High leaf fluctuating asymmetry in two native plants growing in heavy metal-contaminated soil: the case of Metlaoui phosphate mining basin (Gafsa, Tunisia)

In order to estimate pollution impact in soil and plants by phosphates mining activities, three mining sites and one control site were selected around Metlaoui (phosphates basin of Gafsa, southern Tunisia) in March 2019. Heavy metal concentrations in soil and in two native plants (Moricandia arvensis and Diplotaxis harra: Brassicaceae) were measured using atomic absorption spectrometry. Development instability was estimated using leaf fluctuating asymmetry of the two plant species. The results showed that the soils of the Metlaoui sites contain higher levels of Cd, Ni, Zn, and Cr compared with control site (maximum of 33.225 ± 2.588; 100.86 ± 0.314; 180.267 ± 16.103; and 16.554 ± 0.313 ppm, respectively). These levels are higher than the maximal contents tolerated in soils. Heavy metals also occurred at high concentrations in plant organs in Metlaoui sites especially in leaves. Cadmium and Zn concentrations in these plants exceed the phytotoxic level (with maximum of 20.498 ± 0.627 ppm and maximum of 337.901 ± 16.686 ppm, respectively). Statistical analysis showed that fluctuating asymmetries (FA) of leaves of the two sampled plants are higher in mining sites compared with control. Pearson correlation and PCA analysis showed that FA is related to Cd, Ni, and Zn concentrations in soil. The results indicate that phosphate extraction and laundries in the mining sites caused heavy metal pollution in soil that accumulates in plant organs and caused also development instability. Our study showed that Moricandia arvensis may have the potential for phytoremediation.