Time course of carboxylesterase (CE) activity in Chilina gibbosa with respect to control after two days exposure to 20 g L−1 azinphos-methyl (AZM), (a) using p-NPA
and (b) p-NPB as substrates. Control values of CEs correspond to 0.056 ± 0.007 moles min−1 mg protein−1 with p-NPA and 0.086 ± 0.011 moles min−1 mg protein−1 with
p-NPB. Organisms were exposed for 48 h and then transferred to clean water for 21 days. Activity was expressed as percentage of activity in control of each day. Boundary of
boxes closest to zero indicates 25th percentile, full line within boxes marks median while broken line represents mean, and boundary of boxes furthest from zero indicates
75th percentile.