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Vol. 03 Issue 4, Fall 1998

Research Commentary: Mexican Agricultural Worker's Exposure to Organophosphate Pesticides
The Ribbon 

Poverty, Production, and Health: Inhibition of Erythrocyte Cholinesterase via Occupational Exposure to Organophosphate Insecticides in Chiapas, Mexico

R. Tinoco-Ojanguren and D.C. Halpern. Archives of Environmental Health, Jan/Feb 1998 [Vol.53 (No. 1) 29-35]

This very technical sounding title describes a study of exposure of Mexican agricultural workers to a widely used class of insecticides, the organophosphates. Organophosphates are very toxic pesticides that are used on a wide variety of crops. Their effectiveness arises from their ability to inhibit the enzyme cholinesterase which is required to transmit nerve impulses in the body. A good indicator of exposure to organophosphates is the level of erythrocyte cholinesterase in the red blood cells. The level of this enzyme is only depressed by exposure to organophosphates and one other class of pesticides (carbamates). By testing the blood of workers who use organophosphate pesticides (OPPs), one can measure their exposure even if they do not have the usual symptoms of cholinesterase inhibition, i.e., nausea, vomiting, diarrhea, convulsions, coma, and respiratory failure.

Pesticides are responsible for 3 million cases of severe poisoning and 220,00 deaths each year. While most pesticides are used in developed countries, most poisonings from them occur in third world countries. The majority of poisoning deaths in the third world have been due to cholinesterase-inhibiting pesticides such as OPPs.The high rate of poisonings in these countries can probably be attributed to less protection against exposure, inadequate warnings on packages, little formal education of agricultural workers, and minimal understanding of the health risks.

The authors of the study looked at agricultural workers in the Border Region of Chiapas, Mexico in order to determine whether exposure to OPP insecticides affects all groups of workers equally and to suggest interventions that might decrease levels of exposure. They studied three communities, one (1) where farmers use low technology and produce for the local and regional market; one (2) where farmers use irrigation and tractors, apply pesticides extensively and produce for state, national, and international markets; and one (3) where farmers produce for their own consumption, rely on family labor, and use insecticides for pest control. Questionnaires were given to 199 males and blood samples were taken for testing.

Of those surveyed, 159 used OPPs, and others used less toxic pesticides, such as pyrethroids. All workers "ate in the field during the work day, did not use protective equipment, and suffered from accidental spills of pesticides." (p. 32) Those not using OPPs had larger land holdings than those who did (Community 2). They were financially more able and tended to use less toxic pyrethroid pesticides that are 500 times as expensive as the OPPs. Community 3 had the lowest education, but the three groups did not differ with respect to unsafe practices or use of protective gear. All subjects of the study were working their own land, thus needing to be efficient with time. Thus, they ate in the field. The authors also discovered a cultural aversion to wearing protective equipment because it would indicate weakness on the part of the worker.

Groups exposed to OPPs had lower concentrations of cholinesterase than those who had not been exposed (reference group). There was a measurable time element to exposure, i.e., cholinesterase was decreased after exposure as compared with before, and the "before" levels were comparable to those in the reference group. Some workers with blood levels that indicated acute poisoning did not have other symptoms. It was hypothesized that these workers might have developed a threshold for symptoms resulting from chronic exposure.

The major factor affecting pesticide exposure was not the level of technology of the farm workers, but their economic standing. The workers from the poorest communities (3) were at greatest risk from pesticide poisoning. Future work from these authors will focus more fully on why these workers are at greater risk and on intervention strategies to minimize exposure to organophosphate pesticides.

This study is important because it points up subtle differences within a community of workers, all of whom are at risk from pesticide exposure and poisoning. There is a need to educate and motivate all workers about protective clothing, and cultural factors are extremely important in this effort. The economics of being able to afford less toxic pesticides is also an important consideration for these workers. Those on the margin have little choice but to use the least expensive methods. Education about farming methods that use less pesticides might be one way to influence their practices. Another important aspect of this work is the ability to measure cholinesterase levels in the field. Technological advances in measuring the enzyme level in blood using hand-held spectrophotometers has enabled people to study workers in situ, a major advance in such work. It is expected that future studies of this type will provide the background needed to devise the intervention strategies that will work.

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Written by Ann T. Lemley, Ph.D, Associate Director, BCERF, and Chair, Textiles and Apparel, College of Human Ecology, Cornell University

Last Update 06.23.00