Evaluation of Phototrophic Stream Biofilms Under Stress: Comparing Traditional and Novel Ecotoxicological Endpoints After Exposure to Diuron

Abstract

Stream biofilms have been shown to be among the most sensitive indicators of environmental stress in aquatic ecosystems and several endpoints have been developed to measure biofilm adverse effects caused by environmental stressors. Here, we compare the effects of long-term exposure of stream biofilms to diuron, a commonly used herbicide, on several traditional ecotoxicological endpoints (biomass growth, photosynthetic efficiency, chlorophyll-a content, and taxonomic composition), with the effects measured by recently developed methods [community structure assessed by flow cytometry (FC-CS) and measurement of extracellular polymeric substances (EPS)]. Biofilms grown from local stream water in recirculating microcosms were exposed to a constant concentration of 20 μg/L diuron over a period of 3 weeks. During the experiment, we observed temporal variation in photosynthetic efficiency, biomass, cell size, presence of decaying cells and in the EPS protein fraction. While biomass growth, photosynthetic efficiency, and chlorophyll-a content were treatment independent, the effects of diuron were detectable with both FC and EPS measurements. This demonstrates that, at least for our experimental setup, a combination of different ecotoxicological endpoints can be important for evaluating biofilm environmental stress and suggests that the more recent ecotoxicological endpoints (FC-CS, EPS protein content and humic substances) can be a useful addition for stream biofilm ecotoxicological assessment.

Herbicide-Induced Shifts in the Periphyton Community Composition Indirectly Affect Feeding Activity and Physiology of the Gastropod Grazer Physella acuta

“…Likewise, groups with stronger fluorescence, which also constitutes the groups with large cells (compare Figures S2, S3 and S4), increased or remained stable, while those with lower fluorescence decreased or remained stable. In a previous experiment on periphyton exposed to 20 μg/L diuron by Sgier et al, a higher relative abundance of red-algae-like cells, identified as Bangia sp., was detected. In the same study, the proportion of decaying cells was higher.…”

“…We hypothesized that diuron exerts a selection pressure on periphyton during its development leading to a shift in the community composition. − These potential alterations in community composition, in turn, would change the nutritional quality of periphyton for the gastropod grazer and could be reflected in changes in its feeding activity and physiology, with similar effects being observed for fungicides affecting heterotrophic processes (cf. Zubrod et al).…”

Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton

“…This indicates that the phenotypes among the species that changed in abundance were redundant with respect to phenotypic properties. There was also no MP-induced increase in the fraction of decaying cells as observed upon periphyton exposure to, for example, the herbicide Diuron (Sgier et al, 2018a). This suggests that MP do not seem to have a specific mode of action for microorganisms toxic to cells leading to cell death, which is the case for micropollutants (e.g., pesticides).…”

Effect of Temperature, Nutrients and Diuron on Freshwater River Biofilms: A Statistical Approach

“…In such ecosystems, biofilms occur at the boundary between the substrate and the water column. Stream biofilms are sensitive indicators of environmental stress [1] since their development, with regard to structure, taxonomic diversity and function, is extremely reliant on physical and chemical environmental factors [2].…”