Accumulation of Cd in Indian mustard and sunflower for phytoremediation

Phytoremediation is a new method that uses plants to remove contaminants from soil without affecting soil fertility. It can therefore be used for contaminated agricultural land. Indian mustard (Brassica juncea) and sunflower (Helianthus annuus L.) are used in phytoremediation to remove Cadmium (Cd), which they can accumulate in large quantities. It is important to know when plants have accumulated significant Cd, so that we can decide when the plants should be harvested and synthetic chelates applied. Brassica juncea seeds and Helianthus annuus L. seeds were planted in a field in Kyoto University Research Reactor Institute (KUR). Brassica juncea and Helianthus annuus L. were collected at time intervals ranging from 1 to 6 months and 2 to 7 weeks, respectively, after seedling emergence and the concentration of Cd in the plants was analyzed. These results indicated that Brassica juncea should be harvested before beginning flowering and Helianthus annuus L. should be harvested after it becomes old enough. The solubility of Cd in soil is enhanced when the soil is heated or dried, and black vinyl mulch was therefore used to absorb the heat from sunlight. The difference in the Cd uptake of Brassica juncea between mulching cultivation and non-mulching cultivation was investigated in a field, and this indicated that there is no probability that mulching enhances Cd uptake in plants. The solubility of Cd in soil decreases over time. Repeated pot experiments were done. We planted Brassica juncea in pots, and investigated the uptake of Cd and the solid phase fractions in which Cd was present in each pot experiment. These did not change considerably over time, indicating that age has a negligible effect on Cd uptake in plants. (author)