Bhupinder Dhir

Potential of Aquatic Macrophytes for Removing Contaminants from the Environment

The role of both terrestrial and aquatic plants in phytoremediation of various contaminants is well established. Phytoremediation has been successfully implemented at different locations, including military sites, agricultural fields, industrial units, mine tailings, and sewage and municipal wastewater treatment plants, with efficient capacity for removing various organic and inorganic pollutants through processes such as extraction, degradation, or stabilization. Aquatic macrophytes represent a diverse group of plants with an immense potential for removal/degradation of variety of contaminants, including heavy metals, inorganic/organic pollutants, radioactive wastes, and explosives. The present review emphasizes the role of aquatic macrophytes in phytoremediation technologies with due importance to each group irrespective of being free-floating, submerged, or emergent. Realizing the exorbitant abilities of aquatic macrophytes, their suitability for wider use in phytoremediation technologies including constructed wetlands is emphasized.

Physiological and antioxidant responses of Salvinia natans exposed to chromium-rich wastewater

Salvinia natans possess capacity to accumulate high concentrations of chromium (Cr). Studies were carried out to evaluate physiological efficiency and defensive potential of plant exposed to Cr-rich wastewater. Among photochemical reactions, photosystem I (PS I) and photosystem II (PS II) activity noted an increase in plants exposed to Cr-rich wastewater. Fluorescence ratio F(v)/F(m) depicted no alteration in plants exposed to Cr. The activity of ribulose-1,5-biphosphate carboxylase-oxygenase (Rubisco) noted a decline, while transthylakoidal pH gradient (DeltapH) (correlative of photophosphorylation) showed increase in plants exposed to Cr-rich wastewater. Plants lacked the ability to produce malondialdehyde, but possessed efficient enzymic and non-enzymic antioxidant defense mechanisms that played important role in curtailing oxidative stress. The activities of antioxidant enzymes showed alleviation in plants exposed to Cr-rich wastewater. The levels of cellular antioxidants noted decline suggesting a defensive role in protection against oxidative stress caused by Cr. The present findings suggest that Salvinia possess efficient antioxidant machinery that curtails oxidative stress caused by Cr-rich wastewater and protects photosynthetic machinery from damage.

Photosynthetic performance of Salvinia natans exposed to chromium and zinc rich wastewater

Investigations were carried out to evaluate alterations in photosynthetic performance of Salvinia natans (L.) exposed to chromium (Cr) and zinc (Zn) rich wastewater. Accumulation of high levels of Cr and Zn in plants affected photosynthetic electron transport. Photosystem- (PS) II-mediated electron transport was enhanced in plants exposed to Cr rich wastewater while a decline was observed in Zn-exposed plants. Photosystem-I-mediated electron transport increased in plants exposed to Cr and Zn rich wastewater. Efficiency of photosystem II (Fv/Fm) measured by fluorescence did not show any significant change in Cr-exposed plants but a decrease was observed in Zn-exposed plants as compared to the control. The enhancement in PS I-induced cyclic electron transport in Cr and Zn exposed plants led to a build up of the transthylakoidal proton gradient (DpH) which subsequently helped in maintaining the photophosphorylation potential to meet the additional requirement of ATP under stress. The carbon assimilation potential was adversely affected as evident from the decrease in Rubisco (EC 4.1.1.39) activity. The alterations in photosynthetic electron transport affected stromal redox status and induced variations in the level of stromal components such as pyridine nucleotides in plants exposed to Cr and Zn rich wastewater. The present investigations revealed that alteration in the photosynthetic efficiency of Salvinia exposed to Cr could primarily be the result of a decline in carbon assimilation efficiency relative to light-mediated photosynthetic electron transport, though in the case of Zn-exposed plants both these factors were affected equally.

Heavy Metals Alter the Potency of Medicinal Plants

There has been increased use of herbal drugs in recent years. Because of increasing demand and wider use, it is essential that the quality of plant-based drugs should be assured prior to use. When heavy metals contaminate the plants from which herbal drugs are derived, they affect both plant growth characteristics and production of secondary plant metabolites. Plants exposed to heavy metal stress show changes in production of secondary metabolites. High levels of heavy metal contamination in medicinal or other plants may suppress secondary metabolite production. Alternatively, the presence of heavy metals in medicinal plants may stimulate production of bioactive compounds in many plant species. Moreover, some research results suggest that heavy metals may play an important role in triggering plant genes to alter the titers or nature of secondary plant metabolites, although the exact mechanism by which this happens remains unclear. Oxidative stress induced by heavy metals triggers signaling pathways that affect production of specific plant metabolites. In particular, reactive oxygen species (ROS), generated during heavy metal stress, may cause lipid peroxidation that stimulates formation of highly active signaling compounds capable of triggering production of bioactive compounds (secondary metabolites) that enhances the medicinal value of the plant. As usual, further research is needed to clarify the mechanism by which heavy metals induce responses that result in enhanced secondary metabolite production.

Heavy metal induced physiological alterations in Salvinia natans

Salvinia possess inherent capacity to accumulate high levels of various heavy metals. Accumulation of Cr, Fe, Ni, Cu, Pb and Cd ranged between 6 and 9 mg g(-1)dry wt., while accumulation of Co, Zn and Mn was ∼4 mg g(-1)dry wt. Heavy metal accumulation affected the physiological status of plants. Photosystem II activity noted to decline in Ni, Co, Cd, Pb, Zn and Cu exposed plants, while Photosystem I activity showed enhancement under heavy metal stress in comparison to control. The increase in PS I activity supported build up of transthylakoidal proton gradient (ΔpH), which subsequently helped in maintaining the photophosphorylation potential. Ribulose 1,5 dicarboxylase/oxygenase (Rubisco) activity noted a decline. Alterations in photosynthetic potential of Salvinia result primarily from changes in carbon assimilation efficiency with slight variations in primary photochemical activities and photophosphorylation potential. Studies suggest that Salvinia possess efficient photosynthetic machinery to withstand heavy metal stress.

Potential of biological materials for removing heavy metals from wastewater

Agricultural products/by-products are natural sorbent materials that possess capacity for removing contaminants including heavy metals from wastewaters and hence can be exploited as replacement of costly methods for wastewater treatment. The sorption of heavy metals onto these biomaterials is attributed to constituents proteins, carbohydrates, and phenolic compounds that contain functional groups such as carboxylate, hydroxyl, and amine. Natural efficiency of these materials for removing heavy metals can be enhanced by treating them with chemicals. The present review emphasizes their use in developing eco-friendly technology for a large-scale treatment of wastewater.

Alliin obtained from leaf extract of garlic grown under in situ conditions possess higher therapeutic potency as analyzed in alloxan-induced diabetic rats.

Context: Garlic, Allium sativum L. (Liliaceae), possesses high therapeutic and pharmacological properties. Hypoglycemic activity is attributed to alliin (S-allyl cysteine sulfoxide), the main active principle localized in garlic cloves. Objective: To compare the production and therapeutic efficiency of alliin extracted from garlic leaves of plants grown under ex situ and in situ conditions. Materials and methods: Alliin content of leaves was quantified and aqueous leaf extracts (from ex situ and in situ grown plants) were given to normal and alloxan-induced diabetic rats for five weeks. Results: Alliin production noted ~50% enhancement in leaves from plants grown under in situ conditions. Serum glucose, triglycerides, total lipids, total cholesterol, low-density lipoprotein (LDL)-, and very low-density lipoprotein (VLDL)-cholesterol in diabetic rats treated with alliin produced from in situ grown plants noted significant reduction of ~54%, 15%, 14%, 20%, 24%, and 15%, while 35%, 14%, 10%, 12%, 17% and 11% reduction was noted in diabetic rats treated with alliin produced from ex situ grown plants in comparison with those administered with distilled water. High-density lipoprotein (HDL)-cholesterol did not show any significant change. Leaf extract of plants lowered serum enzyme levels (alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase) toward the norm better than glibenclamide. The histopathological alteration in pancreas caused by alloxan was also reduced by leaf extract. Discussion and conclusion: These findings demonstrate leaf extract obtained from plants grown under in situ condition possess higher therapeutic efficiency in comparison with leaf extract obtained from plants grown under ex situ condition. Studies suggest that environmental factors influence production of alliin and its therapeutic potential.

Disposal of Metal Treated Salvinia Biomass in Soil and its Effect on Growth and Photosynthetic Efficiency of Wheat

Phytoremediation technologies generate huge quantities of biomass, the disposal of which is a serious concern. Wastewater samples collected from electroplating industries were treated with Salvinia biomass. The effect of application of metal loaded Salvinia plant biomass in soil on growth and physiological indices of 10-day-old seedlings of Triticum aestivum was evaluated. Controls (A) consisted of soil supplemented with untreated plant biomass. Seed germination, seedling height, total chlorophyll, glucose and protein levels, photosynthetic efficiency (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (qn), quantum yield (Y), and electron transport rate (ETR) were not significantly affected in seedlings raised in soils supplemented with metal loaded biomass from most of the samples (B–F) in comparison to control. However, significant decline was noted in total chlorophyll, glucose, and quantum yield in plants grown in soil supplemented with biomass from sample E. Among elemental levels, C(%) remained largely unaffected, N(%) showed slight enhancement but a decrease in H(%) was noted in plants grown in soil supplemented with biomass from sample E. Our results, therefore, suggest that metal accumulated Salvinia biomass obtained after phytoremediation of heavy metal contaminated wastewater can be supplemented in soil. Further studies are required to assess long-term effects of disposal of metal loaded Salvinia plant biomass in soil.

Heavy Metal Removal Potential of Dried Salvinia Biomass

Investigations were carried out to evaluate heavy metal adsorption capacity of Salvinia. Batch experiments showed that dry plant biomass possess good potential to adsorb heavy metals such as Ni, Co, Cr, Fe, and Cd. The metal adsorption increased with increase in initial metal concentration. The data obtained fitted well with Freundlich equilibrium isotherm. Further characterization of plant biomass showed presence of both acidic and basic surface functionalities that might facilitate binding of metal ions. Fourier transform infrared (FTIR) spectra of plant biomass suggested involvement of carbonyl (C˭O), carboxyl (-COO), and hydroxyl (-OH) groups in binding heavy metals to plant biomass. The studies establish S. natans as an effective biosorbent for removing heavy metals from wastewater and further emphasize biomass utilization in wastewater treatment technologies.

Soil Amendment with Municipal Sludge Does not Alter the Physiological Status of Solanum melongena

Investigations were carried to evaluate the effect of municipal sludge amendment in soil on physiological status of crop plant- Solanum melongena var. Pusa Hybrid 6. Preliminary studies proved sludge to be non-phytotoxic. The germination index (GI), the radicle and hypocotyl length did not exhibit differences between control and sludge treated samples hence reflecting the non-toxic nature. Soil supplementation with sludge in different proportions does alter the physiological status of plants. The parameters such as efficiency of photosystem II (Fv/Fm), electron transport rate (ETR), quantum yields of photosystem II (Y) did not show much differences within the treatments. Chlorophyll content and sugar levels also did not showed much differences in plants rose in sludge supplemented soil and control. The present studies demonstrated that sludge can be utilized as a soil supplement as it improves soil properties without altering the physiological status of plants.