Shalini Srivastava

Cadmium mobilisation and plant availability – the impact of organic acids commonly exuded from roots

The present work highlights metal-organic acid interactions with special reference to their plant availability. Pot experiments were conducted to investigate the effect of various organic (carboxylic and amino) acids on the uptake and translocation of root-absorbed Cd by maize (Zea mays) plants grown in sand and soil culture. Statistically significant increases in Cd accumulation from Cd-treated plants in the presence of increasing concentrations of organic acids, suggest the existence of Cd-organic acid interactions in the soil-plant system. In order to support the above hypothesis of formation of organically bound Cd, separate experiments were performed to synthesize and estimate its various forms viz. cationic, anionic and neutral. The chemical nature of the organically bound forms was ascertained by electrophoretic experiments. Amino acids have been found to be less effective in the mobilisation of cadmium compared to carboxylic acids. The results are discussed on the basis of the potential of organic acids to form complexes with Cd.

Saraca indica leaf powder for decontamination of Pb: removal, recovery, adsorbent characterization and equilibrium modeling

The present study explores the effectiveness of Saraca indica leaf powder, a surplus low value agricultural waste, in removing Pb ions from aqueous solution. The influence of pH, biomass dosage, contact time, particle size and metal concentration on the removal process were investigated. Batch studies indicated that maximum biosorption capacity for Pb was 95.37% at the pH 6.5. The sorption process followed the first order rate kinetics. The adsorption equilibrium data fitted best to both Langmuir and Freundlich isotherms. Morphological changes observed in scanning electron micrographs of untreated and metal treated biomass confirmed the phenomenon of biosorption. Fourier transform infrared spectroscopy of native and exhausted leaf powder confirmed lead biomass interactions responsible for sorption. Acid regeneration was tried for several cycles with a view to recover the sorbed metal ion and also to restore the sorbent to its original state. The findings showed that Saraca indica leaf powder can easily be envisaged as a new, vibrant, low cost biosorbent for metal clean up operations.

Effect of selenite and selenate on plant uptake and translocation of mercury by tomato (Lycopersicum esculentum)

Pot culture experiments containing sand and soil, at two levels of mercury (2 and 5 μg mL-1) added through irrigation with increasing supplementation of selenium (selenite and selenate) led to a decrease in the uptake of mercury by tomato (Lycopersicum esculentum) plant. Both the forms of selenium (selenite and selenate) were found to be equally effective in reducing the mercury accumulation by plants. The observed reduction pattern of mercury accumulation in plant tissues has been discussed on the basis of the formation of insoluble HgSe complex in soil-root environment.

Groundwater Quality Assessment of Tehsil Kheragarh, Agra (India) with Special Reference to Fluoride

Fluoride concentration and other parameters in groundwater from 261 villages in Tehsil Kheragarh of District Agra were assessed and attempts were made to observe the relationship between fluoride and other water quality parameters. Of 658 groundwater samples (collected from separate sources) analysed for fluoride, 27% were in the range of 0–1.0 mg/L, 25% in 1.0–1.5 mg/L, 32% in1.5–3.0 mg/L and 16% above 3.0 mg/L. The highest fluoride concentration recorded was 12.80 mg/L. Significant correlation of fluoride with pH, alkalinity, Na, SiO2 and PO4 were observed. Factor analysis was also attempted in order to identify the contributing sources.

Characterization of novel Zea mays based biomaterial designed for toxic metals biosorption.

Structural modifications onto Zea mays Cob powder, ZMCP lead to the formation of novel biomaterial with increased sorption efficiency and environmental stability for the abatement of Pb (II), Cd (II), Ni (II) and Cr (III) in single as well as multi-metal ion solutions. Synthetic strategy for strengthening the functional groups, COO(-) responsible for binding of metal species has been applied using acetylation, succination and graft co-polymerization processes. The resultant novel biomaterial exhibits enhancement in sorption efficiency from 2 to 15% and stability in terms of regeneration cycles from 3 to 5, evidence to support biomaterial designed has been provided on the basis of SEM, FTIR and TGA. The findings open up new avenues in the modern Green Technology of water treatment using biosorbent-possessing potential for commercialization.

Nanotech Reinforcement onto Cellulosic Fibers: Green Remediation of Toxic Metals

ABSTRACT Strengthening the functional (COO−) group and nanotech reinforcement for binding of cationic metal species has been applied to cellulosic fibers. Modified Nano cellulosic fibers (NCFs) have been used for the remediation of cationic toxic metals from water bodies. Different polymerized NCFs exhibited enhancement in sorption efficiency (3 to 10%) and stability in terms of increased (3 to 5) regeneration cycles for Cd (II), Pb (II), Ni (II), and Cr (III) ions in single and multi-metal solutions. Novel NCFs have been characterized on the basis of Optical, TEM, FTIR, and TGA techniques and found to have enough potential for environmental clean-up.

Effect of organic acids on the availability of cadmium in wheat.

Abstract Pot experiments were conducted to investigate the effect of various organic (carboxylic and amino) acids on the uptake and translocation of root-absorbed cadmium by wheat (Triticum vulgare) plants grown in sand and soil culture. Statistically significant increases in cadmium accumulation from cadmium treated plants in the presence of increasing concentration of organic acids suggest the existence of Cd–organic acid interactions in the soil-plant system resulting into the formation of organically bound cadmium which is mobile and plant available. Separate experiments were performed to synthesise and estimate the various forms of organically bound cadmium. The chemical nature of the organically bound form was ascertained by electrophoretic experiments. Amino acids were less effective in the mobilisation of cadmium compared to carboxylic acids. The results are discussed on the basis of the potential of organic acids to form complexes with cadmium

Biosorption: Application Strategies

Over the past few years, intensifying research into metal biosorption elucidated the principles of this effective metal removal phenomenon. Biosorption can be cost-effective, particularly in environmental applications where low cost of the metal removal process is most desirable. Some efficient natural biosorbents have been identified that require little modification in their preparation. It is particularly in ecological aspects where biosorption can make a difference due to its anticipated low cost. The application aspect is what makes the research and development work in this novel area exciting and worthwhile. While the biosorption process could be used even with a relatively low degree of understanding of its metal-binding mechanisms, better understanding will make for its more effective and optimized applications. If the biosorption processes were to be used as an alternative in the wastewater treatment scheme, the regeneration of the biosorbent may be crucially important for keeping the process cost down and to open the possibility of recovering the metals extracted from liquid phase. For this process it is desirable to desorb the sorbed metals and to regenerate the biosorbent material for another cycle of application.

Biosorption of trivalent and hexavalent chromium from aqueous systems using shelled Moringa oleifera seeds

Abstract The present study explores the sorption properties of shelled Moringa oleifera seeds (SMOS) for removal of two environmentally important oxidation states of chromium (trivalent and hexavalent) from an aqueous system on the laboratory scale. Sorption studies reveal the optimum conditions for the removal of 81.02%; Cr (III) and 88.15% Cr (VI) as follows: biomass dosage (4.0 g), metal concentration [25mg/L for Cr (III); 50mg/L for Cr (VI)], contact time (40 minutes) at pH 6.5 and 2.5 respectively. The adsorption data were found to fit well both the Freundlich and Langmuir isotherms. Characterization of the seed powder by FTIR showed the clear presence of amino acid moieties having both positively charged amino and negatively charged carboxylic groups and confirmed that biosorption involves amino acid-chromium interactions. SEM studies of native and exhausted [Cr(III) and Cr(VI)] treated SMOS revealed large spherical clusters having a pore area of 8.66 µm2 in the case of native SMOS while dense agglomerated etched dendrite type morphology have a pore area of 0.80 µm2 in Cr (III) and 0.78 µm2 in Cr (VI) treated SMOS The spent biosorbent was regenerated and found to be effectively reusable for four cycles.

Effect of selenite and selenate on plant uptake of cadmium by kidney bean (Phaseolus mungo) with reference to Cd—Se interaction

ABSTRACTPot culture experiments have been conducted to study the effect of selenite and selenate pretreatment on the uptake and translocation of root-absorbed cadmium in the kidney bean plant, irrigated with 2 μg mL−1 of Cd. A statistically significant reduction in cadmium uptake with increasing concentration of selenite and selenate (0.5–6.0 μg mL−1) has been observed. Selenite treatment is found to be more effective in decreasing cadmium uptake.