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

Gerardo Grasso,Daniela Zane,Giulia Cocco,Chiara Frazzoli,Roberto Dragone

doi:10.3390/bios12020067

Abstract

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 (Chlamydomonas reinhardtii) induced by environmentally relevant concentrations of the herbicide DCMU. Measurements of steady-state chlorophyll a (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 C. reinhardtii 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 C. reinhardtii 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 C. reinhardtii. Similar environmental exposures could affect natural communities of unicellular autotrophs, with hardly predictable cascading secondary effects on higher trophic levels.

Highlights

In recent years, the increasing use of phenylurea herbicides (PUHs) as well as residual activity PUHs and their degradation products in crops, soils, and freshwaters pose a serious risk to the environment and human health
Percentage indexes of interference on photosynthesis were calculated after comparison of steady-state and kinetic chlorophyll a (Chl-a) fluorescence measurements of DCMU-exposed and control C. reinhardtii 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

Summary

Introduction

The increasing use of phenylurea herbicides (PUHs) as well as residual activity PUHs and their degradation products in crops, soils, and freshwaters pose a serious risk to the environment and human health. DCMU is used for general weed control in non-crop areas (e.g., roads, garden paths, railway lines, industrial sites, rights-of-way, around farm buildings, on irrigation, and drainage ditches) [2,3]. It can be used as mildewcide, as an algaecide in commercial fish productions, and as antifouling in paint biocide production [4]. DCMU showed its efficacy against mosses and as a soil-sterilizing agent [5]

Methods

Results

Conclusion