Enhanced removal of microplastics from wastewater treatment plants by a novel magnetic filter.

Microplastics (MPs) discharged from wastewater treatment plants (WWTPs) have emerged as serious pollutants in aquatic environments. Herein, a new magnetic filter (MFA) was prepared using an acidification-magnetization method with fly ash (FA) as the base material. The filter specifically targeted the removal of 1-µm polystyrene microspheres (PSMPs) because of the challenges they pose in filtration processes. The findings demonstrated that MFA filter exhibited superior PSMPs removal efficiency, with increases of 219%, 250%, and 288% compared to FA at flow rates of 1, 3, and 5 mL min-1, respectively. Scanning electron microscopy and other characterizations provided insights into the removal mechanisms of PSMPs using the MFA filter, which combined electrostatic attraction, π-electron conjugation, hydrogen bonding, and complexation. Environmental variables, such as solution pH, ionic strength, and dissolved organic matter, were identified as considerable influences in the removal process of PSMPs. The practical application confirmed that the MFA filter considerably promoted the elimination of MPs from the secondary treatment effluent of WWTPs without having any toxic effects on freshwater fish. Thus, this study provides a new approach to the resource utilization of FA, which would prominently promote its application prospects in MPs immobilization and removal from wastewater effluent.

A thorough investigation into the adsorption behavior of sophorolipid-modified fly ash towards compound pollution of lead and tetracycline.

Heavy metal ions and antibiotics were simultaneously detected in authentic water systems. This research, for the first time, employed synthesized sophorolipid-modified fly ash(SFA) to eliminate tetracycline(TC) and lead(Pb2+) from wastewater. Various characterization techniques, including SEM-EDS, FTIR, XPS, BET, and Zeta, were employed to investigate the properties of the SFA. The results showed that the sophorolipid modification significantly improved the fly ash's adsorption capacities for the target pollutants. The static adsorption experiments elucidated the adsorption behaviors of SFA towards TC and Pb2+ in single and binary systems, highlighting the effects of different Environmental factors on the adsorption behavior in both types of systems. In single systems, SFA exhibited a maximum adsorption capacity of 128.96 mg/g for Pb2+ and 55.57 mg/g for TC. The adsorption of Pb2+ and TC followed pseudo-second-order kinetics and Freundlich isotherm models. The adsorption reactions are endothermic and occur spontaneously. SFA demonstrates varying adsorption mechanisms for two different types of pollutants. In the case of Pb2+, the primary mechanisms include ion exchange, electrostatic interaction, cation-π interaction, and complexation, while TC primarily engages in hydrogen bonding, π-π interaction, and complexation. The interaction between Pb2+ and TC has been shown to improve adsorption efficiency at low concentrations. Additionally, adsorption-desorption experiments confirm the reliable cycling performance of modified fly ash, highlighting its potential as a cost-effective and efficient adsorbent for antibiotics and heavy metals.

Material flow analysis of heavy metals in large-scale cattle farms and ecological risk assessment of cattle manure application to fields.

This study bridges the knowledge gap pertaining to the pathways of heavy metal accumulation and migration within the industrial chain of large-scale cattle farms. Two such farms in Shaanxi serve as a basis for our exploration into Zn, Cu, Cr, Pb, As, and Cd dynamics. Employing material flow analysis complemented by predictive models, we evaluate the potential ecological risks of arable soil from heavy metal influx via manure application. Our findings indicate that Zn and Cu predominate the heavy metal export from these operations, composing up to 60.00%-95.67% of their total content. Predictive models based on 2021 data reveal a potential increase in Cd soil concentration by 0.08 mg/kg by 2035, insinuating a reduced safe usage period for cattle manure at less than 50 years. Conversely, projections from 2022 data point towards a gradual Cu rise in soil, reaching risk threshold levels after 126 years. These outcomes inform limitations in cattle manure utilisation strategies, underscoring Cu and Cd content as key barriers. The study underscores the criticality of continuous heavy metal surveillance within farm by products to ensure environmental protection and sustainable agricultural practices.

Enhancing the carbon content of coal gangue for composting through sludge amendment: A feasibility study.

Cocomposting coal gangue and sludge eliminates the challenge of utilizing coal gangue. However, there is limited understanding about the feasibility of cocomposting sludge and coal gangue, as well as the composting indicators, functional microorganisms, and safety risks involved. Therefore, this study evaluated the feasibility of enhancing carbon composting in coal gangue by incorporating sludge along with sawdust as a conditioner. Three laboratory-scale reactors were designed and labeled as T1 (20 % coal gangue, 60 % sludge, and 20 % sawdust), T2 (40 % coal gangue, 40 % sludge, and 20 % sawdust), and T3 (60 % coal gangue, 20 % sludge, and 20 % sawdust). Seed germination and plant growth assessments were conducted to ensure compost stability and assess phytotoxicity to cabbage (Brassica rapa chinensis L.) in terms of growth and biomass. The results indicated that the temperature, pH, EC and ammonia nitrogen of all three reactor conditions met the requirements for product decomposition. Composting was successfully achieved when the sludge proportion was 20 % (T3). However, when the sludge proportion was markedly high (T1), the harmlessness of the compost was reduced. The germination indices of T1, T2, and T3 reached 95 %, 122 %, and 119 % at maturity, respectively. This confirmed that the harmless cycle, which involved promoting condensation and aromatization, enhancing decay, and reducing composting time, was shorter in T2 and T3 than in T1. Coal gangue can also serve as a beneficial habitat for microorganisms, promoting an increase in their population and activity. Potting experiments in sandy soil revealed that the mechanism of action of compost products in soil included not only the enhancement of soil nutrients but also the improvement of soil texture. The results of this study suggest that using coal gangue as a raw material for composting is an efficient and environmentally friendly approach for producing organic fertilizers.

Remediation of Pb(II) and Cd(II) in polluted waters with calcium thioglycolate-modified straw biochar.

The pollution of water bodies by heavy metals (HMs) such as Pb(II) and Cd(II) poses a serious environmental risk. Herein, rice straw biochar (RBC) modified with calcium thioglycolate was used to remove Pb(II) and Cd(II) from aqueous solutions. The adsorption performance of the modified biochar was investigated via adsorption kinetics and isotherm model fitting. Furthermore, scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to elucidate the modification and adsorption mechanisms. The results showed that the modification process loaded sulfur-containing functional groups, calcium carbonate, and calcium oxalate crystals on the biochar surface, considerably enhancing its complexation performance and ion-exchange capacity. The equilibrium adsorption amounts for Pb(II) and Cd(II) reached 124.92 and 65.44 mg g-1 in unary systems, respectively; they reached 121.34 and 39.43 mg g-1 in a binary Pb(II) and Cd(II), respectively. Moreover, the optimal adsorption conditions were as follows: pH = 6, temperature = 25 °C, dosage = 0.8 g L-1, and contact time = 2 h. In the binary Pb(II) and Cd(II) system, the adsorption process obeyed the Langmuir competitive adsorption model, which means that one adsorption site on the modified biochar was effective for only one heavy-metal ion, and the modified biochar was more selective for Pb(II) than for Cd(II). The adsorption mechanism, which was dominated by chemisorption, mainly involved complexation, precipitation, ion exchange, and cation-π interactions. Meanwhile, adsorption and desorption experiments indicated that the modified biochar exhibited satisfactory recycling performance, demonstrating its feasibility as an inexpensive and efficient heavy-metal adsorbent for polluted water.

Utilization of KOH-modified fly ash for elimination from aqueous solutions of potentially toxic metal ions.

Long-term accumulation of toxic heavy metals in the environment was a potential hidden danger. High energy consumption, complicated operation and low adsorption capacity were the disadvantages of most current adsorbents. This study used one-step modification of fly ash (FA) by low-temperature melting method with KOH as the activator to generate modified fly ash (KFA) with high adsorption capacity to remove heavy metals from aqueous solutions. Various characterization results revealed a destruction that occurred on the surface structure of adsorbent, 12 times increase in specific surface area, and metal ions were successfully adsorbed onto KFA surface. Furthermore, adsorption proceeded most favorably at pH of 5, the presence of ionic strength and co-existing cations significantly influenced the adsorption effects. The description of adsorption data was more suitable by pseudo-second-order kinetics and Langmuir isotherm models. And in single system at 25 °C, for Pb(II), Cu(II), and Cd (II), the qm were 337.41, 310.09 and 125.00 mg·g-1. However, in ternary system, the qm decreased for all three ions in the order Pb(II) > Cu(II) > Cd(II), which was different from the law in single system, and the Pb(II) adsorption was found to have a significant inhibited effect on adsorption of Cd(II) and Cu(II). The adsorption mechanisms including ion exchange, electrostatic attraction and complexation were revealed. And by exploring the bioaccessibility of absorbed heavy metals in four simulated digestive fluids, it was found that KFA could load heavy metal ions and enable their release in organisms and other aquatic environments, which provided the possibility for subsequent related studies. Therefore, KFA with low energy consumption and high adsorption capacity is equipped a prospective development space on removing heavy metals from wastewater.

The role of available nitrogen in the adsorption of polystyrene nanoplastics on magnetic materials.

Several studies have been conducted on nanoplastics (NPs). However, few studies have investigated the complexity of the interactions between NPs and other aqueous pollutants in multi-solute media. In this study, the adsorption of polystyrene nanoplastics (PSNPs) on magnetic materials (MS) in the presence of available nitrogen (AN) was studied. The results demonstrated that the adsorbed amount of PSNPs increased in the presence of ammonium nitrogen (NH4+-N), whereas no significant difference was detected on the adsorbed amount of PSNPs using nitrate nitrogen (NO3--N) as a cosolute. The increase in the adsorbed amount of PSNPs was attributed to the formation of an MS-PSNPs-NH4+-N complex. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential analyses indicated that the PSNPs with NH4+-N as a cosolute can be bound on the MS surfaces. Moreover, the change in the PSNPs amount adsorbed by MS depends on the valence state, electronegativity of the coexisting ions, and the surface properties and functional groups of PSNPs. Additionally, the ionic strength, dissolved organic matter, solution pH, metal cations and the subsequent release of MS-coated PSNPs and NH4+-N changed considerably in different aquatic systems and artificial nitrating fluids. Among different natural aquatic systems, the PSNPs adsorption on MS was excellent in lake water. The results indicate high potential for the attachment of PSNPs to MS in the presence of AN and further deepen the understanding of removing NPs using magnetic materials in aqueous systems with various coexisting contaminants.

A 3-year field study on lead immobilisation in paddy soil by a novel active silicate amendment.

Lead (Pb) is a toxic metal in industrial production, which can seriously threat to human health and food safety. Thus, it is particularly crucial to reduce the content of Pb in the environment. In this study, raw fly ash (FA) was used to synthesise a new active silicate materials (IM) employing the low-temperature-assisted alkali (NaOH) roasting approach. The IM was further synthesised to form zeolite-A (ZA) using the hydrothermal method. The physicochemical characteristics of IM and ZA amendments before and after Pb2+ adsorption were analysed using the Scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) apparatuses. The results revealed the considerably change in the microstructure and functional groups of IM and ZA amendments, conducive to Pb2+ removal. Moreover, a 3-year field experiment revealed that the IM and ZA significantly improved the growth of rice and reduced available Pb by 21%-26.8% and 9.7%-16.9%, respectively. After 3 years of remediation, the Pb concentration of the rice grain reached the national edible standard (≤0.2 mg kg-1) of 0.171 mg kg-1 and 0.179 mg kg-1, respectively. Meanwhile, the concentration of acid-exchangeable Pb reduced, while those of reducible and residual fractions of Pb increased. There was no significant difference between the IM and ZA treatments. The potential mechanisms of remediation by the amendments were ion-exchange, complexation, precipitation, and electrostatic attraction. Overall, the results indicate that IM is suitable for the remediation of contaminated soil and promotes safe food production, and develops an environmentally friendly and cost-effective amendment for the remediation of polluted soil.

Use of Carbon Nanoparticles to Improve Soil Fertility, Crop Growth and Nutrient Uptake by Corn (Zea mays L.).

The use of carbon nanoparticles (CNPs) as a fertilizer synergist to enhance crop growth has attracted increasing interest. However, current understanding about plant growth and soil response to CNPs is limited. In the present study, we investigated the effects of CNPs at different application rates on soil properties, the plant growth and nutrient use efficiency (NUE) of corn (Zea mays L.) in two agricultural soils (Spodosol and Alfisol). The results showed that CNPs affected corn growth in a dose-dependent manner, augmenting and retarding growth at low and at high concentrations, respectively. The amendment at the optimal rate of 200 mg CNPs kg-1 significantly enhanced corn growth as indicated by improved plant height, biomass yield, nutrient uptake and nutrient use efficiency, which could be explained by the higher availability of phosphorus and nitrogen in the amended soils. The application of CNPs largely stimulated soil urease activity irrespectively of soil types. However, the responses of dehydrogenase and phosphatase to CNPs were dose dependent; their activity significantly increased with the increasing application rates of CNPs up to 200 mg kg-1 but declined at higher rates (>400 mg kg-1). These findings have important implications in the field application of CNPs for enhancing nutrient use efficiency and crop production in tropical/subtropical regions.

Effect and mechanisms of synthesis conditions on the cadmium adsorption capacity of modified fly ash.

In this study, modified coal fly ash (NMFA) was prepared by sodium hydroxide (NaOH) with low-temperature hydrothermal method. The differences of the ash to alkali mass ratio (5:3, 5:4, 5:5, 5:6), calcination temperature (100 â„ƒ, 200 â„ƒ, 300 â„ƒ), and calcination time (1 h, 3 h, 5 h) were investigated. The adsorption experiments obtained the optimal result with the ash to base ratio of 5:5, calcination temperature of 200 â„ƒ, and calcination time of 3 h, adsorbing 90.27 mg/g of Cd2+. The characterization results (SEM-EDS, FTIR, XRD, and XPS) also confirmed the effective adsorption of Cd2+ by NMFA. The functional groups of Si-O, Al-O, and Fe-O played an important role in Cd2+ removal. Meanwhile, the influences of dosage, different pH, and co-existing cations were also investigated. Quasi-secondary adsorption kinetics and Langmuir isotherm model were also referred to the Cd2+ adsorption by NMFA. Therefore, the good adsorption of NMFA-3 on Cd2+ provided new ideas for the safe utilization of fly ash and heavy metal purification in wastewater.

Effect of modified fly ash on environmental safety of two soils contaminated with cadmium and lead.

In this study, a low-temperature roasting and hydrothermal methods were used to modify the fly ash resulting in two new types of adsorption materials - modified fly ash (MFA) and artificial zeolite (ZE). These modified fly ashes, as well as a natural zeolite (ZO) were applied to two types of contaminated soils to explore their effects and mechanisms on the behavior of Cd and Pb through leaching column experiments. The bioavailable of Pb, Cd, pH, dissolved organic carbon (DOC), organic matter, as well as the microbial community changings were detected. The results showed that, 2% ZE has a significant stabilizing effect on Cd and the bioavailable fraction contents in Guanzhong (GZ) and Hunan (HN) soils decreased by 40.5% and 53.2%, respectively. However, for Pb, the 2% MFA showed a better result than that of ZE and ZO; the contents of bioavailable Pb in HN and GZ decreased by 48.3% and 30%, respectively. Furthermore, based on the Illumina NovaSep sequencing platform, 18 soil samples of GZ and HN were sequenced for microbial communities. As compared to the control blank(CK) treatment, the abundance of soil microbial communities was significantly improved in the amended soils.

Potential of using a new aluminosilicate amendment for the remediation of paddy soil co-contaminated with Cd and Pb.

Cadmium (Cd) and lead (Pb) are toxic heavy metals that impact human health and biodiversity. Removal of Cd/Pb from contaminated soils is a means for maintaining environmental sustainability and biodiversity. In this study, we applied a newly modified material fly ash (NA), zeolite (ZE), and fly ash (FA) to the paddy soils and evaluated the effects of Cd/Pb accumulation in rice via a one-year field experiment. The results showed that the application of NA and ZE enhanced the soil pH and nutrients to a large extent and reduced the availability of Cd/Pb in soil. The Cd and Pb concentrations in rice grains decreased by 32.8% and 62.9%, respectively, with the NA treatments. Similarly, the application of ZE reduced the Cd and Pb concentrations in rice grains by a factor of 27.9% and 63.5%, respectively, which indicates that the amendments can promote the transfer of Cd and Pb from acid-exchangeable fraction to oxidizable and residual fractions. The Cd/Pb showed a significant positive correlation to other metal ions and a negative correlation to the nutrients. Generally, the application of NA and ZE was effective in reducing Cd/Pb accumulation and improving rice yield. Moreover, the NA was more cost-effective than ZE. Hence, this study proves that NA may be a better amendment for remediation of Cd/Pb contaminated soils.

Potential of a novel modified gangue amendment to reduce cadmium uptake in lettuce (Lactuca sativa L.).

In this study, the modified gangue (GE) was prepared by calcination at lower temperatures using potassium hydroxide (KOH) as the activating agent. The field emission scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF) methods were employed to analyze the physicochemical characteristics of GE before and after the modification. Besides, the GE and commercial zeolite (ZE) were compared in the remediation of Cd-contaminated soil in field experiments. The results showed that both the GE and ZE had positive effects on the stabilization of Cd, decreasing the available Cd by 21.2-33.9% and 22.1-28.2%, respectively, while no significant difference was observed between the two amendments, indicating that the modification of GE was successful. Moreover, the application of GE decreased the Cd mobilization and uptake in lettuce shoot and root by 54.9-61.5% and 9.3-13.2%, respectively, and at the same time, the bio-available Cd decreased by 20.9-34.5%. Moreover, with the addition of GE, activities of urease and alkaline phosphatase increased in soil, while the peroxidase and superoxide dismutase activities were notably reduced in plants. Therefore, GE could be used as an effective amendment for the alleviation of Cd accumulation and toxicity, and thereby improve food safety.

Optimization of preparation technology for modified coal fly ash and its adsorption properties for Cd2.

This work focused on preparation a novel adsorbent from coal fly ash (CFA) and solid alkali (NaOH) by low temperature roasting method. The modification parameters (mass ratio, calcination time and temperature) were specifically studied and optimized. The adsorption experiment results indicated that, the adsorption amounts of Cd2+ were enhanced with the decreasing mass ratio of CFA and NaOH, and the adsorption amounts of Cd2+ were 32.44, 31.66, 38.5 and 79.85 mg/g at the mass ratio (CFA/NaOH) of 5:5, 5:6, 5:7 and 5:8, respectively. The higher modification temperature was not conducive to the removal of Cd2+, as the adsorption capacities of Cd2+ calculated were 62.42, 69.53 and 41.73 mg/g at the reaction temperature of 250, 300 and 400 ℃. Interestingly, the modification time slightly effects on the adsorption ability of materials. According to the results, the optimum modification condition for preparing adsorbents were CFA/NaOH mass ratio of 5:8 and calcined at 300 ℃ for 3 h. Moreover, the influence of pH, ionic strength and Glycine concentration on Cd2+ uptake were also investigated. The kinetic, adsorption isotherm and thermodynamics models were applied to investigate the adsorption mechanism, which indicated that the adsorption process was better fitted by Langmuir and pseudo-second-order models.

Potential of removing Cd(II) and Pb(II) from contaminated water using a newly modified fly ash.

Modified fly ash was prepared through low-temperature roasting method using NaOH as activator. The techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and the X-ray diffraction (XRD) were introduced to analyze the chemical and physical performance of samples, respectively. It was found that a significant improvements in activity and specific surface area of adsorbent. This work systematically reported the uptake performances of modified materials for single and two mixed toxic cations Pb(II) and Cd(II). The results unveiled that pseudo-second-order model was suitable to analyze the adsorption process. The adsorption process were better fitted by Langmuir model and the maximum uptake capacities were 126.55 and 56.31 mg g-1 for Pb(II) and Cd(II) in single system at 298 K, respectively. Additionally, in mixed solution, the maximum uptake capacity reduced to 120.48 and 36.10 mg g-1 under the same adsorption conditions. Competitive adsorption results demonstrated that adsorption ability was restricted by other metal ions, as while as, the binding affinity of two cations followed the order of Pb(II)>Cd(II). Meanwhile, the co-existed cations as Ca(II), Mg(II) Na(I) and K(I) had antagonistic effects on the uptake of Cd(II) and Pb(II). The results indicate that the modified fly ash was a low-cost and effective adsorbent for the cleaning up metal ions in wastewater, which has a promising application prospect.

Potential of enhancing the phytoremediation efficiency of Solanum nigrum L. by earthworms.

Contamination of the soil by Cadmium (Cd) is emerged as a critical environmental problem in China due to current urbanization and industrial activities that hinder the sustainable future development of agriculture. In this study, a system combined by earthworm and Solanum nigrum L. (S. nigurm) was designed for remediation of Cadmium from contaminated soils. The present study revealed that application of earthworm enhanced the biomass of S. nigrum by 61.71%, maxim; the Cd concentrations in the aboveground part of S. nigrum enhanced 35.8% when 50 g earthworm was added into each pot; the addition of earthworm also have some effect on the bio-concentration factor (BF) of S. nigrum while no effect was detected on the bio-transfer factor (TF). In addition, considering the accumulation of Cd by earthworm, the total amount of Cd extracted by the combined system enhanced 57.7% at least and 264.6% at the most, compared to the Cd extraction amount of S. nigrum alone. Generally, according to this study, the earthworm-S. nigrum system has the potential to be used for the remediation of Cd contaminated soils.

Possibility of removing cadmium pollution from the environment using a newly synthesized material coal fly ash.

Coal fly ash (FA) is a solid waste produced in coal combustion. This study focused on the removal of Cd2+ from wastewater by a newly synthesized adsorbent material, the low-temperature and sodium hydroxide-modified fly ash (SHM-FA). The SEM and BET analyses of SHM-FA demonstrated that the adsorbent was porous and had a huge specific surface area. The XRF, XRD, FTIR and TGA characterization showed that SHM-FA has an amorphous structure and the Si-O and Al-O in the fly ash dissolved into the solution, which improved the adsorption capacity of Cd. The results indicated that SHM-FA has desired adsorption performance. The adsorption performance was significantly affected by the dosage, starting pH, Cd2+ initial concentrations, and temperature, as well as adsorption time. In the optimal conditions, the removal efficiency and adsorption capacity of Cd2+ by SHM-FA were 95.76% and 31.79 mg g-1, respectively. The experiment provided clearly explained adsorption kinetics and isotherms. And the results confirmed that the adsorption behavior was well described by the pseudo-second-order kinetic and Langmuir isotherm model, which means that the adsorption of Cd2+ was controlled by SHM-FA through surface reaction and external diffusion process. In addition, the recycling of SHM-FA for reuse after Cd2+ adsorption showed high removal efficiency up to six times of use. Therefore, it can be concluded that SHM-FA is a low-cost adsorbent for Cd2+ removal from wastewater.

A two-year field study of phytoremediation using Solanum nigrum L. in China.

A two-year in-situ phytoremediation trial was launched in Shenyang Zhangshi (Sewage) Irrigation Area (SZIA). The phytoremediation efficiency of Solanum nigrum L. was determined, by both monitoring the change of soil Cadmium level in the upper 20 cm of soil, and calculating the plant uptake of soil Cd. After two years experimental, by monitoring the soil Cd concentrations, The Cd concentrations decreased on average from 2.75 mg kg(-1)to 2.45 mg kg(-1) in the first year and from 2.33 mg kg(-1) to 1.53 mg kg(-1) in the second year, amounting to a decrease by a factor of 10.6% in the first year and 12% in the second year. After two years phytoremediation by S. nigrum, Cd concentrations of the seven experimental plots with S. nigrum growth decreased from 2.75 mg kg(-1) to 1.53 mg kg(-1), a decrease by a factor of 24.9%. And the soil Cd concentration decreased only 2.1% and 1.7% in the bared experimental plot. And the calculating of Cd uptake by S. nigrum shown that, the plants uptake 4.46% and 5.18% of the total soil Cd in 2008 and 2009, while the soil Cd concentrations decreased by a factor of 10.6% in 2008 and 12.1% in 2009.

Cadmium uptake in above-ground parts of lettuce (Lactuca sativa L.).

Because of its high Cd uptake and translocation, lettuce is often used in Cd contamination studies. However, there is a lack of information on Cd accumulation in the above-ground parts of lettuce during the entire growing season. In this study, a field experiment was carried out in a Cd-contaminated area. Above-ground lettuce parts were sampled, and the Cd content was measured using a flame atomic absorption spectrophotometer (AAS). The results showed that the Cd concentration in the above-ground parts of lettuce increased from 2.70 to 3.62mgkg(-1) during the seedling stage, but decreased from 3.62 to 2.40mgkg(-1) during organogenesis and from 2.40 to 1.64mgkg(-1) during bolting. The mean Cd concentration during the seedling stage was significantly higher than that during organogenesis (a=0.05) and bolting (a=0.01). The Cd accumulation in the above-ground parts of an individual lettuce plant could be described by a sigmoidal curve. Cadmium uptake during organogenesis was highest (80% of the total), whereas that during bolting was only 4.34%. This research further reveals that for Rome lettuce: (1) the highest Cd content of above-ground parts occurred at the end of the seedling phase; (2) the best harvest time with respect to Cd phytoaccumulation is at the end of the organogenesis stage; and (3) the organogenesis stage is the most suitable time to enhance phytoaccumulation efficiency by adjusting the root:shoot ratio.

Potential of Gibberellic Acid 3 (GA3) for Enhancing the Phytoremediation Efficiency of Solanum nigrum L.

A microcosm experiment with artificially contaminated soils was conducted in a greenhouse to evaluate the effect of gibberellic acid 3 (GA3) on phytoremediation efficiency of Solanum nigrum L. The GA3 was applied at three different concentrations (10, 100, 1000 mg L(-1)) to S. nigrum. Results indicated that GA3 can significantly (p < 0.05) increase the biomass of S. nigrum by 56 % at 1000 mg L(-1). Concurrently, GA3 application increased Cd concentrations in the shoot of S. nigrum by 16 %. The combined effects resulted in an increase in the amount of Cd extracted by a single plant by up to 124 %. Therefore, it is possible to use GA3 to promote the Cd phytoremediation efficiency of S. nigrum.