Phytoremediation technology for recovery of Ni by Acacia plants in association with Bacillus amyloliquefaciens isolated from E-waste contaminated site.

Electronic waste (e-waste) illegally disposal in Thailand is becoming more widespread. A sustainable metal recovery technology is needed. A phytotechnology called "phytomining" of metals such as nickel (Ni) is a promising technology providing a sustainable solution to the growing e-waste problems. This study investigated the ability of Acacia species in association with e-waste site isolated, plant growth-promoting rhizobacteria (PGPR), Bacillus amyloliquefaciens. Acacia mangium accumulated higher Ni in their tissues when Ni concentrations in soil were lower than 200 mg kg-1. The inoculation of PGPR B. amyloliquefaciens enhanced Ni uptake and accumulation in the leaves, stem, and root. The results showed that the highest Ni concentration was found in the root ash (825.50 mg kg-1) when inoculated plants were grown in soil containing 600 mg kg-1 Ni. Hence, the Ni recovery process and mass balance were performed on root ashes. The highest Ni recovery was 91.3% from the acid (H2SO4) leachate of the ash of inoculated plant treated with 600 mg kg-1 Ni. This demonstrates the feasibility of PGPR-assisted phytomining from Ni-contaminated soil. Phytomining of Ni from any e-waste contaminated sites using Acacia mangium in combination with B. amyloliquefaciens can promote plant growth and improve the uptake of Ni.

Phytomining from electronic waste is an appealing technology that can provide a long-term waste management strategy while valuable trace metals can be recovered. In this study, we evaluated the nickel phytomining ability of Acacia mangium in association with PGPR Bacillus amyloliquefaciens. The results from this study showed that Ni recovery from phytomass using A. mangium with B. amyloliquefaciens can be further improved leading to a sustainable waste management strategy.

Glyphosate metabolism in Tetrahymena thermophila: A shotgun proteomic analysis approach.

Glyphosate is one of the most widely used herbicides in the world. However, because of its overuse and resistance to degradation, high levels of glyphosate residues in the environment are reported. Therefore, this study aimed to investigate the effects of glyphosate on proteomic aspects of Tetrahymena thermophila and their uses as bioindicators of freshwater ecosystem. First, an acute toxicity test was performed to determine the median inhibition concentration (IC50 ). The toxicity test results showed that glyphosate inhibited the growth (proliferation) of T. thermophila. The 96 h-IC50 value of glyphosate was 171 mg L-1 . No visible changes in aggregation behavior and cell morphology were observed under glyphosate exposure. In addition, the effects of low and high dose glyphosate concentrations (77.5 mg L-1 , 171 mg L-1 ) on the proteomic changes of T. thermophila was investigated using a label-free shotgun proteomic approach. A total of 3191 proteins were identified, 2791 proteins were expressed in the control, 2651 proteins were expressed in 77.5 mg L-1 glyphosates, and 3012 proteins were expressed in 171 mg L-1 glyphosates. Under glyphosate exposure at both low and high dose glyphosate, 400 unique proteins were upregulated. The majority of these proteins was classified as proteins associated with oxidative stress response and intracellular transport indicating the shifts in the internal metabolism. Proteomics revealed that the glyphosate metabolism by T. thermophila is a multi-step process involving several enzymes, which can be divided into four phases, including modification (phase I), conjugation (phase II), transport (phase III), and degradation (phase IV). The accumulation of various biochemical reactions contributes to overall glyphosate resistance. With the proteomics approach, we have found that T. thermophila was equipped with glyphosate detoxification and degradation mechanisms.

Risk assessment and biodegradation potential of PAHs originating from Map Ta Phut Industrial Estate, Rayong, Thailand.

Petroleum hydrocarbon contamination is a serious concern across the globe. Here, the capability of native bacterial consortium enriched from sediment samples of Map Ta Phut Industrial Estate (MTPIE), Rayong, Thailand was described. The distribution of PAHs was assessed from the sediment samples collected from MTPIE by GC-FID and the toxic unit (TU) was calculated to assess the potential ecological risk to the surrounding biota. This study investigated the degradation potential and determined the PAH-degrading bacterial cultures by enriching collected sediments in PAHs mixtures (naphthalene, phenanthrene, and pyrene). The TPH degradation capacity of each bacterial consortium was validated in a soil microcosm using aged crude oil-contaminated soil. The MTPIE sediments were highly contaminated with PAHs (843.99-3904.39 ng g-1) and posed extremely high ecological risks to benthic biota (TU > 1). The consortium S5-P most significantly removed naphthalene (90.03%) and phenanthrene (88.14%) while the highest removal of pyrene was achieved by the S3-P consortium. Other consortia only partially degraded the PAHs. The dominant microbes in the consortia were determined using PCR-DGGE, it was found that the PAH degrading consortia were known PAH degraders such as Annwoodia, Bacillus, Brevibacillus, Lysinibacillus, Paracoccus, Rhodococcus, Sphingopyxis, Sulfurovum, and Sulfurimonas species and unknown PAH degraders such as Lithuaxuella species. The consortium S5-P showed the highest degradation capacity, removing 74.99% of TPHs in the soil microcosm. Furthermore, the inoculation of PAH-biodegrading bacterial consortia significantly promoted the catechol-2,3-dioxygenase (C23O) and dehydrogenase (DHA) activities which directly correlated with the degradation efficiency of petroleum hydrocarbons (p < 0.05).

Assessment of dynamic microbial community structure and rhizosphere interactions during bioaugmented phytoremediation of petroleum contaminated soil by a newly designed rhizobox system.

To understand the plant (Vigna unguiculata) and plant-growth promoting bacteria (PGPB) (Microcococcus luteus WN01) interactions in crude oil contaminated soil, experiments were conducted based on the newly designed rhizobox system. The rhizobox was divided into three main compartments namely the rhizosphere zone, the mid-zone, and the bulk soil zone, in accordance with the distance from the plant. Plants were grown in these three-chambered pots for 30 days under natural conditions. The plant root exudates were determined by analyzing for carbohydrates, amino acids, and phenolic compounds. The degradation of alkane, polycyclic aromatic hydrocarbons (PAHs), and total petroleum hydrocarbons (TPHs) were quantified by GC-FID. Soil catalase, dehydrogenase, and invertase activities were determined. The microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE). Results showed that the inoculation of M. luteus WN01 significantly enhanced cowpea root biomass and exudates, especially the phenolic compounds. Bioaugmented phytoremediation by cowpea and M. luteus promoted rhizodegradation of TPH. Cowpea stimulated microbial growth, soil dehydrogenase, and invertase activities and enhanced bacterial community diversity in oil contaminated soil. The rhizosphere zone of cowpea inoculated with M. luteus showed the highest removal efficiency, microbial activities, microbial population, and bacterial community diversity indicating the strong synergic interactions between M. luteus and cowpea.

This is the first study to characterize the rhizosphere effect of cowpea on microbial activities, population, and community structure in crude oil contaminated soil in the presence and absence of PGPB, M. luteus WN01. The rhizosphere of cowpea was found to be a degradation hotspot where microbial abundance and metabolic activities were most active. Cowpea-M. luteus association can be a good candidate that can be implemented in real field sites.

Responses of oil degrader enzyme activities, metabolism and degradation kinetics to bean root exudates during rhizoremediation of crude oil contaminated soil.

During rhizoremediation process, plant roots secrete the specific exudates which enhance or stimulate growth and activity of microbial community in the rhizosphere resulting in effective degradation of pollutants. The present study characterized cowpea (CP) and mung bean (MB) root exudates and examined their influences on the degradation of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) by the two oil degraders Micrococcus luteus WN01 and Bacillus cereus W2301. The effects of root exudates on soil microbial population dynamic and their enzymes dehydrogenase (DHA), and catechol 2,3 dioxygenase (C23O) activities were assessed. Both root exudates enhanced the degradation by both oil degraders. Cowpea root exudates maximized the removal of TPHs and PAHs by M. luteus WN01. Both bacterial population and DHA increased significantly in the presence of both root exudates. However, the C23O activities were significantly higher in WN01 treated. No significant influence of root exudates was observed on the C23O activities of W2301 treated. By using gas chromatography -mass spectroscopy, the dominant compounds found in cowpea and mung bean root exudates were 4-methoxy-cinnamic acid and terephthalic acid. Found in lower amount were propionic, malonic acid, and citric acid which were associated with enhanced PAHs desorption from soil and subsequent degradation. Novelty statement This is the first study to characterize the low molecular weight organic acids from root exudates of cowpea and mung bean and their influences on hydrocarbon desorption and hence enhancing the biodegradation process. The findings of the present study will greatly contribute to a better understanding of plant-microbe interaction in total petroleum hydrocarbons contaminated soil.

Examination of the Metallothionein Gene Family in Greater Duckweed Spirodela polyrhiza.

Duckweeds are aquatic plants that proliferate rapidly in a wide range of freshwaters, and they are regarded as a potential source of sustainable biomass for various applications and the cost-effective bioremediation of heavy metal pollutants. To understand the cellular and molecular basis that underlies the high metal tolerance and accumulation capacity of duckweeds, we examined the forms and transcript profiles of the metallothionein (MT) gene family in the model duckweed Spirodela polyrhiza, whose genome has been completely sequenced. Four S. polyrhiza MT-like genes were identified and annotated as SpMT2a, SpMT2b, SpMT3, and SpMT4. All except SpMT2b showed high sequence homology including the conserved cysteine residues with the previously described MTs from flowering plants. The S. polyrhiza genome appears to lack the root-specific Type 1 MT. The transcripts of SpMT2a, SpMT2b, and SpMT3 could be detected in the vegetative whole-plant tissues. The transcript abundance of SpMT2a was upregulated several-fold in response to cadmium stress, and the heterologous expression of SpMT2a conferred copper and cadmium tolerance to the metal-sensitive ∆cup1 strain of Saccharomyces cerevisiae. Based on these results, we proposed that SpMT2a may play an important role in the metal detoxification mechanism of duckweed.

Phytoremediation of soil co-contaminated with zinc and crude oil using Ocimum gratissimum (L.) in association with Pseudomonas putida MU02.

Soil adulteration by organic and inorganic contaminants chiefly in industrial and agricultural area is one of the major problems faced by the world today. Phytoremediation using aromatic plant such as Ocimum is a sound, economically reasonable and an eco-friendly approach. Besides, microbial assisted phytoremediation can bring about plant-promoted microbial degradation, plant uptake and phytodegradation of soil contaminants. In this study, the ability of Ocimum gratissimum in association with Pseudomonas putida MU02 to remediate zinc and crude oil contaminated soil (2,000 mg/kg, 1% w w-1 crude oil) was investigated in a 60-day pot experiment. Four different treatments and a control (clean soil + plant) were employed for the study: co-contaminated soil only; co-contaminated soil with O. gratissimum; co-contaminated with P. putida inoculum; co-contaminated soil with O. gratissimum and P. putida. Comparatively, the highest TPH deduction efficiency (75.87%) was shown by the treatment comprising of O. gratissimum and P. putida while highest metal uptake was shown by the treatment with plant only. Better TPH removal associated with higher number of bacteria in the vegetated and inoculated pots could be attributed to the rhizopheric effect of the plants. Altogether, the association of O. gratissimum with P. putida can be a potential candidate for the remediation of co-contaminated soil.

Vacuolar H+ -ATPase is involved in preventing heavy metal-induced oxidative stress in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, vacuolar H+ -ATPase (V-ATPase) involved in the regulation of intracellular pH homeostasis has been shown to be important for tolerances to cadmium, cobalt and nickel. However, the molecular mechanism underlying the protective role of V-ATPase against these metals remains unclear. In this study, we show that cadmium, cobalt and nickel disturbed intracellular pH balance by triggering cytosolic acidification and vacuolar alkalinization, likely via their membrane permeabilizing effects. Since V-ATPase plays a crucial role in pumping excessive cytosolic protons into the vacuole, the metal-sensitive phenotypes of the Δvma2 and Δvma3 mutants lacking V-ATPase activity were supposed to result from highly acidified cytosol. However, we found that the metal-sensitive phenotypes of these mutants were caused by increased production of reactive oxygen species, likely as a result of decreased expression and activities of manganese superoxide dismutase and catalase. In addition, the loss of V-ATPase function led to aberrant vacuolar morphology and defective endocytic trafficking. Furthermore, the sensitivities of the Δvma mutants to other chemical compounds (i.e. acetic acid, H2 O2 , menadione, tunicamycin and cycloheximide) were a consequence of increased endogenous oxidative stress. These findings, therefore, suggest the important role of V-ATPase in preventing endogenous oxidative stress induced by metals and other chemical compounds.

Bacteria-assisted phytoremediation of fuel oil and lead co-contaminated soil in the salt-stressed condition by chromolaena odorata and Micrococcus luteus.

Bioremediation of lead-petroleum co-contaminated soil under salt-stressed condition has been investigated. In this study, the co-contaminated soil (780 mg kg-1 Pb and 27,000 mg kg-1 TPHs) under the high salinity (EC 7.79 ds m-1) was used as a model soil to be remediated by Chromolaena odorata inoculated with Micrococcus luteus. The results showed that salt stress caused a marked reduction in dry biomass and stem height, and high accumulation of proline. The presence of salt did not affect the total amount of chlorophyll in plant tissues. No toxicity symptoms were evident from plant morphology after three months of exposure. Drastic differences in the accumulation patterns of Pb in C. odorata grown on saline and non-saline soils were observed and indicated that salinity negatively affected Pb uptake and accumulation. A high rate of degradation of TPHs was observed in non-saline soils with or without bacterial inoculation. Salinity stress showed no significant different in the proportion of TPH degradation with added or non-added M. luteus. The tolerance of C. odorata and M. luteus to moderate concentrations of Pb and fuel oil made them very good candidates for the use in bacteria-assisted phytoremediation of lead-fuel oil co-contaminated soils under the mild saline soils.

Isolation and characterization of Pb-resistant plant growth promoting endophytic bacteria and their role in Pb accumulation by fast-growing trees.

Lead (Pb) contamination is one of the major environmental problems on a global scale. Bacterial endophytes have been accepted as a promising technique to assist phytoremediation. In this study, three Pb-tolerant endophytic bacteria were isolated from the roots of Pityrogramma calomelanos. Based on partial 16S rRNA gene sequencing analysis, all isolates were similar to Pseudomonas and tolerated Pb concentration up to 1850mg/L, producing siderophores and solubilized phosphate. Among them, Pc isolate closely related to Pseudomonas psychrophila showed the highest water-soluble Pb in solution (Pb solubilization) and in contaminated soil. This isolate was chosen to study the effects on Pb accumulation in the roots of Acacia mangium and Eucalyptus camaldulensis by a hydroponic experiment. The results showed that, in the Hoagland nutrient solution with no Pb spiking, the roots showed no significant difference (p > 0.05), and the concentration of Pb ranged from 10 to 89 mg/kg. In the nutrient solution in the presence of 30 mg/L Pb, there were no significant changes in Pb contents in roots. However, A. mangium showed an increase in Pb concentration in the roots (6829 ± 697 mg/kg), compared to non-inoculation (6242 ± 272 mg/kg). E. camaldulensis inoculation showed a decrease in Pb content (3763 ± 592 mg/kg), compared to non-inoculation (4233 ± 264 mg/kg). These results suggest that the Pc isolate closely related to P. psychrophila was effective in promoting the phytoremediation potential of A. mangium, but it was not useful for E. camaldulensis.

Functional characterization of metallothionein-like genes from Physcomitrella patens: expression profiling, yeast heterologous expression, and disruption of PpMT1.2a gene.

MAIN CONCLUSION: Physcomitrella patens contains four metallothionein-like genes. Three were shown to confer metal tolerance in yeast. Transcript profiling suggests their roles in senescence and reproductive development or cadmium and oxidative stress. Metallothioneins (MTs) have been suggested to play various roles including metal detoxification, nutrient remobilization, ROS scavenging, stress tolerance, and plant development. However, little is known about the forms and functions of MTs in bryophytes. The moss Physcomitrella patens genome was found to contain four MT-like genes. Amino acid sequence composition showed that the P. patens MTs (PpMTs) were clustered with Type 1 plant MTs, and could be further classified into two sub-types, herein referred to as sub-type 1: PpMT1.1a and PpMT1.1b and sub-type 2: PpMT1.2a and PpMT1.2b. Transcript abundance of PpMT1.1b and PpMT1.2b was upregulated in the gametophore compared to protonema, and all, except PpMT1.2a, were highly induced in senescing gametophytes. PpMT1.1a and PpMT1.1b transcripts were upregulated in protonema treated with cadmium and hydrogen peroxide. Unlike many higher plant MTs, the PpMT transcript abundance was not strongly induced in response to copper and zinc. These results suggest that PpMTs may play a role in protecting P. patens from cadmium and oxidative stress and may be involved in tissues senescence and reproductive development. The PpMTs, except PpMT1.2b, were also able to confer metal tolerance and accumulation when heterologously expressed in the ∆cup1 yeast. A P. patens mutant lacking PpMT1.2a through targeted gene disruption was generated. However, it did not show any alteration in growth phenotypes under senescence-induced conditions or hypersensitivity to cadmium, copper, zinc, H2O2, and NaCl stresses. Further characterization of additional P. patens mutants lacking single or multiple PpMTs may provide insight into the physiological roles of bryophytic MTs.

Potential microbial consortium involved in the biodegradation of diesel, hexadecane and phenanthrene in mangrove sediment explored by metagenomics analysis.

Hydrocarbon contamination is a serious problem that degrades the quality of mangrove ecosystems, and bioremediation using autochthonous bacteria is a promising technology to recover an impacted environment. This research investigates the biodegradation rates of diesel, hexadecane and phenanthrene, by conducting a microcosm study and survey of the autochthonous microbial community in contaminated mangrove sediment, using an Illumina MiSeq platform. The biodegradation rates of diesel, hexadecane and phenanthrene were 82, 86 and 8 mg kg-1 sediment day-1, respectively. The removal efficiencies of hexadecane and phenanthrene were >99%, whereas the removal efficiency of diesel was 88%. A 16S rRNA gene amplicon sequence analysis revealed that the major bacterial assemblages detected were Gammaproteobacteria, Deltaproteobacteria, Alphaproteobacteria. The bacterial compositions were relatively constant, while reductions of the supplemented hydrocarbons were observed. The results imply that the autochthonous microorganisms in the mangrove sediment were responsible for the degradation of the respective hydrocarbons. Diesel-, hexadecane- and phenanthrene-degrading bacteria, namely Bacillus sp., Pseudomonas sp., Acinetobacter sp. and Staphylococcus sp., were also isolated from the mangrove sediment. The mangrove sediment provides a potential resource of effective hydrocarbon-degrading bacteria that can be used as an inoculum or further developed as a ready-to-use microbial consortium for the purpose of bioremediation.

Hydroponic Screening of Fast-growing Tree Species for Lead Phytoremediation Potential.

Using trees as phytoremediators has become a powerful tool to remediate lead from contaminated environments. This study aims to identify potential candidates among fast-growing trees by comparing their ability to tolerate and accumulate Pb. Cuttings from Acacia mangium, Azadirachta indica, Eucalyptus camaldulensis, and Senna siamea were cultured in 25% modified Hoagland's solutions supplemented with 10, 30, and 50 mg/L Pb for 15 days. Lead concentrations were determined by a flame atomic absorption spectrophotometer. All species showed high Pb tolerance (over 78%) and low translocation factor (<1) in all treatments. The highest Pb content in roots (>40000 mg/kg) was recorded in A. mangium and E. camaldulensis grown in 50 mg/L Pb solution. Based on high biomass, tolerance index, and Pb content in plants, A. mangium and E. camaldulensis are good candidates for phytoremediation.

Performance of packed bed column using Chara aculeolata biomass for removal of Pb and Cd ions from wastewater.

Biosorption of Pb and Cd from aqueous solution by biomass of Chara aculeolata was studied in a continuous packed bed column. C. aculeolata in the fixed bed column is capable of decreasing Pb and Cd concentrations from 10 mg/L to a value below the detection limit of 0.02 mg/L. Selective uptake of Pb and Cd in a binary solution resulted in Pb having much higher relative affinity than Cd. The experiments were conducted to study the effects of column design parameters, bed depth, and flow rate on the metal biosorption. Pb uptake capacity of C. aculeolata increased with increased bed depth and decreased flow rate, while Cd uptake capacity increased with increased bed depth but remained constant at any flow rate. The Thomas model was found in a suitable fitness with the experiment data for Pb and Cd (R2 > 0.90). The efficiency of biosorbent regeneration achieved by 0.1 M HCl was very high, that was, 98% for Pb and 100% for Cd in the third reused cycle. It can be concluded that C. aculeolata is a good biosorbent for treating wastewater having low concentrations of Pb and Cd contamination.

Phytoremediation of fuel oil and lead co-contaminated soil by Chromolaena odorata in association with Micrococcus luteus.

Phytoremediation is widely promoted as a cost-effective technology for treating heavy metal and total petroleum hydrocarbon (TPH) co-contaminated soil. This study investigated the concurrent removal of TPHs and Pb in co-contaminated soil (27,000 mg kg(-1) TPHs, 780 mg kg(-1) Pb) by growing Siam weed (Chromolaena odorata) in a pot experiment for 90 days. There were four treatments: co-contaminated soil; co-contaminated soil with C. odorata only; co-contaminated soil with C. odorata and Micrococcus luteus inoculum; and co-contaminated soil with M. luteus only. C. odorata survived and grew well in the co-contaminated soil. C. odorata with M. luteus showed the highest Pb accumulation (513.7 mg kg(-1)) and uptake (7.7 mg plant(-1)), and the highest reduction percentage of TPHs (52.2%). The higher TPH degradation in vegetated soils indicated the interaction between the rhizosphere microorganisms and plants. The results suggested that C. odorata together with M. luteus and other rhizosphere microorganisms is a promising candidate for the removal of Pb and TPHs in co-contaminated soils.

Increasing the Triacylglycerol Content in Dunaliella tertiolecta through Isolation of Starch-Deficient Mutants.

The production cost of biodiesel from microalgae is still not competitive, compared with that of petroleum fuels. The genetic improvement of microalgal strains to increase triacylglycerol (TAG) accumulation is one way to reduce production costs. One of the most promising approaches is the isolation of starch-deficient mutants, which have been reported to successfully increase TAG yields. To date, such a stable mutant is not available in an oleaginous marine microalga, despite several advantages of using marine species for biodiesel production. Algae in the genus Dunaliella are known to tolerate high salt concentration and other environmental stresses. In addition, the cultivation processes for large-scale outdoor commercialization have been well established for this genus. In this study, Dunaliella tertiolecta was used to screen for starch-deficient mutants, using an iodine vapor-staining method. Four out of 20,016 UV-mutagenized strains showed a substantial reduction of starch content. A significantly higher TAG content, up to 3-fold of the wild-type level, was observed in three of the mutants upon induction by nitrogen depletion. The carotenoid production and growth characteristics of these mutants, under both normal and oxidative stress conditions, were not compromised, suggesting that these processes are not necessarily affected by starch deficiency. The results from this work open up new possibilities for exploring Dunaliella for biodiesel production.

The Effect of Light Stress and Other Culture Conditions on Photoinhibition and Growth of Dunaliella tertiolecta.

This work aimed to examine the effects of high light stress as well as other culture conditions including HCO3 − concentration, temperature, salinity, and pre-acclimation on photoinhibition and growth of halotolerant alga Dunaliella tertiolecta. Significant photoinhibition of D. tertiolecta was observed during a short period of exposure (6 hours) to high intensity of lights (1000, 1500, and 2000 µmol photons m-2 s-1); however, after 2 days of continuous light exposure, the alga adapted to high light stress and reached similar growth rates as low light exposure. The increase in HCO3 − concentration in the culture medium did not reduce photoinhibition, but the growth rate and chlorophyll contents increased with increasing HCO3 − concentrations. Temperature had significant effects on photoinhibition. Combined high temperature and high light intensity led to more serious photoinhibition and reduced cell growth rates, so did combined low salinity and high light intensity. Pre-acclimation by 50, 200, or 500 µmol photons m-2 s-1 each for 1, 3, or 6 hours (a total of nine treatments) did not significantly influence photoinhibition or cell growth of D. tertiolecta, probably because the acclimation periods were not long enough.

Bioaccumulation and biosorption of Cd(2+) and Zn(2+) by bacteria isolated from a zinc mine in Thailand.

The three bacteria, Tsukamurella paurometabola A155, Pseudomonas aeruginosa B237, and Cupriavidus taiwanensis E324, were isolated from soils collected from a zinc mine in Tak Province, Thailand. Among these bacteria, P. aeruginosa B237 and C. taiwanensis E324 were tolerant of both cadmium and zinc, while T. paurometabola A155 was highly tolerant of zinc only. Bioaccumulation experiment revealed that Cd(2+) and Zn(2+) were mainly adsorbed on the cell walls of these bacteria rather than accumulated inside the cells. During Cd(2+) and Zn(2+) biosorption, P. aeruginosa B237 and T. paurometabola A155 showed the highest removal efficiencies for Cd(2+) and Zn(2+), respectively. The maximum biosorption capacities of P. aeruginosa B237 and T. paurometabola A155 biomasses for Cd(2+) and Zn(2+) biosorptions were 16.89 and 16.75 mg g(-1), respectively, under optimal conditions. The experimental data of Cd(2+) and Zn(2+) biosorptions fitted well with Langmuir isotherm model, suggesting that Cd(2+) and Zn(2+) adsorptions occurred in a monolayer pattern on a homogeneous surface. Furthermore, the pseudo-second order and pseudo-first order kinetic models best described the biosorption kinetics of Cd(2+) and Zn(2+) adsorptions, respectively, suggesting that the Cd(2+) and Zn(2+) adsorptions took place mainly by chemisorption (Cd(2+)) and physisorption (Zn(2+)).

Histopathological changes in snail, Pomacea canaliculata, exposed to sub-lethal copper sulfate concentrations.

The acute toxicity test of Cu including range-finding and definitive test, was performed on golden apple snails, Pomacea canaliculata. The median lethal concentrations (LC50) of Cu at exposure times of 24, 48, 72 and 96 h were 330, 223, 177 and 146 µg/L, respectively. P. canaliculata were exposed to Cu at 146 µg/L for 96 h to study bioaccumulation and histopathological alterations in various organs. Snails accumulated elevated levels of Cu in gill, and lesser amounts in the digestive tract, muscle, and digestive gland. Histopathological investigation revealed several alterations in the epithelia of gill, digestive tract (esophagus, intestine, rectum), and digestive gland. The most striking changes were observed in the epithelium of the gill in which there was loss of cilia, an increase in number of mucus cells, and degeneration of columnar cells. Similar changes occurred in digestive tract epithelium. The digestive gland showed moderate alterations, vacuolization and degeneration of cells and an increase in the number of basophilic cells. We concluded that, P. canaliculata has a great potential as a bioindicator for Cu, and a biomarker for monitoring Cu contamination in aquatic environment.

Evaluation of organic and inorganic amendments on maize growth and uptake of cd and zn from contaminated paddy soils.

Pot and field experiments were conducted to investigate the effects of soil amendments (cow manure, rice straw, zeolite, dicalcium phosphate) on the growth and metal uptake (Cd, Zn) of maize (Zea mays) grown in Cd/Zn contaminated soil. The addition of cow manure and rice straw significantly increased the dry biomass, shoot and root length, and grain yield of maize when compared with the control. In pot study, cow manure, rice straw, and dicalcium phosphate all proved effective in reducing Cd and Zn concentrations in shoots and roots. Cd and Zn concentrations in the grains of maize grown in field study plots with cow manure and dicalcium phosphate amendments to highly contaminated soil (Cd 36.5 mg kg(-1) and Zn 1520.8 mg kg(-1)) conformed to acceptable standards for animal feed. Additionally both cow manure and dicalcium phosphate amendments resulted in the significant decrease of Cd and Zn concentrations in shoots of maize.