Solubilization and Plant Uptake of Zinc and Cadmium from Soils Treated with Elemental Sulfur

In growth chamber experiments we studied the potential use of elemental sulfur (S-8) as an acidifying agent to enhance the uptake of Cd and Zn from three different polluted soils by candidate phytoremediation plants (Brassica juncea, Helianthus annuus, Salix viminalis). Two of the three soils were calcareous, the other slightly acidic. One of the calcareous soils had been contaminated by dust emissions from a nearby brass smelter. The pollution of the other two soils had resulted from sewage sludge applications. Sulfur was added to soils in quantities of 20 to 400 mmol sulfur kg(-1) soil. Plants were grown under fluorescent light in 1.51 (empty set 13 cm) pots for 28 d. Within 700 h soil pH decreased significantly in all soils, depending on S8 dosage. In the acid soil, pH decreased from pH 6.5 to about 4 at the highest treatment level, in one of the calcareous soils dropped even below pH 4. The effect was smaller in the second calcareous soil. NaNO3-extractable Cd and Zn increased up to 26- and 13-fold, respectively, in the acid soil, while in the calcareous soils, maximum increases were 9- and 11-fold, respectively. Increased NaNO3-extractable concentrations translated well into shoot concentrations (dry matter) in plants. Shoot Zn concentrations in H. annuus, for example, increased from 930 in the controls to 4300 mg kg(-1) in the highest S8 treatment. However, effects observed in the plants were generally smaller than in the soils. In addition, in some variants growth was negatively affected, resulting in reduced metal removal from the soils. Our results show that the amendment of soils with elemental sulfur holds potential for usage as a technique to solubilize Zn and Cd in phytoremediation.