Xiaoxun Xu

A newly found cadmium accumulator - Malva sinensis Cavan.

Screening hyperaccumulators and accumulators is a key step in the phytoremediation of soils contaminated by heavy metals. A pot experiment was conducted involving a soil Cd concentration gradient (0, 50, 75, 100, 125, 150, 175, and 200 mg kg(-1)) to determine if Malva sinensis Cavan. from two lead-zinc mines in Kangding and Yajiang in western Sichuan, China, is a Cd-hyperaccumulator. The highest Cd concentrations in plant shoots from Kangding and Yajiang were 154.30 and 122.77 mg kg(-1), respectively, at a soil Cd concentration of 200 mg kg(-1). The largest amounts of accumulation in plant shoots from Kangding and Yajiang were 700.5 and 1403.2 microg pot(-1), respectively. The bioconcentration factors in shoots were 0.53-1.03 for Kangding and 0.69-1.25 for Yajiang. Moreover, all translocation factors of plants from the two sites were over 1.0. Therefore, M. sinensis can be classified as a Cd-accumulator or non-standard Cd-hyperaccumulator.

Tolerance and accumulation characteristics of cadmium in Amaranthus hybridus L.

Because of its toxicity to animals and humans, cadmium (Cd) is an environmentally important heavy metal. Consequently, researchers are interested in using hyperaccumulator and accumulator plants to decontaminate Cd polluted soils. To investigate Cd tolerance, uptake and accumulation by Amaranthus hybridus L., Cd concentration gradients were applied to a soil (at rates of 0, 30, 60, 90, 120, 150 and 180 mg kg(-1)) and hydroponics solutions (at rates of 0, 5, 10, 15, 20, 30, and 40 mg L(-1)) following a field survey. A. hybridus grew normally at added Cd concentrations < or =90 mg kg(-1) and < or =20 mg L(-1) in the soil culture and in the hydroponics solutions, respectively. In the hydroponics solutions, peroxidase activity showed a quadratic relationship and catalase activity changed irregularly with increasing Cd concentrations. The highest Cd concentration and accumulation in shoots were 241.56 mg kg(-1) and 1006.95 microg pot(-1) in the soil culture, and 354.56 mg kg(-1) and 668.42 microg pot(-1) in the hydroponics experiment. Bioconcentration factors in soil culture and hydroponics solutions were 0.58-1.22 and 5.18-17.55, and translocation factors were 0.64-1.50 and 0.33-0.92, respectively. A. hybridus has potential phytoremediation capability in Cd polluted soils.

Efficiency of biodegradable EDDS, NTA and APAM on enhancing the phytoextraction of cadmium by Siegesbeckia orientalis L. grown in Cd-contaminated soils.

Chelant assisted phytoextraction has been proposed to enhance the efficiency of remediation. This study evaluated the effects of biodegradable ethylene diamine tetraacetate (EDDS), nitrilotriacetic (NTA) and anionic polyacrylamide (APAM) on the tolerance and uptake of Siegesbeckia orientalis L. at 10 and 100 mg kg(-1) Cd-contaminated soils. On the 80th and 90th days of transplanting, pots were treated with EDDS and NTA at 0 (control), 1 and 2 mmol kg(-1) soils, and APAM at 0 (control), 0.07 and 0.14 g kg(-1). Generally, the root and shoot biomass of S. orientalis in all treatments reduced not significantly compared with the control, and the activities of peroxidase and catalase in leaves generally increased by the application of chelants (P<0.05). The concentrations of Cd in the shoots were increased significantly by addition of all chelants. As a result, the Cd accumulation of S. orientalis under treatments with higher dosages of the three chelants on the 80th day were 1.40-2.10-fold and 1.12-1.25-fold compared to control at 10 and 100 mg kg(-1) Cd, respectively. Under the addition of 2 mmol kg(-1) NTA on the 80th day, the highest metal extraction ratio reached 1.2% and 0.4% at 10 and 100 mg kg(-1) Cd soils, respectively. Therefore, the applications of EDDS, NTA and APAM may provide more efficient choices in chemical-enhanced phytoextraction.

Application of response surface methodology for the optimization of lead removal from contaminated soil using chelants

The remediation of Pb-contaminated soil has become an international concern in recent decades due to mines exploitation and fertilizer abuse. Batch chemical soil washing experiments were conducted to optimize Pb removal efficiency from contaminated soil by two biodegradable chelants, citric acid (CA) and [S,S]-ethylenediaminedisuccinic acid (EDDS). The influences of chelant concentration, pH and contact time were evaluated. In a single factor test, a maximum Pb removal efficiency of 77.84% was achieved with 100 mM CA solution and pH 2.0 for 60 min, while it reached 81.49% with 400 mM EDDS solution and pH 4.0 for 60 min. Response surface methodology (RSM) based on Box–Behnken design (BBD) was applied to optimize the experimental conditions. The interactions between selective factors were significant (P < 0.05). Polynomial models were developed for the experimental response and optimal conditions were obtained with high determination coefficients (R2 ≥ 0.90, P < 0.05). Furthermore, Pb removal efficiencies by CA and EDDS washing were 70.08 and 80.26%, respectively, under optimal conditions, and close to the predicted values (74.49 and 83.95%) from RSM. The results confirmed the accuracy and reliability of the optimization process using RSM. Therefore, response surface methodology is a suitable approach to determine the optimal parameters for chemical soil washing to remediate heavy metal polluted soil using biodegradable chelants.

Eucalyptus tolerance mechanisms to lanthanum and cerium: subcellular distribution, antioxidant system and thiol pools.

Guanglin 9 (Eucalyptus grandis × Eucalyptus urophlla) and Eucalyptus grandis 5 are two eucalyptus species which have been found to grow normally in soils contaminated with lanthanum and cerium, but the tolerance mechanisms are not clear yet. In this study, a pot experiment was conducted to investigate the tolerance mechanisms of the eucalyptus to lanthanum and cerium. Cell walls stored 45.40-63.44% of the metals under lanthanum or cerium stress. Peroxidase and catalase activities enhanced with increasing soil La or Ce concentrations up to 200 mg kg(-1), while there were no obvious changes in glutathione and ascorbate concentrations. Non-protein thiols concentrations increased with increasing treatment levels up to 200 mg kg(-1), and then decreased. Phytochelatins concentrations continued to increase under La or Ce stress. Therefore, the two eucalyptus species are La and Ce tolerant plants, and the tolerance mechanisms include cell wall deposition, antioxidant system response, and thiol compound synthesis.