vary in the same direction betweencommodity groups. Plasma cholinesterase levels were higher for males than females,but red cell cholinesterase levels were not affected by gender. The plasmacholinesterase levels correlated positively with several tests of liver function whereasthe red cell cholinesterase results were negatively correlated with albumin butpositively correlated with age. This study underscores the fact that several parameterssystematically affect cholinesterase levels. These parameters do not affect both the redcell and plasma cholinesterase similarly. These factors need to be considered whencholinesterase levels are used to compare groups of potentially exposed persons.

Change in Cholinesterase Levels and Self-Reported Symptoms Over Two Years

ABSTRACT In a continuing effort to explore the application and the reliability of self-reported symptoms and cholinesterase levels over time, 22 ginseng producers in central Wisconsin participated in two years of on-site testing. Each year, the participants reported on farming practices and health-seeking behavior and completed a 20-item questionnaire related to possible farm chemical exposure symptoms. Plasma and red cell cholinesterase were measured at the same time. No participant noted seizure symptoms. of the remaining 19 symptoms, the highest yearly correlations were the following: Have your relatives noted that you have trouble remembering (r = 0.82); have you had trouble falling asleep (r = 0.80); and are your fingers numb (r = 0.81). There were no significant changes in farming practices or health-seeking behavior. In 1994, 14 producers applied their own pesticides; nine did in 1995. Only nine (40.9%) of the participants were under a physician's care and three (13.6%) were under chiropractic care. In addition to the initial cholinesterase levels, a second set of cho-linesterase levels was obtained in midseason. The initial (Time 1) plasma (r = 0.84) and red cell (r = 0.49) cholinesterase levels were correlated from 1994 to 1995. At follow-up (Time 2), the plasma (r = 0.90) and red cell (r = 0.68) cholinesterase levels remain correlated. The year to year change in plasma cholinesterase levels was significantly related to the change in symptoms for seven of the 19 items. The greatest correlations were for symptoms related to the following: Loss of muscle strength (r =− 0.68); trouble with balance (r =− 0.64); and complaining of finger numbness (r =− 0.56). Only one of the significant correlations with change in plasma level was posi-tive. No change in symptoms was statistically correlated with the change in red cell cholinesterase levels. The significant negative correlations indicate that a decrease in plasma cholinesterase levels was correlated with increased symptoms. Although symptoms may be in-fluenced by many factors, this study does suggest that the change in neuropsychological symptoms is frequently related to the change in plasma cholinesterase.

Postulated Interaction Between Hydroxychloroquine and Cholinesterase Enzyme Activity:

Serum and red blood cell (RBC) cholinesterase activity testing has been mandatory in the State of California for agricultural pesticide applicators since 1989. The case of a worker with depressed cholinesterase activity levels is presented. When he started taking hydroxychloroquine for systemic lupus erythematosus his serum cholinesterase activity levels decreased and remained decreased while RBC activity levels remained unchanged. Sources of organophosphate exposure were ruled out and other possible causes of cholinesterase depression were excluded. The author postulates that hydroxychloroquine was responsible for the depression of serum cholinesterase activity levels.While this finding has no impact on those taking the drug, it does alert physicians managing a monitoring program to be aware of causes of cholinesterase activity depression other than organophosphate poisoning.

Paralytic ileus as a complication of atropine therapy following severe organophosphate poisoning

A 32-year-old man presented with symptoms of severe organophosphate poisoning and required an atropine infusion for 5 weeks. We believe the development of a paralytic ileus occurred as a rare feature of atropine toxicity when other signs were masked by the underlying condition. The onset of a paralytic ileus coincided with a spontaneous increase in red cell cholinesterase levels and may be an early sign of recovery from organophosphate poisoning.

Rapid potentiometric determination of cholinesterases in plasma and red cells: Application to eptastigmine monitoring

Eptastigmine (MF 201) is a new physostigmine derivative with potent inhibitory activity on cholinesterases. Here we present a new potentiometric cholinesterase activity assay suitable for MF 201 monitoring. The analysis is performed on a differential pH system and has the following characteristics: (a) within-run precision: C.V. 2.0% (plasma cholinesterase), 1.8% (red cell cholinesterase); (b) between-run precision: C.V. 4.0% (plasma cholinesterase); (c) linearity: 1–10 kU/l (plasma cholinesterase), 6–70 U/g Hb (red cell cholinesterase); (d) comparison with a reference method (x, HITACHI 737 Boerhinger Mannheim, Italy): y = 0.785x − 0.07; n = 37; r = 0.998. The assay has been applied to the determination of plasma and red cell cholinesterase activity in volunteers over 60 years of age treated with a single oral dose of 30 mg eptastigmine. We found that red cell cholinesterase is selectively inhibited after MF 201 administration with the following kinetics (time, % of inhibition, mean ± S.E., n = 6): 0 h, 0; 1 h, 17 ± 4.6; 2 h, 24 ± 4; 4 h, 23 ± 4.4; 12 h, 14 ± 3. Eptastigmine plasma levels were also determined by a HPLC method: maximum concentration was found one hour after drug administration.

Organophosphate pesticide exposure in a group of washington state orchard applicators

As part of a study to investigate the potential for organophosphates to cause chronic neurologic sequelae, we assessed the pesticide exposure experience of a group of Washington State apple orchard applicators. Seasonal monitoring of cholinesterase activity for 48 regular organophosphate applicators and a control group of 40 slaughterhouse workers was performed. A subset of the pesticide applicators participated in an in-depth exposure assessment. This involved observation of spraying activities during 1 spray day, as well as cholinesterase monitoring and dermal exposure assessment using a fluorescent tracer in the pesticide formulation. Comparison of seasonal red blood cell cholinesterase change in pesticide workers according to exposure level, characterized by frequency of pesticide spraying and protective equipment use, showed lower cholinesterase levels among higher exposed groups compared to lesser exposed groups. In-depth exposure assessment revealed exposure primarily on the head and hand regions. Subclinical changes (less than 15% inhibition) in red cell cholinesterase correlated well with dermal exposure calculations. This study suggests that cholinesterase monitoring may be a useful biological marker for even subclinical organophosphate pesticide effects.

The effect of pralidoxime chloride in the assay of acetylcholinesterase using 5,5'-dithio-bis(2-nitrobenzoic acid) (Ellman's reagent).

Pralidoxime chloride (PAM) hydrolyzes acetylthiocholine, the substrate used in the assay of red cell cholinesterase. The thiocholine that is produced forms a yellow complex when Ellman's reagent is used in the assay. This was tested in blood samples of patients who were treated with PAM after organophosphorus (OP) poisoning and after the observation of an immediate increase in absorption of light at 412 nm.

A comparison of the decarbamoylation rates of physostigmine-inhibited plasma and red cell cholinesterases of man with other species

Plasma and red cells from a variety of animal species were used to demonstrate that there is a relationship between the decarbamoylation rates of physostigmine-inhibited plasma and red cell cholinesterases in vitro and the effectiveness of carbamate pretreatment against nerve agent poisoning reported in the literature. Decarbamoylation rates were faster in the non-human primates than in the guinea-pig, and carbamate pretreatment is more effective in these species than in the guinea-pig. The data for the decarbamoylation rates of physostigmine-inhibited enzymes suggests that the non-human primates are the best animal model for extrapolation of protection studies from animal species to man. Control values for red cell acetylcholinesterase (AChE) activity (μmol/min/mL blood) using acetylthiocholine (1 mM) were higher in the human (4.98) and the rhesus monkey (4.14) than in the marmoset (0.84) and the guinea-pig (0.83). Plasma cholinesterase (ChE) activity (μmol/min/mL plasma) using butyrylthiocholine (10 mM) was highest in the rhesus monkey (9.29), intermediate in human (5.10) and guinea-pig (6.06), and lowest in the marmoset (4.07). There was a species difference in the relative activity of AChE: ChE in blood, human (65:35), rhesus monkey (45:55), marmoset (30:70) and guinea-pig (20:80). The rate of recovery of red cell AChE and plasma ChE activities, following incubation of whole blood with physostigmine (1 × 10 −7 M), was in the order human > rhesus monkey > marmoset > guinea-pig. During the incubation of red cells with physostigmine there was little recovery of AChE activity for 3–4 hr in any species. During the incubation of plasma with physostigmine there was complete recovery of ChE activity by 2–3 hr in the human and rhesus monkey and a significant recovery by 3 hr in the marmoset and guinea-pig. This suggests that a component of plasma, possibly ChE, was responsible for the degradation of physostigmine, presumably by hydrolysis. There was a marked species difference in the decarbamoylation rates of physostigmine-inhibited enzyme. In the red cell the t 1 2 values (min) were 14.8 (human), 21.2 (rhesus monkey), 17.9 (marmoset) and 31.9 (guinea-pig). In the plasma the t 1 2 values (min) were 11.2 (human), 32.9 (rhesus monkey), 44.1 (marmoset) and 52.4 (guinea-pig).

Investigation of a fatality among parathion applicators in California

Staff of the California Department of Health Services investigated the death of a parathion applicator in California that was thought to be pesticide-related. A crew of eleven workers (including six sprayers, three mixer/loaders, one mixer/sprayer and one foreman) had been applying 0.125% parathion spray to almond orchards for approximately three weeks. On the day of the fatality, a sprayer rapidly developed symptoms of salivation, sweating, and convulsions after a half-day of work. Despite aggressive medical treatment, the worker died within one hour of his initial symptoms. Significant laboratory results for the decreased case included: parathion residue on the inner and outer garments worn by the worker, parathion in the post-mortem gastric contents, and elevated urinary metabolites consistent with acute parathion intoxication. Interviews with the work crew revealed that three of the 10 workers had complaints of headaches, vomiting, and/or sore throat; yet, subsequent plasma and red cell cholinesterase tests of the co-workers did not show any significant depressions in comparison with pre-season baseline values. This worker death is consistent with prior reports of parathion-related sprayer/applicator intoxications and is the first worker-related parathion death in California since 1972. Substitution of pesticides with less toxic active ingredients or the elimination of parathion is recommended.

Variations in blood cholinesterase activity and exposure to chlorpyrifos in termite-control workers.

Chlorpyrifos, an organophosphate insecticide, has often been used as a termite-control agent since the advent of regulatory measures against the use of chlordanes in September 1986. A current concern is hazards such as organophosphorus poisoning among termite-control workers. In this study, the blood cholinesterase activity, the number of hours engaged in termite-control work, general conditions, and various test values were examined regularly in eight workers at a termite-control office. The results are summarized as follows. 1. The plasma cholinesterase level was within the normal range from October 1986 until April 1987 in all workers, but started decreasing after May following the initiation of the full-scale termite-control season. It remained lower than the normal range (0.6 pH) from June until August in five of the six termite-control workers. The lowest level observed during this period was less than 50% of the mean value for each worker prior to the busy season in the six termite-control workers and was less than 10% of the pre-season values in three of them. In two workers, engaged mainly in sales, the plasma cholinesterase activity remained higher than in termite-control workers throughout the season. The lowest level in this minimally-exposed group during this period was not less than 50% of the mean value for each worker before the busy season. With the arrival of the off season, the level began to recover and returned to normal in all workers in January 1988. 2. The red cell cholinesterase activity remained within the normal range throughout the observation period, but it was generally low during the busy season from June to September and relatively high during the off season from December 1987 to January 1988. On the average, the red cell cholinesterase activity during the season was about 30% lower than that in the off season. 3. No marked subjective or objective abnormalities were seen in the workers. The results of other tests were generally normal, although a slight decrease in the red cell and white cell counts as well as abnormalities in serum lipid and lipase were noted in some workers. Further observations are necessary. 4. A significant negative correlation was noted between the number of hours engaged in termite-control work and variations in the plasma cholinesterase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Cumulative toxicity potential of methomyl aerosol by repeated inhalation.

There are few investigations concerning the cumulative toxicity of agricultural chemicals by repeated inhalation. In this study, Wistar male rats were exposed to methomyl powder (mass median aerodynamic diameter, 4.4 microns) for a single 4-hr exposure, or for 4 hr/day, 5 days/week for 3 months. The average exposure concentrations were controlled at 9.9 mg/m3 for the single exposure and at 14.8 mg/m3 for repeated exposures by a dust generator consisting of a continuous fluidized bed with an overflow pipe and a screw feeder. After the repeated exposures, plasma and red cell cholinesterase activities, and lipid concentrations of the rat lungs were measured and histopathological examinations were performed. There was no evidence of cumulative effects on the red cell cholinesterase activity, histopathological changes and lipid concentration in 3-month repeated inhalation.

Cumulative Toxicity Potential of Methomyl Aerosol by Repeated Inhalation

There are few investigations concerning the cumulative toxicity of agricultural chemicals by repeated inhalation. In this study, Wistar male rats were exposed to methomyl powder (mass median aerodynamic diameter, 4.4 µm) for a single 4-hr exposure, or for 4 hr/day, 5 days/week for 3 months. The average exposure concentrations were controlled at 9.9 mg/m3 for the single exposure and at 14.8 mg/m3 for repeated exposures by a dust generator consisting of a continuous fluidized bed with an overflow pipe and a screw feeder. After the repeated exposures, plasma and red cell cholinesterase activities, and lipid concentrations of the rat lungs were measured and histopathological examinations were performed. There was no evidence of cumulative effects on the red cell cholinesterase activity, histopathological changes and lipid concentration in 3-month repeated inhalation.

Water deprivation and food restriction on toxicity of parathion and paraoxon.

Three groups of rats were injected intraperitoneally with either parathion or paraoxon: (1) rats deprived of water for 48 hr, (2) rats allowed water ad lib but restricted in food intake to equal that consumed by water-deprived rats, and (3) controls. Following injection of parathion all groups showed a progressive decrease in enzymatic hydrolysis of acetylcholine over a 2-hr period. The decrease was significantly greater in food-restricted rats. Injection with paraoxon resulted in an immediate decrease in red cell cholinesterase activity, which remained low for 1 hr, but recovered thereafter. The esterase activity of both deprived groups was significantly lower than that of controls. These experiments suggest that persons subject to nutritional deficiency and water deficit may be abnormally susceptible to the effects of anticholinesterase pesticides.

Cholinesterase activity in blood samples collected from field workers and nonfield workers in California

Blood samples (1221) were obtained from workers through cooperating physicians in farm worker health clinics during the growing and harvest season for lettuce, grapes, peaches, and citrus in January, May, July, and September 1975. The blood samples were analyzed for cholinesterase activity using the dual channel Technicon AutoAnalyzer II system. The dual channel system provided for automatic blanking, the use of different buffers for the enzyme (pH 7.7) and color reactions (pH 8.2), and dialyzers to eliminate the interference of blood components with the color reaction. The cholinesterase activity (micromoles of -SH per minute per milliliter) of the red cell was obtained by difference using the activities of whole blood and plasma and the hematocrit of the blood sample. Acetylthiocholine was used as substrate. The mean plasma (8.3) and red cell (27.9) cholinesterase activities of female field workers were not significantly different from those of nonfield workers or field workers who had not worked in the field during the last 30 days. The mean red cell cholinesterase activity (27.7) of male field workers was significantly lower than the red cell activity (29.6) of nonfield workers in 1975 but not different from field workers who had not worked during the last 30 days (27.5) or nonfield workers in 1976 (27.5). The mean plasma cholinesterase activity of male field workers (9.9) was not significantly different from those of nonfield workers (9.4) in 1975 or 1976, whereas field workers who had not worked in the field during the last 30 days had plasma values (8.9) significantly lower than those working. Red cell values of field workers returning for a repeat test were found to increase slightly between the first test and second, although plasma values remained the same.