Rhizofiltration of Cadmium and Zinc in Hydroponic Systems

Abstract

The potential of two aquatic plants, e.g., Typha angustifolia and Acorus calamus, and a terrestrial plant, e.g., Pandanus amaryllifolius, was evaluated in hydroponic experiments for rhizofiltration of cadmium (Cd) and zinc (Zn). Of the three species, T. angustifolia experienced a 100% survival rate and showed no symptoms of toxicity, with substantial values of dry biomass production (11.5–20.8 g) and Cd and Zn uptake (4941.1–14,109.4 mg plant−1 and 14,039.3–59,360.8 mg plant−1), respectively. The other tested plants showed lower performance; P. amaryllifolius experienced phytotoxicity effects in the 40 mg Zn L−1 treatment. Based on our data, T. angustifolia is considered an excluder species for Cd and Zn as this species accumulated high Cd and Zn levels, primarily in roots, with bioconcentration factor (BCF) values > 100 and translocation factor (TF) values < 1 for all Cd and Zn treatments. All study plants exhibited lower heavy metal accumulation and uptake in most metal mixture treatments compared with Cd- or Zn-only treatments due to dilution effects. Percentage uptake of Cd by T. angustifolia increased with increasing Cd concentration (10.8–22.7%). Substantial percentage Zn uptake values were recorded at day 15 in the 40 mg L−1 Zn treatment for A. calamus (89.1%). The study plants are rarely consumed on a daily basis; therefore, such levels of metal uptake should not adversely affect human health. Based on hydroponic system data, hazard quotient (HQ) values of Cd were > 1 for all treatments, indicating possible health risk from Cd via plant consumption. Although HQ values of Zn are also > 1, the maximum permissible level (MPL) (< 20,000 mg kg−1) indicates that it occurs within acceptable levels. Only T. angustifolia is suggested as a suitable candidate plant in constructed wetlands and aquatic plant systems for removal of heavy metals. [Figure not available: see fulltext.]