Interactive effects of As, Cd and Zn on their uptake and oxidative stress in As-hyperaccumulator Pteris vittata.

The effects of arsenic (As), cadmium (Cd) and zinc (Zn) on each other's uptake and oxidative stress in As-hyperaccumulator Pteris vittata were investigated. P. vittata plants were exposed to 50 µM As, Cd and/or Zn for 15 d in 0.2-strength Hoagland solution. When applied alone, P. vittata accumulated 185 mg kg-1 As, 164 mg kg-1 Cd and 327 mg kg-1 Zn in the fronds. While Cd and Zn did not impact each other's uptake, As affected Cd and Zn uptake. Whereas As decreased Zn uptake, Zn affected As speciation in P. vittata fronds, with more arsenate (AsV) than arsenite (AsIII) being present. At 50 µM As, 75 µM Zn increased As accumulation in P. vittata fronds by 10 folds to 2363 mg kg-1 compared to 50 µM Zn. Although AsV was the predominant As species in all tissues, Cd enhanced AsIII levels in the fronds but increased AsV in the roots. Co-exposure of Cd + Zn elevated oxidative stress basing on thiobarbituric acid reactive substances, H2O2 content, Evans blue dye uptake, membrane injury index and reactive oxygen species (ROS) relative to single metal. By lowering Cd and Zn concentrations in P. vittata fronds, As reduced the associated stress comparative to Cd or Zn treatment. The results enhance our understanding of the mechanisms underlying the interactions between As, Cd and Zn in As-hyperaccumulator P. vittata.

Metal tolerance of arsenic-resistant bacteria and their ability to promote plant growth of Pteris vittata in Pb-contaminated soil.

Soils contaminated with Pb and As are difficult to remediate. In this study, the utility of coupling As-hyperaccumulator Pteris vittata with metal-resistant rhizobacteria was explored. Siderophore-producing and P-solubilizing As-resistant bacteria from the P. vittata rhizosphere were screened for resistance to multiple metals. Results indicated Pseudomonas spp. strain PG-12 was most efficient in resisting multiple metals, i.e., up to 0.6 mM Cd and 10 mM Pb. Amplification of gene fragments encoding various metal efflux transporters (PbrA and CadA2) from genomic DNA of PG-12 suggested that metal efflux might play a role in its metal resistance and detoxification. In addition, PG-12 produced significant levels of plant growth hormones including 17.4 µg mL-1 indole acetic acid and 3.54 µg mL-1 gibberellin. P. vittata sporophytes inoculated with PG-12 were grown in Pb-contaminated medium and exhibited improved growth, increased P uptake, and reduced Pb uptake into plant tissue compared to the control. Results demonstrated that viable PG-12 cells were responsible for Pb immobilization and plant growth enhancement in P. vittata. The ability of PG-12 cells to solubilize P and display resistance to multiple metals combined with the production of plant hormones indole acetic acid and gibberellin make PG-12 a suitable candidate for plant growth promotion in metal-contaminated soil.

PAHs in urban soils of two Florida cities: Background concentrations, distribution, and sources.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic contaminants, which are found in soils throughout the U.S. The objective of this study was to determine the background concentrations, distributions, and sources of 16 USEPA priority PAHs in two urban soils. A total of 114 soil samples were collected from two large cities in Florida: Orlando and Tampa. The results showed that soils were dominated by high molecular weight PAHs in both cities. The average ∑16-PAHs in Orlando and Tampa soils were 3227 and 4562 µg kg-1, respectively. The averages of 7 carcinogenic PAHs based on the benzo[a]pyrene-equivalent (BaP-EQ) concentrations in the two cities were 452 and 802 µg kg-1. BaP-EQ concentrations in 60-62% of samples were higher than the Florida Soil Cleanup Target Level (FSCTL) for residential soils at 100 µg kg-1 and 20-25% of samples were higher than FSCTL for industrial soils at 700 µg kg-1. Based on molecular diagnostic ratios and PMF modeling, major sources of soil PAHs in both cities were similar, mainly from pyrogenic sources including vehicle emissions, and biomass and coal combustion. Based on ArcGIS mapping, PAH concentrations in soils near business districts and high traffic roads were higher. Thus, it is important to consider background PAH concentrations in urban soils when considering soil remediation.

Assessment of trace metals in five most-consumed vegetables in the US: Conventional vs. organic.

Metal concentrations (As, Cd, Pb, Cr, Ba, Co, Ni, Cu, and Zn) in conventional and organic produce were assessed, specifically, five most-consumed vegetables from the US including potato, lettuce, tomato, carrot and onion. They were from four representative supermarkets in a college town in Florida. All vegetables contained detectable metals, while As, Cd, Pb, Cr, and Ba are toxic metals, Co, Ni, Cu, and Zn are nutrients for humans. The mean concentrations of As, Cd, Pb, Cr and Ba in five vegetables were 7.86, 9.17, 12.1, 44.8 and 410 µg/kg for organic produce, slightly lower than conventional produce at 7.29, 15.3, 17.9, 46.3 and 423 µg/kg. The mean concentrations of Co, Ni, Cu, and Zn in five vegetables were 3.86, 58.5, 632, and 2528 µg/kg for organic produce, comparable to conventional produce at 5.94, 68.2, 577, and 2354 µg/kg. For toxic metals, the order followed tomato < lettuce < onion < carrot < potato, with root vegetables being the highest. All metals in vegetables were lower than the allowable concentrations by FAO/WHO. Health risks associated with vegetable consumption based on daily intake and non-carcinogenic risk based on hazard quotient were lower than allowable limits. For the five most-consumed vegetables in the US, metal contents in conventional produce were slightly greater than organic produce, especially for Cd and Pb.

Metal concentrations in traditional and herbal teas and their potential risks to human health.

Food and beverage consumption is an important route for human exposure to metals. Traditional tea (Camellia sinensis) is a widely-consumed beverage, which may contain toxic metals. This study determined total and infusion concentrations of 5 metals including Al, As, Cd, Cr, and Pb in 47 traditional and herbal teas from 13 countries and assessed their potential risks to human health. The data showed that herbal teas exhibited higher As (0.26mgkg-1), Cd (0.19mgkg-1) and Pb (2.32mgkg-1) than traditional teas. Black tea from India had high Cr at 31mgkg-1 while white tea from China had low Cr at 0.39mgkg-1. Arsenic, Cd and Pb did not exceed the WHO limit for medicinal plants excluding one herbal tea with 1.1mgkg-1 As and 26.4mgkg-1 Pb. However, Cr in 47% herbal teas and 73% traditional teas exceeded the Canada limit of 2mgkg-1. Metal concentrations in tea infusions were below the MCL for drinking water except for Al. Total Al and its infusion was lower in herbal teas (47-1745mgkg-1 and 0.09-3.95mgL-1) than traditional teas (50.3-2517mgkg-1 and 0.02-7.51mgL-1), with 0.9-22% and 4-49% of the Al being soluble in infusion. The Al concentrations in infusion in all black tea and 83, 75 and 25% of the green, oolong and herbal teas exceeded the secondary MCL for drinking water at 0.2mgL-1. However, the weekly intake of Al from drinking tea (0.001-0.39 and 0.003-0.56mgkg-1 for children and adults) was lower than the provisional tolerable weekly intake for Al at 1.0mgkg-1. Our data showed that it is important to consider metal intake from tea consumptions, especially for Cr and Al in heavy tea drinkers.

Antioxidant enzymes responses in shoots of arsenic hyperaccumulator, Isatis cappadocica Desv., under interaction of arsenate and phosphate.

The present study investigated the effects of arsenate and phosphate interaction on growth, lipid peroxidation, arsenic (As) accumulation, phosphorus (P) accumulation, and the activities of some antioxidant enzymes in Isatis cappadocica. Plants were exposed to (50-1200 µmol L-1) arsenate and (5-1600 µmol L-1) phosphate for 28 days in a hydroponic system. At a phosphate concentration of 1600 µM, biomass production and chlorophyll content increased, demonstrating clearly that phosphate was able to provide protection against As toxicity. In case of joint application of 1600 µM phosphate with arsenate, the As accumulation and then lipid peroxidation were decreased when compared to samples treated with arsenate and 5 µM phosphate. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) increased with increasing arsenate supply levels. Addition of P decreased activities of SOD, APX and CAT, while high phosphate treatments had a positive effect on GR activity, which may be due to regulation of glutathione biosynthesis within the plants. In conclusion, high arsenate treatment (800-1200 µM) could cause an increasing oxidative stress, which can be scavenged by the antioxidant enzyme. Furthermore, P may affect As-induced oxidative stress through nutrient condition and As accumulation.

Metal leachability from coal combustion residuals under different pHs and liquid/solid ratios.

Coal combustion residuals (CCRs) contain variable amounts of trace metals, which can negatively impact the environment. We analyzed metal concentrations and leachability of CCRs from seven coal-fired power plants from Florida. The purpose of this study was to characterize and assess metal leachability in representative CCRs samples from coal-fired power plants, including As, Ba, Cd, Cr, Pb, and Se. The specific objectives were to: (1) measure metal leachability under different pH conditions and liquid-to-solid ratios using USEPA Leaching Environmental Assessment Framework (LEAF) Methods 1313 and 1316, and (2) compare their leachability with those obtained by the Synthetic Precipitation Leaching Procedure (SPLP). All metals excluding Cd showed amphoteric behavior, presenting higher concentrations at low and high pH using LEAF Method 1313. The highest Cd leaching was observed at pH 2-4 and decreased at pH>7. SPLP results were highly variable when compared to the LEAF data. All metals except Ba exceeded the Florida Groundwater Cleanup Target Levels at all pH levels, however, metal leaching was low at typical soil pH of 4-9. Metal concentrations in fly ash decreased in most cases with increasing LS ratio. Therefore, due to potential leaching of some metals, evaluation is needed before beneficial use of CCRs.

Arsenic removal from As-hyperaccumulator Pteris vittata biomass: Coupling extraction with precipitation.

Proper disposal of As-hyperaccumulator Pteris vittata biomass (Chinese brake fern) enhances its application in phytoremediation. The goal of this study was to optimize As removal from P. vittata (PV) biomass by testing different particle sizes, extractants, extraction times and solid-to-liquid ratios. PV biomass was extracted using different extractants followed by different Mg-salts to recover soluble As via precipitation. Water-soluble As in PV biomass varied from 6.8% to 61% of total As depending on extraction time, with 99% of As being arsenate (AsV). Extraction with 2.1% HCl, 2.1% H3PO4, 1 M NaOH and 50% ethanol recovered 81, 78, 47 and 14% of As from PV biomass. A follow-up extraction using HCl recovered 27-32% with ethanol recovering only 5%. Though ethanol showed the lowest extractable As, residual As in the biomass was also the lowest. Among the extractants, 35% ethanol was the best to remove As from PV biomass. Approximately 90% As was removed from PV biomass using particle size <1 mm at solid:liquid ratio 1:50 and pH 6 for 2 h. Adding MgCl2 at As:Mg ratio of 1:400 with pH 9.5 was effective to precipitate soluble As, resulting in 98% removal. Effective removal of As from PV biomass prior to disposal helps make phytoremediation more feasible.

Fluoride concentrations in traditional and herbal teas: Health risk assessment.

Traditional tea (Camellia sinensis) and herbal tea are being consumed across the world. However, long term consumption of tea can increase the chances of fluorosis owing to the presence of fluoride (F) in teas. Therefore, it is imperative to assess the health risk associated with tea consumption. The main objectives of this study were to: 1) estimate total F in 47 popular teas, including traditional and herbal teas and F concentrations in 1% (w/v) infusion of 5 min, and 2) assess the exposure risks of F from tea consumption in children and adults. The data showed that total F was the least in herbal teas (33-102 mg/kg) and their infusions (0.06-0.69 mg/L) compared to traditional teas (296-1112 mg/kg) and their infusions (1.47-6.9 mg/L). During tea infusion, 6-96% and 18-99% of the F was released into the water from herbal and traditional teas, respectively. Ten samples of traditional teas, including five green teas had chronic daily intake (CDI) values of F > 0.05 mg/d/kg bw, the stipulated permissible limits of F intake from all sources. Although the F from teas posed no immediate health hazards with hazard quotient <1, some tea samples could potentially contribute >4 mg F/d, thereby adding to the overall F burden. Therefore, together with F from food and water sources, daily F consumptions from teas might increase its health risks to humans. So, caution should be excised when drinking teas containing high F.

Arsenate and fluoride enhanced each other's uptake in As-sensitive plant Pteris ensiformis.

We investigated the effects of arsenate (AsV) and fluoride (F) on each other's uptake in an As-sensitive plant Pteris ensiformis. Plants were exposed to 1) 0.1 × Hoagland solution control, 2) 3.75 mg L-1 As and 1.9, 3.8, or 7.6 mg L-1 F, or 3) 1 mg L-1 F and 3.75 mg L-1 or 7.5 mg L-1 As for 7 d in hydroponics. P. ensiformis accumulated 14.7-32.6 mg kg-1 As at 3.75 mg L-1 AsV, and 99-145 mg kg-1 F at 1 mg L-1 F. Our study revealed that AsV and F increased each other's uptake when co-present. At 1.9 mg L-1, F increased frond As uptake from 14.7 to 40.3 mg kg-1, while 7.5 mg L-1 As increased frond F uptake from 99 to 371 mg kg-1. Although, AsV was the predominant As species in all tissues, F enhanced AsIII levels in the rhizomes and fronds, while the reverse was observed in the roots. Increasing As concentrations also enhanced TBARS and H2O2 in tissues, indicating oxidative stress. However, F alleviated As stress by lowering their levels in the fronds. Frond and root membrane leakage were also evident due to As or F exposure. The results may facilitate better understanding of the mechanisms underlying the co-uptake of As and F in plants. However, the mechanisms of how they enhance each other's uptake in P. ensiformis need further investigation.

Mechanisms of metal sorption by biochars: Biochar characteristics and modifications.

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production.

Arsenic uptake by lettuce from As-contaminated soil remediated with Pteris vittata and organic amendment.

Leaching of inorganic arsenic (As) from chromated copper arsenate (CCA)-treated wood may elevate soil As levels. Thus, an environmental concern arises regarding As accumulation in vegetables grown in these soils. In this study, a greenhouse experiment was conducted to investigate the ability of As-hyperaccumulator P. vittata and organic amendments in reducing As uptake by lettuce (Lactuca sativa) from a soil contaminated from CCA-treated wood (63.9 mg kg-1 As). P. vittata was grown for 150 d in a CCA-contaminated soil amended with biochar, activated carbon or coffee grounds at 1%, followed by lettuce for another 55 d. After harvest, plant biomass and As concentrations in plant and soil were determined. The presence of P. vittata reduced As content in lettuce by 21% from 27.3 to 21.5 mg kg-1 while amendment further reduced As in lettuce by 5.6-18%, with activated C being most effective. Our data showed that both P. vittata and organic amendments were effective in reducing As concentration in lettuce. Though no health-based standard for As in vegetables exists in USA, care should be taken when growing lettuce in contaminated soils. Our data showed that application of organic amendments with P. vittata reduced As hazards in CCA-contaminated soils.

Arsenic-hyperaccumulator Pteris vittata efficiently solubilized phosphate rock to sustain plant growth and As uptake.

Phosphorus (P) is one of the most important nutrients for phytoremediation of arsenic (As)-contaminated soils. In this study, we demonstrated that As-hyperaccumulator Pteris vittata was efficient in acquiring P from insoluble phosphate rock (PR). When supplemented with PR as the sole P source in hydroponic systems, P. vittata accumulated 49% and 28% higher P in the roots and fronds than the -P treatment. In contrast, non-hyperaccumulator Pteris ensiformis was unable to solubilize P from PR. To gain insights into PR solubilization by plants, organic acids in plant root exudates were analyzed by HPLC. The results showed that phytic acid was the predominant (>90%) organic acid in P. vittata root exudates whereas only oxalic acid was detected in P. ensiformis. Moreover, P. vittata secreted more phytic acid in -P and PR treatments. Compared to oxalic acid, phytic acid was more effective in solubilizing PR, suggesting that phytic acid was critical for PR utilization. Besides, secretion of phytic acid by P. vittata was not inhibited by arsenate. Our data indicated that phytic acid played an important role in efficient use of insoluble PR by P. vittata, shedding light on using insoluble PR to enhance phytoremediation of As-contaminated soils.

Sulfate and chromate increased each other's uptake and translocation in As-hyperaccumulator Pteris vittata.

We investigated the effects of chromate (CrVI) and sulfate on their uptake and translocation in As-hyperaccumulator Pteris vittata. Plants were exposed to 1) 0.1 mM CrVI and 0, 0.25, 1.25 or 2.5 mM sulfate or 2) 0.25 mM sulfate and 0, 0.5, 2.5 or 5.0 mM CrVI for 1 d in hydroponics. P. vittata accumulated 26 and 1261 mg kg(-1) Cr in the fronds and roots at CrVI0.1, and 2197 and 1589 mg kg(-1) S in the fronds and roots at S0.25. Increasing sulfate concentrations increased Cr root concentrations by 16-66% and helped CrVI reduction to CrIII whereas increasing CrVI concentrations increased frond sulfate concentrations by 3-27%. Increasing sulfate concentrations enhanced TBARS concentrations in the biomass, indicating oxidative stress caused lipid peroxidation in plant cell membranes. However, addition of 0.25-2.5 mM sulfate alleviated CrVI's toxic effects and decreased TBARS from 23.5 to 9.46-12.3 µmol g(-1) FW. Though CrVI was supplied, 78-96% of CrIII was in the biomass, indicating efficient CrVI reduction to CrIII by P. vittata. The data indicated the amazing ability of P. vittata in Cr uptake at 289 mg kg(-1) h(-1) with little translocation to the fronds. These results indicated that P. vittata had potential in Cr phytoremediation in contaminated sites but further studies are needed to evaluate this potential. The facts that CrVI and sulfate helped each other in uptake by P. vittata suggest that CrVI was not competing with sulfate uptake in P. vittata. However, the mechanisms of how sulfate and CrVI enhance each other's accumulation in P. vittata need further investigation.

Chromate and phosphate inhibited each other's uptake and translocation in arsenic hyperaccumulator Pteris vittata L.

We investigated the effects of chromate (CrVI) and phosphate (P) on their uptake and translocation in As-hyperaccumulator Pteris vittata (PV). Plants were exposed to 1) 0.10 mM CrVI and 0, 0.25, 1.25, or 2.50 mM P or 2) 0.25 mM P and 0, 0.50, 2.5 or 5.0 mM CrVI for 24 h in hydroponics. PV accumulated 2919 mg/kg Cr in the roots at CrVI0.10, and 5100 and 3500 mg/kg P in the fronds and roots at P0.25. When co-present, CrVI and P inhibited each other's uptake in PV. Increasing P concentrations reduced Cr root concentrations by 62-82% whereas increasing CrVI concentrations reduced frond P concentrations by 52-59% but increased root P concentrations by 11-15%. Chromate reduced P transport, with more P being accumulated in PV roots. Though CrVI was supplied, 64-78% and 92-93% CrIII were in PV fronds and roots. Based on X-ray diffraction, Cr2O3 was detected in the roots confirming CrVI reduction to CrIII by PV. In short, CrVI and P inhibited each other in uptake and translocation by PV, and CrVI reduction to CrIII in PV roots served as its detoxification mechanism. The finding helps to understand the interactions of P and Cr during their uptake in PV.

Antimony uptake, efflux and speciation in arsenic hyperaccumulator Pteris vittata.

Even though antimony (Sb) and arsenic (As) are chemical analogs, differences exist on how they are taken up and translocated in plants. We investigated 1) Sb uptake, efflux and speciation in arsenic hyperaccumulator Pteris vittata after 1 d exposure to 1.6 or 8 mg/L antimonite (SbIII) or antimonate (SbV), 2) Sb uptake by PV accessions from Florida, China, and Brazil after 7 d exposure to 8 mg/L SbIII, and 3) Sb uptake and oxidation by excised PV fronds after 1 d exposure to 8 mg/L SbIII or SbV. After 1 d exposure, P. vittata took 23-32 times more SbIII than SbV, with all Sb being accumulated in the roots with the highest at 4,192 mg/kg. When exposed to 8 mg/L SbV, 98% of Sb existed as SbV in the roots. In comparison, when exposed to 8 mg/L SbIII, 81% of the total Sb remained as SbIII and 26% of the total Sb was effluxed out into the media. The three PV accessions had a similar ability to accumulate Sb at 12,000 mg/kg in the roots, with >99% of total Sb in the roots. Excised PV fronds translocated SbV more efficiently from the petioles to pinnae than SbIII and were unable to oxidize SbIII. Overall, P. vittata displayed efficient root uptake and efflux of SbIII with limited ability to translocate and transform in the roots.