Cadmium uptake and transfer by Sedum plumbizincicola using EDTA, tea saponin, and citric acid as activators

Positive Effects and Optimal Ranges of Tea Saponins on Phytoremediation of Cadmium-Contaminated Soil

“…When the cadmium concentration in the soil was 50 mg/kg, the increasing rate of the proportion of cadmium available fraction in the soil reached 121.37% by adding TS (available cadmium concentration of 0.290 mg/L acquired from Run 2 in the Box-Behnken designs, compared with the available cadmium concentration of 0.131 mg/L in Table 2), confirming that TS increased the available fraction of cadmium. The above result was consistent with the current research, in which TS took an active part in enhancing the exchangeable fraction of cadmium [17][18][19], and the addition of TS at 40 mg/L showed a great advantage of solubilization capability than other surfactants in enhancing the accessible fraction of cadmium [18]. Nevertheless, the concentration of cadmium in the soil was fixed in the above-mentioned studies, and the interaction between cadmium concentration in the soil and TS concentration was not studied.…”

“…At the same time, the treatment time of TS in the above-mentioned studies was also fixed, without the quantitative effects and optimal ranges of TS treatment time discussed and given. In the above-mentioned studies, the quantitative effect of TS concentration was not investigated thoroughly; the effects of TS on the available cadmium concentration were studied at a fixed concentration of 40 mg/L [17]; three values of 20, 40, and 80 mg/L [18]; and four values of 1, 3, 5, and 10 mmol/L [19], respectively. For the TS treatment time, its effect was a parabolic type with an open downward, which indicated that too long or too short of a TS treatment time reduced the proportion of the cadmium available fraction, attributed to the fact that TS may not have had enough time to work and that TS would be decomposed when the treatment time was too long.…”

“…The application of tea saponins (TS), a kind of natural non-ionic surfactants, which are contained in the root, stem, leaf, flower, and seed of Camellia plants [15], has been proven to raise the bioavailability of hyperaccumulators on cadmium, pyrene, and polychlorinated biphenyls (PCBs) in contaminated soil [14,[16][17][18][19]. Despite this, these studies also have their limitations.…”

“…Despite this, these studies also have their limitations. In general, the role of surfactants has two aspects on the phytoremediation of cadmium-contaminated soils: first, to promote the transformation of the chemical form of cadmium from the difficult-to-use form (bound to Fe-Mn oxides and bound to carbonates) to the available form (exchangeable) [17][18][19]; second, on the premise of not changing the form of cadmium in the soil, surfactants only promote the absorption of cadmium by accumulation plants or hyperaccumulators. The second role of surfactants on phytoremediation is a lack of studies, because, in existing studies, accumulation plants or hyperaccumulators were usually grown in pots, and once the surfactant had the first role in changing the form of cadmium, the effect of the second role would be covered.…”

Copper and Cadmium Accumulation and Phytorextraction Potential of Native and Cultivated Plants Growing around a Copper Smelter

“…As for artificially cultivated restoration plant species, they mainly consist of hyper-accumulators, such as Sedum plumbizincicola (a cadmium hyper-accumulator), Pteris vittata L. (an arsenic hyper-accumulator), and Elsholtzia splendens Nakai (a copper-tolerant plant). These species may be replaced by local native plant species in the polluted area once human intervention is withdrawn [13][14][15][16]. On the contrary, native wild plants can grow robustly after undergoing long-term natural selection and can withstand a series of natural disasters, such as local extreme climate conditions, pests, and diseases [11,17].…”