Phytoremediation of cadmium contaminated alkaline soil using the ornamental hyperaccumulator Mirabilis jalapa L. enhanced by double harvesting: a field study.

Abstract

Ornamental hyperaccumulators are considered ideal plants for phytoremediation of cadmium (Cd)-contaminated soils because of their high accumulation capacity and minimal potential to enter the food chain. Aiming to estimate the phytoremediation efficiency and explore the influence of double harvesting, a filed study was carried out in Cd-contaminated alkaline soil using the ornamental hyperaccumulator Mirabilis jalapa L. Seeds of M. jalapa were sawn with spacing in rows of 15cm and in lines of 20cm on April 20th. Three treatments with different harvesting strategies were arranged: all plants were harvested once on September 10th (marked with H0), and the plants were harvested on July 20th for the first time at a height above ground of 50cm and 30cm (marked with H1 and H2, respectively), and then, they were harvested on September 10th for the second time. The plant samples were digested with a mixture of HNO3 and HClO4 and determined using ICP-MS. The results showed that the total biomass of the shoots increased from 505.81 ± 8.29g/m2 in the H0 treatment to 849.72 ± 59.73 and 933.14 ± 96.12g/m2 in the H1 and H2 treatments, respectively, while the total Cd accumulation in the shoots was 42.32 ± 4.44, 52.99 ± 7.32, and 56.30 ± 6.95g/ha in the H0, H1, and H2 treatments, respectively. Phytoremediation efficiencies increased by at least 20% after the application of double harvesting. However, double harvesting also decreased the translocation and bioconcentration factors with a reduction of 30-55% because the Cd concentration in the shoots was low at the first harvest. Our results suggested that double harvesting is a powerful method to improve phytoremediation efficiency with low costs and minimal risk, and other technologies should be applied together to address the accumulation and translocation of Cd.