U. N. Rai

Wastewater treatability potential of some aquatic macrophytes: Removal of heavy metals☆

Abstract Free-floating, submerged and emergent plants ( Hydrodictyon reticulatum, Spirodela polyrrhiza, Chara corallina, Ceratophyllum demersum, Vallisneria spiralis, Bacopa monnieri, Alternanthera sessilis and Hygrorrhiza aristata ) were evaluated for their heavy metal (Cu, Cr, Fe, Mn, Cd, Ph) removal potential under laboratory conditions. Treatability study was carried out using pond water contaminated with the effluents from various industrial sources. Plants differ in the extent of metal accumulation; however, metals present in relatively high concentrations were accumulated more. Results showed a decrease in Cr level from 4.866 μM to below maximum permissible limit by C. demersum, H. reticulatum and S. polyrrhiza within 15 d. Similarly, elevated levels of Fe were reduced to below permissible limit by C. demersum and H. reticulatum after 15 d. Manganese concentration (6.63 μM) were reduced to 1.63 p M by C. demersum and H. reticulatum in 7 d. Bacopa monnieri and H. aristata decreased Cd levels from 0.155 μM to 0.009 μM whereas S. polyrrhiza and H. reticulatum reduced levels to 0.036 μM after 15 d of treatment. More than 70% Pb was removed by C. demersum, H. aristata and H. reticulatum within 15 d. Results suggest the use of these plants for metal abatement in dilute wastewaters.

Chromium (VI) accumulation reduces chlorophyll biosynthesis, nitrate reductase activity and protein content in Nymphaea alba L.

Plants of Nymphaea alba L. grown at various levels of chromium (VI) ranging from 1 to 200 microM accumulated chromium in concentration and duration-dependent manner. At all Cr levels, chromium accumulation by various plant tissues followed the order roots > leaves > rhizomes. Approximately 93% of total chromium present in the medium was accumulated by plants at lowest conentration (1 microM) used in the experiment. Chromium-induced toxicity appears at 1 microM chromium resulting in the build-up of delta-aminolevulinic acid (ALA) and reduced activities of delta-aminolevulinic acid dehydratase (ALAD) and nitrate reductase (NR), total chlorophyll (Chl) and protein contents. Ch1a was more sensitive than Ch1b to chromium toxicity. It could be inferred that chromium toxicity is not located at the level of ALA synthesis, but, probably at the ALAD activity which was more severely affected during chlorophyll biosynthesis. Finally, impaired chlorophyll biosynthesis resulted in reduced total chlorophyll content.

Role of glutathione and phytochelatin in Hydrilla verticillata (l.f.) Royle and Vallisneria spiralis L. under mercury stress

Abstract Both free (Hydrilla verticillata) and rooted (Vallisneria spiralis) submerged plants showed high potential to accumulate mercury, maximum being in roots of V. spiralis. During mercury stress these plants synthesized different species of phytochelatins (PCs), which bind with the accumulated mercury and showed high levels of cysteine and non-protein thiols. The induction of phytochelatins was accompanied by a decline in cellular levels of glutathione in both the plants, although the decline was only observed at high concentration and long duration of Hg in V. spiralis. Buthionine sulfoximine inhibited accumulation of non-protein thiols and glutathione, indicating the involvement of glutathione in phytochelatin synthesis. However, cycloheximide had no effect on early PC synthesis. Results showed that phytochelatins are synthesized in these plants and play a role in mercury detoxification.

Lead induced changes in glutathione and phytochelatin in Hydrilla verticillata (l. f.) Royle

Abstract Effects of lead were studied on cysteine, acid-soluble thiol, glutathione contents and synthesis of phytochelatins (PCs) in a submerged aquatic macrophyte, Hydrilia verticillata grown under cultural conditions. All concentrations of Pb ranging from 0.5–10.0 μM enhanced cysteine content and accumulation of acid-soluble thiols inside plant tissue and synthesis of phytochelatins. Isolated fractions of the Pb-binding complex indicated involvement of phytochelatins in Pb detoxification. The synthesis of these peptides was concomitant with a decline in total glutathione content. Buthionine sulfoximine, an inhibitor of glutathione synthesis, reduced accumulation of acid soluble thiols and total glutathione content. However, the protein synthesis inhibitor cycloheximide did not affect initial accumulation of acid soluble -SH. Results indicated that PC synthesis was induced under lead stress utilizing glutathione as a substrate.

Physico-chemical characteristics and pollution level of Lake Nainital (U.P., India): role of macrophytes and phytoplankton in biomonitoring and phytoremediation of toxic metal ions.

Lake Nainital is the sole source of drinking water for the local people and even to majority of tourists. In background of lake utility and its importance at national level, such study is essential which is focused on toxic metal pollution and current nutrient status of the lake and their magnification by algae and macrophytes. Study has shown that lake water is rich in nutrients which supports growth of many aquatic macrophytes and algal blooms. Besides, water is contaminated with metals like Cr, Cu, Fe, Mn, Ni, Pb and Zn. Concentration of some of them like Fe, Pb and Ni were higher than the recommended maximum permissible limits. Concentration of these metals were also found high in lake sediments. The level of metals amongst various components of lake varied considerably in different season. Plants and algae growing therein accumulated appreciable amount of metals and water roots of Salix being more efficient than others. High metal removing potential of these plants may be significant for biomonitoring studies and could be a useful phytoremediation technology to restore water quality by harvesting submerged and floating biomass inhabiting littoral zone of the lake.

Metal contamination of soil and translocation in vegetables growing under industrial wastewater irrigated agricultural field of Vadodara, Gujarat, India ☆

The present investigation was carried out to evaluate metals concentration in ten vegetable crops growing in mixed industrial effluent irrigated agricultural field near Vadodara, Gujarat, India. Differential accumulation and translocation of various metals in selected vegetables plant species was observed. A higher concentration of metals were found in order of Fe>Mn>Zn>Cd>Cu>Pb>Cr>As in soil irrigated with industrial effluent than soil irrigated with tube well water; however, the concentration of As, Cr and Pb found below detection limit in tube well water irrigated soil. Metal accumulation in root and top of vegetables varied significantly both in relations to metal concentration in the soil and the plant genotype. Among ten vegetable species studied five vegetable species, i.e. Spinach, Radish, Tomato, Chili and Cabbage growing in mixed industrial effluent irrigated agricultural field showed high accumulation and translocation of toxic metals (As, Cd, Cr, Pb and Ni) in their edible parts, thus, their cultivation are unsafe with respect to possible transfer in food chain and health hazards. However, it is suggested that vegetable crops restricting toxic metal in non-edible port may be recommended for cultivation in such metal contaminated agricultural field.

Bioaccumulation of toxic metals (Cr, Cd, Pb and Cu) by seeds of Euryale ferox Salisb. (Makhana) ☆

The level of toxic metals Cr, Cd, Pb and Cu was determined in seeds, water and sediments collected from nine closed waterbodies of Darbhanga, north Bihar, used for cultivation of the edible aquatic macrophyte Euryaleferox Salisb. during harvesting season of the crop for two successive years (1996 and 1997). Seeds bioconcentrated appreciable amount of these toxic metals in the order Pb > Cr > Cu > Cd. The increased load of metal pollution due to domestic and municipal discharges threatened the habitats of the plant. The toxic metal contents in seeds were found positively correlated with the ambient concentration of metals in water and sediments. The importance of these findings has been discussed for national water resource economy of the country and human health perspectives.

Constructed wetland as an ecotechnological tool for pollution treatment for conservation of Ganga river

With aim to develop an efficient and ecofriendly approach for on-site treatment of sewage, a sub-surface flow constructed wetland (CW) has been developed by raising potential aquatic macrophytes; Typha latifolia, Phragmites australis, Colocasia esculenta, Polygonum hydropiper, Alternanthera sessilis and Pistia stratoites in gravel as medium. Sewage treatment potential of CW was evaluated by varying retention time at three different stages of plant growth and stabilization. After 6 months, monitoring of fully established CW indicated reduction of 90%, 65%, 78%, 84%, 76% and 86% of BOD, TSS, TDS, NO3-N, PO4-P and NH4-N, respectively in comparison to inlet after 36 h of retention time. Sewage treatment through CW also resulted in reduction of heavy metal contents. Thus, CW proved an effective method for treatment of wastewater and may be developed along river Ganga stretch as an alternative technology. Treated water may be drained into river to check further deterioration of Ganga water quality.

Involvement and interaction of microbial communities in the transformation and stabilization of chromium during the composting of tannery effluent treated biomass of Vallisneria spiralis L

Tannery effluent treated with aquatic macrophyte Vallisneria spiralis L. for 14 d showed significant improvement in physico-chemical properties and reduction in Cr concentration. Accumulation of Cr was found maximum in roots (358 microg g(-1)dw) as compared to shoot (62 microg g(-1)dw) of the plant. A laboratory scale composter was designed with the objectives to investigate the physico-chemical changes and role of microbes in stabilization and transformation of Cr in the composting material. Results revealed that the composting process was quick within 7-21 d as indicated by peak time for various physico-chemical parameters and drop in C/N ratio up to acceptable limit. The profile of microbial communities indicated that population of anaerobic, aerobic and nitrifying bacteria increased quickly at the initial phase, and reached a peak level of 4.2 x 10(6), 9.78 x 10(8) and 9.32 x 10(9) CFU g(-1), respectively at 21 d; while population of actinomycetes and fungi was found maximum i.e. 3.29 x 10(7) and 9.7 x 10(6) CFU g(-1), respectively, after 35 d of composting. Overall bacterial population dominated over the actinomycetes and fungi during the composting process. Cr((VI)) was transformed to Cr((III)) due to the microbial activity during the process. Sequential extraction of Cr fractionation showed its stabilization via changing into organic matter-bound and residual fractions during the composting.

Chromate tolerance and accumulation in Chlorella vulgaris L.: Role of antioxidant enzymes and biochemical changes in detoxification of metals

A concentration-dependent increase in activity of antioxidant enzymes (catalase, ascorbate peroxidase, glutathione, superoxide dismutase) and carotenoid, MDA level have been observed in the green alga Chlorella vulgaris following chromium exposure at different concentrations (0.01-100 μg ml(-1)). Simultaneously, decrease in growth rate, chlorophyll and protein contents was observed. In case of ascorbate peroxidase, glutathione peroxidase and superoxide dismutase a bell shaped dose response was evident, however, lipid peroxidation followed a linear relationship along with catalase activity, which could be used as biomarker of Cr toxicity and played important role in providing tolerance and subsequently, high accumulation potential of chromium in C. vulgaris. In present investigation, the green alga C. vulgaris respond better under chromium stress in terms of tolerance, growth and metal accumulating potential at higher concentration of Cr (VI) which could be employed in decontamination of chromium for environmental cleanup.