Phytostabilization of metals in mine soils using Brassica juncea in combination with organic amendments

BACKGROUND AND AIMS: The high metal bioavailability and the poor conditions of mine soils yield a low plant biomass, limiting the application of phytoremediation techniques. A greenhouse experiment was performed to evaluate the effects of organic amendments on metal stabilization and the potential of Brassica juncea L. for phytostabilization in mine soils. METHODS: Plants were grown in pots filled with soils collected from two mine sites located in Central Spain mixed with 0, 30 and 60 t ha⁻¹of pine bark compost and horse- and sheep-manure compost. Plant biomass and metal concentrations in roots and shoots were measured. Metal bioavailability was assessed using a rhizosphere-based method (rhizo), which consists of a mixture of low-molecular-weight organic acids to simulate root exudates. RESULTS: Manure reduced metal concentrations in shoots (10–50 % reduction of Cu and 40–80 % of Zn in comparison with non-amended soils), bioconcentration factor (10–50 % of Cu and 40–80 % of Zn) and metal bioavailability in soil (40–50 % of Cu and 10–30 % of Zn) due to the high pH and the contribution of organic matter. Manure improved soil fertility and was also able to increase plant biomass (5–20 times in shoots and 3–30 times in roots), which resulted in a greater amount of metals removed from soil and accumulated in roots (increase of 2–7 times of Cu and Zn). Plants grown in pine bark treatments and in non-amended soils showed a limited biomass and high metal concentrations in shoots. CONCLUSIONS: The addition of manure could be effective for the stabilization of metals and for enhancing the phytostabilization ability of B. juncea in mine soils. In this study, this species resulted to be a potential candidate for phytostabilization in combination with manure, differing from previous results, in which B. juncea had been recognized as a phytoextraction plant.