Microalgae-Based Fluorimetric Bioassays for Studying Interferences on Photosynthesis Induced by Environmentally Relevant Concentrations of the Herbicide Diuron

• Published in: Biosensors (Basel) 2022-01, Vol.12 (2), p.67
• Main Authors: Grasso, Gerardo, Cocco, Giulia, Zane, Daniela, Frazzoli, Chiara, Dragone, Roberto
• Format: Article
• Language: English
• Subjects: Agrochemicals; Algae; Aquatic ecosystems; Aquatic microorganisms; Autotrophs; Bioassays; Biofilms; Cell suspensions; Chlorophyll; chlorophyll fluorescence; Diuron; Drinking water; ecosystem health; ecotoxicology; Emission spectra; Exposure; Fluorescence; Freshwater ecosystems; Herbicides; Kautsky effect; Microalgae; Organisms; Phenylurea; Photochemistry; Photosynthesis; Photosystem II; Soil investigations; Soils; Steady state; Trophic levels
• ISSN: 2079-6374; 2079-6374
• DOI: 10.3390/bios12020067

The widespread agricultural use of the phenylurea herbicide Diuron (DCMU) requires the investigation of ecotoxicological risk in freshwater and soil ecosystems in light of potential effects on non-target primary producers and a heavier effect on higher trophic levels. We used microalgae-based fluorimetric bioassays for studying the interferences on the photosynthesis of a freshwater and soil model green microalga ( ) induced by environmentally relevant concentrations of the herbicide DCMU. Measurements of steady-state chlorophyll (Chl-a) fluorescence emission spectra were performed; as well, the kinetics of the Chl-a fluorescence transient were recorded. Percentage indexes of interference on photosynthesis were calculated after comparison of steady-state and kinetic Chl-a fluorescence measurements of DCMU-exposed and control cell suspensions. The results obtained after 30 min exposure to the herbicide DCMU confirmed a significant inhibitory effect of DCMU 2 μg/L, and no significant differences between %ι values for DCMU 0.2 μg/L and 0.02 μg/L exposures. Positive %ε values from kinetic measurements of the Chl-a fluorescence transient confirmed the same interfering effect of 2 μg/L DCMU on PSII photochemistry in the exposed cell suspensions. Negative values of %ε observed for 0.2 and 0.02 μg/L DCMU exposures could be attributable to a presumptive 'stimulatory-like' effect in the photochemistry of photosynthesis. Short-term exposure to sub-μg/L DCMU concentration (≤0.2 μg/L) affects the photosynthetic process of the model microalga . Similar environmental exposures could affect natural communities of unicellular autotrophs, with hardly predictable cascading secondary effects on higher trophic levels.