Risk Assessment of Trace Metals Using Chemical Speciation, Bioavailability, and Cluster Analysis Around Wadi EL Bey (Gulf of Tunis, Tunisia)

The Wadi El Bey is one of the most vulnerable areas to pollution in the northeast of Tunisia, altered by anthropogenic and natural processes. This study uses the Community Bureau of Reference (BCR) approach and statistical tools, particularly the student's t-test and the cluster analysis, to evaluate the danger of metals zinc (Zn), nickel (Ni), lead (Pb), cadmium (Cd), and copper (Cu) pose. This work is to assess the long-term evolution and mobility of heavy metals in the core soils of the Wadi El Bey River Bed. Heavy metals in SC1 followed the descending order Fe>Cu>Zn>Ni>Pb>Cd and in SC2 it was Fe>Cu>Zn>Ni>Cd>Pb. The (BCR) procedure showed that in soil cores SC1 and SC2, Ni was mainly associated with the exchangeable fractions (F1). However, the Zn and Cu were linked to the residual fractions (F4). The student's t-test confirmed that the difference in vertical distribution between the SC1 and SC2 of Zn and Pb is statistically significant (p-value<.05) contrary to Ni (P = .06), Cd (P = .79), Cu (P = .38) demonstrated a common origin for these metals in the Wadi El Bey. The cluster analysis revealed that pH was the main responsible factor influencing the migration of Cu, Ni, and Zn toward the labile fractions in SC1. Whereas the total organic carbon influenced the Zn fixation in the most stable fraction in SC2. The use of pollution indices showed strong contamination by Ni, Cu, and Cd and moderate contamination by Zn and Pb. The risk assessment code (RAC) showed that Zn and Cu had a low to medium risk whereas medium to high risk for Ni. For better management and better control of heavy metal pollution in ecosystems with intermittent regimes, we advise a tertiary treatment of wastewater before evacuating it in Wadi el Bey.