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Rapid and safe treatment of harvested fresh biomass of hyperaccumulators is essential for phytoremediation of metal-contaminated soils. Here, an electro-Fenton (EF) process was used to remove cadmium (Cd) and chemical oxidation demand (COD) from waste liquor from the dewatering of biomass of the hyperaccumulator Sedum plumbizincicola after flocculation precipitation. The results showed that the order of impact of the factors on the removal rate of COD and Cd was pH > electrical current density > H2O2 dosage. Increasing pH promoted Cd removal but hindered COD removal. As current density and H2O2 dosage increased the removal rates of both Cd and COD initially increased and then decreased. Compared to an electrocoagulation process, the addition of H2O2 in EF process greatly enhanced Cd and zinc (Zn) removal. Speciation analysis showed that most of the Cd and Zn in the initial liquor were organically and inorganically complexed. At optimal conditions, e.g., pH 5, current density 15 mA cm−2 and H2O2 dosage 9 g L−1, the removal efficiencies of Cd, Zn and COD reached 99.4, 99.9 and 55.5% after 80 min of EF treatment. Electro-Fenton process can therefore be used to quickly remove trace metals from the waste liquor of the hyperaccumulator. [ABSTRACT FROM AUTHOR]

Agricultural soil contaminated with potentially toxic metals poses great health risk to humans and it requires long-term remediation. Here, we investigate the remediation of metal-polluted agricultural soil by combining chemical washing with repeated phytoextraction. The polluted field was initially washed with 40 mmol L−1 FeCl3 (F) or 20 mmol L−1 FeCl3 + 40 mmol L−1 citric acid (F + C). After the application of organic fertilizer (O), lime (L), and sepiolite (S), Sedum plumbizincicola was cultivated for three successive crops from 2017 to 2019. Results showed that the soil washed with FeCl3 had high removal efficiencies of Cd (35.2%), Pb (24.3%), and Zn (26.6%). Although the shoot biomass and metal concentrations of S. plumbizincicola decreased significantly in the first crop, there were no significant differences in the subsequent two crops. Throughout the remediation process, the higher total removal efficiencies of Cd, Pb, and Zn were conducted in F + OLS treatment which observed in 71.0, 34.0, and 47.7%, respectively. The results, therefore, conclusively indicated that combining chemical washing with repeated phytoextraction showed considerable potential for the remediation of agricultural soils polluted with multiple metals. However, further studies are required to focus on the amelioration of the degraded soil quality and safe agricultural production. [ABSTRACT FROM AUTHOR]

A three-crop repeated phytoextraction experiment was conducted using four soils (S1-S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator Sedum plumbizincicola. Shoot biomass showed no significant difference during the repeated phytoextraction experiment on the four test soils and shoot Cd content showed a decreasing trend with the three consecutive crops in soils S1, S2, and S3 but not in soil S4. The Cd removal rates in soils S1, S2, S3, and S4 were 84.5, 81.6, 45.3, and 32.4%, respectively. Rice straw application increased Cd extraction efficiency by 42.6% but the addition of ethylenediaminedisuccinic acid, biochar or nitrogen had no effect on Cd remediation. Shoot Cd content increased significantly (1.57 and 1.71 times, respectively) at low (S0-1) and high (S0-2) sulfur addition rates. Soil extractable-Cd in S0-1 after the experiment showed no significant difference from the control but was 2.43 times higher in S0-2 than in the control. These results indicate that S. plumbizincicola shows good prospects for the phytoextraction of Cd from highly polluted soils and that the process can be enhanced by adding straw and/or sulfur to the soil. [ABSTRACT FROM AUTHOR]

Differences in growth conditions in the glasshouse and in the field may affect the consistency of phytoextraction results. Two crops of the hyperaccumulator Sedum plumbizincicola were grown in six contrasting soils in pot experiments under three different sets of growth conditions (glasshouse, polytunnel and field) to compare the phytoextraction of cadmium (Cd) and zinc (Zn). The total shoot biomass of two crops in the glasshouse was significantly smaller than in the polytunnel or field. However, in general there were no significant differences in total shoot metal uptake of two crops per pot among three sets of growth conditions. And greater decreases in soil metal than plant uptake in the polytunnel and field in an acid soil indicate high leaching losses of soil metals in the polytunnel and field, and this was confirmed by analysis of metal concentrations in soil profiles. This brings into question on the validity of estimating the practical applicability of phytoextraction based only on plant metal uptake in glasshouse conditions. It is advisable to examine leaching losses in acid soils in the field when estimating the duration of phytoextraction. [ABSTRACT FROM AUTHOR]

Most studies on the phytoextraction of cadmium (Cd) and zinc (Zn) by the hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) have been conducted in metal contaminated acidic and neutral soils. However, little information is available on phytoremediation of calcareous soils. Two experiments were conducted to investigate the phytoextraction efficiency of S. plumbizincicola in a contaminated calcareous soil in He'nan province, north China. In a field experiment there was no significant decrease in shoot biomass production or metal (Cd and Zn) concentration in the shoots after three successive repeated phytoextractions. Repeated phytoextraction had no significant effect on the percentage distribution of Cd or Zn fractions in the soil even though the soil total Cd and Zn concentrations decreased by 32.8 and 19.7%, respectively. In a pot experiment the shoot biomass production and Zn and Cd uptake by S. plumbizincicola increased significantly with growth in metal contaminated calcareous soil amended with organic fertilizer, perlite and vermiculite. The results indicate that S. plumbizincicola can maintain sustainable uptake of Cd and Zn from the calcareous soil and enhancement of soil fertility and structure will significantly increase the phytoextraction efficiency. [ABSTRACT FROM AUTHOR]

The accumulation, chemical speciation and distribution of polychlorinated biphenyls (PCBs) were investigated in various parts of alfalfa. Moreover, the adsorption characteristics for PCB 28 by alfalfa and the influencing factors of the adsorption characteristics were studied. There were different degrees of PCB accumulation in alfalfa roots, root nodules and shoots. The decreasing order of the accumulation of PCBs in plant tissues was root nodules > roots > shoots, and the decreasing order of the total PCB contents was roots > shoots > root nodules, indicating that the roots were the main sink for PCB accumulation. There were three modes of PCB speciation in alfalfa roots and root nodules, comprising strong sorption (78%) and weak sorption (19%) on tissue surfaces and absorption within tissues (2%). The adsorption isotherms of PCB 28 indicate that the adsorption capacities of root nodules and shoots were both significantly higher than that of the roots. Both lipids and carbohydrates, and especially lipids, affected the PCB adsorption capacities of the tissues. These results may help in the elucidation of the mechanisms of sorption and accumulation of PCBs in the plants and their main influencing factors and thus contribute to the development of phytoremediation technologies for PCB-contaminated soils. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to explore the phytoremediation of a diphenylarsinic acid (DPAA)-spiked soil usingPteris vittataassociated with exogenousPhyllobacterium myrsinacearumRC6b. Removal of DPAA from the soil, soil enzyme activities, and the functional diversity of the soil microbial community were evaluated. DPAA concentrations in soil treated with the fern or the bacterium were 35–47% lower than that in the control and were lowest in soil treated withP. vittataandP. myrsinacearumtogether. The presence of the bacterium added in the soil significantly increased the plant growth and DPAA accumulation. In addition, the activities of dehydrogenase and fluorescein diacetate hydrolysis and the average well-color development values increased by 41–91%, 37–78%, and 35–73%, respectively, in the treatments withP. vittataand/orP. myrsinacearumcompared with the control, with the highest increase in the presence ofP. vittataandP. myrsinacearumtogether. Both fern and bacterium alone greatly enhanced the removal of DPAA and the recovery of soil ecological function and these effects were further enhanced byP. vittataandP. myrsinacearumtogether. Our findings provide a new strategy for remediation of DPAA-contaminated soil by using a hyperaccumulator/microbial inoculant alternative to traditional physicochemical method or biological degradation. [ABSTRACT FROM PUBLISHER]

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulatorSedum 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. plumbizincicolaintercropped with maize” was higher than inS. plumbizincicolamonocropping, 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−1gave the maximum rate. These results indicated thatS. plumbizincicolaat 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. [ABSTRACT FROM AUTHOR]

Long-term application of sewage sludge resulted in soil cadmium (Cd) and zinc (Zn) contamination in a pot experiment conducted to phytoextract Cd/Zn repeatedly usingSedum plumbizincicolaandApium graceolensin monoculture or intercropping mode eight times. Shoot yields and soil physicochemical properties changed markedly with increasing number of remediation crops when the two plant species were intercropped compared with the unplanted control soil and the two monoculture treatments. Changes in soil microbial indices such as average well colour development, soil enzyme activity and soil microbial counts were also significantly affected by the growth of the remediation plants, especially intercropping withS. plumbizincicolaandA. graveolens. The higher yields and amounts of Cd taken up indicated that intercropping of the hyperaccumulator and the vegetable species may be suitable for simultaneous agricultural production and soil remediation, with larger crop yields and higher phytoremediation efficiencies than under monoculture conditions. [ABSTRACT FROM PUBLISHER]

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction bySedum plumbizincicolausing 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−1of Cd and 241 mg kg−1Zn. 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)2SO4and NaNO3treatment 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 NaNO3treatment. Plant shoots grown with NaNO3had 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. [ABSTRACT FROM PUBLISHER]

A glasshouse pot experiment was conducted to study the effects of phytoextraction bySedum plumbizincicolaand application of rapeseed cake (RSC) on heavy metal accumulation by a subsequent rice(Oryza sativa L.)crop in a contaminated paddy soil collected from east China. After phytoextraction byS. plumbizincicolathe soil and brown rice Cd concentrations effectively declined. After phytoextraction, RSC application reduced brown rice Cd concentrations in the subsequent rice crop to 0.23–0.28 mg kg−1, almost down to the standard limit (0.2 mg kg−1). After phytoextraction and then application of RSC, the soil solution pH, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations increased during early stages of rice growth resulting directly and indirectly in lowering the bioavailability of the heavy metals. Thus the grain yield of the subsequent rice crop increased and the heavy metals in the brown rice declined significantly. In this contaminated acid soil, growing the hyperaccumulatorS. plumbizincicolaand rice in rotation together with RSC application may therefore be regarded as a viable strategy for safe grain production and bioremediation. [ABSTRACT FROM PUBLISHER]

A field experiment was conducted to study the phytoremediation of phthalic acid esters (PAEs) by legume (alfalfa, Medicago sativa L.)-grass (perennial ryegrass, Lolium perenne L. and tall fescue, Festuca arundinacea) intercropping in contaminated agricultural soil at one of the largest e-waste recycling sites in China. Two compounds, DEHP and DnBP, were present in the soil and in the shoots of the test plants at much higher concentrations than the other target PAEs studied. Over 80% of ‘total’ (i.e., all six) PAEs were removed from the soil across all treatments by the end of the experiment. Alfalfa in monoculture removed over 90% of PAEs and alfalfa in the intercrop of the three plant species contained the highest shoot concentration of total PAEs of about 4.7 mg kg−1 DW (dry weight). Calculation of phytoextraction efficiency indicated that the most effective plant combinations in eliminating soil PAEs were the three-species intercrop (1.78%) and the alfalfa monocrop (1.41%). Phytoremediation with alfalfa was effective in both monoculture and intercropping. High bioconcentration factors (BCFs) indicated the occurrence of significant extraction of PAEs by plants from soil, suggesting that phytoremediation may have potential for the removal of PAEs from contaminated soils. [ABSTRACT FROM PUBLISHER]

Organic materials with different functional groups can be used to enhance metal bioavailability. Traditional organic materials (rice straw and clover) and ethylenediamine disuccinic acid (EDDS) were applied to enhance metal uptake from polluted soil by Sedum plumbizincicola after repeated phytoextraction. Changes in pH, dissolved organic carbon (DOC) and metal concentrations were determined in the soil solution after EDDS application. Amendment of the soil with ground rice straw or ground clove resulted in higher concentrations of Cd only (by factors of 1.92 and 1.71 respectively) in S. plumbizincicola compared to control soil. Treatment with 3 mmol kg−1 EDDS increased all the metals studied by factors of 60.4, 1.67, and 0.27 for Cu, Cd, and Zn, respectively. EDDS significantly increased soil solution DOC and pH and increased soil plant-available metals above the amounts that the plants could take up, resulting in high soil concentrations of soluble metals and high risk of ground water contamination. After repeated phytoremediation of metal contaminated soils the efficiency of metal removal declines as the concentrations of bioavailable metal fractions decline. Traditional organic materials can therefore be much more effective and environmentally friendly amendments than EDDS in enhancing phytoremediation efficiency of Cd contaminated soil. [ABSTRACT FROM PUBLISHER]

A pot experiment and a field trial were conducted to study the remediation of an aged field soil contaminated with cadmium, copper and polychlorinated biphenyls (PCBs) (7.67 ± 0.51 mg kg−1 Cd, 369 ± 1 mg kg−1 Cu in pot experiment; 8.46 ± 0.31 mg kg−1 Cd, 468 ± 7 mg kg−1 Cu, 323 ± 12 μg kg−1 PCBs for field experiment) under different cropping patterns. In the pot experiment Sedum plumbizincicola showed pronounced Cd phytoextraction. After two periods (14 months) of cropping the Cd removal rates in these two treatments were 52.2 ± 12.0 and 56.1 ± 9.1%, respectively. Total soil PCBs in unplanted control pots decreased from 323 ± 11 to 49.3 ± 6.6 μg kg−1, but with no significant difference between treatments. The field microcosm experiment intercropping of three plant species reduced the yield of S. plumbizincicola, with a consequent decrease in soil Cd removal. S. plumbizincicola intercropped with E. splendens had the highest shoot Cd uptake (18.5 ± 1.8 mg pot−1) after 6 months planting followed by intercropping with M. sativa (15.9 ± 1.9 mg pot−1). Liming with S. plumbizincicola intercropped with M. sativa significantly promoted soil PCB degradation by 25.2%. Thus, adjustment of soil pH to 5.56 combined with intercropping with S. plumbizincicola and M. sativa gave high removal rates of Cd, Cu, and PCBs. [ABSTRACT FROM AUTHOR]

A growth chamber pot experiment and a field plot experiment were conducted with the installation of rhizobags to study the effects of repeated phytoextraction by Sedum plumbizincicola on the bioavailability of Cd and Zn in the rhizosphere and bulk soil. Repeated phytoextraction gave significantly lower Cd and Zn concentrations in both rhizosphere and bulk soil solutions compared with soil without repeated phytoextraction. The depletion rates of NH4OAc-extractable Zn in rhizosphere soil in each treatment (L-PS, L-NPS, H-PS, and H-NPS) were 59.7, 18.0, 16.3, and 18.6%, respectively. For NH4OAc-extractable Cd, the depletion rates in treatments L-PS, L-NPS, H-PS, and H-NPS were 6.67, 29.4, 40.3, and 41.4%, respectively. Plant shoot biomass decreased in the order H-PS > H-NPS > L-PS > L-NPS, with dry weights of 0.56, 0.42, 1.43, and 1.21 g pot-1, respectively. Plant Cd uptake increased with increasing aqua-regia extractable metal concentrations. The NH4OAc extraction procedure was satisfactory to predict the bioavailability of Cd and Zn in rhizosphere soil in terms of shoot uptake by S. plumbizincicola with positive correlation coefficients of 0.545 (p < 0.05) and 0.452 (p < 0.05), respectively. The field study results show a slight decrease in water soluble and NH4OAc-extractable metals, a trend similar to that found in the pot experiment. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of inoculation with the arbuscular mycorrhizal fungus Glomus caledonium and/or Rhizobium meliloti on phytoremediation of an agricultural soil contaminated with weathered PCBs by alfalfa grown for 180 days. Planting alfalfa (P), alfalfa inoculated with G. caledonium (P+AM), alfalfa inoculated with R. meliloti (P+R), and alfalfa co-inoculated with R. meliloti and G. caledonium (P+AM+R) decreased significantly initial soil PCB concentrations by 8.1, 12.0, 33.8, and 43.5%, respectively. Inoculation with R. meliloti and/or G. caledonium (P+AM+R) increased the yield of alfalfa, and the accumulation of PCBs in the shoots. Soil microbial counts and the carbon utilization ability of the soil microbial community increased when alfalfa was inoculated with R. meliloti and/or G. caledonium. Results of this field study suggest that synergistic interactions between AMF and Rhizobium may have great potential to enhance phytoremediation by alfalfa of an agricultural soil contaminated with weathered PCBs. [ABSTRACT FROM AUTHOR]

Field survey, hydroponic culture, and pot experiments were carried out to examine and characterize cadmium (Cd) and zinc (Zn) uptake and accumulation by Sedum jinianum, a plant species native to China. Shoot Cd and Zn concentrations in S. jinianum growing on a lead/Zn mine area reached 103-478 and 4165-8349 mg kg-1 (DM), respectively. The shoot Cd concentration increased with the increasing Cd supply, peaking at 5083 mg kg-1 (DM) when grown in nutrient at a concentration of 100 µmol L-1 for 32 d, and decreased as the solution concentration increased from 200 to 400 µmol L-1. The shoot-to-root ratio of plant Cd concentrations was > 1 when grown in solution Cd concentrations = 200 µmol L-1. Foliar, stem, and root Zn concentrations increased linearly with the increasing Zn level from 1 to 9600 µmol L-1. The Zn concentrations in various plant parts decreased in the order roots > stem > leaves, with maximum concentrations of 19.3, 33.8, and 46.1 g kg-1 (DM), respectively, when plants were grown at 9600 µmol Zn L-1 for 32 d. Shoot Cd concentrations reached 16.4 and 79.8 mg kg-1 (DM) when plants were grown in the pots of soil with Cd levels of 2.4mg kg-1 and 9.2 mg kg-1, respectively. At soil Zn levels of 619 and 4082 mg kg-1, shoot Zn concentrations reached 1560 and 15,558 mg kg-1 (DM), respectively. The results indicate that S. jinianum is a Cd hyperaccumulator with a high capacity to accumulate Zn in the shoots. [ABSTRACT FROM AUTHOR]