## 3 Results and Discussion  
### Longitudinal Removal of BPA in HSSF-CWs  
Figure 2 shows the influent and effluent BPA concentrations for the (a) _Heliconia_-CW, (b) unplanted (control), and (c) _Plragmites_-CW, as well as the longitudinal removal efficiencies for each (parts (d), (e), and (f), respectively). A significant reduction in the BPA concentrations was observed at the internal sampling points H1, C1 and P1--each at two-thirds of the horizontal length of the CW--compared to the influent (Figure 2). This implies that BPA was transformed, sorbed, or consumed in the first two-thirds of each CW. From this point until the effluent discharge point, the BPA concentrations were fairly consistent, and decreased only marginally. The differences in the partial and total BPA removal for the internal sample point and effluent were established by a [PERSON] signed rank test in each CW and displayed significant differences for the _Heliconia_-CW and unplanted-CW. Regarding the _Plragmites_-CW, the final third of the CW did not contribute to the improvement of the total BPA removal. From the literature, the main removal mechanism of BPA in a CW is sorption [14; 15; 16], due to a higher octanol-water partition coefficient of the hydrophobic BPA molecule (log \(K_{ox}\) is 3.4), as well as a large surface area in the CW, which enhances sorption onto the biofilm, suspended solids, support media, and rhizosphere [17]. The sorption capacity of a compound can be better expressed in terms of the organic carbon partition coefficient (\(K_{\infty}\) or \(K_{d}\)) related to the quantity of the sorbed compound in the solid phase with respect to the concentration in the aqueous phase [18]. This is important because BPA has two hydroxyphenyl groups, which tend to promote sorption in soils (or support media) and sediments [19]. The research of this manuscript did not include BPA measurements on the sediments or support media, but based on other research of BPA partitioning in wastewater sediment [20], a log \(K_{d}\) (L\(\cdot\)kg\({}^{-1}\)) value of 4.37 was calculated for BPA at the average concentration reported in Table 1. If the log \(K_{d}\) < 2.47, sorption can be neglected, while for values higher than 4.0, sorption onto the solid phase is one of the major removal processes [18; 20]. The calculated log \(K_{d}\) value of BPA suggests that it is likely that sorption of BPA was one of the significant removal processes in each of the three CW types investigated. Sorption onto the support media or onto the biofilm and sediments on the media implies a longer EDC residence time for BPA in the CW. This may favor bioremediation by increasing exposure to plant uptake or microbial degradation. Indeed, phytoremediation can also be an important removal pathway, where the EDC may possibly be degraded by phytostimulation or rhizodegradation, phytodegradation, phytodextraction, sequestration or volatilization [13; 21]. In some cases, the plants growing in the CW may play a significant role in the direct uptake of many organic pollutants from wastewater. For instance, the presence of _Phragmites australis_ in a CW improved the removal efficiency of BPA compared to an unplanted CW [12; 22; 23]. In a study by [PERSON] et al. [24], the plant uptake of BPA, 4-NP, diclofenac (DCL), and naproxen (NPX) during the hydroponic cultivation of _Lactuca sativa_ (lettuce) and _Brassica oleraca_ (collard) was investigated, and EDC accumulation was observed in both plant species with a trend in descending order of BPA > NP > DCL > NPX [24]. The Friedman Test indicates significant differences (\(p\)-value: 0.03) for the removal of BPA (Figure 2) at the intermediate sampling point (H1, C1, and P1). The post hoc test revealedthat P1 obtained the highestaverage removal efficiency (64.3%) compared with C1 (55.2%) and H1 (61.4%).