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[From page: Pesticides]

Pesticide Exposure Among Agricultural Workers
"See also: Environmental Impact of Pesticides"The World Health Organization and the UN Environment Programme estimate that 3 million agricultural workers in the developing world experience severe poisoning from pesticides each year, resulting in 18,000 deaths. According to one study, as many as 25 million workers in developing countries may suffer mild pesticide poisoning yearly. Other occupational exposures besides agricultural workers, including pet groomers, groundskeepers, and fumigators, may also put individuals at risk of health effects from pesticides.

Pesticide use is widespread in Latin America, as around US$3 billion are spent each year in the region. Records indicate an increase in the frequency of pesticide poisonings over the past two decades. The most common incidents of pesticide poisoning is thought to result from exposure to organophosphate and carbamate insecticides. At-home pesticide use, use of unregulated products, and the role of undocumented workers within the agricultural industry makes characterizing true pesticide exposure a challenge. It is estimated that 50–80% of pesticide poisoning cases are unreported.

Underreporting of pesticide poisoning is especially common in areas where agricultural workers are less likely to seek care from a healthcare facility that may be monitoring or tracking incidence of acute poisoning. The extent of unintentional pesticide poisoning may be much greater than available data suggest, particularly among developing countries. Globally, agriculture and food production remains one of the largest industries. In East Africa, the agricultural industry represents the largest source of income, and many farmers rely on pesticide products to maintain high crop yields.[source?]

In some countries in East Africa, governments are shifting towards commercial agriculture, and opportunities for foreign conglomerates to operate commercial farms has led to more accessible research on pesticide use and exposure among workers.[source?] In other areas where large proportions of the population rely on subsistence, small-scale farming, estimating pesticide use and exposure is more difficult.

Measuring Exposure to Pesticides
There are multiple approaches to measuring a person's exposure to pesticides, each of which provides and estimate of an individual's internal dose. Two broad approaches include measuring biomarkers and markers of biological effect. The former involves taking direct measurement of the parent compound or its metabolites in various types of media: urine, blood, serum. Biomarkers may include a direct measurement of the compound in the body before it’s been biotransformed during metabolism. Other suitable biomarkers may include the metabolites of the parent compound after they’ve been biotransformed during metabolism. Toxicokinetic data can provide more detailed information on how quickly the compound is metabolized and eliminated from the body, and provide insights into the timing of exposure.

Markers of biological effect provide an estimation of exposure based on cellular activities related to the mechanism of action. For example, many studies investigating exposure to pesticides often involve the quantification of the acetylcholinesterase enzyme at the neural synapse to determine the magnitude of the inhibitory effect of organophosphate and carbamate pesticides.

Another method of quantifying exposure involves measuring, at the molecular level, the amount of pesticide interacting with the site of action. These methods are more commonly used for occupational exposures where the mechanism of action is better understood, as described by WHO guidelines published in “Biological Monitoring of Chemical Exposure in the Workplace". Better understanding of how pesticides elicit their toxic effects is needed before this method of exposure assessment can be applied to occupational exposure of agricultural workers.

Alternative methods to assess exposure include questionnaires to discern from participants whether they are experiencing symptoms associated with pesticide poisoning. Self-reported symptoms may include headaches, dizziness, nausea, joint pain, or respiratory symptoms.

Pesticide Poisoning
See also: Environmental Impact of Pesticides

Toxicity of pesticides depends on the rate of absorption, distribution, metabolism and elimination of compounds from the body, as described in the subsection of Environmental Impact of Pesticides "Humans". Commonly used pesticides like organophosphates and carbamates act by inhibiting cholinesterase activity at the neural synapse. Studies show that farm workers in Ethiopia, Kenya, and Zimbabwe have decreased concentrations of plasma acetylcholinesterase, the enzyme responsible for breaking down acetylcholine acting on synapses in the central nervous system. Other studies in Ethiopia have observed reduced respiratory function among farm workers who spray crops with pesticides. Numerous exposure pathways for farm workers increase the risk of pesticide poisoning, including dermal absorption walking through fields and applying products, as well as inhalation exposure.

Challenges in Assessing Pesticide Exposure
Multiple challenges exist in assessing exposure to pesticides in the general population, and others that are specific to occupational exposures to agricultural workers. Beyond farm workers, estimating exposure to family members and children presents additional challenges, and may occur through “take-home” exposure from pesticide residues collected on clothing or equipment belonging to parent farm workers and inadvertently brought into the home. Children may also be exposed to pesticides prenatally from mothers who are exposed to pesticides during pregnancy. Characterizing children’s exposure resulting from drift of airborne and spray application of pesticides is similarly challenging, yet well documented in developing countries. Because of critical development periods of the fetus and newborn children, these non-working populations are more vulnerable to the effects of pesticides, and may be at increased risk of developing neurocognitive effects and impaired development.

While measuring biomarkers or markers of biological effects may provide more accurate estimates of exposure, collecting these data in the field is often impractical and many methods are not sensitive enough to detect low level concentrations. Acetylcholinesterase kits exist to collect blood samples in the field, but conducting large scale assessments of agricultural workers in remote regions of developing countries makes implementation of these kits a challenge. Additionally, there is considerable variability in baseline enzyme activity among individuals, and comparing acetylcholinesterase activity to a reference dose does not necessarily predict health risk associated with exposure. Another challenge researchers face in deriving a reference dose is identifying health endpoints that are relevant to exposure. More epidemiological research is needed to identify critical health endpoints, particularly among populations who are occupationally exposed.

Prevention
Minimizing harmful exposure to pesticides can be achieved by proper use of personal protective equipment, adequate reentry times into recently sprayed areas, and effective product labeling for hazardous substances as per FIFRA regulations. Training high risk populations, including agricultural workers, on the proper use and storage of pesticides can reduce the incidence of acute pesticide poisoning and potential chronic health effects associated with exposure. Research into the toxic health effects of pesticides may also be useful in deriving enforceable standards that are health protective to all populations.