Occupational exposure to agricultural chemicals: effect on the activities of some enzymes in the blood of farm workers

Objective: To determine the effect of different durations of exposure to agricultural chemicals on the activities of the blood enzymes delta-aminolevulinic acid dehydratase (ALAD), superoxide dismutase (SOD), and cholinesterase (ChE) in tobacco field workers. Methods: For this preliminary investigation, 8 volunteers (all smoked tobacco) who were working on a small tobacco farm were monitored over a period of 2 years along with a comparable urban unexposed group (n = 4). During the growing season between 1994 and 1996, dermal and respiratory exposure were determined and blood samples were drawn after the following durations of field work: (1) preexposure (0 DAY); (2) after 1 day of field work (1 DAY) - workers reentered fields at 24 h after spraying of acephate and maleic hydrazide, (3) after 30 days of field work (postspraying; 30 DAYS); and (4) Postexposure - no tobacco production. Standard analytical methods were used. Results: Activity of ALAD was depressed by 30% after 1 DAY and there was no further decrease in ALAD activity after 30 DAYS of field work. SOD activity, in contrast, declined by 29% and 50% after 1 DAY and 30 DAYS, respectively, as compared with 0-DAY activity and that of the urban control, which was similar to 0-DAY activity (P less than or equal to 0.05). Plasma ChE activity declined by 19% after both 1 and 30 DAYS of exposure/field work. The activities of all three enzymes were restored to urban control or preexposure levels during postexposure. Plasma Cd levels were high in the samples taken after 30 DAYS as compared with the preexposure levels. Respiratory nicotine exposure was highest after 30 DAYS of field work. Conclusion: This preliminary study suggests that erythrocyte SOD is a sensitive indicator of exposure to agricultural chemicals in tobacco field workers.