title: Modelling the effects of pulse exposure of several PSII inhibitors on two algae.
abstract: Subsequent to crop application and during precipitation events, herbicides can reach surface waters in pulses of high concentrations. These pulses can exceed the Annual Average Environmental Quality Standards (AA-EQS), defined in the EU Water Framework Directive, which aims to protect the aquatic environment. A model was developed in a previous study to evaluate the effects of pulse exposure for the herbicide isoproturon on the alga Scenedesmus vacuolatus. In this study, the model was extended to other substances acting as photosystem II inhibitors and to other algae. The measured and predicted effects were equivalent when pulse exposure of atrazine and diuron were tested on S. vacuolatus. The results were consistent for isoproturon on the alga Pseudokirchneriella subcapitata. The model is thus suitable for the effect prediction of phenylureas and triazines and for the algae used: S. vacuolatus and P. subcapitata. The toxicity classification obtained from the dose-response curves (diuron>atrazine>isoproturon) was conserved for the pulse exposure scenarios modelled for S. vacuolatus. Toxicity was identical for isoproturon on the two algae when the dose-response curves were compared and also for the pulse exposure scenarios. Modelling the effects of any pulse scenario of photosystem II inhibitors on algae is therefore feasible and only requires the determination of the dose-response curves of the substance and growth rate of unexposed algae. It is crucial to detect the longest pulses when measurements of herbicide concentrations are performed in streams because the model showed that they principally affect the cell density inhibition of algae.
authors.affiliation: Institut des dynamiques de la surface terrestre (IDYST), Faculté des Géosciences et de l'Environment, Université de Lausanne, Géopolis, Quartier Mouline, CH-1015 Lausanne, Switzerland. Electronic address: pierre-jean.copin@unil.ch.
authors.forename: Pierre-Jean
authors.initials: PJ
authors.lastname: Copin
authors.affiliation: Institut des dynamiques de la surface terrestre (IDYST), Faculté des Géosciences et de l'Environment, Université de Lausanne, Géopolis, Quartier Mouline, CH-1015 Lausanne, Switzerland. Electronic address: nathalie.chevre@unil.ch.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Chèvre
mesh_terms: D054750:Ecotoxicology; D004781:Environmental Exposure / Q000009:adverse effects*; D004791:Enzyme Inhibitors / Q000633:toxicity*; D006540:Herbicides / Q000633:toxicity*; D008954:Models, Biological; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors*; D045483:Rivers / Q000737:chemistry; D044444:Scenedesmus / Q000187:drug effects*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D004791:Enzyme Inhibitors; D006540:Herbicides; D045332:Photosystem II Protein Complex; D014874:Water Pollutants, Chemical
keywords: Algae; Modelling; Phenylureas; Pulse exposure; Recovery; Triazines