Phosphorus fractions and iron oxides responsible for the variations in the Cd retention capacity in tropical soil aggregates under different cropping patterns.

The environmental behavior of Cd in soil has been widely studied because of its close relationship with food security and soil environmental pollution. In this study, the roles of P fractions and Fe oxides in the retention of Cd in typical tropical soil from five cropping patterns were investigated. Although there was no evident relationship between the Cd adsorption capacity and soil aggregate particle sizes, strong spatial associations of P, Fe, and Cd at the soil aggregates were observed via energy dispersive spectroscopy analysis. Among five cropping patterns, citrus plantations exhibited highest ratios (calculated by pixel area) of P overlapped with Cd (8.61%) and Fe overlapped with Cd (9.53%) in the microaggregates. Furthermore, the random forest model revealed that humic P and labile organic P greatly contributed to the sorptivity of Cd2+ by < 0.053 mm (13.3%) and 0.25-0.053 mm (13.4%) soil aggregates, respectively. Compared with the P fractions in different-sized soil aggregates, the contribution of Fe oxides to the sorption of Cd2+ by soil aggregates was more significant. Amorphous ferric oxide had the most significant contribution to the sorptivity of Cd2+ by < 0.053 mm (26.0%), 0.25-0.053 mm (23.0%), 2.0-0.25 mm (25.1%), and > 2.0 mm (33.9%) soil aggregates.

A review on the thermal treatment of heavy metal hyperaccumulator: Fates of heavy metals and generation of products.

Phytoremediation is perceived as a promising technique for remediation of heavy metal (HM) contaminated soils, while the harvested HM-enriched hyperaccumulator biomass should be appropriately disposed. Recently, various thermal treatments of hyperaccumulator have drawn increasing attention. After thermal treatment, the hyperaccumulator was converted to bio-oil, bio-gas, biochar, or ash in accordance with the corresponding conditions, and the HMs were separated, immobilized, or trapped. The migration and transformation of HMs during the thermochemical conversion processes are critical for the safe disposal and further utilization of HM hyperaccumulator. This paper provides a systematic review on the migration and transformation of typical HMs (Cd, Ni, Mn, As, and Zn) in hyperaccumulator during various thermochemical conversion processes, and special emphasis is given to the production and application of targeted products (e.g. biochar, hydrochar, bio-oil, and syngas). Besides, future challenges and perspectives in the thermal treatment of hyperaccumulator are presented as well. The distribution and speciation of HMs were influenced by thermal technique type and reaction conditions, thereby affecting the utilization of the derived products. This review suggests that speciation and availability of HMs in hyperaccumulator are tunable by varying treatment techniques and reaction conditions. This information should be useful for the selective conversion of hyperaccumulator into green and valuable products.

Foliar application of zinc and selenium alleviates cadmium and lead toxicity of water spinach - Bioavailability/cytotoxicity study with human cell lines.

The present study investigated the effects of foliar application of zinc (Zn) and selenium (Se) on bioavailability of Zn and Se and toxicity of cadmium (Cd) and lead (Pb) to different water spinach ecotypes (LA and HA) grown in slightly (XZ) or moderately (LJY) contaminated fields via in vitro digestion combined with Caco-2/HL-7702 cell model. The obtained results revealed that foliar application of Zn and Se promoted yield, increased total, bioaccessible and bioavailable fractions of Zn and Se in plants, indicating that foliar application is a feasible way of biofortification. Although there was no significant effect on liver cell proliferation (MTT), membrane stability (LDH) and hepatocyte enzyme (ALT and AST) activities, the obvious ecotype and soil dependent fluctuations of lipid peroxidation (MDA) and antioxidant enzyme (SOD, POD and CAT) activities in serum highly suggest that the low accumulator and clean field should be used in agricultural production rather than the high accumulator and contaminated farmland. Moreover, foliar application of Zn and Se improved nutritional quality of all water spinach genotypes in both fields, including increased Fe, vitamin C, cellulose and chlorophyll, maintained concentrations of potassium (K), manganese (Mn), copper (Cu), protein, and nitrate. These results demonstrate that this agricultural management practice may prove to be an effective approach for minimizing health risk and alleviating "hidden hunger" in the developing countries.

Biomass decay rate and influencing factors of four submerged aquatic vegetation in Everglades wetland.

Submerged aquatic vegetation (SAV) enhances assimilation efficiency of nutrients in wetlands, and improves the water quality, but may serve as secondary sources when their litter residues are decomposed. A laboratory incubation was conducted to investigate the biomass decay rate of four common SAV species: Hydrilla (Hydrilla verticillata), Naiad (Najas guadalupensis), Potamogeton (P. illinoensis), and Chara (Chara spp). Plant biomass samples were collected from the stormwater treatment areas in south Florida, USA and incubated in water at 40 °C for 126 days. At the end of incubation, the mixtures were passed through a 1 m sieve, and the plant debris above the screen were rinsed, oven-dried, and weighed. Biomass (dry matter) was measured and the decay rate was calculated, and total concentration of carbon (C), nitrogen (N), phosphorus (P) and other elements (K, Na, Ca, Mg, Al, Fe, and Mn) in the SAV plants were determined. Subsamples (5 mL) of the suspension (representing floc solution) were used for bacteria and fungi colony counting. The relationships between the decay rate and nutrient features or chemical components were analyzed. The results showed that Hydrilla had the highest decay rate (0.007930 d-1), and Chara had the lowest (0.002798 d-1). Concentrations of N, P, C and cations (K, Na, and Mn), and the ratio (K + Na)/(Ca + Al) in the SAVs had positive correlations with the biomass decay rate, whereas concentrations of Ca and Al, and the ratios of C/N and C/P in the plants were negatively correlated with the decay rate. However, the effect of microorganisms in the biomass decay rate of SAVs was not significant. These results suggest that high C concentration and more Ca and Al in the plant tissues can retard SAV biomass decomposition.

Foliage application of selenium and silicon nanoparticles alleviates Cd and Pb toxicity in rice (Oryza sativa L.).

Direct discharge of untreated industrial waste water in water bodies and then irrigation from these sources has increased trace metals contamination in paddy fields of southern China. Among trace metals, cadmium (Cd) and lead (Pb) are classified as most harmful contaminants in farmland to many organisms including plants, animals and humans. Rice is a staple food which is consumed by half population of the world; due to longer growth period it can easily absorb and accumulate the trace metals from soil. The objective of study was to check the efficacy of Se and Si NPs (nanoparticles) alone or in combination on metals accumulation and Se-fortified rice (Oryzasativa L.) production as their efficiency remained untested. Alone as well as combined application of Se- and Si-NPs (5, 10 and 20 mg L-1) was achieved along with CK. All the treatments significantly reduced the Cd and Pb contents in brown rice, except CK, Se3, Si1 and Se1Si3. Combined application of Se and Si (Se3Si2) was more effective in reducing the Cd and Pb contents by 62 and 52%, respectively. In addition, foliar application of both NPs improved the rice growth and quality by increasing the grain yield, rice biomass, and Se contents in brown rice. Highest concentration of Se (1.35 mg kg-1) in brown rice was observed with combined application of Se- and Si-Nps (Se3Si2). Selenium speciation revealed the presence of organic species (74%) in brown rice. The combinations of different doses of Se- and Si-Nps are the main determining factor for total concentration of metals in grains. These results demonstrate that foliage supplementation of Se and Si-Nps alleviate the Cd and Pb toxicity by reducing the metals' concentration in brown rice. Additionally foliage supplementation improved the nutritional quality by reducing the phytic acid contents in rice grains.

Hydrothermal carbonization of different wetland biomass wastes: Phosphorus reclamation and hydrochar production.

Hydrothermal carbonization (HTC) has drawn increasing interest for the disposal of solid wastes with a high moisture content, while minimal attention has been paid to HTC treatment of wetland plants and the corresponding phosphorus (P) transformation. In order to evaluate its feasibility for wetland plants treatment, hydrochars from different wetland plants were produced at different temperatures (200 °C, 220 °C, 240 °C, and 260 °C) and characterized, and the transformation of P was investigated. In comparison with wetland plant derived biochars, the derived hydrochars had a moderate pH (5.0-7.7), more oxygen-containing groups, and higher energy density (18.0-27.1 MJ kg-1). These properties were affected by hydrothermal temperature and feedstock choice. In contrast to high water-soluble P in biomass (71.0-73.2% of total P), more recalcitrant P species formed in hydrochars, implying that HTC treatment could achieve P immobilization and reduce P leaching loss. Nuclear magnetic resonance (NMR) results indicated that monoester-P and soluble orthophosphate were transformed to insoluble orthophosphate during the HTC treatment. Therefore, HTC is a promising treatment technique for wetland plants to produce valuable char with P reclamation.

Identification of high cadmium-accumulating oilseed sunflower (Helianthus annuus) cultivars for phytoremediation of an Oxisol and an Inceptisol.

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.

Activated dolomite phosphate rock fertilizers to reduce leaching of phosphorus and trace metals as compared to superphosphate.

Use of water-soluble phosphorus (P) fertilizers such as superphosphates (SP) has been increasingly concerned due to the loss of P and trace metals such as cadmium (Cd) into the environment. Activated phosphate rock holds promising as an alternate due to non-destructive and slow release nature. The objective of this study was to assess the leaching potential of P and trace metals from newly developed activated dolomite phosphate rock (HA-DPR and SLS-DPR), as compared to water-soluble fertilizers, including superphosphate (SP), diammonium phosphate (DAP) and original dolomite phosphate rock (DPR). Two representative agricultural soils (Alfisol and Spodosol soil) were sampled at the 0-20 cm depth from two farms for the column leaching experiments. Seven leachings were conducted at day 1, 3, 7, 14, 21, 28, and 56, respectively, and a total of 1050 mL of deionized water (equivalent to half year's rainfall in the Indian River area) was applied for leaching. Leachates were collected from each leaching event and analyzed for water-soluble P and metals. Activated DPR application led to an increase in soil pH by 1.4-1.7 units, whereas SP resulted in a decrease in soil pH by 0.4-1.6 units. P leaching from activated DPR were 33-61 times less than that from SP or DAP. HA-DPR and SLS-DPR treatments reduced cumulative trace metals in leachate by 1.3-12.3 times for the Alfisol soil, and 1.4 to 8.4 times for the Spodosol soil, respectively. These results indicate that activated DPR fertilizers are more environmentally friendly than water-soluble fertilizers.

Effect of lead on plant availability of phosphorus and potassium in a vegetable-soil system.

Two typical red soils were sequentially cultivated with celery (Apium graveolens L.) and Chinese cabbage (Brassica chinensis L.) in a greenhouse to determine the effect of lead (Pb) on plant availability of phosphorus (P) and potassium (K) in the soils. The concentrations of available P as estimated by the 0.05 mol L-1 HCl-0.025 mol L-1 (1/2 H2SO4) extraction and available K estimated by the NH4OAc extraction method in the crop-free soils were not affected by Pb treatment. Plant P concentrations in the above-ground part of celery and Chinese cabbage exposed to Pb were either lower or showed no significant difference to the control.

Inhibition of the bioavailability of heavy metals in sewage sludge biochar by adding two stabilizers.

Agricultural application of sewage sludge (SS) after carbonization is a plausible way for disposal. Despite its benefits of improving soil fertility and C sequestration, heavy metals contained in sewage sludge biochars (SSB) are still a concern. In this study, two types of heavy metal stabilizers were chosen: fulvic acid (FA) and phosphogypsum (with CaSO4, CS, as the main component). The two stabilizers were incorporated into SS prior to 350°C carbonization for 1 h at the rates of 1%, 2%, or 4%. The obtained SSBs were then analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Total and available concentrations of four heavy metals, i.e., Zn, Pb, Cd, and Ni, in the SSBs were determined. In addition, a series of pot soil culture experiments was conducted to investigate the effects of stabilizers incorporation into SSB on heavy metal bioavailability and the uptake by plants (corn as an indicator) and plant biomass yield, with SS and SSB (no stabilizers) as controls. The results showed that incorporation of both FA and CS increased functional groups such as carboxyl, phenol, hydroxyl, amine and quinine groups in the SSBs. The percentage of heavy metals in sulfuric and oxidizable state and residual state of SSBs were significantly increased after carbonization, and hence the mobility of the heavy metals in SSBs was decreased. The introduction of the stabilizers (i.e., FA or CS) significantly lowered the total and available concentrations of Zn, Pb, Cd, and Ni. The reduction in available heavy metal concentration increased with incorporation rate of the stabilizers from 1% to 4%. In the treatments with FA or CS incorporated SSB, less heavy metals were taken up by plants and more plant biomass yields were obtained. The mitigating effects were more pronounced at higher rates of FA or CS stabilizer. These findings provide a way to lower bioavailability of heavy metals in SS or SSB for land application or horticulture as a peat substitute.

Fertilization using sewage sludge in unfertile tropical soils increased wood production in Eucalyptus plantations.

Fertilization of Eucalyptus plantations using sewage sludge on unfertile tropical soils represents an alternative to using mineral N and P fertilizers. A 44-month field experiment was conducted to study the effects of increasing application of sludge, and its interactions with mineral N and P fertilizers, on wood volume. Four rates of sludge (0, 8, 15 and 23 Mg ha-1, dry base), N (0, 47, 95 and 142 kg ha-1) and P (0, 28, 56 and 84 kg ha-1 of P2O5) were combined in a 4 × 4 × 4 factorial scheme in a totally randomized block design. Response surface and age-shift modeling was used to establish an initial recommendation for mineral fertilization of the Eucalyptus plantations treated with sludge and to analyze the implications of increased growth on the duration of the forest cycle in a tropical climate. The results showed that from 8 to 44 months after planting, the sludge application (with or without N and P) yielded a statistically larger wood volume (P < 0.05), compared to application of N and P fertilizers only. The response surface modeling showed the following outcomes: i) application of sludge based on N criterion reduced the need for N and P fertilizers by 100%; and ii) an increase in wood volume by 7% could be achieved, compared to NPK fertilizers only, if 2/3 of the recommended P was applied. The cultivation time to produce 150 m3 ha-1 of wood volume was 45 months for the control and was reduced by two, three, four, or five months, respectively, through application of recommended P, sludge dose, sludge plus one third of P, and sludge plus two thirds of P. On the whole, sewage sludge could represent an excellent unconventional N and P fertilizer source for wood production on unfertile tropical soils.

Phosphorus Availability and Release Pattern from Activated Dolomite Phosphate Rock in Central Florida.

In this study, novel technology was developed to convert dolomite phosphate rock (DPR) into slow release P fertilizers. The DPR was powdered to <100 mesh and activated with organic molecules under optimal reaction conditions. As compared to original DPR, available P, estimated by water-soluble P released from the three DPRs activated with three types of organic molecules, increased by 6.86, 3.32, and 7.46 times, respectively. Phosphorus supply from the activated DPRs was greater than that of superphosphates (SP). Use of activated DPRs resulted in a significant increase in plant biomass of maize (Zea mays) and millet (Pennisetum glaucum) (succeeding crop), as compared to original DPR, and displayed better effectiveness than monoammonium phosphate or SP. The XRD and FTIR analyses showed that activation did not change the crystal structure of DPR, but the interactions between organic molecules and the P-bearing minerals stimulated P release from DPR.

Spatiotemporal change of phosphorous speciation and concentration in stormwater in the St. Lucie Estuary watershed, South Florida.

Phosphorous (P) concentration in stormwater runoff varies at different spatial and temporal scales. Excessive P loading from agriculture system into the St. Lucie Estuary (SLE) contributed to water quality deterioration in southern Indian River Lagoon. This study examines the spatial and temporal shifts of different P forms in runoff and storm water under different land use, water management, and rainfall conditions. Storm water samplings were conducted monthly between April 2013 and December 2014 in typical farmland and along the waterway (Canal C-24) that connects lands to the SLE. Concentrations of different P forms and related water quality variables were measured. Approximately 89% of the collected water samples contained total P (TP) concentrations exceeding the total maximum daily load (TMDL) level (0.081 mg L-1). Concentrations of different P forms declined from agricultural field furrows to the canal and then increased from the upstream to the downstream in the canal where urban activities dominated land use. Total dissolved P (TDP) was the predominant form of TP, followed by PO4-P. Speciation and concentrations of P varied with sites and sampling times, but were significantly higher in the summer months (from June to September) than in the winter. Water pH explained ∼20% of TP variation. Spatiotemporal variations of P concentrations and compositions provide a data-based guide for development of best management practices (BMPs) to minimize P export from the SLE watershed.

Spatial and temporal variation of nitrogen concentration and speciation in runoff and storm water in the Indian River watershed, South Florida.

Nitrogen (N) is considered as a key element that triggers algal boom in the Indian River Lagoon (IRL), South Florida. Intensive agriculture may have contributed to increased N input into the IRL. Runoff and storm water samples were collected in representative agricultural fields and along waterways that connect lands to the IRL from April 2013 to December 2014. Concentrations of different N species (particulate N, dissolved organic N, dissolved NH4 (+)-N, and NO3 (-)-N) and related water physical-chemical properties were measured. Total N (TN) concentrations generally decreased from agricultural field furrows to discharging point of the waterways but were generally above the US EPA critical level (0.59 mg L(-1)) for surface water. Organic N was the dominant form of dissolved N, followed by NO3 (-)-N, and dissolved NH4 (+)-N. Concentrations and speciation of N in water varied with sites and sampling times but were generally higher in summer and fall and lower in spring and winter, as affected by the seasonality of regional hydrology and agricultural practices. Correlations occurred between N concentration, water physical properties, and rainfall. This information has important implications in the development of best management practices to minimize the impacts of agricultural practice on N loading in the Indian River Lagoon.

Pyrolysis of wetland biomass waste: Potential for carbon sequestration and water remediation.

Management of biomass waste is crucial to the efficiency and sustainable operation of constructed wetlands. In this study, biochars were prepared using the biomass of 22 plant species from constructed wetlands and characterized by BET-N2 surface area analysis, FTIR, TGA, SEM, EDS, and elemental compositions analysis. Biochar yields ranged from 32.78 to 49.02%, with mesopores dominating the pore structure of most biochars. The biochars had a R50 recalcitrance index of class C and the carbon sequestration potential of 19.4-28%. The aquatic plant biomass from all the Chinese constructed wetlands if made into biochars has the potential to sequester 11.48 Mt carbon yr(-1) in soils over long time periods, which could offset 0.4% of annual CO2 emissions from fossil fuel combustion in China. In terms of adsorption capacity for selected pollutants, biochar derived from Canna indica plant had the greatest adsorption capacity for Cd(2+) (98.55 mg g(-1)) and NH4(+) (7.71 mg g(-1)). Whereas for PO4(3-), Hydrocotyle verticillata derived biochar showed the greatest adsorption capacities (2.91 mg g(-1)). The results from this present study demonstrated that wetland plants are valuable feedstocks for producing biochars with potential application for carbon sequestration and contaminant removal in water remediation.

Sorption of ammonium and phosphate from aqueous solution by biochar derived from phytoremediation plants.

The study on biochar derived from plant biomass for environmental applications is attracting more and more attention. Twelve sets of biochar were obtained by treating four phytoremediation plants, Salix rosthornii Seemen, Thalia dealbata, Vetiveria zizanioides, and Phragmites sp., sequentially through pyrolysis at 500 °C in a N2 environment, and under different temperatures (500, 600, and 700 °C) in a CO2 environment. The cation exchange capacity and specific surface area of biochar varied with both plant species and pyrolysis temperature. The magnesium (Mg) content of biochar derived from T. dealbata (TC) was obviously higher than that of the other plant biochars. This biochar also had the highest sorption capacity for phosphate and ammonium. In terms of biomass yields, adsorption capacity, and energy cost, T. dealbata biochar produced at 600 °C (TC600) is the most promising sorbent for removing contaminants (N and P) from aqueous solution. Therefore, T. dealbata appears to be the best candidate for phytoremediation application as its biomass can make a good biochar for environmental cleaning.

Dolomite phosphate rock (DPR) application in acidic sandy soil in reducing leaching of phosphorus and heavy metals-a column leaching study.

A column leaching study was designed to investigate the leaching potential of phosphorus (P) and heavy metals from acidic sandy soils applied with dolomite phosphate rock (DPR) fertilizers containing varying amounts of DPR material and N-Viro soils. DPR fertilizers were made from DPR materials mixing with N-Viro soils at the ratios of 30, 40, 50, 60, and 70 %, and applied in acidic sandy soils at the level of 100 mg available P per kilogram soil. A control and a soluble P chemical fertilizer were also included. The amended soils were incubated at room temperature with 70 % field water holding capacity for 21 days before packed into a soil column and subjected to leaching. Seven leaching events were conducted at days 1, 3, 7, 14, 28, 56, and 70, respectively, and 258.9 mL of deionized water was applied at each leaching events. The leachate was collected for the analyses of pH, electrical conductivity (EC), dissolved organic carbon (DOC), major elements, and heavy metals. DPR fertilizer application resulted in elevations up to 1 unit in pH, 7-10 times in EC, and 20-40 times in K and Ca concentrations, but 3-10 times reduction in P concentration in the leachate as compared with the chemical fertilizer or the control. After seven leaching events, DPR fertilizers with adequate DPR materials significantly reduced cumulative leaching losses of Fe, P, Mn, Cu, and Zn by 20, 55, 3.7, 2.7, and 2.5 times than chemical fertilizer or control. Even though higher cumulative losses of Pb, Co, and Ni were observed after DPR fertilizer application, the loss of Pb, Co, and Ni in leachate was <0.10 mg (in total 1,812 mL leachate). Significant correlations of pH (negative) and DOC (positive) with Cu, Pb, and Zn (P<0.01) in leachate were observed. The results indicated that DPR fertilizers had a great advantage over the soluble chemical fertilizer in reducing P loss from the acidic sandy soil with minimal likelihood of heavy metal risk to the water environment. pH elevation and high dissolved organic carbon concentration in soils after DPR fertilizer application are two influential factors.

Heavy metal phytoextraction by Sedum alfredii is affected by continual clipping and phosphorus fertilization amendment.

Improving the efficacy of phytoextraction is critical for its successful application in metal contaminated soils. Mineral nutrition affects plant growth and metal absorption and subsequently the accumulation of heavy metal through hyper-accumulator plants. This study assessed the effects of di-hydrogen phosphates (KH2PO4, Ca(H2PO4)2, NaH2PO4 and NH4H2PO4) application at three levels (22, 88 and 352 mg P/kg soil) on Sedum alfredii growth and metal uptake by three consecutive harvests on aged and Zn/Cd combined contaminated paddy soil. The addition of phosphates (P) significantly increased the amount of Zn taken up by S. alfredii due to increased shoot Zn concentration and dry matter yield (DMY) (P < 0.05). The highest phytoextraction of Zn and Cd was observed in KH2PO4 and NH4H2PO4 treatment at 352 mg P/kg soil. The amount of Zn removed by phytoextraction increased in the order of 1st clipping < 2nd clipping < 3rd clipping, and for Cd extraction the order was 2nd clipping < 1st clipping < 3rd clipping. These results indicate that the application of P fertilizers coupled with multiple cuttings can enhance the removal of Zn and Cd from contaminated soils by S. alfredii, thus shortening the time needed for accomplishing remediation goals.

Natural variation of folate content and composition in spinach (Spinacia oleracea) germplasm.

Breeding to increase folate levels in edible parts of plants, termed folate biofortification, is an economical approach to fight against folate deficiency in humans, especially in the developing world. Germplasm with elevated folates are a useful genetic source for both breeding and direct use. Spinach is one of the well-know vegetables that contains a relatively high amount of folate. Currently, little is known about how much folate, and their composition varies in different spinach accessions. The aim of this study was to investigate natural variation in the folate content and composition of spinach genotypes grown under controlled environmental conditions. The folate content and composition in 67 spinach accessions were collected from the United States Department of Agriculture (USDA) and Asian Vegetable Research and Development Center (AVRDC) germplasm collections according to their origin, grown under control conditions to screen for natural diversity. Folates were extracted by a monoenzyme treatment and analyzed by a validated liquid chromatography (LC) method. The total folate content ranged from 54.1 to 173.2 µg/100 g of fresh weight, with 3.2-fold variation, and was accession-dependent. Four spinach accessions (PI 499372, NSL 6095, PI 261787, and TOT7337-B) have been identified as enriched folate content over 150 µg/100 g of fresh weight. The folate forms found were H(4)-folate, 5-CH(3)-H(4)-folate, and 5-HCO-H(4)-folate, and 10-CHO-folic acid also varied among different accessions and was responsible for variation in the total folate content. The major folate vitamer was represented by 5-CH(3)-H(4)-folate, which on average accounted for up to 52% of the total folate pool. The large variation in the total folate content and composition in diverse spinach accessions demonstrates the great genetic potential of diverse genotypes to be exploited by plant breeders.

Immobilization of copper in contaminated sandy soils using calcium water treatment residue.

Chemical remediation has attracted increasing attention for heavy metal contaminated soils because of its relatively low cost and high efficiency. In this study laboratory incubation and column leaching experiments were conducted to understand the mechanisms of copper (Cu) immobilization by calcium water treatment residue (Ca-WTR) and to estimate the optimal rate for remediating Cu-contaminated soils. The results showed that Ca-WTR amendment significantly raised soil pH and decreased water soluble and exchangeable Cu by 62-90% in the contaminated soils. Most of the bioavailable Cu was converted into more stable Cu fractions, i.e. oxides-bound and residual Cu. The cumulative amount of Cu in the leachate after 10 leaching events was reduced by 80% and 73%, respectively for the two tested soils at the Ca-WTR rate of 20 g kg(-1) for Alfisol and 100 g kg(-1) for Spodosol. These results indicate that Ca-WTR is effective in raising soil pH and converting labile Cu to more stable forms in the contaminated soils. A pH value of 6.5 was found to be critical for lowering Cu availability in the soils. Based on this criterion and pH response curve to Ca-WTR application, the optimal rates of Ca-WTR can be estimated for different Cu-contaminated soils.