# Spatial Connections between Microplastics and Heavy Metal Pollution within Floodplain Soils
## 3 Results
### Heavy Metals in Macroplastics and Coarse Microplastics  
The macroplastics and coarse microplastic particles used for analyses of heavy metal content comprise fragments, films, and plates with sizes > 2 mm from nine soil samples with mainly white or transparent colors and an average particle mass of 42.13 mg plastic per soil sample (Table S1). The analyzed plastic particles comprise low-density polyethylene (PE-LD), polypropylene (PP), chlorosulfonated polyethylene (CSM), polyamide (PA), and poly(methyl methacrylate) (PMMA) (Table S1). The heavy metal concentrations quantified for these particles can include both adsorbed metals and metals added to the plastic as additives [57].  
With regard to the average concentrations, the order of metal concentrations is as follows: Zn (94.63 ppm) > Cr (67.56 ppm) > Pb (34.23 ppm) > Cu (28.13 ppm) > Ni (23.52 ppm) > V (20.28 ppm) > Sb (18.43 ppm) > Sn (10.21 ppm) > Cd (8.43 ppm) > Co (3.82 ppm) > As (2.55 ppm) > Se (1.30 ppm) (Figure 6). The highest sums (>300 ppm) of heavy metal concentrations were found in samples STD-4-1 (PP, film), ROT-1-2 (PE-LD,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Row**} & \multirow{2}{*}{**Column**} & \multicolumn{2}{c}{**Entire Soil Profile**} & \multicolumn{2}{c}{\
\begin{tabular}{c} **Upper Soil** \\ **(0-50 cm)** \\ \end{tabular} } & \multicolumn{2}{c}{
\begin{tabular}{c} **Subsoil** \\ **(50-200 cm)** \\ \end{tabular} } \\ \cline{3-8}  & & **Cor** & \(\mathbf{p}\) & **Cor** & \(\mathbf{p}\) & **Cor** & \(\mathbf{p}\) \\ \hline \multirow{9}{*}{**Plot**} & V & 0.18 & 0.06 & **0.26** & **0.04** & \(-\)0.04 & 0.79 \\  & Cr & **0.36** & **0.00** & **0.51** & **0.00** & 0.04 & 0.80 \\  & Fe & 0.16 & 0.10 & **0.33** & **0.01** & \(-\)0.04 & 0.78 \\  & Co & **0.24** & **0.01** & **0.39** & **0.00** & \(-\)0.01 & 0.93 \\  & Ni & **0.25** & **0.01** & **0.47** & **0.00** & \(-\)0.08 & 0.59 \\  & Cu & **0.32** & **0.00** & **0.47** & **0.00** & \(-\)0.11 & 0.42 \\  & Zn & **0.37** & **0.00** & **0.53** & **0.00** & \(-\)0.11 & 0.46 \\  & As & 0.15 & 0.11 & 0.25 & 0.06 & \(-\)0.14 & 0.31 \\  & Cd & **0.39** & **0.00** & **0.57** & **0.00** & \(-\)0.12 & 0.39 \\  & Pb & **0.34** & **0.00** & **0.41** & **0.00  
massive fragment), and STD-1-2 (CSM, fragment and film). The maximum values (outliers in Figure 6) can also be traced back element-specifically to these three samples. Since comparative and reference values (by law) for the evaluation of the metal contents are missing, the focus here can only be on the presentation of the concentrations and the connection with the sample matrix.  
Figure 5: Spearman correlation matrix in first principal component order (\(n=110\), insignificant values with \(p<0.05\) excluded). (**a**): Heavy metals and metalloids; (**b**): Pollution indices and floodplain soil properties (RI: ecological risk index; PLI: pollution load index; EF: enrichment factor; OM: organic matter content (%); CSI: contamination security index; Ptot: total plastic concentration (p kg\({}^{-1}\)); C.fSi.mSi: sum of fine soil fraction containing clay as well as fine and middle silt (%); S: sand content (%).  
Figure 6: Heavy metal loads extracted from macroplastic particles (\(n=10\)).  
From the entire dataset, total plastic loads, pollution indices, and soil properties can be used for comparison with the sum of heavy metals from the particles (Figure 11). Whereas the comparison with PLI and Ef shows no clear trend, the comparison with Ptot suggests a decrease in the sum of heavy metals with increasing Ptot content (Figure 11a). The same decrease is observable in comparison to pH values (Figure 11b). In contrast, heavy metal content appears to decrease with decreasing OM or clay content. Due to the limited number of samples (\(n=10\)) and the heterogeneous data distribution, correlation analyses lead to insignificant results.