Relationships of time–response for Lemna minor growth under
continuous and pulsed exposures at 1mg/L metsulfuron-methyl
are illustrated in Figure 1. Nominal Lemna minor 42-d growth rate
EC50 values for metsulfuron-methyl ranged from 0.90 to
0.99 mg/L (Table 3). Calculated EC50 values demonstrated that
continuous exposure was less toxic than the pulsed exposures.
Inhibition of Lemna minor growth rate under pulsed and continuous
exposures at each test concentration are summarized in
Figure 2. There were no significant differences in growth rate
across all treatment scenarios compared with the control
(p>0.05) at a treatment concentration of 0.1mg/L. At
0.25 mg/L, the continuous application scenario demonstrated
a significantly higher rate of growth than the 2-d pulse application
scenario (p