## 3 Results and Discussion
### Growth Inhibition Assay with Rapiddocelis subcapitata  
The results obtained for the growth inhibition test with _R. subcapitata_ (Figure 1) showed significant differences between the control and the effluent dilutions for the RE (F\({}_{8,31}\) = 133.56, \(p\) < 0.05), recording an EC\({}_{20}\) value of 79.5% (CI95 = 71.5-87.5). For the TE1, significant differences were also recorded (F\({}_{8,31}\) = 135.84, \(p\) < 0.05); however, at the lowest concentration, a significant stimulation in the growth of the algae was observed (Figure 1), indicating the high potential of this effluent to cause eutrophication in the received medium, especially when diluted, since it minimised the toxic effect of the contaminants present but enhanced the positive role of available the nutrients. In fact, [PERSON] [38] states that the stimulation of algal growth can predict the potential of the effluent to eutrophication and emphasises the importance of considering this phenomenon in an ecotoxicological evaluation, giving it the same importance as that given to the inhibitory effects. While the TE2 showed a significant inhibitory effect on the growth of _R. subcapitata_ for concentrations above 74.73% (F\({}_{8,31}\) = 156.00, \(p\) < 0.05) (Figure 1), with a NOEC, LOEC and EC\({}_{20}\) of 70.50%, 74.73% and 98.5% (CI95 = 96.8-100.3), respectively. The inhibitory effects on the growth of _R. subcapitata_ were more pronounced in the RE, followed by TE2, and at last, TE1, whose EC\({}_{20}\) value recorded was greater than 100%, probably due to the pH of the RE. However, comparing the toxicity of the RE toward _R. subcapitata_ with the artificially prepared textile effluents (W1, W2, W3 and W4) studied by [PERSON] et al. [5], the real effluent (RE) presented a much lower toxicity to the algae. For the artificial effluents, the values of EC\({}_{50}\) were 18.8% (CI95 = 16.6-21.1), 17.7% (CI95 = 10.8-24.6), 2.2% (CI95 = 1.9-2.5) and 31.7% (CI95 = 23.6-39.7) for the samples W1 (acid bath for wool), \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **EC\({}_{50}\)** & **EC\({}_{20}\)** & **Reference** \\ \hline
**RE** & 7.18\% (0.42–100) & 2.92\% (0.152–56) & Present study \\
**TE1** & HE \(<\) 20\% (NT) & HE \(<\) 20\% (NT) & \\ \hline
**W1** & 36.40\% (29.4–45.5) & - & [5] \\
**W2** & HE \(<\) 50\% (NT) & - & \\ \hline \hline \end{tabular} W1—artificial effluent produced during a wool dyeing process; W2—artificial effluent produced during a leather dyeing process; HE—aighest effect (percentage of bioluminescence inhibition); NT—not toxic.  
\end{table} 
Table 3: Values of EC\({}_{50}\) and EC\({}_{20}\) for bioluminescence inhibition of _A. fischeri_, expressed in effluent percentage, and the corresponding 95% confidence intervals (CI95) for the treated effluent 1 (TE1) and the raw effluent (RE). W2 (acid bath for leather), W3 (reactive bath for cotton) and W4 (direct bath for cotton), respectively [5]. These artificial effluents, although advantageous at the laboratory level, are not representative of the actual toxicity of textile effluents, since the actual effluents are a complex mixture of chemical compounds that can promote additive, synergistic and antagonistic effects on the aquatic organisms. In addition, the quality of the textile effluent can be variable over time, which is not possible to simulate under laboratory conditions. In the study of [PERSON] et al. [5], the W3 sample was the most toxic to \(R\). _subcapitata_, showing the toxicity of the reactive dyes and Na\({}_{2}\)SO\({}_{4}\). Several authors have reported that the dyes are normally less toxic than other components of the textile effluents, such as the surfactants, metals, salts, acids and alkalis [3; 39]. However, according to a model for predicting the toxicity of mixtures, the model of concentration addition, tested by [PERSON] et al. [5], found that in the toxicity test with \(R\). _subcapitata_, the dyes alone were more toxic than the salt (Na\({}_{2}\)SO\({}_{4}\)) alone. Meanwhile, the two combined compounds showed a moderate antagonistic effect.