## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Local**} & \multicolumn{2}{c}{**Zn(II) (\(\mu\)g/L)**} & \multicolumn{2}{c}{**Cu(II) (\(\mu\)g/L)**} & \multicolumn{2}{c}{**Pb(II) (\(\mu\)g/L)**} & \multirow{2}{*}{**Ref.**} \\ \cline{2-2} \cline{6-7}  & **Mean** & **Range** & **Mean** & **Range** & **Mean** & **Range** & \\ \hline European standard & - & - & 2000  & - & 5.0  & - & [8] \\ Portuguese standard & 5.0  & - & - & - & [9] \\ Tehran, Iran & 53 & 15–74 & 12 & 4–18 & 15 & 5.5–22 & [11] \\ Spitsbergen, Svalbard & - & 1.4–184 & - & - & 0.21–3.7 & [12]  \\ Jaipur, India & - & 2.0–113 & - & 0.02–14 & - & 0.3–3.6 & [14] \\ Indo-Gangetic, India & 6.0 & 1.0–3 & 2.5 & 1.0–7.0 & 9.3 & 1.0–17 & [15] \\ Moscow, Russia & - & 11–49 & - & 0.97–6.4 & - & 2.6–75 & [10] \\ Seoul, South Korea & - & 14–98 & - & 1.1–20 & - & - & [16] \\ Targoviste, Romania & 847 & - & 3.1 & - & 0.67 & - & [2] \\ Moscow, Russia & 66 & 13–284 & 13 & 3.1–63 & 148 & 23–973 & [17] \\ Kolkata, India & 26 & 11–49 & 3.7 & 0.79–11 & 0.68 & 0.14–1.6 & [18] \\ Mahshahr, Iran & 231 & - & 1.7 & - & 0.53 & - & [19] \\ Shiraz, Iran & 63 & 4.0–220 & 13.4 & 7.7–19.6 & 10 & 4.0–22 & [20] \\ Salta, Argentina & 16 & 1.0–142 & 3.9 & 0.20–42 & 0.72 & 0.04–12 & [21] \\ Bangi, Malaysia & 28 & 3.4–87 & 2.4 & 0.58–5.65 & 2.2 & 0.37–4.7 & [22] \\ Jiaozhou Bay, China & 59 & - & - & - & 4.4 & - & [23] \\ Mt. Qomolangma, China & 470 & 98–931 & 60 & 7.4–170 & 36 & 5.2–122 & [24] \\ Gwangju, Korea & - & ND-567 & - & ND-15 & - & ND-25 & [25] \\ Beijing, China & 96 & - & 5.0 & - & - & - & [26] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concentrations of Zn(II), Cu(II), and Pb(II) in rainwater events reported in the literature since 2015, presenting the mean value, interval of values, and maximum allowable values in accordance with European and Portuguese standards. treatment, mainly with natural biomaterials, which are not chemically modified and, thus, more sustainable. To the best of our knowledge, only one study has evaluated the use of natural biomaterials as biosorbents for rainwater treatment [31]. [PERSON] et al. [31] evaluated the use of the whole white bean (_Phaseolus vulgaris_ L.) as sorbent for the removal of zinc from rainwater, having shown it is a viable solution for the removal of more than 60% of Zn(II) from rainwater. However, besides white bean sorbent being cheap, eco-friendly, environmentally sustainable, and easily separated from water after treatment (allowing for its use as a homemade method for rainwater treatment), it can be used as food, which should be considered when hunger exists in different parts of the world. Therefore, it becomes important to assess only the use of bean peel (without the core and with both sides of the peel available for removal) for rainwater treatment while preserving the bean core for food consumption. The main aim of this work was to assess the sorption efficiency of the peel of white bean (_Phaseolus vulgaris_ L.) on the removal of a mixture of PTEs, namely Zn(II), Cu(II) and Pb(II), from rainwater, under realistic conditions and concentrations. The effects of the initial concentration of the elements in water, the initial pH of the solution, and the contact time between the sorbent and water-containing elements were evaluated. The experimental uniform design was applied for the evaluation of the previously mentioned effects and to assess the possibility of optimization of the sorption process using response surface methodology. The removal of PTEs was evaluated for model water solutions and for real rainwater samples. The variation of elements concentration in the water was assessed using Inductively Coupled Plasma Mass Spectrometry. Chemical, structural, and morphological features of the white bean peel along the process of sorption were assessed by Fourier transform infrared (FTIR-ATR) spectroscopy, scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDX).