## 3 Results and Discussion
### Longitudinal Removal of NP in HSSF-CWs  
The average total NP concentration in the influent was (1671 \(\pm\) 838) \(\upmu\)g\(\cdot\)L\({}^{-1}\). A reduction of the NP concentration was observed at the internal sampling point (two-thirds of the length)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Removal Efficiencies (\%)**} & \multicolumn{3}{c}{**BPA**} \\ \cline{2-4}  & _Heliconia_ & _Unplanted_ & _Phragmites_ \\ \hline \(\hat{y}\) & 73.3\% & 62.2\% & 70.2\% \\ Maximum & 98.6\% & 97.1\% & 98.3\% \\ Minimum & 50.0\% & 3.7\% & 27.9\% \\ \(\sigma\) & 19.6\% & 33.1\% & 27.1\% \\ C.V. & 0.27 & 0.53 & 0.39 \\ \(n^{*}\) & 7 & 7 & 6 \\ \hline \hline \end{tabular}  
* The third _Phragmites_ sample was broken in shipping. Notes: \(\hat{y}\): mean value; \(\sigma\): standard deviation; C.V.: coefficient of variation; and \(n\) number of samples.  
\end{table}
Table 2: Average effluent BPA removal for _Heliconia_-CW, unplanted-CW and _Phragmites_-CW.  
Figure 2: Longitudinal BPA concentrations in CWs of **(a)**_Heliconia_ (H); **(b)** unplanted control (C), and (c)_Phragmites_ (P), for influent (Inf), two-thirds internal (1), and effluent (2) sample points.Removal efficiency of BPA in **(d)**_Heliconia_; **(e)** unplanted control; and **(f)**_Phragmites_.  
of each wetland (H1, P1, and C1), with average concentrations of (724 \(\pm\) 453), (1150 \(\pm\) 499) and (1041 \(\pm\) 446) \(\mathrm{\SIUnitSymbolMicro g\cdot}\mathrm{L}^{-1}\), respectively. The lowest final effluent concentrations were obtained for the _Heliconia_-CW (629 \(\pm\) 318 \(\mathrm{\SIUnitSymbolMicro g\cdot}\mathrm{L}^{-1}\)) and _Phragmites_-CW (736 \(\pm\) 284 \(\mathrm{\SIUnitSymbolMicro g\cdot}\mathrm{L}^{-1}\)), showing more NP removal in the final third of the CW. The NP removal efficiencies were less than those of BPA. A Wilcoxon signed rank test was used to establish significance of differences between the internal sampling point and effluent concentrations in each CW. Although the plantedCWs had a higher average NP removal efficiency in the effluent than the internal sample point, these results are not statistically different.  
The unplanted-CW displayed a different behavior, showing an increment of the NP concentration in the effluent (1103 \(\pm\) 538 \(\mathrm{\SIUnitSymbolMicro g\cdot}\mathrm{L}^{-1}\)) compared with its internal point. NP desorption was observed in the final third of the CW, despite NPs having high \(K_{ow}\) values (log \(K_{ow}\) 3.80 to 4.77). This negative removal efficiency in CW was also reported in other research [18] for seven different PPCPs, attributed to an initial retention and sorption, but subsequent release during passage of the wastewater through the medium of the CW.  
The _Heliconia_-CW showed the highest average effluent NP removal efficiency of 62.8 \(\pm\) 20.1%, while the _Phragmites_-CW and unplanted-CW had a removal efficiency of 25.3 \(\pm\) 37.1% and 52.1 \(\pm\) 23.2%, respectively (Table 3). These results confirm a statistically significant difference between planted and unplanted CWs with \(p\)-values of 0.042 for the internal sample point and 0.03 for the effluent. The posthoc test corroborated this conclusion, confirming that the _Heliconia_-CW showed a higher NP removal efficiency than the _Phragmites_-CW and the unplanted-CW.