Hemanta Kumar Patra

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.

An in situ study of growth of Lemongrass Cymbopogon flexuosus (Nees ex Steud.) W. Watson on varying concentration of Chromium (Cr +6 ) on soil and its bioaccumulation: Perspectives on phytoremediation potential and phytostabilisation of chromium toxicity

Chromium (Cr) contamination in soil is a growing concern in sustainable agricultural production and food safety. Remediation of Cr from contaminated soils is a challenging task which may not only help in sustaining agriculture but also in minimizing adverse environmental impacts. Pot culture experiments were performed with the application of varied concentration of Cr+6 to assess the Chromium accumulation potential of Lemongrass and to study the impact of toxic concentration of Cr+6 on morphological, physiological and biochemical parameters of the plant. The results showed an increasing accumulation trend of Chromium with increasing Chromium concentrations in both root and shoot of 60 days old Lemongrass plants, while the protein and chlorophyll contents decreased. Similarly, accumulation of Cr increased the levels of proline and antioxidant enzymes indicating the enhanced damage control activity. The potentiality of the plant with the capacity to accumulate and stabilize Cr compound in Cr contaminated soil by phytoremediation process has been explored in the present investigation.

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.

Effects of Chelate-Assisted Chromium (Cr+6) on Growth, and Chromium Bioaccumulation in Paragrass (Brachiaria mutica Forssk.Stapf)

The growth pattern, toxicology and chromium bioavailability in 45 days grown Paragrass (Brachiaria mutica Forssk.Stapf) in response to applications of ionic Chromium (Cr+6) and chelate-assisted Cr+6 were undertaken. Root and shoot length of Paragrass significantly decreased with increasing concentration of Cr+6. Paragrass plants grown both in Cr+6 (300 ppm) and chelate(EDTA/CA)-assisted Cr+6 (300 ppm) showed noticeable decrease in root and shoot length, fresh and dry matters whereas ionic Cr+6 or chelate assisted Cr+6- EDTA/ Cr+6-CA stimulated growth at low concentration (10 ppm). Root phytotoxicity was highest (56%) in Cr+6-EDTA (300 ppm) treatment whereas shoot phytotoxicity was 36% in Cr+6 (300 ppm) treatment. High Cr accumulation was found in root (46.65 mg kg- 1) when supplemented with Cr+6-EDTA (300 ppm) as compared to other treatments. Transportation index (Ti) values are high depicting the plants with high translocation for the seedlings grown in ionic and chelate assisted Cr using 10 and 100 ppm concentrations of Cr+6.Bioconcentration Factor (BCF) of Cr increases in chelate assisted chromium treatment than chromium treatment only. Total Accumulation Rate (TAR) in different treated plants (both ionic and chelate assisted) showed increasing trend with increase in chromium treatments which indicates that the plant is tolerant in nature could survive under diverse chemospheric conditions.

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.