• Energy Research

Field experiments were conducted in two consecutive rice-wheat cropping seasons on a yellow clay soil to assess the efficacy of organic and inorganic amendments for cadmium (Cd) and lead (Pb) immobilization. Amendments were applied alone and in combinations to compare their efficacy for metals immobilization. Composite amendment of GSA-4 (Green Stabilizing Agent) and biochar resulted in higher biomass and grains yield for both rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Liming, DEK1 (Di Kang No. 1) or GSA-4 amendment increased soil pH from 6.34 to 7.35, 7.20 and 7.15, respectively. Soil amendments significantly reduced DTPA extractable Cd and Pb in soil at wheat harvest. Cadmium and Pb fractionation showed a significant decrease in the extractable fractions by the amendment of biochar (34% and 25%) or GSA-4 (35% and 26%, respectively). GSA-4 and biochar amendment enhanced metals immobilization and reduced their uptake by plant and subsequent accumulation in the grains of rice and wheat, particularly with GSA-4. These results indicate that GSA-4 and biochar, especially their combination, have great potential for application to remediate Cd and Pb contaminated soils.

Phytoremediation is a valuable technology for mitigating soil contamination in agricultural lands, but phytoremediation without economic revenue is unfeasible for land owners and farmers. The use of crops with high biomass and bioenergy for phytoremediation is a unique strategy to derive supplementary benefits along with remediation activities. Sunflower (Helianthus annuus L.) is a high-biomass crop that can be used for the phytoremediation of polluted lands with additional advantages (biomass and oil). In this study, 40 germplasms of sunflower were screened in field conditions for phytoremediation with the possibility for oil and meal production. The study was carried out to the physiological maturity stage. All studied germplasms mopped up substantial concentrations of Pb, with maximum amounts in shoot > root > seed respectively. The phytoextraction efficiency of the germplasm was assessed in terms of the Transfer factor (TF), Metal removal efficiency (MRE) and Metal extraction ratio (MER). Among all assessed criteria, GP.8585 was found to be most appropriate for restoring moderately Pb-contaminated soil accompanied with providing high biomass and high yield production. The Pb content in the oil of GP.8585 was below the Food safety standard of China, with 59.5% oleic acid and 32.1% linoleic acid. Moreover, amino acid analysis in meal illustrated significant differences among essential and non-essential amino acids. Glutamic acid was found in the highest percentage (22.4%), whereas cysteine in the lowest percentage (1.3%). Therefore, its efficient phytoextraction ability and good quality edible oil and meal production makes GP.8585 the most convenient sunflower germplasm for phytoremediation of moderately Pb-contaminated soil, with fringe benefits to farmers and landowners.

The presence of potentially toxic metals in water causes a strong impact on environment and human health. In this study, activated biochar was produced by using chemical oxidation method from wheat straw as natural adsorbent and was employed for heavy metals competitive remediation. The morphology, structure, and chemical properties of biochar before and after adsorption were characterized by FTIR, XRD, SEM and EDX mapping techniques. The competitive adsorption efficiency of adsorbent for divalent cadmium (Cd) and lead (Pb) from contaminated water was investigated by using wide range of several initial metal concentration, contact time and pH. Maximum adsorption of Cd(II) and Pb(II) was found in the pH range of 6–8. The adsorption capacity for Cd(II) and Pb(II) was 8.85 and 9.03 mg/g, respectively. Thermodynamics parameters and kinetic models were applied to adsorption data. The isotherm data followed Langmuir model, corresponding to monolayer adsorption of the two ions in the contaminated water. The kinetic data followed the pseudo 2nd order kinetics model, which authenticates the chemisorption nature. The thermodynamic study indicated that Cd adsorption is a spontaneous exothermic process while Pb adsorption is an endothermic process. Mineral precipitation, surface complexation, and cation-π interactions are the major remediation strategies for Cd(II) and Pb(II).

The identification of high yield genotypes that are capable of accumulating multiple heavy metals in the non-edible parts (roots and shoots), but not in the edible parts (seeds) and have desired nutritional value is necessary for accomplishing phytoremediation coupled with agro-production. In this study, 17 fava bean genotypes were screened in two different field conditions to examine their phytoremediation potential in terms of uptake and translocation of Cd and Pb. Ten genotypes, LBAO, JNJX, DCAN, QXCJ, QIKM, LXYC, YDL6, RBCD, QPID and ZHW6 were found as the best accumulators for Cd and Pb with permissible limit of metals in seeds. The concentration of plant nutrients were genotype and soil type dependent and there was a significant correlation between these two factors. Furthermore, the three genotypes DCAN, LBAO and LXYC showed best performance in alluvial soil type while QPID, RBCD and LXYC were the best in red soil type. Genotype LXYC was similar for both soil types and appeared to be the best fit for phytoremediation coupled with agro-production for slightly or moderately Cd and Pb co-contaminated soil. Therefore, fava bean LXYC genotype is suggested as a potential candidate for phytoremediation of Cd/Pb co-contaminated soils coupled with agro-production.

Vegetables are important constituents of the human diet. Heavy metals and nitrate are among the major contaminants of vegetables. Consumption of vegetables and fruits with accumulated heavy metals and nitrate has the potential to damage different body organs leading to unwanted effects. Breeding vegetables with low heavy metal and nitrate contaminants is a cost-effective approach. We investigated 38 water spinach genotypes for low Cd and nitrate co-accumulation. Four genotypes, i.e. JXDY, GZQL, XGDB, and B888, were found to have low co-accumulation of Cd (<0.71 mg/kg dry weight) and nitrate (<3100 mg/kg fresh weight) in the edible parts when grown in soils with moderate contamination of both Cd (1.10 mg/kg) and nitrate (235.2 mg/kg). These genotypes should be appropriate with minimized risk to humans who consume them. The Cd levels in the edible parts of water spinach were positively correlated with the concentration of Pb or Zn, but Cd, Pb, or Zn was negatively correlated with P concentration. These results indicate that these three heavy metals may be absorbed into the plant in similar proportions or in combination, minimizing the influx to aerial parts. Increasing P fertilizer application rates appears to prevent heavy metal and nitrate translocation to shoot tissues and the edible parts of water spinach on co-contaminated soils.

The prevalence of abiotic stresses hampers soil health and plant growth in most ecosystems. In this study, rice husk iron-enriched biochar (BC) was prepared and its superiority in terms of nutrients enrichment, porosity and different acidic functional group (O-H, C=O) relative to simple biochar was confirmed through scanning electron microscopic, X-ray fluorescence and Fourier transform infrared analysis. To further evaluate its nickel (Ni), salt (NaCl) and carbonate (CaCO3) stress mitigating impact on wheat physiology and biochemical attributes, a pot experiment was conducted using; BC (1%), Ni (0.5 mM NiNO3), Na (100 mM NaCl) and CO3 (100 mM CaCO3) and with twelve treatments; T1; Control, T2; NiNO3, T3; CaCO3, T4; NaCl, T5; BC, T6; Ni + BC, T7; CaCO3 + BC, T8; NaCl + BC, T9; Ni + CaCO3 + BC, T10; Ni + NaCl + BC, T11; CaCO3 + NaCl + BC, T12; Ni + NaCl + CaCO3 + BC. The Langmuir isotherm model revealed the maximum Ni adsorption capacity (2433 mg g−1) in treatments where Ni was applied with BC soil. Maximum soil DTPA-extractable Ni was found in the T9 treatment; however, Ni concentration was not reported in wheat roots while only trace amounts of Ni were found in wheat shoots with the T9 treatment. It was suggested that BC has the capacity to induce the immunization effect in plant roots by providing additional Fe so their ionic homeostasis and redox metabolism worked properly. This argument was further paved by the enhanced adsorption of these toxic ions in the presence of BC-favored wheat growth as indicated by maximum increases in shoot iron and potassium concentrations under Ni + CaCO3 + BC, relative to control. Furthermore, the decrease in shoot hydrogen peroxide (H2O2) (20%) and malondialdehyde (32%) concentrations and increase in shoot ascorbate peroxidase (81%) and catalase (three-fold) activities under Ni + BC relative to Ni + NaCl + CaCO3 + BC controlled the cell membrane damage. In conclusion, BC proved to be an excellent amendment to reduce the toxic effects of Ni, NaCl and CaCO3 stresses and enhance wheat growth and nutrition.

Phytoremediation coupled with crop rotation (PCC) is a feasible strategy for remediation of contaminated soil without interrupting crop production. The objective of this study was to develop a PCC technology system for greenhouse fields co-contaminated with Cd and nitrate using hyperaccumulator Sedum alfredii. In this system, endophytic bacterium M002 inoculation, CO2 fertilization, and fermentation residue were continuously applied to improve the growth of S. alfredii, and low-accumulator Ipomoea aquatica and low-accumulator Brassica chinensis were rotated under reasonable water management. These comprehensive management practices were shown to increase S. alfredii biomass and Cd uptake and reduce Cd and nitrate concentration in I. aquatica and B. chinensis. This crop rotating system could remove 56.5% total Cd, 62.3% DTPA extractable Cd, and 65.4% nitrate, respectively, from the co-contaminated soil in 2 years of phytoremediation, and is an effective way of remediating moderately co-contaminated soil by Cd and nitrate.

Forty oilseed sunflower cultivars were screened in two soil types for phytoremediation of Cd coupled with maximum biomass yield and oil production. Several cultivars exhibited a significant difference in biomass and yield with enhanced uptake in shoots and low accumulation in roots from two Cd-contaminated soil types, an Oxisol and an Iceptisol. The Transfer Factor of Cd was >1 in several cultivars in both soil types, where as a significant difference in phytoextraction of Cd was observed in the Oxisol (acidic soil), greater than in the Inceptisol (alkaline soil). The results revealed that of the 40 cultivars, S9178, Huanong 667in the Oxisol and cvs. DW 667, HN 667, Huanong 667 and 668F1 in the Inceptisol showed a high biomass, better yield and enhanced accumulation of Cd in the shoots but a lesser accumulation in oil. The screened cultivar S 9178 produced the greatest amount of oil (55.6%) with 77% oleic acid, which makes it suitable for human consumption. Cultivar Huanong 667 was found to be the highest accumulating cultivar in both soil types. It is therefore suggested that some sunflower cultivars do exhibit phytoremediation potential together with agro-production potential.