Original Contribution

A Study of Serum Cholinesterase Activity in Agricultural and Industrial Workers Occupationally Exposed to Organophosphate Insecticides

B. Singh, MD,
Dr. T.D. Dogra, Dr. C.B. Tripathi

Int J Med Toxicol 2002; 5(2): 9

Corresponding Author

Dr. Bhoopendra Singh
Assistant Professor
Dept. Forensic Medicine & Toxicology
Kasturba Medical College
Mangalore, 575001, India
Telephone & Fax No. 91-824-446983
Email: tox_13@indiatimes.com
Or singh_b13@hotmail.com


This paper presents the findings of a study of serum cholinesterase (SChE) activity in a group of 50 industrial and 50 agricultural workers exposed to organophosphate compounds. Fifty subjects with no known exposure to organophosphates were enrolled as controls. The mean SChE level was significantly lower in the worker group than the control group. Furthermore, the SChE levels were significantly lower in the industrial worker group versus the agricultural worker group.

Key words

Serum cholinesterase, organophosphate insecticides exposed agricultural workers, and industrial workers


Cholinesterase inhibiting insecticides are extensively used in agriculture and community health programs. People in developing countries are at higher risk for chronic exposure to these insecticides because of poor working conditions and an unawareness of the potential hazards in manufacturing and application of these insecticides1. There are only a few reports of health effects of chronic occupational exposure to organophosphate pesticides in developing countries.1-6 Cholinesterase inhibition is an indirect indicator used to monitor organophosphate pesticide exposure.3 Exposure to these compounds can be monitored using serum cholinesterase, RBC cholinesterase or whole blood cholinesterase enzyme levels. Because serum cholinesterase is an easy and sensitive indicator of organophosphate pesticide overexposure, the measurement of this enzyme was used in our study.

Materials & Methods

Two hundred and forty male subjects were interviewed for detailed history of age, socioeconomic status, working condition, dietary and addiction habits. Presence of clinical features of anemia or malnutrition, and liver disease were also recorded for exclusion of the subjects. Eighty subjects were engaged in spraying of organophosphate pesticides, while 80 other subjects were engaged in organophosphate pesticides manufacturing industry located near Delhi and the remaining 70 agricultural workers not involved in spraying or handling pesticides served as controls. The subjects were selected for the study from the 240 interviewed on the basis of matching age, socioeconomic status, dietary habits and duration of exposure. Fifty agricultural workers selected who were engaged in spraying of organophosphate pesticides for a number of years (3-5 yrs) and duration of exposure of these pesticides ranged from 4-5 hrs weekly. As far as the 50 factory workers were concerned, only those who worked for a period of ranged 2-5 yrs were included. They were exposed to pesticide 6-8 hrs per day except during holidays. An equal number of subjects of matched age, socioeconomic status, and dietary habits were selected as controls.

The factory worker group was further subdivided into 39 individuals who were involved in manufacture and packing section as directly exposed group, and 11 individuals from other sections of the same industry such as administration and security as indirectly exposed group. Blood samples (8-10 ml) were collected from each group and serum for cholinesterase levels determined by the method of Rappaport et al 7 using a Sigma Diagnostic Cholinesterase Kit. The normal range of cholinesterase by this method is 40-120 U/ml.

Statistical analysis of the data

The Mann-Whitney 'U' test was applied in the statistical analysis of the data.


The mean ages of factory, agricultural workers and controls were 34.26.9, 32.07.2 and 33.16.1 years respectively. There was no statistically significant variation in age.

Table 1 compares the mean SChE levels of the exposed workers and control subjects. SChE levels were significantly lower in the exposed groups. The percent decrease of SChE values for the agricultural workers and factory workers when compared to the mean control group was found to be 23.51% and 30.73% respectively (Table 1, p<0.001). Figure 1 shows the distribution of SChE levels of exposed workers and control subjects. The SChE level of indirectly and directly exposed industrial workers was 63.73 15.97 and 42.1717.49 respectively (Table 2). Approximately one-half (48%) of the factory workers and one quarter (28%) of the farm workers had below normal levels (<40 U/ml) of SChE (Figure 1).


This study found that mean levels of SChE in workers exposed to pesticides were significantly lower as compared to controls. However, although the mean was lower, the majority of workers in the 2 exposed groups had SChE within the normal range (40-120 U/ml) (Figure 1). The percent decrease of SChE values for the agricultural worker and factory worker when compared to the mean control group was found to be 23.51% and 30.73% respectively (Table-1, p<0.001). Warnic and Carter, Bogden et al, Kahn, Bhatnagar et al, and Mishra et al have reported similar findings.5,8,9,2,4 The mean value of SChE in exposed agricultural workers was found to be higher as compared to exposed factory workers in this study. This may be due to the fact that agricultural workers were exposed to organophosphate compounds only intermittently, (e.g. weekly or biweekly), while factory workers were required to work daily for up to 6-8 hrs except during holidays. Within the industrial worker group, those workers who were in direct contact with pesticides in manufacturing and packing section had a significantly lower mean SChE as compared to the indirectly exposed group, who were not in direct contact with pesticides due to due to having administrative jobs (p<0.001). This significant decrease of SChE levels in the directly exposed group is most likely due to more absorption of organophosphate pesticides through direct contact. These findings are supported by the previous similar studies.10-13

We therefore suggest that SChE levels should be monitored in all workers engaged in organophosphate application and manufacturing.


The authors thank Mr. M.S. Kotian, Assistant Professor, Department of Bio-statistics, for help with statistical analysis.

Table 1

Comparison of serum cholinesterase levels of exposed workers and Control subjects (N=50 in each group)

GroupMean SD (U/ml)
Control68.14 19.54
Agricultural worker52.12 18.04*
Factory worker47.20 19.88**

*P<0.001, ** p<0.001 as compared to control group

Table 2

Comparison of serum cholinesterase level of Indirect and Direct Contact Industrial workers.

GroupNo.Mean SD (U/ml)
Indirect contact1163.7315.97
Direct contact1142.5417.49*

*P<0.001 as compared to indirect contact group

Figure 1 : Frequency distribution of Serum Cholinesterase Enzyme


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