Evaluation of the potential of two halophytes to extract Cd and Zn from contaminated saltwater

The contamination of saltwater by toxic heavy metals has become a worldwide problem. The application of phytoextraction to remove these pollutants seems to be more efficient and cheaper compared to physicochemical methods. In this work, we evaluated the potential of two halophyte species to accumulate cadmium and zinc from contaminated water. Seedlings of Carpobrotus edulis L. and Sesuvium portulacastrum L. were cultivated during 1 month on pots filled with saltwater (200 mM NaCl) containing different concentrations of Cd²⁺ (0, 50, 100 μM) and of Zn²⁺ (0, 200, and 400 μM) applied separately. Results showed that both halophytes were more resistant to Zn²⁺ than Cd²⁺ and that Sesuvium better tolerates the two metals. Zn²⁺ and Cd²⁺ concentrations in the shoot as well as the values of translocation factors suggest that these species are able to absorb and to concentrate Cd²⁺ and Zn²⁺ in their roots and shoots. Hence, after 1 month of culture on 50 μM Cd²⁺, plants were able to extract 31% and 21% of Cd, respectively, in S. portulacastrum and C. edulis. The Zn-extraction efficiency was less important and reached 18 and 19%, respectively, in S. portulacastrum and C. edulis cultivated under 200 μM Zn²⁺. Given together, data demonstrate the efficiency of the use of halophytes, especially S. portulacastrum, to extract Zn²⁺ and Cd²⁺ from salt wastewater.