The current study demonstrates differential effects in
Lemna minor from pulsed versus continuous exposure regimes
for selected pesticides. Lipohphilicity, mechanism of action,
potential for recovery between pulses, and pulse concentration
appear to define the relative impact of a compound under pulsed
exposure scenarios. Consequently, the time-weighted average
approach may not be appropriate for predicting effects of pulsed
exposures. Several authors [2,5,47] have identified the requirement
for research to underpin the linking of regulatory exposure
and effects assessment as a priority. Consequently, a framework
for assessing effects of pulsed exposures could potentially
include (1) development of generalized pesticide exposure
scenarios; (2) development of guidelines describing the design,
performance, and interpretation of experimental pulsed exposure
studies; and (3) development and evaluation of mechanistic-
based models for predicting effects of pulsed exposures
on aquatic organisms. Such research, in addition to other studies
addressing uncertainties in extrapolation from standard tests to
field impacts, will be invaluable in more accurately assessing
the environmental risk of chemicals.