Combined effects of antifouling biocides on the growth of three marine microalgal species

Abstract

The toxicity of the antifouling compounds diuron, irgarol, zinc pyrithione (ZnPT), copper pyrithione (CuPT) and copper was tested on the three marine microalgae Tisochrysis lutea, Skeletonema marinoi and Tetraselmis suecica. Toxicity tests based on the inhibition of growth rate after 96-h exposure were run using microplates. Chemical analyses were performed to validate the exposure concentrations and the stability of the compounds under test conditions. Single chemicals exhibited varying toxicity depending on the species, irgarol being the most toxic chemical and Cu the least toxic. Selected binary mixtures were tested and the resulting interactions were analyzed using two distinct concentration-response surface models: one using the concentration addition (CA) model as reference and two deviating isobole models implemented in R software; the other implementing concentration-response surface models in Excel, using both CA and independent action (IA) models as reference and three deviating models. Most mixtures of chemicals sharing the same mode of action (MoA) were correctly predicted by the CA model. For mixtures of dissimilarly acting chemicals, neither of the reference models provided better predictions than the other. Mixture of ZnPT together with Cu induced a strong synergistic effect on T. suecica while strong antagonism was observed on the two other species. The synergy was due to the transchelation of ZnPT into CuPT in the presence of Cu, CuPT being 14-fold more toxic than ZnPT for this species. The two modelling approaches are compared and the differences observed among the interaction patterns resulting from the mixtures are discussed.

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

“…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).…”

“…Binary mixtures were then made to evaluate the interaction effects of selected pesticide mixtures on algae growth, using the concentration-response surface approach (Gessner, 1995;White et al, 2004). The detailed procedure is described in Dupraz et al (2018), and additional information is given as supplementary material (Table S4 and Figure S4). Briefly, toxicity assays were run for 96 h in sterile 48-well transparent polystyrene microplates (Greiner Bio-One GmbH, cat.…”

“…Procedures of the two mixture modelling approaches (isobole model and MIXTOX tool) are described in detail in Dupraz et al (2018). Therefore, only the concepts and basic principles that are useful to understand the results and discussion are described in §2.4.2.1 and §2.4.2.2 below.…”

“…Predictions from the two reference isobole models, CA and IA, were calculated for each mixture based on the concentration-response parameters of the single chemicals. The detailed procedure is described in Dupraz et al (2018). Briefly, when the CA model did not provide an acceptable fit to the experimental data, more advanced Hewlett and Vølund models (Hewlett, 1969;Vølund, 1992), which are extensions of the CA model, were tested.…”

“…Individual concentrations of substances x and y in the mixture were calculated so that the corresponding ΣTU50:50 values were equal to 0.5, 1 and 1.5 TU, as described in Eq. 3 (example with 1 TU, for further details see Dupraz et al, 2018),…”