## 2 Materials and Methods
### Analytical Characteristics of the Method  
To assess the accuracy and precision of the analysis, certified plant, soil, and sediment reference materials were used. Since certified values after aqua regia digestion are available only in STSD-3 and STSD-4 for a limited number of elements, total digestion was performed. The complete digestion of the soil/sediment reference materials requires the addition of hydrofluoric acid to dissolve the silica skeleton of the matrix [44]. Table S1 presents the results from the analysis of some of the plant, soil, and sediment reference materials. The mean experimental values (average of six measurements, characterized by the respective standard deviations) were calculated for each element and compared with certified or information values. For the elements for which certified values were not available, the literature values are presented. The comparison of the results showed a good agreement between the experimental and certified or published values [45; 46; 47; 39]. The result's precision was determined by three independent replicates (each six measurements) within two months. The precision for all 31 elements in the analyzed CRMs was around or below 10%. To assess the instrument drift, a recalibration was performed after every tenth sample. To eliminate a memory effect, a washing step of 60 s with 3% HNO\({}_{3}\) was applied,  
\begin{table}
\begin{tabular}{l l} \hline \hline
**ICP-MS** & **Instrumental Conditions** \\ \hline Argon plasma gas flow & 15 L/min \\ \hline Auxiliary gas flow & 1.20 L/min \\ \hline Nebulizer gas flow & 0.90 L/min \\ \hline Lens voltage & 6.00 V \\ \hline ICP-RF power & 1100 W \\ \hline Pulse stage voltage & 950 V \\ \hline Dwell time & 50 ms \\ \hline Acquisition mode & Peak hop \\ \hline Peak pattern & One point per mass at maximum peak \\ \hline Number of runs & 4 \\ \hline  & \({}^{27}\)Al(0.015),\({}^{42,43,44}\)Ca(\({}^{42}\)Ca-0.014;\({}^{43}\)Ca-0.013; \\  & \({}^{44}\)Ca-0.015),\({}^{54,56,57}\)Fe(\({}^{45}\)Fe-0.014;\({}^{56}\)Fe-0.015; \\ Determined isotopes of major elements & \({}^{57}\)Fe-0.013),\({}^{23}\)Na(0.017),\({}^{24,25,26}\)Mg(\({}^{24}\)Mg-0.016,\({}^{25,26}\)Mg-0.015),\({}^{55}\)Mn(0.015),\({}^{39}\)K(0.017),\({}^{31}\)P(0.013),\({}^{46,47,48,49}\)Ti \\  & (0.012) \\ \hline  & \({}^{107}\)Mg, \({}^{75}\)As (1.0/.07), \({}^{136,138}\)Ba, \({}^{9}\)Be, \({}^{112,114}\)Cd, \({}^{59}\)Co, \({}^{52}\)Cr, \({}^{63,65}\)Cu, \({}^{139}\)La, \({}^{96,98}\)Mo, \({}^{60,62}\)Ni, \({}^{207,208}\)Pb, \({}^{85,87}\)Rb, \\ trace elements *(Oxygen flow rate & \({}^{121,123}\)Sb, \({}^{77,78}\)Se (1.5/.0/.3) *, \({}^{80,82}\)Se (0.9/.03) *, \({}^{118,120}\)Sn, \\ [mL/min]/RPq [V]) & \({}^{232}\)Th, \({}^{205}\)Ti, \({}^{238}\)U, \({}^{51}\)V, \({}^{66}\)Zn \\ \hline \hline \end{tabular}
\end{table}
Table 1: ICP-MS measurement conditions (Perkin Elmer SCIEX Elan DRC-e).  
followed by the measurement of a blank sample. Cleaning of the sampler and the skimmer cones was performed before each analysis. The instrumentally determined detection limits (3\(\sigma\), three times the standard deviation of ten repeated measurements of a blank) are also presented and were below 1 ng/mL, except for the macroelements K, Na, Fe, and Ti, being between 1 and 2 ng/mL.