Microalgal sensitivity varies between a diuron-resistant strain and two wild strains when exposed to diuron and irgarol, alone and in mixtures

Abstract

A wild strain of Chaetoceros calcitrans and wild and diuron-resistant strains of Tetraselmis suecica, were exposed to the PSII inhibitor herbicides diuron and irgarol, individually and in mixtures. The effects of three concentrations of diuron and irgarol and four binary mixtures were evaluated on doubling time, relative reactive oxygen species and lipid content by flow cytometry, and on photosynthetic efficiency by pulse amplitude modulated fluorescence. In both wild strains, significant effects were observed for each molecule at the highest concentration tested: at irgarol 0.5 μg L(-1), C. calcitrans was shown to be more sensitive than T. suecica (+52% and +19% in doubling time, respectively), whereas at diuron 5 μg L(-1), T. suecica was more affected (+125% in doubling time) than C. calcitrans (+21%). Overall, irgarol had a higher toxicity at a lower concentration than diuron (no effect at diuron 0.5 μg L(-1)) for both wild strains. The strongest mixture (irgarol 0.5 μg L(-1) + diuron 5 μg L(-1)) increased doubling time by 356% for T. suecica, thus showing amplified effects when the two compounds were mixed. Sequencing of the diuron-resistant strain demonstrated a single mutation in the psbA gene coding sequence. Although resistance of this strain to diuron was confirmed with no effect at the highest diuron concentration, no resistance to irgarol was shown. In addition, the mutant strain exposed to the strongest mixture showed a 3.5-fold increase in doubling time compared with irgarol alone, thereby supporting the hypothesis of a biochemical interaction between these two compounds.

Toxicity of binary mixtures of pesticides to the marine microalgae Tisochrysis lutea and Skeletonema marinoi: Substance interactions and physiological impacts

“…Another consequence of photosynthesis inhibition is the potential accumulation of intracellular ROS, as previously described in many studies (Knauert and Knauer, 2008;Prado et al, 2012;Stachowski-Haberkorn et al, 2013;Esperanza et al, 2015;Dupraz et al, 2016). In the present study, significant effects, measured using either H2DCFDA or dihydroethidium, were observed after exposure to all individual substances ( Figures 3, 4 and 5A).…”

“…In addition to cell density measurements, flow cytometry can be used to analyse several morphological parameters, such as relative cell size and complexity and relative fluorescence, which is related to pigment content (Marie et al, 2005;Stachowski-Haberkorn et al, 2013;Mansano et al, 2017). Using fluorescent dyes specific to particular physiological functions, several studies have shown the usefulness of flow cytometry to indicate the toxicity of certain chemicals to microalgae (Prado et al, 2009(Prado et al, , 2012Rioboo et al, 2011;Stachowski-Haberkorn et al, 2013;Seoane et al, 2014Seoane et al, , 2017Esperanza et al, 2015;Dupraz et al, 2016;González-Pleiter et al, 2017). The most commonly investigated physiological functions in these studies are viability, general metabolic activity (often measured by non-specific esterase activity) and reactive oxygen species (ROS), whose accumulation following exposure to certain contaminants can cause oxidative stress and thus cell damage.…”

“…Today their use is only permitted as films or construction material preservatives (European Chemicals Agency, 2018). Their high toxicity towards microalgae has been reported in numerous studies (Arzul et al, 2006;Bao et al, 2011;Stachowski-Haberkorn et al, 2013;Sjollema et al, 2014;Dupraz et al, 2016Dupraz et al, , 2018. Metazachlor is a herbicide belonging to the chloroacetamide family that inhibits the synthesis of very long chain fatty acids (VLCFAs) thus disturbing cell division (Götz and Böger, 2004;Vallotton et al, 2008).…”

“…and Dupraz et al (2016) and preliminary experiments were carried out to determine the optimal BODIPY 505/515 concentration and incubation time to use for T. lutea and S. marinoi cultures. For both species, samples containing 0.50 mL of microalgal culture ( §2.3.2) were incubated with 0.48 µM (0.01% DMSO)…”

Transferring mixtures of chemicals from sediment to a bioassay using silicone-based passive sampling and dosing

“…Yet, there is an increasing body of evidence of mixture toxicity, demonstrating that even if each chemical is present at the no-effect concentration or below, the mixture of all chemicals present may cause toxic effects. [3][4][5][6] The theoretical basis for mixture toxicity assessment focuses mainly on the concepts of concentration addition and independent action that describe the mixture effects of components having similar and dissimilar modes of action, respectively. 3,[7][8][9] However, these concepts can only be applied if the mixture composition is known.…”