Phytoremediation with Kenaf (Hibiscus Cannabinus L.) for Cadmium-Contaminated Paddy Soil in Southern China: Translocation, Uptake and Assessment of Cultivars

Kenaf (Hibiscus cannabinus L.) is suitable for growing in heavy metal-polluted soil for non-food purposes, and can be used as a potential crop to remediate heavy metal-contaminated soil. The main objective of this study was to investigate kenaf phytoextraction of cadmium (Cd), including uptake, translocation, and accumulation differences in tissues among kenaf cultivars. A field experiment was conducted in a Cd contaminated paddy field in southern China area with 13 kenaf cultivars in 2015 and 2016. Agronomic performance, Cd concentrations in plant tissues (root, xylem, and phloem), and biomass of different tissues of each cultivar were measured and evaluated. Significant differences in Cd concentrations and accumulation among tissues and cultivars were observed. The phloem had the highest Cd accumulation and transfer capability compare with the roots and xylem. Approximately 35 ~ 65g of Cd could be taken up by the aerial parts of different kenaf cultivars within every hectare of soil. The percentage of Cd uptake by the phloem ranged from 47–61% and by the xylem ranged from 38–53%. By evaluating the agronomic traits and Cd bioaccumulation capacity, Fuhong 952, Fuhong 992, and Fuhong R1 were regarded as Cd accumulators for the phytoremediation of Cd-contaminated soil. Our study clearly demonstrated that a significant level of Cd in the soil was taken up through the phytoremediation with kenaf. In addition, harmless utilization of kenaf planting in Cd-contaminated paddy soil was discussed.

Adsorption and Desorption Characteristics of Cadmium on Different Contaminated Paddy Soil Types: Kinetics, Isotherms, and the Effects of Soil Properties

The adsorption and desorption characteristics of cadmium (Cd) in uncontaminated soils have been investigated in numerous studies. However, similar studies on Cd-polluted soils from different sources, which exhibit complex physicochemical characteristics and internal interactions between Cd and the soil particles, are scarce. Therefore, in order to elucidate the adsorption and desorption characteristics of Cd in Cd polluted soils, six representative Cd-contaminated paddy soil samples were collected from farmlands in the vicinity of a steel plant (Soil 1), a smelter (Soil 2), a thermal power plant (Soil 3), two mining areas (Soil 4, the Dabaoshan mine, Shaoguan; Soil 5, a lead-zinc mine located at Lechang), and a paddy field irrigated with sewage at Zhongshan (Soil 6) in Guangdong Province, China. The analysis of the six soil samples showed that Cd adsorption fitted well to pseudo-second order as well as pseudo-first order kinetics; however, the pseudo-second order equation showed a better fit (R2 = 0.860–0.962), while Elovich and intraparticle kinetic models fitted the adsorption kinetics poorly. Further, the adsorption isotherms fitted well to both the Langmuir and Freundlich models, with the Freundlich model showing a better fit (R2 = 0.96–0.98). The following order was observed for the Cd(II) adsorption amount and rate: S5 > S6 > S1 > S3 > S2 > S4; meanwhile, the desorption amount and rate followed the opposite trend. Furthermore, the pH and soil organic matter were identified as the soil characteristics with the most significant impact on the adsorption and desorption behaviors of Cd(II) in the Cd-polluted soils.