In 2011, the Bureau of Occupational and Environmental Diseases of the Thai
Ministry of Public Health evaluated the health risk of 533,524 agricultural workers
in seventy-four provinces in Thailand using the services of the primary care
units (PCUs) and community hospitals. The agricultural workers were interviewed
and fingertip blood samples taken to test for plasma pseudocholinesterase,
which is inhibited when workers are exposed to excessive levels of certain
insecticides (organophosphates, carbamates). The results showed that 173,243
(32 percent) of the agricultural workers had levels of plasma pseudocholinesterase
enzyme considered “risky” or “unsafe” (>75 units/ml).24 In 2012, the blood
tests for another 117,131 agricultural workers in sixteen provinces found that 30
percent of them again had “risky” or “unsafe” levels of plasma pseudocholinesterase.
24 Another study of chili farmers also found high rates of “risky” or
“unsafe” plasma pseudocholinesterase inhibition using the colorimetric reactive
paper test.12 However, these studies may represent an underestimate of the true
risk faced by agricultural workers, since depression of the plasma enzyme after
exposure persists for only a few days to weeks. Thus, the timing of sample
collection relative to when the pesticide was sprayed is crucial for understanding
the extent of the true risk from organophosphate and carbamate pesticide exposures
experienced by agricultural workers.