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Field exposure during application of
organophosphates using knapsack
sprayers in the Philippines
Carmen P. Castaneda
Department of Pharmacology, College of Medicine,
University of the Philippines,
Manila, Philippines
Three field studies were undertaken in the Philippines to measure exposure
to pesticides using World Health Organization (WHO) protocols. Farmers
used methyl parathion (50% emulsifiable concentrate) and
monocrotophos (28.5% water-soluble concent rate) under field conditions.
Potential exposure and dermal exposure were determined by measuring
the concentration of pesticide on pieces of clothing and gauze patches worn
under the clothing. The protection afforded by locally designed protective
clothing was assessed, the urinary metabolites, p-nitro phenol and
dimethylphosphate were monitored, and cholinesterase activity in red
blood cells was measured before and after exposure to the pesticides.
For the Philippines, a developing country with a population of about 60
million people, agriculture is the backbone of the national economy. To ensure
crop protection, pesticides are an important agricultural input. Anticholinesterase
insecticides are the most widely available and frequently used pesticides.
With increased use, however, there is growing concern about the
potential adverse effects of pesticides on man and the environment. Based on
sales value of imports, pesticide consumption in the Philippines has increased
steadily from 1983 to 1987 (Table 1). Estimates for 1984 show that 36.6% of total
pesticide spending was for rice crops, 25.5% for bananas, and 14.3% for
vegetables (Fig. 1).
In the Philippines, there are two growing seasons for rice: February to April
and July to October. Sprayable insecticides are applied up to three times
during a season. Applications normally take place about 2 weeks after planting
and up to 4 weeks before harvest. The height of the crop during spraying
varies from 20 to 100 cm.
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