Effects of the herbicide bentazon on growth and photosystem II maximum quantum yield of the marine diatom Skeletonema costatum

Chlorophyll fluorescence techniques are used for the detection of toxic substances in samples of photosynthetic cells by measuring chlorophyll a fluorimetric parameters, which are a response of the PSII physiological status. This work was conducted to determine the effects of the herbicide bentazon (CASRN 25057-89-0) on growth and maximum quantum yield of photosystem II (Fv/Fm) in cells of the marine diatom Skeletonema costatum. Unialgal cultures were exposed to several bentazon concentrations and its effects on algal growth and Fv/Fm were determined. The traditional algal growth inhibition test (algal biomass measurements) and DCMU-induced chlorophyll a variable fluorescence measurements were determined. Our results showed that even low concentrations of bentazon rapidly lead to Fv/Fm decrease, while the effects on algal growth were detected after 24 h of exposure. The LOEC (2.81 mg L−1) and EC50 (13.0 mg L−1) determined through Fv/Fm experiments were lower than the LOEC (22.5 mg L−1) and EC50 (24.0 mg L−1) determined through algal growth inhibition experiments. This confirms that the Fv/Fm is a more sensitive parameter than algal growth for monitoring the effects of bentazon. The present results have demonstrated the applicability of Fv/Fm parameter to access the early toxicity of bentazon, as well as other PSII-inhibition compounds, before significant changes occurred in the original concentration and bioavailability of these toxicants during longer exposure times.