Relationships of time–response for Lemna minor growth under
continuous and pulsed exposures at 5 mg/L PCP are illustrated
in Figure 1. Nominal 42-d growth rate EC50 values for PCP
ranged from 1.26 to 4.00 mg/L (Table 3). Calculated EC50
values demonstrated that the 2-d pulsed exposure scenario was
more toxic than the 4-d pulsed treatment, which was in turn
more toxic than the continuous exposure scenario. Inhibition of
Lemna minor growth rate under pulsed and continuous exposures at
each test concentration is summarized in Figure 2. At a treatment
concentration of 0.10 mg/L, none of the exposure scenarios
differed significantly from the control or from each other
over time (p>0.05). At a treatment concentration of 0.5 mg/L,
the 2-d pulsed and continuous exposure scenarios induced a
significant reduction in growth rate compared with the control
(p