Monalisa Mohanty

Attenuation of Chromium Toxicity by Bioremediation Technology

Chromium is an important toxic environmental pollutant. Chromium pollution results largely from industrial activities, but other natural and anthropogenic sources also contribute to the problem. Plants that are exposed to environmental contamination by chromium are affected in diverse ways, including a tendency to suffer metabolic stress. The stress imposed by Cr exposure also extends to oxidative metabolic stress in plants that leads to the generation of active toxic oxygen free radicals. Such active free radicals degrade essential biomolecules and distort plant biological membranes. In this chapter, we describe sources of environmental chromium contamination, and provide information about the toxic impact of chromium on plant growth and metabolism. In addition, we address different phytoremediation processes that are being studied for use worldwide, in contaminated regions, to address and mitigate Cr pollution. There has been a long history of attempts to successfully mitigate the toxic effects of chromium-contaminated soil on plants and other organisms. One common approach, the shifting of polluted soil to landfills, is expensive and imposes environmental risks and health hazards of its own. Therefore, alternative eco-friendly bioremediation approaches are much in demand for cleaning chromium-polluted areas. To achieve its cleaning effects, bioremediation utilizes living organisms (bacteria, algae, fungi, and plants) that are capable of absorbing and processing chromium residues in ways which amend or eliminate it. Phytoremediation (bioremediation with plants) techniques are increasingly being used to reduce heavy metal contamination and to minimize the hazards of heavy metal toxicity. To achieve this, several processes, viz., rhizofiltration, phytoextraction, phytodetoxification, phytostabilization, and phytovolatilization, have been developed and are showing utility in practice, or promise. Sources of new native hyperaccumulator plants for use at contaminated sites are needed and constitute a key goal of ongoing phytoremediation research programs. Such new plants are needed to enhance the attractiveness of phytoremediation as an effective, affordable, and eco-friendly technique to achieve successful clean-up of metal-contaminated sites worldwide.

Chromium Bioaccumulation in Rice Grown in Contaminated Soil and Irrigated Mine Wastewater—A Case Study at South Kaliapani Chromite Mine Area, Orissa, India

The level of chromium (Cr) contamination in soils and irrigated mine wastewater at South Kaliapani chromite mine region of Orissa, (India) were investigated. Chromium bioaccumulation in rice plants (Oryza sativa L. cv. Khandagiri) irrigated with Cr+6 contaminated mine wastewater was analyzed along with its attenuation from mine wastewater. The levels of Cr+6 in irrigated mine wastewaters in successive rice grown plots were analyzed on 75 days and 100 days after transplantation of seedlings. Total chromium content in different parts of rice plants and soil samples from different plots was analyzed during harvesting stage (125 days after transplantation). Cr accumulation was significantly high in surface soils (0–20 cm) with a mean value of 11,170 mg kg−1, but it decreased significantly after the crop harvest. About 70% to 90% reduction of Cr+6 levels was observed in irrigated mine wastewater when passed through successive rice plots. High bio-concentration of Cr in leaves with values ranging from 125–498 mg kg−1 as compared to stem (25–400 mg kg−1) and grain (5–23 mg kg−1) was noticed. The reduction of Cr+6 levels is related to plant age, high biomass and area of water passage and was attributed to rhizofiltration technique.

Phytoremediation potential of paragrass--an in situ approach for chromium contaminated soil.

The present in situ phytoextraction approach uses paragrass (Brachiaria mutica (Forssk) Stapf) as a hyper accumulator for attenuation of chromium level in soil and mine waste water at South Kaliapani chromite mine area of Orissa. The bioconcentration factor (BCF) for Cr was maximum (0.334) in 100 days grown paragrass weeds. Transportation index (Ti) i.e. 6.16 and total accumulation rate (TAR) i.e. 8.2 mg kg−1day−1 was maximum in 125 days old paragrass grown in Cr contaminated experimental cultivated plots. Cr bioaccumulation in roots was nearly 1000 times more than shoots. Paragrass showed luxuriant growth with massive fibrous roots when grown over Cr contaminated soils (11,170 mg/ kg dry soil). Cr bioaccumulation varies significantly with plant age, biomass and level of Cr contamination in irrigated mine waste water and soil. Paragrass could be used as hyperaccumulators as it showed rapid massive growth with a high tolerance to Cr.

Effect of Chelate-Assisted Hexavalent Chromium on Physiological Changes, Biochemical Alterations, and Chromium Bioavailability in Crop Plants—An In Vitro Phytoremediation Approach

ABSTRACT This study revealed heavy metal–induced physiological and biochemical alterations in crop seedlings by supplementing chelating agents in the nutrient solution. Hexavalent chromium (Cr+6) induces several toxic effects in hydroponically grown rice, wheat, and green gram seedlings. A noticeable decrease was observed in root length, shoot length, biomass content, and chlorophyll biosynthesis of the seedlings grown in the nutrient solutions supplemented with Cr+6 at 100 μM. The seedling growth was stimulated with supplement of chelating agents such as EDTA, DTPA, and EDDHA. An increase in proline content was noticed with the application of Cr+6 (100 μM) in nutrient solutions. Stimulated activities of antioxidant enzymes such as catalase and peroxidase were noticed with increasing concentrations of chromium. Cr bioaccumulation was significantly high in roots of seedlings treated with Cr+6 at 100 μM in nutrient solution. Shoot translocation of Cr as depicted by transportation index (Ti) values for different crops were enhanced with the application of chelating agents. The total accumulation rate (TAR) for Cr was enhanced with the supplementation of DTPA in rice and wheat, whereas the application of EDDHA was found effective for increasing the accumulation rate of Cr in green gram seedlings. This study demonstates the role of chelating agents in lessening the toxic effects of Cr+6. The chelating agents supplemented with Cr+6 in the culture medium enhanced the Cr bioavailability in plants.

Submergence Stress: Responses and adaptations in crop plants

Submergence stress frequently encountered in crop plants is a widespread limiting factor for crop production throughout the world especially in irrigated and high-rainfall environments which results in huge economic losses. This chapter covers various features of submergence stress with special reference to crop plants, viz. causes of submergence and biophysical and biochemical alterations in crops, and various defence mechanisms adopted by crop plants. A brief discussion on different types of naturally or artificially developed tolerance mechanisms are presented here.

Chromium translocation, concentration and its phytotoxic impacts in in vivo grown seedlings of Sesbania sesban L. Merrill.

The present in vivo pot culture study showed hexavalent chromium (Cr+6) induced phytotoxic impacts and its translocation potential in 21 days old sesban (Sesbania sesban L. Merrill.) seedlings. Cr+6 showed significant growth retardation in 21 days old sesban (Sesbania sesban L. Merrill.) seedlings. Germination of seeds at 10,000 mg L-1 of Cr+6 exhibit 80% inhibition in germination. Seedling survival was 67% after 7 days of seedling exposure to 300 mg kg-1 of Cr+6. Shoot phytotoxicity was enhanced from 6% to 31% with elevated supply of Cr+6 from 10 mg kg-1 to 300 mg kg-1. Elevated supply of Cr+6 exhibited increasing and decreasing trends in % phytotoxicity and seedling tolerance index, respectively. Elevated supply of chromium showed decreased chlorophyll and catalase activities. Peroxidase activities in roots and leaves were significantly higher at increased supply of Cr+6. Cr bioconcentration in roots was nearly 10 times more than stems whereas leaves showed nearly double accumulation than stems. Tissue specific chromium bioaccumulation showed 53 and 12 times more in roots and shoots respectively at 300 mg kg-1 Cr+6 than control. The present study reveals potential of sesban for effective Cr translocation from roots to shoots as evident from their translocation factor and Total Accumulation Rate values.

Phytochemical screening and comparative bioefficacy assessment of Artocarpus altilis leaf extracts for antimicrobial activity

Artocarpus altilis (breadfruit) leaf extracts in different solvent media (petroleum ether, methanol, and ethyl acetate) were assessed for antimicrobial activity. Breadfruit leaf extracts have been reported to have different phytoconstituents. The effect of leaf extracts in different solvent media on pathogenic organisms like Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus mutans, and Enterococcus faecalis was studied by disc diffusion assay and MIC (minimal inhibitory concentrations) values were investigated. Phytochemical compounds like steroids, phytosterols, gums and resins were found to be present in leaf extracts with different extraction media. Phenols and terpenoids were detected in ethyl acetate and methanol leaf extracts. Flavonoids were present in the petroleum ether and ethyl acetate leaf extracts, whereas tannins were detected only in the methanol leaf extract. Maximum zone of inhibition was observed for Strep. mutans, E. faecalis, S. aureus, and P. aeruginosa by using 50 μl of ethyl acetate and methanol leaf extracts, 20 μl of petroleum ether leaf extract, 25 μl of petroleum ether leaf extract, and 50 μl of methanol leaf extract, respectively. The MIC values were reported in between 0.3 and 0.6 mg/ml corresponding to variations in different solvent media used for leaf extracts against four different pathogenic bacteria.

Hexavalent Chromium Induced Toxicological, Physiological and Biochemical Alterations in Sesbania sesban L. Seedlings

Hexavalent Chromium Induced Toxicological, Physiological and Biochemical Alterations in Sesbania sesban L. Seedlings Widespread use of chromium in several industrial and mining activities leads to the release of toxic hexavalent chromium (Cr6+) to environment. Screening and identification of hyperaccumulators for possible phytoremediation of Cr6+ from these contaminated sites has gained utmost importance in recent years. A pot culture experiment was conducted to observe the possible phytotoxic effects of Cr6+ in an agroforestry species, i.e. Sesbania sesban L., commonly known as sesban. Cr6+ showed significant growth retardation in 21 days old sesban seedlings, which includes 80% inhibition in seed germination at 10,000 ppm, 59.6% germination index.