Accumulation of Sulphur in Atriplex nummularia Cultivated in Mine Tailings and Effect of Organic Amendments Addition

In several countries, mining generates a high volume of tailing deposits, significantly impacting on soils. One of the non-metallic elements found in high concentrations in mine tailings is sulphur (S), in the form of sulphide minerals, whose oxidation causes acid drainage and metal mobility. The absorption of S in plants cultivated in mine tailings has been scarcely investigated. The objective of this study was to evaluate the extent to which a commercial humic substances and a vegetable waste compost can enhance the phytoremediation capacity of Atriplex nummularia for S and metals (Cu, Mo) in mine tailings. The plants were cultivated for 120 days under greenhouse conditions in pots with mine tailings (MT), with the addition of vegetable waste compost (VC) and a commercial humic substance (HS) in a 5% dose (W/W). At the end of the assay, the concentration of S in the aerial parts of plants cultivated in mine tailings, without amendments, reached 19,538 ± 4554 mg kg−1, indicating a potential thiophore plant. In MT in which HS were applied, S and Cu concentration decreased significantly in aerial parts, while VC significantly increased Mo. The addition of HS generated significantly greater dry weight, reaching 11.55 ± 1.92 g in the aerial parts versus 2.08 ± 0.52 g in MT, which increased significantly S and Cu content in plant root and therefore favourable to phytostabilization. Regarding organic amendments, their chemical characteristics, availability, cost and quality in relation to organic matter are very important aspects for phytoremediation of mine tailings.