## 3 Results and Discussion  
### Physico-Chemical Characterisation of Textile Effluent Samples  
A textile company from the centre of Portugal provided the textile effluent used in the toxicity tests. One raw effluent sample (RE) and two treated effluents (TE1 and TE2) were analysed. According to the information given by the textile company, the TE2 effluent sample resulted from the dyeing process. This process can be divided into two steps, both giving rise to a wastewater. The first step was the bleaching process, which prepared the raw material for the next step, which was the dyeing process. The bleaching process was carried out with hydrogen peroxide at pH values between 10 and 11, and was used to remove unwanted natural colour from the fibres. The dyes used in the company were 98% vat dyes that dye in alkaline medium (pH 12-14) in the absence of oxygen. Afterwards, to fix the dye on the fibres, they must be oxidised with a diazo compound, followed by hydrogen peroxide. Thus, the resulting effluent was typically alkaline (pH 9-11), with high levels of nitrates resulting from the oxidation process and with colour as well. However, the RE sample had an acidic pH, greyish colour, fibres wastes, high conductivity and a foam characteristic with the presence of surfactants (Table 1). According to INETI [28], high conductivity, acidic pH, nitrates and colour are characteristics of an effluent resulting from dyeing with solubilised vat dyes, which was the case of the RE sample. Table 1 shows the effluent samples used in the toxicity tests and the respective physical and chemical characteristics. Comparing the effluents treated (TE1 and TE2) with the raw effluent (RE), there was a clear improvement in terms of colour and pH, but the total dissolved solids (TDS) and conductivity increased after the treatment. The high levels of dissolved solids may indicate that there was inorganic salts (calcium, magnesium, potassium, sodium, bicarbonate, chlorides and sulfates) and small amounts of dissolved organic matter [29], which were not removed by the applied treatments. According to the Portuguese Law by Decrere n\({}^{\circ}\) 236/98 of 1 August, the maximum allowable value (VMA) for TDS in water is 1500 mg L\({}^{-1}\)[30]. The value of conductivity indicates the presence of dissolved and ionised salts and is proportionally related to the presence of total dissolved solids. These results suggest the ineffectiveness of the treatment applied in terms of these parameters. Another hypothesis is that this increase in TDS resulted from the treatment itself because flocculants and reagents were added for pH adjustment. Table 2 shows the chemical composition of the two textile effluent samples used (RE and TE1). For all the components present in the effluent, higher concentrations were recorded for the RE when compared to the TE1, as expected. The percentage of removal after the treatment recorded for each component ranged from 20 to 32% (Table 2), indicating that the treatment applied by the textile company had a similar efficiency for all compounds assessed. The textile effluent used in this study consisted of a complex mixture of phenolic compounds, phthalates, aliphatic carboxylic acids, aromatic carboxylic acids, amines, alkanes and linear aliphatic alcohols (Table 2). As also reported by [PERSON] et al. [31], several of the compounds reported in Table 2 belong to the group of nonylphenols and their degradation products, which are often used as surfactant agents in the preparation of textile fibres. Nonylphenol is one of the substances identified as \"priority hazardous substances\" under the Directive 2008/105/EC of 16 December [16]; however, the values recorded in the effluent did not exceeded the values of the environmental quality standards (EQS) established for surface waters (maximum allowable concentration--2 ug L\({}^{-1}\)) (Table 2). From the group of phenolic compounds, derivatives from ionol (2,6-di-tert-butyl-4-methylphenol) and bisphenol A were detected; these compounds are used as additives in plastics and rubbers.