[Uptake and Accumulation of Cadmium and Zinc by Two Energy Grasses: A Field Experiment].

The remediation potential of large biomass energy grasses in cadmium-contaminated soil remains ambiguous. A field experiment was carried out in a cadmium-contaminated farmland using two energy grasses and two control plants. The two energy grasses were hybrid pennisetum (Pennisetum americanum×P. purpureum, PAP) and purple elephant grass (P. purpureum 'Purple', PPP), and the two control plants were Iris lactea var. chinensis (ILC) and a cadmium hyperaccumulator, Noccaea caerulescens (NC). The results showed that the aboveground biomass of PAP was the largest among the four plants, and 126 and 36 times that of NC and ILC, respectively, but no significant difference with that of PPP. The concentrations of cadmium and zinc in the shoots and roots of NC were significantly higher than in the other plants. Zinc concentrations in the shoots and roots of ILC were lower than in the other plants, while cadmium concentrations were significantly higher than in PAP and PPP (P<0.05). The amounts of cadmium and zinc accumulated in the shoots of PPP were the highest among the four plants, while cadmium concentrations in the shoots and roots of PPP were significantly lower than in ILC and NC (P<0.05). Cadmium amounts accumulated in PPP shoots were 7.0 and 4.1 times that of ILC and NC, respectively. Zinc amounts accumulated in PPP shoots were 41 and 11 times that of ILC and NC, respectively (P<0.05). Cadmium accumulation in the shoots of PAP was 19.4% lower than in PPP, and zinc accumulation had no significant difference with that of PPP. NC, having a bioconcentration factor of shoot (BCFS) and a translocation factor (TF) for cadmium and zinc both larger than 1, is usable for phytoextraction of soils contaminated by cadmium and zinc. ILC, having a bioconcentration factor of root (BCFR) larger than 1 and a TF lower than 1 for cadmium, is usable for the phytostabilization of soils contaminated by cadmium. PPP, having a BCFR larger than 1 and a TF lower than 1 for zinc, can be used in the phytostabilization of soils contaminated by zinc. Under field conditions, PPP and PAP showed great potential for the extraction and removal of cadmium and zinc from soil due to their large biomass and ability to produce economic benefits, have good application prospects.

[Effects of Boron Treatment on Arsenic Uptake and Efflux in Rice Seedlings].

The impacts of boron (B) root application and foliar spray on arsenic (As) uptake, translocation, and efflux by/in rice seedlings (Oryza sativa L.) were investigated in three hydroponic experiments. The addition of B to culture medium did not alter concentrations of arsenite (As[Ⅲ]), arsenate (As[Ⅴ]), and total As, nor did it alter transfer coefficients or uptake efficiency of As in rice seedlings under either As(Ⅲ) or As(Ⅴ) exposure. Foliar B supply increased shoot B concentrations 15.8-fold, and decreased root As concentrations and As uptake efficiency by 20.9% and 18.0% under As(Ⅴ) treatment, and by 12.6% and 13.8% under As(Ⅲ) treatment, respectively, yet did not significantly decrease shoot As concentrations (P>0.05). Interestingly, foliar B supply reduced root B concentrations by up to 47.1% under exposure to As(Ⅴ) but not As(Ⅲ), and corresponding root B concentrations were 85.3% higher in As(Ⅴ) treatment than in As(Ⅲ) treatment on average (P<0.05). Both total As and As(Ⅴ) concentrations were positively related to B concentration in rice roots under As(Ⅴ) treatment following foliar B supply (P<0.05). Rice seedlings extruded 105.2% more As after As(Ⅲ)-pretreatment than after As(Ⅴ)-pretreatment. Foliar B supply increased the amount of As excreted by As(Ⅲ)-pretreated rice root by 14.0%-16.9% (P>0.05), and had no effect on the As efflux of As(Ⅴ)-pretreatment seedlings. A range of 45.9%-70.7% of root As was excreted to solution during one week. These results indicate that the root application of B at four times the concentration of As can slightly decrease As accumulation by rice, whereas foliar B supply is conducive to a decline in As acquisition by rice roots. It is likely that the B channel is at least not the main pathway for As(Ⅲ) entering into rice roots, and the As(Ⅴ) distribution mechanism in rice plants may be shared with that of B.

Evaluation of bioaugmentation and biostimulation on arsenic remediation in soil through biovolatilization.

Arsenic (As) removal through microbially driven biovolatilization can be explored as a potential method for As bioremediation. However, its effectiveness needs to be improved. Biostimulation with organic matter amendment and bioaugmentation with the inoculation of genetic engineered bacteria could be potential strategies for As removal and site remediation. Here, the experiments were conducted to evaluate the impacts of rice straw and biochar amendment, inoculation of genetic engineered Pseudomonas putida KT2440 (GE P. putida) with high As volatilization activity, on microbial mediated As volatilization and removal from three different arseniferous soils. In general, the addition of rice straw (5%) significantly enhanced As methylation and volatilization in comparison with corresponding non-amended soils. Biochar amendments and inoculation of the GE P. putida increased As methylation and volatilization, respectively, but less than that of rice straw addition. The effectiveness of As volatilizations are quite different in the various paddy soils. The combined amendments of rice straw and GE P. putida exhibited the highest As removal efficiency (483.2 µg/kg/year) in Dayu soil, with 1.2% volatilization of the total As annually. The highest water-soluble As concentration (0.73 mg/kg) in this soil could be responsible for highest As volatilization besides the rice straw and bacteria in this soil.

The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings.

A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (C(pw)) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8-5.7 and 1.4-2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the C(pw) of Cd and Zn, increasing the C(pw) of As, and increasing the iron plaque blocking capacity for Cd and Pb.

[Effect of the soil bulk density on the root morphology and cadmium uptake by Thlaspi caerulescens grown on Cd-contaminated soil].

A pot experiment was conducted using a soil contaminated with 2.12 mg x kg(-1) Cd to study the effect of the variety of the soil bulk density on the Zn/Cd uptake by the hyperaccumulator Thlaspi caerulescens and the removal of Cd and Zn from the soil. The contaminated soil received 0, 0.1%, 2% of soil conditioner and the plants were harvested after 100 days. The results showed that soil amendment with the soil conditioner (EB. a) significantly decreased the soil bulk density. Compared to the control, the bulk density value decreased from 1.27 g x cm(-3) to 1.09 g x cm(-3) at the level of 2% soil conditioner. The increased biomass of shoot and root was observed at the treatment of EB. a amendment. The total root length, root hair length and root/shoot ratio were all significantly enhanced (p < 0.05) by the addition of EB. a. The significant positive relationships between the total root length and the removed Cd/Zn from soil were determined (p < 0.05). Compared with the control,the total root length was increased by 2.6 folds at the addition of 2% soil conditioner; the Cd concentration and removal of Cd from soil were significantly elevated by 20% and 30% respectively. The phytoextraction efficiency of Cd was improved from 15% to 19%. However, the Zn concentration and removal of Zn were not significantly elevated by the addition of soil conditioner. The present results demonstrate that the decreased soil bulk density may improve the root system of T. caerulescens and enhance the phytoextraction efficiency of Cd.

Cadmium accumulation in the edible parts of different cultivars of radish, Raphanus sativus L., and carrot, Daucus carota var. sativa, grown in a Cd-contaminated soil.

Cadmium accumulation among 12 cultivars of radish (Raphanus sativus) and 10 cultivars of carrot (Daucus carota var. sativa) was studied in a Cd-contaminated soil. The Cd concentration in the edible parts of radish and carrot ranged from 0.04 to 0.14 and 0.14 to 0.19 mg kg(-1) fresh weight, respectively. All the tested carrot cultivars and 33% of the tested radish cultivars exceeded the Chinese allowable limit for Cd. The study showed a greater scope for selecting radish cultivars than for carrot to avoid the excess of the Cd limit when grown on lightly contaminated soils.