Objectives To determine the inhibition effects of four herbicides including Simazine, Prometryn, Chlorotoluron and Propanil on photosynthetic activity in algae suspension by chlorophyll fluorescence technique.

Methods Phaeodactylum tricornutum was selected as an indicator. The inhibition effects of Simazine, Prometryn, Chlorotoluron and Propanil on photosynthetic activity in samples of algae suspension were detected by dual-channel PAM chlorophyll fluorometer, and the singular and mixed inhibition effects of four herbicides were analyzed.

Results The singular inhibition effects ranking from high to low were Chlorotoluron, Prometryn, Propanil, and Simazine. In the linear range, mixed effects were equivalent to summation of the singular effect of each component. Out of the linear range, the interaction of Chlorotoluron and Prometryn showed antagonistic effect. The median inhibition concentration (IC₅₀) of Simazine, Prometryn, Chlorotoluron and Propanil were 143、18、17.5 and 53 μg/L respectively. The correlation coefficients (r) of the standard curves were 0.998 5~0.999 9. The RSD was less than 15%. The average recoveries for tap water were 85.5%~86.3%.

Conclusions The chlorophyll fluorescence technique had a good response on the inhibition effects of Simazine, Prometryn, Chlorotoluron and Propanil on photosynthetic activity in algae suspension. The apparatus occupy little space and the detection was fast. With a high sensitivity and a good stability, the technique was fit for on-site monitoring of emergency, detection and forecasting on outbreaking events caused by pesticide in water.