Biomarkers of exposure, such as antioxidant systems, are widely used for their sensitivity within the scope of toxicological studies [10; 11]. As chemical pollutants induce oxidative damage to biological systems, the activity levels of antioxidant enzymes, like superoxide dismutase (SOD) and catalase (CAT)--which are vitally involved in the detoxification of reactive oxygen species (ROS) and in the reduction of oxidative stress--can be evaluated and understood [7; 10]. Likewise, biomarkers of lipid peroxidation (LPO) are vastly investigated [10], especially through the thiobarbituric acid reactive substances (TBARS) test, which measures the levels of secondary lipid oxidation products, such as malondialdehydedehyde (MDA) formation [12]. This set of biomarkers provides a standing of the overall oxidative stress state of cells under a certain compound exposure at a specific dose [13]. While from the scientific point of view, the mode of action of these antioxidant processes and how they are affected by different emerging contaminants is of upmost importance, these biochemical results are often difficult to communicate to non-scientific communities, such as stakeholders and decision makers [14; 15]. The pressing need for methodologies and information that can effectively connect researchers and environmental managers, linked to international environmental frameworks, led to the development of a variety of indexes that can easily communicate scientific results to stakeholders, as applicable tools for decision making in environmental managing [16; 17; 18]. An array of scoring indexes have emerged in the past few years [16], thus adopting an ecologically transversal approach of great importance in order to develop meaningful community management tools towards addressing contaminants of emerging concern [5; 19; 20]. Therefore, following biochemical evaluations, new index development must accurately reflect the biological status, follow suitable validation and consider result communication, so that management entities can approach similar new environmental matters within the scope of policy development [16; 17]. As mentioned above, several approaches have been developed to translate vast arrays of biochemical data into numeric indexes, such as the integrated biomarker response index (IBR) [5], the bioeffect assessment index (BAI) [19] and the principal component analysis scoring based index (denoted as PCA-index hereafter) [20; 21]. These indexes are based on different approaches to the same biochemical data. The IBR index uses the normalization of biochemical data to overcome differences in the magnitude between the different biochemical traits it integrates, and requires expert judgment or previous experience from an operator to define how a certain biochemical trait is altered (enhanced or inhibited) by a given compound [5]. The BAI approach divides each biochemical trait at each exposure level into statistical cohorts, considering quartile distribution, and scoring each biochemical trait accordingly [19]. The PCA index uses the values obtained from a PCA plot of biochemical traits to normalize the values and to weigh each variable according to its importance to the PCA model [20; 21]. Thus, these three indexes range from univariate (BAI) to multivariate approaches (IBR and PCA-based indexes), with or without operator intervention (IBR and PCA-based respectively), and a comparative analysis allows to assess which approach is more suitable to be applied in emerging contaminants ecotoxicological studies. In the present work, the suitability of the three different multivariate indexes (BAI, IBR, and PCA-based indexes) was tested through application of previously obtained oxidative stress biomarker data, using marine diatoms as a study model.