Geneviève Arzul

Comparison of allelopathic properties in three toxic Alexandrium species

Abstract The allelopathic property of three toxic Alexandrium species was studied using bioassays. The repressive action of the filtrate of Alexandrium cultures on growth of Chaetoceros gracile , Gymnodinium mikimotoi and Scrippsiella trochoidea was compared with the haemolytic activity of these filtrates, and published values of toxin content in Alexandrium cells. The results revealed that in the exponential phase of growth in all three species of Alexandrium cultured, allelopathic activity was positively related to both haemolytic and toxic activities, as suggested by previous workers for the same Alexandrium strains. However, in the stationary phase, the allelopathic activity was observed to be higher in relation to haemolytic and toxic activity than in the log phase.

Comet assay in phytoplankton as biomarker of genotoxic effects of environmental pollution

The alkaline comet assay was tested on different microalgae: the dinoflagellates, Karenia mikimotoi and Alexandrium minutum, and the diatom, Chaetoceros gracilis. The microalgae were exposed during their exponential growth to the model direct genotoxicant, hydrogen peroxide (1h, 5 and 100muM H2O2). Following H2O2 exposure, the comet assay was validated only for K. mikimotoi for which genotoxicity was observed from the lowest tested concentration of 5 microM with a concentration-dependent effect. C. gracilis was too small in size (4 microm) to be correctly analysed. For A. minutum, our lysis buffer was not strong enough to digest the cellulosic thecal plates. For K. mikimotoi, the comet assay was thus applied for the study of the genotoxic effects of different pesticides: epoxiconazole (as Opus formulation), chlorpyriphos-ethyl (as Dursban formulation) and endosulfan at 1, 10 and 100 microg of active substance/L for 24h. Exposure to epoxiconazole in formulation resulted in an increase in the extent of DNA strand breaks at the highest tested concentration icro/L. Endosulfan exposure resulted in DNA damage for K. mikimotoi nuclei. Genotoxicity was observed from 1 microg/L of endosulfan and was not concentration dependent.

A haemolytic test to assay toxins excreted by the marine dinoflagellate Gyrodinium cf. Aureolum

Abstract The haemolytic properties of phytoplankton toxins have been already demonstrated in many red tides. Although the detection of red blood cell (RBC) lysis is straightforward, it is not always easy to choose the most suitable type of RBC and incubation time. We have investigated these two points in order to obtain reproducible and quantifiable results, by applying the test to known haemolytic molecules. The dose-response curve is sigmoidal. The spiking technique allows a lowering of the detectable haemolytic threshold. Saponin and Kanagawas haemolysin were used. Without previous concentration, the detection limit was at 4000 HU 1 −1 . A chloroform-methanol extraction allowed the detection limit to be lowered to 0.1 HU 1 −1 . This method has been applied to the detection of a marine dinoflagellate whose exotoxin is haemolytic. It may be used for in situ detection of any haemolytic substance.

Influence of pig farming on the copper content of estuarine sediments in Brittany, France

Abstract Total copper content in sediment from different estuaries has been measured along Brittany coast (France). There is a direct relationship between grain size and copper concentration, with higher concentrations in the fine grain fraction. Relation between copper content and organic matter approximates to a linear relationship. The best correlation was a semilogarithmic relationship between total copper concentration and pigs (excluding suckling pigs) per ha cultivated in the same canton.

Effect of Bentazon on Growth and Physiological Responses of Marine Diatom: Chaetoceros gracilis

The herbicide bentazon (CASRN 25057-89-0) is extensively used in agriculture in Brittany (France) to replace atrazine. Bentazon is not readily adsorbed by soil and therefore it enters adjacent freshwater ecosystems, making its way to estuarine and marine waters areas. Information regarding its effects on marine ecosystems is scarce. Phytotoxicity assessments were conducted in the laboratory on the common diatom Chaetoceros gracilis using both the active ingredient and its formulated product (Basamaïs). The 3 day EC50 using cell counts were, respectively, 150 mg/L and 60 μg/L for bentazon active ingredient and for bentazon-formulated while cellular volume was increased. Although bentazon is known as a photosystem II inhibitor, it produced an increase of pigment (chlorophylls a, c, and carotenoids) content, ATP synthesis, rates of photosynthesis and respiration, and TBARS formation. Therefore, pigments cannot be used as biomarkers of toxicity. Algal cell recovery from bentazon effects occurred after 6–9 days, suggesting a tolerance mechanism.

In vitro test-based comparison of pesticide-induced sensitivity in marine and freshwater phytoplankton.

This study aims to assess the effects of two pesticides, namely the insecticide carbofuran and the herbicide isoproturon, on monospecifically cultivated marine and freshwater phytoplankton according to standard methods. In the presence of pesticide, growth rates were lower in marine species Chaetoceros gracilis and Phaeodactylum tricornutum than in freshwater species Chlorella vulgaris and Selenastrum capricornutum after 72 hours. The EC50 values were obtained with the REGTOX Macro software, and the NEC values by applying the DEBtox model.