Effects of Heavy Metals on the Growth of the Edible Cactus Nopalea cochenillifera Grown Under Hydroponic Conditions

Abstract

　This study aimed to investigate the effects of heavy metals on the growth of an edible cactus Nopalea cochenillifera. We exposed hydroponically grown cladodes of N. cochenillifera to different concentrations of heavy metals [arsenic (As), cadmium, and lead at 1, 10, and 100 ppm; Zinc (Zn) at 120, 1,200, and 12,000 ppm] for 14 weeks and assessed their growth. The underwater parts of the cladodes exposed to 10 and 100 ppm of As and 12,000 ppm of Zn showed rotting and did not produce any daughter cladodes. However, at all other concentrations, daughter cladodes emerged from the mother cladodes and continued to grow. The total fresh weight of the daughter cladodes and the dry weight of the emerged roots negatively correlated with heavy metal concentration. These results suggest that although high concentrations of heavy metals negatively affect the growth of N. cochenillifera cladodes, sometimes even killing them, this cactus can survive exposure to heavy metals at concentrations 100- to 10,000-fold higher than environmental standards of soil elution in Japan, indicating the potential of N. cochenillifera for phytoremediation.