## 4 Discussion  
As stated recently, toxicological data for microalgae are scanty when compared with other taxa [56]. Most of the information on the toxicity of several pollutants in the aquatic environments, the compounds under study included, comes from tests carried out on crustaceans and fish, although algae can be more sensitive than animals to aquatic toxicity [57; 58; 59; 60]. Another problem is the prevalence in lab repositories of freshwater species with high tolerance to the pollution that have been frequently used as a model in ecotoxicological studies [56]. These species can be unsuitable surrogates for estuarine or marine microalgae [61]. A way to directly compare our data with those of the literature is not easy to find, since these three algae have never employed together, just two on three sporadically. Moreover, we focused our work on the long-term effects. Previous studies included different species of microalgae [19; 34], or sometimes _Raphidocelis subcapitata_[62; 63; 64]. Very often, one of the tests in the panel employed to evaluate the biotoxicity is the Microtox(r) one [62; 65; 66] based on _Vibrio fisheri_, but it is an acute test (15 min), for which results are very far from our chronic toxicity data. Nevertheless, we tested a wide range of concentrations of the investigated pollutants similarly to the most part of previous studies and, consistently with them, the first conclu  
Figure 7: Bioluminescent bacteria light emission intensities recorded at short toxicity intervals (3 h (**A**) and 48 h (**B**)) after contact with the various compounds at the 50 and 100 ug L\({}^{-1}\) concentration. With the exception of BSA, showing no effect, HOBT and BT at 50 ug L\({}^{-1}\), shown eutrophic effects, and other compounds resulted in a clearer toxic effect. sion was that all the compounds had some effects at the higher concentrations, but at the levels detected in freshwaters, they did not pose a risk for aquatic ecosystems. The tested algae should be applied, for example, to reveal the high concentrations found in wastewaters from sewage treatment plants. Sensitivity for specific families of pollutants was not observed, and each species showed different behaviors with respect to the three groups of compounds. It must be underlined that the differences in the response of microorganisms to the same or to similar pollutants may depend on various factors, ranging from lipid peroxidation to metabolic energy deficiency, decreased photosynthetic energy, or endocrine disrupting effects, and are therefore species-specific and related to the ecology and physiology of the organism [67]. Except for benzenesulfphonamides, the freshwater alga, in particular, and the diatomea seemed to be the most sensitive to these compounds, not only concerning the degree of growth inhibition produced by the high concentration, but mainly with respect to the response to the lowest ones. In this family of pollutants, benzothiazoles and benzotriazoles showed the most marked effect on our algal species. According to our expectations, the freshwater _Raphidocelis subcapitata_ was more sensitive to benzo-fused nitrogen heterocyclic pollutants than the marine ones, which are well adapted to fast changes in the chemical balance of their habitat. On the contrary, an unexpected result was the absence of acute adverse effects on the _Vibrio fisher_ light emission, at least at the 50 and 100 \(\mathrm{\SIUnitSymbolMicro L}^{-1}\) concentrations. A detrimental effect was observed only at the chronic toxicity intervals (24 and 48 \(\mathrm{\SIUnitSymbolMicro h}\)), and was not produced by all compounds. In fact, two compounds showed at that time a stimulation of light emission, and this phenomenon is quite frequent when the tested compounds do not produce an acute toxicity effect toward the _V. fisher_. Over time, the light induced degradation or the bacterial metabolism transform the organic pollutants into carbon sources for bacteria.