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pyrethroid poisoning. Therefore, the importance of differential diagnosis
should be emphasized. Overdiagnosis, misdiagnosis, and maldiagnosis
should be avoided.
The diagnostic criteria were used in the epidemiologic study to assess the
extent of the acute pyrethroid poisoning problem in cotton farmers. The results
showed that 834 out of 3 113 sprayers surveyed (27%) were clinically affected
by exposure to pyrethroids, complaining of abnormal facial sensations (a
symptom specific to pyrethroid exposure) as well as dizziness, headache, or
fatigue, but with minimal signs. Only 10 sprayers were diagnosed with mild
acute pyrethroid poisoning according to the diagnostic criteria. In this study,
the prevalence of acute poisoning was 0.31% for subjects exposed to pyrethroids
only and 0.38% in those exposed to pyrethroid and organophosphate
mixtures. The risk of acute pyrethroid poisoning did not differ significantly
between the two groups. The prevalence of acute pyrethroid poisoning in this
study is lower than that of acute organophosphate poisoning in cotton farmers,
reported to be 0.16-11.6% in China. Cases of acute pyrethroid poisoning
in this survey were mild and the prognosis was good.
In 38 of the subjects selected from the studied clusters, the measurement of air
concentration, dermal exposure, and urinary excretion of pyrethroids or deltamethrin
metabolites showed that dermal exposure was the most significant
route of absorption. This indicates that minimizing dermal exposure is of
paramount importance in the prevention of acute pyrethroid poisoning.
Urinary deltamethrin and fenvalerate were both detectable, confirming the
absorption of pyrethroids by spray operators, although these two pyrethroids
metabolize rapidly. After I day of spraying, deltamethrin was present in urine
up to 12 h after the beginning of spraying, but the deltamethrin metabolite
Br2A was detectable at a higher level and for a longer time. Urinary fenvalerate
was also present longer - up to 24 h after exposure began. Hence, the deltamethrin
metabolite Br2A and fenvalerate in urine may be possible indicators
for biological monitoring in pyrethroid-exposed subjects.
Of 2 131 spray operators who had used pyrethroids every year from 1982 to
1987,25.7% experienced adverse effects due to pyrethroid exposure similar to
the symptoms in this survey, but they recovered rapidly and entirely. No
sequelae or long-lasting symptoms were found. This indicates that pyrethroids
are unlikely to have chronic toxic effects in humans. However, the
biological monitoring of 32 cotton growers spraying pyrethroids for 3 days
showed that urinary pyrethroids were not detectable more than 24 h after
exposure.
In addition, 24 spray operators exposed to deltamethrin showed a prolonged
supernormal period of median-nerve excitability after 3 days of spraying and
2 days after spraying had stopped; this increase of nerve excitability was
reported by Parkin and Le Quesne (1982) and Takahashi and Le Quesne (1982)
in animal experiments. Prolongation of the supernormal period and urinary
pyrethroid excretion were not significantly correlated. However, these
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