## 4 Discussion
### Alkylphenols and Chlorophenols Removal in CW Systems
The adsorption/absorption process suggests transfer of the compound from the water column to the substrate which is not a definitive elimination, as in the future the residues adsorbed could become bioavailable and be a source of toxicity to aquatic environments. In this sense, the degradation and/or transformation in a less toxic compound needs to take place for a permanent elimination. As mentioned, the undetected or low detected concentration of the target compounds in effluent and substrate of CWs exposed to doped stream water, showed that, beyond the adsorption/absorption process, other biologic processes promoted by plants and/or microbial communities (i.e., uptake, accumulation and degradation and/or transformation) probably took place in CWs systems. In fact, NP and OP introduced in the CW systems were eliminated and for PCP ca. 33% was also removed (only 66% of the doped PCP amount was detected in the CW substrate). Wetland macrophytes have shown great potential for the phytoremediation of organic contaminants [63; 64; 65; 19]. According to [PERSON] et al. [66], when the molecular mass (MM) of an organic pollutant is below 1000, it can be easily taken up by plant roots. Based on this information, in the present work, the uptake NP (MM = 220 g\(\cdot\)mol\({}^{-1}\)), OP (MM = 206 g\(\cdot\)mol\({}^{-1}\)) and PCP (MM = 266.3 g\(\cdot\)mol\({}^{-1}\)) by _P. australis_ might have occurred. For instance, [PERSON] et al. [67] observed that emergent macrophytes (_P. communi, T. orientalis, S. validus_) can uptake and accumulated PCP in their belowground parts. The difficulty in the transport from root tissues to upper part tissues of the plant observed by [PERSON] et al. [67] was attributed to the high hydrophobicity of PCP (log Kow 5.01). High log Kow indicate a limited ability of compounds to be taken up through the plant cell membrane [68], but can imply absorption by root epidermis [66]. In this sense, the high hydrophobicity of the NP (log Kow 5.76) and OP (log Kow 4.8) might have promoted the accumulation of these compounds in belowground part of _P. australis_ in the present work. Furthermore, hydrophobic chemicals have affinity to be retained in the lipids of the root epidermis and surrounding mucilage [69]. The high root density of _P. australis_ allows the interaction of the influent to contact with a high area of root surface and associated biological films facilitating microbial degradation and possibly plant uptake of estrogenic compounds [21]. Moreover, numerous studies have shown that plants promote microbial degradation of organic pollutants [14; 70] by an increase in microbial abundance, enhancement of microbial activity and/or modifications of the microbial community structure in the rhizosphere [71]. For instance, [PERSON] et al. [19] observed a clear increased in removal percentage of NP in the presence of plants. These authors also observed that _Heliconia_ sp. showed a higher efficiency for NP removal than _P. australis_, possibly due to microenvironments associated to the _Heliconia_ sp. rhizosphere. In the case of PCP, similar results was observed by [PERSON] et al. [72], with PCP removal rate increasing significantly (between 15 and 20%) in the presence of _P. australis_. Additionally, these authors also observed a significant positive correlation between indicators of soil microbial activity (dehydrogenase activity-DHA) and removal of PCP in planted soil, which implied that plant root exudates promoted the rhizosphere microorganisms and enzyme activity, thereby improving biodegradation of PCP. Additionally, [PERSON] et al. [73] observed that _P. australis_ rhizosphere soil compared to the other terrestrial plants also showed a greater PCP biodegradation efficiency. According to [PERSON] et al. [74], the definitive removal of compounds from sediments/soils can be the synergetic effects of plants and microorganisms, and sometimes the effect of microorganisms may contribute the most.