| Abstrakt: |
The Jbel Ressas site is an ancient Pb-Zn mine located in the northwest of Tunisia. The long activity of the mine has produced a huge volume of waste (3 tailings) rich in bioavailable fractions of Pb+Zn+Cd which have heavily polluted the surrounding agricultural soil. However, the results obtained from previous studies of this site are so variable that some authors have considered it unpolluted. It was suspected that the improper choice of sampling strategy and the extraction procedures for evaluation of the labile toxic trace element fractions were the sources of these differences. Therefore, the objective of this comparative study was to prove the interest of the choice of the sampling strategy and the extraction procedure in having a representative evaluation of mobile pollutants fractions. The critical step in any geochemical study is having representative site samples and considering that each site is unique. Therefore, environmental concerns, soil texture, principal wind directions, land slopes and topography, run flow directions, and equidistance's between the sampled plots were considered. Based on the mean total Pb+Zn+Cd concentrations obtained from analyzed samples collected in 2009, 2017, and 2021 (the present study) and previous results, the regularity and irregularity over time of the chronological evolution of the physiochemical parameters and the pollution status, respectively, were strong arguments that proved the right choice of our sampling strategy. To select the appropriate extraction procedure for labile TTE fractions, the commonly used procedures, including those used in previous studies, were tested. Using simple mode extractions, the previous authors extracted variable and even very small quantities of labile TTE, compared to similar contexts, and considered that the polluted Jbel Ressas site presented no or a low environmental risk. However, the BCR (European Community Bureau of Reference) procedure used in the present studies leached high quantities of the available toxic trace elements, which confirmed the high pollution level of the site and its environmental threat. The significant correlations among soil physicochemical parameters and total and labile TTE contents of the present study, deduced from statistical analysis, confirmed that the selected sampling strategy and the selected extraction procedure provided representative samples of the site and a fairly accurate assessment of its pollution levels. [ABSTRACT FROM AUTHOR] |
Full text from SpringerLink