HERBICIDES in Asian rice - IRRI books - International Rice ...

An increase in insecticide exposure, from an average of one application per season
to two, increased the probability of eye problems by 22%. Farmers who followed
the recommended three applications faced a probability of 0.53 of having chronic eye
problems.
Skin effects
Pesticides primarily enter the body through the skin, not (contrary to common belief)
through the respiratory tract. Mixing and transferring pesticide concentrates pose a
greater health hazard to farm workers than does pesticide application. For spray operators,
dermal exposure levels are higher than inhalation levels. The degree of contamination
is proportional to the concentration of the chemical and the proximity to
the source of emission (Hamilton 1982). Spraying or dusting pesticides leaves residues
on exposed skin that are about 20-1700 times the amount that reaches the respiratory
tract. The quantity varies with working conditions, application techniques, protective
equipment, and duration of exposure (Bainova 1982). Dermal contamination
is greater when a knapsack sprayer is used than when a spinning disc applicator or an
electrodyne sprayer is used (Durand et al 1984). The hands and forearms are most
exposed and have the highest potential for pesticide contamination (Zweig et al 1985,
Castañeda et al 1990).
Of the pesticides used in rice, herbicides such as 2,4-D and acetamides, and the
organochlorine insecticides are mild to moderate skin irritants and potential sensitizers
(Morgan 1977). Eczema, a chronic allergic dermatitis characterized by lichenification
and fissuring, is a health indicator of pesticide exposure. The skin appears
thickened and has accentuated markings. Other health indicators are destruction of
the distal portions of the toenails, which gives them an “eaten-up” appearance.
The incidence of skin problems among pesticide users was related positively to
the use of both insecticides and herbicides, although only herbicide use was significant.
Farmers at the respondent average for age and nutritional status who did not
apply any herbicides had a probability of 0.12 of having skin problems. The probability
of skin problems rose to 0.30 for farmers who made one herbicide application per
season, and to 0.50 for farmers who made two applications.
Respiratory tract effects
Long-term exposure to chemical irritants can cause such respiratory symptoms as
cough, cold, sputum formation, wheezing, rales, tenderness, and decreased chest expansion
(Morgan 1982, Hock 1987, Nemery 1987). Incipient lung disorders can be
detected by a thorough physical examination and medical history. Bronchial asthma
and other abnormal lung findings are two respiratory tract indicators of pesticide exposure.
The incidence of respiratory abnormalities among the farmers studied was significantly
related to age, smoking, and exposure to insecticides. Herbicides had the
expected positive sign, although the regression was not significant. Nutritional status
Herbicides and rice farmer health 61