title: Effects of the herbicide bentazon on growth and photosystem II maximum quantum yield of the marine diatom Skeletonema costatum.
abstract: 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.
authors.affiliation: Programa de Pós-Graduação em Ecologia e Conservação, Universidade Federal do Paraná, Centro Politécnico, Curitiba, Paraná, Brazil. macedoceano@gmail.com
authors.forename: R S
authors.initials: RS
authors.lastname: Macedo
authors.forename: A T
authors.initials: AT
authors.lastname: Lombardi
authors.forename: C Y
authors.initials: CY
authors.lastname: Omachi
authors.forename: L R
authors.initials: LR
authors.lastname: Rörig
mesh_terms: D001581:Benzothiadiazines / Q000633:toxicity*; D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism; D003627:Data Interpretation, Statistical; D017377:Diatoms / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure*; D004237:Diuron / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D005453:Fluorescence; D006540:Herbicides / Q000633:toxicity*; D045332:Photosystem II Protein Complex / Q000378:metabolism*
chemical_list: D001581:Benzothiadiazines; D006540:Herbicides; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D004237:Diuron; C002003:bentazone