**4. Results**

In this study, integrated soil and stream sediments geochemical maps are presented for selected elements (Fe, Al, Cu, Mo, As, and Hg in Figure 2; Ni, Cr, Co, V, Mn, and Zn in Figure 3). Additional geochemical maps for the remaining PTE (Ag, B, Ba, Bi, Cd, Pb, Sb, Se, Sn, and U) are provided in the supplementary material (Figure S1). In these maps, the catchment-based representation (polygons) was used to display the distribution of elements in stream sediment samples, whereas the point representation was used for soil samples.

The spatial distribution of each element (cf. Figures 2 and 3, Figures S1 and S2) revealed a clear difference between the Northern PB (NPB) and Southern PB (SPB). The NPB region corresponds almost exactly to the BD and CB and the SPB to the RM-S-CC. The chemical compositions of soils and stream sediments from those regions are strongly influenced by the dominant lithologies occurring in their respective geological domains (Figure 1d). Boxplots for Fe, Al, and selected PTE (Figure 4) were constructed by taking into account the compositions of soil and stream sediment samples from the three different geological domains distinguished in the PB. Additional boxplots are provided in the supplementary material (Figure S3). It is apparent that the distributions of some elements (e.g., Al, As, Bi, and Cr; Figure 4) are similar in both BD and CB, representing the NPB, and contrast with that observed in the RM-S-CC domains that occupy the SPB. On the contrary, Cu spatial distribution exhibit remarkable differences among all geological domains (Figure 4).

**Figure 2.** Geochemical maps for Fe, Al, Cu, Mo, As, and Hg in stream sediments (catchment area—polygon) and surface soil (in-situ sampling site—point) in the Parauapebas River Basin (PB). Note that the same concentration range for each element is used for the map representation on both sampling media. Inset shows the Northern (NPB) and Southern (SPB) PB. Refer to Figures S1 and S2 for the geochemical maps of the remaining PTE.

**Figure 3.** Geochemical maps for Ni, Cr, Co, V, Mn, and Zn in stream sediments (catchment area—polygon) and surface soil (in-situ sampling site—point) in the Parauapebas River Basin (PB). Note that the same concentration range for each element is used for the map representation on both sampling media. Inset shows the Northern (NPB) and Southern (SPB) PB. Refer to Figures S1 and S2 for the geochemical maps of the remaining PTE.

**Figure 4.** Boxplots for Fe, Al, and 12 potentially toxic elements (PTE; As, Ba, Bi, Co, Cr, Cu, Hg, Mn, Ni, Se, V, and Zn) in surface soils and stream sediments samples of the Parauapebas River Basin (PB), according to the major geological domains of the study area: BD = Bacajá Domain and CB = Carajás Basin, both domains comprised at the Northern PB (NPB); and RM-S-CC = Rio Maria—Sapucaia—Canaã dos Carajás domains, comprised at the Southern PB. Refer to Figure 1 for the geological setting of the study area. Refer to Figure S3 for the boxplot of the remaining PTE.

In addition, the MWW test was carried to devaluate if the composition of soil and stream sediment samples from BD and CB are statistically similar. Table 1 summarizes the *p*-values of the MWW calculated for each element in surface soils and stream sediments separately. In these results, the null hypothesis states that there is no difference between the distribution of a given element in a given sampling media in BD and CB. By assuming a significance level (σ) of 0.05, the *p*-values below σ imply rejecting the null hypothesis and inform that the distributions of the respective element in BD and CB are statistically different. In summary, Al, Ag, As, Bi, Cr, Hg, Ni, Sn, V, and Zn presented similar distribution in both sampling medium; Fe, B, Ba, Cd, Co, Mo, Pb, Sb, Se, and U presented similar distribution only in stream sediments; Mn presented similar distribution only in soils, and Cu presented different distribution in both sampling medium.

The integrated evaluation of the data (geochemical maps, Figures 2 and 3, Figures S1 and S2; boxplots, Figure 4 and Figure S3; and, MWW results, Table 1) highly indicates that the study area can be divided into two separate geochemical regions, the NPB and SPB. For this reason, the original data set was split into two subsets for further investigation. Table 2 summarizes the descriptive statistics (mean, SD, Min, Med, and Max) of the studied elements in surface soils and stream sediments in the entire PB (soils = 364 samples; stream sediments = 189 samples), which was retrieved from previous studies [24,58] using the same data set, and for each subregion, NPB (soils = 223 samples; stream sediments = 122 samples) and SPB (soils = 141 samples; stream sediments = 67 samples).

**Table 1.** Summary of the *p*-values obtained from Mann–Whitney–Wilcoxon (MWW) Test used to verify the similarities in the distribution of the studied elements in a sampling medium (Surface soils and stream sediments) from two different geological domains (BD = Bacajá Domain and CB = Carajás Basin). Refer to Figure 1d for the location of the geological domains.


Note: Blank entries indicate *p*-value < 0.05.

**Table 2.** Descriptive statistics for Fe, Al, and 10 potentially toxic elements (PTE; As, Co, Cr, Cu, Hg, Mn, Mo, Ni, V, and Zn) in surface soils and stream sediments. Values were calculated for the entire Parauapebas River Basin (PB; soils = 364 samples; stream sediments = 189 samples) and for the northern (NPB; soils = 223 samples; stream sediments = 122 samples) and southern (SPB; soils = 141 samples; stream sediments = 67 samples) regions separately. Refer to Table S1 for the descriptive statistics of the remaining elements.



**Table 2.** *Cont.*

Note: The concentration unit is expressed in mg kg−1, except for Fe and Al in wt.%; DL = Lower limit of detection; % < DL = % of data below LLD; Mean = Arithmetic mean; SD = Standard deviation; Min = Minimum; Med = Median; Max = Maximum; '\*' = Surface soil data from [24].

> The use of intersection function under geoprocessing environment allowed plotting and merging of soil samples with stream sediment catchment areas. It is important to highlight that a single microcatchment, which is represented by only one stream sediment sample, can be merged to multiple soil samples, or even none in the rare cases of no collected samples in the catchment area. Scatter plots comparing the concentrations of selected elements in surface soil (y-axis) and stream sediment (x-axis) samples were constructed to verify a possible relationship between them by using linear regression analysis (Figure 5 and Figure S4). Spearman's correlation coefficient (ρ) and *p*-value of the linear regression are presented. In general, the majority of the selected elements presented a significant correlation (*p* < 0.05), excepting for Cd, Ba, B, and Zn (*p* > 0.05; Figure S4). Three groups were observed: (i) Strongly (ρ ≥ 0.5) correlated materials: Fe, As, Cu, and U in Figure 5; Bi, Sn, Mo, and V in Figure S4; (ii) Moderately (0.49 < ρ ≤ 0.3) correlated materials: Hg, Ni, Cr, and Sb in Figure 5; (iii) Weakly (ρ ≤ 0.29) to non-significant (*p* > 0.05) correlated materials: Al, Mn, and Co in Figure 5; Se, Ag, Pb, Cd, Ba, B, and Zn in Figure S4.

> In this study, geochemical threshold concentration values were determined for all 22 studied elements in soils and stream sediments, but contrarily to the approach adopted in previous studies [24,58], distinct threshold values for the NPB and SPB were calculated, by using a variety of statistical methods (MMAD, TIF, and percentile-based techniques, e.g., P98 and P95; Table 3). Threshold values of each individual subregion were then compared to threshold values proposed for the whole PB, determined in previous studies of soil [24] and stream sediments [58].

**Figure 5.** Scatter plot comparing the concentrations of selected elements in surface soil samples against stream sediment samples. Three groups of elements were observed: (i) Strongly correlated materials (e.g., Fe, As, Cu, and U); (ii) Moderately correlated materials (e.g., Hg, Ni, Cr, and Sb); (iii) Weakly to non-significant correlated materials (e.g., Al, Mn, and Co); Additional scatter plots for the remaining elements are presented in Figure S4.

**Table 3.** Geochemical threshold values for Fe, Al, and 10 potentially toxic elements (PTE; As, Co, Cr, Cu, Hg, Mn, Mo, Ni, V, and Zn) in surface soils and stream sediments, estimated by a variety of methods [Median + 2 Median Absolute Deviation (MMAD), Tukey's inner fences (TIF), the 98th (P98) and 95th (P95) percentiles]. Values are provided for the entire Parauapebas River Basin (PB, retrieved from previous studies), for the northern (NPB) and the southern (SPB) regions separately, determined in the present study. Guideline values reposted by Brazilian environmental agencies are presented as references. Refer to Table S2 for the results of the remaining elements.


Note: The concentration unit is expressed in mg kg−1, except for Fe and Al in wt.%; *Italic* or "-" (value not available): threshold values greater than the maximum value; a Results reported in previous studies of soil [24] and stream sediments [58] of the PB; b Quality reference value (QRV) reported by the Sao Paulo Sanitation Technology Company (CETESB) [59]; c Prevention guideline value (PGV) reported by the National Council of the Environment (CONAMA) of Brazil [50]; d Threshold levels 1 (L1) and 2 (L2) reported by CONAMA [60]. Blank entries indicate data not available.
