Modelling the effect of exposing algae to pulses of S-metolachlor: How to include a delay to the onset of the effect and in the recovery

• Published in: The Science of the total environment 2016-01, Vol.541, p.257-267
• Main Authors: Copin, Pierre-Jean, Perronet, Léa, Chèvre, Nathalie
• Format: Article
• Language: English
• Subjects: Acetamides - toxicity; Algae; Dose-Response Relationship, Drug; Engineering Sciences; Herbicides; Herbicides - toxicity; Modelling; Models, Chemical; Recovery; Scenedesmus - drug effects; Time-dependence; Water Pollutants, Chemical - toxicity
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2015.08.154

In agriculture, herbicides are applied to improve crop productivity. During and after rain event, herbicides can be transported by surface runoff in streams and rivers. As a result, the exposure pattern in creeks is time-varying, i.e., a repeated pollution of aquatic system. In previous studies, we developed a model to assess the effects of pulse exposure patterns on algae. This model was validated for triazines and phenylureas, which are substances that induce effects directly after exposure with no delay in recovery. However, other herbicides display a mode of action characterized by a time-dependency effect and a delay in recovery. In this study, we therefore investigate whether this previous model could be used to assess the effects of pulse exposure by herbicides with time delay in effect and recovery. The current study focuses on the herbicide S-metolachlor. We showed that the effect of the herbicide begins only after 20h of exposure for the alga Scenedesmus vacuolatus based on both the optical density and algal cells size measurements. Furthermore, the duration of delay of the recovery for algae previously exposed to S-metolachlor was 20h and did not depend on the pulse exposure duration or the height of the peak concentration. By accounting for these specific effects, the measured and predicted effects were similar when pulse exposure of S-metolachlor is tested on the alga S. vacuolatus. However, the sensitivity of the alga is greatly modified after being previously exposed to a pulse of S-metolachlor. In the case of scenarios composed of several pulses, this sensitivity should be considered in the modelling. Therefore, modelling the effects of any pulse scenario of S-metolachlor on an alga is feasible but requires the determination of the effect trigger, the delay in recovery and the possible change in the sensitivity of the alga to the substance. [Display omitted] •Effect of S-metolachlor pulse exposure on the alga S. vacuolatus is modelled.•Time-dependency of S-metolachlor was incorporated in the model.•Delay in effect and in recovery was recorded for S-metolachlor on S. vacuolatus.•The sensitivity of the alga increases after being previously exposed to a pulse.•The model was found to be effective for S-metolachlor and for alga S. vacuolatus.