Regarding neurotoxicity, during the recovery period, individuals
showing lack of adherence or abnormally protruded head-food
diminished from 82 and 96%, respectively, to 15 and 21% after
7 days in pesticide-free water. At 21 days, 15% of the snails still
presented lack of adherence by, 15% showed weak adherence to
vessels and none of them had their head-foot region abnormally
exposed. A considerable lethality was observed (30%) at day 14.
It is probable that the individuals with severe neurotoxic signs at
48 h of exposure to azinphos-methyl (lack of adherence and headfoot
region protrusion) remained intoxicated during recovery and
consequently then died. When comparing ChE inhibition and neurotoxic
effects at 48 h and during the recovery period we could
not observe a clear correlation between the parameters; while ChE
activity remained reduced, the severe intoxication signs could be
reversed even though lethality was registered. During exposure,
with an 85% inhibition of ChEs the snails showed important neurotoxic
effects but, at 21 days, during recovery, with a 70% of ChE
inhibition no severe neurotoxicity was observed. There are very
few works that have studied the reversion of neurotoxic signs.
Kristoff (2010) reported that L. variegatus, exposed for 48 h at the
IC90 of azinphos-methyl, showed no recovery of ChE activity after
21 days in pesticide-free water, but a marked reduction of intoxication
signs. Recovery from toxic effects not only depends on
the interaction of the contaminant with its target enzyme, it is
a much more complex process, where physiological resilience of
the organism plays a very important role to overcome the induced
stress. The study of biomarkers with slow recovery following
exposure to a contaminant gives valuable information. It allows
to detect effects of contaminants when they are no longer present
in the environment, also it shows that toxic effects may last longer
than the exposure time and may be underestimated in acute exposure
experiments