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

Abstract

This study screened binary mixtures of pesticides for potential synergistic interaction effects on growth of the marine microalgae Tisochrysis lutea and Skeletonema marinoi. It also examined the single and combined effects of three of the most toxic substances on microalgal physiology.Single substances were first tested on each microalgal species to determine their respective EC 50 and concentration-response relationships. The toxicity of six and seven binary mixtures was then evaluated in microplate experiments on the growth of T. lutea and S. marinoi, respectively, using two mixture modelling approaches: isobolograms and the MIXTOX tool, based on Concentration Addition (CA) or Independent Action (IA) models. Significant cases of antagonism (for both species) and synergism (for S. marinoi) were observed for the mixtures of isoproturon and spiroxamine, and isoproturon and metazachlor, respectively.These two mixtures, together with that of isoproturon and diuron, for which additivity was observed, were further studied for their impacts on the physiology of each species. Exposures were thus made in culture flasks at three concentrations, or concentration combinations for mixtures, selected to cause 25%, 50% and 75% growth rate inhibition. The effects of the selected pesticides singly and in combination were evaluated at three perceived effect concentrations on esterase metabolic activity, relative lipid content, cytoplasmic membrane potential and reactive oxygen species (ROS) content by flow cytometry, and on photosynthetic quantum yield (ϕ' M ) by PAM-fluorescence.Isoproturon and diuron singly and in mixtures induced 20-40% decreases in ϕ' M which was in turn responsible for a significant decrease in relative lipid content for both species. Spiroxamine and metazachlor were individually responsible for an increase in relative lipid content (up to nearly 300% for Highlights ► The toxicity of binary pesticide mixtures was evaluated on two microalgal species. ► Effects of three selected mixtures were then examined on five physiological functions. ► Effects on microalgal physiology were linked to the pesticide's toxic mode of action. ► Mixed isoproturon and metazachlor had significant synergistic effects on S. marinoi. ► Observed synergy could be due to a combined effect on the photosynthetic apparatus.

A critical review of effect modeling for ecological risk assessment of plant protection products

“…By comparing the isoboles based on the CA and IA prédictions and experimental mixture data, con clusions can be drawn on the type(s) of interaction occurring (Cedergreen, 2014). Moreover, Dupraz et al (2019) described the Hewlett and Vplund mod els that are extensions of the CA model. Other methods relying on the same approaches (CA/IA models) hâve been proposed such as the Computational Approach to the Toxicity Assessment of Mixtures (Schmidt et al, 2017), the Accelerated Failure Time (AFT) model (Qiu et al, 2017), the CI method (Yang et al, 2017), the calculation of Mixture Toxicity Index (MTI) or Safety Factor Index (SFI) (Toumi et al, 2018).…”

Trophic transfer of copper decreases the condition index in Crassostrea gigas spat in concomitance with a change in the microalgal fatty acid profile and enhanced oyster energy demand

“…Detailed information regarding the staining protocols are presented in supplementary Table S1. The staining protocols were from Stachowski-Haberkorn et al (2013) for DCFH-DA, from Coquillé et al (2018) for BODIPY 505/515 , from Prado et al (2012) for HE and DiBAC 4 (3) and adapted from Dupraz et al (2019) for FDA. In addition to dyes, high-intensity green fluorescent beads (Polysciences Europe) were added to each tube (8.5 µL per tube) to permit a normalisation of the fluorescence values of cells for further comparisons among samples and over time.…”

Single and Combined Effects of Cypermethrin and UVR Pre-Exposure in the Microalgae Phaeodactylum Tricornutum

“…In this sense, most of the studies on the tolerance of microalgae to pesticides are focused on herbicides due to their action on the photosynthetic system (Jamers and De Coen 2010;Lozano et al 2014) and mainly on freshwater species (Nestler et al 2012;Baruah and Chaurasia 2020). However, information about the effect of insecticides or fungicides, designed to act against non-photosynthetic organisms, in coastal marine microalgae is scarce (Wang et al 2011;Dupraz et al 2019). Particularly, some pesticides, such as the pyrethroid insecticide cypermethrin (Cyp), could be used in agricultural fields and aquaculture activities or for domestic pest control (Burridge et al 2000;Tucca et al 2014;Gao et al 2016).…”