Pengjie Hu

Water management affects arsenic and cadmium accumulation in different rice cultivars

Paddy rice (Oryza sativa L.) is a staple food and one of the major sources of dietary arsenic (As) and cadmium (Cd) in Asia. A field experiment was conducted to investigate the effects of four water management regimes (aerobic, intermittent irrigation, conventional irrigation and flooding) on As and Cd accumulation in seven major rice cultivars grown in Zhejiang province, east China. With increasing irrigation from aerobic to flooded conditions, the soil HCl-extractable As concentrations increased significantly and the HCl-extractable Cd concentrations decreased significantly. These trends were consistent with the As and Cd concentrations in the straw, husk and brown rice. Water management both before and after the full tillering stage affected As and Cd accumulation in the grains. The intermittent and conventional treatments produced higher grain yields than the aerobic and flooded treatments. Cd concentrations in brown rice varied 13.1–40.8 times and As varied 1.75–8.80 times among the four water management regimes. Cd and As accumulation in brown rice varied among the rice cultivars, with Guodao 6 (GD6) was a low Cd but high-As-accumulating cultivar while Indonesia (IR) and Yongyou 9 (YY9) were low As but high-Cd-accumulating cultivars. Brown rice Cd and As concentrations in the 7 cultivars were significantly negatively correlated. The results indicate that As and Cd accumulated in rice grains with opposite trends that were influenced by both water management and rice cultivar. Production of ‘safe’ rice with respect to As and Cd might be possible by balancing water management and rice cultivar according to the severity of soil pollution.

Repeated phytoextraction of four metal-contaminated soils using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

A cadmium/zinc hyperaccumulator extracted metals from four contaminated soils over three years in a glasshouse experiment. Changes in plant metal uptake and soil total (aqua regia-extractable) and available metals were investigated. Plant Cd concentrations in a high-Cd acid soil and plant Zn concentrations in two acid soils decreased during repeated phytoextraction and were predicted by soil available metal concentrations. However, on repeated phytoextraction, plant Cd concentrations remained constant in lightly Cd-polluted acid soils, as did plant Cd and Zn in alkaline soils, although soil available metal concentrations decreased markedly. After phytoextraction acid soils showed much higher total metal removal efficiencies, indicating possible suitability of phytoextraction for acid soils. However, DGT-testing, which takes soil metal re-supply into consideration, showed substantial removal of available metal and distinct decreases in metal supply capacity in alkaline soils after phytoextraction, suggesting that a strategy based on lowering the bioavailable contaminant might be feasible.

Effects of water management on arsenic and cadmium speciation and accumulation in an upland rice cultivar

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic (As) and cadmium (Cd) in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3-16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid (from 11.3% to 61.7%) made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal(loid)s in the grain of rice grown in soils polluted with both As and Cd.

Assessment of EDTA heap leaching of an agricultural soil highly contaminated with heavy metals

The efficiency of heavy metal removal from soil by EDTA leaching was assessed in a column leaching experiment at the laboratory scale and field heap leaching at the pilot scale using a sandy loam sierozem agricultural soil contaminated with Cd, Cu, Pb, and Zn. Soil amendment and aging were conducted to recover leaching soils. The percentages of Cd, Cu, Pb, and Zn removed by column leaching were 90%, 88%, 90%, and 67%, respectively, when 3.9 bed volumes of 50mM EDTA were used. At the pilot scale, on-site metal removal efficiencies using the selected leaching procedure were 80%, 69%, 73% and 62% for Cd, Cu, Pb and Zn, respectively. EDTA leaching decreased soil CEC, total P, total K and available K concentrations but increased organic matter and total Kjeldahl N concentrations. The subsequent amendment and soil aging further reduced the DTPA-extractable heavy metals in the leached soils. Growth of the first crop of pak choi in the leached soil was inhibited but the second crop grew well after the soil was aged for one year and the concentrations of Cd and Pb in the edible parts were below the Chinese statutory limits. The results demonstrate the potential feasibility of the field leaching technique using EDTA combined with subsequent amendment and soil aging for the remediation of heavy metal-contaminated agricultural soils.

Long-term field phytoextraction of zinc/cadmium contaminated soil by Sedum plumbizincicola under different agronomic strategies

abstract In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment “S. plumbizincicola intercropped with maize” was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha−1 gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.

Copper changes the yield and cadmium/zinc accumulation and cellular distribution in the cadmium/zinc hyperaccumulator Sedum plumbizincicola

Non-accumulated metals in mixed metal contaminated soils may affect hyperaccumulator growth and metal accumulation and thus remediation efficiency. Two hydroponics experiments were conducted to investigate the effects of copper (Cu) on cadmium (Cd) and zinc (Zn) accumulation by the Cd/Zn hyperaccumulator Sedum plumbizincicola, Cu toxicity and plant detoxification using chemical sequential extraction of metals, sub-cellular separation, micro synchrotron radiation based X-ray fluorescence, and transmission electron microscopy. Compared with the control (0.31 μM Cu), 5-50 μM Cu had no significant effect on Cd/Zn accumulation, but Cu at 200 μM induced root cell plasmolysis and disordered chloroplast structure. The plants held Cu in the roots and cell walls and complexed Cu in insoluble forms as their main detoxification mechanisms. Exposure to 200 μM Cu for 4 days inhibited plant Cd uptake and translocation but did not affect Zn concentrations in roots and stems. Moreover, unloading of Cd and Zn from stem to leaf was restrained compared to control plants, perhaps due to Cu accumulation in leaf veins. Copper may thus interfere with root Cd uptake and restrain Cd/Zn unloading to the leaves. Further investigation of how Cu affects plant metal uptake may help elucidate the Cd/Zn hyper-accumulating mechanisms of S. plumbizincicola.

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers, a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg−1 of Cd and 241 mg kg−1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH4)2SO4+DCD treatment produced higher NH4+−N concentrations in soil solution than the (NH4)2SO4 and NaNO3 treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg−1, respectively. The (NH4)2SO4+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO3 treatment. Plant shoots grown with NaNO3 had higher Cd concentrations than (NH4)2SO4+DCD treatment at 24.0 and 15.4 mg kg−1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.

Phytoremediation of Cadmium-Contaminated Soils Using the Cadmium and Zinc Hyperaccumulator Sedum plumbizincicola

Sedum plumbizincicola X. H. Guo et S. B. Zhou ex L. H. Wu (Crassulaceae), a new Sedum species, was firstly found in 2005 when our research team undertook extensive field investigations for searching metal hyperaccumulator species in Zhejiang Province. It was identified as new cadmium (Cd)/zinc (Zn) hyperaccumulator in 2007. During the past decade, great efforts have been taken to understand its metal-hyperaccumulating capacities, physiological metal hypertolerance and hyperaccumulation, enhancement of phytoextraction, and field application practice of phytoremediation. This paper provides a brief review on the progress on phytoremediation of Cd-contaminated soils using this species. Agronomic measures to enhance Cd and Zn phytoextraction efficiency by S. plumbizincicola were studied, including cultivation management, intercropping with other plant species, nutrient management, microbial assistant, and so on. Repeated phytoextraction of Cd- and Zn-contaminated soils using S. plumbizincicola was conducted in pot experiments to determine plant metal uptake, the changes of soil metal concentration and speciation, and soil microbial properties. So far, several research and demonstration bases have been established in numerous Chinese provinces including Zhejiang, Hunan, Henan, Jiangxi, Jiangsu, Guangdong, and Guizhou. Field assessment results confirmed that phytoextraction using S. plumbizincicola is a promising technique for the remediation of slightly Cd-polluted soils without halting normal agricultural production. Safe disposal or treatment of S. plumbizincicola biomass is also an important part for practical use of phytoextraction. Incineration and pyrolysis were employed to treat S. plumbizincicola biomass.

Element Case Studies: Cadmium and Zinc

Sedum plumbizincicola (Crassulaceae), a new Sedum species, was originally discovered in 2005 in Zhejiang Province, eastern PR China. It was identified as a Cd-Zn hyperaccumulator in 2007. During the past decade, great efforts have been made to understand its metal-accumulating capacities, physiological mechanisms for metal hypertolerance and hyperaccumulation, enhancing measures of phytoextraction, field application phytoremediation practice, and disposal of harvested biomass. This chapter provides a brief review of the progress on phytoremediation of Cd- and Zn-contaminated soils using this species. Agronomic measures to enhance Cd and Zn phytoextraction efficiency by S. plumbizincicola were studied, including cultivation management, intercropping with other plant species, and nutrient management. Changes in soil and plant metal uptake were investigated during long-term and repeated phytoextraction of Cd- and Zn-contaminated soils using S. plumbizincicola. Field assessment results confirm that phytoextraction using S. plumbizincicola is a promising technique for the remediation of slightly Cd-polluted soils without the need to halt normal agricultural production.

Modulation of the efficiency of trace metal phytoremediation by Sedum plumbizincicola by microbial community structure and function

AimsRecent research on the rhizosphere microbiome indicates that plants may benefit more from microbial communities than from individual members in a community. The link between soil microbiome and plant performance remains poorly understood during trace metal phytoremediation by hyperaccumulator plants. The effect of different microbiomes on the cadmium (Cd)/zinc (Zn) phytoextraction efficiency of Sedum plumbizincicola was therefore explored.MethodsDifferent microbiomes were set up using γ-irradiation and vancomycin addition and a pot experiment was conducted. The microbial communities were characterized using high-throughput sequencing and their functions were predicted.ResultsPlant Cd and Zn contents in the vancomycin-amended treatment were about 38–46% and 35%–53% respectively lower than those in the other treatments. Bacterial composition and diversity were substantially changed by γ-irradiation and vancomycin addition but plant trace metal accumulation did not change subsequently. The bacterial functional profiles were very different following treatment with vancomycin compared with the other treatments at KEGG orthology hierarchy level 3. Genes related to up-regulated biofilm formation and down-regulated siderophore synthesis may partly contribute together to the low plant trace metal accumulation following vancomycin treatment.ConclusionsSpecific bacterial community function rather than bacterial community diversity and composition may affect trace metal uptake by hyperaccumulator plants.