Combined effect of humic acid and vetiver grass on remediation of cadmium-polluted water

Effective treatment of water pollution is an economic and social requirement globally. Humic acid (HA) is a popular mitigator for such waters. However, the combined effect of HA and restorative plants on cadmium (Cd) remediation is not well understood. Therefore, we experimented on Cd remediation using HA along with vetiver grass and HA-vetiver grass. We observed that vetiver grass effectively removed Cd at 15～30 mg/L. The accumulation capacity of the root was significantly higher than the shoots (P < 0.05), and Cd distribution followed the trend: cell wall > organelle > soluble substance (F1 > F2 > F3). The plant's accumulation capacity against 25 mg/L Cd was higher than for other treatments. The root accumulation capacity was much higher (702.3 mg/L) than those without added HA. However, upon adding 200 and 250 mg/L HA, the phytoremediation of Cd in the root and shoot significantly reduced (P < 0.05). Conversely, HA improved the Cd removal efficiency of the plants, notably at a lower HA concentration (150 mg/L). In addition, HA (especially at 150 mg/L) influences Cd distribution in vetiver cells (P < 0.05) and can significantly increase the proportion of Cd in the root cytoplasm. Consequently, a low HA concentration can significantly improve Cd accumulation in the vetiver, shorten the metal's bioremediation cycle, and improve the biological absorption efficiency.