ChE and CE activity of solvent controls remained constant during
the bioassay period and were not statistically different between
days (ChE: Kruskal–Wallis; H = 0.12; CE p-NPA: one-way ANOVA;
F = 2.12; df = 3; CE p-NPB: one-wayANOVA; F = 0.34; df = 3; P > 0.05).
In treated snails, ChE and CE activities were expressed as percentages
of the solvent control activity of the same day.
After 48 h of exposure to azinphos-methyl, ChEs were inhibited
by 85 % with respect to control. During the following 21 days in
clean water, even though the enzyme remained inhibited, there
was a slight increase in the activity. At day 21ChE inhibition was
approximately 70% with respect to the control (Kruskal-Wallis;
H = 13.28; P < 0.05) (Fig. 1).