Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns.

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

Biocompatible metal decontamination from soil using Ageratum conyzoides.

Metal pollution in soil is a serious problem among waste landfill sites and associated environment all over the globe. Amelioration of contaminated soil by plant bioaccumulation is an important strategy to protect the soil environment. Ageratum conyzoides is a common weed species that can grow easily in any contaminating site and bioaccumulate heavy metals present in the e-waste dumping/recycling sites as a natural scavenger. Soil selected for the study was contaminated with waste cathode ray tube (CRT) and printed circuit board (PCB) powder in the concentration range of 1-10 g/kg. Soil decontamination was achieved by using weed plants with ethylene diamine tetraacetic acid (EDTA, 0.1 g/kg) and kinetin (100 µM) combination in pot experiments. Fe, Mn, Zn, and Cu accumulation was found to be highest in leaves (6.51-38.58; 0.14-73.12; 5.24-269.07; 9.38-116.59%); Pb and Cr in stem (22.83-113.41; 21.05-500%), respectively, as compared with blank. Ion chromatography was used as a tool for the measurement of essential ions present in plant under different conditions. Plants showed better growth in terms of shoot, root length, biomass weight, and chlorophyll content with the proposed combination. EDTA allows the metals available for the accumulation through possible complexation. Also, the compatibility of kinetin to manage stress in plant is found to be enhanced in the presence of EDTA due to possible π-π interaction. Metal stress condition causes the deficiency of essential ions in the plants thereby disturbing its biochemistry and results in its eventual death. EDTA-kinetin hybrid treatment was found to be compatible for metal decontamination from soil, its detoxification in plants by changing its environment and restoring the essential ions for the survival of plant.

Structural basis for expanding the application of bioligand in metal bioremediation: A review.

Bioligands (BL) present in plant and microbes are primarily responsible for their use in metal decontamination. Both primary (proteins and amino acid) and secondary (proliferated) response in the form of BL is possible in plants and microbes toward metal bioremediation. Structure of these BL have specific requirement for preferential binding towards a particular metal in biomass. The aim of this review is to explore various templates from BL (as metal host) for the metal detoxification/decontamination and associated bioremediation. Mechanistic explanation for bioremediation may involve the various processes like: (i) electron transfer; (ii) translocation; and (iii) coordination number variation. HSAB (hard and soft acid and base) concept can act as guiding principle for many such processes. It is possible to investigate various structural homolog of BL (similar to secondary response in living stage) for the possible improvement in bioremediation process.

Perturbations and 3R in carbon management.

Perturbations in various carbon pools like biological, geological, oceanic, and missing carbon sink affect its global data, which are generally neglected or ignored in routine calculations. These natural and anthropogenic events need to be considered before projecting a sustainable carbon management plan. These plans have both general and experimental aspects. General plans should focus on (a) minimizing emission; (b) maximizing environmentally sound reuse, reduce, and recycling; (c) effective treatment; and (d) converting carbon into valuable products with atom economy. Experimental carbon management plans involving various biological and chemical techniques with limitation in terms of research level and economic feasibility. Chemical options have benefits of higher productivity and wider product range, but it suffers from its higher-energy requirements and environmental unfriendliness. In contrast to this, biological options are more selective and less energy intensive, but their productivity is very low. Hence, there is a requirement of hybrid process where the benefits of both the options, i.e., biological and chemical, can be reaped. In view of above, the proposed review targets to highlight the various perturbations in the global carbon cycle and their effects; study the currently practiced options of carbon management, specifically in light of 3R principle; and propose various new hybrid methods by compatible combinations of chemical and biological processes to develop better and safer carbon management. These methods are hypothetical so they may require further research and validations but may provide a comprehensive base for developing such management methods.

Pb detoxification in Equisetum diffusum.

Current research highlights the use of aquatic macrophyte Equisetum diffusum (Himalayan horsetail) for lead detoxification. This plant species can grow in waste cathode ray tube (CRT) powder and absorbs its Pb. X-ray fluorescence spectroscopy (XRF) analysis of plant ash shows that 68 mg/kg lead concentration in the untreated plant was improved to 7600 mg/kg in CRT powder after 90 days. The role of monosilicic and/or monoplumbic acid as reaction intermediates for Pb detoxification and associated bioaccumulation is proposed. Pb detoxification in E. diffusum is mainly rendering around the iso-electronic nature of Pb and Si and forms similar phytochelatin (PC) complexes with available family of peptide ligands. The study focuses on the underlying functions of silicon containing plants in metal detoxification.

Analysis of the essential oil of large cardamom (Amomum subulatum Roxb.) growing in different agro-climatic zones of Himachal Pradesh, India.

BACKGROUND: The aim of the present study was to investigate variations in the chemical composition of the essential oil from seeds of large cardamom grown at different altitudes in Himachal Pradesh, India. The composition of the essential oil was determined by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O). RESULTS: The oil components showed qualitative and quantitative variations in the composition. GC and GC-MS analysis led to the identification of 55 compounds representing 98% of total oil. Major components in the oil were 1,8-cineole, α-terpineol, DL-limonene, nerolidol, 4-terpineol, δ-terpineol, δ-3-carene, ß-myrcene, germacrene D, α-terpinene and longifolenaldehyde. The oil yields obtained were 9.8-19.5 g kg(-1). Cardamom oil from Himachal Pradesh was found to contain new compounds, viz. 4-terpineol, δ-3-carene, trans-sabinene hydrate, 1-phellandrene, α-terpinene, bicyclo-germacrene, isopinocarveol and ledenoxid-II. α-Terpenyl acetate, the major constituent of small cardamom, was also detected in the oil of large cardamom grown in Himachal Pradesh. Application of aroma extract dilution analysis revealed 35 compounds having aroma impact with the flavour dilution factor ranging from 2 to 1024, and 34 of these compounds were identified. The five most intense aromatic components are dl-limonene, 1,8-cineole, ß-myrcene, α-pinene, α-basabolol. This is the first time that the characterisation of odour-active compounds has been carried out on large cardamom. CONCLUSION: The presence of 4-terpineol, δ-3-carene, trans-sabinene hydrate, 1-phellandrene, α-terpinene, 1-terpineol, bicyclogermacrene, isopinocarveol, ledenoxid-II, longifolenaldehyde and α-terpenyl acetate make the aroma of the oil different from large cardamom oil of Sikkim and could offer potential as a new food flavour.