Sulfide influence on metal behavior in a polluted southern Mediterranean lagoon: implications for management

Abstract

The degree of pyritization and degree of trace metal pyritization (DTMP) were investigated in sediments from Ghar El Melh Lagoon (northern Tunisia) in order to study metal deposition. A sediment core and 28 samples were thus taken in summer 2008, and metals and sulfate were analyzed in pore water/pyrite. Acid-volatile sulfide and metals were simultaneously extracted from these two fractions and the role of pyrite in the metal cycling studied. To examine pyrite presence and mineralogical form in sediments, X-ray diffraction of the washed and decarbonated sediment was performed along with scanning electron microscopy. Results showed that pyrite is present in fromboidal and euhedral forms. Thermodynamic calculation highlighted the formation of metallic sulfides and the co-precipitation of metals with iron sulfides. The DTMP increases with depth, indicating that these metals are either sequestered as sulfides or that they co-precipitate with pyrite into the deep sediment.

Coupling mechanisms of S–Fe–P in surface sediments under the stresses of high salinity and heavy metals in coastal rivers

“…Additionally, the mean AVS/CRS ratios in JL and JH were 0.34 and 0.19, respectively; thus, efficient conversion of AVS to CRS could occur in JL and JH. The result was in agreement with a previous study, in which effective conversion of AVS to CRS occurred in sediments (Oueslati et al 2018).…”

“…A previous study showed that Eq. 4 predominated when the pH was approximately 7 in sediments (Oueslati et al 2018). According to the pH values (5.4, Table S4), the formation of CRS in JL might be attributed to Eq.…”

“…Instead, the sulfides in JL sediments could efficiently trap and inhibit the rerelease of these metals to the overlying water. Therefore, trace metals could form strong ligand complexes, coprecipitate with Fe sulfides, or be adsorbed to the surfaces of AVS and CRS (Audry et al 2010;Oueslati et al 2018). Due to oxidation and conversion into CRS, the AVS content near the sediment-water interface was low (Fig.…”

“…Moreover, the continued dissolution of metastable Fe oxyhydroxides and the release of high heavy 1998). Such processes enhanced metal-ligand formation while increasing the net anion exchange between AVS and trace metals, thereby promoting the coprecipitation of trace metal sulfides with AVS (Oueslati et al 2018;Yi et al 2020). However, continued sulfate reduction will ultimately exhaust the finite supply of metastable Fe oxyhydroxides due to an insufficient supply of oxidants under high salinity (Henneke et al 1997;Jordan et al 2008).…”

“…Subsequently, sulfate reduction, which produced sulfides, was enhanced, and Fe-containing particles were released from Fe(oxy)hydroxides in the anoxic environment. Insoluble sulfide minerals (e.g., pyrite and mackinawite) were formed via the reaction of sulfides and Fe-containing particles, which are referred to as sinks for trace metals due to their affinity for metal ions (Audry et al 2010;Oueslati et al 2018). Additionally, sulfides can be reoxidized into elemental S (ES) by Fe(III) (oxyhydr) oxides (FeOOH) under anoxic conditions, thereby inducing chemical Fe reduction and remobilization of previously bound P (FeOOH-P) (Pan et al 2019).…”