## 3 Results
### Oxidative Stress Biomarkers  
To evaluate potential cell damage due to oxidative stress conditions induced by contaminant exposure, several oxidative stress biomarkers were evaluated in the diatom cells exposed to different pollutant levels. Oxidative stress biomarker values (average \(\pm\) std deviation), linear regression slope and the statistical relation between each biomarker and the external concentration of the different contaminants applied are presented in Supplementary Material Table S1. Further discussion on the biological considerations of these results can be found in the studies contributing to the present work [15; 22; 23; 24; 25]. To study the dose-response relationship of each of the analyzed biomarkers, correlations between the biomarker response and the exogenous dose applied were also determined (Supplementary Material Table S1). Propranolol gradient concentrations showed a positive dose relationship for SOD antioxidant enzyme (r\({}^{2}\) = 0.87, \(p\) < 0.05) and TBARS (r\({}^{2}\) = 0.72, \(p\) < 0.05), whereas CAT and APX showed no significant relation to this compound. A significant rise in lipid peroxidation products (TBARS) was observed in _P. tricornutum_ cells exposed to fluoxetine concentration gradient, revealing a positive and significant correlation (r\({}^{2}\) = 0.73, \(p\) < 0.05). Among the tested antioxidant enzymes, SOD and APX followed a similar a trend similar to the lipid peroxidation, though not significant, but showing the highest activity levels under the highest applied concentration (80 ug L\({}^{-1}\)), whereas CAT activity did not respond to any of the exogenous fluoxetine concentrations. A positive correlation with the applied exogenous ibuprofen dose is shown for TBARS (r\({}^{2}\) = 0.77, \(p\) < 0.05) and APX activities (r\({}^{2}\) = 0.62, \(p\) < 0.05). On the other hand, CAT and SOD antioxidant enzymes were irresponsive to this contaminant concentration variation. Glyphosate exposure revealed a positive correlation to APX (r\({}^{2}\) = 0.60, \(p\) < 0.05) and TBARS (r\({}^{2}\) = 0.92, \(p\) < 0.05) activities, where TBARS activity levels showed an increasing trend up to the maximum glyphosate exogenous concentration (500 ug L\({}^{-1}\)). CAT antioxidant enzyme revealed no correlation to glyphosate exposure but a great increase in activity under the applied highest concentration (500 ug L\({}^{-1}\)). SOD activity decreased as the compound concentration increased, revealing a negative but significant dose-response correlation (r\({}^{2}\) = 0.64, \(p\) < 0.05). The applied set of oxidative stress biomarkers showed no correlation to the exogenous SDS exposure concentrations applied to the _P. tricornutum_ cell culture.  
To determine the efficiency of the considered biomarkers in classifying the sample exposures, a multivariate canonical analysis was conducted for each of the studied compounds (Figure 1). Fluoxetine (Figure 1B) and glyphosate (Figure 1D) multivariate analysis revealed the lowest classification efficiency of the samples (38.9%) using the considered biomarkers. This was attributed to a high degree of misclassification of the samples exposed to intermediate concentrations, indicative of a low impact of these compounds at these concentrations on the considered biomarkers. On the other hand, the assessed biomarkers in the cells exposed to propranolol (Figure 1A) and SDS (Figure 1E) were able to provide a correct classification of more than half of the evaluated samples (55.6% and 53.3%, respectively). Once again, in intermediate concentrations the considered biomarkers had lower efficiency in classifying the samples, due to possible reduced impacts of these compounds in intermediate concentrations.