## 3 Results and Discussion  
### Physicochemical Characteristics  
Physicochemical characteristics related to the mobility of lead in the sampled agricultural, industrial and urban soils and sediments are shown in Table 6. A range of pH from 5.38 to 8.47 with a mean of 7.21; and from 6.73 to 8.22 with a mean of 7.39 was observed in soils and sediments, respectively. According to the Mexican Standard NOM-021, this indicates that the soils were weakly acid or weakly alkaline and sediments were neutral or weakly alkaline. A mean EC of 426.7 \(\mu\)S cm\({}^{-1}\) was measured in soils, with no single sample exceeding 1000 \(\mu\)S cm\({}^{-1}\), thus suggesting negligible effects of salinity. The mean of EC measured in sediment was 716.5 \(\mu\)S cm\({}^{-1}\). It is noteworthy that sample S15 slightly exceeded the 1000 \(\mu\)S cm\({}^{-1}\) in both seasons, probably due to industrial discharges into the river, thus classifying it as slightly saline. Sample S1 exceeded 2000 \(\mu\)S cm\({}^{-1}\) in rainy season, probably due to mining waste runoff, thus classifying it as moderately saline. Eh varied between 106.5 and 484.5 mV, suggesting the prevalence of oxidizing conditions (aerobic zone). Organic matter content ranged from 0.13 to 18.72%, according to the scale used in the NOM-021. This categorized soils as having medium organic matter content (between 1.6 and 3.5%), and the sediments, high organic matter content (between 3.6 and 6.0%). The CEC ranged from 16.69 to 389.78 cmolc kg\({}^{-1}\) with a mean of 155.78 for soils and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Class** & **Igeo Value** & **Pollution Degree** \\ \hline
0 & \textless{}0 & Unpolluted \\
1 & 0–1 & Unpolluted to moderately polluted \\
2 & 1–2 & Moderately polluted \\
3 & 2–3 & Moderately to highly polluted \\
4 & 3–4 & Highly polluted \\
5 & 4–5 & Highly to extremely polluted \\
6 & \textgreater{}5 & Extremely polluted \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Igeo and classification of heavy metal pollution. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Class** & **Value** & **Enrichment Degree** \\ \hline
1 & \textless{}2 & Deficiency to minimal enrichment \\
2 & 2–5 & Moderate enrichment \\
3 & 5–20 & Significant enrichment \\
4 & 20–40 & Very high enrichment \\
5 & \textgreater{}40 & Extremely high enrichment \\ \hline \hline \end{tabular}
\end{table} 
Table 5: EF classes with respect to quality. ranged from 11.09 to 492.96 with a mean of 131.73 cmolc kg\({}^{-1}\) for sediments, indicating a wide heterogeneity of the sites. Ranges of 489.2-1585.5 and 670.7-1625.3 mg kg\({}^{-1}\) of CO\({}_{3}\)\({}^{2-}\) content were observed in the soils and sediments respectively; with bicarbonate being the only chemical specie detected. The values for pH, EC, Eh, OM, and CO\({}_{3}\)\({}^{2-}\) showed no statistically significant differences (\(p<0.05\)) between dry season and rainy season; only CEC showed statistically significant differences between seasons, probably due to the effect of rainwater on the solubility of chemical compounds present in soils and sediments; the \(p\)-values are shown in Table 6.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Site** & **pH** & \begin{tabular}{c} **EC** \\ **(\(\mu\)S cm\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **Eh** \\ **(mV)** \\ \end{tabular}  & \begin{tabular}{c} **OM** \\ **(\%)** \\ \end{tabular}  & \ \begin{tabular}{c} **CEC** \\ **(cmolc kg\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **CO\({}_{3}\)\({}^{2-}\)[a]** \\ **(mg kg\({}^{-1}\))** \\ \end{tabular}  \\ \hline \multicolumn{6}{c}{a.