Screening flax, kenaf and hemp varieties for phytoremediation of trace element-contaminated soils

Phytomanagement is a phytoremediation sub-technology in which industrial cash crops are cultivated on contaminated lands to produce useful biomass feedstock for bioproducts and bioenergy. Flax (Linum usitatissimum L.), kenaf (Hibiscus cannabinus L.), and hemp (Cannabis sativa L.) are suitable crops for this purpose since they have been reported to show a tolerance to toxic trace elements in soils, are fast-growing, yield a high biomass, have low input requirements, use well-known agricultural practices, and are multipurpose. The objectives of this research was to explore the potential of these crops for cultivation at sites highly contaminated with Cd, Ni, Pb, Zn, Cu, and Sb, to assess their ability to accumulate these elements and to reveal their capacity for use as phytoaccumulators or phytostabilizers. Three varieties per crop were tested, i.e. for flax: Y2I328, Y2I329 and Zhongyama No. 1; for kenaf: Hongyou No. 2, GGS, HP; and for hemp: Guangxibama, Yunma No. 1 and Zhongdama No. 1. A pot experiment was conducted outdoors and two soil concentrations of each element were tested against a control, namely: Cd at 0, 40, 80 mg/kg; Ni at 0, 110, 220 mg/kg; Pb at 0, 1500, 3000 mg/kg; Zn at 0, 1500, 3000 mg/kg; Cu at 0, 1000, 2000 mg/kg; and Sb at 0, 50, 100 mg/kg. The effects of these elements on seed germination and growth parameters were measured. In addition, their concentrations in and uptake by the plants were determined. The results showed that the concentrations of Cu and Zn applied were lethal for all three crops and varieties. All crops were excluders of Sb. The kenaf varieties were more tolerant than the varieties of the other two crops, and at the same time, they had the best uptake potential for Cd and Ni. Under Pb treatment, two flax varieties concentrated this element in tissue at levels higher than 1000 mg/kg, an interesting result that has to be verified under field conditions.