Cadmium accumulation in winter crops and the assessment of paddy soil phytoremediation in southern China.

Heavy metal pollution, in particular with cadmium (Cd), threatens both the environment and human health. The phytoremediation of contaminated soil is one recently developed eco-friendly technique that can be applied to mitigate this issue. Repairing Cd-contaminated paddy soil during the fallow winter period can ensure future rice production while reducing heavy metal pollution. Seven winter crops were planted in this study to investigate the accumulation of this metal in mid-level Cd and low-level lead (Pb) and zinc (Zn)-contaminated paddy soils. Results show that after 4 or 5 months of growth, all crops had become moderately tolerant to toxicity; indeed, shoot Cd bioconcentration factor (BCF) values were 37.4, 17.0, 11.5, 10.5, 5.8, 3.9, and 1.4 for Sedum alfredii (SA), Witloof chicory (WC), edible-leaf beet (EB), Cardamine hupingshanensis (CH), leafy mustard (LM), oil mustard (OM), and perennial ryegrass (PR), respectively, while shoot Pb and Zn BCF values were less than 1 and 5, respectively. And SA, WC, EB, and CH all had higher shoot Cd accumulation capacities, especially SA in which the level reached 53.9 mg kg-1. The calculation results of restoration potential show that it will take at least 5 years for WC, 7 years for SA and EB, and 10 years for CH to reach the repair target. These results show that it is possible to grow winter crops to repair soil Cd pollution, with WC, EB, CH, and SA, the best candidates for making full use of fallow periods while simultaneously achieving soil phytoremediation. The results of this study will prove useful for establishing a new summer production model by ensuring the winter repair of contaminated paddy soil.

Phytoextraction of heavy metals from contaminated soil by co-cropping with chelator application and assessment of associated leaching risk.

Phytoextraction using hyperaccumulating plants is generally time-consuming and requires the cessation of agriculture. We coupled chelators and a co-cropping system to enhance phytoextraction rates, while allowing for agricultural production. An experiment on I m3 lysimeter beds was conducted with a co-cropping system consisting of the hyperaccumulator Sedum alfredii and low-accumulating corn (Zea Mays, cv. Huidan-4), with addition ofa mixture of chelators (MC), to assess the efficiency of chelator enhanced co-crop phytoextraction and the leaching risk caused by the chelator. The results showed that the addition of MC promoted the growth of S. alfredii in the first crop (spring-summer season) and significantly increased the metal phytoextraction. The DTPA-extractable and total metal concentrations in the topsoil were also reduced more significantly with the addition of MC compared with the control treatments. However, mono-cropped S. alfredii without MC was more suitable for maximizing S. alfredii growth and therefore phytoextraction of Zn and Cd during the autumn-winter seasons. No adverse impact to groundwater due to MC application was observed during the experiments with three crops and three MC applications. But elevated total Cd and Pb concentrations among subsoils compared to the initial subsoil concentrations were found for the co-crop + MC treatment after the third crop.